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Objective: To perform non-invasive Electroarthrography (EAG) on live horses and establish relationships between EAG and direct measurements of cartilage streaming potentials in weight bearing areas of the equine metacarpophalangeal joint., Design: EAG was performed bilaterally on the metacarpophalangeal joints of live horses (n = 3). Separate experiments used metacarpophalangeal joint explants (n = 11) to measure EAG obtained during simulated loading followed by direct measurements of cartilage streaming potentials on joint surfaces using the Arthro-BST probe. Joints were assigned to relatively normal (n = 5) and mildly degraded (n = 6) groups based on histological scoring of Safranin-O/Fast Green stained sections., Results: EAG, involving application of electrodes to skin surrounding the joint and repeated weight shifting, was well-tolerated in live horses. One pair of distal forelimbs were available for analogous ex vivo EAG testing and measurements were strongly correlated to in vivo EAG measurements obtained on the same joints (r = 0.804, p = 0.016, n = 8). Both indirect (EAG) and direct (Arthro-BST) measurements of cartilage streaming potentials distinguished between normal and mildly degraded cartilage with statistically significant differences at 5 of 6 and 4 of 6 electrodes during simulated standing and walking, respectively. Strong and moderate correlations for weight bearing regions on the dorsal phalanx and central metacarpus were detected during both standing and walking. At the metacarpus/sesamoid interface a moderate correlation occurred during walking., Conclusion: Non-invasive EAG was used successfully in a clinical scenario and correlated to direct measurements of streaming potentials in weight bearing cartilage. These data support the potential of EAG to contribute to the diagnosis and treatment of degenerative joint diseases., Competing Interests: Declaration of Competing Interest MG and EQ are the owners of Biomomentum Inc., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

This pilot study aims to evaluate concurrent validity using the goniometer as a reference tool and test-retest reliability of flexion of metacarpal phalangeal joint (MCP) measurements taken from a finger training device (air-guitar system) in healthy participants. There were ten self -reported asymptomatic participants recruited to test the devices. The measurements of all metacarpophangeal joints of the dominant hands were conducted using a finger goniometer and the air-guitar system. Two measuring sessions were conducted on the same day. The concurrent validity of the air-guitar indicated by strong concordance correlation coefficient (0.62-0.90) with the goniometer and mean difference (approximately 1°) between the two instruments are well below the limit of 5°. The test-retest reliability of MCP measurements from the air-guitar glove (0.82-0.99) was acceptable as a clinically meaningful measurement tool as the intraclass correlation coefficients were higher than 0.7. The standard error of measurement and minimal detectable change of the air-guitar are similar to those of the goniometer. The air-guitar tracking features, when used as a home-based therapy tool, may assist in monitoring change of MCP flexion over a time course with good reliability and strongly associated with the measurements from the goniometer., (© 2024. The Author(s).)

Background: The metacarpophalangeal (MCP) joint's collateral ligaments have been extensively debated, with no clear consensus on their mechanics. Understanding their function is crucial for comprehending joint movement and stability., Methods: A thorough search was conducted across databases, including PubMed, Scopus, Cochrane library and grey literature. A total of 59 articles were identified, and after rigorous evaluation, six articles were included in the review., Results: The analysis underscores two principal findings. Firstly, the principal and accessory collateral ligaments exhibit consistent tension influenced by the MCP joint's position. This tension varies across different sections of the ligaments. Secondly, the ligaments' interaction with the joint structure plays a pivotal role in defining the range of motion of the joint., Conclusion: Preliminary findings from this review indicate that MCP joint collateral ligament tension varies with joint position. Increased tension in the principal collateral ligament during flexion and isometric behavior of its volar portion in extension are observed. The accessory ligament may tighten during extension. The shape of the metacarpal head appears to influence this tension. These insights, while informative, call for further detailed research to deepen our understanding of MCP joint mechanics., (Copyright © 2024 The Author(s). Published by Elsevier Masson SAS.. All rights reserved.)

Abstract: Peveler, WW, Schoffstall, J, Coots, J, Kilian, J, and Glauser, J. The effects of boxing glove design on thumb position when making a fist for striking. J Strength Cond Res 38(5): 948-950, 2024-It has been suggested that boxing glove design alters thumb position increasing the risk of injury. The purpose of this study was to determine the effects of boxing glove design on thumb joint angles when making a fist. Ten experienced fighters participated in this study. A DEXA scan was used to produce an x-ray image of thumb position for all conditions (no gloves and 10-oz boxing gloves). Mean values for dependent measures were compared using a paired-sample T test and an alpha of 0.05. The carpometacarpal (CMC) joint angle was significantly different between no glove (14.1 ± 6.54°) and boxing glove (34.2 ± 7.60°) at p ≤ 0.001. The metacarpophalangeal (MP) joint angle was significantly different between no glove (132.6 ± 12.74°) and boxing glove (149.40 ± 8.15°) at p ≤ 0.001. The IP joint angle was not significantly different between no glove (135.50 ± 19.12°) and boxing glove (144.40 ± 17.39°) at p = 0.269. The perpendicular distance from the second metacarpal of the hand to the center of the MP joint was significantly different between no glove (0.48 ± 0.54 cm) and boxing glove (1.84 ± 0.29 cm) at p ≤ 0.001. Use of a boxing glove resulted in abduction of the thumb away from the hand and increased CMC and MP joint angles that were significantly different in relation to making a fist without a glove. Information from this study may provide insight into the high rate of thumb injury and provide insight for future boxing glove design., (Copyright © 2023 National Strength and Conditioning Association.)

Objectives: The aim of this study was to calculate the stress acting on the trapeziometacarpal joint during an key pinch grip., Method: We used profile X-rays of the thumb to measure the various bony and muscle lever arms. We assessed the angles of action of the muscular elements involved in the thumb column. Based on this data, we established a two-dimensional geometric model that enabled us to determine the forces at each joint level, as a function of stresses and muscular contributions. We were also able to calculate the participation of the different muscle groups in obtaining a balanced situation., Results: Our results, as a function of the degree of flexion of the interphalangeal and metacarpophalangeal joints, show a multiplying factor of 2.9-3.19 in relation to the key pinch grip force., Discussion: Previous studies modelling a key pinch grip are showed multiplying factors from 6 to 13 in relation to the key pinch grip force. They are not compatible with the characteristics of the polyethylene used for trapeziometacarpal prostheses, whereas numerous articles in the literature show survival rates that are more or less comparable to those of total hip prostheses. These studies required an excessive number of assumptions, which could lead to error. Our results are compatible with the results of trapeziometacarpal prosthesis and with those of a recent study measuring intra-articular trapeziometacarpal pressure in a cadaveric model. Our model allows us to test different configurations of the thumb spine depending on the degree of flexion of the interphalangeal and metacarpophalangeal joints., (Copyright © 2023 SFCM. Published by Elsevier Masson SAS. All rights reserved.)

Objectives: The effect of metacarpophalangeal joint position and finger joint movement speed on lumbrical muscle activity remains unproven and was examined in this study., Material and Methods: Twenty-four healthy adults performed flexion-extension movements of the index finger in different metacarpophalangeal joint positions (extension or flexion) and movement speeds (60, 120, 240, and 360 beats per minute). The activities of the first lumbrical, first dorsal interosseous, and extensor digitorum muscles were evaluated using surface electromyography, and compared with those during finger joint extension., Results: The metacarpophalangeal joint positions affected only lumbrical muscle activity, which was greater during extension. Further, finger movement speed affected the lumbrical and extensor digitorum muscle activities, which increased with increasing movement speeds., Conclusion: The present study suggests that position and movement speed can influence the lumbrical muscle activity during metacarpophalangeal joint extension. These findings may help expound lumbrical function and develop suitable strategies for inducing lumbrical muscle activity., (Copyright © 2023 SFCM. Published by Elsevier Masson SAS. All rights reserved.)

Background: As a first-line surgical treatment for treating metacarpophalangeal (MCP) joint extension contractures, mobilization surgery with open dorsal approach has been indicated. However, this procedure has the possibility to result in postoperative recurrence over the course of time because its invasive open dorsal approach has a negative impact on the postoperative gliding of the extensor mechanism. We report the preliminarily outcomes of patients who underwent a minimally invasive arthroscopic mobilization to alter and enhance their existing surgical strategy in place of MCP joint extension contractures., Methods: This retrospective study included seven patients with 13 MCP joint extension contractures who had received an arthroscopic release of the bilateral collateral ligament and/or dorsal capsule of affected MCP joint. The extension contractures were caused by long-time immobilization with inadequate extended position of the MCP joint after either hand and wrist fractures, extensor tendon injury, or peripheral nerve palsy. All patients received sufficient exercise under the supervision of a physical therapist for more than 3 months before surgery. However, physical therapy did not improve the MCP joint extension contractures. We measured the active and passive flexion angles preoperatively at 1 and 6 months after surgery. The passive flexion angle was also measured after arthroscopic mobilization on the operation table. Surgery-related complications regarding nerve, vessel, skin, and tendon were also assessed., Results: In all patients, significant improvements were observed in both the active and passive flexion angles 1 month after surgery, and continued to improve 6 months after surgery. Two out of 13 metacarpophalangeal joints developed blisters on the dorsal side of the joint, but conservatively recovered., Conclusions: Based on the positive improvements observed in our patients, we conclude that this minimally invasive arthroscopic technique has the potential to alter and enhance the surgical treatment strategy for MCP joint extension contractures., Competing Interests: Conflict of interest We have nothing to disclose., (Copyright © 2021 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)

Applying an external force to a person's hyperextended fingertip produces electrical activity in the extensor digitorum communis, even if the person does not try to open their hand. Based on this, a finger extensor facilitation technique conducted by therapists was developed. In this study, we developed a finger extensor facilitation training device named iPARKO that imitates this technique. We examined the relationship between the metacarpophalangeal (MP) joint angle of the four fingers and the activities in the extensor digitorum communis resulting from active training using iPARKO. At the same time, the relationship between the MP joint angle and the reduced activities in the flexor digitorum superficialis was also examined. The experiments were conducted on five healthy subjects. It was found that as the MP joint approached its own maximum hyperextension position, the amount of activity of the extensor digitorum communis increased, and the amount of activity of the flexor digitorum superficialis decreased.

Objectives : Previous studies of high-resolution peripheral quantitative computed tomography (HR-pQCT) imaging of hand joints in patients with rheumatoid arthritis (RA) have suggested that erosion healing may occur. Our objective was to examine changes in erosion volume, joint space width (JSW), bone mineral density (BMD), and bone remodelling, and their association with clinical outcomes and measures of patient hand function. Method : We examined 48 patients who achieved a good response to a newly initiated biologic therapy. HR-pQCT images of the dominant hands' second and third metacarpophalangeal joints were obtained 3 and 12 months after therapy initiation. Bone erosion volume, JSW, BMD, and bone remodelling were quantified from HR-pQCT images, with improvement, no change (unchanged), or progression in these measures determined by least significant change. Disease activity and hand function measures were collected. Results : There were no significant group changes in HR-pQCT outcomes over the 9 month period. Twenty-two patients had total erosion volumes that remained unchanged, nine showed improvement, and two progressed. The majority of JSW and BMD measures remained unchanged. There was a significant association between the baseline Health Assessment Questionnaire score and the change in minimum JSW, but no other significant associations between HR-pQCT outcomes and function were observed. Conclusions : The vast majority of patients maintained unchanged JSW and BMD over the course of follow-up. Significant improvements in total erosion volume occurred in 27% of patients, suggesting that biologic therapies may lead to erosion healing in some patients, although this did not have an impact on self-reported and demonstrated hand function.

This study aimed to determine by ultrasonography, and cadaveric dissection, whether the firm cords felt by palpation at the sides of the proximal phalanx (PP), actively flexing, and extending the proximal interphalangeal (PIP) joint while keeping the metacarpophalangeal (MCP) joint extended are the lateral bands (LBs) of the extensor apparatus. If so, palpation of the LBs could help evaluate hand conditions that impact the digits' intrinsic muscles. To this end, the PP of the middle and ring fingers of the dominant hand of seven subjects were studied by palpation on both sides. Ultrasonography (US) was performed with a hockey-stick transducer placed on the ulnar side. Five cadaveric hands were dissected, exposing the dorsal extensor apparatus. On palpation, a firm cord was consistently felt at the PP's sides in all subjects. These cords moved widely forward on PIP flexion and backward with PIP extension. By US scanning, the cords corresponded to the LBs. However, the forward movement had only a median of 1.8 mm (range 0.7-3 mm) in the middle finger and a median of 1.1 mm (range 0.3-2.7 mm) in the ring finger compared with an estimated 5-10 mm upon palpation. Cadaveric dissection confirmed the forward movement of the LBs in PIP flexion. We concluded that the firm cords felt at the PP sides are the LBs of the extensor apparatus. We confirmed their movement with the active flexion/extension of the PIP joint. Comparing the wide palpatory and the meager US motion, a haptic illusion of motion may be present., (© 2021 Anatomical Society.)

Background: The metacarpophalangeal joint has a unique morphology with a high degree of freedom. However, few studies have analyzed the kinematics of fingers owing to the rapid movement of the small bones involved. The in-vivo kinematics of metacarpophalangeal joints were analyzed by four-dimensional computed tomography (4DCT) and associated with its morphology., Methods: The flexion motion of the fingers of bilateral hands in 10 volunteers were examined using 4DCT. Iterative surfaces were registered to trace the surface of the proximal phalanges with respect to metacarpals. Rotation angles were calculated using Euler/Cardan angles., Findings: In the index finger, the proximal phalange supinated to a maximum flexion of 40° and then pronated, and its range of rotation was larger than the previous reports. In the other fingers, the proximal phalanges continued to supinate during flexion. The helical axis of the proximal phalange passed a point extremely close to the center point of bilateral condyles, and it moved toward the proximal and palmar directions until the middle stage of flexion and toward the proximal and dorsal directions during the late stage of flexion. The translation of the rotation axis was larger in the ring and little fingers., Interpretation: The rotation in the index finger was larger than previously reported. The helical axes moved in the dorsal direction and proximally during the latter phase of the flexion. These results can be employed to better understand the causes of implant failure of the metacarpophalangeal joints., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The knowledge of local stress distribution in hand joints is crucial to understand injuries and osteoarthritis occurrence. However, determining cartilage contact stresses remains a challenge, requiring numerical models including both accurate anatomical components and realistic tendon force actuation. Contact forces in finger joints have frequently been calculated but little data is available on joint contact pressures. This study aimed to develop and assess a hybrid biomechanical model of the index finger to estimate in-vivo joint contact pressure during a static maximal strength pinch grip task. A finite element model including bones, cartilage, tendons, and ligaments was developed, with tendon force transmission based on a tendon-pulley system. This model was driven by realistic tendon forces estimated from a musculoskeletal model and motion capture data for six subjects. The hybrid model outputs agreed well with the experimental measurement of fingertip forces and literature data on the physiological distribution of tendon forces through the index finger. Mean contact pressures were 6.9 ± 2.7 MPa, 6.2 ± 1.0 MPa and 7.2 ± 1.3 MPa for distal, proximal interphalangeal and metacarpophalangeal joints, respectively. Two subjects had higher mean contact pressure in the distal joint than in the other two joints, suggesting a mechanical cause for the prevalence of osteoarthritis in the index distal joint. The inter-subject variability in joint contact pressure could be explained by different neuromuscular strategies employed for the task. This first application of an effective hybrid model to the index finger is promising for estimating hand joint stresses under daily grip tasks and simulating surgical procedures.

Background: The purpose of this study was to report the clinical outcomes of ready-made J-shaped intramedullary nail fixation for unstable metacarpal fractures. Methods: A total of 25 unstable fractures from 24 patients were evaluated in this retrospective study, comprising 20 metacarpal neck and 5 metacarpal shaft fractures. The mean follow-up was 22 weeks. Functional outcomes were assessed based on the range of motion of the metacarpophalangeal joint. Radiographic outcomes were evaluated by four projections of the postoperative plain radiographs at the final follow-up, and then were rated as excellent if projections at the fracture site showed no correction loss or angular deformity greater than 10°. Surgery time and complications during the treatments were recorded for each case. Results: All 25 fractures obtained bony union. The mean range of motion of the metacarpophalangeal joint was 78° (range, 45°-90°). Radiographic outcomes were excellent in 24 (96%) of 25 fractures. Only one fracture had correction loss. The mean surgery time was 29 minutes (range, 14-61 minutes). Two cases had extensor tendon adhesion at the insertion site, which was easily released when the implant was removed. Conclusions: This study demonstrates that intramedullary fixation with a ready-made J-shaped nail is a reliable treatment option for unstable metacarpal fractures.

Background: Physical exercise is known to cause significant joint changes. Thus, monitoring joint behavior of athletic horses is essential in early disorders recognition, allowing the proper management., Objectives: The aims of this study were to determine the morphological patterns, physical examination characteristics and ultrasound findings of show jumping horses in training and to establish a score-based examination model for physical and ultrasound follow-ups of metacarpophalangeal joint changes in these animals., Methods: A total of 52 metacarpophalangeal joints from 26 horses who were initially in the taming stage were evaluated, and the horses' athletic progression was monitored. The horses were evaluated by a physical examination and by B-mode and Doppler-mode ultrasound examinations, starting at time zero (T0), which occurred concomitantly with the beginning of training, and every 3 months thereafter for a follow-up period of 18 months., Results: The standardized examination model revealed an increase in the maximum joint flexion angles and higher scores on the physical and ultrasound examinations after scoring was performed by predefined assessment tools, especially between 3 and 6 months of evaluation, which was immediately after the horses started more intense training. The lameness score and the ultrasound examination score were slightly higher at the end of the study., Conclusions: The observed results were probably caused by the implementation of a training regimen and joint adaptation to physical conditioning. The joints most likely undergo a pre-osteoarthritic period due to work overload, which can manifest in a consistent or adaptive manner, as observed during this study. Thus, continuous monitoring of young athlete horses by physical and ultrasound examinations that can be scored is essential., Competing Interests: The authors declare no conflicts of interest., (© 2020 The Korean Society of Veterinary Science.)

Inferring the locomotor behaviour of the last common ancestor (LCA) of humans and African apes is still a divisive issue. An African great-ape-like ancestor using knuckle-walking is still the most parsimonious hypothesis for the LCA, despite diverse conflicting lines of evidence. Crucial to this hypothesis is the role of the centrale in the hominoid wrist, since the fusion of this bone with the scaphoid is among the clearest morphological synapomorphies of African apes and hominins. However, the exact functional significance of this fusion remains unclear. We address this question by carrying out finite element simulations of the hominoid wrist during knuckle-walking by virtually generating fused and unfused morphologies in a sample of hominoids. Finite element analysis was applied to test the hypothesis that a fused scaphoid-centrale better withstands the loads derived from knuckle-walking. The results show that fused morphologies display lower stress values, hence supporting a biomechanical explanation for the fusion as a functional adaptation for knuckle-walking. This functional interpretation for the fusion contrasts with the current inferred positional behaviour of the earliest hominins, thus suggesting that this morphology was probably retained from an LCA that exhibited knuckle-walking as part of its locomotor repertoire and that was probably later exapted for other functions.

Introduction: For extraarticular proximal phalanx fractures, two methods are employed, transarticular fixation in which the metacarpophalangeal joint is crossed and the extraarticular method in which the pins are introduced through the base of the proximal Phalanx., Materials and Methods: This study was a prospective one on patients with proximal phalanx transverse or short oblique fractures. In one of the groups we used parallel pins from metacarpal head through MCP joint to proximal phalanx. In the second, we used two cross pins from proximal phalanx the base of the proximal phalanx to fix the fracture. We evaluated metacarpophalangeal, proximal and distal interphalangeal joints active range of motion and how long it took the patient to resume their daily activities and work without difficulty, as well as post-operative complications such as wound infection, malunion, and nonunion in 3 and 6 months follow-up., Results: Ultimately, 61 people entered the study, 29 in the parallel pins and 31 in the cross pins group. There was no significant difference between the two groups, but the improvement in all of the joints range of motion showed a statistically significant difference (P < 0.0001) from the 3 to 6 months follow-up. The final range of motion showed an inverse correlation with age of the patient (P < 0.05). Most of the patients were in the excellent grade of range of motion class and no serious complication was observed in any of them., Conclusion: The results of treatment in proximal phalangeal fractures with both methods were comparable and so the surgeon may select each based on the experience and training.

Background: Metacarpal lengthening by distraction osteogenesis has been well documented in pediatric patients but limited in older patients. Fewer studies have assessed the success of the procedure through outcome measure scores. The purpose of this study is to assess the outcomes of distraction osteogenesis in skeletally mature adults with brachymetacarpia and patients' perspectives on their satisfaction through outcome measure scores., Methods: Retrospective chart review of a consecutive series of metacarpal lengthenings for the treatment of brachymetacarpia was performed. Key parameters collected include starting metacarpal length, amount lengthened, range of motion of metacarpophalangeal joint, type of fixator used, distraction time, and total time in fixator. Relevant comorbidities and complications encountered were recorded as well. The Body Image Quality of Life Inventory (BIQLI) and Limb Deformity Modified Scoliosis Research Society (LD-SRS) score were given to evaluate patients' perspectives on their satisfaction of surgery., Results: Seven metacarpal lengthenings were performed in 4 adult females (average age: 22.8 years) between 2005 and 2016. The average amount lengthened was 1.5 cm (range, 1.2-2.1 cm), corresponding to a mean percent lengthening of 44.4% (range, 33.3%-57.1%). The mean distraction rate was 0.432 mm/day (range, 0.286-0.724 mm/day). The mean distraction time was 38 days (range, 28-55 days). External fixation index was 71.8 days/cm (range, 53.5-99.2 days/cm). No functional loss was observed., Conclusions: Progressive distraction osteogenesis can obtain functionally successful results and improvement in aesthetics and body image without severe complications in skeletally mature adults with brachymetacarpia.

Background: Collateral ligament injury of the metacarpophalangeal joint of the fingers is underreported in the literature and widely underestimated by the medical community. Here, the authors present results from a large series of patients and review factors influencing success of surgery., Methods: The authors performed a retrospective study of 46 patients who underwent surgical fixation of the metacarpophalangeal collateral ligament using bone anchor in an acute or chronic setting. The diagnosis was predominantly clinical, based on laxity testing of the joint. The authors collected demographic data and intraoperative findings and postoperative results., Results: Following surgery, with a median follow-up of 17 months, all patients presented with a stable joint and complete resolution of pain. The mean flexion of the metacarpophalangeal joint was 77.11 degrees, and mean extension was 0.84 degrees. The authors measured the injured grip strength at a mean of 88.52 percent of the opposite hand, and the mean Quick Disabilities of the Arm, Shoulder and Hand questionnaire score used to evaluate disability was 9.56 on a scale of 100 (with 100 being complete disability)., Conclusions: Surgical treatment of metacarpophalangeal collateral ligament rupture of the fingers is a safe technique that gives reproducible positive results in terms of mobility, strength, and disability scale score. The authors' results show that anchoring of the ligament should be performed even with prolonged time from injury to surgery.

Background: The metacarpophalangeal joints exhibit range of motion that is influenced by wrist position. Synergistic motion occurs between the wrist and the metacarpophalangeal joints with different static wrist positions affecting joints' motion capability. The aim of this study was to determine how different wrist positions influence the active range of motion of the index through small finger metacarpophalangeal joints., Methods: The active range of motion of the index through small finger metacarpophalangeal joints of 31 healthy subjects was measured in flexion/extension and radial/ulnar deviation in 5 different flexion/extension wrist positions, using biaxial electrogoniometers., Results: There was a difference in range of motion of all fingers depending on the wrist position. The minimum metacarpophalangeal joint range of motion was found in 80° wrist extension, the maximum in neutral wrist position. For the index finger, flexion/extension was 84.7° (±8.6°) to 25.9° (±10.2°) and radial/ulnar deviation was 32.1° (±11.3°) to 22.6° (±12.8°). For the middle finger, flexion/extension was 84.8° (±8.5°) to 25.9° (±10.1°) and radial/ulnar deviation 28.8° (±11.1°) to 22.1° (±8.9). The fourth finger showed a range of motion for flexion/extension of 87.2° (±11.5°) to 22.8° (±11.6°) and radial/ulnar deviation of 8.1° (±5.8°) to 32.3° (±12.4°). The highest range of motion was measured at the fifth finger with flexion/extension of 84.0° (±8.6°) to 32.1°(±16.8°) and radial/ulnar deviation of 15.1° (±12.9°) up to 54.6° (±18.7°)., Conclusions: The range of motion of the index through small finger metacarpophalangeal joints was significantly influenced by wrist position. The highest metacarpophalangeal joint range of motion of all fingers was conducted in neutral wrist positions. Apart from ergonomic implications, we conclude that metacarpophalangeal joint motion should be assessed under standardized wrist positions.

Background: The most common implant options for the metacarpophalangeal joint arthroplasty include silicone, pyrocarbon and metal-polyethylene. A systematic review of outcomes of silicone and pyrocarbon implants was conducted; however, a similar exercise for metal-polyethylene implants revealed a scarcity of published results and lack of long-term follow-up studies. The aim of the present work is to test the hypothesis that the magnitude of metacarpophalangeal joint cyclic loads generates stress and strain behaviour, which leads to long-term reduced risk of metal-polyethylene component loosening., Methods: This study was performed using synthetic metacarpals and proximal phalanges to experimentally predict the cortex strain behaviour for both intact and implanted states. Finite element models were developed to assess the structural behaviour of cancellous-bone and metal-polyethylene components; these models were validated by comparing cortex strains predictions against the measurements., Findings: Cortex strains in the implanted metacarpophalangeal joint presented a significant reduction in relation to the intact joint; the exception was the dorsal side of the phalanx, which presents a significant strain increase. Cancellous-bone at proximal dorsal region of phalanx reveals a three to fourfold strain increase as compared to the intact condition. Interpretation The use of metal-polyethylene implant changes the strain behaviour of the metacarpophalangeal joint yielding the risk of cancellous-bone fatigue failure due to overload in proximal phalanx; this risk is more important than the risk of bone-resorption due to the strain-shielding effect. By limiting the loads magnitude over the joint after arthroplasty, it may contribute to the prevention of implant loosening., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Study Design: A within-subject research design was used in this study. The difference of the range of motion (ROM) with and without ulnar nerve block was analyzed., Introduction: For the clinical evaluation of the functional effects of ulnar nerve palsy at the hand the relevance of clinical tests is in discussion., Purpose of the Study: The aim of the study was to evaluate the predictive value of 2 clinical tests for a simulated ulnar nerve lesion by motion analysis with a sensor glove., Methods: In 28 healthy subjects, dynamic measurements of the finger joints were performed by a sensor glove with and without ulnar nerve block at the wrist. In the 0° metacarpophalangeal (MCP) stabilization test, the subjects were asked to stabilize the MCP joints actively in 0° while moving the interphalangeal joints, whereas at the 90° MCP stabilization test, the subjects stabilized the MCP joints actively in the 90° position., Results: In the 0° MCP stabilization test, no remarkable changes of the ROM were found at the MCP joints; at the proximal interphalangeal joints 2-5, the ROM decreased with ulnar nerve block, significantly at the index, middle, and ring fingers (P < .05). In the 90° MCP stabilization test, the average ROM of the MCP joints 2-5 significantly increased with ulnar nerve block (P < .05), whereas at the PIP joints, the average ROM decreased (P < .05)., Discussion: The 90° MCP stabilization test had a high predictive value for the discrimination between healthy subjects and subjects with a simulated peripheral ulnar nerve lesion., Conclusions: The results could be relevant for the determination of the functional effect of ulnar nerve palsy and the quantification of clawing in hand rehabilitation., Level of Evidence: II., (Copyright © 2017 Hanley & Belfus. Published by Elsevier Inc. All rights reserved.)

Our aims were to study the anatomical feasibility of triceps brachii long head (TBLH) transfer to the extensor digitorum communis (EDC) and extensor pollicis longus (EPL) tendons through a medial route, and to report on its first clinical application. Dissections were conducted on 10 fresh-frozen cadaver specimens. Using a posteromedial approach, the TBLH was separated from the remaining triceps and extended distally with a fascia lata strip. This strip was then tunneled through a medial route and secured distally to the EDC and EPL tendons. The transfer tenodesis effect during elbow extension was assessed with metacarpophalangeal (MCP) joint motion of the thumb and index finger, and the distance between the thumb and index finger tips (TI distance). This transfer was performed in an eight-year-old boy with incomplete recovery of a right brachial plexus birth palsy; preoperatively, shoulder and elbow functions were recovered as well as active gripping distally, but he had no active wrist or finger extension. With the trapeziometacarpal and radiocarpal joints stabilized, 90° elbow extension provided a mean extension of the thumb and index finger MCP joints of 34 ± 5° and 90 ± 11°, respectively, with a mean TI distance of 116 ± 16 mm. Twelve months after surgery, the boy had full active MCP joint extension, independent from elbow extension. Transferring the TBLH to the EDC and EPL tendons is anatomically feasible. Larger clinical studies will be needed to assess more adequately its functional outcomes., (Copyright © 2018 SFCM. Published by Elsevier Masson SAS. All rights reserved.)

Introduction: Because the hand joints possess a broad range of motion, the muscle length can vary importantly which might result in significant variations of the muscle force-generating capacities. However, facing the complexity of this musculoskeletal system, no study has examined the effect of hand muscle length change on muscle force. This study aimed to characterize the force-length relationship of muscles involved in wrist and metacarpophalangeal flexion., Methods: Eleven participants performed two sessions: (i) one for the wrist flexor muscles and (ii) one for the finger flexor muscles. For each session, the participants performed two maximal voluntary contractions and then two progressive isometric ramps from 0% to 100% of their maximal force capacity at five different wrist/metacarpophalangeal angles. Torque, kinematic, and electromyographic data were recorded. An ultrasound scanner was used to measure the myotendinous junction displacement of flexor carpi radialis (FCR) and flexor digitorum superficialis (FDS) during isometric contractions. A three-dimensional relationship between muscle length, force, and activation level was modeled using optimization procedure., Results: Globally, the FCR was stronger and shorter compared with FDS. The results showed that the three-dimensional relationships fitted well the experimental data (mean R = 0.92 ± 0.07 and 0.87 ± 0.11 for FCR and FDS, respectively). Using joint angle and EMG data, this approach allows to estimate the muscle force with low estimation errors (<9% of Fmax)., Conclusions: This study proposes a new method to investigate the force-length relationship by combining ultrasound measurement, musculoskeletal modeling and optimization procedures. The data and relationships provide a new insight into hand biomechanics and muscle function that could be useful for designing hand tools or surgical operations.

Purpose: It is a common belief that extension of the metacarpophalangeal (MCP) joint of the finger is achieved via the sagittal bands acting as a sling or lasso to attach the extensor tendon to the base of the proximal phalanx. The aim of this study was to test the hypotheses that (1) division of the sagittal bands reduces extension force or torque of the MCP joint, and (2) division of the extensor tendon distal to the sagittal band will not affect the extension force or torque of the MCP joint., Methods: Ten cadaver limbs were secured to a jig to allow for testing of the extension force of the MCP joints of the index, middle, and ring fingers. A 1-kg load was applied to the forearm extensor digitorum communis tendon and the extension force was measured with the MCP joint positioned at 0° (neutral extension) and again at 45° flexion. These measurements were repeated after the sagittal bands were divided in 15 specimens; in the other 15 specimens, the extensor tendon was divided just distal to the sagittal bands., Results: After sagittal band division, extension force was similar in the 2 groups (0.11 N reduction after division with the MCP joints in neutral and 0.14 N in 45° flexion). There was significantly less extension force after division of the extensor tendon in both joint positions (0.95 N reduction after division in neutral extension and 0.66 N in 45° flexion)., Conclusions: The sagittal bands do not primarily extend the MCP as a sling or lasso. The extensor tendon continuation to the extensor hood and middle phalanx is the major extension motor. The MCP joint is extended by the torque generated by the extensor tendon passing the joint carrying a force and possessing an extension moment arm., Clinical Relevance: This principle should be correctly understood in the literature to ensure that clinical decisions related to injury and/or repair of the extensor tendon and sagittal bands are based on a sound understanding of their mechanics., (Copyright © 2018 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.)

The objectives of this study were to investigate middle finger movements and dynamics of ball movements around the instant of ball release during baseball pitching. Baseball pitching from an indoor mound among 14 semi-professional pitchers was captured using a motion capture system with 16 high-speed cameras (1,000 Hz). Kinematics of middle finger joints, ball rotation, and force applied to the ball were calculated. The proximal and distal interphalangeal joints continued to extend until the instant of ball release, then abruptly flexed. The abrupt flexion lasted for only several milliseconds, followed by a short extension phase. The finger made a quick double cycle of extension-flexion movement, suggesting that it attained high stiffness resulting from co-contraction. The ball began to roll up to the tip of the finger 8 ± 1 ms before ball release owing to the start of extension or the increased angular velocity of extension for the proximal interphalangeal joint. A mean force of 195 ± 27 N was applied in the proximal direction of the hand at the same time as the beginning of ball rolling, and a mean force of 109 ± 22 N was applied to the throwing direction just before ball release.

Background: The functional range of motion (fROM) of the metacarpophalangeal (MCP) joints during the performance of activities of daily living (ADL) has not yet been established. This study aimed to determine the fROM of all five digits and verify the accuracy and reproducibility of dynamic angle measurement using a single-axis electric goniometer (EG) during ADL movements of the hand., Methods: This was a cross-sectional study. In EG suitability testing, we first confirmed the angles of a three-dimensional calibration device 10 times, and then compared EG readings with those determined by tomosynthesis images. Next, we determined the fROM of the MCP joints by evaluating all five digits of the dominant hands of 10 healthy adults performing 16 ADL. Intra-rater reproducibility of MCP joint data during task performance was assessed in two healthy adults., Results: Static measurements of the triangular object showed variance to be within one degree in 39 of 40 trials. Differences between angles measured by the EG and those depicted by radiograph were a range of plus or minus five degrees in 88 of 96 digits. The fROM values for the thumb and index, middle, ring, and little fingers were -7.5 to 35.3, 10.6 to 67.8, 4.0 to 79.9, 3.0 to 83.9, and 2.9-91.4 degrees of flexion, respectively. Flexion angle in the fROM of the index finger was significantly smaller than those of the ring and little fingers. The flexion and extension angles of the thumb were significantly smaller than those of the four ulnar fingers. The intra-rater correlation coefficients of two participants were high at 0.94 and 0.93, respectively., Conclusions: The method adopted in this study exhibited excellent accuracy and reproducibility and was therefore considered suitable for the real-time establishment of fROM flexion-extension angles of the MCP joints for all five digits. Our data are useful as a target arc of motion in the treatment of MCP joint disease or injury., (Copyright © 2018. Published by Elsevier B.V.)

The articular release of the metacarpophalangeal joint produces a typical cracking sound, resulting in what is commonly referred to as the cracking of knuckles. Despite over sixty years of research, the source of the knuckle cracking sound continues to be debated due to inconclusive experimental evidence as a result of limitations in the temporal resolution of non-invasive physiological imaging techniques. To support the available experimental data and shed light onto the source of the cracking sound, we have developed a mathematical model of the events leading to the generation of the sound. The model resolves the dynamics of a collapsing cavitation bubble in the synovial fluid inside a metacarpophalangeal joint during an articular release. The acoustic signature from the resulting bubble dynamics is shown to be consistent in both magnitude and dominant frequency with experimental measurements in the literature and with our own experiments, thus lending support for cavitation bubble collapse as the source of the cracking sound. Finally, the model also shows that only a partial collapse of the bubble is needed to replicate the experimentally observed acoustic spectra, thus allowing for bubbles to persist following the generation of sound as has been reported in recent experiments.

Quantitative characterisation of upper limb motion allows the evaluation of the effect of pathology on functional task performance, potentially directing rehabilitation strategies. Movement patterns of the distal upper limb in healthy adults during functional tasks have not been extensively characterised. During five loaded functional tasks (drinking from a glass, pouring from a kettle, turning a handle, lifting a bag to a shelf, turning a key) the movement patterns were characterised using three-dimensional motion analysis with a minimal marker set in 16 healthy adults (10 M,6F, 27 (IQR:25-43)years). Joint angles reported include flexion/extension at the elbow and wrist, forearm supination/pronation and digits 2-5 metacarpophalangeal (MCP) joint flexion/extension. Additionally for the thumb the angle between the metacarpal of the thumb and the 2nd digit (Thumb base), the thumb MCP (Thumb MCP) and interphalangeal (Thumb IP) joint angles are presented. Durations of activities performed at self-selected comfortable speeds (3.36 (IQR:3.07,3.66)s turning a key to 6.20 (IQR:5.44,6.38)s drinking from a glass) are reported. The maximum joint angles used (median of participants' maxima) were 141° of elbow flexion, 116° forearm supination, 36° wrist extension, 56° Thumb base, 14° Thumb MCP flexion, 18° Thumb IP flexion, 85° MCP2-5 flexion. The tasks of drinking from a glass, lifting a bag to a shelf and turning a key appeared to have the least variation in performance, suggesting that these activities are better suited to be selected as standardized tasks for assessing the impact of pathology on movement than pouring from a kettle and turning a handle., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Background: Traumatic amputation of the digit requiring revision amputation at the level of the proximal phalanx provides the opportunity to improve flexor function via tenodesis of the remaining flexor digitorum superficialis (FDS) tendon. Salvage of the remaining FDS and performing flexor tenodesis to the proximal phalanx allows increased flexion at the metacarpophalangeal (MCP) joint., Methods: This series reviews FDS tenodesis, outlining its surgical technique with clinical and functional outcomes. Institutional review board-approved retrospective study was performed. Twelve digits in 8 patients were included., Results: Average flexion-extension arc of affected MCP joint was 82°, and average grip strength was 70% of unaffected extremity. No patients required revision surgery or revision amputation. One patient had a minor wound infection treated successfully with oral antibiotics., Conclusions: FDS tenodesis is a reliable motion-preserving procedure for patients with amputations at the level of the proximal phalanx to maintain flexion at the MCP joint.

Purpose: To introduce the "on-top plasty" technique and report our long-term outcomes., Methods: We evaluated 5 thumbs in 5 patients who underwent radial polydactyly reconstruction using the "on-top plasty" technique between 1998 and 2003. This technique was used when it was felt that neither thumb possessed adequate proximal and distal structures to provide a functional and aesthetically pleasing thumb. Our study group included 1 Flatt type III and 4 Flatt type VII thumbs. The average age at time of surgery was 1.4 years and at final follow-up was 13.5 years. Subjective patient evaluation, objective outcomes values, and validated patient-oriented outcome measures were obtained., Results: There was no soft tissue loss and union was achieved in all thumbs with no further surgery required in any thumb. Mean flexion-extension arc for the metacarpophalangeal joint was 60° (range, 10° extension to 70° flexion) and at the interphalangeal joint was 19° (range, 25° extension to 35° flexion). Mean percentage of age-matched norms for lateral, tripod, and tip pinch were 47.0%, 45.9%, and 47.8%, respectively. Mean grip strength was 54.2% of age-matched norm. The mean Pediatric Quality of Life Inventory (PedsQL) score for parent questionnaires was 89.0 and for teen/child questionnaires was 89.1. The Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire revealed a mean score of 4.3., Conclusions: For patients with radial polydactyly in which neither thumb possesses adequate distal and proximal components, the on-top plasty is a reliable method of polydactyly reconstruction with durable results at longer than 10 years' follow-up., Type of Study/level of Evidence: Therapeutic V., (Copyright © 2017 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.)

Background: The metacarpophalangeal joint (fetlock) is the most commonly affected site of racehorse injury, with multiple observed pathologies consistent with extreme fetlock dorsiflexion. Race surface mechanics affect musculoskeletal structure loading and injury risk because surface forces applied to the hoof affect limb motions. Race surface mechanics are a function of controllable factors. Thus, race surface design has the potential to reduce the incidence of musculoskeletal injury through modulation of limb motions. However, the relationship between race surface mechanics and racehorse limb motions is unknown., Objective: To determine the effect of changing race surface and racehorse limb model parameters on distal limb motions., Study Design: Sensitivity analysis of in silico fetlock motion to changes in race surface and racehorse limb parameters using a validated, integrated racehorse and race surface computational model., Methods: Fetlock motions were determined during gallop stance from simulations on virtual surfaces with differing average vertical stiffness, upper layer (e.g. cushion) depth and linear stiffness, horizontal friction, tendon and ligament mechanics, as well as fetlock position at heel strike., Results: Upper layer depth produced the greatest change in fetlock motion, with lesser depths yielding greater fetlock dorsiflexion. Lesser fetlock changes were observed for changes in lower layer (e.g. base or pad) mechanics (nonlinear), as well as palmar ligament and tendon stiffness. Horizontal friction and fetlock position contributed less than 1° change in fetlock motion., Main Limitations: Simulated fetlock motions are specific to one horse's anatomy reflected in the computational model. Anatomical differences among horses may affect the magnitude of limb flexion, but will likely have similar limb motion responses to varied surface mechanics., Conclusions: Race surface parameters affected by maintenance produced greater changes in fetlock motion than other parameters studied. Simulations can provide evidence to inform race surface design and management to reduce the incidence of injury., (© 2017 EVJ Ltd.)

Dynamic movement trajectories of low mass systems have been shown to be predominantly influenced by passive viscoelastic joint forces and torques compared to momentum and inertia. The hand is comprised of 27smallmass segments. Because of the influence of the extrinsic finger muscles, the passive torques about each finger joint become a complex function dependent on the posture of multiple joints of the distal upper limb. However, biomechanical models implemented for the dynamic simulation of hand movements generally don't extend proximally to include the wrist and distal upper limb. Thus, they cannot accurately represent these complex passive torques. The purpose of this short communication is to both describe a method to incorporate the length-dependent passive properties of the extrinsic index finger muscles into a biomechanical model of the upper limb and to demonstrate their influence on combined movement of the wrist and fingers. Leveraging a unique set of experimental data, that describes the net passive torque contributed by the extrinsic finger muscles about the metacarpophalangeal joint of the index finger as a function of both metacarpophalangeal and wrist postures, we simulated the length-dependent passive properties of the extrinsic finger muscles. Dynamic forward simulations demonstrate that a model including these properties passively exhibits coordinated movement between the wrist and finger joints, mimicking tenodesis, a behavior that is absent when the length-dependent properties are removed. This work emphasizes the importance of incorporating the length-dependent properties of the extrinsic finger muscles into biomechanical models to study healthy and impaired hand movements., (Published by Elsevier Ltd.)

Purpose: To analyze the effect of simulated proximal interphalangeal (PIP) joint arthrodesis on distal interphalangeal (DIP) joint free flexion-extension (FE) and maximal voluntary pinch forces., Methods: Five healthy subjects were tested with the PIP joint unconstrained and constrained to selected angles to produce (1) free FE movements of the DIP joint at 2 selected angles of the metacarpophalangeal joint, and (2) maximal voluntary tip (thumb and index finger) and chuck (thumb, index, and middle fingers) pinch forces. Kinematic data from a motion analysis system, pinch force data from a mechanical pinch meter, and electromyography (EMG) data recorded from 2 flexor and extensor muscles of the index finger were collected during free FE movements of the DIP joint and pinch tests for distinct PIP joint constraint angles., Results: The EMG root mean square (RMS) values of the flexor digitorum profundus (FDP) and extensor digitorum (ED) did not change during free FE of the DIP joint. The extension angle of the range of motion of the DIP joint changed during free FE. It increased as the PIP constraint angle increased. The EMG RMS value of FDP and ED showed maximum values when the PIP joint was unconstrained and constrained at 0° to 20° of flexion during tip and chuck pinch. Neither the index finger metacarpophalangeal and DIP joint positions nor pinch force measurements differed with imposed PIP joint arthrodesis., Conclusions: The PIP joint arthrodesis angle affects DIP joint extension. A minimal overall impact from simulated PIP arthrodesis in muscle activity and pinch force of the index finger was observed. The EMG RMS values of the FDP and ED revealed that a PIP arthrodesis at 0° to 20° of flexion leads to a more natural finger posture during tip and chuck pinch., Clinical Relevance: This study provided a quantitative comparison of free FE motion of the DIP joint, as well as FDP and ED forces during pinch, under simulated index finger PIP arthrodesis angles., (Copyright © 2017 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.)

X-ray reconstruction of moving morphology (XROMM) uses biplanar videoradiography and computed tomography (CT) scanning to capture three-dimensional (3D) bone motion. In XROMM, morphologically accurate 3D bone models derived from CT are animated with motion from videoradiography, yielding a highly accurate and precise reconstruction of skeletal kinematics. We employ this motion analysis technique to characterize metacarpophalangeal joint (MCPJ) motion in the absence and presence of protective legwear in a healthy pony. Our in vivo marker tracking precision was 0.09 mm for walk and trot, and 0.10 mm during jump down exercises. We report MCPJ maximum extension (walk: -27.70 ± 2.78° [standard deviation]; trot: -33.84 ± 4.94°), abduction/adduction (walk: 0.04 ± 0.24°; trot: -0.23 ± 0.35°) and external/internal rotations (walk: 0.30 ± 0.32°; trot: -0.49 ± 1.05°) indicating that the MCPJ in this pony is a stable hinge joint with negligible extra-sagittal rotations. No substantial change in MCPJ maximum extension angles or vertical ground reaction forces (GRFv) were observed upon application of legwear during jump down exercise. Neoprene boot application yielded -65.20 ± 2.06° extension (GRFv = 11.97 ± 0.67 N/kg) and fleece polo wrap application yielded -64.23 ± 1.68° extension (GRFv = 11.36 ± 1.66 N/kg), when compared to naked control (-66.11 ± 0.96°; GRFv = 12.02 ± 0.53 N/kg). Collectively, this proof of concept study illustrates the benefits and practical limitations of using XROMM to document equine MCPJ kinematics in the presence and absence of legwear.

We investigated the in vivo length changes of the collateral ligaments of metacarpophalangeal joint during flexion. We obtained computed tomography scans of index, middle, ring and little fingers at 0°, 30°, 60° and 90° of joint flexion from six hands of six healthy adult volunteers. Three of them had their dominant right hand studied, and the other three had their non-dominant left hand studied. We measured and analysed the radial and ulnar collateral ligaments of each metacarpophalangeal joint from the reconstructed images. We found that the dorsal and middle portions of the both radial and ulnar collateral ligament lengthened progressively during digital flexion and reached the maximum at 90° flexion. The length of the volar portion increased from 0° to 30° flexion and then decreased from 30° to 60° flexion, reaching the minimum at 90°. In conclusion, three portions of collateral ligaments on both sides of the metacarpophalangeal joint have variable length changes during flexion, which act to stabilize the joint through its flexion arc.

This paper proposes a novel and simple method to compute all possible solutions of the inverse kinematics problem of the five-oblique-axis thumb model with intersecting axes at the metacarpophalangeal joint. This thumb model is one of the suggested results by a magnetic-resonance-imaging-based study that, in contrast to those based on cadaver fingers or on the tracking of the surface of the fingers, takes into account muscle and ligament behaviors and avoids inaccuracies resulting from the movement of the skin with respect to the bones. The proposed distance-based inverse kinematics method eliminates the use of arbitrary reference frames as is usually required by standard approaches; this is relevant because the numerical conditioning of the resulting system of equations with such traditional approaches depends on the selected reference frames. Moreover, contrary to other parametrizations (e.g., Denavit-Hartenberg parameters), the suggested distance-based parameters for the thumb have a natural, human-understandable geometric meaning that makes them easier to be determined from any posture. These characteristics make the proposed approach of interest for those working in, for instance, measuring and modeling the movement of the human hand, developing rehabilitation devices such as orthoses and prostheses, or designing anthropomorphic robotic hands.

Complications following extensor indicis proprius (EIP) tendon transfer are loss of strength, independence and mobility in the index finger in extension. The main goal of this study was to measure the index finger's independent and dependent extension strength after a tendon transfer. Secondary goals were to determine if the index finger retained the ability to extend independently after the transfer and to evaluate second metacarpophalangeal (MCP) joint mobility. Our study consisted of 19 patients in whom the EIP tendon had been divided proximally to the extensor hood. The EIP tendon was retrieved through a proximal approach at the distal radius level and rerouted towards a recipient tendon. At an average follow-up of 41 months, the average independent extension strength was 5.6N versus 11N on the contralateral side and the dependent strength was 10.9N versus 20N. No patient complained of a loss of extension strength and all had retained independent active extension on the operated index finger. The second MCP joint on the operated side had an independent extension lag of 15.3° compared to the contralateral healthy side and a dependent extension lag of 0.2°. Two patients were impaired in their daily activities when moving the operated index finger. Our results show that EIP harvesting for tendon transfer leads to decreased independent and dependent strength as well as decreased active extension of the second MCP joint. However, the functional impact was negligible and should not compromise the use of the EIP as a tendon transfer., Level of Evidence: III., (Copyright © 2016 SFCM. Published by Elsevier Masson SAS. All rights reserved.)

Simple, lumped-parameter musculoskeletal models may be more adaptable and practical for clinical real-time control applications, such as prosthesis control. In this study, we determined whether a lumped-parameter, EMG-driven musculoskeletal model with four muscles could predict wrist and metacarpophalangeal (MCP) joint flexion/extension. Forearm EMG signals and joint kinematics were collected simultaneously from 5 able-bodied (AB) subjects. For one subject with unilateral transradial amputation (TRA), joint kinematics were collected from the sound arm during bilateral mirrored motion. Twenty-two model parameters were optimized such that joint kinematics predicted by EMG-driven forward dynamic simulation closely matched measured kinematics. Cross validation was employed to evaluate the model kinematic predictions using Pearson׳s correlation coefficient (r). Model predictions of joint angles were highly to very highly positively correlated with measured values at the wrist (AB mean r=0.94, TRA r=0.92) and MCP (AB mean r=0.88, TRA r=0.93) joints during single-joint wrist and MCP movements, respectively. In simultaneous multi-joint movement, the prediction accuracy for TRA at the MCP joint decreased (r=0.56), while r-values derived from AB subjects and TRA wrist motion were still above 0.75. Though parameters were optimized to match experimental sub-maximal kinematics, passive and maximum isometric joint moments predicted by the model were comparable to reported experimental measures. Our results showed the promise of a lumped-parameter musculoskeletal model for hand/wrist kinematic estimation. Therefore, the model might be useful for EMG control of powered upper limb prostheses, but more work is needed to demonstrate its online performance., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Mobility of the fingers metacarpophalangeal (MCP) joints depends on the posture of the adjacent ones. Current Biomechanical hand models consider fixed ranges of movement at joints, regardless of the posture, thus allowing for non-realistic postures, generating wrong results in reach studies and forward dynamic analyses. This study provides data for more realistic hand models. The maximum voluntary extension (MVE) and flexion (MVF) of different combinations of MCP joints were measured covering their range of motion. Dependency of the MVF and MVE on the posture of the adjacent MCP joints was confirmed and mathematical models obtained through regression analyses (RMSE 7.7°).

Background: The flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) are critical for finger flexion. Although research has recently focused on these tendons' coactivity, their contributions in different tasks remain unclear. This study created a novel simultaneous approach to investigate the coactivity between the tendons and to clarify their contributions in different tasks., Methods: Ten human cadaveric hands were mounted on our custom frame with the FDS and FDP of the third finger looped through a mechanical pulley connected to a force transducer. Joint range of motion, tendon excursion and loading force were recorded during individual joint motion and free joint movement from rest to maximal flexion. Each flexor tendon's moment arm was then calculated., Results: In individual motions, we found that the FDP contributed more than the FDS in proximal interphalangeal (PIP) joint motion, with an overall slope of 1.34 and all FDP-to-FDS excursion (P/S) ratios greater than 1.0 with force increase. However, the FDP contributed less than the FDS in metacarpophalangeal (MCP) joint motion, with an overall slope of 0.95 and P/S ratios smaller than 1.0 throughout the whole motion except between 1.9% and 13.1% force. In free joint movement, the FDP played a greater role than the FDS, with an overall ratio of 1.37 and all P/S ratios greater than 1.0., Conclusions: The new findings include differences in finger performance and excursion amounts between the FDS and FDP throughout flexion. Such findings may provide the basis for new hand models and treatments.

Ulnar nerve paralysis results in classic stigmata, including weakness of grasp and pinch, poorly coordinated flexion, and clawing of digits. Restoration of grasp is a key portion of the reconstructive efforts after loss of ulnar nerve function. Improving flexion at the metacarpophalangeal joint can be done by static and dynamic means, although only the latter can improve interphalangeal extension. Deformity and digital posture are more predictably corrected with surgical intervention. Loss of strength from intrinsic muscle paralysis cannot be fully restored with tendon transfer procedures. Preoperative patient education is paramount to success if realistic expectations are to be met., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The objective of this study was to identify three-dimensional finger joint angles for various hand postures and object properties. Finger joint angles were measured using a VICON system for 10 participants while they pinched objects with two, three, four and five fingers and grasped them with five fingers. The objects were cylinders and square pillars with diameters of 2, 4, 6 and 8 cm and weights of 400, 800, 1400 and 1800 g. Hand posture and object size more significantly affected the joint flexion angles than did object shape and weight. Object shape affected only the metacarpophalangeal (MCP) joint angle of the index finger and the flexion angle of the MCP joint of the little finger. Larger flexion angles resulted when the hand posture was grasping with five fingers. The joint angle increased linearly as the object size decreased. This report provides fundamental information about the specific joint angles of the thumb and fingers. Practitioner Summary: Three-dimensional finger joint angles are of special interest in ergonomics because of their importance in handheld devices and musculoskeletal hand disorders. In this study, the finger joint angles corresponding to various hand postures and objects with different properties were determined.

Collateral ligaments are difficult to repair due to large amount of fraying in detached ligaments and attenuated stumps that may not provide enough strength after the repair. Although strong locking sutures are used to repair the ligament with proper tension, these damages can cause pull-out failure or relaxation of the repaired ligaments even from undersized load that may extend postoperative splinting or casting time. Furthermore, current suture techniques can repair varus or valgus instability of the elbow and radial or ulnar instability of the fingers, but these techniques do not offer rotatory stability of these areas. We have developed a novel suture anchor technique that has overcome this problem of current suture techniques, and this can be used to correct rotatory instability in the elbow and fingers. We used this procedure in seven cases with injury of collateral ligament in the elbow and eight cases with detached collateral ligaments of finger joint. No patient experienced rerupture or any kind of residual instability. We believe that the proposed method can produce much stronger repair and may shorten the postoperative immobilization period.

Background: The goals of this study were to compare maximal metacarpophalangeal joint (MCPJ) flexion angles after application of a volar short arm splint at 3 different locations and verify the relations between the three different physical and radiological locations., Methods: Forty dominant hands of healthy subjects were analyzed in the study. We defined a transverse skin folding line as a line drawn from the radial aspect of the thenar crease to the ulnar aspect of the distal transverse palmar crease. The distal end of the volar short arm splint was applied on 3 parallel locations to this line. Location A was on this transverse skin folding line; location B was 1 cm proximal to location A; and location C was 1 cm distal to location A. Two orthopedic surgeons measured the maximal MCPJ flexion angles of each finger except the thumb with the application of a volar short arm splint at 3 different locations as well as without a splint as a control. Radiological locations of the 3 different distal ends of the volar short arm splint were also assessed by anteroposterior radiographs of the wrist., Results: When the splint was applied at location A and C, the maximal MCPJ flexion angle decreased to a mean of 83° (91% of control value) and 56° (62% of control value), respectively (compared to the control, p < 0.001). At location B, the maximal MCPJ flexion angle was a mean of 90° (99% of control value); no significant difference was observed compared to the control or without the splint (p = 0.103). On radiography, the average length from the metacarpal head to the distal end of the splint at all fingers decreased in the order of location B, A, and C (29 mm, 19 mm, and 10 mm, respectively; p < 0.001)., Conclusions: We recommend applying the distal end of a volar short arm splint at proximal 1 cm to the transverse skin folding line to preserve MCPJ motion perfectly, which is located at distal 44% of the whole metacarpal bone length radiologically.

Three-dimensional fingertip trajectory was examined under different force levels of the lumbrical muscle to clarify the function of the lumbrical muscle in free index finger motion. The metacarpophalangeal joint balancing effect of the lumbrical muscle in the thumb-up position was also examined. The motions of the finger bones were recorded during simulated contraction of flexor digitorum profundus when different forces (0.000-1.960 N) were applied to the lumbrical muscle in cadaveric specimens. The greater the force with which the lumbrical muscle was pulled, the larger the arc formed by the fingertip, and the greater the rebalancing influence on the metacarpophalangeal joint. This result indicates that the lumbrical muscle functions simultaneously to enlarge the fingertip trajectory and to balance the metacarpophalangeal joint against gravity in the axial plane. A 0.980 N force was ideal for maximal finger movement. The lumbrical muscle rebalanced the metacarpophalangeal joint against gravity in the thumb-up position with a force ⩾0.980 N., (© The Author(s) 2015.)

A synovial plica is present at the dorsoproximal aspect of the fetlock joint. The objective of this study was to describe the location of the synovial plica during induced hyperextension using Magnetic Resonance Imaging. For this study 20 cadaver limbs from five Warmblood horses were used. Measurements were made of the dorsal; palmar/plantar length and the thickness of the plica with the joint in a normal position. During induced hyperextension of the joint, the position of the plica was described; the dorsal angle of extension and angle of contact between the proximal phalanx (P1) and the condyle were measured. The dorsal length differed between front/hind limbs and between the medial/lateral aspect of the joint. The angle of contact between P1 and condyle differed between front/hind limbs; between the lateral and medial aspect of the joint and between different positions of the plica. Four different positions of the plica were observed: shortened with the tip curved towards palmar/plantar; projecting distally; projecting towards dorsal and projecting distally with the tip interposed between P1 and the condyle. During induced hyperextension, a close relation is present between the synovial plica, P1 and the condyle with a variable position of the plica; which is suggestive for a contact interface between P1 and the metacarpal/metatarsal bone. However the plica does not seem to act consistently as a cushioning surface., (© 2014 Blackwell Verlag GmbH.)

A kinematic model representing the versatility of the human hand is needed to evaluate biomechanical function and predict injury risk in the workplace. We improved upon an existing optoelectronic-based kinematic hand model with grouped metacarpals by defining segmented metacarpals and adding the trapeziometacarpal joint of the thumb. Eight participants performed three static postures (neutral pose, cylinder grip, cap grip) to evaluate kinematic performance of three different models, with one, two, and four metacarpal segment(s). Mean distal transverse metacarpal arch angles in the four-segment metacarpal model were between 22.0° ± 3.3° (neutral pose) and 32.1° ± 3.7° (cap grip). Representation of the metacarpals greatly influenced metacarpophalangeal joint rotations. Both the two- and four-segment metacarpal models displayed significantly lower metacarpophalangeal joint 'supination' angles (than the one-segment model) for the fourth and fifth fingers. However, the largest reductions were for the four- versus one-segment models, with mean differences ranging from 9.3° (neutral pose) to 17.0° (cap grip) for the fourth finger and 16.3° (neutral pose) to 33.0° (cylinder grip) for the fifth finger. MCP joint abduction/adduction angles of the fourth and fifth fingers also decreased with segmentation of the metacarpals, although the lowest magnitudes generally occurred in the four-segment model. Overall, the four-segment metacarpal model produced the lowest accessory rotations in non-dominant axes, and best matched previous radiological studies that found MCP joint pronation/supination angles were typically less than 10°. The four-segment metacarpal model, with improved anatomic fidelity, will better serve future studies of detailed actions of the hand in clinical or work applications.

Background: Although extensor tendon rupture associated with distal radioulnar joint disorder is often encountered, its treatment has not yet been established. We report the postoperative results for reconstruction of finger extensor tendon rupture due to distal radioulnar lesion and analyse the factors affecting postoperative extension lag., Methods: We examined 74 index, middle, ring, or little fingers with extensor tendon rupture of 34 hands. Primary diseases were rheumatoid arthritis in 24 hands and osteoarthritis in 10. Reconstruction methods included tendon graft in 45 fingers, extensor indicis proprius tendon transfer in 15, and end-to-side adjacent tendon suture in 14. At final postoperative follow-up ranging from 12 to 40 (mean: 18) months, we measured metacarpophalangeal (MCP) joint range of motion and extension lag and statistically evaluated the relationship between postoperative extension lag and several clinical factors., Results: We encountered no cases of re-rupture or worsening of finger flexion range after reconstruction. Mean postoperative active flexion of the MCP joint was 78.1 (range: 45-95) degrees. Mean postoperative extension lag was 10.3 (range: 0-50) degrees. We observed that postoperative extension lag was significantly larger in fingers associated with extensor tendon rupture in two or three additional fingers in the affected hand or in fingers of patients aged 80 years or over. The interval from rupture to reconstruction, reconstruction method, or arthritis type did not remarkably affect outcome., Conclusions: This study uncovered that surgical intervention for extensor tendon rupture should be performed before three fingers become affected., (Copyright © 2015 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)

Knowledge of the spatial layout of bodies is mediated by a representation called the body structural description, damage to which results in the condition of autotopagnosia in which patients are impaired in judgments about the location and configuration of body parts. While a large literature has investigated disruption of the body structural description, little research has examined its accuracy in healthy individuals. I show that people have systematically distorted knowledge of the configuration of hands. Participants judged the location of their knuckles (i.e., the metacarpophalangeal joint) by pointing with a baton on their palm. Participants showed clear distal biases, judging their knuckles as farther forward in the hand than they actually are for all fingers except the thumb. This effect appeared both when participants localized the knuckles of their own hand and another person's hand. These results suggest that intuitive beliefs about body form are systematically distorted., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Purpose: A 2-part biomechanical study was constructed to test the hypothesis that coronal morphology of the thumb metacarpophalangeal joint impacts the assessment of instability in the context of radial collateral ligament (RCL) injury., Methods: Fourteen cadaveric thumbs were disarticulated at the carpometacarpal joint. Four observers measured the radius of curvature of the metacarpal (MC) heads. In a custom jig, a micrometer was used to measure the RCL length as each thumb was put through a flexion and/or extension arc under a 200 g ulnar deviation load. Strain was calculated at maximal hyperextension, 0°, 15°, 30°, 45°, and maximal flexion. Radial instability was measured with a goniometer under 45 N stress. The RCL was then divided and measurements were repeated. Analysis of variance and Pearson correlation metrics were used., Results: The RCL strain notably increased from 0° to 30° and 45° of flexion. With an intact RCL, the radial deviation was 15° at 0° of flexion, 18° at 15°, 17° at 30°, 16° at 45°, and 14° at maximal flexion. With a divided RCL, instability was greatest at 30° of flexion with 31° of deviation. The mean radius of curvature of the MC head was 19 ± 4 mm. Radial instability was inversely correlated with the radius of curvature to a considerable degree only in divided RCL specimens, and only at 0° and 15° of flexion., Conclusions: The RCL contributes most to the radial stability of the joint at flexion positions greater than 30°. The results suggest that flatter MC heads contribute to stability when the RCL is ruptured and the joint is tested at 0° to 15° of metacarpophalangeal flexion., Clinical Relevance: The thumb MC joint should be examined for RCL instability in at least 30° of flexion., (Copyright © 2015 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.)