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Our aim was to clarify the anatomy and function of the retinacular ligaments. Forty-eight fingers were dissected and the thickness of the oblique retinacular ligament (ORL) was graded. In four fingers, the motion in the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints was subjected to an in-depth analysis before and after sectioning of either the lateral bands (LB) or the ORLs. The function of the ORLs in restricting flexion of the DIP joint with full extension of the PIP joint was measured in 10 fingers. An ORL could be identified on both sides in all 48 fingers. The distribution of the insertion on the proximal phalanx was 7/96 (7%) in the distal third, 70/96 (73%) in the middle third and 19/96 (20%) in the proximal third. Among the specimens, 29% were graded as having a strong bundle of fibers, 51% as having well-defined and regular fibers and 20% as having thin and sparse fibers. With the PIP joint extended, there was a statistically significant increase in flexion of the DIP joint after the ORL was cut. After the LB was sectioned, the ORL was able to extend the DIP joint with an extension lag of 10-22°. Cutting the ORL did not affect the ability to extend that joint. We conclude that the retinacular ligaments are consistent. Their major role is not connected with finger movement, but to provide stabilizing links between the PIP and DIP joints. They are active in not only specific, uncommon finger positions but also in ordinary use of the fingers., (© 2023 American Association of Clinical Anatomists and British Association of Clinical Anatomists.)

Objectives: The objectives of this ultrasound and anatomical study were: (1) To evaluate the reliability of ultrasound identification of the enthesis of the central slip of the extensor digitorum tendon (CSET) using cadaver specimens; (2) To assess the concordance of the measurement of the CSET thickness by ultrasound and gross anatomy; (3) To evaluate the variation in ultrasound identification of the CSET enthesis in a cadaveric experimental model of PIP synovitis., Methods: Four rheumatologist ultrasonographers blindly and independently measured by ultrasound the CSET enthesis thickness in the second to fifth fingers of 8 hands from fresh-frozen human cadavers in two rounds. These fingers were dissected and the thickness of the CSET measured by the anatomist. In addition, an artificial synovitis was created in the proximal interphalangeal (PIP) joints of a different cadaveric hand. The ultrasonographic CSET enthesis thickness was measured by the four investigators before and after intra-articular ultrasound guided injection of material., Results: Intra- and inter-observer reliability of CSET enthesis thickness measurement were good to excellent (ICC 0.93 for intra-observer agreement and 0.89-0.92 for inter-observer agreement). Ultrasound measurements were consistent and only slightly smaller than the anatomical ones (µ = -0.039 mm). The differences between the measurements of CSET enthesis thickness before and after the synovitis model were not statistically significant., Conclusion: Ultrasound demonstrated high multiobserver reliability and agreement with gross anatomy in identifying the CSET enthesis and discriminated it from the capsular tissue of the PIP. Furthermore, an experimental model of PIP synovitis did not interfere with its identification., Competing Interests: Conflict of interest None., (Copyright © 2024 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

Background: Surgical approaches to the proximal interphalangeal (PIP) joint often require disruption of soft tissue stabilizers. Additionally, PIP joint injuries frequently result in soft tissue disruption. This study evaluates the necessity of repairing soft tissue stabilizers by assessing their role in maintaining native joint congruity., Methods: Eight specimens were used to evaluate congruity at 0° and 30° flexion when loaded with 2 N of valgus force. This was performed in the native joint and after sequential sectioning of the surrounding ligaments in order: volar plate (VP), radial collateral ligament (CL), and ulnar CL. The skin flap was sutured with the ligaments unrepaired and the load was reapplied. Radiographs were taken after each load and used to measure the joint line convergence angle (JLCA)., Results: Mean JLCA increased in both degrees of flexion after ligaments were sectioned but was only significantly different from the native joint after the VP was disrupted along with 1 CL. Joint congruity improved following repair of the skin flap in both degrees of flexion but was not significant. Joints were more congruent in 30° flexion for all subgroups, but none were significantly different compared to 0° flexion., Conclusions: Disruption of the VP is insufficient to significantly alter PIP joint congruity. While sectioning of both the VP and CLs resulted in a statistically significant change in joint congruity, mean JLCA demonstrated changes of minor clinical significance. The osseous anatomy of the phalanges imparts inherent stability that maintains a congruent joint despite loss of the soft tissue stabilizers.

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.)

Based on CT scan, the finite element models of human arm were constructed. Modal analysis of the arm was performed, and the natural vibration characteristics were evaluated. The dynamic simulation of the vibration transmission process was carried out when grasping the handle, and the vibration response and transmission characteristics were investigated. Resonance was likely to occur in the ranges of 5-10 Hz and 35-40 Hz, which caused fatigue damage to the arm. Vibrations in the ranges should be avoided having direct contact with the handle. The analysis results were found to be consistent with those of modal analysis.

The proximal interphalangeal joint (PIPJ) is a complex anatomical structure. In managing fracture dislocations about the PIPJ, the aim is to restore a congruent joint that allows for smooth gliding motion. Detailed knowledge of the anatomy and biomechanics of the PIPJ is necessary in managing these injuries with predictable success. The breadth of techniques previously described in the treatment of such injuries is testament to the difficulties faced in achieving optimal clinical and radiological outcomes. In this article we detail the anatomy and biomechanics of the PIPJ and summarize current literature and principles for the treatment of dorsal fracture dislocations.

Our purpose was to compare the contributions of these two systems to assess PIP joint extension in fresh cadaver models. Nine middle fingers of fresh cadavers were used. The PIP joint angle was measured while an extension load was applied on the extensor tendons. Specimens on which extension load was applied on the extrinsic extensors were classified as the extrinsic group, and those on which extension load was applied on the intrinsic extensors were classified as the intrinsic group. Linear regression analyses were performed to obtain regression equation and the extension load-PIP joint angle curve. The mean of slope of the curve was compared between the two groups using paired t -test. The same experiments were done for the metacarpophalangeal (MP) joint in 0° and 60° flexion to evaluate the effect of MP joint flexion on PIP joint extension. The mean slope of the extension load-PIP joint angle curve of the extrinsic group was significantly greater than that of the intrinsic group. With the MP joint in 0° flexion, the mean slope of the extrinsic and intrinsic groups was -0.148 and -0.117, respectively (greater absolute value means greater slope, p = 0.01). With the MP joint in 60° flexion, the mean slopes were -0.147 and -0.104, respectively ( p = 0.015). The contribution of the intrinsic extensor for PIP joint extension shows decreasing trends with MP joint flexion. The extrinsic extensors have greater contribution for PIP joint extension compared with the intrinsic extensors., Competing Interests: All authors have no conflicts of interests to be declared., (Copyright © 2020 Junho Park et al.)

"Stiff finger," defined as a finger with decreased range of motion in one or more joints, is commonly found after hand injury and is classified into flexion or extension deformities. Pathogenesis is due to dysfunction in one or more of the following anatomic components: (1) osseous and articular; (2) capsuloligamentous; (3) musculotendinous units; (4) soft tissue and fascia. Evaluation and treatment are based on accurate identification and correction of pathologic structures. The mainstay of treatment is directed hand therapy with exercises and splinting to mobilize stiff joints. Operative interventions are offered after gains from therapy have been exhausted., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Background: Flexor zone II is defined as the region spanning the proximal aspect of the A1 pulley to the insertion of the flexor digitorum superficialis (FDS) tendon. Descriptions of the FDS insertion are inconsistent in the literature, but zones of injury are frequently determined with reference to superficial landmarks. The purpose of this study was to describe the footprint of the FDS insertion and define its relationship to the proximal interphalangeal (PIP) skin crease., Methods: The FDS insertion on the index, middle, ring, and small fingers was dissected in 6 matched pairs of fresh-frozen cadaveric hands. A Kirschner wire was used to mark the level of the PIP skin crease on bone before measurements of the FDS footprint and its position relative to the PIP skin crease were made using digital calipers., Results: The radial and ulnar FDS slips inserted a mean distance of 3.22 mm from the distal aspect of the PIP skin crease and varied by digit. The mean distal extent of the FDS insertion was 8.29 mm. The mean length of the insertion of each FDS slip was 5.15 mm and the mean width was 1.9 mm., Conclusions: The radial and ulnar FDS slips insert on average 3.22 mm distal to the PIP skin crease and vary by digit. Knowledge of the FDS insertion is clinically relevant when differentiating between flexor zone I and zone II injuries, planning surgical approaches to the finger, and in guiding patient expectations for surgery given the variability in outcome based on zone of injury.

This lecture will focus on posttraumatic finger contractures affecting the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints in adults. The pathophysiology, main causes and essential rehabilitation methods that can be used before resorting to surgical treatment are described, along with the clinical examination. The goal is to define the surgical indications, even though the literature shows the functional outcomes are disappointing. While there is little to no change in a joint's angular amplitude, the functional range of motion can be improved. There is practically no functional improvement except in cases of MCP extension contracture. For the PIP joint, the aim is to shift the range of motion into the functional range. Surgical approaches, surgical techniques and rehabilitation protocols are described in detail., (Copyright © 2018 SFCM. Published by Elsevier Masson SAS. All rights reserved.)

Introduction: An abnormal distal insertion of the extensor pollicis brevis (EPB) tendon into the thumb interphalangeal joint (IP) has been observed in refractory cases of de Quervain's disease. This is associated with the extensor being wider at the midpoint of the proximal phalanx; however, there is no method to noninvasively measure this. This study evaluated the accuracy of measuring the extensor width using ultrasonography, to establish a noninvasive method for predicting an EPB extending the IP insertion., Materials and Methods: Of 23 arms from 12 fresh frozen cadavers, the extensor tendon width at the midpoint of the proximal phalanx was measured using ultrasonography and directly at dissection. The association between these values was evaluated using correlation analysis. A cut-off value of extensor tendon width was obtained using receiver operating characteristic analysis., Results: A strong correlation was observed between the ultrasonography and the measured values. The EPB tendons were normal in 13 arms (57%) and extended in 10 (43%), with a significant difference between these groups in the mean width of the extensor tendon (6.8 ± 1.1 vs. 8.4 ± 1.0 mm). A cut-off extensor tendon width of 8.0 mm yielded an EPB extending the IP., Conclusion: An EPB extending the IP tendon can be predicted by measuring the extensor tendon width at the midpoint of the proximal phalanx using ultrasonography. The cut-off tendon width value of ≥ 8.0 mm may be useful for assessments prior to surgery and for conservative care.

Background: Arthroscopy is a widely used minimally invasive technique. Nevertheless, no report describes the arthroscopic anatomy of the proximal interphalangeal (PIP) joint for portal creation. To facilitate arthroscopy, this study elucidated the anatomy of the lateral bands of the extensor mechanism and collateral ligaments of PIP joints., Methods: A total of 39 fingers from the right hands of 10 cadavers (4 males, 6 females) were evaluated in this study. We defined the extension line from the proximal interphalangeal volar crease as the C-line. We also defined an imaginary line along the distal edge of the proximal phalanx, which is parallel to the C-line, as the J-line. The distance between J-line and C-line was measured. On the C-line and J-line, we measured the following: from the dorsal skin to the lateral edge of the lateral band (LB), the dorsal edge of the collateral ligament (CL) and from the lateral band and the collateral ligament (D), the width of the finger (W). The finger half-width (M) was measured on the J-line. Comparison between the digits and comparison between radial and ulnar distance were measured and statistical analysis was performed., Results: All PIP joint spaces were distal from the C-line, except for one ring finger. The average distances between the J-line and C-line were 1.8-3.2 mm. On the C-line, only 11 cases (14.1%) showed an interval between the lateral bands and the collateral ligaments, but, on the J-line 72, cases (92.3%) had such an interval. The interval was located 1.6-2.9 mm in a dorsal direction from the midlateral on the J-line., Conclusions: Portal creation at the J-line is safer than at the C-line. This study revealed that safe portals for arthroscopy of the PIP joint are 2 mm dorsal to the midlateral line of the finger on the J-line.

Proximal interphalangeal (PIP) joint arthritis causes debilitating hand pain and instability leading to significant functional impairment. Arthrodesis remains the gold standard for treatment of PIP arthritis. We present a minimally invasive PIP arthrodesis that provides rigid fixation with a headless compression screw. Seven patients who presented to the senior author with PIP joint arthritis underwent PIP arthrodesis by minimally invasive technique. A 1 cm transverse incision is made over the PIP joint, incising skin, central band, and articular capsule. PIP joint is flexed to expose the articular surface. Articular surfaces are prepared with a fine tipped rongeur, exposing subchondral bone until flat surfaces are obtained. Under fluoroscopy a guide wire for cannulated headless screw (3.0, 2.4, or 2.0 mm) is inserted in an antegrade manner. It progresses from the center of the proximal phalangeal articular surface until it exits through the dorsal cortex and the distal end lies within the subchondral bone. This is the most critical step of the procedure because the guide wire angle determines the degree of flexion of the fusion. A 5 mmincision is made over the guide wire and the wire is advanced through the center of the medullary canal of the middle phalanx. The wire is then overdrilled, length is measured, and a headless compression screws is inserted. Reevaluate alignment after insertion of the screws because malrotation may be induced by torque during compression. Six consecutive patients underwent the procedure by the senior author. All patients healed the arthrodesis without complications and hardware removal was not needed. Minimally invasive PIP joint arthrodesis is a safe and viable procedure. Critical portions of the procedure include placing the wire at the angle of the desired angle of fusion and avoiding malrotation during screw insertion.

Proximal interphalangeal joint (PIPJ) flexion contracture is a challenging and often frustrating problem. Treatment of PIPJ contracture begins with conservative measures. With good compliance and prolonged use, favorable results can be achieved using these modalities. For contractures that fail to respond to conservative treatment, surgical intervention can be considered. The affected structures that can be released during surgery include the accessory collateral ligaments, volar plate, checkrein ligaments, retinacular ligaments, and the flexor and extensor tendons. A stepwise approach to release is typically favored in which active motion is tested after each release to determine the need for subsequent releases., (Copyright © 2018 Elsevier Inc. All rights reserved.)

A complete understanding of the normal anatomy and biomechanics of the proximal interphalangeal joint is critical when treating pathology of the joint as well as in the design of new reconstructive treatments. The osseous anatomy dictates the principles of motion at the proximal interphalangeal joint. Subsequently, the joint is stabilized throughout its motion by the surrounding proximal collateral ligament, accessory collateral ligament, and volar plate. The goal of this article is to review the normal anatomy and biomechanics of the proximal interphalangeal joint and its associated structures, most importantly the proper collateral ligament, accessory collateral ligament, and volar plate., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Fracture dislocations of the proximal interphalangeal (PIP) joint of the finger are often caused by axial load applied to a flexed joint. The most common injury pattern is a dorsal fracture dislocation with a volar lip fracture of the middle phalanx. Damage to the soft-tissue stabilizers of the PIP joint contributes to the deformity seen with these fracture patterns. Unfortunately, these injuries are commonly written off and left untreated. A late-presenting PIP joint fracture dislocation has a poor chance of regaining normal range of motion. The provider must be suspicious of these injuries. Treatment options and algorithm are reviewed., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Proximal interphalangeal joint injuries are one of the most common injuries of the hand. The severity of injury can vary from a minor sprain to a complex intra-articular fracture. Because of the complex anatomy of the joint, complications may occur even after an appropriate treatment. This article provides a comprehensive review on existing techniques to manage complications and imparts practical points to help prevent further complications after proximal interphalangeal joint injury., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Introduction: The extensor pollicis brevis (EPB) tendon normally inserts into the base of the proximal phalanx of the thumb. However, a distal insertion of the EPB tendon into the thumb interphalangeal joint has been reported in refractory cases of de Quervain's disease. We hypothesized that the EPB tendon is wider beyond the thumb metacarpophalangeal joint in patients with extended EPB. This study aimed to evaluate the relationship between the extensor tendon width and the point of distal insertion of the EPB tendon., Materials and Methods: In 45 hands from 18 male and 27 female adult cadavers, the first extensor compartment was dissected and the existence of the intertendinous septum was assessed. The extensor tendon width was measured at the midpoint of the proximal phalanx, and relationships between extended EPB tendon, existence rate of the intertendinous septum, sex, and extensor tendon width were examined., Results: Of 45 cases, intertendinous septum and extended EPB tendon were observed in 37 (82.2%) and 23 (51.1%), respectively. There was no significant difference between the existence rates of both these factors and sex. The mean extensor tendon width in the extended EPB group was significantly greater than in the normal EPB group. The cut-off value of extensor tendon width in the extended EPB group was 7.12 mm., Conclusions: The extensor tendon width was wider in the extended EPB group than in the normal EPB group, suggesting that the differences in the EPB tendon width can be used to identify various anatomical variations in extended EPB.

Background  This study aimed to evaluate the size of the joint surfaces of the proximal and distal interphalangeal finger joints. Material and Methods  117 proximal and distal interphalangeal joints of 30 formalin-fixed hands of body donors were included in this study. The size of the articular surface was determined for each joint. Results  The mean size of the proximal joint surface of the distal interphalangeal joint is 56.1 mm 2 ; the distal joint surface averages 30.9 mm 2 (ratio: 1.8:1). The size of the proximal articular surface of the proximal interphalangeal joint is 92.5 mm 2 . The size of the distal articular surface averages 52.4 mm 2 (ratio 1.7:1). Conclusions  This is the first study to describe the articular surface area of the proximal and distal interphalangeal joints of the hand., Competing Interests: Interessenkonflikt: Die Autoren geben an, dass kein Interessenkonflikt besteht., (Georg Thieme Verlag KG Stuttgart · New York.)

Context: Jam injuries of the finger are frequently encountered in general orthopaedic and sports medicine practice. The finger joints in particular are very susceptible to traumatic injury, but in the absence of severe deformity, digital trauma is often downplayed in the hopes of a more rapid return to game play., Evidence Acquisition: Articles published from 1966 to 2015 were reviewed to capture historical and current views on the presentation, diagnosis, and treatment of jam injuries in athletes., Study Design: Clinical review., Level of Evidence: Level 5., Results: Although jam injuries are frequently grouped together, they represent a host of injuries that can be challenging to differentiate. A thorough knowledge of finger joint anatomy and injury mechanism is critical to perform an appropriate examination, establish an accurate diagnosis, and identify a treatment plan for each patient., Conclusion: Every member of the athletic care team must be aware of the spectrum of digital injuries, including the basic signs present on examination, which may indicate the need for more formal workup. Additionally, preventing injury through athlete education is paramount to athletic care., Competing Interests: The authors report no potential conflicts of interest in the development and publication of this article., (© 2016 The Author(s).)

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.

Purpose: Post-traumatic arthritis is common in long-term follow-up of patients undergoing hemi-hamate arthroplasty (HHA). We hypothesize that anatomic mismatch could play a role in the development of arthritis. The purpose of this study is to establish a novel, computed tomography (CT)-based imaging technique for pre-operative assessment in HHA. With this technique, our group aims to identify digits with a high likelihood for anatomical mismatch between the donor graft and recipient interphalangeal joint. Using this technique to eliminate cases with high-likelihood of incongruent anatomy, we hypothesize the rates of arthritis could be reduced., Methods: We conducted a retrospective review of upper extremity CT scans from 2007 to 2014 at our institution. Those studies meeting our inclusion criteria were exported to a clinical radiology software suite. Subsequently, angular and linear measurements of the hamate and potential recipient proximal interphalangeal joints were collected. Angular and linear comparisons were then made between the donor hamate graft and the individual recipient sites. Using pre-established cutoff values, matches were deemed to be inconsistent or consistent., Results: The study included 31 CT scans. The rate of anatomical consistency was low; the small finger was most often consistent (38.7 %) and the index finger was least often consistent (12.9 %). Linear inconsistency was common in all joints besides the small finger; angular inconsistency was most prevalent in the index and long fingers., Conclusions: This novel use of CT scans as a tool for pre-operative HHA planning is a crucial first step in trying to reduce the observed rates of arthritis after HHA.

The purpose was to identify the A1 pulley's exact location and thickness by comparing measurements from a clinical high-frequency ultrasound scanner system (CHUS), a customized high-frequency ultrasound imaging research system (HURS) and a digital caliper. Ten cadaveric hands were used. We explored the pulley by layers, inserted guide pins and scanned it with the CHUS. After identifying the pulley, we measured each long finger's thickness using the CHUS and excised the pulley to measure its thickness with a digital caliper and the HURS. The thin hypo-echoic layer was revealed to be the synovial fluid space, and the pulley appears hyper-echoic regardless of scan direction. We also defined the pulley's boundaries. Moreover, the CHUS provided a significantly lower measurement of the pulley's thickness than the digital caliper and HURS. Likewise, based on the digital caliper's measurement, the HURS had significantly lower mean absolute and relative errors than the CHUS., (Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

Photoacoustic (PA) imaging of interphalangeal peripheral joints is of interest in the context of using the synovial membrane as a surrogate marker of rheumatoid arthritis. Previous work has shown that ultrasound (US) produced by absorption of light at the epidermis reflects on the bone surfaces within the finger. When the reflected signals are backprojected in the region of interest, artifacts are produced, confounding interpretation of the images. In this work, we present an approach where the PA signals known to originate from the epidermis are treated as virtual US transmitters, and a separate reconstruction is performed as in US reflection imaging. This allows us to identify the bone surfaces. Furthermore, the identification of the joint space is important as this provides a landmark to localize a region-of-interest in seeking the inflamed synovial membrane. The ability to delineate bone surfaces allows us to identify not only the artifacts but also the interphalangeal joint space without recourse to new US hardware or a new measurement. We test the approach on phantoms and on a healthy human finger., (© The Author(s) 2015.)

Background: Pulling the wrist into flexion with the elbow in extension and forearm in pronation has been used as the stretching technique of wrist extensors for lateral epicondylitis. Simultaneous stretching of the fingers in addition to the wrist flexion has also been applied. However, the mechanism of this simultaneous stretching has not been clarified. This study is designed to clarify the mechanism underlying this simultaneous stretching technique based on the anatomical features of the origins of the extensor carpi radialis brevis (ECRB) and extensor digitorum communis (EDC)., Methods: Thirty-nine arms from formalin-embalmed Japanese human specimens were dissected. The features of the origins of the ECRB and EDC were macroscopically observed, and the locations of each origin on the lateral epicondyle were measured., Results: The ECRB had a long and wide, purely tendinous origin which originated from the anterior slope of the lateral epicondyle. The tendinous origin of the index finger of the EDC (EDC-IF) arose from the posterior aspect of the ECRB tendinous origin, with a coexisting muscular portion observed at the level of the proximal forearm. The middle finger of the EDC (EDC-MF) had a short tendinous origin with an associated muscular portion and originated proximo-laterally to the origin of the ECRB on the lateral epicondyle. In addition, the muscular origin of the EDC-MF arose on the superficial and posterior aspect of the ECRB tendinous origin. In contrast, the ring and little fingers of the EDC originated from the tendinous septum of the extensor digiti minimi and extensor carpi ulnaris, and had no connection with the ECRB tendinous origin., Conclusions: On the basis of our anatomical findings, simultaneous stretching of the wrist extensors by wrist, index and middle fingers flexion could provide stretching force to both the tendinous origins of the ECRB and EDC through the EDC-IF and EDC-MF.

Rupture of the extensor pollicis longus (EPL) tendon in the wrist is a delayed complication that can occur after wrist injury. Several etiology-related hypotheses have been made to explain these ruptures. The one most commonly accepted is necrosis at the musculotendinous junction of the EPL, which is compressed between the extensor retinaculum and dorsal aspect of the radius. To confirm this hypothesis, we performed an anatomical study to show the close relationship between the extensor retinaculum and the musculotendinous junction of the EPL muscle. We calculated the distance between the musculotendinous junction of the various finger extensor muscles and the proximal edge of the extensor retinaculum. We were able to show that this junction is located under the extensor retinaculum for the extensor indicis (EI) and EPL muscles, but the latter is in the third extensor compartment, which is a tight, confined space. Any pressure increase in this space following trauma, for example, can bring about compartment syndrome at this musculotendinous junction, which some authors have found to be poorly vascularized.

Primates, and particularly humans, are characterized by superior manual dexterity compared with other mammals. However, drawing the biomechanical link between hand morphology/behaviour and functional capabilities in non-human primates and fossil taxa has been challenging. We present a kinematic model of thumb-index precision grip and manipulative movement based on bony hand morphology in a broad sample of extant primates and fossil hominins. The model reveals that both joint mobility and digit proportions (scaled to hand size) are critical for determining precision grip and manipulation potential, but that having either a long thumb or great joint mobility alone does not necessarily yield high precision manipulation. The results suggest even the oldest available fossil hominins may have shared comparable precision grip manipulation with modern humans. In particular, the predicted human-like precision manipulation of Australopithecus afarensis, approximately one million years before the first stone tools, supports controversial archaeological evidence of tool-use in this taxon., (© 2015 The Author(s) Published by the Royal Society. All rights reserved.)

We determined muscle attachment points for the index, middle, ring and little fingers in an OpenSim upper-extremity model. Attachment points were selected to match both experimentally measured locations and mechanical function (moment arms). Although experimental measurements of finger muscle attachments have been made, models differ from specimens in many respects such as bone segment ratio, joint kinematics and coordinate system. Likewise, moment arms are not available for all intrinsic finger muscles. Therefore, it was necessary to scale and translate muscle attachments from one experimental or model environment to another while preserving mechanical function. We used a two-step process. First, we estimated muscle function by calculating moment arms for all intrinsic and extrinsic muscles using the partial velocity method. Second, optimization using Simulated Annealing and Hooke-Jeeves algorithms found muscle-tendon paths that minimized root mean square (RMS) differences between experimental and modeled moment arms. The partial velocity method resulted in variance accounted for (VAF) between measured and calculated moment arms of 75.5% on average (range from 48.5% to 99.5%) for intrinsic and extrinsic index finger muscles where measured data were available. RMS error between experimental and optimized values was within one standard deviation (S.D) of measured moment arm (mean RMS error = 1.5 mm < measured S.D = 2.5 mm). Validation of both steps of the technique allowed for estimation of muscle attachment points for muscles whose moment arms have not been measured. Differences between modeled and experimentally measured muscle attachments, averaged over all finger joints, were less than 4.9 mm (within 7.1% of the average length of the muscle-tendon paths). The resulting non-proprietary musculoskeletal model of the human fingers could be useful for many applications, including better understanding of complex multi-touch and gestural movements.

The tendon of the extensor indicis (EI) is frequently used to restore the loss of function in other digits. However, it shows many variations which include splitting of the extensor indicis proprius (EIP) into two or three distal slips, attachment to fingers other than the index such as the extensor medii proprius (EMP), attachment onto the index and the third finger such as the extensor indicis et medii communis, or attachment to both the index and the thumb such as the extensor pollicis et indicis (EPI). This systematic review gathers the available data on the prevalence of EI tendon and its variation in the hand. Twenty-nine cadaveric studies met the inclusion criteria with a total of 3858 hands. Meta-analysis results yielded an overall pooled prevalence estimate (PPE) of EI of 96.5% and PPEs of 92.6, 7.2 and 0.3% for the single-, double- and triple-slip EIP, respectively. The single-slip EIP is frequently inserted on the ulnar side of the extensor digitorum communis of the index (EDC-index) in 98.3%. The double-slip EIP is located on the ulnar side of the EDC-index in 53.5%, on its radial side in 17% and on both sides in 28.7%. Indian populations showed the highest rate of single-slip EIP and the lowest rate of double-slip EIP when compared to Japanese, Europeans and North Americans. The pooled prevalence of EMP, EMIC and EPI were 3.7, 1.6 and 0.75%, respectively. Knowledge of the variants of the EI tendon and their prevalence should help surgeons in correctly choosing the tendon to transfer in hand surgery.

Using radiographs of a cross section of patients, measurements of phalanges were done to aid in surgical planning for distal interphalangeal joint (DIPJ) arthrodesis using a headless compression screw. Measurements were performed of the distal and middle phalanx of all fingers and the proximal and distal phalanx of the thumb. Three independent reviewers measured 50 patients. The average measurements (in mm) of anteroposterior (AP) dimensions were as follows: for the thumb P1 and P2: 5.7 and 5.5, lateral 4.2 and 3.5; for the index P2 and P3 AP: 4.2 and 3.3, lateral 2.1 and 1.8; for the long P2 and P3 AP: 4.5 and 3.5, lateral 2.2 and 1.8; for the ring P2 and P3 AP: 4.3 and 3.1, lateral 1.8 and 1.7; and for the small P2 and P3 AP: 3.7 and 2.2, lateral 1.8 and 1.5. Careful surgical planning by measuring the involved digit and knowledge of screw size is paramount to avoid complications from DIPJ arthrodesis with a compression screw.

Finger joint dislocations and collateral ligament tears are common athletic hand injuries. Treatment of the athlete requires a focus on safe return to play and maximizing function. Certain dislocations, such as proximal interphalangeal and distal interphalangeal volar dislocations, may be associated with tendon injuries and must be treated accordingly. Treatment of other dislocations is ultimately determined by postreduction stability, with many dislocations amenable to nonoperative treatment (ie, immobilization followed by rehabilitation). Protective splinting does not necessarily preclude athletic participation. Minor bone involvement typically does not affect the treatment plan, but significant articular surface involvement may necessitate surgical repair or stabilization. Percutaneous and internal fixation are the mainstays of surgical treatment. Treatment options that do not minimize recovery or allow the patient to return to protected play, such as external fixation, are generally avoided during the season of play. Undertreated joint injuries and unrecognized ligament injuries can result in long term disability., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Objective: This research investigates the anatomic basis for the repair and reconstruction of hand joints using transposition of the carpometacarpal (CMC) joint of the hamatum., Methods: The morphology and structure of the CMC joints of the hamatum and the base joints of the middle phalanx were observed on 22 freshly frozen wrist specimens at Shanghai 6th People's Hospital Research Institute of Microsurgery. The volar dorsal dia, radioulnar dia, depth of concave, and area of the joints were measured. Data were obtained through statistical analysis, and the resemblance of joints was compared in terms of morphology, structure, area, length, and diameter., Results: The radioulnar dia of the CMC joints of the hamatum (13.54 ± 1.15 mm) did not exhibit any evident differences in the middle phalanx of the forefinger, middle finger, and ring finger, and in the distal phalanx of the thumb. The volar dorsal dia of the CMC joints of the hamatum (10.71 ± 0.93 mm) exhibited an evident difference in the middle phalanx of the ring finger. In all fingers, the depth of the ulnar and radial concave of the CMC joints of the hamatum (1.30 ± 0.08 and 0.95 ± 0.05 mm, respectively) and the area of the CMC joints of the hamatum (139.89 ± 5.44 mm(2)) showed an evident difference., Conclusion: The CMC joint of the hamatum could be considered a new and viable joint donor site that could be used to repair and reconstruct the base joints of the middle phalanx.

The Ascension PyroCarbon prosthesis has been used in proximal interphalangeal joint osteoarthritis. The dimensions of the intramedullary distal metadiaphyseal canal (isthmus) of the proximal phalanx and the base of the middle phalanx of cadaver fingers were investigated radiographically (n = 304) and macroscopically (n = 152). In up to 30% of the phalanges, the isthmus was smaller than the stem of the smallest proximal component size. The distal component head was always smaller than the middle phalanx base. Insertion and success of the Ascension PyroCarbon prosthesis is strongly dependent on bone morphology. A critical examination of the isthmus in radiographs is recommended in planning. If the isthmus is clearly smaller than the smallest proximal component, insertion of the prosthesis could be inadvisable. A clear mismatch between the distal component and the middle phalanx base should be avoided due to the potential risk for late subsidence and failure of the prosthesis., (© The Author(s) 2014.)

The tendons of flexor digitorum profundus are most often interconnected and making them less able to move independently than the superficial tendons. The reason for this is the cross connective tissue-ligamentous connection between the tendons of the profundus. The recognition of this so called quadriga phenomenon is important in the clinical practice, when the presence of this syndrome hinders the strength and the movement of the tendons after operative reconstruction. In his work the author describes the anatomical foundation, the biomechanical correlations and the clinical importance of the quadriga syndrome in the mirror of literature data.

This study reviews the literature on the anatomy of the connective tissues surrounding the distal interphalangeal joint and further characterizes the three-dimensional relationships of these structures with ultra-high field magnetic resonance imaging. Ten cadaver fingers, fixed in a solution of 5% agar and 4% formalin, were imaged utilising an ultrashield 16.4 Tesla ultra-high field magnetic resonance imaging, yielding a total of 4000 images. Images were analysed using Osirix™ (version 5.5.1 32 bit edition) for three-dimensional reconstruction. We found numerous conflicting descriptions of the connective tissue structures around the distal interphalangeal joint. Based upon our literature review and imaging studies we have defined precisely Cleland's ligaments, the oblique proximal septum, Grayson's ligaments, the dorsal plate, and the interosseous ligaments of the distal interphalangeal joint.

The purpose of this study was to analyze the palmar plate complex at the proximal interphalangeal joint using a three-dimensional (3D) technique, which makes it easier to understand the dimensions of structures and their relationship to the adjacent components. This method allows individual elements to be removed virtually, facilitating clearer observation of each component. Sixteen cadaveric specimens were dissected and reconstructed in a 3D virtual environment. The palmar plate is made up of a distal, fibrous portion and a proximal, membranous portion, which anchors distally on the base of the middle phalanx and is continuous with the bilateral check-rein ligaments proximally. The accessory collateral ligaments and the A3 pulley suspend the palmar plate laterally.

The human hand has a wide range of possible functional abilities that can change with age, disease, and injury, and can vary from individual to individual and subsequently can affect a person's quality of life. The objective of this work was to develop a theoretical model of the space that is reachable by the hand, weighted to represent three types of functionality, and to compare this model to an experimental data set obtained from a healthy hand population. A theoretical model, termed the Weighted Fingertip Space, was developed using 50th percentile published hand data and ranges of finger motion. The functional abilities calculated in the model were the abilities to position the fingertip pad, orient the fingertip pad, and apply directional forces through the fingertip pad at all the reachable points in space with respect to the palm. Following the development of this theoretical model, experimental data sets from nine individuals with healthy hands were obtained through motion capture techniques. The experimental data were then compared to the theoretical model. Comparisons between a 50th percentile theoretical model and a subject with a similar sized hand showed good agreement in weighting parameters and overall size and shape of the model spaces. The experimental data set from the entire sample, which ranged from the 2nd to 95th percentile hand sizes, showed resultant models that, on average, reached smaller volumes of space, but yielded higher values of the functional measures within those volumes. Additionally, in comparison to the theoretical model, the variability of the experimental models showed that small changes in hand dimensions and ranges of motion of the finger joints had a large influence in the functional measures of the model. Combined, these results suggest that the modeling technique can calculate functional ability of the hand, but should be used on an individualized basis for evaluating changes in function (e.g., rehabilitation). Further, scaling to hand size has the potential to yield "average" models for larger population samples.

An anatomically realistic biomechanical model of the index finger was created using a force-based approach in order to predict the isometric fingertip force or dynamic movement based on the forces of 7 index finger musculotendons. The model was validated for static forces through comparison with experimental results from 5 cadaver specimens. The model reliably simulated the isometric fingertip force produced by loading individual tendons. The average error in fingertip force direction was less than 2° and the average error in magnitude was less than 10% across finger postures for each muscle. Subsequent employment of the model to examine force transmission from the long flexors revealed a strong dependence of joint contact force on finger posture for a given tendon load. This may have ramifications for osteoarthritis as high joint contact forces are thought to contribute to the disease.

Injuries to the proximal interphalangeal joint are commonly encountered by the hand surgeon. Proper diagnosis and treatment are vital for optimal outcomes. Proper treatment of these injuries requires a working knowledge of the anatomy of the joint and an appreciation for principles for reduction, stabilization, and early rehabilitation to provide the best outcomes possible. Injuries can include fractures of the head of the proximal phalanx, dislocations, fracture dislocations, and fractures of the base of the middle phalanx. Similar to other aspects of plastic surgery, there is little high-level evidence guiding treatment and thus most treatment is based on level III or IV evidence. The goal for treatment of any injury around the proximal interphalangeal joint is to establish a congruent joint and allow for early motion. Stiffness and posttraumatic arthritis are common following these injuries. Salvage procedures are limited to arthrodesis and arthroplasty, neither of which can restore the normal function of the hand.

The aim of this study was to determine the fibre types of the muscles moving the index fingers in humans. Fifteen forearms of eight adult cadavers were used. The sampled muscles were the first lumbrical (LM), first volar interosseous (VI), first dorsal interosseus (DI), second flexor digitorum profundus (FDP), second flexor digitorum superficialis (FDS), and extensor digitorum (ED). Six micrometer thick sections were stained for fast muscle fibres. The procedure was performed by applying mouse monoclonal anti-skeletal myosin antibody (fast) and avidin-biotin peroxidase complex staining. Rectangular areas (0.38 mm × 0.38 mm) were photographed and the boundaries of the muscle areas were marked on the translucent film. The numbers and sizes of the muscle fibres in each part were evaluated by the image analyser program and calculated per unit area (1 mm(2)). The proportion of the fast fibres was significantly (p = 0.012) greater in the intrinsic muscles (55.7 ± 17.1%) than in the extrinsic muscles (45.9 ± 17.1%). Among the six muscles, the VI had a significantly higher portion (59.3%) of fast fibres than the FDS (40.6%) (p = 0.005) or the FDP (45.1%) (p = 0.023). The density of the non-fast fibres was significantly (p = 0.015) greater in the extrinsic muscles (539.2 ± 336.8/mm(2)) than in the intrinsic muscles (383.4 ± 230.4/mm2). Since the non-fast fibres represent less fatigable fibres, it is thought that the extrinsic muscles have higher durability against fatigue, and the intrinsic muscles, including the LM, should move faster than the FDS or FDP because the MP joint should be flexed before the IP joint to grip an object.

Background: While "diagrammatic" evaluation of finger joint angles using two folded paper strips as goniometric arms has been proposed and could be an alternative to standard goniometry and a means for self-evaluation, the measurement differences and reliability are unknown., Questions/purposes: This study assessed the standard and diagrammatic finger goniometry performed by an experienced examiner on patients in terms of (1) intragoniometer and intergoniometer (ie, intrarater) differences and reliability; (2) interrater differences and reliability relative to patients' diagrammatic self-evaluation; and (3) the interrater differences related to patient's hand dominance., Methods: Sixty-one patients without previous training self-evaluated active extension of all joints of the fifth finger of one hand once using two rectangular strips of paper. A practitioner used a goniometer and a diagram to perform parallel evaluations once in 12 patients and three times in 49 patients. The diagrams were scanned and measured. All evaluations and proportions of differences between the paired measurements of 5° or less were combined for analysis., Results: Intrarater intraclass correlation coefficients (ICC) based on the second and third practitioner's trials for the proximal interphalangeal joint were greater than 0.99. Reliability was poor when calculations involved the first measurement of the practitioner (ICCs < 0.38). Interrater reliability was poor regardless of the practitioner's trial (ICCs < 0.033). The proportions of the absolute differences of 5° or less between all paired practitioner's measurements were similar. The proportions of the acceptable differences between paired practitioner's and patients' measurements were nonequivalent for the interphalangeal joints. The interrater differences did not depend on patients' handedness., Conclusions: In experienced hands both techniques produce clinically comparable reliability, but patients' performance in extempore diagrammatic self-evaluation is inadequate. Further studies are necessary to explore whether appropriate training of patients can improve consistency of diagrammatic self-evaluation.

Purpose: The proximal interphalangeal (PIP) joint is a challenging joint to access reliably for corticosteroid injection. Literature has confirmed both a relatively high failure rate for injections performed with the traditional dorsal approach and an improved clinical response rate for confirmed intra-articular injections. We describe a technique for injecting the PIP joint through a volar approach, assess its reliability through cadaveric dissection, and determine its reproducibility by comparing success rates with the dorsal approach in a cadaver model., Methods: We dissected the PIP joint of 10 cadaveric digits to document necessary anatomic landmarks for this technique. We then used 20 matched pairs of cadaver hands for the remainder of our study. Four PIP joints on each hand (thumb excluded) were injected with a solution of saline and radio-opaque dye using the dorsal approach. We injected each joint on the contralateral matched hand through the volar approach. We obtained standardized fluoroscopic images of each joint immediately after injection, which were reviewed by an independent observer who was blinded to the technique and who rated outcomes as success, failure, or mixed. Success rates were evaluated based on approach used, digit injected, and degree of pre-existing arthritis., Results: We found reproducible anatomic landmarks that justified our injection technique. The rates of absolute failure were similar in the 2 cohorts. The volar approach demonstrated a higher percentage of successful injections with a smaller percentage of mixed results, although results did not reach statistical significance. There was no statistically significant difference in success rates based on digit injected or grade of arthritis in either cohort., Conclusions: The volar approach to injecting the PIP joint demonstrated success similar to that of the traditional dorsal approach. Reproducible surface landmarks exist to guide practitioners using this technique. Further study is needed to determine the potential complications and clinical outcomes of the volar approach., Type of Study/level of Evidence: Therapeutic IV., (Copyright © 2013 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.)

Background: Diagrammatic recording of finger joint angles by using two criss-crossed paper strips can be a quick substitute to the standard goniometry. As a preliminary step toward clinical validation of the diagrammatic technique, the current study employed healthy subjects and non-professional raters to explore whether reliability estimates of the diagrammatic goniometry are comparable with those of the standard procedure., Methods: The study included two procedurally different parts, which were replicated by assigning 24 medical students to act interchangeably as 12 subjects and 12 raters. A larger component of the study was designed to compare goniometers side-by-side in measurement of finger joint angles varying from subject to subject. In the rest of the study, the instruments were compared by parallel evaluations of joint angles similar for all subjects in a situation of simulated change of joint range of motion over time. The subjects used special guides to position the joints of their left ring finger at varying angles of flexion and extension. The obtained diagrams of joint angles were converted to numerical values by computerized measurements. The statistical approaches included calculation of appropriate intraclass correlation coefficients, standard errors of measurements, proportions of measurement differences of 5 or less degrees, and significant differences between paired observations., Results: Reliability estimates were similar for both goniometers. Intra-rater and inter-rater intraclass correlation coefficients ranged from 0.69 to 0.93. The corresponding standard errors of measurements ranged from 2.4 to 4.9 degrees. Repeated measurements of a considerable number of raters fell within clinically non-meaningful 5 degrees of each other in proportions comparable with a criterion value of 0.95. Data collected with both instruments could be similarly interpreted in a simulated situation of change of joint range of motion over time., Conclusions: The paper goniometer and the standard goniometer can be used interchangeably by non-professional raters for evaluation of normal finger joints. The obtained results warrant further research to assess clinical performance of the paper strip technique.

Background: Dynamic joint motion recording combined with CT-based 3D bone and joint surface data is accepted as a helpful and precise tool to analyse joint. The purpose of this study is to demonstrate the feasibility of these techniques for quantitative motion analysis of the interphalangeal joint in 3D., Materials and Method: High resolution motion data was combined with an accurate 3D model of a cadaveric index finger. Three light-emitting diodes (LEDs) were used to record dynamic data, and a CT scan of the finger was done for 3D joint surface geometry. The data allowed performing quantitative evaluations such as finite helical axis (FHA) analysis, coordinate system optimization, and measurement of the joint distances in 3D., Results: The FHA varies by 4.9 ± 1.7° on average. On average, the rotation in adduction/abduction and internal/external rotation were 0.3 ± 0.91° and 0.1 ± 0.97°, respectively. During flexion, a translational motion between 0.06 mm and 0.73 mm was observed., Conclusions: The proposed technique and methods appear to be feasible for the accurate assessment and evaluation of the PIP joint motion in 3D. The presented method may help to gain additional insights for the design of prosthetic implants, rehabilitation, and new orthotic devices.

Skilled piano performance requires considerable movement control to accomplish the high levels of timing and force precision common among professional musicians, who acquire piano technique over decades of practice. Finger movement efficiency in particular is an important factor when pianists perform at very fast tempi. We document the finger movement kinematics of highly skilled pianists as they performed a five-finger melody at very fast tempi. A three-dimensional motion-capture system tracked the movements of finger joints, the hand, and the forearm of twelve pianists who performed on a digital piano at successively faster tempi (7-16 tones/s) until they decided to stop. Joint angle trajectories computed for all adjacent finger phalanges, the hand, and the forearm (wrist angle) indicated that the metacarpophalangeal joint contributed most to the vertical fingertip motion while the proximal and distal interphalangeal joints moved slightly opposite to the movement goal (finger extension). An efficiency measure of the combined finger joint angles corresponded to the temporal accuracy and precision of the pianists' performances: Pianists with more efficient keystroke movements showed higher precision in timing and force measures. Keystroke efficiency and individual joint contributions remained stable across tempo conditions. Individual differences among pianists supported the view that keystroke efficiency is required for successful fast performance.

The debatable relationship of functional human hand proportion with the Fibonacci series has remained an obscure scientific enigma short of clinical interest. The main difficulty of proving such a relationship lies in defining what should constitute true functional proportion. In this study, we re-evaluate this unique relationship using hand flexion creases as anatomical surrogates for the functional axes of joint rotation. Standardised desktop photocopies of palmar views of both hands in full digital extension and abduction were obtained from 100 healthy male volunteers of Chinese ethnicity. The functional axes were represented by the distal digital crease (distal interphalangeal joint, DIPJ), proximal digital crease (proximal interphalangeal joint, PIPJ), as well as the midpoint between the palmar digital and transverse palmar creases (metacarpophalangeal joint, MCPJ). The ratio of DIPJ-Fingertip:PIPJ-DIPJ:MCPJ-PIPJ (p3:p2:p1) was measured by two independent observers and represented as standard deviation about the mean, and then compared to the theoretical ratio of 1:1:2. Our results showed that, for the 2nd to 5th digits, the p2:p3 ratios were 0.97 ± ± 0.09, 1.10 ± 0.10, 1.04 ± 0.12, and 0.80 ± 0.08, respectively; whilst the p1:p2 ratios were 1.91 ± 0.17, 1.98 ± 0.14, 1.89 ± 0.16, and 2.09 ± 0.24, respectively. When the data were analysed for all digits, they showed a combined p3:p2:p1 ratio of 1:0.98:2.01. In conclusion, our results suggest that functional human hand proportion, as defined by flexion creases, is approximated by the Fibonacci series.

A method of kinematic analysis of the fingers using stereo-photogrammetry, referred to as the phalanx transformation technique, has been proposed. Functional methods were used to define the joint axes and subsequently each finger segments' anatomical coordinate system. Thirteen subjects were tested and the accuracy of the technique assessed. The average error across the three joints of the finger was found to be 0.6 mm, which translates to a 2.2% error in predicted joint reaction force when using a biomechanical model. The subjects were required to have sufficient movement in their joints to define the joint axes functionally. Some subjects of clinical interest can have a significantly reduced mobility owing to injury or pathology, therefore, the effect of calibration range of motion on accuracy was analysed. It was found that, for a range of motion typical of a subject with rheumatoid arthritis, the errors in predicted joint reaction force were < 7%. The accuracy of this technique compared favourably with others previously proposed and, considering the other errors inherent in modelling, those found in this study were deemed to be acceptable.

The lumbrical muscles are unique in having their origin and insertion on tendons. The lumbricals assist in metacarpophalangeal joint flexion; they contribute to interphalangeal joint extension by acting as deflexors of the proximal interphalangeal joint. Anatomically, they are highly specialized in terms of their architectural properties, with a small physiologic cross-sectional area but long fiber length. Their unique properties indicate that they are probably important in fast, alternating movements and fine-tuning digit motion., (Copyright © 2012 Elsevier Inc. All rights reserved.)