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Study Design Cohort cadaveric study. Introduction Ring finger metacarpal fractures are often treated with ulnar gutter orthoses incorporating the ring and small fingers. Iatrogenic pronation of the distal metacarpal fragment may occur from overzealous orthotic “molding”, resulting in a crossover deformity of the ring finger over the small finger. Purpose of the Study The goal of this cadaveric study is to determine whether including the middle finger in an ulnar gutter orthotic could lessen the chances of iatrogenic ring finger metacarpal fracture rotation. Methods Transverse ring finger metacarpal shaft fractures were created in 24 cadaver hands. The ring and small fingers were then placed into an intrinsic plus position, simulating the application of an ulnar gutter orthotic. Weights of 2.5, 5, and 10 pounds were applied to the ring and small fingers to simulate iatrogenic-induced fracture pronation. The amount of rotational displacement at the fracture was measured, and the protocol was repeated, including the middle finger in the intrinsic plus position. Mann-Whitney-Wilcoxon test was used for statistical analysis. Results There was an increase in distal fragment rotation with increasing weight. Fracture displacement was greater with the 2-finger position than the 3-finger at all weight levels; this reached statistical significance at 10 lbs (2.8 vs 1.8 mm). Conclusions Application of an ulnar gutter orthotic including only ring and small fingers can rotate the distal fragment of a ring finger metacarpal shaft fracture such that overlap could occur with the small finger. Including the middle finger in ulnar gutter splints will mitigate against the rotation of the ring finger metacarpal shaft fracture.

Upper limb absence has an impact on both physical and mental health of a human being. Nowadays, the costs of commercial, externally powered prosthetic hands range between 25.000 € and 70.000 €. A first demonstrator of a lightweight low-cost prosthetic hand is produced with 3D-printing technology (Fused Deposition Modeling). Due to integration of single-axis solid-state joints the five fingers can be printed in one piece. Thermoplastic polyurethane is used for this purpose. The flexion of all fingers is achieved by moving cords which are positioned on the palmar side of each finger. Two twisted string actuators are integrated to allow the movement of the thumb and the remaining four fingers. These actuators consist of two polyethylene strands which are twisted along their main axis by a DC motor, providing a tensile force to bend the fingers. In order to achieve simultaneous but differential actuation of the four fingers (small finger, ring finger, middle finger and index finger), a differential mechanism is used. The thumb is driven by a separate unit. In order to open the hand, the elasticity of the joints’ material is taken advantage of. With the developed mechanics it is possible to perform precision and cylindrical grasps with an opposed thumb. Weights up to 260 g can be held according to the shape and size of an object. To increase the adaption to different sizes and weights of objects, the design should be modified. It can be concluded, that the presented device is a promising basis for a lightweight, low-cost prosthetic hand in the future.

Background Within a virtual environment (VE) the control of locomotion (e.g., self-travel) is critical for creating a realistic and functional experience. Usually the direction of locomotion, while using a head-mounted display (HMD), is determined by the direction the head is pointing and the forward or backward motion is controlled with a hand held controllers. However, hand held devices can be difficult to use while the eyes are covered with a HMD. Free hand gestures, that are tracked with a camera or a hand data glove, have an advantage of eliminating the need to look at the hand controller but the design of hand or finger gestures for this purpose has not been well developed. Methods This study used a depth-sensing camera to track fingertip location (curling and straightening the fingers), which was converted to forward or backward self-travel in the VE. Fingertip position was converted to self-travel velocity using a mapping function with three parameters: a region of zero velocity (dead zone) around the relaxed hand position, a linear relationship of fingertip position to velocity (slope or/J) beginning at the edge of the dead zone, and an exponential relationship rather than a linear one mapping fingertip position to velocity (exponent). Using a HMD, participants moved forward along a virtual road and stopped at a target on the road by controlling self-travel velocity with finger flexion and extension. Each of the 3 mapping function parameters was tested at 3 levels. Outcomes measured included usability ratings, fatigue, nausea, and time to complete the tasks. Results Twenty subjects participated but five did not complete the study due to nausea. The size of the dead zone had little effect on performance or usability. Subjects preferred lower β values which were associated with better subjective ratings of control and reduced time to complete the task, especially for large targets. Exponent values of 1.0 or greater were preferred and reduced the time to complete the task, especially for small targets. Conclusions Small finger movements can be used to control velocity of self-travel in VE. The functions used for converting fingertip position to movement velocity influence usability and performance. Keywords: Human computer interaction, Virtual environment, Gesture design

Highlights • The lateral band snapping syndrome (LBSS) in the proximal interphalangeal joint (PIPJ) is the subluxation of lateral band of the extensor tendon resulting from injury of the retinacular ligament, causing finger snapping during flexion of the PIPJ. • Ultrasonography can visualize the subluxation of lateral band, facilitating diagnosis of LBSS in the PIPJ. • Patients with LBSS may benefit from prompt repair of the retinacular ligament without sequela., Background Snapping fingers resulting from flexor tendon tenosynovitis at the metacarpophalangeal (MCP) joint, is common. However lateral band snapping syndrome (LPSS) in the proximal interphalangeal joint (PIPJ) are extremely rare. Case presentation A 43-year-old female was diagnosed with LPSS in the PIPJ of fifth finger which was confirmed by dynamic evaluation upon ultrasound. Repair of retinacular ligament of the extensor tendon was performed. At the six-month follow up, the patient had regained full ROM with no discomfort, without evidence of recurrence. Discussion The diagnosis of LPSS at the PIPJ is challenging. Dynamic evaluation of the extensor tendon over PIPJ is necessary to diagnose LBSS. Ultrasound was used to assess the movement of the lateral band of the extensor tendon when the fingers flexed and to demonstrate dynamically the snapping and subluxation of the lateral band, so as to facilitate confirming the diagnosis of LBSS. Conclusion Given clinical suspicion of LBSS, we recommend ultrasonography as a feasible tool to confirm the diagnosis. Patients with LBSS may thus benefit from prompt repair of the retinacular ligament without sequela.

This article describes the authors' experience with, and recent advancement in, the techniques that have allowed the development of many new arthroscopic procedures in the finger joints. It also describes the role and techniques of arthroscopy in small finger joints. Because the intra-articular anatomy of the first to the fifth metacarpophalangeal (MCP) joints is similar, this article discusses the hand MCP joints without distinguishing thumb from fingers.

The ideal rehabilitation regimen of paediatric flexor tendon injuries of the hand is discussed controversially. In this study, the clinical outcome of paediatric patients with flexor tendon injuries treated with a dynamic postoperative protocol was assessed. All children with flexor tendon injuries of the hand who were treated by a dynamic postoperative protocol between 1999 and 2011 were included. Patients were invited for a follow-up examination consisting of clinical examination, the TAM and Buck-Gramcko scores, and the linear measurement system. In total, 144 patients (mean age 9.1 years, range 1-17 years) with 267 flexor tendon injuries (128 flexor digitorum superficialis (FDS), 126 flexor digitorum profundus (FDP) and 13 flexor pollicis longus (FPL)) of 191 digits were treated. Of them, 43% (n = 62; 49 male, 13 female) with 88 digits (thumb n = 4, index finger n = 17, middle finger n = 25, ring finger n = 20, small finger n = 22) with 123 injured tendons (FDS n = 62, FDP n = 57, FPL n = 4) were included in the follow-up at a mean post-operative interval of 7.2 years (range 1-13 years). Using the Total Active Motion (TAM) score, an excellent and good outcome could be achieved in 41% and 48% of the patients, respectively. The zone of injury did not influence the objective outcome measures. Subjective and objective outcomes were not statistically different between young children (≤6 years) and older children (>6 years). The present study demonstrates good to excellent outcome in a large cohort of paediatric patients with flexor tendon injuries of the hand treated with a dynamic mobilisation protocol irrespective of patient age.

Malrotation is common after oblique or spiral proximal and middle phalangeal fractures. Although a small degree of malrotation may be acceptable for many patients, greater degrees of malrotation result in functional impairment, pain due to distortion of the joints, and diminished grip strength [1]. Osteotomy is usually required, preferably through the phalanx. Recent progress in computed tomography (CT) imaging and computer technology has enabled clinicians to evaluate the 3-dimensional (3D) kinematics of joint motion and to simulate accurate 3D corrective osteotomy using CT bone models [2,3]. We developed a novel simulation system named “linkage simulation” in which each phalanx is considered a linked arm, which makes it possible to analyze multiple joint motions preoperatively. Here, we report the case of a patient with a malunited little finger proximal phalangeal fracture that was successfully treated using the linkage simulation system. This system consisted of an original 3D computer program, which was designed to reproduce preoperative 3D motion. We have not identified any previous reports of corrective osteotomy for a malunited upper extremity fracture using 3D kinematics and linkage simulation.

Avulsion of the flexor digitorum profundus (FDP) tendon associated to an enchondroma fracture in the distal phalanx is very rare. We report a subacute case of a type II FDP tendon avulsion of the small finger at its insertion, in combination with a fracture of the distal phalanx due to enchondroma. The bone lesion was curated and grafted using autogenous bone harvested from the ipsilateral radius. The FDP tendon was reattached to the distal phalanx using the pullout transosseous technique. Delayed protected active mobilization was used to treat the repaired tendon. According to the adjusted Strickland score, a good result was obtained and grip strength was similar between hands and PRWHE score was very low at 5 months from surgery. Early diagnosis leads to a fast surgery with good functional mobility and pain outcomes. If closely monitored by an experienced medical team, as this case demonstrates, an attempt to treat the benign tumor with a curettage, bone filling and reattachment of the tendon through the pullout technique in young motivated patients can be an alternative.

Purpose To assess whether or not attempted closed reduction of fifth metacarpal neck fractures results in decreased fracture angulation at final follow-up. Methods Retrospective chart review of all patients aged 18 and older managed for isolated fifth metacarpal neck fractures between 2004 and 2014. Results Sixty-six patients managed for an isolated boxer fracture met inclusion criteria. Twenty-three patients underwent attempted reduction and 43 patients did not. Patients undergoing attempted reduction had a statistically significant improvement in fracture angulation following reduction compared with patients not undergoing attempted reduction. At final follow-up, there was no difference in fracture angle between the 2 groups. Conclusions Closed reduction and splint immobilization of fifth metacarpal neck fractures was not an effective means of maintaining a significant improvement in fracture alignment upon healing. Other means, such as closed reduction with pin fixation or open reduction internal fixation, should be considered when maintenance of reduction is desired. Type of study/level of evidence Therapeutic III.

Purpose To evaluate the outcomes of the Thompson procedure for chronic mallet finger deformity and review the utility of this procedure. Methods Seven cases of chronic mallet finger with a swan neck deformity were treated by the Thompson procedure. Ranges of motion for the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints were measured, and complications were investigated at the final examination. Patients were evaluated using the criteria reported by Abouna and Brown. Results Four patients were men, and 3 were women. The average age at the time of surgery was 44 years (range, 25 to 71 y). The middle finger was affected in 4 cases, and the index, ring, and small finger were involved in 1 case each. The average extensor lag on the DIP joint was 42° (range, 35° to 50°). All cases were treated with the Thompson procedure. The swan neck deformity was corrected in all cases. The average motion at the final examination was −4° (range, −30° to 0°) in extension and 91° (range, 85° to 110°) in flexion for the PIP joint and −5° (range, −10° to 0 °) in extension and 63° (range, 45° to 85°) in flexion for the DIP joint. A buttonhole deformity and a dimple at the proximal tied end of the graft were seen in 1 case. Assessment by the criteria of Abouna and Brown revealed that 6 of 7 patients were categorized as cured and one as improved. No patient was categorized as unchanged. Conclusions The procedure provides a predictable method for correcting loss of DIP joint extension with or without PIP joint hyperextension. We believe that the Thompson procedure is an effective technique for the salvage, following failed treatment, of a closed mallet injury with an associated swan neck deformity. Type of study/level of evidence Therapeutic IV.

A composite graft for reattachment of an amputated fingertip is a very controversial and challenging procedure. An osteocutaneous composite graft is rarely conducted and has a low success rate following fingertip amputation. A 21-year-old male patient was referred to our emergency clinic with dorsal oblique amputation of the middle, ring and small fingers of the left hand through the distal interphalangeal joint and middle phalanx. The amputated parts of the middle and ring fingers were reattached with osteocutaneous composite grafts. The amputated part of the small finger was revascularised to the ulnar palmar digital artery of the small finger. The composite grafts of the middle and ring fingers and the revascularised small finger survived completely. We suggest that careful patient selection will allow an osteocutaneous composite graft to become an acceptable method for the treatment of fingertip amputation. A large-scale study of osteocutaneous graft of amputated fingertips is required to improve the survival rate.

Purpose There is a need for objective measures of pediatric intrinsic hand muscle strength as the current standard, the manual muscle test, lacks sensitivity to clinically important changes in muscle strength. We report the development, reliability, and normative values of the Peg Restrained Intrinsic Muscle Evaluator (PRIME), a device that quantifies intrinsic hand muscle strength. Methods Typically developing children, ages 4 to 16 years (n = 119), established normative values of intrinsic strength for thumb palmar abduction, thumb opposition, and index and small finger abduction. A subset of 30 children (15 boys, 15 girls), ages 7 to 16 years, determined inter-rater and intra-rater reliability. We calculated mean, standard deviation, intraclass correlation coefficients, and smallest detectable differences. Results Normative results indicate that gender and age were significant predictors of strength. Although the dominant hand generated higher strength measurements on average, differences were not statistically significant. Mean index and small finger abduction strength was significantly lower than thumb abduction and opposition in both genders. Intraclass correlation coefficients ranged from 0.85 to 0.94 for inter-rater reliability and 0.88 to 0.98 for intra-rater reliability. Bland-Altman plots showed an even distribution across the zero line. Conclusions The PRIME device is a reliable tool for the quantification of intrinsic hand muscle strength in children. Age-specific and gender-specific normative values in typically developing children can serve as a future resource for clinicians treating pediatric hand or neuromuscular conditions. Type of study/level of evidence Diagnostic II.

Summary Background Flexor tendon injuries are common problems faced by hand surgeons. To minimise the surgical trauma associated with localisation and retrieval of the proximal tendon end, we investigated the use of surgeon-performed ultrasound in the evaluation of injured flexor tendons in a cadaver model. Our goal was to use surgeon-performed ultrasound: (1) to correctly diagnose flexor tendon injuries and (2) to correctly localise the proximal tendon ends within 1cm. Methods Flexor tendon injuries with varying degrees of retraction were randomly created in individual digits of cadaver upper extremities, with a number of tendons left uninjured. A surgeon, blinded to the injury status of each digit, imaged each tendon by ultrasound. Predicted injury status of each tendon and localisation of the proximal stump was recorded. A total of 81 tendons were studied. Findings Correct diagnosis of flexor tendon injury was made in 78 of 81 tendons (96.2% success). Correct localisation of the proximal tendon stump was made in 39 of 50 lacerated tendons (78% success). Small finger injuries were most difficult to assess (66.7% success). With the small finger excluded from our analysis, the localisation success rate increased to 86.8%. The average time taken to image each digit was just under 2.5min. Conclusions Surgeon-performed ultrasound evaluation of the hand is a reliable means to diagnose flexor tendon injuries and to accurately localise the proximal tendon ends. This imaging modality may limit the need for extensive surgical exploration during flexor tendon repair. We do not recommend using this technique to image flexor tendon injuries of the small finger at this time.

We report a rare case of closed rupture of both flexor digitorum profundus (FDP) and flexor digitorum superficialis tendons in zone II in the small finger. We performed delayed, primary end-to-end suture of the FDP and excision of the flexor digitorum superficialis, because myostatic contracture of the FDP tendon was not severe and the FDP tendon remnants were not frayed.

Purpose Patients with carpal tunnel syndrome commonly present with paresthesias and pain extending into the small finger and proximal to the hand. This study was conducted to assess the ability of carpal tunnel release to relieve symptoms outside of the median nerve distribution. Methods We enrolled 34 consecutive surgical patients (40 wrists) diagnosed exclusively with carpal tunnel syndrome based on the history, physical examination, and electrodiagnostic studies. Preoperative symptoms were categorized as pain, numbness, tingling, or "burning and electrical shocks." The presence or absence of each symptom type was recorded in 5 topographical areas (zone I, palmar thumb/index/long; zone II, small finger; zone III, volar forearm; zone IV, volar arm; and zone V, dorsal hand/forearm/arm). Patients were contacted at 4 to 6 weeks postoperatively to assess resolution of each symptom type by topographic zone. Results Preoperatively, the cohort reported symptoms in all zones: zone I, 120 reports; zone II, 47 reports; zone III, 33 reports; zone IV, 7 reports; and zone V, 23 reports. Numbness (n = 40) and tingling (n = 38) were the most common symptoms, followed by pain (n = 29) and "burning/shocks" (n = 16). Postoperatively, the total number of reports within the 5 zones decreased from 230 to 20. The probability that surgery would eliminate patient symptoms was 88% (104 of 120) in zone I, 96% (45 of 47) in zone II, 97% (32 of 33) in zone III, 86% (6 of 7) in zone 4, and 100% (23 of 23) in zone V. Across zones, the overall probability of symptom resolution was as follows: pain > 80%, numbness/tingling > 85%, and "burning/shocks" > 90%. Conclusions Symptoms experienced outside of the median nerve distribution had a high likelihood of resolution after carpal tunnel release. Over 85% of symptoms in each of the anatomic zones studied resolved. Feelings of burning or shock-like sensations were most reliably relieved at early follow-up. Type of study/level of evidence Therapeutic IV.

Purpose The purpose of this study is to quantify finger/digit rotation, overlap, parallelism, and convergence to the scaphoid tuberosity in normal volunteers to establish standards for comparison. Methods We examined 240 uninjured fingers in 30 volunteers. There were 14 men and 16 women with an average age of 35 years. Rotation was determined with the palm flat and fingers extended. Digit overlap, parallelism (angular relationship between the index, ring, and small fingers with respect to the middle finger) and scaphoid convergence were determined with simultaneous flexion of metacarpophalangeal and proximal interphalangeal joints. Linear and angular measurements were performed with imaging software. Results Rotation, parallelism, and scaphoid convergence measurements were similar comparing left with right hands. Rotation: All digits were found to be in supination relative to the horizontal plane; the small fingers averaged 9°, the ring fingers 4°, the middle fingers 8°, and the index fingers 12°. Parallelism: Angular measurements between the middle finger and the small finger averaged 19°, between the middle finger and the ring finger 9°, and between the middle finger and the index finger 11°. Scaphoid convergence: In no hand did all 4 fingers converge onto scaphoid tuberosity. Whereas small and ring finger trajectories averaged −0.1 to 1.2 mm from the scaphoid tubercle, the middle finger averaged 4.0 to 4.6 mm and the index finger 8.1 to 9.5 mm. Overlap: Ninety percent of individuals demonstrated digit overlap, although none covered more than 50% of the adjacent nail plate. Seventy-seven percent of these were bilateral, and 73% were asymmetric. Conclusions This study establishes the normal parameters for digit rotation, overlap, parallelism, and scaphoid convergence. For digit rotation, parallelism, and scaphoid convergence, the contralateral (uninjured) hand can be used reliably for comparison. However, for digit overlap, the contralateral hand should not be used for comparison because of side-to-side asymmetry and variability. Type of study/level of evidence Diagnostic IV.

Purpose Persistent abduction of the small finger has usually been treated by transfer of the extensor digiti minimi muscle. However, anatomic variations of the extensor system may limit the potential for a successful extensor digiti minimi transfer. Therefore, we evaluated the outcomes of an alternative reconstruction method for the abducted small finger using an extensor indicis proprius (EIP) transfer. Methods We performed 8 EIP transfers in 8 patients with persistent, flexible abduction posturing of the small finger. The primary etiology of the deformity was incomplete motor reinnervation after surgeries for ulnar neuropathy in 6 patients, rupture of the third palmar interosseous musculotendinous unit in 1 patient, and intrinsic muscle fibrosis in 1 patient. The EIP was elongated by splitting the tendinous portion and was transferred to the distal and radial part of the extensor hood. Surgical outcomes were assessed by comparing preoperative and postoperative active adduction and abduction motion of the 2 ulnar digits. Results At the mean follow-up of 23 months, the average adduction angle improved from 19° to 1° postoperatively. In terms of active finger motion, 6 patients showed excellent results, 1 good, and 1 fair, without loss of flexion and extension. No patient had an extension lag or complained of functional deficits of the donor index finger. There was not adverse change to digital function or range of motion for the middle and ring fingers that are crossed by the EIP. Conclusions Extensor indicis proprius transfer can be a reliable option for correction of abduction deformity of the small finger, maintaining active abduction and full flexion and extension. Type of study/level of evidence Therapeutic IV.

Gestational choriocarcinoma is a malignant epithelial neoplasm of trophoblastic cells derived from any form of a previously normal or abnormal pregnancy. Choriocarcinoma is a rapidly invasive, widely metastasizing, malignant neoplasm. Hand and cutaneous metastases are rare and only one other report describing hand involvement was found in the literature. A 33-year-old woman was referred for evaluation of a papular lesion (6 x 4 mm) at the junction of the hyponychium and the nail bed of the dominant right small finger. At the time, she was being treated for choriocarcinoma with lung and brain metastases. Histopathology studies showed that the soft-tissue lesion from the patient's finger was a cutaneous metastasis of choriocarcinoma.

Purpose Most digital nerve defects can be reconstructed by means of nonvascularized nerve grafts or artificial tubes, for example. When the bed is poor, the defect is long, or there is a concomitant soft-tissue loss; however, a vascularized nerve graft may be a better option. Our purpose is to introduce a method of 1-stage reconstruction of complex neurocutaneous defects in the fingers and to report the results and clinical effectiveness at a minimum 1-year follow-up period. Methods From 1997 to 2005 there were 6 consecutive patients who had a combined soft-tissue and digital nerve defect reconstructed by a vascularized neurocutaneous flap from the tibial (medial) side of the second toe. Three were acute and 3 were chronic cases. One flap was used for the ulnar side of the thumb, 2 for the radial aspect of the index finger, 1 for the radial of the small finger, and 2 for the ulnar side of the small finger. The nerve gap averaged 4.2 cm, and the flap size averaged 3.2 × 2.1 cm. The flaps were revascularized with standard microsurgical techniques to local vessels in the fingers. The nerves were sutured with epineural stitches. A split-thickness skin graft was used to close the donor site of the toe. Results All flaps survived without complications. At the latest follow-up evaluation static two-point discrimination (s2PD) averaged 8 mm on the pulp. Three patients had normal sensation when tested with Semmes-Weinstein filaments. Subjective feeling was 78% of that of the normal side. Five patients rated their feeling as excellent on a subjective scale. The Disabilities of the Arm, Shoulder, and Hand questionnaire score averaged 5. Conclusions The tibial neurocutaneous second toe free flap is suitable for reconstructing a missing nerve and soft-tissue defect in the finger. We found good functional recovery and high satisfaction in this group of patients. The donor site morbidity has been minimal, although delayed healing is common. Type of study/level of evidence Therapeutic IV.

Purpose To determine if there is an optimal grip span for determining the maximum handgrip strength in male and female teenagers, and if the optimal grip span was related to hand span. If they are related then the second aim was to derive a mathematic equation relating hand span and optimal grip span. Methods One hundred healthy teenage boys (15.1 ± 1.1 y) and 106 girls (15.4 ± 1.3 y) were evaluated (age range, 13–18 y). Each hand was randomly tested on 10 occasions using 5 different grip spans, allowing a 1-minute rest between attempts. The hand span was measured from the tip of the thumb to the tip of the small finger with the hand opened as wide as possible. Results The results showed that an optimal grip span to determine the maximum handgrip strength was identified for both genders, and the optimal grip span and hand span correlated in both genders. Conclusions The results suggest that there is an optimal grip span to which the dynamometer should be adjusted when measuring handgrip strength in teenagers. The optimal grip span was influenced by hand span in both genders. For males the optimal grip span can be derived from the equation y = x/7.2 + 3.1 cm, and for females from the equation y = x/4 + 1.1 cm. where y is the optimal grip span and x is the hand-span. These equations may improve the reliability and accuracy of the results and may guide clinicians and researchers in selecting the optimal grip span on the hand dynamometer when measuring handgrip strength in teenagers.

Purpose To analyze the relative contribution of the intrinsic muscles to the flexion moment potential of the metacarpophalangeal (MCP) joints of the middle, ring, and small fingers and to calculate the moment potential loss occurring with deep motor branch, low, or high ulnar nerve palsy or low median nerve palsy. Methods Eleven fresh cadaver hands were used. A small wire sutured to each tendon was connected to an excursion transducer containing a constant-tension spring. The tendon excursion and the MCP joint rotation were measured simultaneously during 10 to 16 cycles of passive flexion/extension cyclic motion. The moment arm was calculated from the tendon excursion–joint rotation curve as the derivative of the curve. The flexion moment potential was calculated by multiplying the moment arm with the known tension fractions of the muscles. Results When the MCP joint was at 0° of flexion the relative moment potential contributions of the intrinsic muscles to MCP joint flexion were 8%, 13%, and 28% in the middle, ring, and small fingers, respectively. Moment potential losses were 7%, 13%, and 6% in the middle, ring, and small fingers, respectively, in deep motor branch ulnar nerve palsy. In low ulnar nerve palsy the losses were 7%, 13%, and 28%, respectively. In high ulnar nerve palsy they were 7%, 64%, and 82%, respectively. Low median nerve palsy, however, resulted in a moment potential loss at the middle finger MCP joint of less than 2%. Conclusions The relative contribution of the intrinsic muscles to the total flexion moment at the MCP joint was different for each finger. The small finger had a large intrinsic contribution, primarily because of the larger moment arms of the hypothenar muscles.

Purpose To investigate the hand motion of pianists when they performed an octave and a chord, which accounted for 74% of the piano techniques that the subjects practiced at the onset of overuse hand problems. The octave position was to strike 2 keys that were 16.7 cm apart simultaneously with the thumb and small finger, and the chord position was to strike 3 keys with 4.8 cm between the borders. Methods The abduction angle of both the thumbs and the small fingers of 10 pianists while playing a chord and an octave were measured repeatedly with a video-based passive marker detection system. The angles were compared between pianists with large hand spans and those with small hand spans. Results When playing the octave both the maximal and minimal abduction angles of the thumb were significantly larger for the smaller-hand pianists as compared with the pianists with larger hand spans. When playing the chord the maximal abduction angle of the thumb of small–hand-span pianists was significantly larger than that of large–hand-span pianists. The abduction of the small finger, however, did not differ during performance of either the octave or the chord. Conclusions These results suggest that the small–hand-span pianists must abduct the thumb more than large–hand-span pianists while minimizing movement of the small finger. This may cause de Quervain's tenosynovitis in pianists.

Background Dynamic hand grasping implies sophisticated motor coordination. Most knowledge on motor synergies used in grasping is deduced from experiments based on static precision grip. This experiment was aimed at better understanding the mechanisms of finger force-sharing in an active, dynamic hand task under repetitive strain conditions. Methods A multi-digit task consisting of holding a cylinder with the digit tips, in which the thumb and the finger opposed each other, was investigated during repetitive unidirectional wrist flexion and extension cyclic motion. Finger and thumb forces and wrist angular position were simultaneously recorded during repetitive wrist motion against 0.3–0.6 N m load in 10 healthy adults. Findings Load torques acting during wrist movements produced in-phase increases of the thumb and the finger forces with the wrist extension and the wrist flexion, respectively. Digit forces increased proportionally to the applied load. The alternating rise of thumb and finger forces changed instantaneously at the end of the flexion and extension phases of the movement, respectively. Six subjects predominantly used the index finger, two the middle finger, one the ring finger, and the remaining one used the small finger during wrist flexion against 0.6 N m to perform the task. Variations among individual finger forces were negatively correlated during the phase of constant rotational velocity of the wrist flexion. Repeated measures ANOVA revealed that the percentage of individual finger contribution to the total fingers’ force significantly varied during the wrist flexion ( P P Interpretation Variations in finger force-sharing among cycles were not necessitated by task dependent activities, as the task was identical. These findings indicated that motor coordination of repeated multi-finger task allowed redundant solutions in finger force-sharing. The force-sharing variation may reflect a minimal intervention principle of the central nervous system controlling only the goal-directed parameters and might help to prevent muscle fatigue in repetitive tasks through modulation of activity in multi-digit muscles.

Opposition is an important movement of the hand and rotation of the first metacarpal is the essential component. There is no agreement on the exact magnitude of rotation of the first metacarpal during opposition. This study used computed tomography to describe rotation measurement of the first metacarpal in the hands of a group of healthy individuals.The rotation of the first metacarpal was measured with reference to the fixed unit of the hand. Computed tomographic images were taken of the hands of 10 healthy individuals with the thumb in retroposition, resting position, and opposition to the index, middle, ring, and small fingers. On each image a tangential line was drawn along the dorsal margin of the second and third metacarpals. A second line was drawn through the head of the first metacarpal at the level of the sesamoids. The angle between the 2 lines was measured as the angle of rotation of the first metacarpal in different thumb positions.The mean angle of rotation of the first metacarpal in retroposition was 54 degrees+/-10 degrees with reference to the fixed unit of the hand. In the resting position the angle of rotation of the first metacarpal changed to 74 degrees+/-10 degrees. In the position of opposition to the index, middle, ring, and small fingers the angle of rotation of the first metacarpal increased to 100 degrees+/-7 degrees , 103 degrees+/-6 degrees, 105 degrees+/-6 degrees, and 110 degrees+/-7 degrees, respectively.The first metacarpal rotates 56 degrees when it moves from retroposition to the position of opposition to the small finger.

Kaplan's accessory branch is an aberrant branch of the dorsal cutaneous branch of the ulnar nerve that arises proximal to the styloid process of the ulna and courses ulnar to the pisiform. Variations of this anomaly have been described as having an end point of connection to the sensory branch of the ulnar nerve, to the motor branch of the ulnar nerve (rare), to the digital nerve at the level of the midhypothenar eminence, or to the proximal interphalangeal joint of the small finger or as running as an independent branch to the volar aspect of the small finger. We report a variant of Kaplan's accessory branch that coursed through the insertion of the flexor carpi ulnaris, a groove on the ulnar aspect of the pisiform, and connected to the ulnar nerve trunk proximal to its bifurcation into its motor and sensory branch. Based on the findings of the case presented and a review of the literature we offer a classification system for this anomaly.

Purpose The abductor digiti minimi (ADM) and the flexor digiti minimi (FDM) brevis muscles could be used as flaps with their low functional morbidity, especially in severe crushed injuries of the hand. The vascular anatomy of both of the muscles were investigated to classify the muscles according to the Mathes-Nahai classification. Methods Nine cadavers embalmed with formaline were dissected under loupe magnification (×4) from the wrist proximally to the proximal phalanx of the small finger distally, delineating the branches of the ulnar artery along the ADM and FDM muscles. Results The dissections and the microangiography of the muscles revealed 1 major and 2 minor pedicles. Both of the muscles could be classified as type II muscles according to the Mathes-Nahai classification. Conclusions The vascular pattern of the ADM muscle has been described previously, this study explored the vascular anatomy of the FDM muscle. The information regarding the vascular supplies of these muscles could be of help to the clinician when manipulating the muscles. The FDM muscle could be a suitable alternative for the ADM muscle in opponensplasty. When the pedicles are preserved the muscles could be used-based proximally or distally.

A case of traumatic laceration of the small finger flexor digitorum profundus (FDP) tendon in the distal forearm with retained partial active flexion at the small finger distal interphalangeal joint (DIP) joint is described. Tendinous interconnections between the ring and small FDP tendons and lumbrical muscles may permit partial FDP function at the DIP joint despite a complete deficit of the proximal tendon.

The occurrence of motor dysfunction as a sign of schizophrenia, in addition to being a side effect of medication, has received considerable support in recent years. The current study aimed to systematically investigate both the presence and pattern of one such motor dysfunction, motor overflow. It was hypothesised that patients with schizophrenia would show significantly greater motor overflow than controls, and that the pattern of motor overflow occurrence would also vary significantly between the groups. A finger flexion task was used to examine the presence and pattern of motor overflow. Subjects were asked to maintain target forces, using either their index or small finger, representing 25, 50 or 75% of the maximum strength capacity for whichever finger was performing the task. Patients were found to exhibit significantly greater motor overflow than controls. There were also significant findings with respect to the patterns of motor overflow produced, specifically in regards to fine motor control and performance variability. In summary, patients differed significantly from controls in both the degree and pattern of overflow exhibited.

Purpose The purpose of this study was to detail the pathomechanics and pathoanatomy of fracture dislocations of the ring finger and small finger carpometacarpal (CMC) joint by duplicating the pathomechanics of the fist blow. Methods A custom-made jig was used to position 20 fresh-frozen cadaver upper extremities in forearm neutral rotation, 90° of elbow flexion, 20° of wrist extension, and 20° and 30° of flexion at the ring and small finger CMC joint, respectively. First 7.7 kg of weight were dropped from a height of 0.76 m to 1.1 m to axially load the ring and small metacarpal (MC) heads through a custom-made apparatus. Fluoroscopic examination before and after loading, and detailed dissection after loading, were used to identify any osseous and/or ligamentous injuries. Results The most common fractures were a dorsal capitate fracture and a middle MC dorsal base fracture. The most common combinations of fractures were the dorsal capitate and dorsal hamate fractures. Multiple fractures often were identified in a number of locations including dorsally: the capitate, hamate, and index through small metacarpal bases, and volarly: the hook of the hamate and the middle through the small MC bases. Conclusions The patterns of injuries encountered at the ring and small CMC joints can be explained by the direction and force of the applied load, position of the CMC joint at the time of loading, and the constraints imposed by specific CMC ligaments. A detailed analysis of the fracture patterns and associated ligament anatomy suggests that the typical ring and small carpometacarpal fracture dislocations are a more complex combination of fractures than identified by plain radiographs alone. The complexity of these injuries is greater than previously recognized and is most likely the result of a combination of axial load and shear stresses resulting in carpal fractures and ligament avulsions as well as fracture dislocations. This study suggests that computed tomography may be the preferred diagnostic imaging method for complete assessment of these injuries.

Previous studies have determined abnormalities in the fifth small finger flexor digitorum superficialis (FDS) tendons as interconnected (common) to the fourth finger (FDS) or absent. This study examined the effect of FDS-absent and FDS-common presentations of the fifth finger on grip strength in a mixed-gender group of rehabilitation science students and faculty members from the Medical University of South Carolina. This study evaluated 171 subjects. After controlling for gender, age, and hand dominance, the grip strength of subjects in the FDS-absent group was 6.9 lb weaker than the FDS-common group and 8.14 lb weaker than the FDS-independent group. The common group was 1.2 lb weaker than the normal group. Absence of the FDS occurred in 18.6% of female subjects and 15.3% of male subjects. Our findings suggest that hand therapists should expect lower results when measuring grip strength of FDS-absent or FDS-common individuals.

Purpose: To assess the longitudinal radiographic osseous changes of the wrist and hand other than interphalangeal joints in rheumatoid disease. Methods: Serial wrist and hand x-rays in 96 patients with long-standing rheumatoid disease were reviewed. The average number of years between initial and most recent x-rays was 15.1. The Larsen scoring system was used to assess the degree and severity of joint involvement. We identified patterns of involvement in the wrist, thumb, and finger metacarpophalangeal (MCP) joints. Results: The radioscaphoid and radiolunate joints had the earliest and most severe progression of all joints studied. Scaphoid erosions often were seen early (27%) and their presence was a predictor of progressive involvement. Ulnar styloid erosions commonly were seen as early isolated findings (25%). The distal radioulnar joint showed a rapid increase in Larsen score and was involved in 78% of patients on late x-rays. The thumb showed considerable late MCP joint disease that often led to boutonniere deformity and the trapeziometacarpal joint had the least rate of progression of all joints studied. The most severely and frequently involved MCP joints were the radial (index and middle), which also had the greatest increase in score over the span of the study. Finger MCP joint disease was observed to progress temporally in a predictable pattern: first radial MCP joints of the dominant hand, followed by the nondominant radial MCP joints, and last the ulnar MCP joints of the nondominant hand with small finger involvement preceding that of the ring finger. Of all MCP joints, the ring finger was least affected. Conclusions: This study clarified the longitudinal osseous radiographic changes of the wrist and hand (excluding interphalangeal joint) in rheumatoid disease. (J Hand Surg 2003;28A:427-434. Copyright © 2003 by the American Society for Surgery of the Hand.)

Summary Rheumatoid arthritis (RA) is the most frequent chronic inflammatory arthropathy that often leads to joint destruction. Essential for the progress of the disease are both an early diagnosis and a sensitive follow-up of synovitis. In this paper, we present new laser based imaging techniques for the transillumination of small finger joints. The “Laserscan” technique allows the transillumination of small finger joints using red laser light with a wavelength of 675nm. The laser is positioned above the finger joint and a CCD camera detects the scattering distribution below the joint. After processing the data through a statistical machine learning method, we could show in a preliminary clinical study that it was possible to correctly classify the inflammatory status of 62 of 72 joints from 22 patients with RA compared to precise clinical examination. Sagittal optical tomography is a further development of “Laserscan”. In this technique, a red laser is moved in sagittal plane above the proximal interphalangeal finger joint while a detector underneath the joint measures the scattered light distribution in the same plane. Using model-based iterative image reconstruction algorithms, sagittal cross-sectional images are obtained based on the acquired data. These images reflect the distribution of scattering and absorption properties within and around the joint cavity of a first healthy volunteer.

Purpose: The motion path of the digits follows the path of an equiangular spiral in which a constant angle is formed by all radial vectors along the curve. This implies that the lengths of the metacarpals, proximal, middle, and distal phalanges approximate a Fibonacci sequence in which the ratio of any 2 consecutive numbers approaches the number 1.61803 (phi). This study tested the hypothesis that the metacarpal and phalangeal bone lengths follow the Fibonacci relationship. Methods: Standardized x-rays were taken of the hands of 100 healthy volunteers. The proximal phalanx length was subtracted from the sum of the lengths of the middle and distal phalanges and the metacarpal length was subtracted from the sum of the lengths of the middle and proximal phalanges. Confidence intervals for the quotients of the measured lengths of the adjacent bones of the hand also were used for statistical analysis. Results: Only 1 of 12 bone length ratios contained the ratio phi in the 95% confidence interval, that of the small finger metacarpal and proximal phalanx. The largest variability was seen in the small finger phalangeal relationships. Conclusion: The application of the Fibonacci sequence to the anatomy of the human hand, although previously accepted, is a relationship that is not supported mathematically. The difference between individual bone lengths as measured at the joint line and the center of rotation of the joints may explain our finding. (J Hand Surg 2003;28A:157–160. Copyright © 2003 by the American Society for Surgery of the Hand.)

When suspecting proximal injury to the ulnar nerve, it is common to assess the integrity of the small finger flexor digitorum profundus muscle via methods such as isolated blocking exercises, active exercises, and applied resistance. This author describes another method of assessing the integrity of proximal ulnar nerve motor function.—Victoria Priganc, PhD, OTR, CHT, CLT, Practice Forum Editor

Nine healthy subjects sustained maximum grip of an instrumented handle while voluntarily moving the wrist joint within their available range of motion of the wrist in a continuous and random manner. Individual finger forces and wrist angular positions in flexion/extension and radial/ulnar deviation were recorded simultaneously. Wrist position had a significant effect on individual finger force and total force production. Peak finger forces were produced at 20 degrees of wrist extension and 5 degrees of ulnar deviation. At this position, a mean total grip force of 114.9 (+/-12.8) N was produced with force-sharing percentages of 32.2% (+/-3.8%), 32.6% (+/-4.3%), 23.5% (+/-4.5%), and 11.7% (+/-4.9%) among the index, middle, ring, and small finger, respectively. As the wrist was moved farther away from this position, the forces produced by individual fingers decreased incrementally; however, the decreases in individual finger forces were not proportional, leading to a dependence of finger force-sharing patterns on wrist position.

Treatment recommendations for metacarpal neck fractures of the small finger are generally based on the degree of apex dorsal angulation at the fracture site. We evaluated the variability of measurement of fracture angulation and the effect this variability has on treatment recommendations for these injuries. A total of 96 radiographs (anteroposterior, lateral, oblique views) of 32 patients with fractures of the small finger metacarpal neck were evaluated independently by 3 fellowship-trained orthopedic hand surgeons. Treatment recommendations for each fracture were tabulated. This process was repeated 6 weeks later to evaluate intraobserver variability. Kappa coefficients of inter- and intraobserver reliability of fracture angulation measurement and treatment plans were generated. The mean reliability coefficient of the measurement of fracture angulation between the 3 different observers was slight. Similarly, the reproducibility of fracture angulation measurement within observers was fair. Agreement between observers for appropriate treatment recommendations for each fracture was fair and agreement within observers for treatment was only slightly better. The measurement of fracture angulation of small finger metacarpal neck fractures seems to be subject to a high degree of inter- and intraobserver variability.

We studied the microanatomy of the communicating branch between the ulnar and median nerves in 26 adult cadaver hands to explain diminished sensibility in the fourth and fifth fingers we had observed in 2 patients after complete transection of the median nerve. Two new variations of the communicating branch were observed. In the first variation the communicating branch originated proximally from the third common digital nerve to distally join the ring finger ulnar digital nerve and the small finger radial digital nerve. In the second variation the ramus communicans traversed perpendicularly between the third and fourth common digital nerves with a crossover of nerve fibers.

A total of 548 upper limbs (276 right and 272 left hands) from Japanese cadavers were dissected. The arrangements of extensor indicis proprius, extensor digitorum communis (EDC), and extensor digiti minimi tendons and the intertendinous connections were studied. The most common pattern of extensor tendons was as follows: the index finger had a single EDC tendon, the middle finger had a single EDC tendon, the ring finger had a single EDC tendon, and the small finger had a single EDC tendon or a single common EDC tendon distributed to the ring and small finger. A single extensor indicis proprius tendon ran along the ulnar side of the EDC, and the extensor digiti minimi tendon consisted of 2 slips. Intertendinous connections were classified into 3 types: type 1 with a filamentous band, type 2 with a fibrous band, and type 3 with a tendinous band subdivided to r-shaped and y-shaped. The most common patterns were type 1 in the second intermetacarpal space (IMCS), type 3r in the third IMCS, and type 3y in the fourth IMCS.

The objective of this study is to evaluate the influences of activation mode, torque and horizontal operating distance on hand–arm response while operating in-line pneumatic screwdrivers. Hand–arm response was investigated in terms of finger force exertion, flexor digitorum electromyography, and hand-transmitted vibration. Two activation modes (push-to-start, and trigger-to-start), two torque levels (low, and high) and three horizontal operating distance (far, middle, and near) were evaluated. Thirteen healthy male subjects drove screws into an iron plate with pre-tapped screw holes using in-line pneumatic screwdrivers in randomly ordered experimental conditions. The results indicate that the use of push-to-start mode, not only required a greater holding force involving forearm muscular exertion and middle, ring and small finger forces, but also incurred a greater hand-transmitted vibration than the use of trigger-to-start mode. Higher torque caused a greater hand-transmitted vibration and required a firmer grip than lower torque. A middle distance level (18–30 cm away from the table edge) is recommended as it is found to have the least hand-transmitted vibration and requires less finger force exertion. Relevance to industry The findings on the evaluation of the influence of activation mode, torque, and horizontal operating distance on hand–arm response can provide useful information for the design of assembly tasks using pneumatic screwdrivers as well as the design of powered hand tools.

We present a rare case of attritional rupture of the flexor tendons to the small finger caused by an osteophyte of the volar aspect of the ulnar head.

We investigated the influence of hand osteoarthritis on skeletal quantitative ultrasound (QUS) measurement through the proximal phalanges in female geriatic inpatients. In a cross-sectional study, bone status was assessed with QUS at the distal metaphysis of the first phalanges of fingers II–V. Thirty-three of 101 female geriatric inpatients met the clinical criteria of the American College of Rheumatology for osteoarthitis of the hands (median age: 85 yr) and were compared with 68 female inpatients without swellings of the small finger joints (median age: 88 yr). Amplitude-dependent speed of sound at the distal metaphysis, the electronic signal of the ultrasonic wave after crossing the phalanx (graphic trace), and the thickness of each phalanx were measured and compared between the two groups by a phalangeal QUS device (DBM-Sonic 1200). There were no significant differences between the phalangeal QUS readings of both groups. The only statistically significant difference was observed in the comparison of the small finger thickness with a lower value in the osteoarthritis group ( p = 0.02). This findings suggest that at the metaphyseal level of phalanges, the degenerative process of osteoarthritis does not influence QUS assessment. This could be explained by the finger thickness at the metaphyseal level, which was not increased in patients with osteoarthritis compared with control subjects, at least as detected by the applied finger ultrasound method.

Closed rupture of the deep transverse metacarpal ligament (DTML) is an unusual injury. We have managed 2 patients with closed rupture of the DTML between the ring and small fingers resulting from crush injuries to the hand. Both patients presented with painful ulnar deviation of the small finger with extension. The diagnosis was confirmed by exploration through a volar incision. Repair of the ligament with use of the adjacent A1 pulleys to butress the repair was successful in both patients and restored a painless finger flexion-extension arc. Closed rupture of the DTML can be confused with a metacarpophalangeal joint collateral ligament rupture due to the characteristic deviation of the small finger.

A finger flexion task was used to investigate intensity of mirror movement. Subjects were asked to maintain target forces, with either their index or small finger, that represented 25, 50 or 75 percent of their maximum strength capacity for the finger performing the task. Relative to the force produced, males and females exhibited the same amount of mirror movement. However, mirror movement relative to force exerted was greater when the left hand performed the task, a finding consistent with previous research. Greater amounts of mirror movement were recorded for movements of the small finger compared to the index finger, consistent with the cortical activation explanation (Todor and Lazarus, 1986). These results suggest that strength differences are not the principal determinant of intensity of mirror movement. Rather, differing functional roles of the hands and fingers, reflecting differences in cortical activation and organisation, appear to mediate the intensity of mirror movement occurrence.

We present a case of snapping dislocation of the flexor digitorum superficialis tendon to the small finger over the hook of the hamate that was noted after carpal tunnel release and trigger digit release.

Twenty-eight nonrheumatoid patients were treated for sagittal band injuries. The digits involved, in order of frequency, were long, small, index, and ring. We observed three clinical types of sagittal band injuries: type I, injury without extensor tendon instability; type II, injury with tendon subluxation; and type III, injury with tendon dislocation. Eight of nine patients with small finger involvement had radial sagittal band injuries; four of them presented with abduction deformity of the small finger. Satisfactory results were achieved with nonoperative treatment when it was initiated within 3 weeks of injury. Splinting was the initial treatment for all patients. Ten patients were treated either by centralization of the extensor tendon of the central two digits to provide pain-free stability or tendon transfer to correct small finger abduction deformity.

Both hands of 39 patients who had symptoms of pain and/or numbness in one or both hands were tested by two hand therapists using the full kit of Semmes-Weinstein monofilaments (SWMFs). The SWMF thresholds were obtained for the thumb, the index finger, and the long and small fingers. These thresholds were classified as normal or abnormal based on four decision rules and two criterion measures. Decision rules were based on whether SWMF 2.83 or 3.22 would be the best limit of normality, and whether the small finger should be used for within-subject comparisons. The criterion measures were the highest threshold of all three radial digits and the highest threshold of the long finger alone. Intertherapist agreement on normality was fair to moderate (kappa = 0.22-0.51), varying according to decision rules and criterion measures. Reliability was higher when the additional comparison with the small finger was omitted. High accuracy in identifying cases of carpal tunnel syndrome (CTS) was possible, but accuracy varied moderately between testers and greatly according to decision rules and criterion measurements. The best overall accuracy (81%-82% sensitivity and 57%-86% specificity) was achieved when SWMF 2.83 was used as the upper limit of normality and the small finger was used for within-subject comparison, and when data from the long finger alone were used for decision making.

Dynamic values of key vessel diameter, blood velocity, and flow rate in the upper extremity were obtained in 20 healthy volunteers by means of color flow Doppler imaging with a 7.5 MHz transducer. Recordings were made of the brachial, radial, posterior radial recurrent, ulnar, and digital arteries. Radial and ulnar vessels were evaluated at both wrist and midcarpal levels. Diameter and velocity changes were followed throughout the cardiac cycle, and a true mean flow was computed. Mean diameters of the digital vessels ranged from 0.9 mm in the small finger to 1.3 mm in the thumb. Brachial flows ranged from 4.6 to 89.9 ml/min, radial flows from 0.9 to 15.3 ml/min, and ulnar flows from 0.6 to 79.9 ml/min. At the midcarpal level, flows ranged from 0.2 to 68.4 ml/min for the ulnar artery and from 0.8 to 42.9 ml/min for the radial artery. Variability between individuals was also demonstrated in artery dominance: eleven ulnar dominant, seven radial dominant, and two equal (within 25% of each other). The accuracy and ease of use of this technique in measurement of vessels are limited when vessels are less than 1.5 mm in diameter although the technique provides quantitative values to 0.5 mm.

The architectural features of twenty-one different forearm muscles (n = 154 total muscles) were studied. Muscles included the extensor digitorum communis to the index, middle, ring, and small fingers, the extensor digit quinti, the extensor indicis proprius, the extensor pollicis longus, the flexor digitorum superficialis, the flexor digitorum profundus, the flexor pollicis longus, the pronator quadratus, the palmaris longus, the pronator teres, and the brachioradialis. Muscle length, mass, fiber pennation angle, fiber length, and sarcomere length were determined with the use of laser diffraction techniques. From these values, physiologic cross-sectional area and fiber length/muscle length ratio were calculated. The individual digital extensor muscles were found to be relatively similar in architectural structure. Similarly, the deep and superficial digital flexors were very similar architecturally, with the exception of the small finger flexor digitorum superficialis, which was much smaller and shorter than the rest of the digital flexors. The brachioradialis and the pronator teres had dramatically different architectural properties. While the masses of the two muscles were nearly identical, the muscles had significantly different predicted contractile properties based on their different fiber arrangement. The brachioradialis, with its long fibers arranged at a small pennation angle, had a physiologic cross-sectional area that was only one third that of the pronator teres, with its short fibers that were more highly pennated. Using these architectural data and the statistical method of discriminant analysis, we provide additional information that might be useful in the selection of potential donor muscles to restore thumb flexion, thumb extension, finger extension, and finger flexion.