Relationship Between Ulnar Variance, Cortical Bone Density, and Load to Failure in the Distal Radius at the Typical Site of Fracture Initiation.

PURPOSE: Increased ulnar variance has been shown to lead to diminished load borne by the distal radius. The purpose of this study was to determine the correlations among ulnar variance, bone mineral density, and load to failure at the distal radius. METHODS: Posteroanterior radiographs and computed tomographic scans were taken of 12 cadaveric forearms in neutral rotation. Ulnar variance was measured for each wrist by the method of perpendiculars. Measurements of cortical, trabecular, and combined bone density were made at the distal radius. We performed linear regression analysis and correlation analysis to determine the relationship between bone densities and ulnar variance measurements. Next, we loaded the 12 cadaveric radii to failure under axial compression. Linear regression analysis and correlation analysis were then performed to determine the relationship between load to failure and both ulnar variance and cortical density. RESULTS: Increased ulnar variance was significantly correlated with decreased cortical bone density at the distal radius and both were correlated with decreased load to failure. We found no correlation between ulnar variance and trabecular density or combined trabecular and cortical bone density at the distal radius. CONCLUSIONS: Our study found that increased ulnar variance and decreased cortical bone mineral density correlates with decreased load to failure under axial compression. CLINICAL RELEVANCE: Ulnar variance is linked to both bone quality and load to failure at the distal radius.

Incidence of Patients With Knee Strain and Sprain Occurring at Sports or Recreation Venues and Presenting to United States Emergency Departments.

CONTEXT: Knee injuries account for a substantial percentage of all athletic injuries. The relative rates of knee injury for a variety of sports by sex and age need to be understood so we can better allocate resources, such as athletic trainers, to properly assess and treat injuries and reduce injury risk. OBJECTIVE: To describe the epidemiology of patients with sport-related knee strain and sprain presenting to US emergency departments from 2002 to 2011. DESIGN: Cross-sectional study. SETTING: Using the Consumer Products Safety Commission's National Electronic Injury Surveillance System and the US Census Bureau, we extracted raw data to estimate national rates of patients with knee strain and sprain presenting to emergency departments. PATIENTS OR OTHER PARTICIPANTS: Participants were individuals sustaining a knee strain or sprain at sports or recreation venues and presenting to local emergency departments for treatment. We included 12 popular sports for males and 11 for females. Ages were categorized in six 5-year increments for ages 5 to 34 years and one 10-year increment for ages 35 to 44 years. MAIN OUTCOME MEASURE(S): Incidence rates were calculated using weights provided by the National Electronic Injury Surveillance System and reported with their 95% confidence intervals for sport, sex, and age. RESULTS: Strain and sprain injury rates varied greatly by sport, sex, and age group. The highest injury rates occurred in football and basketball for males and in soccer and basketball for females. The most at-risk population was 15 to 19 years for both sexes. CONCLUSIONS: Athletes experience different rates of knee strain and sprain according to sport, sex, and age. Increased employment of athletic trainers to care for the highest-risk populations, aged 10 to 19 years, is recommended to reduce emergency department use and implement injury-prevention practices.

Allograft Reconstruction of the Lisfranc Ligament.

UNLABELLED: For Lisfranc injuries, screw fixation of the medial and middle columns is currently the standard of treatment. The purpose of this study was to biomechanically evaluate the use of allograft for a severed Lisfranc ligament compared to standard screw fixation and the intact condition. Six pairs of fresh-frozen cadaveric lower extremities were prepared with reflective marker arrays and cyclically loaded to simulate partial weight bearing under 4 sequential testing conditions: (1) intact ligament, (2) disrupted ligament, (3) tendon allograft reconstructed ligament, and (4) rigid screw fixation. The relative displacement between the medial cuneiform and the second metatarsal was assessed via motion analysis. A mixed model analysis of variance was used to determine the significance (α = .05) of displacement differences. Mean displacements and 95% confidence intervals for each condition were as follows: (1) intact 9.1 (7.1-11.2) mm, (2) cut ligament 9.4 (7.4-11.5) mm, (3) allograft fixation 8.8 (6.8-10.9) mm, and (4) screw fixation 8.2 (6.2-10.3) mm. There were no significant differences among the specimens according to condition. Allograft fixation provided adequate strength and stability and did not differ significantly compared to intact or screw fixation. LEVELS OF EVIDENCE: Level V: Bench testing.

A biomechanical comparison of 2 hybrid techniques for elbow ulnar collateral ligament reconstruction.

PURPOSE: To compare the valgus laxity and fixation strength of 2 hybrid techniques for elbow ulnar collateral ligament reconstructions. METHODS: Reflective markers were placed near the ligament attachments of the ulnar collateral ligament on the humerus and ulna of 12 fresh-frozen cadaveric upper extremities for tracking displacement with 4 motion analysis cameras. Valgus laxity testing was performed on the intact, disrupted ligament, and reconstructed elbows by applying a 3.0 Nm moment across the joint at 15° intervals throughout elbow motion from 0° to 120°. Two hybrid techniques for ulnar collateral ligament reconstruction were performed: a proximal docking method and a single-point distal fixation method. Failure testing was performed with the elbow at 90° by applying a cyclic valgus load 12 cm distal to the joint that we increased in 10-N intervals. RESULTS: Valgus laxity testing revealed no difference in ligament displacements between the 2 techniques over the entire range of elbow motion. Ligament displacement for the proximal docking hybrid technique was significantly higher than the intact at 0° and 15° of elbow flexion. Failure testing revealed no differences in ligament displacements or failure load between the 2 techniques. CONCLUSIONS: Both the proximal docking and the single-point fixation hybrid reconstructions provided sufficient joint stability and strength compared to the intact elbows, with the exception of the proximal docking method at low flexion angles. The reconstructions were not significantly different with respect to valgus laxity or graft fixation displacement at failure. CLINICAL RELEVANCE: The proximal docking and single-point fixation hybrids tested here are both viable surgical options with sufficient strength and valgus laxity mechanics, warranting clinical evaluation.

Biomechanical comparison of first metatarsophalangeal joint arthrodeses using triple-threaded headless screws versus partially threaded lag screws.

BACKGROUND: Triple-threaded, cannulated headless screws of varying thread diameters and pitch are designed to maintain thread length across the arthrodesis plane, provide joint compression, and reduce countersinking. This study tested the biomechanical fixation strength of conventional partially threaded lag screws compared to triple-threaded headless screws in first metatarsophalangeal joint arthrodesis. METHODS: First metatarsophalangeal joint arthrodesis using a crossed screw technique was performed on 11 paired, preserved cadaver first rays with two 4.0-mm triple-threaded, cannulated headless screws or two 4.0-mm partially threaded, cannulated lag screws. The constructs were tested to failure through dorsally directed cantilever bending. RESULTS: The triple-threaded, cannulated headless screws displayed significantly greater bending stiffness (p=0.017) and failure load (p=0.040) during load-to-failure testing compared to the partially threaded, cannulated lag screws. CONCLUSIONS: Triple-threaded, cannulated headless screws may be a viable alternative to partially threaded lag screws in first metatarsophalangeal arthrodesis.

Three-dimensional computed tomography-based modeling of sagittal cadaveric femoral bowing and implications for intramedullary nailing.

OBJECTIVES: To establish the nature and extent of femur sagittal bowing by determining outer and inner anterior cortex geometries and sizes using analytical 3-dimensional computed tomography modeling and relate the resultant femoral curvature with the curvatures of available intramedullary nails. METHODS: Computed tomography scans were rendered in 3D using modeling software to reconstruct 2 geometries: (1) outer cortex and (2) medullary canal. Femoral bow in the sagittal plane and the anterior cortical thickness were measured. Three curvature points were selected on both the geometries. Exterior anterior cortex radius of curvature (AROC) and medullary canal radius of curvature (MROC) were compared within and between each femur pair. RESULTS: Three groups of femurs exhibiting significantly different geometry patterns emerged: (1) AROC significantly greater than MROC, (2) AROC equivalent to MROC, and (3) AROC significantly smaller than MROC. Anterior cortical thickness ranged from 2.2 to 7.0 mm was significantly different for males versus females, and it varied inversely with age. CONCLUSIONS: The study confirms that the radius of curvature of most intramedullary nails exceeds the sagittal radius of curvature of most adult femurs (both AROC and MROC). An intramedullary nail selected based on the anterior curvature would impinge on the anterior cortices at the proximal and distal anterior aspects of the femur in specimens with AROC > MROC. Conversely, in specimens with AROC < MROC, an intramedullary nail selected based on the anterior curvature would impinge on the proximal and distal posterior cortices. That cortical thickness varied significantly in accordance with gender and age is also relevant to surgical planning. MROC, in addition to the AROC alone, should be one of several design parameters used to match specific intramedullary nail design to an individual patient.

Fixation strength of anteriorly inserted headless screws for talar neck fractures.

BACKGROUND: For noncomminuted talar neck fractures, traditional fixation is with small fragment screws or cannulated screws. Newer screw systems on the market allow placement of cannulated headless screws, which provide compression by virtue of a variable-pitch thread. The headless construct has an inherent advantage, particularly for the talus, when the screws must be countersunk to prevent wear of the joint articular surfaces. This study tested the biomechanical fixation strength of cannulated headless variable-pitch screws compared with conventional cannulated screws, both placed in an anterior to posterior direction. METHODS: A reproducible talar neck fracture was created in nine paired, preserved, cadaver talar necks using a materials testing machine. Talar head fixation was then performed with two cannulated headless variable-pitch 4/5 screws or two 4.0-mm conventional cannulated screws. The specimens were tested to failure and the fixations were normalized to their intact pairs and compared. RESULTS: The headless variable-pitch screw fixation had significantly lower failure displacement than the conventional screw fixation. No significant differences were found between the two fixations for failure stiffness, load at failure or energy absorbed. CONCLUSIONS: Cannulated headless variable-pitch screws significantly improved failure displacement when compared to conventional cannulated screws in a cadaveric model, and may be a viable option for talus fracture fixation. CLINICAL RELEVANCE: Headless, fully threaded, variable-pitch screws have inherent advantages over conventional screws in that they may be less damaging to the articular surface and can compress the fracture for improved reduction. This study demonstrates these screws are also biomechanically similar to conventional screws.

Specimen specific, 3D modeling of the elbow--prediction of strain in the medial collateral ligament.

In this project 3D interactive models of twelve cadaver elbows are developed using the author's kinematic simulation software. The effective flexion-extension axes for each specimen's model are iteratively defined based upon congruent joint motion and individual limits in range-of-motion. Origins and insertions of both parts of the medial collateral ligament are digitized following careful dissection of each specimen. Ligament paths are then defined using cubic B-spline models of the principal fibers of each part, flexion extension motion of each elbow is carried out in real-time and the strain of each fiber model is calculated. Results indicate the existence of two distinct populations of medial collateral ligament - one whose anterior part stretches during flexion of the elbow and the other whose anterior part stretches during extension.

Computer simulation of pectoralis major muscle strain to guide exercise protocols for patients after breast cancer surgery.

STUDY DESIGN: Descriptive study. OBJECTIVES: To quantify and rank the order of strain (length change in proportion to the resting length) of 3 portions of the pectoralis major (PM) muscle during various exercises. BACKGROUND: A biomechanical foundation on which to base exercise prescriptions for patients after breast cancer surgery is lacking. METHODS: An interactive, 3-D, computer graphic simulation system, developed to study biomechanical properties of the musculoskeletal system, was used to simulate movements of the glenohumeral, scapulothoracic, and scapuloclavicular joints of the shoulder, and to estimate strain in 3 portions of the pectoralis major (PM) muscle throughout the motions. The computed tomography scans of 2 male cadavers and literature review formed the basis for the estimations used in the model. Strains in the clavicular, midsternum, and abdominal regions of the PM were expressed as percent strain: [(change in muscle length/resting length) × 100]. Exercise motions were based on PM muscle anatomy and published breast cancer rehabilitation protocols. RESULTS: Strains of the PM regions ranged from -21% shortening of the clavicular region during flexion to 55% lengthening of the abdominal region during the overhead stretch. Strain between adjacent regions was most uniform for the movement of abduction with external rotation, and least uniform with flexion. CONCLUSION: PM muscle lengthening estimates were not linearly proportioned to shoulder joint motions, and varied for 3 portions of the PM. This information may help clinicians and researchers to estimate lengthening of PM portions throughout measurable shoulder motions.

The sacroiliac spine - computer simulation of motion and modeling of the ligaments.

Using an interactive, 3D, kinematic simulation of the human skeleton, the motion of the sacro-iliac (SI) joint is modeled based upon descriptions available in the literature. The major ligaments are added to the simulation data structure using deformable cubic B-spline curve paths. Ligament strains were generated and studied in response to the motion simulations. Results improve our understanding of sacro-iliac kinematics and highlight the importance of further studies to elucidate pathological as well as normal SI joint and ligament function.

Three femoral fixation devices for anterior cruciate ligament reconstruction: comparison of fixation on the lateral cortex versus the anterior cortex.

PURPOSE: To evaluate the biomechanical properties of 3 anterior cruciate ligament (ACL) reconstruction femoral fixation devices in a porcine model with implantation on both the lateral femoral cortex and the anterior femoral cortex. METHODS: ACL reconstructions with an 8-mm porcine tendon graft were performed on 48 porcine femurs with the EndoButton CL (Smith & Nephew, Andover, MA), ToggleLoc with ZipLoop technology (Biomet Sports Medicine, Warsaw, IN), or EZLoc (Biomet Sports Medicine). In 8 specimens for each implant, the femoral tunnel was drilled from the 10:30 surgical position out the lateral cortex. In another 8 specimens for each implant, the tunnel was drilled from the 10:30 position to a standardized anterior femoral surface. Cyclic testing was performed on an MTS testing machine (MTS, Eden Prairie, MN) from 50 N to 450 N for 2,000 cycles, followed by load-to-failure testing in specimens that survived. The cortical thickness and location of the implant exit were recorded. RESULTS: In the lateral femur group, 0 of the EZLoc devices, 2 of the ToggleLoc devices, and 3 of the EndoButtons completed cyclic testing. In the anterior femur group, 1 of the EZLoc devices, 5 of the ToggleLoc devices, and 5 of the EndoButtons completed cyclic testing (P = .012). In the anterior femur group, the ToggleLoc exhibited higher 2,000-cycle elongation (5.46 +/- 1 mm) than the EndoButton (3.55 +/- 0.6 mm) (P = .005). The EndoButton showed a higher first failure load (1,190.9 +/- 150.0 N) than the ToggleLoc (912.6 +/- 82.4 N) (P = .007). The anterior cortex (1.4 mm) was thinner than the lateral cortex (1.7 mm) (P = .0002). CONCLUSIONS: The EndoButton provided the strongest ACL femoral fixation with significantly less graft-implant elongation and significantly higher failure loads. It was also shown in a porcine model that implants on the anterior cortical surface perform better than those on the lateral surface. Increased cortical thickness, in the range tested, was not associated with improved implant performance in the porcine model. CLINICAL RELEVANCE: The EndoButton provided the best ACL femoral fixation of the devices tested.

The effect of modern total knee arthroplasty on muscle balance at the knee.

Total Knee Arthroplasty (TKA) may affect the muscles operating at the flexion/extension (FE) or internal /external rotation (IE) axes. This study tested the hypothesis that a modern posterior stabilizing TKA will change the mechanical balance of the knee joint by altering the moment arms of muscles acting about two separate axes of rotation. Moment arms were determined for the normal knee, the knee after resection of the Anterior Cruciate Ligament (the ACL - knee) and the knee after a PCL-sacrificing TKA. Five fresh cadaver hemi pelvis specimens were used with 5 posterior stabilizing prostheses (a single model available from one manufacturer). Moment arms for the individual muscle tendons were multiplied by the muscle's tension fraction (fractional physiological cross-sectional area [PCSA]) to estimate its potential for moment production relative to the other muscles at the knee, and this value was labeled as the muscle's moment potential. Unlike earlier studies that looked at TKA across many manufacturers' types, this study concluded that there were no significant differences in muscle balance when comparing the intact knee and the posterior stabilized TKA.

Thumb interphalangeal joint extension by the extensor pollicis brevis: association with a subcompartment and de Quervain's disease.

PURPOSE: First dorsal compartment anatomy was analyzed for the presence of a separate compartment for the extensor pollicis brevis (EPB) tendon and the ability of the EPB to extend the thumb interphalangeal (IP) joint in order to determine if these characteristics were associated with each other, and with de Quervain's disease. METHODS: Two groups were studied: (1) 90 cadaver wrists, 28 to 89 years, 38 male and 52 female specimens; and (2) 143 patient wrists, 21 to 82 years, 18 men and 125 women, in which the first dorsal compartment was released for treatment of de Quervain's disease. RESULTS: The EPB was in a separate compartment in 102 of 143 of the surgical group and 18 of 90 of the cadaver group. The EPB was able to extend the IP joint in 56 of 143 of the surgical group and 19 of 90 of the cadaver group. When the EPB was able to extend the IP joint, it was in a subcompartment in 49 of 56 of the surgical group and 9 of 19 of the cadaver group. When the EPB was able to produce IP extension in the cadaver group, it was inserted on the distal phalanx or the extensor hood. CONCLUSIONS: In a substantial number of people undergoing surgery for de Quervain's disease and in cadavers, the EPB can extend the thumb IP joint. When it does, particularly in patients with de Quervain's disease, it is likely to reside in a subcompartment of the first dorsal compartment. The incidences of a subcompartment for the EPB and the ability of the EPB to extend the thumb IP joint were higher in the de Quervain's patient population than in the cadaver group.

Use of a patient-controlled stretching device to improve the ankle range of motion.

BACKGROUND: Ankle and subtalar stiffness are widely associated with many foot and ankle conditions and functional deficits. Loss of range of motion, particularly dorsiflexion, results in significant gait dysfunction. A variety of methods have been evaluated to address this problem, including yoga, manipulation, dance training, jogging and static stretching exercises. No tools have been described that effectively and efficiently stretch the ankle and subtalar joint without requiring supervision or assistance of a trained physical therapist. MATERIALS AND METHODS: Twenty-two subjects with varying foot and ankle diagnoses who had little or no improvement in range of motion after traditional assisted physical therapy were recruited from a foot and ankle orthopaedic clinic. The subjects' ankle and subtalar range of motion (ROM) in plantarflexion (PF), dorsiflexion (DF), inversion (INV), and eversion (EVR) were measured using a standard goniometer by a single physiotherapist prior to using the stretching device. The subjects were trained on the proper use of the stretching device and then instructed to use it daily for a 6-week period. Then the same examiner repeated the above measurements. Statistical analysis was performed using a two sample t-test assuming unequal variances. RESULTS: There were statistically significant increases in ROM in all planes tested: DF to PF (p = 0.0052), and INV to EVR (p = 0.018). CONCLUSION: Stretching with the device significantly increased ankle and subtalar ROM. CLINICAL SIGNIFICANCE: The stretching device can be used at home on a regular basis with minimal training and can effectively treat stiffness of the ankle and subtalar joints. It can be cost-effective when compared to use of physiotherapy services.

Tensioning of anterior cruciate ligament hamstring grafts: comparing equal tension versus equal stress.

PURPOSE: A biomechanical study was undertaken to determine whether equal-stress or equal-tension tensioning of anterior cruciate ligament 4-stranded semitendinosus and gracilis grafts provides a stronger graft construct when testing to ultimate failure. METHODS: Eighteen fresh-frozen cadaveric semitendinosus and gracilis tendons were each positioned over a cylinder rod/cryo-clamp connected to an MTS machine (MTS Systems, Eden Prairie, MN) by another cryo-clamp. In the equal-tension group the 4 strands were equally tensioned by weights. In the equal-stress group a tensioning device applied equal stress based on the cross-sectional areas of the tendons. The tendons were preconditioned with 10 cycles and then tested to failure. Graft creep during the preconditioning cycle was determined by MTS measurement of the change in clamp distance. RESULTS: The maximum loads of 4-stranded semitendinosus and gracilis grafts tensioned by equal stress were found to be similar to those of the grafts tensioned by equal tension (2,803 +/- 431 N and 2,772 +/- 461 N, respectively). The loads at first failure were 2,640 +/- 468 N and 2,452 +/- 461 N, respectively (P = .17). The preconditioning cycles showed that the equal-stress group resisted graft creep significantly better (P = .0003). CONCLUSIONS: The strength of the 4-stranded hamstring graft when equally tensioned or equally stressed was equivalent when tested to failure. After 10 preconditioning cycles, equal stress resisted graft creep significantly better. Equal-stress tensioning offers an alternative tensioning method for 4-stranded hamstring grafts. CLINICAL RELEVANCE: Equal-stress tensioning offers an alternative tensioning method for 4-stranded hamstring grafts.

Upper-limb kinematics of the presumed-to-be-unaffected side after brain injury.

OBJECTIVE: The purpose of this pilot study was to investigate the kinematics of the presumed-to-be-unaffected upper limbs of people with brain injury (BI) compared with people without brain injury (WBI) during reaching. METHOD: Seventeen people with BI with no apparent motor deficit and 17 people WBI were measured and compared. A six-camera motion analysis system was used to determine movement duration, average speed, and smoothness during reaching. RESULTS: The group of people with BI was found to be significantly longer in movement duration (p < .0001), were slower in average speed (p < .0001), and had decreased smoothness (p < .0001) during reaching than the group of people WBI. CONCLUSION: The results suggest that people with BI may have undetected motor deficit in their presumed-to-be-unaffected upper extremities. Further research is needed to explore the upper-limb motor performance and the impact on function and safety.

Osteoformin accelerates fresh fracture healing in rats.

PURPOSE: Negatively charged resins have been shown to stimulate bone repair. In previous studies, the negatively charged polypeptide polyaspartate, which has been named Osteoformin, has been shown to stimulate osteoblast differentiation in vitro. The objective of the current study was to investigate the potential effect of Osteoformin on experimental femoral fracture healing in vivo. MATERIALS AND METHODS: Thirty-six male Sprague-Dawley rats were used. The femurs of anesthetized rats were stabilized with intramedullary pins and subjected to closed midshaft transverse facture by bending to failure. In experimental rats, fracture sites were injected with 100 microg of Osteoformin dissolved in 0.1 mL phosphate buffered saline (PBS) at day 1 and day 7 after surgery; in controls groups, fracture sites received 0.1 mL PBS at the intervals indicated above. Between 2 and 4 weeks after fracture, the animals were sacrificed and the healing femurs were removed for radiographic and histologic analysis. RESULTS: Osteoformin decreased the healing time of fresh fractures in rats, as indicated by histologic and radiographic assessments. CONCLUSION: The results of this study show that Osteoformin improves femoral fracture healing in rats.

Modeling avian kinematics using software developed for the human musculoskeletal system.

Using an interactive computer graphic system developed for the simulation of human musculoskeletal kinematics and detailed Computerized Tomography (CT) imaging of the domestic turkey, a kinematic structure of the avian trunk and wings is defined. The result is a simulation that provides interactive study of avian muscle-tendon joint kinematics, the ability to elucidate the essential components of bird flight and visual verification of heuristic muscle-tendon-joint models through real-time, 3D interaction. This application demonstrates the flexibility and applicability of this simulation software to define the kinematic structure of any animal or robotic mechanism given a segmented, 3D skeletal structure and to define the necessary and sufficient joints (linked revolutes and degrees-of-freedom) and muscle-tendon paths for that animal. The result is an interactive, real-time, 3D, kinematic model providing immediate understanding of muscle-tendon-joint function specific to that animal.

Three-dimensional analysis of the ligamentous attachments of the second through fifth carpometacarpal joints.

The purpose of this study is to clarify, measure, and show the anatomic locations and areas of specific ligamentous attachments and paths of the second through fifth carpometacarpal (CMC) joints on a three-dimensional (3D) surface model. Ten fresh-frozen cadaver wrists were used to dissect and identify the second through fifth CMC ligaments. Their ligamentous attachments and whole bone surfaces were digitized three-dimensionally and their areas calculated. The attachments of each ligament were represented in a model combining CT surfaces overlaid by a digitized 3D surface, and were also visually demonstrated with a specific color on 3D images of the bones. Nine dorsal and 11 palmar CMC ligaments and one CMC interosseous ligament were identified in the second through fifth CMC joints. An intra-articular ligament between the third metacarpal (MC), the fourth MC, capitate, and hamate was also identified. Five dorsal and five palmar intermetacarpal ligaments and three intermetacarpal interosseous ligaments were also identified in the second through fifth intermetacarpal joints. A previously undescribed palmar intermetacarpal ligament was located between the third, fourth, and fifth MC bases. The anatomic 3D attachment sites of the second through fifth CMC ligaments were visually depicted qualitatively, and their areas quantified. This 3D information will not only afford a better understanding of the anatomy and mechanics of the second through fifth CMC joints, but will also assist in the assessment of radiographic images and treatment of various injuries.

Intrinsic muscle contribution to the metacarpophalangeal joint flexion moment of the middle, ring, and small fingers.

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 degrees 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.