Quantification of carpal tunnel morphology using centroid-to-boundary distance shape signatures.

Morphology analysis is valuable to understanding risk factors and the etiology of carpal tunnel (CT) syndrome. The objective of this study was to investigate morphology changes along the length of the CT using shape signatures (SS). Analysis was performed on ten cadaveric specimens in neutral wrist posture. Centroid-to-boundary distance SS were generated for proximal, middle, and distal CT cross-sections. Phase shift and Euclidean distance were quantified relative to a template SS for each specimen. Medial, lateral, palmar, and dorsal peaks were identified on each SS to generate metrics of tunnel width, tunnel depth, peak amplitude, peak angle. Width and depth measures were also performed using previously reported methods to serve as a basis of comparison. The phase shift revealed twisting of 21° between the ends of the tunnel. Distance from the template and width varied significantly over the length of the tunnel, while depth did not. Measures of width and depth using the SS method were consistent with previously reported methods. The SS method afforded the advantage of peak analysis with overall trends of peak amplitude indicating flattening of the tunnel at the proximal and distal ends relative to a rounder shape in the middle.

Predicting Wrist Posture during Occupational Tasks Using Inertial Sensors and Convolutional Neural Networks.

Current methods for ergonomic assessment often use video-analysis to estimate wrist postures during occupational tasks. Wearable sensing and machine learning have the potential to automate this tedious task, and in doing so greatly extend the amount of data available to clinicians and researchers. A method of predicting wrist posture from inertial measurement units placed on the wrist and hand via a deep convolutional neural network has been developed. This study has quantified the accuracy and reliability of the postures predicted by this system relative to the gold standard of optoelectronic motion capture. Ten participants performed 3 different simulated occupational tasks on 2 occasions while wearing inertial measurement units on the hand and wrist. Data from the occupational task recordings were used to train a convolutional neural network classifier to estimate wrist posture in flexion/extension, and radial/ulnar deviation. The model was trained and tested in a leave-one-out cross validation format. Agreement between the proposed system and optoelectronic motion capture was 65% with κ = 0.41 in flexion/extension and 60% with κ = 0.48 in radial/ulnar deviation. The proposed system can predict wrist posture in flexion/extension and radial/ulnar deviation with accuracy and reliability congruent with published values for human estimators. This system can estimate wrist posture during occupational tasks in a small fraction of the time it takes a human to perform the same task. This offers opportunity to expand the capabilities of practitioners by eliminating the tedium of manual postural assessment.

Carpal tunnel volume distribution and morphology changes with flexion-extension and radial-ulnar deviation wrist postures.

Non-neutral wrist postures have been reported to cause decreased carpal tunnel volume (CTV) contributing to impingement of the median nerve and development of carpal tunnel syndrome. Recent analysis found CTV did not change with ±20° flexion-extension (FE), however, CTV decreased with ulnar deviation over the range of -5° to 15° radial-ulnar deviation (RUD). These findings suggest CTV may be too coarse of a measure to reflect the effects of slight non-neutral postures, or that volume is conserved and redistributed due to changes in tunnel morphology with posture. The objective of this study was to assess volume distribution along the length of the carpal tunnel and to quantify regional morphology changes with deviated wrist postures in both FE and RUD. Analysis was performed on a dataset of computed tomography scans collected on ten cadaveric specimens (5 male, 5 female, mean age = 80.7 ± 10.9 years) over a range of FE and RUD postures. The carpal tunnel of each scan was divided into four quartiles of equal length along the tunnel to quantify volume distribution. Volume within the carpal tunnel was seen to redistribute with both FE and RUD. Decreased volume in the distal aspect of the tunnel with flexion and proximal aspect of the tunnel with ulnar deviation may contribute to localized compression of the medial nerve. Measures of mean cross-sectional area, width and depth by quartile provided an indication of the morphology changes associated volume redistribution. Morphology analysis also revealed twisting between the proximal and distal aspects of the tunnel which increased with flexion and ulnar deviation and may further contribute to strain on the median nerve.

Effects of slight flexion-extension and radial-ulnar deviation postures on carpal tunnel volume.

BACKGROUND: Non-neutral wrist postures are a commonly reported risk factor for carpal tunnel syndrome. It is unclear how slight flexion-extension and radial-ulnar deviation postures affect the carpal tunnel. The objective was to determine the effects of slight non-neutral postures by quantifying carpal tunnel volume. METHODS: Computed tomography images were collected on ten cadaveric specimens in target postures of -20°, -10°, -5°, 0°, 5°, 10°, and 20° of flexion and - 10°, -5°, 0°, 5°, and 10° of radial-ulnar deviation. Surface meshes of the carpal tunnel, carpal bones, radius, and third metacarpal were generated with manual segmentation. Carpal tunnel volume was calculated as the volume between proximal and distal boundaries defined with anatomical landmarks and the orientation of the tunnel. The precise wrist posture of each scan was determined with inertial-based coordinate systems of the radius and third metacarpal. FINDINGS: Through multiple linear regression it was determined that, over the observed range of postures, flexion-extension angle does not have a significant effect (p = 0.99) while radial-ulnar deviation angle has a significant effect of -5.9 mm3/degree (p = 0.003). The findings were consistent with previous studies of postural effects on carpal tunnel pressure. INTERPRETATION: For the treatment and prevention of carpal tunnel syndrome, results suggest that attention should be given to slight radial-ulnar deviation postures (<10°), while slight flexion-extension postures (<20°) are of lesser consequence to carpal tunnel volume.

Accuracy of a Low-Cost 3D-Printed Wearable Goniometer for Measuring Wrist Motion.

Wrist motion provides an important metric for disease monitoring and occupational risk assessment. The collection of wrist kinematics in occupational or other real-world environments could augment traditional observational or video-analysis based assessment. We have developed a low-cost 3D printed wearable device, capable of being produced on consumer grade desktop 3D printers. Here we present a preliminary validation of the device against a gold standard optical motion capture system. Data were collected from 10 participants performing a static angle matching task while seated at a desk. The wearable device output was significantly correlated with the optical motion capture system yielding a coefficient of determination (R2) of 0.991 and 0.972 for flexion/extension (FE) and radial/ulnar deviation (RUD) respectively (p < 0.0001). Error was similarly low with a root mean squared error of 4.9° (FE) and 3.9° (RUD). Agreement between the two systems was quantified using Bland-Altman analysis, with bias and 95% limits of agreement of 3.1° ± 7.4° and -0.16° ± 7.7° for FE and RUD, respectively. These results compare favourably with current methods for occupational assessment, suggesting strong potential for field implementation.

Design and validation of a novel 3D-printed wearable device for monitoring knee joint kinematics.

Gait analysis provides an important tool for the study and clinical evaluation of conditions which affect knee joint biomechanics. Collection of knee joint kinematics in real world environments during locomotor activities of daily living could provide quantitative evidence to help understand functional impairment. Unfortunately, the high cost and necessary technical expertise associated with current commercially available systems for kinematic monitoring serve as an impediment to their adoption outside of specialized research groups. We have developed a low-cost, custom wearable device to address these shortcomings. The 3D printed device is capable of measuring knee flexion/extension (F/E) and adduction/abduction (AD/AB) angles. Here, we present a gold standard validation of the novel device against an optoelectronic motion capture system (MCS). Data were collected during a treadmill walking task from 8 participants on 2 separate occasions. Agreement with the MCS was quantified via root mean squared error (RMSE), coefficients of multiple correlation (CMC), paired dependent t-tests and Bland-Altman analyses. The wearable device had an overall RMSE of 3.0° and 2.7° and a CMC of 0.97 and 0.91 in F/E and AD/AB respectively. Wearable device error showed no significant differences between test occasions, and Bland-Altman analyses showed low bias with narrow limits of agreement. These results demonstrate the capability of the device to accurately and reliably monitor knee F/E and AD/AB angles showing strong potential for field implementation.

Finite-Element Analysis of Bone Stresses on Primary Impact in a Large-Animal Model: The Distal End of the Equine Third Metacarpal.

OBJECTIVE: To assess whether the transient stresses of foot impact with the ground are similar to those found during midstance loading and if the location of high stress correlate with the sites most commonly associated with mechanically induced osteoarthritis (OA). We compared impact stresses in subchondral bone between two subject-specific, three-dimensional, finite-element models of the equine metacarpophalangeal (MCP) joint-one with advanced OA and one healthy, and with similar published data on the stresses that occur at midstance. METHODS: Two right MCP joints (third metacarpal and proximal phalanx) were scanned using micro-computed tomography (µCT). Images were segmented, and meshed using modified 10-node quadratic tetrahedral elements. Bone material properties were assigned based on the bone density. An impact velocity of 3.55 m/s was applied to each model and contact pressures and stress distribution were calculated for each. In a separate iteration, the third metacarpal was loaded statically. A sampling grid of 160 equidistant points was superimposed over selected slices, and average peak stresses were calculated for 6 anatomical regions. Within-region maximal peak and average von Mises stresses were compared between healthy and OA bones in both midstance and impact loading. RESULTS: Average impact stresses across all regions, in both locations (palmar and dorsal) were greater in the OA model. Highest impact stresses were located in the dorsal medial condyle in the healthy (12.8 MPa) and OA (14.1MPa) models, and were lowest in the palmar medial and lateral parasagittal grooves in the healthy (5.94 MPa) and OA (7.07 MPa) models. The healthy static model had higher peak (up to 49.7% greater) and average (up to 38.6% greater) stresses in both locations and across all regions compared to the OA static model. CONCLUSIONS: Under simulated footfall a trot, loading on the dorsal aspect of the third metacarpal at impact created stresses similar to those found during midstance. The high accelerations that occur under impact loading are likely responsible for creating the high stresses, as opposed to midstance loading where the high stresses are the result of high mass loading. Although the stress magnitudes were found to be similar among the two loading conditions, the location of the high stress loading occurred in sites that are not typically associated with osteoarthritic changes.

Quantification of the transverse carpal ligament elastic properties by sex and region.

BACKGROUND: The transverse carpal ligament is an integral factor in the etiology of carpal tunnel syndrome. The purpose of this study was to report the biomechanical properties of this ligament and quantify sex-based differences and regional variation in tissue response. We hypothesized that the mechanical response would not be uniform across the surface, and that female ligament properties would have higher strain profiles and lower mechanical properties. METHODS: Uniaxial testing of twelve (six males, six females) human fresh frozen cadaveric transverse carpal ligaments was carried out using an Instron Materials Testing Machine. Strain was measured via a non-contact optical method. FINDINGS: The following biomechanical properties of the transverse carpal ligament were reported in this work: failure strain (male: 9.2 (SD 5.0), female: 15.5 (SD 7.1)%), strength (male: 4.9 (SD 1.5), female: 4.5 (SD 1.6) MPa), and modulus of elasticity (male: 52.9 (SD 19.6), female: 38.2 (SD 21.9) MPa). The radial side displayed significantly more strain at failure compared to ulnar (P<0.0001). INTERPRETATION: The results of this study provide evidence that manipulative treatments should focus stretching on the radial half of the tissue, which experiences larger strains under uniform loading conditions. In addition, this work suggests possible sex-based differences in mechanical properties of the transverse carpal ligament, which could provide a basis for the development of improved non-surgical treatment methods for carpal tunnel syndrome. The results can also be applied to generate more accurate computational models of the wrist.

A new laser reflectance system capable of measuring changing cross-sectional area of soft tissues during tensile testing.

Determination of the biomechanical properties of soft tissues such as tendons and ligaments is dependent on the accurate measurement of their cross-sectional area (CSA). Measurement methods, which involve contact with the specimen, are problematic because soft tissues are easily deformed. Noncontact measurement methods are preferable in this regard, but may experience difficulty in dealing with the complex cross-sectional shapes and glistening surfaces seen in soft tissues. Additionally, existing CSA measurement systems are separated from the materials testing machine, resulting in the inability to measure CSA during testing. Furthermore, CSA measurements are usually made in a different orientation, and with a different preload, prior to testing. To overcome these problems, a noncontact laser reflectance system (LRS) was developed. Designed to fit in an Instron 8872 servohydraulic test machine, the system measures CSA by orbiting a laser transducer in a circular path around a soft tissue specimen held by tissue clamps. CSA measurements can be conducted before and during tensile testing. The system was validated using machined metallic specimens of various shapes and sizes, as well as different sizes of bovine tendons. The metallic specimens could be measured to within 4% accuracy, and the tendons to within an average error of 4.3%. Statistical analyses showed no significant differences between the measurements of the LRS and those of the casting method, an established measurement technique. The LRS was successfully used to measure the changing CSA of bovine tendons during uniaxial tensile testing. The LRS developed in this work represents a simple, quick, and accurate way of reconstructing complex cross-sectional profiles and calculating cross-sectional areas. In addition, the LRS represents the first system capable of automatically measuring changing CSA of soft tissues during tensile testing, facilitating the calculation of more accurate biomechanical properties.

Development of a testing methodology to quantify bone load transfer patterns for multiple stemmed implants in a single bone with an application in the distal ulna.

Optimal parameters for many orthopaedic implants, such as stem length and material, are unknown. Geometry and mechanical properties of bone can vary greatly amongst cadaveric specimens, requiring a large number of specimens to test design variations. This study aimed to develop an experimental methodology to measure bone strains as a function of multiple implant stem designs in a single specimen, and evaluate its efficacy in the distal ulna. Eight fresh-frozen cadaveric ulnae were each instrumented with 12 uniaxial strain gauges on the medial and lateral surfaces of the bone. The proximal portion of each ulna was cemented in a custom-designed jig that allowed a medially directed force to be applied to the distal articular surface. An implant with a finely threaded stem was cemented into the canal by an experienced upper extremity orthopaedic surgeon. Six loads (5-30 N) were applied sequentially to the lateral surface of the prosthetic head using a materials testing machine. Testing was repeated after breaking the stem-cement bond, and after removing and reinserting the stem several times into the threaded cement mantle. Near the end of the testing period, the initial stem was reinserted and data were collected to determine if there was any change in bone properties or testing setup over time. Finally, a smooth stem was inserted for comparison to the threaded stem. Strain varied linearly with load (R(2)> or =0.99) for all testing scenarios. Bending strains were not affected by breaking the stem-cement bond (P=0.7), testing durations up to 18 h (P=0.7), nor the presence of threads when compared to a smooth stem (P>0.4). Furthermore, for all gauges, there was no interaction between the effect of the threads and level of applied load (P>0.1). This methodology should prove to be useful to compare stem designs of varying lengths and materials in the same bone, allowing for a direct comparison between implant designs for the ulna and other bones subjected primarily to bending loads. Furthermore, it will minimize the need for large numbers of specimens to test multiple implant designs. The ultimate goal of using this protocol is to optimize implant stem properties, such as length and material, with respect to load transfer.

The effect of distal ulnar implant stem material and length on bone strains.

PURPOSE: Implant design parameters can greatly affect load transfer from the implant stem to the bone. We have investigated the effect of length or material of distal ulnar implant stems on the surrounding bone strains. METHODS: Eight cadaveric ulnas were instrumented with 12 strain gauges and secured in a customized jig. Strain data were collected while loads (5-30 N) were applied to the medial surface of the native ulnar head. The native ulnar head was removed, and a stainless steel implant with an 8-cm-long finely threaded stem was cemented into the canal. After the cement had cured, the 8-cm stem was removed, leaving a threaded cement mantle in the canal that could accept shorter threaded stems of interest. The loading protocol was then repeated for stainless steel stems that were 7, 5, and 3 cm in length, as well as for a 5-cm-long titanium alloy (TiAl(6)V(4)) stem. Other stainless steel stem lengths between 3 and 7 cm were tested at intervals of 0.5 cm, with only a 20 N load applied. RESULTS: No stem length tested matched the native strains at all gauge locations. No significant differences were found between any stem length and the native bone at the 5th and 6th strain gauge positions. Strains were consistently closer to the native bone strains with the titanium stem than the stainless steel stem for each gauge pair that was positioned on the bone overlying the stem. The 3-cm stem results were closer to the native strains than the 7-cm stem for all loads at gauges locations that were on top of the stem. CONCLUSIONS: The results from this study suggest that the optimal stem characteristics for distal ulnar implants from a load transfer point of view are possessed by shorter (approximately 3 to 4 cm) titanium stems.

Effect of simulated muscle activity on distal radioulnar joint loading in vitro.

This study investigated the relationship between simulated forearm muscle loads and the joint reaction force in the distal radioulnar joint using an in vitro model. Seven fresh frozen cadaveric specimens were mounted in an upper extremity joint simulator capable of applying pneumatic loads to various (muscle) tendons while restraining the forearm in the three positions of pronation, supination, and neutral rotation. Loads were applied to model four forearm muscles (biceps, pronator teres, pronator quadratus, and supinator) in 10 N increments ranging from 10 N to 80 N for the biceps and pronator teres and in 10 N increments from 10 N to 50 N for the pronator quadratus and the supinator. Distal ulnar arthroplasty was performed on each specimen with a custom instrumented ulnar head replacement implant that quantified loads (via strain gauge instrumentation). The relationship between increasing muscle load and joint load was found to be positive and quasilinear in most cases. The biceps had the greatest influence on the distal radioulnar joint reaction force with a joint force in the range of 8% to 33% of the applied muscle load. The pronator teres, supinator, and pronator quadratus were less influential with a joint reaction force ranging between 6% to 19%, 4% to 9% and 2% to 10% of the applied muscle load, respectively.

Design and implementation of an instrumented ulnar head prosthesis to measure loads in vitro.

The development of a novel instrumented implant for ulnar head replacement is presented in this study. This implant was instrumented with strain gauges to quantify bending moments about the anatomic axes of the distal ulna, and subsequently the distal radioulnar joint (DRUJ) reaction force magnitude. The implant was surgically inserted in seven cadaveric upper extremities, which were subsequently mounted in a custom joint simulator. Simulated active unresisted pronation and supination motion trials were conducted using computer-controlled pneumatic actuators to simulate forearm musculature. Passive (unloaded) trials were also conducted. The reaction force across the DRUJ ranged from 2 to 10 N in magnitude during this unresisted motion. Increased bending moment magnitudes were measured when the forearm was positioned in supination compared to pronation. The magnitude of joint bending moments showed a consistent pattern with forearm position, regardless of simulated active or passive rotation, or supination and pronation motion trials. This result illustrates that the primary influence on joint load is likely the position and contact with the radial articulation. This study of DRUJ loading should be useful for biomechanical modeling, implant design considerations and improved knowledge of articular mechanics.

Comparison of distal radioulnar joint reconstructions using an active joint motion simulator.

PURPOSE: Distal radioulnar joint (DRUJ) instability can result in pain and functional disability. Numerous DRUJ reconstructive options have been described with minimal biomechanical analysis. The purpose of this study was to evaluate the ability of 4 well-described DRUJ reconstructions to restore joint kinematics using a dynamic, motion-controlled simulator. METHODS: Eleven cadaveric upper extremities had computer-controlled simulated active forearm rotation. Joint kinematics were quantified by using an electromagnetic tracking system. We compared the passive and simulated active kinematics of the intact, unstable, and reconstructed DRUJ (capsular repair, 2 described radioulnar ligament reconstructions, and a radioulnar tethering procedure). RESULTS: All reconstructions improved significantly the kinematics of the unstable DRUJ. The capsule repair restored simulated active joint kinematics closest to the intact DRUJ. CONCLUSIONS: All 4 reconstructions improved DRUJ stability significantly. The capsule repair most closely matched intact DRUJ kinematics and the radioulnar ligament reconstructions were found to be superior to a radioulnar tethering procedure.

Kinematics and stability of the fractured and implant-reconstructed radial head.

Controversy exists as to the optimal management of radial head fractures. Biomechanical studies have been conducted to quantify elbow stability for simulated wedge fractures, head excision, and head replacement, with and without the integrity of the collateral ligaments. Our in vitro studies have demonstrated that in the ligamentously intact elbow, kinematics and stability are slightly altered with simulated depressed wedge fractures up to 120 degrees of the radial head, markedly altered with head resection, and improved after radial head replacement. Radial head excision decreases elbow stability in the ligament-deficient elbow, and radial head replacement improves stability similar to that of the native radial head. The ligaments have the most marked influence on stability, particularly when the upper limb is positioned such that valgus and varus gravity loads are applied to the elbow. Whereas the radial head acts as a secondary stabilizer to the collateral ligaments with the arm in these positions, its relative role is greater when the arm is in the dependent position and elbow flexion is simulated, particularly in extension. Further studies are needed to elucidate the complex interaction of the radial head with the capitellum, the ulnohumeral joint, and the ligamentous structures for different activities of daily living.

The effect of radial head fracture size on elbow kinematics and stability.

This study determined the effect of radial head fracture size and ligament injury on elbow kinematics. Eight cadaveric upper extremities were studied in an in vitro elbow simulator. Testing was performed with ligaments intact, with the medial collateral (MCL) or lateral collateral (LCL) ligament detached, and with both the MCL and LCL detached. Thirty degree wedges were sequentially removed from the anterolateral radial head up to 120 degrees . Valgus angulation and external rotation of the ulna relative to the humerus were determined for passive motion, active motion, and pivot shift testing with the arm in a vertical (dependent) orientation. Maximum varus-valgus laxity was calculated from measurements of varus and valgus angulation with the arm in horizontal gravity-loaded positions. No effect of increasing radial head fracture size was observed on valgus angulation during passive and active motion in the dependent position. In supination, external rotation increased with increasing fracture size during passive motion with LCL deficiency and both MCL and LCL deficiency. With intact ligaments, maximum varus-valgus laxity increased with increasing radial head fracture size. With ligament disruption, elbows were grossly unstable, and no effect of increasing radial head fracture size occurred. During pivot shift testing, performed with the ligaments intact, subtle instability was noted after resection of one-third of the radial head. In this in vitro biomechanical study, small subtle effects of radial head fracture size on elbow kinematics and stability were seen in both the ligament intact and ligament deficient elbows. These data suggest that fixation of displaced radial head fractures less than or equal to one-third of the articular diameter may have some biomechanical advantages; however, clinical correlation is required.

The effect of radial head excision and arthroplasty on elbow kinematics and stability.

BACKGROUND: Radial head fractures are common injuries. Comminuted radial head fractures often are treated with radial head excision with or without radial head arthroplasty. The purpose of the present study was to determine the effect of radial head excision and arthroplasty on the kinematics and stability of elbows with intact and disrupted ligaments. We hypothesized that elbow kinematics and stability would be (1) altered after radial head excision in elbows with intact and disrupted ligaments, (2) restored after radial head arthroplasty in elbows with intact ligaments, and (3) partially restored after radial head arthroplasty in elbows with disrupted ligaments. METHODS: Eight cadaveric upper extremities were studied in an in vitro elbow simulator that employed computer-controlled actuators to govern tendon-loading. Testing was performed in stable, medial collateral ligament-deficient, and lateral collateral ligament-deficient elbows with the radial head intact, with the radial head excised, and after radial head arthroplasty. Valgus angulation and rotational kinematics were determined during passive and simulated active motion with the arm dependent. Maximum varus-valgus laxity was measured with the arm in a gravity-loaded position. RESULTS: In specimens with intact ligaments, elbow kinematics were altered and varus-valgus laxity was increased after radial head excision and both were corrected after radial head arthroplasty. In specimens with disrupted ligaments, elbow kinematics were altered after radial head excision and were similar to those observed in specimens with a native radial head after radial head arthroplasty. Varus-valgus laxity was increased after ligament disruption and was further increased after radial head excision. Varus-valgus laxity was corrected after radial head arthroplasty and ligament repair; however, it was not corrected after radial head arthroplasty without ligament repair. CONCLUSIONS: Radial head excision causes altered elbow kinematics and increased laxity. The kinematics and laxity of stable elbows after radial head arthroplasty are similar to those of elbows with a native radial head. However, radial head arthroplasty alone may be insufficient for the treatment of complex fractures that are associated with damage to the collateral ligaments as arthroplasty alone does not restore stability to elbows with ligament injuries.

Soft-tissue stabilizers of the distal radioulnar joint: an in vitro kinematic study.

PURPOSE: Distal radioulnar joint (DRUJ) stability is dependent on osseous anatomy, soft-tissue stabilizers, and muscle activity. The relative importance of DRUJ soft-tissue stabilizers remains controversial and has not been examined in the more physiologic setting of simulated muscle loading in the intact specimen. The purpose of this study was to examine the role of static stabilizers on the kinematics of the DRUJ during active simulated motion. METHODS: Twelve cadaveric upper extremities underwent computer-controlled, simulated, active forearm rotation. Joint kinematics were measured in the intact specimen and after sequential sectioning of soft-tissue stabilizers including the dorsal and palmar radioulnar ligaments (RULs) and the triangular fibrocartilage (TFC), dorsal and palmar capsule, ulnocarpal ligaments (UCL), extensor carpi ulnaris (ECU) subsheath, pronator quadratus (PQ), and the interosseous membrane (IOM). RESULTS: After sectioning of soft tissues significant changes in the DRUJ kinematics were observed. With a distal to proximal sectioning sequence significant alterations in kinematics were not identified until sectioning of the IOM; with a proximal to distal sectioning sequence intact DRUJ kinematics were maintained until the final soft-tissue (RULs and TFC) sectioning. CONCLUSIONS: Sectioning of all soft-tissue stabilizers produced significant DRUJ instability and abnormal joint kinematics. The RULs and TFC play a key role in DRUJ kinematics because they can help to maintain normal joint rotation in the absence of all other soft-tissue stabilizers. With the preservation of other soft-tissue stabilizers, however, the RULs and TFC are not essential for the maintenance of normal kinematics of the DRUJ.

Electromyographic activity and strength during maximum isometric pronation and supination efforts in healthy adults.

There exists a lack of quantitative data in the literature related to the torque produced during axial forearm rotation and the electromyographic (EMG) activity of the muscles involved. Therefore, the purpose of this study was to compare the relative EMG activity of four forearm muscles during resisted forearm rotation. A custom-built device capable of measuring torque in the absence of grip was employed. Fourteen healthy volunteers performed maximum isometric voluntary contractions in five positions of axial forearm rotation for both pronation and supination. EMG data were collected simultaneously from the supinator, biceps, pronator quadratus (deep and superficial heads), and pronator teres muscles using fine-wire bipolar electrodes. Data were analyzed to determine the contributions of each muscle to pronation and supination torque over five positions of forearm rotation. In the absence of grip no significant difference was found between supination and pronation torque in neutral position. Supination torque generation was greater in the pronated forearm positions, and pronation torque was greater in the supinated positions (p<0.05). A root-mean-square EMG analysis verified the major contributions of the pronator teres and both heads of the pronator quadratus muscle to pronation torque, and supinator and biceps to supination torque. The deep head of the pronator quadratus was active during both pronation and supination, lending support to the theory that it may act primarily as a dynamic distal radioulnar joint stabilizer. This information may be helpful in upper extremity modeling, surgical treatments, and rehabilitation strategies.

Influence of the pronator quadratus and supinator muscle load on DRUJ stability.

PURPOSE: To determine the effects of altering the load contributions of the pronator quadratus and supinator muscles on in vitro distal radioulnar joint (DRUJ) stability during pronation and supination and before and after ulnar head excision. METHODS: Multiple pronation trials were conducted with incremental loading of the pronator quadratus relative to the pronator teres muscle; supination trials were similarly conducted with incremental loading of the supinator relative to the biceps muscle. All trials were conducted using an upper-limb apparatus capable of simulating muscle/tendon loading and displacement. Stability measurements included dorsal-volar translations of the radius relative to the ulna and DRUJ diastasis and convergence. RESULTS: Increased pronator quadratus loading did not affect intact DRUJ stability but effects were noted after ulnar head excision when the forearm was positioned between neutral and full pronation. Incremental loading of the supinator muscle did not modify DRUJ stability in the intact or ulnar head excised state. CONCLUSIONS: Pronator quadratus muscle activity aggravates forearm instability after ulnar head excision. Immobilization of the forearm in mid- to full supination should minimize pronator quadratus activity and optimize soft-tissue healing. This information may be useful to develop in vitro muscle-loading scenarios and analytical forearm models.