Wrist joint motion simulator

Evaluation of a cadaveric wrist motion simulator using marker-based X-ray reconstruction of moving morphology

Surgical intervention is a common option for the treatment of wrist joint arthritis and traumatic wrist injury. Whether this surgery is arthrodesis or a motion preserving procedure such as arthroplasty, wrist joint biomechanics are inevitably altered. To evaluate effects of surgery on parameters such as range of motion, efficiency and carpal kinematics, repeatable and controlled motion of cadaveric specimens is required. This study describes the development of a device that enables cadaveric wrist motion to be simulated before and after motion preserving surgery in a highly controlled manner. The simulator achieves joint motion through the application of predetermined displacements to the five major tendons of the wrist, and records tendon forces. A pilot experiment using six wrists aimed to evaluate its accuracy and reproducibility. Biplanar X-ray videoradiography (BPVR) and X-Ray Reconstruction of Moving Morphology (XROMM) were used to measure overall wrist angles before and after total wrist arthroplasty. The simulator was able to produce flexion, extension, radioulnar deviation, dart thrower's motion and circumduction within previously reported functional ranges of motion. Pre- and post-surgical wrist angles did not significantly differ. Intra-specimen motion trials were repeatable; root mean square errors between individual trials and average wrist angle and tendon force profiles were below 1° and 2 N respectively. Inter-specimen variation was higher, likely due to anatomical variation and lack of wrist position feedback. In conclusion, combining repeatable intra-specimen cadaveric motion simulation with BPVR and XROMM can be used to determine potential effects of motion preserving surgeries on wrist range of motion and biomechanics.

Scaphoid, lunate and capitate kinematics in the normal and ligament deficient wrist: A bi-plane X-ray fluoroscopy study

The ligamentous structures of the wrist stabilise and constrain the interactions of the carpal bones during active wrist motion; however, the three-dimensional translations and rotations of the scaphoid, lunate and capitate in the normal and ligament deficient wrist during planar and oblique wrist motions remain poorly understood. This study employed a computer-controlled simulator to replicate physiological wrist motion by dynamic muscle force application, while carpal kinematics were simultaneously measured using bi-plane x-ray fluoroscopy. The aim was to quantify carpal kinematics in the native wrist and after sequential sectioning of the scapholunate interosseous ligament (SLIL) and secondary scapholunate ligament structures. Seven fresh-frozen cadaveric wrist specimens were harvested, and cycles of flexion-extension, radial-ulnar deviation and dart-thrower's motion were simulated. The results showed significant rotational and translational changes to these carpal bones in all stages of disruptions to the supporting ligaments (p < 0.05). Specifically, following the disruption of the dorsal SLIL (Stage II), the scaphoid became significantly more flexed, ulnarly deviated, and pronated relative to the radius, whereas the lunate became more extended, supinated and volarly translated (p < 0.05). Sectioning of the dorsal intercarpal (DIC), dorsal radiocarpal (DRC), and scaphotrapeziotrapezoid (STT) ligaments (Stage IV) caused the scaphoid to collapse further into flexion, ulnar deviation, and pronation. These findings highlight the importance of all the ligamentous attachments that relate to the stability of the scapholunate joint, but more importantly, the dorsal SLIL in maintaining scapholunate stability, and the preservation of the attachments of the DIC and DRC ligaments during dorsal surgical approaches. The findings will be useful in diagnosing wrist pathology and in surgical planning.

Effect of Various Wrist and Forearm Motions on Distal Radius Forces

Background  Dart throw motions are frequently used during rehabilitation but the ideal orientation of a dart throw motion is unknown. Questions/Purposes  The purpose of this study was to measure the axial force on the distal radius during different dart throw motions with the wrist and forearm in various positions. Our hypothesis was that there would be a significant difference on the axial force between various forearm positions and different dart throw orientations. Methods  Eight fresh frozen cadaver wrists were moved through 10 different orientations of a dart throw motion with the forearm in neutral, in pronation, and during a dynamic forearm rotation motion while the axial force was measured. Results  Significantly smaller axial force occurred with the forearm in pronation than during the dynamic forearm motion. The shorter dart throw motions which were oriented equally toward the flexion/extension and radioulnar deviation axes had significantly smaller distal radius forces than nearly all of the other dart throw motions. Conclusion/Clinical Relevance  Rehabilitation protocols incorporating a dart throw motion may be of benefit after injury or surgery. To minimize the axial force transmitted through a healing distal radius fracture, short dart throw motions, oriented at 45 degrees from the sagittal and coronal planes, with the forearm in pronation, might be preferable for range of motion activities during rehabilitation.

Design and Performance Analysis of a Dynamic Magnetic Resonance Imaging-Compatible Device for Triangular Fibrocartilage Complex Injury Diagnosis

Pain and injury of the triangular fibrocartilage complex (TFCC) due to overuse or trauma are commonly diagnosed through static MRI scanning, while TFCC is always involved in radial and ulnar deviation of the wrist. To the best of our knowledge, a dynamic MRI diagnostic method and auxiliary tool have not been applied or fully developed in the literature. As such, this study presents the design and evaluation of a dynamic magnetic resonance imaging (MRI) auxiliary tool for TFCC injury diagnosis. First, 3D scanning and Python are used to measure and fit the radial and ulnar deviation trajectories of healthy participants and patients. 3D printing is then used to manufacture the auxiliary tool for dynamic MRI, and dynamic MRI diagnosis is then conducted to explore the clinical effect. The radial and ulnar deviation trajectory is presented as an asymmetric curve without an obvious circular centre, and the results indicate that the designed auxiliary device meets the requirements of the ulnar and radial movements of the human wrist. According to the MRI contrast test results, the image quality score of patients wearing the auxiliary device is higher than for those without. Such devices could assist clinicians in the diagnosis of TFCC damage, and our method could not only serve as the reference standard for clinical noninvasive diagnosis but also help in understanding the disease and improving the accuracy of TFCC diagnosis.

An in vitro hand simulator for simultaneous control of hand and wrist movements

A human hand is a complex biomechanical system, in which bones, ligaments, and musculotendon units dynamically interact to produce seemingly simple motions. A new physiological hand simulator has been developed, in which electromechanical actuators apply load to the tendons of extrinsic hand and wrist muscles to recreate movements in cadaveric specimens in a biofidelic way. This novel simulator simultaneously and independently controls the movements of the wrist (flexion/extension and radio-ulnar deviation) and flexion/extension of the fingers and thumb. Control of these four degrees of freedom (DOF) is made possible by actuating eleven extrinsic muscles of the hand. The coupled dynamics of the wrist, fingers, and thumb, and the over-actuated nature of the human musculoskeletal system make feedback control of hand movements challenging. Two control algorithms were developed and tested. The optimal controller relies on an optimization algorithm to calculate the required tendon tensions using the collective error in all DOFs, and the action-based controller loads the tendons solely based on their actions on the controlled DOFs (e.g., activating all flexors if a flexing moment is required). Both controllers resulted in hand movements with small errors from the reference trajectories (<3.4); however, the optimal controller achieved this with 16% lower total force. Owing to its simpler structure, the action-based controller was extended to enable feedback control of grip force. This simulator has been shown to be a highly repeatable tool (<0.25 N and <0.2 variations in force and kinematics, respectively) for in vitro analyses of human hand biomechanics.

The effects of pistol grip power tools on median nerve pressure and tendon strains

Objectives. Tendonitis and carpal tunnel syndrome are common cumulative trauma disorders that can occur with repetitive usage of pistol grip power tools. The role of reaction torque resulting in a forceful rotary displacement of the tool handle, as well as the role of applied grip force, is not clear in the development of these disorders. This study aimed to quantify the flexor tendon strains and median nerve pressure during a typical power tool operation securing a threaded fastener. Methods. Six fresh-frozen cadaver arms were made to grip a replica pistol grip power tool using static weights to apply muscle forces. A 5-Nm torque was applied to the replica power tool. The median nerve pressure and strains in the flexor digitorum profundus and superficialis tendons were measured using a catheter and strain gauges, at three wrist flexion angles. Results. The peak tendon strains were between 1.5 and 2% and were predominantly due to the grip force more than the transmitted torque. Median nerve pressure significantly increased with the wrist flexed versus extended. Conclusion. The results indicate that the contribution of the grip force to the tendon strain and median nerve pressure was greater than the contribution from the reaction torque.

Carpal Motion in Chronic Geissler IV Scapholunate Interosseous Ligament Wrists

PURPOSE

This study evaluated the biomechanics of Geissler IV (G4) wrists in cadavers and compared them with intact specimens after multiple ligament sectioning to create scapholunate instability. It also evaluated carpal motion changes after sectioning of the lunotriquetral interosseous ligament (LTIL).

METHODS

Eight cadaver wrists determined to be G4 arthroscopically were tested using a wrist joint motion simulator. The LTIL was then sectioned, and carpal motion was recorded again. Carpal motions were compared with 37 normal wrists after sectioning of the scapholunate interosseous ligament and other ligaments to create a G4 wrist.

RESULTS

Carpal motion of the 37 normal wrists after ligamentous sectioning was similar to motion of the 8 specimens noted to be G4. These wrists did not demonstrate subluxation of the scaphoid that may occur after ligament sectioning. After sectioning of the LTIL, there were significant changes in lunate and triquetral motion.

CONCLUSIONS

These findings support the hypothesis that sectioning multiple ligaments in normal wrists to create scapholunate instability causes average motion comparable to that seen in G4 wrists. Ligamentous sectioning can cause a range of scaphoid instability. Lunotriquetral interosseous ligament sectioning in native G4 wrists caused greater changes in triquetral than scaphoid range of motion.

CLINICAL RELEVANCE

Patients with arthroscopically determined G4 lesions have an incompetent SLIL and scapholunate instability but do not necessarily have scapholunate dissociation and subluxation. Cadaver studies that evaluate instability by sectioning specific intact wrist ligaments are similar to the G4 specimens and thus are a good approximation of naturally occurring wrist instability. The functionality of secondary stabilizers not seen arthroscopically may explain the differences in motion. Geissler IV wrists and ligament-sectioned wrists are points on the spectrum of carpal instability, which is determined by the extent of damage to multiple ligamentous structures.

A Biomechanical Evaluation of the ECRL Tenodesis for Reconstruction of the Scapholunate Ligament

PURPOSE

Reconstruction of the scapholunate ligament (SLL) in the setting of dynamic instability remains a surgical challenge, with lack of consensus on the best reconstructive procedure. Reconstruction of only the dorsal component may lead to volar gapping and abnormal wrist kinematics. This cadaveric active motion simulation study determined whether scapholunate (SL) motion, angulation, and contact are restored following open reconstruction using the extensor carpi radialis longus (ECRL) tenodesis, which reconstructs both the volar and the dorsal SLL components.

METHODS

Seven fresh-frozen cadaveric upper limbs (mean age, 68 ± 10.1 years) underwent a 4-stage protocol of cyclic dart-throw motion and flexion-extension motion (utilizing an active wrist motion simulator that used tendon load/motion-controlled actuation. Scaphoid and lunate motion, relative scaphoid translation, SL angle, and dorsal-volar SL diastasis were measured with (1) wrist ligaments intact, (2) following complete sectioning of the SLL, and (3) following SL reconstruction using the ECRL tenodesis technique.

RESULTS

Complete SLL sectioning resulted in a typical pattern of SL instability. Following the ECRL tenodesis, lunate extension was not corrected. Scaphoid flexion, however, was not significantly different from the native state in FEM but remained significantly flexed during dart-throw motion. Differential dorsal and volar gapping did not significantly improve following ECRL tenodesis (dorsal, 1.2-2.3 mm; volar, 1.1-1.7 mm).

CONCLUSIONS

This biomechanical study demonstrates that the ECRL tenodesis did not fully restore native carpal kinematics, despite dorsal and volar SLL, and scaphotrapeziotrapezoid reconstruction.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Biomechanical Evaluation of Distal Radioulnar Joint Instability and Adams Procedure

PURPOSE

Distal radioulnar joint (DRUJ) instability may occur after an injury, resulting in pain and reduced strength. When primary repair is not possible or initial fixation has failed, chronic instability may result, requiring a reconstructive procedure such as the Adams procedure. The first purpose of this study was to evaluate the role of the triangular fibrocartilage complex and various components of the interosseous membrane as they were sectioned. The second purpose was to evaluate the Adams procedure in stabilizing the forearm.

METHODS

Eight fresh cadaver forearms were dynamically moved through an average range of 56.8° pronation to 54.8° supination and tested first with the forearm intact and then after sectioning each of the following structures: the dorsal (DRUL) and palmar radioulnar ligaments (PRUL), the distal interosseous membrane, and the central band. Finally, they were tested after reconstruction using the Adams procedure. During each forearm motion and provocative shuck, the motion of the radius and ulna were measured and the locations of the radial attachments of the DRUL, PRUL, and sigmoid notch and ulnar fovea were computed.

RESULTS

Significant increases in the gap between the ulnar fovea and the attachment sites of the DRUL and PRUL were observed with incremental sectioning, most notably after sectioning of the central band. Reconstruction significantly reduced the gap at the DRUL and PRUL sites during dynamic motion.

CONCLUSIONS

This study reinforces the concept that DRUJ stability depends on more than the radioulnar ligaments, ulnocarpal ligaments, and triangular fibrocartilage complex, but is also significantly affected by the distal and central interosseous membrane. Reconstruction reduces gapping.

CLINICAL RELEVANCE

These results suggest that the Adams reconstruction is a reasonable option to address DRUJ instability but may be an incomplete solution in the setting of a ruptured interosseous ligament.

The effect of coordinate system selection on wrist kinematics

Three-dimensional motion analysis of the hand and wrist is common in in-vitro and in-vivo biomechanical research. However, all studies rely on post testing analysis, where anatomical joint coordinate systems (JCS) are created to generate clinically relevant data to describe wrist motion. The purpose of this study was to present a comparison of four JCS that have been previously described in literature. Five cadaveric upper limbs were passively cycled through a flexion-extension and radial-ulnar deviation motion pathways using a wrist motion simulator. During testing, clinical wrist angle was measured using a goniometer. Following testing, wrist angle was calculated using four previously described methods of generating wrist coordinate systems, to facilitate their comparison. For flexion-extension wrist motion, only subtle difference between JCSs were detected. When comparing the performance of each JCS to the measured wrist angle during flexion-extension wrist motion, the RMSE for all three analyzed axes were all within 6.6°. For radial-ulnar deviation wrist motion, again only subtle difference between JCSs were detected. When comparing the performance of each JCS to the measured wrist angle during radial-ulnar deviation wrist motion, the RMSE for all three analyzed axes were all within 7.1°. The results of this coordinate system comparison do not favor one JCS generation method over another, as all were found to be similar and the small differences that were found are likely not clinically significant. We support using any of the analyzed coordinate system generation methods; however, a practical advantage of using certain methods is that the required digitized points to form the coordinate systems are palpable on the skin's surface.

An Approach to Robotic Testing of the Wrist Using Three-Dimensional Imaging and a Hybrid Testing Methodology

Robotic technology is increasingly used for sophisticated in vitro testing designed to understand the subtleties of joint biomechanics. Typically, the joint coordinate systems in these studies are established via palpation and digitization of anatomic landmarks. We are interested in wrist mechanics in which overlying soft tissues and indistinct bony features can introduce considerable variation in landmark localization, leading to descriptions of kinematics and kinetics that may not appropriately align with the bony anatomy. In the wrist, testing is often performed using either load or displacement control with standard material testers. However, these control modes either do not consider all six degrees-of-freedom (DOF) or reflect the nonlinear mechanical properties of the wrist joint. The development of an appropriate protocol to investigate complexities of wrist mechanics would potentially advance our understanding of normal, pathological, and artificial wrist function. In this study, we report a novel methodology for using CT imaging to generate anatomically aligned coordinate systems and a new methodology for robotic testing of wrist. The methodology is demonstrated with the testing of 9 intact cadaver specimens in 24 unique directions of wrist motion to a resultant torque of 2.0 N·m. The mean orientation of the major principal axis of range of motion (ROM) envelope was oriented 12.1 ± 2.7 deg toward ulnar flexion, which was significantly different (p < 0.001) from the anatomical flexion/extension axis. The largest wrist ROM was 98 ± 9.3 deg in the direction of ulnar flexion, 15 deg ulnar from pure flexion, consistent with previous studies [1,2]. Interestingly, the radial and ulnar components of the resultant torque were the most dominant across all directions of wrist motion. The results of this study showed that we can efficiently register anatomical coordinate systems from CT imaging space to robotic test space adaptable to any cadaveric joint experiments and demonstrated a combined load-position strategy for robotic testing of wrist.

Carpal Kinematics following Sequential Scapholunate Ligament Sectioning

Background  The scapholunate ligament (SLL) is the most commonly injured intercarpal ligament of the wrist. It is the primary stabilizer of the scapholunate (SL) joint, but the scaphotrapeziotrapezoid (STT) and radioscaphocapitate (RSC) ligaments may also contribute to SL stability. The contributions of SL joint stabilizers have been reported previously; however, this study aims to examine their contributions to SL stability using a different methodology than previous studies. Purpose  The purpose of this in vitro biomechanical study was to quantify changes in SL kinematics during wrist flexion and extension following a previously untested sequential sectioning series of the SL ligament and secondary stabilizers. Methods  Eight cadaveric upper extremities underwent active wrist flexion and extension in a custom motion wrist simulator. SL kinematics were captured with respect to the distal radius. A five-stage sequential sectioning protocol was performed, with data analyzed from 45-degree wrist flexion to 45-degree wrist extension. Results  Wrist flexion and extension caused the lunate to adopt a more extended posture following sectioning of the SLL and secondary stabilizers compared with the intact state ( p  < 0.009). The isolated disruption to the dorsal portion of the SLL did not result in significant change in lunate kinematics compared with the intact state ( p  > 0.05). Scaphoid kinematics were altered in wrist flexion following sequential sectioning ( p  = 0.013). Additionally, disruption of the primary and secondary stabilizers caused significant change to SL motion in both wrist flexion and wrist extension ( p  < 0.03). Conclusions  The SLL is the primary stabilizer of the SL articulation, with the STT and RSC ligaments playing secondary stabilization roles. Clinical Relevance  Understanding the role primary and secondary SL joint stabilizers may assist in the development of more effective treatment strategies and patient outcomes following SLL injuries.

The Effect of Dorsally Angulated Distal Radius Deformities on Carpal Kinematics: An In Vitro Biomechanical Study

PURPOSE

The purpose was to quantify the effect of distal radius dorsal angulation (DA) on carpal kinematics and the relative roles of the radiocarpal and midcarpal joints during wrist motion.

METHODS

Six cadaveric specimens (69 ± 17 y) were mounted at 90° elbow flexion in a custom wrist motion simulator. The wrist was guided through planar passive flexion and extension motion trials (∼ 5°/s). A custom modular distal radius implant was used to simulate native alignment and 3 distal radius DA deformities (10°, 20°, 30°). An optical tracking system captured carpal bone motion, from which radiocarpal and midcarpal joint motion was determined.

RESULTS

The radiocarpal joint made a greater contribution to wrist motion than the midcarpal joint in flexion, and the midcarpal joint made a greater contribution to motion than the radiocarpal joint in wrist extension. Increasing DA caused the radiocarpal joint contribution to increase throughout the motion arc, with the effect being more pronounced in wrist flexion. Conversely, as DA increased, the midcarpal joint contributed less rotation to the total wrist motion and its overall motion arc decreased; the magnitude of effect was greater in wrist extension. Dorsal angulation resulted in increased lunate flexion with respect to the distal radius.

CONCLUSIONS

Our findings agree with current literature that suggests that, in an uninjured wrist, the radiocarpal joint predominates flexion, and the midcarpal joint predominates extension. In addition, the radiocarpal joint has an amplified contribution in wrist flexion with greater DA malunion.

CLINICAL RELEVANCE

The altered contributions of the radiocarpal and midcarpal joints may contribute to pain, stiffness, and the development of arthritis, which is commonly seen at the radiocarpal joint after malunion of the distal radius.

Force Required to Maintain Reduction of a Preexisting Scapholunate Dissociation

PURPOSE

To determine the force required to maintain reduction of Geissler grade 4 scapholunate dissociations during physiological wrist motions.

METHODS

Fresh-frozen cadaveric wrists with Geissler grade 4 scapholunate dissociations were identified by arthroscopy. Following reduction, a load cell was attached to measure the force across the scapholunate joint at a neutral position and during 4 different wrist motions re-created using a servohydraulic wrist simulator, including a large flexion-extension motion (FEM), small and large dart-thrower's motions (DTMs), and a large DTM with ulnar offset.

RESULTS

Five wrists with isolated preexisting scapholunate interosseous ligament (SLIL) tears were analyzed. The force required to maintain reduction was significantly greater in extension than in flexion during the large FEM and large DTM with ulnar offset. The forces were significantly larger in this study of preexisting SLIL dissociations compared with results from a prior study of acutely sectioned SLILs. In addition, forces to maintain reduction during DTMs were significantly less than forces during FEMs. Finally, a set of 3 wrists with preexisting scapholunate and lunotriquetral interosseous ligament (LTIL) tears were identified and had significantly decreased forces to maintain reduction at maximum extension and had decreased maximal forces during a cycle of motion compared with the wrists with isolated SLIL tears.

CONCLUSIONS

The forces required to maintain reduction of a Geissler grade 4 wrist are higher than forces after acutely sectioned SLIL. The forces are greater in extension than in flexion and less during the DTM compared with the FEM. Wrists with both SLIL and LTIL tears required less force to maintain reduction than those with isolated SLIL tears.

CLINICAL RELEVANCE

This study helps determine the strength of reconstruction required to maintain reduction of a Geissler grade 4 scapholunate dissociation.

Carpal Pronation and Supination Changes in the Unstable Wrist

Background  Little is known about changes in scaphoid and lunate supination and pronation following scapholunate interosseous ligament (SLIL) injury. Information on these changes may help explain why some SLIL reconstructions have failed and help in the development of new techniques. Purpose  To determine if following simulated SLIL injury there was an increase in scaphoid pronation and lunate supination and to determine if concurrently there was an increase in the extensor carpi ulnaris (ECU) force. Materials and Methods  Scaphoid and lunate motion were measured before and after sectioning of the SLIL and two volar ligaments in 22 cadaver wrists, and before and after sectioning of the SLIL and two dorsal ligaments in 15 additional wrists. Each wrist was dynamically moved through wrist flexion/extension, radioulnar deviation, and a dart-throwing motion. Changes in the ECU force were recorded during each wrist motion. Results  Scaphoid pronation and lunate supination significantly increased following ligamentous sectioning during each motion. There were significant differences in the amount of change in lunate motion, but not in scaphoid motion, between the two groups of sectioned ligaments. Greater percentage ECU force was required following ligamentous sectioning to achieve the same wrist motions. Conclusion  Carpal supination/pronation changed with simulated damage to the scapholunate stabilizers. This may be associated with the required increases in the ECU force. Clinical Relevance  In reconstructing the SLIL, one should be aware of the possible need to correct scaphoid pronation and lunate supination that occur following injury. This may be more of a concern when the dorsal stabilizers are injured.

Forces in the Distal Radius During a Pushup or Active Wrist Motions

PURPOSE

To determine the 6 degrees of freedom forces and moments in the distal radius that occur during a pushup or other active wrist motions.

METHODS

Eight fresh-frozen cadaveric wrists were moved through 6 physiological motions and held at 1 static pushup position while the force through the distal radius was measured with a 6 degrees of freedom load cell. Three levels of compressive force were applied at the pushup position.

RESULTS

Active wrist motions caused axial forces up to 283 N and moments up to 0.7 N-m. Those motions with a smaller range had significantly smaller axial forces than the larger flexion-extension or dart-thrower's motions. With an 89-N pushup force applied, the average maximum axial force was 69 N, the radially directed force was 12 N, and the moment about the radioulnar axis was 2.3 N-m. Linear extrapolation of the forces to 100% body weight indicate that the axial force going through the distal radius would be 663 N, the radial force would be 147 N, and the moment about the radioulnar axis would be 18.6 N-m.

CONCLUSIONS

Large distal radius forces and moments can occur during pushup and active wrist motions. There are not only large axial compressive forces but also nontrivial radially directed forces.

CLINICAL RELEVANCE

This study may help surgeons and therapists better treat complicated distal radius fractures as well as provide for better comparisons of existing or new distal radius plates and constructs that are designed to treat these complicated loading patterns.

The importance of abductor pollicis longus in wrist motions: A physiological wrist simulator study

The abductor pollicis longus (APL) is one of the primary radial deviators of the wrist, owing to its insertion at the base of the first metacarpal and its large moment arm about the radioulnar deviation axis. Although it plays a vital role in surgical reconstructions of the wrist and hand, it is often neglected while simulating wrist motions in vitro. The aim of this study was to observe the effects of the absence of APL on the distribution of muscle forces during wrist motions. A validated physiological wrist simulator was used to replicate cyclic planar and complex wrist motions in cadaveric specimens by applying tensile loads to six wrist muscles - flexor carpi radialis (FCR), flexor carpi ulnaris, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis, extensor carpi ulnaris (ECU) and APL. Resultant muscle forces for active wrist motions with and without actuating the APL were compared. The absence of APL resulted in higher forces in FCR and ECRL - the synergists of APL - and lower forces in ECU - the antagonist of APL. The altered distribution of wrist muscle forces observed in the absence of active APL control could significantly alter the efficacy of in vitro experiments conducted on wrist simulators, in particular when investigating those surgical reconstructions or rehabilitation of the wrist heavily reliant on the APL, such as treatments for basal thumb osteoarthritis.

Prolonged high force high repetition pulling induces osteocyte apoptosis and trabecular bone loss in distal radius, while low force high repetition pulling induces bone anabolism

We have an operant rat model of upper extremity reaching and grasping in which we examined the impact of performing a high force high repetition (High-ForceHR) versus a low force low repetition (Low-ForceHR) task for 18weeks on the radius and ulna, compared to age-matched controls. High-ForceHR rats performed at 4 reaches/min and 50% of their maximum voluntary pulling force for 2h/day, 3days/week. Low-ForceHR rats performed at 6% maximum voluntary pulling force. High-ForceHR rats showed decreased trabecular bone volume in the distal metaphyseal radius, decreased anabolic indices in this same bone region (e.g., decreased osteoblasts and bone formation rate), and increased catabolic indices (e.g., microcracks, increased osteocyte apoptosis, secreted sclerostin, RANKL, and osteoclast numbers), compared to controls. Distal metaphyseal trabeculae in the ulna of High-ForceHR rats showed a non-significant decrease in bone volume, some catabolic indices (e.g., decreased trabecular numbers) yet also some anabolic indices (e.g., increased osteoblasts and trabecular thickness). In contrast, the mid-diaphyseal region of High-ForceHR rats' radial and ulnar bones showed few to no microarchitecture differences and no changes in apoptosis, sclerostin or RANKL levels, compared to controls. In further contrast, Low-ForceHR rats showed increased trabecular bone volume in the radius in the distal metaphysis and increased cortical bone area its mid-diaphysis. These changes were accompanied by increased anabolic indices, no microcracks or osteocyte apoptosis, and decreased RANKL in each region, compared to controls. Ulnar bones of Low-ForceHR rats also showed increased anabolic indices, although fewer than in the adjacent radius. Thus, prolonged performance of an upper extremity reaching and grasping task is loading-, region-, and bone-dependent, with high force loads at high repetition rates inducing region-specific increases in bone degradative changes that were most prominent in distal radial trabeculae, while low force task loads at high repetition rates induced adaptive bone responses.

Test–retest reliability of wrist joint position sense in healthy adults in a clinical setting

Introduction

Proprioceptive assessments of the wrist inform clinical decision making. In wrist rehabilitation, joint position sense has emerged as one way of assessing conscious proprioception with varying methods and minimal psychometric analysis reported. The purpose of this study was to standardise the wrist joint position sense test method for clinical use and to determine its test–retest reliability in a healthy population.

Methods

Four wrist positions (20° and 45° flexion, 20° and 45° extension) were measured twice in a random order, by a single rater, using a universal goniometer on the same day. The absolute error in degrees between each position and reposition was calculated. For relative reliability analysis, the intraclass correlation coefficient (3,1) was calculated. For absolute reliability the standard error of the measurement was calculated and Bland–Altman plots visually inspected.

Results

Fifty-five healthy volunteers (mean age 31.1 SD±10.25 years) were assessed. The mean absolute error, summarised for all positions for test and retest, was 3.98°. The intraclass correlation coefficients were poor to fair (0.07–0.47), and standard error of the measurement was 2° (rounded) for all positions. The limits of agreement were fairly narrow, and the Bland–Altman plots showed random distribution of errors for each position, therefore the measurement error was clinically acceptable.

Conclusions

The active wrist joint position sense test using goniometry demonstrated poor to fair test–retest reliability and acceptable measurement error in healthy volunteers. The wrist joint position sense angle of 20° flexion was the most reliable.

Biomechanical Analysis of Palmar Midcarpal Instability and Treatment by Partial Wrist Arthrodesis

PURPOSE

To create a biomechanical model of palmar midcarpal instability by selective ligament sectioning and to analyze treatment by simulated partial wrist arthrodesis.

METHODS

Nine fresh-frozen cadaver arms were moved through 3 servohydraulic actuated motions and 2 passive wrist mobilizations. The dorsal radiocarpal, triquetrohamate, scaphocapitate, and scaphotrapeziotrapezoid ligaments were sectioned to replicate palmar midcarpal instability. Kinematic data for the scaphoid, lunate, and triquetrum were recorded before and after ligament sectioning and again after simulated triquetrohamate arthrodesis (TqHA) and radiolunate arthrodesis (RLA).

RESULTS

Following ligament sectioning, the model we created for palmar midcarpal instability was characterized by significant increases in (1) lunate angular velocity, (2) lunate flexion-extension, and (3) dorsal/volar motion of the capitate during dorsal/volar mobilizations. Simulated TqHA caused significantly more scaphoid flexion and less extension during the wrist radioulnar deviation motion. It also increased the amount of lunate and triquetral extension during wrist flexion-extension. Simulated RLA significantly reduced scaphoid flexion during both wrist radioulnar deviation and flexion-extension.

CONCLUSIONS

Both simulated arthrodeses eliminate wrist clunking and may be of value in treating palmar midcarpal instability. However, simulated RLA reduces proximal row motion whereas simulated TqHA alters how the proximal row moves. Long-term clinical studies are needed to determine if these changes are detrimental.

CLINICAL RELEVANCE

Palmar midcarpal instability is poorly understood, with most treatments based on pathomechanical assumptions. This study provides information that clinicians can use to design better treatment strategies for this unsolved condition.

Muscle activity during maximal isometric forearm rotation using a power grip

This study aimed to provide quantitative activation data for muscles of the forearm during pronation and supination while using a power grip. Electromyographic data was collected from 15 forearm muscles in 11 subjects while they performed maximal isometric pronating and supinating efforts in nine positions of forearm rotation. Biceps brachii was the only muscle with substantial activation in only one effort direction. It was significantly more active when supinating (µ = 52.1%, SD = 17.5%) than pronating (µ = 5.1%, SD = 4.8%, p < .001). All other muscles showed considerable muscle activity during both pronation and supination. Brachioradialis, flexor carpi radialis, palmaris longus, pronator quadratus and pronator teres were significantly more active when pronating the forearm. Abductor pollicis longus and biceps brachii were significantly more active when supinating. This data highlights the importance of including muscles additional to the primary forearm rotators in a biomechanical analysis of forearm rotation. Doing so will further our understanding of forearm function and lead to the improved treatment of forearm fractures, trauma-induced muscle dysfunction and joint replacements.

Responsiveness of the active wrist joint position sense test after distal radius fracture intervention

STUDY DESIGN

Prospective cohort study.

INTRODUCTION

The active wrist joint position sense (JPS) test has been determined to be a clinically useful test for assessing wrist sensorimotor (SM) status after distal radius fracture (DRF). Its responsiveness is yet to be determined.

PURPOSE OF THE STUDY

Primary study aim was to determine the active wrist JPS test responsiveness to detect change in wrist SM status at 8 and 12 weeks after DRF treatment intervention. Secondary aims were to compare group (nonsurgical, surgical, high, and low pain) test responsiveness; compare pain-level group participants test scores; determine the relationship between test minimal clinically important difference (MCID) value and function; compare functional outcomes across assessment times; and determine the Patient Global Impression of Change Scale intrarater reliability.

METHODS

A total of 33 male and female participants were tested at baseline, 8, and 12 weeks after nonsurgical (n = 13) and surgical (n = 20) DRF treatment interventions. Distribution-based analysis encompassed both group- (ie, effect size, standardized response mean) and individual-based (ie, minimum detectable change) statistical indices. Anchor-based analysis determined the MCID value by linking test scores to the Patient Global Impression of Change Scale.

RESULTS

The active wrist JPS test is highly responsive based on effect size (8 weeks = 1.53 and 12 weeks = 2.36) and standardized response mean (8 weeks = 1.57 and 12 weeks = 2.14). Statistically significant minimum detectable change values were 4.28° and 4.94° at 8 and 12 weeks, respectively. Clinically meaningful MCID values were 5.00° and 7.09° at 8 and 12 weeks, respectively. Between treatment type and pain-level group responsiveness levels were not significantly different. High-pain participants demonstrated significantly greater JPS deficit. Test MCID values and function were significantly associated.

DISCUSSION

This is the first study to determine the active wrist JPS test responsiveness as reflected by its group- and individual-based statistical indices following DRF surgical and non-surgical interventions among low- and high-pain level participants. The statistical analysis approach, which was used to determine the aforementioned variables of the active wrist JPS test, is consistent with current research. This study's strengths included its design, methodology, and statistical approach. The study findings must be interpreted, however, within the content of several methodological limitations.

CONCLUSIONS

The active wrist JPS test was determined to be highly responsive to detect wrist SM status change at 8 and 12 weeks regardless of treatment type or pain level. Clinicians can use this test with confidence to measure clinically meaningful SM impairment after DRF treatment.

LEVEL OF EVIDENCE

2b.

Importance of Consistent Datasets in Musculoskeletal Modelling: A Study of the Hand and Wrist

Hand musculoskeletal models provide a valuable insight into the loads withstood by the upper limb; however, their development remains challenging because there are few datasets describing both the musculoskeletal geometry and muscle morphology from the elbow to the finger tips. Clinical imaging, optical motion capture and microscopy were used to create a dataset from a single specimen. Subsequently, a musculoskeletal model of the wrist was developed based on these data to estimate muscle tensions and to demonstrate the potential of the provided parameters. Tendon excursions and moment arms predicted by this model were in agreement with previously reported experimental data. When simulating a flexion–extension motion, muscle forces reached 90 N among extensors and a co-contraction of flexors, amounting to 62.6 N, was estimated by the model. Two alternative musculoskeletal models were also created based on anatomical data available in the literature to illustrate the effect of combining incomplete datasets. Compared to the initial model, the intensities and load sharing of the muscles estimated by the two alternative models differed by up to 180% for a single muscle. This confirms the importance of using a single source of anatomical data when developing such models.

The effects of wrist motion and hand orientation on muscle forces: A physiologic wrist simulator study

Although the orientations of the hand and forearm vary for different wrist rehabilitation protocols, their effect on muscle forces has not been quantified. Physiologic simulators enable a biomechanical evaluation of the joint by recreating functional motions in cadaveric specimens. Control strategies used to actuate joints in physiologic simulators usually employ position or force feedback alone to achieve optimum load distribution across the muscles. After successful tests on a phantom limb, unique combinations of position and force feedback – hybrid control and cascade control – were used to simulate multiple cyclic wrist motions of flexion-extension, radioulnar deviation, dart thrower’s motion, and circumduction using six muscles in ten cadaveric specimens. Low kinematic errors and coefficients of variation of muscle forces were observed for planar and complex wrist motions using both novel control strategies. The effect of gravity was most pronounced when the hand was in the horizontal orientation, resulting in higher extensor forces (p < 0.017) and higher out-of-plane kinematic errors (p < 0.007), as compared to the vertically upward or downward orientations. Muscle forces were also affected by the direction of rotation during circumduction. The peak force of flexor carpi radialis was higher in clockwise circumduction (p = 0.017), while that of flexor carpi ulnaris was higher in anticlockwise circumduction (p = 0.013). Thus, the physiologic wrist simulator accurately replicated cyclic planar and complex motions in cadaveric specimens. Moreover, the dependence of muscle forces on the hand orientation and the direction of circumduction could be vital in the specification of such parameters during wrist rehabilitation.

Role of the Interosseous Membrane in Preventing Distal Radioulnar Gapping

Background Damage to the interosseous membrane (IOM) can alter load transmission between the radius and ulna and decrease their axial stability. Less is known about the effect of IOM sectioning on the transverse stability between the radius and ulna. Purpose The purpose of this study was to quantify the radioulnar gapping at the distal radioulnar joint (DRUJ) during forearm rotation when the IOM was experimentally sectioned while maintaining the integrity of the distal radioulnar ligaments. Methods In 12 fresh-frozen cadaver forearms tested in a combined wrist-forearm simulator, the increase in gap between the radius and ulna, at the level of the DRUJ, was determined during cyclic forearm rotation following IOM sectioning. Results IOM sectioning caused a significant increase in dorsal gapping at the DRUJ by 2.1 mm in supination and 0.6 mm in pronation. It also caused an increase in palmar gapping by 1.3 mm in supination and 0.5 mm in pronation. Conclusion This experiment has shown that the IOM has an important role in stabilizing the DRUJ, especially in supination, and that IOM sectioning caused greater loads on the palmar and dorsal radioulnar ligaments. Since DRUJ instability is primarily treated by fixing the laxity at the dorsal radioulnar ligament (DRUL) and palmar radioulnar ligament (PRUL), untreated IOM damage could permit additional injury and instability to the radioulnar ligaments or their reconstruction. Clinical Relevance Reconstruction of a torn IOM should be considered in the presence of persistent DRUJ instability following DRUJ reconstruction.

Rehabilitation strategies for wrist sensorimotor control impairment: From theory to practice

This clinical review discusses the organization, neuroanatomy, assessment, clinical relevance, and rehabilitation of sensorimotor (SM) control impairment after wrist trauma. The wrist SM control system encompasses complex SM pathways that control normal wrist active range of motion and mediate wrist joint neuromuscular stability for maintaining joint function. Among various known assessment methods of wrist SM control impairment, the active wrist joint position sense test is determined to be a clinically meaningful and responsive measure for wrist SM control impairment after wrist fracture. Wrist trauma may involve significant soft tissue injury (ie, skin, ligament, muscle), which could disrupt the generation and transmission of adequate proprioceptive input from wrist mechanoreceptors, thus leading to significant joint SM impairment. Various clinical examples of wrist trauma (eg, distal radius fracture, scapholunate joint injury) along with known prognostic factors (eg, pain) that may influence wrist SM control impairment recovery are discussed to illustrate this point. This article proposes promising rehabilitation strategies toward restoring wrist joint conscious and unconscious SM control impairments, integrating current research evidence with clinical practice. These strategies require more rigorous evaluation in clinical trials.

LEVEL OF EVIDENCE

5.

Control of a wrist joint motion simulator: A phantom study

The presence of muscle redundancy and co-activation of agonist-antagonist pairs in vivo makes the optimization of the load distribution between muscles in physiologic joint simulators vital. This optimization is usually achieved by employing different control strategies based on position and/or force feedback. A muscle activated physiologic wrist simulator was developed to test and iteratively refine such control strategies on a functional replica of a human arm. Motions of the wrist were recreated by applying tensile loads using electromechanical actuators. Load cells were used to monitor the force applied by each muscle and an optical motion capture system was used to track joint angles of the wrist in real-time. Four control strategies were evaluated based on their kinematic error, repeatability and ability to vary co-contraction. With kinematic errors of less than 1.5°, the ability to vary co-contraction, and without the need for predefined antagonistic forces or muscle force ratios, novel control strategies - hybrid control and cascade control - were preferred over standard control strategies - position control and force control. Muscle forces obtained from hybrid and cascade control corresponded well with in vivo EMG data and muscle force data from other wrist simulators in the literature. The decoupling of the wrist axes combined with the robustness of the control strategies resulted in complex motions, like dart thrower׳s motion and circumduction, being accurate and repeatable. Thus, two novel strategies with repeatable kinematics and physiologically relevant muscle forces are introduced for the control of joint simulators.

Analysis of wrist bone motion before and after SL-ligament resection

The analysis of the three-dimensional motion of wrist joint components in the physiological and injured wrist is of high clinical interest. Therefore, the purpose of this in vitro study was to compare the motion of scaphoid, lunate and triquetrum during physiological wrist motion in flexion and extension, and in radial- and ulnar-deviation, with those motion patterns after complete resection of the scapho-lunate-ligament. Eight fresh frozen cadaver wrists were carefully thawed and prepared for the investigation with an electromagnetic tracking system by implantation of measurement coils with 6 degrees of freedom. Electromagnetic tracking enabled the motion analysis of the scaphoid, lunate, and triquetrum bones with respect to the fixed radius in three planes of passive motion. After scapho-lunate-ligament injury changes in the translational and rotational motion pattern especially of the scaphoid bone occurred in dorsal-volar directions during flexion and extension, radial- and ulnar-deviation, and during rotation around the radio-ulnar- and longitudinal-axis of the wrist.

The Effect of Scaphoid Fracture Site on Scaphoid Instability Patterns

Background Scaphoid fractures are common carpal fractures that are often misdiagnosed as wrist sprains and may go on to nonunion. The location of the fracture site may influence the stability of scaphoid nonunions. Purpose To determine whether the stability of a scaphoid nonunion depends upon the fracture's location, we tested the hypothesis that a simulated fracture distal to the apex of the scaphoid dorsal ridge will have greater interfragmentary motion than proximal. Methods Eleven cadaver wrists were moved through three wrist motions using a wrist simulator. In six wrists, a fracture was created distal to the scaphoid apex, and in five a fracture was created proximal to the apex. Sensors attached to the distal and proximal parts of each scaphoid measured the interfragmentary motion during wrist motion. Results In those wrists in which the scaphoid was sectioned distal to the apex, the distal fragment became significantly more unstable relative to the proximal fragment. It flexed, ulnarly deviated, and pronated. These motion changes were less when the scaphoid was sectioned proximally. Discussion Scaphoid fractures distal to the scaphoid apex will have greater interfragmentary motion. The mobility of the fragments at the fracture site is possibly a more important contributory factor of nonunion in scaphoid waist fractures than for proximal scaphoid fractures. Clinical Relevance Understanding the effect that the location of a scaphoid fracture has on the potential for nonunion may influence the modalities of treatment and follow-up.

Scaphoid tuberosity excursion is minimized during a dart-throwing motion: A biomechanical study

PURPOSE

The purpose of this study was to determine whether the excursion of the scaphoid tuberosity and therefore scaphoid motion is minimized during a dart-throwing motion.

METHODS

Scaphoid tuberosity excursion was studied as an indicator of scaphoid motion in 29 cadaver wrists as they were moved through wrist flexion-extension, radioulnar deviation, and a dart-throwing motion.

RESULTS

Study results demonstrate that excursion was significantly less during the dart-throwing motion than during either wrist flexion-extension or radioulnar deviation.

CONCLUSION

If the goal of early wrist motion after carpal ligament or distal radius injury and reconstruction is to minimize loading of the healing structures, a wrist motion in which scaphoid motion is minimal should reduce length changes in associated ligamentous structures. Therefore, during rehabilitation, if a patient uses a dart-throwing motion that minimizes his or her scaphoid tuberosity excursion, there should be minimal changes in ligament loading while still allowing wrist motion.

STUDY DESIGN

Bench research, biomechanics, and cross-sectional.

LEVEL OF EVIDENCE

Not applicable. The study was laboratory based.

Role of the interosseous membrane and annular ligament in stabilizing the proximal radial head

HYPOTHESIS

The purpose of our study was to determine the relative contributions of the annular ligament, proximal band, central band, and distal band of the interosseous membrane in preventing dislocation of the proximal radius.

METHODS

In part 1 of the study, 8 forearms were loaded transversely with the forearm intact, and the central band, proximal band, and annular ligament were sequentially sectioned to determine the percentage contribution of each structure in preventing transverse radial displacement. In part 2, 12 forearms were cyclically supinated and pronated while optical sensors measured radial and ulnar motion. Transverse radial head motion was computed as the distal band, central band, and proximal band (and annular ligament) were sequentially sectioned.

RESULTS

In part 1, there was no significant difference in the percentage contribution of each structure in preventing radial transverse displacement. In part 2, only after sectioning of the central band did significant radial head displacement occur. Greater displacements occurred in supination than in pronation. Dislocation of the proximal radius occurred in 2 arms after sectioning of all 3 structures.

DISCUSSION

Under pure transverse displacement, the central band, annular ligament, and proximal band equally contributed to stabilizing the radius. However, during forearm rotation, the central band contributed more to radial head stability than the annular ligament and proximal band. Our study contributes to our knowledge of forearm biomechanics, demonstrating the importance of the central band in providing proximal radial head stability. Forceful supination should be avoided after surgical procedures designed to stabilize the radial head.

Force in the Scapholunate Interosseous Ligament During Active Wrist Motion

PURPOSE

To examine the force experienced by the scapholunate interosseous ligament (SLIL) during movements of the wrist.

METHODS

Six fresh-frozen cadaveric wrists were freed of soft tissue and tested in a computer controlled, servohydraulic simulator. Each wrist was tested cyclically through simulated active arcs of flexion-extension and dart throw motion. Tensile forces were recorded across the scapholunate joint with the SLIL cut through a cable placed through the scaphoid to the lunate and fixed to a force transducer external to the wrist.

RESULTS

The average recorded maximal tensile force across the scapholunate joint during all tested motions was 20 N. During wrist flexion-extension and the dart throw motion, SLIL force was greater at maximum extension than at maximum flexion. No significant differences among the different motions at maximum flexion or extension or for maximal force during motion were found.

CONCLUSIONS

Forces during the flexion-extension and dart throw motions were significantly higher in extension than in flexion. However, during simple unresisted wrist motions, the force did not exceed 20 N.

CLINICAL RELEVANCE

This information can be used to evaluate surgical methods used for SLIL repairs and thus provide better outcomes for patients.

Anatomy and biomechanics of the forearm interosseous membrane

PURPOSE

To examine the anatomy and function of the forearm interosseous membrane by exploring the anatomical insertions of the central band (CB) on the radius and the ulna and by quantifying the length of the intact ligament and replacement grafts located at the original CB attachment sites and alternative locations.

METHODS

Eight fresh cadaver forearms were supinated and pronated and the wrist was extended and flexed while the motion between the distal radius and ulna were recorded. The length of the CB was computed for the intact CB as well for several alternative graft orientations and positions.

RESULTS

The maximum length of the CB did not significantly change among different wrist motions. However, with the wrist in a static neutral position, the CB length was significantly shorter in forearm supination than in neutral. During active forearm rotation when CB replacement grafts were positioned distal or proximal to the original CB site, yet still parallel to it, each had a similar trend to be longer in neutral than in supination. If a graft was more transversely oriented, the computed CB length would be 1.6 mm shorter in supination than in neutral.

CONCLUSIONS

These results support tensioning a CB graft with the forearm in supination if the goal is to maximize graft tension and to maintain the native 22° angle for a CB graft between the radius and ulna. The results also suggest that the CB graft can probably be located slightly distal or slightly proximal to its original attachment sites.

CLINICAL RELEVANCE

Reconstruction of the interosseous membrane has been hampered by a lack of understanding of its length changes with forearm or wrist motion. These results provide a starting point in helping clinicians understand how to more precisely reconstruct this ligament in an anatomical manner.

Force variations in the distal radius and ulna: effect of ulnar variance and forearm motion

PURPOSE

To better define normal wrist joint forces during wrist motion and forearm motion at specific wrist and forearm positions and to see if there is a relationship between these forces and the amount of ulnar variance. A secondary purpose was to determine the relationship between the thickness of the articular disk of the triangular fibrocartilage complex and the amount of force transmitted through the distal ulna.

METHODS

Multi-axis load cells were attached to the distal radius and ulna of 9 fresh cadaver forearms. The axial radial and ulnar compressive forces were recorded while each wrist was moved through wrist and forearm motions using a modified wrist joint simulator. During each motion, the tendon forces required to cause each motion were recorded. The ulnar variance and triangular fibrocartilage complex articular disc thickness were measured.

RESULTS

The axial force through the distal ulna and the wrist extensor forces were greatest with the forearm in pronation. No relationship was found between the amount of force through the distal ulna and the amount of ulnar variance. A strong inverse relationship was found between the triangular fibrocartilage complex thickness and the ulnar variance.

CONCLUSIONS

Wrists with positive ulnar variance have generally been thought to transmit greater loads across the distal ulna, which has been felt to predispose these wrists to the development of ulnar impaction. The results of this study appear to show that all wrists have similar loading across the distal ulna regardless of ulnar variance. By comparison, pronation relatively increases loading across the distal ulna.

CLINICAL RELEVANCE

Because these results suggest that within reasonable ranges of ulnar variance loading across the distal ulna is independent of ulnar variance, the clinically observed incidence of ulnar impaction is more likely the result of increased wear on a thinner and less durable triangular fibrocartilage complex than due to increased distal ulna loading in ulnar positive variant wrists.

A novel method to replicate the kinematics of the carpus using a six degree-of-freedom robot

Understanding the kinematics of the carpus is essential to the understanding and treatment of wrist pathologies. However, many of the previous techniques presented are limited by non-functional motion or the interpolation of points from static images at different postures. We present a method that has the capability of replicating the kinematics of the wrist during activities of daily living using a unique mechanical testing system. To quantify the kinematics of the carpal bones, we used bone pin-mounted markers and optical motion capture methods. In this paper, we present a hammering motion as an example of an activity of daily living. However, the method can be applied to a wide variety of movements. Our method showed good accuracy (1.0-2.6°) of in vivo movement reproduction in our ex vivo model. Most carpal motion during wrist flexion-extension occurs at the radiocarpal level while in ulnar deviation the motion is more equally shared between radiocarpal and midcarpal joints, and in radial deviation the motion happens mainly at the midcarpal joint. For all rotations, there was more rotation of the midcarpal row relative to the lunate than relative to the scaphoid or triquetrum. For the functional motion studied (hammering), there was more midcarpal motion in wrist extension compared to pure wrist extension while radioulnar deviation patterns were similar to those observed in pure wrist radioulnar deviation. Finally, it was found that for the amplitudes studied the amount of carpal rotations was proportional to global wrist rotations.

Effect of pisiform excision or pisotriquetral arthrodesis as a treatment for pisotriquetral arthritis: a biomechanical study

PURPOSE

To determine whether flexor carpi ulnaris (FCU) forces and tendon displacements change after pisotriquetral arthrodesis or after pisiform excision.

METHODS

Nine cadaver wrists were moved through 4 variations of a dart throw motion, each having an oblique plane of motion, but with different ranges of motion and different antagonistic forces. The FCU tendon force and movement were measured in the intact wrist, following pisotriquetral arthrodesis, and following pisiform excision. Changes in force and tendon movement were compared using a repeated measures analysis of variance.

RESULTS

After excision of the pisiform, a significantly greater FCU force was required during the 2 variations of the dart throw motion having a larger range of motion and during the smaller motion having a larger antagonistic force. Pisotriquetral arthrodesis did not cause a significant increase in the peak FCU force. Excision of the pisiform caused the FCU tendon to significantly retract during all wrist motions as compared to the intact wrist or after pisotriquetral arthrodesis.

CONCLUSIONS

Greater FCU forces are required to move the wrist when the pisiform with its moment arm function has been removed. This occurs during large oblique plane wrist motions and also in a smaller motion when greater antagonistic forces are applied. Excision of the pisiform also allows the FCU to move proximally, again because its moment arm function has been eliminated.

CLINICAL RELEVANCE

Excision of the pisiform requires greater FCU forces during large wrist motions and during motions that include large gripping forces such that excision may be a concern in high-demand patients with pisotriquetral arthritis. Although pisotriquetral arthrodesis does not alter the mechanical advantage of the FCU, its use in high-demand patients with pisotriquetral osteoarthritis cannot yet be recommended until the effects of that arthrodesis on midcarpal kinematics are further clarified.

Biomechanical analysis of the distal metaphyseal ulnar shortening osteotomy

PURPOSE

To investigate the effect of a closing wedge osteotomy at the distal ulnar metaphysis on unloading the ulnar side of the wrist.

METHODS

Seven fresh frozen cadaver arms mounted in a wrist simulator were used for the analysis. A 6-degrees-of-freedom load cell was mounted on the distal radius and another on the distal ulna. Radioulnar carpal joint forces and transverse distal radioulnar joint (DRUJ) load were measured at static wrist positions and during dynamic wrist motions before and after the distal metaphyseal ulnar shortening osteotomy (DMUSO) was performed.

RESULTS

At each static position, significant decreases in ulnar load were noted after DMUSO. In addition, mean and maximum loads decreased for each dynamic wrist motion. There were no statistically significant differences in transverse forces across the DRUJ after DMUSO.

CONCLUSION

This study showed that DMUSO is an effective way to decrease the load across the ulnocarpal joint. The geometry of the osteotomy and resultant change in the position of the ulnar head did not increase transverse joint reaction forces.

CLINICAL RELEVANCE

This technique is an alternative to open diaphyseal techniques or methods that damage the articular surface of the distal ulna. Clinical studies will be necessary to associate the biomechanical correction noted in this study with clinical symptom improvement.

Clinical and biomechanical investigation of an increased articular cavity depth after distal radius fractures: effect on range of motion, osteoarthrosis and loading patterns

INTRODUCTION

After fracture, distal radius malunion with dissociation of the volar and dorsal ulnar fracture fragments can lead to an increased articular cavity.

PATIENTS AND METHODS

To investigate its clinical impact we retrospectively analyzed the outcome of 81 patients and simulated this form of malunion in a biomechanical experiment with six cadaver specimens in a dynamic loading set-up.

RESULTS

In clinics, a higher arthritis stage was significantly correlated with an increased articular cavity depth and an increased anterioposterior distance. In cadaver specimens, a significantly decreased range of motion and significantly altered intraarticular contact characteristics were recognized for an increased cavity.

CONCLUSION

Alterations in contact biomechanics could be one reason for the higher incidence of posttraumatic osteoarthritis when a deeper central impaction of the distal radius is present. From a clinical and experimental point of view, restoration of the normal shape of the distal radius is considered to minimize the risk for posttraumatic radiocarpal osteoarthritis.

4-corner arthrodesis and proximal row carpectomy: a biomechanical comparison of wrist motion and tendon forces

PURPOSE

Controversy exists as to whether a proximal row carpectomy (PRC) is a better procedure than scaphoid excision with 4-corner arthrodesis for preserving motion in the painful posttraumatic arthritic wrist. The purpose of this study was to determine how the kinematics and tendon forces of the wrist are altered after PRC and 4-corner arthrodesis.

METHODS

We tested 6 fresh cadaver forearms for the extremes of wrist motion and then used a wrist simulator to move them through 4 cyclic dynamic wrist motions, during which time we continuously recorded the tendon forces. We repeated the extremes of wrist motion measurements and the dynamic motions after scaphoid excision with 4-corner arthrodesis, and then again after PRC. We analyzed extremes of wrist motion and the peak tendon forces required for each dynamic motion using a repeated measures analysis of variance.

RESULTS

Wrist extremes of motion significantly decreased after both the PRC and 4-corner arthrodesis compared with the intact wrist. Wrist flexion decreased on average 13° after 4-corner arthrodesis and 12° after PRC. Extension decreased 20° after 4-corner arthrodesis and 12° after PRC. Four-corner arthrodesis significantly decreased wrist ulnar deviation from the intact wrist. Four-corner arthrodesis allowed more radial deviation but less ulnar deviation than the PRC. The average peak tendon force was significantly greater after 4-corner arthrodesis than after PRC for the extensor carpi ulnaris during wrist flexion-extension, circumduction, and dart throw motions. The peak forces were significantly greater after 4-corner arthrodesis than in the intact wrist for the extensor carpi ulnaris during the dart throw motion and for the flexor carpi ulnaris during the circumduction motion. The peak extensor carpi radialis brevis force after PRC was significantly less than in the intact wrist.

CONCLUSIONS

The measured wrist extremes of motion decreased after both 4-corner arthrodesis and PRC. Larger peak tendon forces were required to achieve identical wrist motions with the 4-corner arthrodesis compared with the intact wrist. We observed smaller forces for the PRC.

CLINICAL RELEVANCE

These results may help explain why PRC shows early clinical improvement, yet may lead to degenerative arthritis.

Wrist tendon forces with respect to forearm rotation

PURPOSE

Early motion therapy protocols are desirable to reduce wrist stiffness after carpal injuries and distal radius fractures. Based on our assumption that a reduction in wrist tendon forces will be associated with a reduction in radioulnar carpal joint reaction force, the goal of this study was to determine the forearm position at which the wrist tendon forces required to initiate wrist motion were the least.

METHODS

We tested 8 fresh-frozen cadaver forearms in a wrist and forearm motion simulator. In each specimen, we generated a wrist flexion-extension motion and a radioulnar deviation motion by pulling on the wrist flexor and extensor tendons with the forearm in supination, pronation, or neutral. We also performed a wrist flexion-extension motion during active forearm rotation. During each motion, we continuously recorded the forces in the 5 wrist tendons. We used repeated-measure analyses of variance to compare tendon forces.

RESULTS

During the wrist flexion-extension motion, the summed peak wrist extensor forces were significantly less with the wrist in forearm supination than with the forearm in neutral or during active forearm rotation. For the summed peak wrist flexor forces, flexor tendon forces were significantly less with the forearm in supination compared with active forearm rotation. The extensor carpi radialis longus and flexor carpi ulnaris forces were significantly less in supination than during active forearm motion. During wrist radioulnar deviation motion, peak extensor carpi ulnaris force was significantly less with the forearm in supination than in neutral, and peak flexor carpi radialis force was significantly less with the forearm in supination than in pronation.

CONCLUSIONS

Peak wrist tendon forces were least in the static forearm supinated position.

CLINICAL RELEVANCE

To reduce deforming forces on a fresh carpal injury or distal radial fracture, active rehabilitation appears to be best initiated with the forearm held in supination.

The biomechanical effects of a deepened articular cavity during dynamic motion of the wrist joint

BACKGROUND

A deepened articular cavity of the distal radius due to a metaphyseal comminution zone is associated with early osteoarthritis and reduced joint motion. As this deformity has not been investigated biomechanically, the purpose of this study was to evaluate the effects of a deepened articular cavity on contact biomechanics and motion range in a dynamic biomechanical setting.

METHODS

Six fresh frozen cadaver forearms were tested in a force controlled test bench during dynamic flexion and extension and intact mean contact pressure and contact area as well as range of motion were evaluated. Malunion was then simulated and intraarticular as well as motion data were obtained. Intact and malunion data were compared for the scaphoid and lunate facet and the total radial joint surface.

FINDINGS

Due to malunion simulation, cavity depth increased significantly. Motion decreased significantly to 54-69% when compared to the intact state. Malunion simulation led to a significant decrease of contact area in maximum extension for all locations (by ~50%). In maximum flexion and neutral position, contact area decrease was significant for the scaphoid fossa (by 51-54%) and the total radial joint surface (by 47-50%). Contact pressure showed a significant increase in maximum extension in the scaphoid fossa (by 129%).

INTERPRETATION

Already a small cavity increase led to significant alterations in contact biomechanics of the radiocarpal joint and to a significant range of motion decrease. This could be the biomechanical cause for degenerative changes after the investigated type of malunion. We think that restoration of the normal distal radius shape can minimize osteoarthritis risk post trauma and improve radiocarpal motion.

Scaphoid excision and midcarpal arthrodesis: the effect of triquetral excision--a biomechanical study

PURPOSE

To evaluate the biomechanical alterations that occur after traditional scaphoid excision and midcarpal arthrodesis with and without excision of the triquetrum. The hypothesis of this study was that removal of the triquetrum increases the radiolunate contact pressure.

METHODS

We cyclically moved 10 fresh cadaver wrists using a wrist joint motion simulator while measuring the contact pressures between the proximal carpal row and the distal radius and ulna using a dynamic pressure sensor. We acquired data in the intact wrist, after a midcarpal arthrodesis with the scaphoid excised, and then again with the triquetrum removed, which is also known as a capitolunate arthrodesis.

RESULTS

The peak pressures in the radiolunate fossa significantly increased with either of the midcarpal arthrodeses compared with the intact wrist during each of the 3 dynamic wrist motions. In comparing the 2 midcarpal arthrodeses, the peak pressure in the ulnocarpal fossa significantly decreased after the triquetrum was removed during wrist radioulnar deviation and in the static ulnarly deviated position. After arthrodesis, we could identify no differences during any motion or static wrist position in the peak radiolunate pressures with or without the triquetrum.

CONCLUSIONS

We found that scaphoid excision and 4-corner arthrodesis shifts loads to the radiolunate joint. Isolated capitolunate arthrodesis with excision of the scaphoid and triquetrum further alters carpal kinematics and loading patterns.

CLINICAL RELEVANCE

These findings raise concern about routine excision of the triquetrum when performing a midcarpal arthrodesis.

Measurement of intraarticular wrist joint biomechanics with a force controlled system

Pathologies of the wrist, such as fractures or instabilities, can lead to alterations in joint biomechanics. Accurate treatment of these pathologies is a frequent challenge for the surgeon. For biomechanical investigations, a test-setup that applies physiological loading of the wrist joint is necessary. A force controlled test-bench with agonistic and antagonistic muscle forces was built to move six fresh frozen human upper extremities through flexion and extension of the wrist joint. Tendon forces, range of motion, intraarticular contact area and contact pressure of the lunate and scaphoid facet as well as tendon excursion were investigated and compared with the current literature. During wrist motion the extensors exerted double the force of the flexors. Capsulotomy and sensor insertion decreased the range of motion from 63.4° (SD 14.1) to 45.9° (SD 23.7). The ratio of force transmitted through the radius and ulna was 77:23 and pressure distribution between the scaphoid and lunate facet showed a 70:30 relationship. The obtained data indicate a good agreement with the available literature. Therefore, the force controlled test-bench in combination with intraarticular radiocarpal measurements can be used to investigate the influence of wrist pathologies on joint biomechanics.

Scaphoid and lunate translation in the intact wrist and following ligament resection: a cadaver study

PURPOSE

To determine the amount of scaphoid and lunate translation that occurs in normal cadaver wrists during wrist motion, and to quantify the change in ulnar translation when specific dorsal and volar wrist ligaments were sectioned.

METHODS

We measured the scaphoid and lunate motion of 37 cadaver wrists during wrist radioulnar deviation and flexion-extension motions using a wrist joint motion simulator. We quantified the location of the centroids of the bones during each motion in the intact wrists and after sectioning either 2 dorsal ligaments along with the scapholunate interosseous ligament or 2 volar ligaments and the scapholunate interosseous ligament.

RESULTS

In the intact wrist, the scaphoid and lunate statistically translated radially with wrist ulnar deviation. With wrist flexion, the scaphoid moved volarly and the lunate dorsally. After sectioning either the dorsal or volar ligaments, the scaphoid moved radially. After sectioning the dorsal or volar ligaments, the lunate statistically moved ulnarly and volarly.

CONCLUSIONS

Measurable changes in the scaphoid and lunate translation occur with wrist motion and change with ligament sectioning. However, for the ligaments that were sectioned, these changes are small and an attempt to clinically measure these translations of the scaphoid and lunate radiographically may be limited. The results support the conclusion that ulnar translocation does not occur unless multiple ligaments are sectioned. Injury of more than the scapholunate interosseous ligament along with either the dorsal intercarpal and dorsal radiocarpal or the radioscaphocapitate and scaphotrapezial ligaments is needed to have large amounts of volar and ulnar translation.

Wrist tendon forces during various dynamic wrist motions

PURPOSE

A common treatment of arthritis of the thumb carpometacarpal joint requires all or a portion of the flexor carpi radialis tendon (FCR) to be used as an interpositional graft. The purpose of this study was to examine the in vitro tendon forces in 6 wrist flexors and extensors to determine whether their force contribution changes during various dynamic wrist motions along with a specific application to the FCR.

METHODS

We tested 62 fresh-frozen cadaver wrists in a wrist joint motion simulator. During wrist flexion-extension, radioulnar deviation, dart throwing, and circumduction motions, the peak and average tendon forces were determined for the extensor carpi ulnaris, extensor carpi radialis brevis and longus, abductor pollicis longus, flexor carpi radialis, and flexor carpi ulnaris.

RESULTS

During a dart-throwing motion, the mean and peak FCR forces were statistically less than during the other 3 motions. Conversely, the mean and peak flexor carpi ulnaris forces were statistically greater during the dart-throwing motion than during the other 3 motions.

CONCLUSIONS

Patients who have undergone a surgical procedure in which all or a portion of the FCR has been harvested may experience a decrease in wrist strength with wrist motion, as the FCR tendon normally applies force during wrist motion. The motion least likely to be affected by such surgery is the dart-throwing motion when the force on the remaining FCR is minimized.

Validation of a Feedback-Controlled Elbow Simulator Design: Elbow Muscle Moment Arm Measurement

The Allegheny General Hospital (AGH) elbow simulator was designed to be a closed-loop physiologic simulator actuating movement in cadaveric elbow specimens via servoelectric motors that attach to the tendons of the biceps, brachialis, triceps, and pronator teres muscles. A physiologic elbow simulator should recreate the appropriate moment arms throughout the elbow’s range of motion. To validate this design goal, muscle moment arms were measured in three cadaver elbow specimens using the simulator. Flexion-extension moment arms of four muscles were measured at three different pronation/supination angles: fully pronated, fully supinated, and neutral; pronation-supination moment arms were measured at three different flexion-extension angles: 30 deg, 60 deg, and 90 deg. The tendon-displacement method was used in these measurements, in which the ratio of the change in musculotendon length to the change in joint angle was computed. The numeric results compared well with those previously reported; the biceps and pronator teres flexion-extension moment arms varied with pronation-supination position, and vice versa. This is one of the few reports of both flexion-extension and pronation-supination moment arms in the same specimens, and represents the first use of closed-loop feedback control in the AGH elbow simulator. The simulator is now ready for use in clinical studies such as in analyses of radial head replacement and medial ulnar collateral ligament repair.

Dynamic biomechanical evaluation of the dorsal intercarpal ligament repair for scapholunate instability

PURPOSE

A variety of soft tissue surgical procedures have been developed for treatment of scapholunate dissociation. One reconstruction method, using the dorsal intercarpal ligament, has been used clinically with some success. The purpose of this study was to evaluate biomechanically use of the dorsal intercarpal ligament for static scapholunate dissociation.

METHODS

Eight cadaver wrists were tested in a wrist joint motion simulator. Each wrist was moved in continuous cycles of flexion-extension and radial-ulnar deviation. Kinematic data for the scaphoid and lunate were recorded for each wrist in the intact state, after the scapholunate interosseous, dorsal radiocarpal, and dorsal intercarpal ligaments were sectioned, and after reconstruction using the dorsal intercarpal ligament.

RESULTS

Ligamentous sectioning resulted in static scapholunate dissociation. Visually, the repair initially reduced the gap between the scaphoid and lunate, but within a few cycles of wrist motion, there were statistically significant increases in scaphoid flexion, scaphoid ulnar deviation, and lunate extension. In 6 arms, gapping between the scaphoid and lunate was observed. In 2 arms, a gap occurred and the repair also pulled out of the bone junction.

CONCLUSIONS

This study does not support the hypothesis that the dorsal intercarpal ligament repair alone will stabilize the scaphoid and lunate after scapholunate instability in the immediate postoperative period.

Identifying scapholunate ligamentous injury

The first purpose of this study was to develop a noninvasive clinical tool that could predict whether the scapholunate interosseous ligament and other secondary stabilizing ligaments are injured in the presence of suspected scapholunate instability. The second purpose of this study was to determine which of those ligaments or ligament groups have been injured. Kinematic and three-dimensional (3D) meaurements from 62 cadaver wrists moved in a wrist joint motion simulator were used to develop various neural network predictive models. One group of models was based on angular changes in scaphoid and lunate motion before and after ligament sectioning (representing scapholunate instability). A second group of models was based on changes in the minimum distance between the scaphoid and lunate as well as other 3D gap measurements. The models, based on the scaphoid and lunate angular data, could predict with a 93% accuracy rate whether the wrist ligaments were intact. These models could also predict whether it was the dorsal ligaments or the volar ligaments that were sectioned 84% of the time. The models worked best using data with the wrist in 10 to 30 degrees of wrist flexion. The viability of a CT-based predictive model has been demonstrated by obtaining high prediction rates, sensitivity, specificity, and kappa statistic values.

Proximal row carpectomy: role of a radiocarpal interposition lateral meniscal allograft

PURPOSE

The purpose of this study was to determine whether use of a lateral meniscal interposition allograft combined with proximal row carpectomy would reduce the peak joint contact pressures and increase the contact area when compared with proximal row carpectomy alone.

METHODS

Six cadaver wrists were cyclically moved through flexion-extension and radioulnar deviation ranges of motion. Joint contact pressure was measured with the carpus intact, after proximal row carpectomy, and after insertion of a lateral meniscal allograft. Contact pressure data were also collected with the wrist in 5 static positions.

RESULTS

Proximal row carpectomy caused statistically greater peak pressures and smaller contact areas when compared with the intact wrist. Insertion of the allograft statistically restored the pressures and areas to that observed in the intact wrist.

CONCLUSIONS

These results support the clinical trial of a lateral meniscal interposition allograft in patients with contraindications for proximal row carpectomy, such as pre-existing arthritis in the capitate head or lunate facet of the radius.