Biomechanics of the wrist

Detection of scapholunate interosseous ligament injury using dynamic computed tomography-derived arthrokinematics: A prospective clinical trial

Scapholunate interosseous ligament injuries are a major cause of wrist instability and can be difficult to diagnose radiographically. To improve early diagnosis of scapholunate ligament injuries, we compared injury detection between bilateral routine clinical radiographs, static CT, and dynamic four-dimensional CT (4DCT) during wrist flexion-extension and radioulnar deviation. Participants with unilateral scapholunate ligament injuries were recruited to a prospective clinical trial investigating the diagnostic utility of 4DCT imaging for ligamentous wrist injury. Twenty-one participants underwent arthroscopic surgery to confirm scapholunate ligament injury. Arthrokinematics, defined as distributions of interosseous proximities across radioscaphoid and scapholunate articular surfaces at different positions within the motion cycle, were used as CT-derived biomarkers. Preoperative radiographs, static CT, and extrema of 4DCT were compared between uninjured and injured wrists using Wilcoxon signed rank or Kolmogorov-Smirnov tests. Median interosseous proximities at the scapholunate interval were significantly greater in the injured versus the uninjured wrists at static-neutral and maximum flexion, extension, radial deviation, and ulnar deviation. Mean cumulative distribution functions at the radioscaphoid joint were not significantly different between wrists but were significantly shifted at the scapholunate interval towards increased interosseous proximities in injured versus uninjured wrists in all positions. Median and cumulative distribution scapholunate proximities from static-neutral and 4DCT-derived extrema reflect injury status.

Surgical Management of Acute on Chronic Distal Radius Fractures: Correcting Malunion Deformities Through the Secondary Fracture Plane

It is challenging to restore the clinically acceptable alignment of the distal radius after an acute on chronic fracture or after a secondary fracture occurring after malunion of a primary distal radius fracture. In cases of insignificant primary deformity, restoration to the primary deformity may suffice to obtain a successful clinical result. A borderline acceptable primary radial deformity can be unacceptable after the second injury, resulting in functional disability. If surgery is indicated, the surgeon must contend with both primary and secondary deformities to restore proper distal radius anatomy. We present our technique to correct both primary and secondary distal radius deformities through the new or secondary fracture plane.

Morphological Associations between the Distal Radioulnar Joint and the Lunate

Background  Variations in morphology of the carpal bones have been described. Their implication in wrist disease and specific kinematic features has been recognized, and a better knowledge of these variations is essential. Questions/Purpose  To radiographically determine any association between the morphological variations of the distal radioulnar joint (DRUJ) and the lunate bone. Materials and Methods  Radiographs of 100 wrists of patients presenting to the emergency department with wrist pain and referred to our outpatient clinic were retrospectively reviewed for DRUJ inclination, ulnar variance, and radiocarpal and midcarpal morphology of the lunate. Results  There were 51 females and 49 males, mean age 51.2 years (range: 21-94). There was a statistically significant association between the DRUJ inclination and the morphology of the radiocarpal side of the lunate ( p  < 0.001). The mean values of ulnar variance changed according to DRUJ inclination and the radiocarpal side of the lunate ( p  < 0.001) but not according to the midcarpal side of the lunate. There was no significant association between the morphology of the DRUJ and the midcarpal side of the lunate or between the midcarpal and the radiocarpal morphology of the lunate. Conclusion  This study demonstrated a statistically significant association at the radiocarpal level between the DRUJ inclination, ulnar variance, and the morphology of the lunate. No association was found with the morphology of the midcarpal side of the lunate. Accordingly, a classification of these carpal associations is proposed, highlighting seven main wrist configurations. Clinical Relevance  These associations can guide future studies of wrist kinematics.

Evaluation of midcarpal capitate contact mechanics in normal, injured and post-operative wrists

BACKGROUND

Scapholunate ligament injury is a commonly occurring carpal ligament injury. Pathology associated with scapholunate ligament injury depends on several factors such as the time after injury, type of injury (instability) and the development of osteoarthritis. The aim of this study was to investigate and compare contact mechanics in the lunocapitate and scaphocapitate joints in the normal, injured (scapholunate dissociation) and repaired (postoperative) wrist.

METHODS

Four human subjects with scapholunate ligament dissociation participated in this study. MR images of normal (contralateral), injured and postoperative wrists were obtained during relaxed condition and during active light grasp. Relaxed MR images were used to construct model geometry (bones with cartilage) for the capitate, lunate and scaphoid. Kinematic transformations were obtained by using image registration between the unloaded and functionally loaded image sets. Joint surface contact mechanics were then calculated.

FINDINGS

All contact measures (contact force, pressure, mean pressure and area) tended to increase with injury in both articulations. A significantly higher contact area was found in the injured scaphocapitate joint compared to normal. A significant increase in peak pressure was observed in the postoperative state compared to normal.

INTERPRETATION

Injury to the scapholunate ligament increased contact measures, suggesting a risk for onset of osteoarthritis in both the scaphocapitate and lunocapitate joints. Surgical repair appeared to restore most measures of contact mechanics to near normal values, more so for the lunocapitate joint when compared to scaphocapitate joint. The elevated postoperative peak pressures indicate the difficulty to fully restore joint mechanics.

Validation of a new multiscale finite element analysis approach at the distal radius

High-resolution peripheral computed tomography is commonly used to evaluate mechanical behavior of the distal radius microstructure using micro-finite element (FE) modeling. However, only a 9mm section is considered and boundary conditions (BCs) are usually simplified (platen-compression), and may not represent physiologic loading. Regardless, these methods are increasingly being used for clinical evaluations. Our goal was to develop and validate a novel multiscale solution that allows for physiologically relevant loading simulations (such as bracing during a fall), and show that mechanical behavior in the distal radius is different under platen BCs. Our approach incorporated bone microstructure together with organ-level radius geometry, by replacing matching continuum regions with micro-FE sections in user-defined regions of interest. Multiscale model predicted strains showed a strong correlation and a significant relationship with measured strains (r=0.836, p<0.001; slope=0.881, intercept=-12.17 µε, p<0.001). Interestingly, platen BC simulated strains were almost 50% lower than measured strains (r=0.835, p<0.001), and strain distributions were clearly different. Our multiscale method demonstrated excellent potential as a computationally efficient alternative for observing true mechanical environment within distal radius microstructure under physiologically accurate loading.

Wrist function in malunion: Is the distal radius designed to retain function in the face of fracture?

Introduction Fractures of the distal radius are the most common fracture in humans and are the sempiternal hazard of 3.5 million years of bipedalism. Despite the antiquity of the injury, one of the most controversial topics in current orthopaedics is the management of distal radius fractures. It has been suggested that radiographic appearances rarely correlate with functional outcomes. As the success of the human species is predicated almost exclusively on its dexterity and intelligence, it is conceivable that the distal radius has evolved to preserve function even in the face of injury. We therefore hypothesise that the distal radius is designed to accommodate the possibility of fracture. Methods We conducted a review of studies comparing fracture pattern and form with function. We also explore the paleoanthropological evidence and comparative studies with other primates. Findings The evidence points to the human distal radius being highly tolerant of post-fracture deformity in terms of preservation of function. In addition, the distal radius appears to have apparently anatomically 'redundant' features that confer this capability. We believe these phenomena to be an evolved trait that developed with bipedalism, increasing the chances of survival for a species whose success depends upon its dexterity.

Computationally efficient magnetic resonance imaging based surface contact modeling as a tool to evaluate joint injuries and outcomes of surgical interventions compared to finite element modeling

Joint injuries and the resulting posttraumatic osteoarthritis (OA) are a significant problem. There is still a need for tools to evaluate joint injuries, their effect on joint mechanics, and the relationship between altered mechanics and OA. Better understanding of injuries and their relationship to OA may aid in the development or refinement of treatment methods. This may be partially achieved by monitoring changes in joint mechanics that are a direct consequence of injury. Techniques such as image-based finite element modeling can provide in vivo joint mechanics data but can also be laborious and computationally expensive. Alternate modeling techniques that can provide similar results in a computationally efficient manner are an attractive prospect. It is likely possible to estimate risk of OA due to injury from surface contact mechanics data alone. The objective of this study was to compare joint contact mechanics from image-based surface contact modeling (SCM) and finite element modeling (FEM) in normal, injured (scapholunate ligament tear), and surgically repaired radiocarpal joints. Since FEM is accepted as the gold standard to evaluate joint contact stresses, our assumption was that results obtained using this method would accurately represent the true value. Magnetic resonance images (MRI) of the normal, injured, and postoperative wrists of three subjects were acquired when relaxed and during functional grasp. Surface and volumetric models of the radiolunate and radioscaphoid articulations were constructed from the relaxed images for SCM and FEM analyses, respectively. Kinematic boundary conditions were acquired from image registration between the relaxed and grasp images. For the SCM technique, a linear contact relationship was used to estimate contact outcomes based on interactions of the rigid articular surfaces in contact. For FEM, a pressure-overclosure relationship was used to estimate outcomes based on deformable body contact interactions. The SCM technique was able to evaluate variations in contact outcomes arising from scapholunate ligament injury and also the effects of surgical repair, with similar accuracy to the FEM gold standard. At least 80% of contact forces, peak contact pressures, mean contact pressures and contact areas from SCM were within 10 N, 0.5 MPa, 0.2 MPa, and 15 mm2, respectively, of the results from FEM, regardless of the state of the wrist. Depending on the application, the MRI-based SCM technique has the potential to provide clinically relevant subject-specific results in a computationally efficient manner compared to FEM.

Scapholunate ligament injury adversely alters in vivo wrist joint mechanics: an MRI-based modeling study

We investigated the effects of scapholunate ligament injury on in vivo radiocarpal joint mechanics using image-based surface contact modeling. Magnetic resonance images of 10 injured and contralateral normal wrists were acquired at high resolution (hand relaxed) and during functional grasp. Three-dimensional surface models of the radioscaphoid and radiolunate articulations were constructed from the relaxed images, and image registration between the relaxed and grasp images provided kinematics. The displacement driven models were implemented in contact modeling software. Contact parameters were determined from interpenetration of interacting bodies and a linear contact rule. Peak and mean contact pressures, contact forces and contact areas were compared between the normal and injured wrists. Also measured were effective (direct) contact areas and intercentroid distances from the grasp images. Means of the model contact areas were within 10 mm(2) of the direct contact areas for both articulations. With injury, all contact parameters significantly increased in the radioscaphoid articulation, while only peak contact pressure and contact force significantly increased in the radiolunate articulation. Intercentroid distances also increased significantly with injury. This study provides novel in vivo contact mechanics data from scapholunate ligament injury and confirms detrimental alterations as a result of injury.

Effectiveness of surgical reconstruction to restore radiocarpal joint mechanics after scapholunate ligament injury: an in vivo modeling study

Disruption of the scapholunate ligament can cause a loss of normal scapholunate mechanics and eventually lead to osteoarthritis. Surgical reconstruction attempts to restore scapholunate relationship show improvement in functional outcomes, but postoperative effectiveness in restoring normal radiocarpal mechanics still remains a question. The objective of this study was to investigate the benefits of surgical repair by observing changes in contact mechanics on the cartilage surface before and after surgical treatment. Six patients with unilateral scapholunate dissociation were enrolled in the study, and displacement driven magnetic resonance image-based surface contact modeling was used to investigate normal, injured and postoperative radiocarpal mechanics. Model geometry was acquired from images of wrists taken in a relaxed position. Kinematics were acquired from image registration between the relaxed images, and images taken during functional loading. Results showed a trend for increase in radiocarpal contact parameters with injury. Peak and mean contact pressures significantly decreased after surgery in the radiolunate articulation and there were no significant differences between normal and postoperative wrists. Results indicated that surgical repair improves contact mechanics after injury and that contact mechanics can be surgically restored to be similar to normal. This study provides novel contact mechanics data on the effects of surgical repair after scapholunate ligament injury. With further work, it may be possible to more effectively differentiate between treatments and degenerative changes based on in vivo contact mechanics data.

MRI-based modeling for radiocarpal joint mechanics: validation criteria and results for four specimen-specific models

The objective of this study was to validate the MRI-based joint contact modeling methodology in the radiocarpal joints by comparison of model results with invasive specimen-specific radiocarpal contact measurements from four cadaver experiments. We used a single validation criterion for multiple outcome measures to characterize the utility and overall validity of the modeling approach. For each experiment, a Pressurex film and a Tekscan sensor were sequentially placed into the radiocarpal joints during simulated grasp. Computer models were constructed based on MRI visualization of the cadaver specimens without load. Images were also acquired during the loaded configuration used with the direct experimental measurements. Geometric surface models of the radius, scaphoid and lunate (including cartilage) were constructed from the images acquired without the load. The carpal bone motions from the unloaded state to the loaded state were determined using a series of 3D image registrations. Cartilage thickness was assumed uniform at 1.0 mm with an effective compressive modulus of 4 MPa. Validation was based on experimental versus model contact area, contact force, average contact pressure and peak contact pressure for the radioscaphoid and radiolunate articulations. Contact area was also measured directly from images acquired under load and compared to the experimental and model data. Qualitatively, there was good correspondence between the MRI-based model data and experimental data, with consistent relative size, shape and location of radioscaphoid and radiolunate contact regions. Quantitative data from the model generally compared well with the experimental data for all specimens. Contact area from the MRI-based model was very similar to the contact area measured directly from the images. For all outcome measures except average and peak pressures, at least two specimen models met the validation criteria with respect to experimental measurements for both articulations. Only the model for one specimen met the validation criteria for average and peak pressure of both articulations; however the experimental measures for peak pressure also exhibited high variability. MRI-based modeling can reliably be used for evaluating the contact area and contact force with similar confidence as in currently available experimental techniques. Average contact pressure, and peak contact pressure were more variable from all measurement techniques, and these measures from MRI-based modeling should be used with some caution.

PRELIMINARY VALIDATION OF MRI-BASED MODELING FOR EVALUATION OF JOINT MECHANICS

The objective of this study was to perform preliminary validation of MRI-based joint contact modeling methodology in the radiocarpal joints by comparison with the results of invasive radiocarpal contact measurements in three cadaver experiments. For each experiment, either Pressurex film or a Tekscan sensor was placed into the radiocarpal joints during a simulated grasp. Computer models were based on magnetic resonance imaging (MRI) of the cadaver specimens without load as well as on images acquired with the same loading used for the direct measurements. Geometric surface models of the radius, scaphoid, and lunate (including cartilage) were constructed from the images acquired without load. The carpal bone motions from the unloaded to the loaded state were determined using three-dimensional (3D) voxel image registration. Cartilage thickness was assumed to be uniform at 1.0 mm with an effective compressive modulus of 4 MPa. Resulting data included peak contact pressure, contact area, and contact force in the radioscaphoid and radiolunate joints. Contact area was also measured directly from MR images acquired with load and compared to model data. Qualitatively, there was good correspondence between the MRI-based model data and experimental data, with consistent relative size, shape, and location of radioscaphoid and radiolunate contact areas. Quantitative comparison of model and experimental data was reasonable, but less consistent. Contact area from the MRI-based model was always similar to the contact area measured directly from the MR images. With additional experiments, we believe that MRI-based joint contact modeling will soon be fully validated in the radiocarpal joints.

A kinematics-based method for generating cartilage maps and deformations in the multi-articulating wrist joint from CT images

We present a non-invasive method for estimating individual-specific cartilage maps directly from in vivo kinematic data and computed tomography (CT) volume images, and a novel algorithm for computing cartilage surface deformations. Our proposed cartilage model, a meshless incompressible height-field captures the physical properties important for estimating the shape, contact area, and deformation magnitude of cartilage at each articulation. This cartilage model can serve as an effective building block for a future forward-dynamic predictive model of the human wrist.

Early active rehabilitation for operatively stabilized distal radius fractures

From the young to the elderly, distal radius fractures are very common. Extensive literature has been written regarding surgical management of distal radius fractures, but the same degree of attention has not been given to the critical rehabilitation that follows. Successful functional outcomes for distal radius fractures are a result of appropriate surgical treatment as well as timely and specific rehabilitation. Surgical treatment strategies available for unstable distal radius fractures include percutaneous pinning, external fixation, dorsal plating, and volar fixed-angle plating. Arthroscopically assisted as well as other minimally invasive techniques are now gaining acceptance. The ideal surgical treatment would provide stable fixed-angle fragment-specific support with minimal soft tissue disturbance and allow safe, early active wrist rehabilitation. This article reviews the normal anatomy of the region, the pathoanatomy created by the different stabilization strategies, and specific therapy techniques, including static and static progressive splints, that correlate with each of the surgical procedures.

[A adaptive proximal scaphoid implant]

INTRODUCTION

In this study, the insertion of a pyrocarbon implant (APSI) has been described, which is shaped to allow adaptive mobility during carpal movement in the first row of carpals. This implant replaces the proximal part of the scaphoid; it is designed to treat styloscaphoid arthritis, and to prevent further deterioration and carpal collapse by restoring the first carpal row to its original height, i.e., 'SNAC wrist' after scaphoid pseudoarthritis, and 'SLAC wrist' following scapho-lunate dissociation.

MATERIALS AND METHOD

This retrospective series included 25 cases which were examined and analyzed at an average of six years post-surgery (between three and ten years) by an independent observer using the EVAL expert database system: 1) 14 cases involved pseudoarthritis, which developed from the scaphoid ('SNAC wrist'); 2) ten cases were connected with scapho-lunate nonunion ('SLAC wrist'); 3) one case involved carpal collapse with siliconite, which had previously been inserted as a scaphoid silicone partial implant for the treatment of pseudoarthritis involving a stage II fracture.

RESULT

In all cases, the reason for the preoperative-consultation for degenerative arthritis was the presence of pain, which post-surgery was no longer apparent in 60% of cases, and only persisted during effort in 28% of cases. Thus 88% of the patients were satisfied with the results, and were able to resume their normal professional and sports activities at the same level as before. Strength connected with digitopalmar grip and pinch force were found to have increased compared to the function in the healthy hand. No implant dislocation was detected by radiological investigation. Dynamic X-rays of the implant in flexion, extension, and frontal inclination confirmed this adaptive mobility. Carpal height was in all cases maintained. The radio-lunate angle remained unchanged in 15 cases, was improved in six cases, and was worse in four cases. Two poor results were connected with severe ligament lesions prior to surgery.

CONCLUSION

The preliminary results regarding the APSI implant seem to be promising for cases of polar pseudoarthritis in which curative treatment is no longer possible. This technique avoids further deterioration and carpal collapse ('SNAC wrist'). However, in cases of scapho-lunate nonunion ('SLAC wrist') where ligament lesions are severe, this method does not resolve the problem of ligament destabilization, which requires further treatment.