Changes in Wrist Motion After Simulated Scapholunate Arthrodesis: A Cadaveric Study

Biomechanical Comparison of Dart-Throw Motions after Partial Wrist Fusions

Background  Multiple partial wrist fusions exist for the management of arthritic disease. Limited information is available on their effect on wrist range of motion in the dart-throwing direction of wrist motion, even though it is used in most activities of daily living. Purpose  The purpose of this study was to measure the retained motion for different orientations of dart-throwing motion for seven different partial wrist fusions and proximal row carpectomy (PRC). Methods  Eight fresh frozen right cadavers were tested with the wrist intact and followed simulated fusions. Fusions were performed using an external fixation technique and included scaphocapitate, scapholunate (SL), capitolunate, radiolunate, radioscapholunate, scaphotrapeziotrapezoid, 4 corner fusion, and PRC. Results  In the intact wrist, the average arc of wrist motion with the wrist oriented at 20 degrees away from the flexion-extension axis was significantly larger than at any other orientation of motion. All partial wrist fusions and the PRC had significantly smaller average dart-throw arc of motion compared with intact at an orientation 20 and 25 degrees away from flexion-extension. The SL fusion provided a significantly larger arc of motion than most of the other fusions at most orientations. Conclusion/Clinical Relevance  This study provides a comprehensive compilation of the range of motion in a functional plane, "the dart-throw motion," for limited wrist fusions and PRC. These data provide the clinician with important information that can be used to educate patients regarding expectations after surgery.

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.

Approach to the Perpendicular Fixation of a Scaphoid Waist Fracture-A Computer Analyzed Cadaver Model

PURPOSE

In scaphoid fracture screw fixation, the screw is commonly placed along the long axis of the bone, without consideration of the fracture plane. This position is not perpendicular to transverse waist fractures or to the more common horizontal oblique fractures. Our aim was to examine the feasibility and describe possible approaches to, placing a screw perpendicular and in the center of the scaphoid waist fracture.

METHODS

Computed tomography of 12 cadaver wrists was performed in 3 positions to examine possible approaches in flexion, neutral, and extension of the wrist. The scans were evaluated using a 3-dimensional model that simulated horizontal oblique (60°) and transverse (90°) fractures. We examined all possible approaches for screw positioning and their deviation from the axis perpendicular to the fracture and in the center of its plane.

RESULTS

The preferred approaches for a perpendicular screw in a horizontal oblique fracture were found to be proximal-dorsal in flexion or transtrapezial in the extended or neutral positions (through the volar-radial trapezium). In transverse fractures, the possible approaches were proximal-dorsal or transtrapezial in the flexed or neutral positions and distal in the extended position (volar to volar-radial trapezium). In these approaches, the screw could be placed perpendicularly (deviating by < 10°) and in the center of the fracture in all specimens.

CONCLUSIONS

According to this model, it appears feasible to place a perpendicular screw in the center of a horizontal oblique waist fracture using a proximal-dorsal approach in flexion or a transtrapezial approach in neutral or extension positions of the wrist. Palpable landmarks may be used as additional guides to direct these approaches according to the clinical setting.

CLINICAL RELEVANCE

Perpendicular screw fixation of horizontal oblique or transverse scaphoid waist fractures is a possible option, if chosen for its biomechanical advantages.

First-stage scapholunate fusion for the treatment of a chronic lunate dislocation: A case report

RATIONALE

Lunate dislocation is a rare injury to the wrist caused by high-energy trauma, and poor prognosis is often associated with missed initial diagnosis. To date, there is no consensus regarding an effective treatment plan for such cases.

PATIENT CONCERNS

Here, we describe the case of a 36-year-old man who presented with lunate dislocation following a delay in diagnosis of over 7 weeks, and further illuminate its diagnosis and treatment.

DIAGNOSIS

The diagnosis of chronic lunate dislocation was rendered.

INTERVENTIONS

The patient was treated using reduction via the dorsal approach brachial plexus anesthesia. After the reduction, a headless compression screw fixation was performed for first-stage scapholunate fusion, and Kirschner wire fixation of the lunate-triquetrum-hamate was used to stabilize the distal and proximal carpal rows.

OUTCOMES

The patient was followed up for 1 year and showed wrist function recovered well; radiographic examination showed no lunate dislocation and successful scapholunate bony fusion. A satisfactory outcome was achieved.

LESSONS

The case study presented here provide evidence that performing an effective first-stage scapholunate fusion is recommended to achieve better therapeutic outcomes for a chronic lunate dislocation. Furthermore, this approach led to a good long-term clinical outcome in our case.