Walter H. Short

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.

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.

Treatment of Scapholunate Dissociation With a Bioresorbable Polymer Plate: A Biomechanical Study

PURPOSE Untreated scapholunate dissociation can lead to pain and eventually arthritis. There has been minimal limited success of soft tissue surgical procedures to repair or functionally replicate the torn structures. In this study, we evaluated a new surgical repair for scapholunate dissociation using a bioresorbable polymer approved for human applications. METHODS Eight cadaver wrists were tested in a wrist joint motion simulator. Each wrist was moved in continuous cycles of flexion-extension and radioulnar 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; after repair using a 4-hole bioresorbable plate; and after 1,000 cycles of wrist motion to mimic continued use after surgery. RESULTS Sectioning of these 3 wrist ligaments resulted in static scapholunate dissociation. Application of the polymer plate statistically restored the scaphoid and lunate kinematics to that of the intact specimen. Scapholunate instability and any gap between the bones was eliminated. After 1,000 cycles of motion, the plate maintained intact kinematics in 5 of 8 arms. During cyclic motion, either the plate failed or the screws pulled out in the remaining 3 arms. This occurred in the smallest and most osteoporotic cadavers in which positioning a sensor post and the 2 screws for the plate in the small lunate compromised the pullout strength of the screws. CONCLUSIONS Use of a resorbable polymer plate in restoring normal kinematics in patients with scapholunate dissociation is supported by this study.

Biomechanical Evaluation of Scaphoid and Lunate Kinematics Following Selective Sectioning of Portions of the Scapholunate Interosseous Ligament

PURPOSE To determine the relative roles of the dorsal and volar portions of the scapholunate interosseous ligament (SLIL) in the stability of the scaphoid and lunate. METHODS Sixteen fresh cadaver wrists were moved through physiological motions using a wrist joint simulator. Electromagnetic sensors measured the motion of the scaphoid and lunate. Data were collected with the wrist intact, after randomly sectioning the dorsal SLIL first (8 wrists) or the volar SLIL first (8 wrists), and after full ligamentous sectioning. Differences in the percent increase in scaphoid flexion or lunate extension were compared using a t test with significance set at P < .05. RESULTS Sectioning the dorsal SLIL accounted for 37%, 72%, and 68% of the increase in scaphoid flexion in wrist flexion-extension, radioulnar deviation, and dart throw motion as compared with complete SLIL sectioning. Sectioning the volar SLIL accounted for only 7%, 6%, and 14%, respectively. In the same 3 motions, sectioning the dorsal SLIL accounted for 55%, 57%, and 58% of the increase in lunate extension, whereas volar SLIL sectioning accounted for 27%, 28%, and 22%. CONCLUSIONS The dorsal SLIL provides more stability to the scaphoid and lunate in biomechanical testing. The volar SLIL does provide some, although less, stability. CLINICAL RELEVANCE Although this study supports the critical importance of dorsal SLIL repairs or reconstructions, it also shows that there may be some value in implementing a volar SLIL repair or reconstruction.

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.

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 fractures 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.

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.

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.