American Association for Hand Surgery
Theme: Beyond Innovation

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A Biomechanical Analysis of Extensor Carpi Radialis Longus Tenodesis for Scapholunate Ligament Reconstruction
Andrea HW Chan, MD, MA, FRCSC; Clare Padmore, MEng; Daniel Langohr, BESc, MESc Nina Suh, MD, FRCSC;
Roth McFarlane Hand & Upper Limb Centre, London, ON, Canada

Introduction
Surgical management of dynamic scapholunate (SL) instability remains controversial as unpredictable clinical outcomes hamper the establishment of a gold standard procedure. As a result, multiple reconstructive techniques have been proposed in the literature with dorsal-based techniques traditionally being favored. However, more recent evidence suggests that the volar SL ligament also plays a contributory role in SL stability and hence, may also require reconstruction. The Extensor Carpi Radialis Longus (ECRL) tenodesis is a newly proposed technique that reconstructs both the dorsal and volar SL ligament. The purpose of this in vitro cadaveric biomechanical study is to investigate the ability of a combined dorsal-volar ligament reconstruction to restore native carpal kinematics.
Materials and Methods
Six fresh-frozen cadaveric upper limbs (6 males; mean age 6810.2) were run through a three-staged protocol of cyclic dart-throw motion (DTM) using a previously-validated active wrist motion simulator. Scaphoid and lunate motion, relative scaphoid translation, and SL motion were measured with wrist ligaments intact, after complete sectioning of the SL ligament, and after SL reconstruction using the ECRL tenodesis technique.
Results
Greater scaphoid flexion and lunate extension were observed after complete sectioning of the SL ligament through simulated wrist DTM (scaphoid p=0.012; lunate p=0.03). The scaphoid also translated volar, distal, and radial relative to the lunate after complete SL ligament sectioning (p=0.04). The ECRL tenodesis reconstruction restored the SL angle at the extremes of DTM yet overall had minimal effect across wrist motion (p=0.021). The tenodesis was unable to correct scaphoid flexion in the wrist flexed position (p=0.02), and unable to correct lunate extension in the neutral position (p=0.041). In two tested specimens, the tenodesis overcorrected the lunate position into greater flexion than the intact state while the wrist was flexed; in the remaining specimens, the tenodesis failed to restore lunate posture (p=0.042).
Conclusions
This is the first study that analyzes wrist biomechanics following SL reconstruction using an active motion simulator. It demonstrates that the ECRL tenodesis is effective in normalizing the scapholunate angle at the extremes of DTM. This technique, however, is unable to restore scaphoid or lunate kinematics, or correct scaphoid translation relative to the lunate throughout DTM in this model. Despite reconstructing both the dorsal and volar SL ligaments, the ECRL reconstruction does not reliably restore carpal kinematics back to the native state.


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