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Wrist Joint Kinematics is Affected by Forearm Position during Active Flexion and Extension
Clare Padmore, MEng1, Andrea HW Chan, MD, MA, FRCSC1, G Daniel Langohr, PhD2, Nina Suh, MD, FRCSC1 and Jim A Johnson, PhD2, (1)Roth McFarlane Hand & Upper Limb Centre, London, ON, Canada, (2)Western University, London, ON, Canada

Introduction: In-vitro biomechanical studies play a key role in assessing surgical reconstruction techniques and rehabilitation protocols. The effect of forearm position in biomechanical testing on kinematics has yet to be investigated. This study examines the effect of 3 forearm positions (gravity flexion, gravity extension, and gravity neutral) on carpal kinematics and contact mechanics.

Purpose: The purpose of this study is to determine whether forearm orientation has an effect on wrist contact mechanics and carpal kinematics.

Methods: Eight cadaveric upper extremities underwent active wrist flexion and extension (FEM) (50° wrist flexion to 50° wrist extension) in a custom motion wrist simulator that produced tendon-controlled motion. The gravity neutral, gravity flexion, and gravity extension positions were assessed. Scaphoid and lunate kinematics were captured with respect to the distal radius and a CT based registration technique was used to assess the contact mechanics of the radiolunate and radioscaphoid during FEM in all three forearm positions.

Results: The greatest radioscaphoid contact area across wrist motion was observed in the gravity extension position and was located radially and midway between the dorsal and volar aspects of the radioscaphoid fossa (Fig. 1A & 2A, p=0.02,). There was a statistically significantly difference in radioscaphoid contact area between forearm orientation at the extremes of wrist motion (p<0.05). Although there was a noticeable increase in radiolunate contact area in the gravity flexion and extension orientations compared to the gravity neutral orientation, this was not statistically significant (Fig. 1B & 2B, p=0.13).

Conclusions: This study showed that forearm orientation does affect radiocarpal contact and should be considered as a relevant variable for biomechanical studies. Additionally, the results illustrated that there was greater contact in the horizontal gravity positions. It is anticipated that these results will influence future biomechanical studies, and in turn generate more effective biomechanical assessment approaches for wrist and carpal motion assessments as well as inform therapy protocols.

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