Wrist movements induce torque and lever force in the scaphoid: an ex vivo study
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(2020) 15:368
RESEARCH ARTICLE
Open Access
Wrist movements induce torque and lever force in the scaphoid: an ex vivo study Jochen Erhart1*, Ewald Unger2, Philip Schefzig1, Peter Varga3, Michael Hagmann4, Robin Ristl4, Stefan Hajdu1, Anna Gormasz1, Patrick Sadoghi5 and Winfried Mayr2
Abstract Purpose: We hypothesised that intercarpal K-wire fixation of adjacent carpal bones would reduce torque and lever force within a fractured scaphoid bone. Methods: In eight cadaver wrists, a scaphoid osteotomy was stabilised using a locking nail, which also functioned as a sensor to measure isometric torque and lever forces between the fragments. The wrist was moved through 80% of full range of motion (ROM) to generate torque and force within the scaphoid. Testing was performed with and without loading of the wrist and K-wire stabilisation of the adjacent carpal bones. Results: Average torque and lever force values were 49.6 ± 25.1 Nmm and 3.5 ± 0.9 N during extension and 41 ± 26.7 Nmm and 8.1 ± 2.8 N during flexion. Torque and lever force did not depend on scaphoid size, individual wrist ROM, or deviations of the sensor versus the anatomic axis. K-wire fixation did not produce significant changes in average torque and lever force values except with wrist radial abduction (P = 0.0485). Other than wrist extension, torque direction was not predictable. Conclusion: In unstable scaphoid fractures, we suggest securing rotational stability with selected implants for functional postoperative care. Wrist ROM within 20% extension and radial abduction to 50% flexion limit torque and lever force exacerbation between scaphoid fragments. Keywords: Scaphoid fracture, Biomechanics, Wrist movement, Torque and lever force
Introduction The scaphoid is the most frequently fractured bone in the wrist and presents clinical challenges that include inadequate diagnosis as well as healing. Among these, vascular supply has been viewed as the main reason for problems in treating scaphoid fractures and non-unions [1]. Recent anatomical studies have demonstrated that difficulties in scaphoid bone healing cannot be attributed solely to vascularisation [2]. The fractured scaphoid causes stability problems in its dual function as a force transmitter and simultaneous coordinator of movements * Correspondence: [email protected] 1 Department of Trauma Surgery, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria Full list of author information is available at the end of the article
in adjacent wrist bones [3]. The most important forces involved in micro-motion at the fracture site are bending and shear forces [4]. The efficiency of single-screw osteosyntheses, in particular in fractures and non-unions of the scaphoid bone, has not been thoroughly analysed. Providing the best possible fracture stabilisation and postoperative treatment management requires considering the direction and magnitude of isometric torque and lever force within the scaphoid bone [5, 6]. Postoperative functional therapy requires knowing the dimension and
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