Wrist movements induce torque and lever force in the scaphoid: an ex vivo study

• Main Authors: Jochen Erhart, Ewald Unger, Philip Schefzig, Peter Varga, Michael Hagmann, Robin Ristl, Stefan Hajdu, Anna Gormasz, Patrick Sadoghi, Winfried Mayr
• Format: Article
• Language: English
• Published: BMC 2020-08-01
• Series: Journal of Orthopaedic Surgery and Research
• Subjects: Scaphoid fracture; Biomechanics; Wrist movement; Torque and lever force
• Online Access: http://link.springer.com/article/10.1186/s13018-020-01897-y

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.