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

J Orthop Surg Res. 2020 Aug 31;15(1):368. doi: 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.

Keywords: Biomechanics; Scaphoid fracture; Torque and lever force; Wrist movement.

MeSH terms

  • Biomechanical Phenomena
  • Bone Wires*
  • Cadaver
  • Carpal Bones / surgery*
  • Fracture Fixation, Internal / methods*
  • Fractures, Bone / physiopathology*
  • Fractures, Bone / surgery
  • Humans
  • Osteotomy
  • Range of Motion, Articular*
  • Scaphoid Bone / injuries*
  • Scaphoid Bone / physiopathology*
  • Scaphoid Bone / surgery
  • Torque*
  • Wrist / physiopathology*