How Much Scaphoid Can be Safely Resected? A Biomechanical Analysis of the Effects of Distal Scaphoid Resection.

Abstract

Resection of the distal pole of the scaphoid has been advocated as a simple alternative to other wrist salvage procedures for scaphoid nonunion advanced collapse and scaphotrapezio-trapezoid arthritis. However, the extent of scaphoid that may be resected without adversely affecting carpal kinematics has never been clearly defined. Seven cadaveric upper extremities were tested in a custom motion wrist simulator. A 3-stage sequential sectioning of the distal scaphoid protocol was performed in 25% increments then cyclic active wrist flexion-extension and dart thrower's motion trials were recorded. The extent of distal scaphoid resection had no effect on overall wrist range of motion. The lunate assumed a more extended position following resection of the distal scaphoid compared to intact. At 25%, 50%, and 75% of distal scaphoid resection, the lunate extended to 13.32° ± 9.4°, 23.43° ± 7.5°, and 15.81° ± 16.9°, respectively. The capitate migrated proximally with 25% and 50% distal scaphoidectomy, and proximally and radially with 75% of the scaphoid resected. Resection of 75% of the scaphoid resulted in unstable wrist kinematics. Resection of up to 25% of the distal scaphoid did not significantly influence carpal kinematics and induced mild lunate extension deformity. Resection of 50% of the scaphoid induced further and potentially clinically significant lunate extension and dorsal intercalated segment instability. Further removal of 75% of the distal scaphoid induced capitate migration radially and unpredictable wrist kinematics. Consequently, removal of over 25% of the scaphoid should be avoided or supplemented with partial wrist fusion.