Interfragmentary Screws Versus Intramedullary Implants For Proximal Phalanx Fractures: A Biomechanical Study in Matched Hands.

Purpose: Displaced proximal phalanx fractures are common injuries that often require surgical intervention. Intramedullary screw (IMS) fixation has recently gained popularity as a minimally invasive approach, but the relative resistance to fracture displacement when undergoing early motion is unknown. The purpose of this study was to determine whether the stability of IMS fixation is comparable or superior to the stability of interfragmentary screws for oblique fractures.

Methods: Twenty-four matched cadaveric specimens were cut to produce standardized 60° oblique fractures and then randomized to stabilization with a 2.4-mm IMS or two 1.5-mm interfragmentary cortical screws. Specimens were loaded at 20 N for 2,000 cycles to simulate flexor tendon range of motion and were then loaded to failure, where failure was defined as 3 mm of movement from initial position.

Results: After 2,000 cycles of 20 N loading, the cortical screws averaged significantly less movement than the IMS screws, with movements of 0.7 mm and 1.3 mm, respectively. When loaded to failure, the cortical screws withstood slightly higher forces than the IMS, averaging 79.8 N and 65.4 N, respectively. Under cyclic loading, 1 cortical screw specimen and 2 IMS specimens failed before reaching the completion point of 2,000 cycles.

Conclusions: Two orthogonal interfragmentary screws demonstrate less displacement than the IMS after cyclic loading of oblique proximal phalanx fractures under physiologic loads. Two bicortical interfragmentary screws are a robust option for long-oblique fractures and may tolerate an early motion protocol.

Clinical relevance: This study suggests that interfragmentary screws provide robust fixation of long-oblique proximal phalanx fractures. Given the initial displacement of intramedullary screws, further research should assess the role of canal fill, fracture morphology, and screw configuration on the selection of internal fixation strategy.