Radial head arthroplasty restores axial construct stiffness in a Monteggia-like injury model: a biomechanical study.

INTRODUCTION: Monteggia-like lesions are rare but complex elbow injuries involving fractures of both the proximal ulna and the radial head. While the influence of ulnar alignment and soft tissue integrity on radial head stability has been extensively studied, the effect of radial head integrity on the stability of ulnar fixation remains poorly understood. Given the high rates of nonunion and revision surgery after proximal ulna fractures, improved understanding of forearm biomechanics in these combined injuries is highly clinically relevant as it influences the surgical strategy in primary care of these injuries. Accordingly, this study aimed to evaluate the biomechanical impact of radial head resection and radial head arthroplasty on forearm stiffness in a simulated Monteggia-like injury model. We hypothesized that radial head resection would reduce construct stiffness compared with both the native state and radial head arthroplasty, and that arthroplasty would partially restore stiffness toward native levels MATERIALS AND METHODS: Eight fresh-frozen human cadaveric elbow specimens were biomechanically tested under axial loading. After baseline testing in the native state, a standardized segmental comminution model was created and stabilized using locking plate osteosynthesis. Sequential testing was then performed after radial head resection and after implantation of a modular radial head prosthesis. Specimens were loaded cyclically up to 450 N for 1,000 cycles with the elbow positioned at 30° of flexion. Construct stiffness was calculated and compared between testing conditions.

RESULTS: Mean construct stiffness in the native state was 49.3 ± 4.29 N/mm and decreased significantly after creation and fixation of the ulnar defect (36.05 ± 6.71 N/mm). Radial head resection resulted in a further significant reduction in stiffness (25.83 ± 6.65 N/mm). Following radial head arthroplasty, stiffness increased to 33.8 ± 7.89 N/mm, representing a significant improvement compared with the resection state (p ≤ 0.0026). No significant difference was observed between stiffness after prosthesis implantation and the condition with intact radial head and stabilized ulna.

CONCLUSION: Radial head integrity significantly contributes to forearm stiffness in Monteggia-like lesions. Radial head arthroplasty partially restores biomechanical stability after resection and may alter load distribution in a manner that could be relevant for fixation durability. These findings support the need to address the radial column to optimize stability in complex elbow injuries.

LEVEL OF EVIDENCE: Biomechanical study.