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Introduction: Radial head arthroplasty is widely utilized for the treatment of irreparable radial head fractures in order to provide valgus elbow stability and radial longitudinal stability. The metal-on-cartilage articulation may alter the native contact pressures at the radial head-capitellum interface leading to excessive capitellar articular wear. The objective of the study was to determine the optimal radial length to reproduce the native radiocapitellar contact pressures.

Methods: Eight cadaveric upper extremities (four matched-pairs) were utilized in the study. Prior to experimentation, all specimens were confirmed to be ligamentously stable and without significant cartilage wear. All specimen manipulations and dissections were performed without violating the native elbow ligaments. Radiocapitellar contact pressures were digitally analyzed during simulated loading at 0, 45, and 90 degrees of elbow flexion in the intact specimens and after modular radial head arthroplasty at -2 mm, 0 mm, and +2 mm of the native length. The results were analyzed using two-way repeated measure analysis of variance and paired analysis with Tukey contrasts.

Results: Mean and maximum contact pressures were highest at 0 degrees and lowest at 90 degrees flexion at all radial lengths. Radial head arthroplasty at -2 mm produced significantly lower mean and maximum contact pressures at all angles of elbow flexion (p = 0.0013 and p = 0.00128, respectively). There were no significant differences in mean or maximum contact pressures between native and 0 mm arthroplasty (p = 0.1396 and p = 0.15515, respectively). There were no significant differences in mean or maximum contact pressures between native and +2 mm arthroplasty (p = 0.86 and p = 0.822, respectively). At all angles of elbow flexion, there was a trend towards higher contact pressures at +2 mm. The mean and maximum contact pressures for the 0 mm radial head arthroplasty length at all angles of flexion were closest to the native contact pressures without being elevated.

Conclusions: The results of this biomechanical investigation support inserting the radial head implant at less than or equal to native radial length to avoid excessive radiocapitellar contact pressures. Slight overstuffing of the radiocapitellar joint could possibly lead to accelerated capitellar articular wear.