Progressive Capitellar Osteochondral Defects Adversely Affect Valgus Angulation and Radiocapitellar Contact Based on Size and Location With Native and Strained Ulnar Collateral Ligaments: A Biomechanical Rationale for Pathogenesis.

Background: Osteochondritis dissecans of the humeral capitellum can occur in adolescent baseball players owing to repetitive compressive shear forces within the radiocapitellar joint.

Purpose: To quantify the relationship between valgus angle and radiocapitellar joint contact with varying size and location of osteochondral defects and to compare these effects with a native and strained medial ulnar collateral ligament (UCL).

Study design: Controlled laboratory study.

Methods: Twenty-four cadaveric elbows were tested (mean ± SD, 62.5 ± 8.1 years old). Capitellar osteochondral defects were created at 2 locations (proximal and distal) and with 2 sizes (smaller central and larger laterally extended). Three conditions were tested: proximal defect with a native UCL, distal defect with a native UCL, and distal defect with a strained UCL. Valgus angulation and radiocapitellar contact characteristics were measured with 0, 2, and 3 N·m of additional valgus torque.

Results: When compared with no additional load, there were statistically significant increases in valgus angle with an intact capitellum at both torques for elbows with native and strained UCLs at all elbow flexion angles (P < .001). Elbows with a strained UCL had a higher increase in valgus angulation with 3-N·m valgus torque when compared with the native UCL (P < .048). Larger proximal defects significantly increased the valgus angle at 45° and 105° (P < .012) of flexion, whereas larger distal defects increased the valgus angle at 15° to 75° of flexion (P < .022). There was a significantly decreased radiocapitellar contact area for both osteochondral defect locations (P < .05).

Conclusion: Osteochondral defects show location- and size-dependent alterations in valgus angulation and radiocapitellar contact characteristics in the UCL-strained and native conditions. Relatively low valgus loads with a native UCL increase radiocapitellar contact, which can serve as a rationale for the basis of the formation of an osteochondral defect, with exacerbation of valgus instability and changes in contact characteristics demonstrable with progressively enlarging osteochondral defects.

Clinical relevance: This study provides a biomechanical rationale to understand the interplay between the medial and lateral sides of the elbow in pitchers when considering osteochondral defect pathogenesis and pathomechanics.