Radiographic findings following sequential transection of the medial collateral ligament and flexor-pronator mass

Elbow valgus stability relies on both static and dynamic stabilizers. The medial collateral ligament, particularly the anterior bundle (AB), provides primary resistance to valgus stress, whereas the flexor-pronator mass (FPM) offers secondary, dynamic support. Combined disruption of these structures-especially following trauma-can result in significant elbow instability. This cadaveric study aimed to quantify radiographic changes in the medial ulnohumeral joint (UHJ) space and valgus alignment following sequential transection of the AB, posterior bundle (PB), and FPM.

Twelve cadaveric elbows were sequentially tested after sequential transection of the AB, PB, and FPM. Radiographs were obtained at 60° of flexion under standardized valgus stress. Changes in mean medial UHJ space and α-angle were compared across stages using the Friedman test with Wilcoxon post-hoc analysis (P < .05).

The mean specimen age was 63 years (70% male). Mean medial UHJ space increased progressively from 5.4 ± 1.1 mm in the intact state to 12.4 ± 3.0 mm after AB transection, 16.1 ± 3.9 mm after combined AB + PB transection, and 26.4 ± 7.8 mm after additional FPM release. Correspondingly, mean α-angle rose from 2.8° ± 1.7° to 3.4° ± 3.0°, 5.0° ± 4.2°, and 13.6° ± 8.6°, respectively. All comparisons were statistically significant (P < .001).

In this cadaveric model, UHJ opening ≈15 mm suggested full medial collateral ligament disruption, and >20 mm or α-angle ≈13° indicated additional FPM compromise; these values are experimental reference ranges for medial soft-tissue injuries.