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The Journal of Bone and Joint Surgery (American) 86:2268-2274 (2004)
© 2004 The Journal of Bone and Joint Surgery, Inc.

Dynamic Contributions of the Flexor-Pronator Mass to Elbow Valgus Stability

Maxwell C. Park, MD1 and Christopher S. Ahmad, MD2

1 Kerlan-Jobe Orthopaedic Clinic, 6801 Park Terrace, Los Angeles, CA 90045. E-mail address: mcp16{at}columbia.edu
2 Center for Shoulder, Elbow and Sports Medicine, Department of Orthopaedic Surgery, Columbia University, 622 West 168th Street, PH-11, New York, NY 10032

Investigation performed at the Center for Shoulder, Elbow and Sports Medicine, Department of Orthopaedic Surgery, Columbia University Medical Center, New York, NY

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Background: Previous studies have indicated that the demands placed on the medial ulnar collateral ligament of the elbow when it is subjected to valgus torque during throwing exceed its failure strength, which suggests the necessary dynamic contribution of muscle forces. We hypothesized that the flexor-pronator mass assists the medial ulnar collateral ligament in stabilizing the elbow against valgus torque.

Methods: Six cadaveric elbows were tested at 30° and 90° of flexion with no other constraints to motion. A full medial ulnar collateral ligament tear was simulated in each elbow. Muscle forces were simulated on the basis of the centroids and physiological cross-sectional areas of individual muscles. The biceps, brachialis, and triceps were simulated during flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum superficialis and flexor carpi ulnaris, and pronator teres-loading conditions. Kinematic data were obtained at each flexion angle with use of a three-dimensional digitizer.

Results: Release of the medial ulnar collateral ligament caused a significant increase in valgus instability of 5.9° ± 2.4° at 30° of elbow flexion and of 4.8° ± 2.0° at 90° of elbow flexion (p < 0.05). The differences in valgus angulation between each muscle-simulation condition and the medial ulnar collateral ligament-intact condition were significantly different from each other (p < 0.05), except for the difference between the flexor carpi ulnaris contraction condition and the flexor digitorum superficialis-flexor carpi ulnaris co-contraction condition. This co-contraction provided the most correction of the valgus angle in comparison with the intact condition at both 30° and 90° of elbow flexion (1.1° ± 1.8° and 0.38° ± 2.3°, respectively). Simulation of the flexor carpi ulnaris alone provided the greatest reduction of the valgus angle among all individual flexor-pronator mass muscles tested (p < 0.05), whereas simulation of the pronator teres alone provided the least reduction of the valgus angle (p < 0.05).

Conclusions: The flexor-pronator mass dynamically stabilizes the elbow against valgus torque. The flexor carpi ulnaris is the primary stabilizer, and the flexor digitorum superficialis is a secondary stabilizer. The pronator teres provides the least dynamic stability.

Clinical Relevance: The flexor-pronator mass is capable of contributing valgus stability to the elbow. When considering injury prevention, surgical techniques, and rehabilitation in throwing athletes, the physician should give particular attention to optimizing the function of the flexor carpi ulnaris and flexor digitorum superficialis.


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