Biomechanics of the elbow

Elbow stability is provided by a complex interplay of static and dynamic stabilizers that are of variable importance depending upon the position of the elbow and upon which structures have been damaged. Static stabilizers include the conformity of the ulnotrochlear joint, the coronoid process, the concavity-convexity of the radial head and capitellum, the anterior band of the ulnar collateral ligament, and the lateral collateral ligament complex. The anterior band of the ulnar collateral ligament is the primary stabilizer against valgus stress, with the radial head serving as a secondary stabilizer. The lateral collateral ligament complex, which consists of the radial collateral ligament, the lateral ulnar collateral ligament, and the annular ligament, is the primary stabilizer to varus stress, with the coronoid serving as a secondary stabilizer. Dynamic stabilizers of the ulnotrochlear joint include the biceps, brachialis, triceps, and anconeus. These structures act to center contact pressures. The flexor-pronator mass serves as a dynamic stabilizer to valgus stress and the extensors serve as a dynamic stabilizer to varus stress, completing the "concavity-compression" mechanism of the radiocapitellar joint. A thorough understanding of the anatomy, function, and interaction of these structures is crucial for understanding the rationale for the surgical treatment of elbow instability.