Valgus stability of the elbow. A definition of primary and secondary constraints.

TLDR

Using a tracking device in a simulated active elbow model, the study sequentially released the medial collateral ligament complex and removed the radial head to quantify each structure’s contribution to valgus stability under gravity. The medial collateral ligament is the primary valgus constraint, while the radial head is secondary; its removal alone does not alter elbow kinematics, but combined release causes laxity and subluxation, guiding treatment of radial head fractures without implant when MCL is intact.

Abstract

The stabilizing structures of the elbow that resist valgus stress were studied with a tracking device in a model simulating active motion and muscle activity. By varying the order of serial release of the medial collateral ligament complex and removal of the radial head, each structure's contribution to valgus stability against the effect of gravity was determined. In the otherwise intact elbow, absence of the radial head does not significantly alter the three-dimensional characteristics of motion in the elbow joint. Isolated medial collateral release, on the other hand, causes increases in abduction rotation of about 6 degrees-8 degrees in magnitude. Releasing both structures results in gross abduction laxity and elbow subluxation. This study defines the medial collateral ligament (MCL) as the primary constraint of the elbow joint to valgus stress and the radial head as a secondary constraint. This definition facilitates the proper management of patients with radial head fractures and MCL disruption. The comminuted radial head fracture uncomplicated by MCL insufficiency should be treated by excision without the need for an implant and without concern of altering the normal kinematics of the elbow.