• Shoulder/Elbow Surgery

Aim. To evaluate the trauma pathokinematics and the inherent joint stability of the human elbow joint in relation to posterior joint dislocation. Three series of experiments involved: 1. Determination of the flexion position of the osseous joint with the least constraint to external forearm rotation, a generally accepted condition for dislocation to occur. 2. Evaluation of the isolated capsuloligamentous structures as constraints to posterior dislocation. 3. Evaluation of the effect on stability of combined osteoligamentous lesions following dislocation, and of clinically used reconstructive procedures as well. Methods. A total of 36 human elbow joint specimens were tested in a new Joint Analysis System (JAS) able to simulate the posterior dislocation. In Study 1, denuded elbow joint specimens were used under change of joint flexion position, valgus-varus stress, and supination-pronation position. Sequential section of capsuloligamentous structures followed by stability tests was performed in Study 2. Typical fractures after dislocation were applied on the specimens in Study 3, alone or in combination with ligamentous damage and radial head prosthetic replacement or lateral ligament reconstruction. Results. The osseous stability increased during valgus stress (p=0.0001), at 30 degrees of elbow flexion and also tended to increase in pronation. The conditions of the elbow in a slightly flexed position and varus stress seemed, combined with a forearm external rotation trauma, to be the important biomechanical factors in posterior elbow dislocation. The primary stabilizers against external forearm rotation in the extended elbow were the anterior capsule and the lateral collateral ligament complex (LCLC), whereas in the flexed elbow the anterior capsule did not have stabilizing effect. The LCLC appears to be one functional unit. Both the radial head and the coronoid process act as independent restraints in relation to external forearm rotation in our experimental set-up. When both are fractured, the joint subluxates regardless of intact collateral ligaments, and in our study the subluxation was terminated by insertion of radial head prosthesis which also virtually normalized the laxity to external rotation. Lateral collateral ligament reconstruction and insertion of radial head prosthesis to the “Terrible Triad” yielded restraint against gross joint instability in our experimental set-up.

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