Stabilizers of the elbow

Recurrent posterolateral rotatory instability of the elbow is an apparently undescribed clinical condition that is difficult to diagnose. We treated five patients, ranging in age from five to forty years, who had such a lesion and in whom the instability could be demonstrated only by what we call the posterolateral rotatory-instability test. This test involves supination of the forearm and application of a valgus moment and an axial compression force to the elbow while it is flexed from full extension. The elbow is reduced in full extension and must be subluxated as it is flexed in order to obtain a positive test result (a sudden reduction of the subluxation). Flexion of more than about 40 degrees produces a sudden palpable and visible reduction of the radiohumeral joint. The elbow does not subluxate without provocation. The cause for this condition, we think, is laxity of the ulnar part of the lateral collateral ligament, which allows a transient rotatory subluxation of the ulnohumeral joint and a secondary dislocation of the radiohumeral joint. The annular ligament remains intact, so the radio-ulnar joint does not dislocate. Operative repair of the lax ulnar part of the lateral collateral ligament eliminated the posterolateral rotatory instability, as revealed intraoperatively in our five patients.

A review of thirty-five patients who had a fracture of the coronoid process of the ulna revealed three types of fracture: Type I--avulsion of the tip of the process; Type II--a fragment involving 50 per cent of the process, or less; and Type III--a fragment involving more than 50 per cent of the process. A concurrent dislocation or associated fracture was present in 14, 56, and 80 per cent of these patients, respectively. The outcome correlated well with the type of fracture. According to an objective elbow-performance index used to assess the results for the thirty-two patients who had at least one year of follow-up (mean, fifty months), 92 per cent of the patients who had a Type-I fracture, 73 per cent who had a Type-II fracture, and 20 per cent who had a Type-III fracture had a satisfactory result. Residual stiffness of the joint was most often present in patients who had a Type-III fracture. We recommend early motion within three weeks after injury for patients who have a Type-I or Type-II fracture. Reduction and fixation, followed by early motion when possible, may be the preferred treatment for patients who have a Type-III fracture.

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.