Surgical treatment of posterolateral rotatory instability of the elbow

Introduction

The elbow is the second most commonly dislocated major joint, after the shoulder. The incidence in the general population is estimated to be 6/100,000. Most elbow dislocations are in the posterior or posterolateral direction which may result in posterolateral rotatory instability (PLRI). The forearm rotates externally in relation to the humerus, causing posterior dislocation or subluxation of the radial head. The term posterolateral rotatory instability was coined by O’Driscoll and colleagues in 1991. It is a complex injury to the lateral ulnar collateral ligament (LUCL) complex, leading to posterolateral subluxation or dislocation of the radius on the capitellum without disruption of the proximal radioulnar joint. PLRI is most often caused by a traumatic event such as an elbow dislocation or a significant varus stress combined with an axial load (fall on an outstretched hand). ^, But another possible etiology, though less common, is an iatrogenic complication from prior surgery; previous corticosteroid injections can also cause PLRI. Ligamentous laxity and childhood elbow fracture with a resultant cubitus varus deformity have also been reported to be predisposing factors.

The elbow functions in both open and closed chain conditions. It is an important link between the shoulder and hand. The open chain activity of the elbow is defined as a type of elbow movement when the hand is in the air, such as throwing, or reaching for an object. In closed chain activities, the hand is on a stable platform, such as a push-up. The stability of the elbow is maintained by bony anatomy, ligamentous complexes, and muscles. The elbow joint has three bony articulations: ulnohumeral, radiocapitellar, and the proximal radioulnar articulation. The lateral and medial sides of the elbow have distinct ligamentous complexes. The medial, or ulnar, collateral ligament complex has three components: the anterior oblique ligament, also known as the anterior bundle; the posterior oblique ligament, also known as the posterior bundle; and the transverse ligament, also known as Cooper’s ligament. The anterior oblique ligament is functionally subdivided into anterior and posterior bands; it is widely considered to be the primary restraint to valgus stress.

The lateral or radial side, known as the lateral collateral ligament complex, is Y shaped. It has four components: the LUCL, the radial collateral ligament (RCL), the annular ligament (AL), and the accessory lateral collateral ligament (ALCL). The AL acts to stabilize the proximal radio-ulnar joint. The RCL tensions when a varus load is placed on the elbow. The LCL complex is a restraint to varus stress and also acts to stabilize the radial head as a posterior sling to prevent posterior subluxation or dislocation.

It is known that the LUCL is the essential lesion in PLRI, but studies have shown that the other ligaments of the LCL complex need to be injured in order to create PLRI. ^, Cadaveric studies have demonstrated that PLRI is evident only when both the LUCL and RCL are injured, but not when either is cut in isolation.

The LUCL originates proximally on the lateral epicondyle of the humerus and attaches distally to the tubercle of the supinator crest of the ulna. The distal attachment of the ligament is a broad fan-shaped thickening of the capsule that blends with and arches superficial and distal to the AL to insert onto the ulna. The humeral attachment is historically considered to be the isometric point on the lateral side of the elbow. A “true” isometric point does not exist since the ligament length changes with flexion and extension. In order for correct fixation and tensioning of the LCL complex or graft, it is important to identify the isometric point intra-operatively.

In PLRI the proximal radioulnar joint relationship is maintained, and both the ulna and radius move together as one unit relative to the humerus. PLRI consists of three stages ranging from instability to frank dislocation, described in O’Driscoll’s classification system. The instability begins laterally and, as the injury progresses, circles to medially based on structure involvement. The first stage is a subluxation from the elbow in a posterolateral rotatory direction such that there is posterior radial head subluxation underneath the humerus. In the second stage, the injury involves the anterior and posterior capsule so that the coronoid is perched under the trochlea and the elbow dislocates incompletely. In the third stage, the elbow dislocates completely and the coronoid rests behind the humerus. This stage is subclassified into three categories. In Stage 3A, the anterior band of the medial collateral ligament is intact, and the elbow is stable to valgus stress after reduction. In Stage 3B, the anterior medial collateral ligament is disrupted so that the elbow is unstable in valgus. In Stage 3C, the entire distal humerus is stripped of soft tissues, rendering the elbow grossly unstable even when a splint or cast is applied with the elbow in a semi-flexed position. Each stage has specific clinical, radiographic, and pathologic features that are predictable and have implications for treatment.

In the setting of trauma, the lateral ligamentous injury that results in PLRI usually occurs proximally, at the lateral epicondyle. After an elbow dislocation there is usually a “bare area” visible at the lateral epicondyle where the LCL complex has become avulsed with associated involvement of the RCL and the common extensor tendon origin.

Preoperative considerations