The elbow is a congruent, complex hinge joint.

Although constrained by bony architecture at the extremes of flexion and extension with ligamentous stability in the mid-range of motion, it accounts for 20% of all dislocations (5).

Most instabilities result from either a single trauma (straight posterior or posterolateral rotatory instability) or chronic overuse in the overhead athlete (valgus instability). Varus instability can also occur and is frequently associated with a anteromedial coronoid fracture.

The elbow joint comprises the radiocapitellar, ulnohumeral, and proximal radioulnar joints.

The lateral portion of the distal humerus, the capitulum, articulates with the radial head. The medial portion of the humerus, the trochlea, articulates with the trochlear notch or “greater sigmoid notch” of the ulna. The radial notch of the ulna articulates with the radial head (7).

The ulnohumeral joint affords flexion and extension of the elbow while the proximal radioulnar joint affords pronation and supination. The radiocapitellar joint moves in both rotation and flexion/extension.

The primary restraints of the elbow are the osseous ulnohumeral articulation, particularly at the extremes of flexion and extension, and the ligamentous structures medially and laterally (9).

The medial (or ulnar) collateral ligament (MCL) is the main constraint to valgus instability. It originates on the anteroinferior medial epicondyle and consists of an anterior band inserting on the sublime tubercle of the coronoid process (and provides most stability at all arcs of flexion) and the posterior band inserting on the medial margin of the semilunar notch of the ulna (and provides stability at 90 degrees of flexion). An injury pattern of valgus force tends to rupture the MCL off of the humeral origin.

The lateral collateral ligament (LCL) complex originates from the lateral epicondyle and consists of 4 parts: (a) the radial collateral ligament; (b) the lateral ulnar collateral ligament (LUCL), which provides most lateral stability; (c) the annular ligament, which encircles the radial head; and (d) the accessory LCL. A common injury pattern is an avulsion of the complex from the humeral origin.

MCL injuries are most common in overhead-throwing athletes (2).

The most common complaint is pain typically felt during late cocking and early deceleration of the throwing motion. Throwing velocity may also be diminished.

Athletes do not complain of symptoms of elbow instability, such as popping, locking, or clicking; however, associated abnormalities, such as synovitis, plica, or loose bodies, may present with these symptoms. Most athletes if rested for a significant period of time or retired from overhead throwing will recover painless function, but few are willing to undergo nonoperative treatment for many months.

It is rare to have an acute rupture of the MCL during an athletic event. Catastrophic tearing of the MCL occasionally can be seen, but patients often have had recurrent symptoms prior to ligament failure.

Acute rupture of the MCL is most commonly seen in a full dislocation of the elbow, which may also avulse the origin of the flexor-pronator group.

Patients may also have neuritis of the ulnar nerve, with numbness and tingling in the ulnar digits, as well as loss of strength in the finger intrinsic muscles. This may occur due to inflammatory changes along the medial side of the elbow and rarely requires isolated ulnar nerve decompression.

Injury to the LCL complex is usually the result of trauma causing a dislocation or fracture-dislocation, such as a fall on an outstretched hand. An occasional iatrogenic cause may occur secondary to previous lateral tennis elbow surgery, especially if a full release was performed instead of a partial resection. Tennis elbow releases that stray posterior to the midportion of the capitellum may detach the LCL complex.

Insufficiency of the LUCL is the essential lesion leading to lateral elbow instability.

A constellation of injuries called “the terrible triad” of radial head fracture, coronoid fracture, and elbow dislocation is a common cause of lateral ligament instability.