Ligamentous injuries of the elbow can be either caused by repetitive microtraumatic activities or by a single acute traumatic event, such as an elbow dislocation. We focused on injuries caused by repetitive activities that produce overuse damage: chronic overuse implies repetitive microtrauma of the elbow and can occur in both athletes and nonathletes.
Even though diagnosis is often made at clinical examination, imaging is helpful to confirm clinical interpretation, grade the injury, and guide treatment. The radiologist should be able to identify commonly seen patterns of injury since different structures are variably involved (tendons, ligaments, bones, cartilage).
In our article, we decided to focus specifically on ligamentous injuries secondary to overuse. In this setting, instability may affect the medial compartment, involving the MCL, or the lateral compartment, involving the LCL.
Medial compartment: major elbow instability and posteromedial elbow impingement
Medial major elbow instability typically affects patients involved in athletic performances and results from acute or chronic injuries to the MCL. The most frequent presentation is chronic elbow pain localized to the medial side and valgus instability, worsened by overhead activities. Overhead throwing athletes, such as baseball pitchers, are particularly subjected to repetitive microtrauma to the MCL: the acceleration phase of throwing is characterized by great valgus and extension forces, leading to major tensile stress on medial structures, compressive forces on lateral structures, and shear forces posteriorly.
Surrounding bony structures and muscles acting as dynamic stabilizers reduce the stress distribution through the MCL by about half [43], but as these muscles fatigue, the amount of force transmitted to the MCL increases. The chronic tensile forces involved lead to inflammation, micro-tearing, and patholaxity of the ligament, which may eventually progress to disruption of the MCL (Fig. 5).
A combined valgus-extension overload can result in formation of posteromedial osteophytes that give rise to posterior elbow pain, as well as ulnar nerve irritation symptoms. Less commonly, the MCL may be injured after a traumatic elbow dislocation [44].
The anterior bundle of the MCL (A-MCL) is the main stabilizer against valgus stress; as such, it is most frequently injured in tennis players and baseball pitchers, due to the high forces involved in the tennis serve and the late-cocking phase of throwing, respectively (Figs. 6, 7) [4, 30, 33, 45].
MCL injuries are generally well-tolerated during daily activities. On the other hand, athletic performance can be severely impaired by either medial or posteromedial instability.
Posteromedial elbow impingement, also known as valgus extension overload (VEO) syndrome, is a rather uncommon disorder in the general population; however, it is a cause of disability in the overhead throwing athlete [46, 47].
As previously mentioned, progressive medial laxity may occur from increased and repetitive combined hyperextension, valgus stress, and supination of the elbow. Such repetitive overload at the level of the posteromedial fossa may lead to posteromedial impingement, a bony and soft tissue mechanical abutment in the posterior fossa of the elbow, resulting in focal synovitis and olecranon spurring (Fig. 8a) [48].
The resultant soft tissue swelling, loose bodies, or osteophyte formation, or a combination of these, associated with abutment may result in symptoms localized to the posterior side of the elbow [46, 47, 49].
Over time, osteophytes may fracture, leading to loose bodies and mechanical symptoms (Fig. 8b).
The athlete complains of posterior pain, joint effusion, locking, crepitus, and a decrease in range of motion, most notably an extension deficit [49, 50]. Physical examination shows posteromedial tenderness and/or synovitis with possible associated extension loss and/or MCL laxity [51].
Posteromedial impingement can also be associated with ligament-related elbow instability, especially MCL insufficiency; it may also present in the setting of a rather stable MCL with a certain degree of developmental laxity [52].
Lateral compartment: major (PLRI) and minor (SMILE) elbow instability
The LCL complex stabilizes the elbow against excessive varus and external rotational stress. Varus stress applied to the elbow is more common in the setting of an acute injury and only rarely related to a repetitive stress, which is more common at the medial compartment.
Tears can involve one or more of the three bundles, but the LUCL is the most important in terms of stability [53]. However, kinematic studies have described the LUCL and the RCL as working in concert to resist varus stress.
Damage to the LCL complex can lead to posterolateral rotatory instability (PLRI) of the elbow (Fig. 9), which is considered one of the major elbow instabilities involving the lateral compartment. This condition, as first described by O'Driscoll et al. [54], results in transient external rotatory subluxation of the ulna on the humerus, producing both humero-radial and humero-ulnar instability.
This represents the most common pattern of recurrent elbow instability, especially in the setting of chronic symptoms [55]; recurrent symptoms of lateral pain, locking, snapping, or popping may be present.
The feeling of instability most commonly occurs when the elbow is actively moved from flexion into extension, with a supinated forearm.
The primary cause of PLRI involves the partial or complete disruption of the LCL complex, which usually results in its avulsion off the lateral epicondyle [56] and is typically the result of trauma. A posterolateral luxation of the elbow can thus lead to chronic PLRI.
Other causes of injury to the LCL complex include chronic cubitus varus, sequelae of corticosteroid injections employed in the treatment of lateral epicondylitis, connective tissue disease [57,58,59,60], and/or other iatrogenic causes.
Dynamic ultrasound can be used to confirm clinical suspicion of instability (Fig. 10).
Recalcitrant lateral elbow pain, mostly diagnosed as lateral epicondylitis, is associated with a high incidence of intra-articular findings which may be related to a condition of patholaxity termed “symptomatic minor instability of the lateral elbow” (SMILE) (Figs. 11, 12, 13) [61].
This condition may result from repetitive low-energy stress or shear forces, occurring in simple, repetitive or prolonged daily or working activities performed with the shoulder in moderate abduction, pronation of the hand and 50°–70° of elbow flexion. In this position, the hand and the forearm create a varus/pronation load on the lateral elbow, with progressive stretching and elongation of the RCL and the annular ligament, both associated to a relative hypermobility of the radial head.