Page 39 - ISAKOS 2019 Newsletter Volume 1
P. 39

 Posterolateral Rotatory Instability of the Elbow
The LUCL is a restraint to varus stress and stabilizes the radial head against posterior subluxation or dislocation.
The concept of the LUCL as the only soft-tissue stabilizer of the radiocapitellar joint is controversial. Multiple anatomical studies have demonstrated that, in order to create radiocapitellar instability, additional lateral elbow structures must also be injured, including the radial collateral ligament, part of the annular ligament, and/or the common extensor mechanism2,3.
Clinical Presentation
Patients often present with lateral elbow pain, especially following activities in which the elbow is placed into extension and supination. Lateral elbow pain may be accompanied by mechanical symptoms such as clicking, locking, or snapping, which are most prominent at 40° of flexion as the arm is extending1.
Stability of the lateral collateral ligaments (the radial collateral ligament and LUCL) and medial collateral ligaments (MCL) should be assessed with varus and valgus stress tests at 30° of flexion to unlock the olecranon from its fossa. A valgus stress test should be performed with the forearm in both full supination and full pronation. When the forearm is in full pronation, the interosseous membrane is not tense, which allows for proximal migration of the radius and thereby enhances the stability of the radiocapitellar joint. Thus, one can test the MCL with no risk of a false-positive valgus stress test. However, when the forearm is in supination, bone stability of the radiocapitellar joint is decreased and use of the LUCL is increased. If the patient has PLRI during the exam, this finding may be a false-positive result.
The pivot-shift test, described by O’Driscoll et al., is used to confirm PLRI1. This test is performed with the patient supine on the examination table with the arm overhead, the shoulder in full external rotation to stabilize the shoulder joint, and the forearm in full supination. The maneuver starts with the elbow extended and supinated; in this position, the radial head will be subluxated. As the examiner brings the arm from extension to flexion, valgus stress and axial compression are applied to the elbow and the forearm is allowed to become less supinated. This allows the forearm to pivot around the MCL and results in reduction of the elbow joint as the triceps becomes taught at around 40° flexion, often causing an audible or palpable click. In the awake patient, it is unusual to be able to detect a positive pivot shift because of guarding by the patient. Therefore, apprehension during the pivot-shift maneuver is often considered to be a positive result even without frank instability.
The chair-up test can also be used to test for PLRI. For this test, the patient pushes up from a chair with the hands on the armrests. If apprehension or dislocation occurs, the test is considered to be positive for PLRI.
Jose Carlos Garcia Jr., MD, PhD
São Paulo, BRAZIL
Felipe Machado do Amaral, MD
São Paulo, BRAZIL
Matheus Ribeiro Barcelos, MD
São Paulo, BRAZIL
O’Driscoll et al., in 1991, described posterolateral rotatory instability (PLRI) of the elbow as a condition resulting from an injury to the lateral ulnar collateral ligament (LUCL)1. This lesion leads to posterolateral subluxation and/or dislocation of the radius over the capitellum without disruption of the proximal radioulnar joint and is most often caused by a traumatic event resulting in significant valgus stress combined with axial load and forearm supination.
Iatrogenic causes of PLRI include multiple corticosteroid injections and aggressive debridement for the treatment of lateral epicondylitis. Ligamentous attenuation resulting from chronic cubitus varus is also considered a potential cause.
Although O’Driscoll et al. initially described an injury to the LUCL as the primary cause of PLRI, this theory has become controversial in the literature. Some authors have shown that additional injuries to the remaining lateral soft-tissue structures of the elbow are also required in order for a patient to develop PLRI2,3.
Pathoanatomy of Posterolateral Rotatory Instability
The osseous structures of the elbow stabilize the joint at the extremes of flexion (>120°) and extension (0° to 20°), whereas the lateral and medial ligamentous complexes are the primary stabilizers throughout the remainder of motion.
The LUCL is a thickening of the capsule that extends from the lateral epicondyle to the tubercle on the supinator crest.

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