Review Question - QID 211920

This patient sustained injury to the posterior and superior acromioclavicular (AC) ligaments resulting in posterior AC joint instability.

The AC joint is a diarthrodial joint that articulates the scapula with the clavicle. It contains a fibrocartilaginous intraarticular disc analogous to the meniscus of the knee and has a small articular surface area with relatively high axial and rotational loads. The ligaments of the AC joint play a pivotal role in its stability. Unlike the coracoclavicular ligaments (conoid and trapezoid) which are important in superior stability of the distal clavicle, the AC ligaments are most important with anterior-posterior stability. Injury to the AC ligaments most commonly occurs secondary to aggressive surgical distal clavicle resection ( >1-1.5cm). Injury to the posterior and superior AC ligaments result in primary posterior instability of the distal clavicle. Conversely, injury to the anterior and superior AC ligaments results in anterior instability of the clavicle.

Strauss et al. review the causes of failure following distal clavicle excision (DCE) including over-resection leading to joint instability. They report that persistent symptoms and disability after DCE requires the formulation of a treatment plan, which may include conservative management, revision surgery, or ligament reconstruction. They conclude that proper surgical technique and appropriate rehabilitation during the index procedure can minimize the likelihood of poor outcome.

Nuber et al. reviewed AC joint injuries. They report on the usefulness of an injection of bupivicaine into the AC joint to evaluate the source of pain about the symptomatic shoulder. They also note that the amount of bone resection necessary with arthroscopic technique is less than with the open procedure due to the ability to preserve the stabilizing properties of the superior AC ligaments. They conclude that resection of 4 mm to 8 mm of bone is all that may be required to give uniformly good results with arthroscopic DCE.

Figure A is an axial view depicting the AC joint ligaments

Incorrect Answers:
Answer 1: Injury to the anterior and superior AC ligaments would result in anterior instability of the distal clavicle
Answer 2: The coracoclavicular ligaments prevent superior displacement of the distal clavicle. Inferior instability is a rarely observed type of distal clavicle instability
Answer 4: The AC joint experiences rotational forces at baseline. Rotational instability is rarely observed
Answer 5: Superior instability may be observed with injury to the coracoclavicular (conoid and trapezoid) ligaments