Arthroscopic Acromioclavicular Joint Stabilization

Andrew Pastor

Winston J. Warme

DEFINITION

Acromioclavicular (AC) separations are relatively rare injuries that result in disruption of the AC joint complex.
Overall incidence of injury is 3 to 4 per 100,000 in the general population, with up to 52% occurring during sporting events.⁴
The degree of injury is based on the amount of force transmitted through the acromion to the distal clavicle and the surrounding deltotrapezial fascia.¹,¹⁸,²⁴
Increasing force leads to dissociation of the AC joint and tearing of the coracoclavicular ligaments.
Determination of the injury type will indicate operative versus nonoperative management.¹⁸

ANATOMY

The AC joint is a diarthrodial joint composed of the medial acromial margin and distal clavicle.
A fibrocartilaginous intra-articular disc between the two bony ends decreases contact stresses.¹⁷,¹⁸,¹⁹
Dynamic stability of the AC joint is provided by the trapezial fascia and the overlying anterior deltoid.
The AC joint is statically stabilized by the following:
- AC ligaments
  - Anterior and posterior capsular thickenings
  - Superior and inferior capsular thickenings
- Coracoclavicular ligaments
  - Conoid: arises from the posteromedial aspect of the coracoid and inserts on the posteromedial clavicle
    - Measures up to 2.5 cm long and 1 cm wide⁵,¹⁸,²⁰
    - Provides resistance to anterior and superior loading⁶,⁸,¹³,¹⁴
  - Trapezoid: arises from the anterolateral coracoid just posterior to the pectoralis minor and attaches to the lateral/central clavicle
    - Measures up to 2.5 cm long and 2.5 cm wide⁵,¹⁸,²⁰
    - Provides resistance to compression and posterior loading⁶,⁸,¹⁴

PATHOGENESIS

Mechanism of Injury

AC separations are the result of a direct force to the lateral aspect of the shoulder with the arm adducted (ie, fall on point of the shoulder).¹,⁸,¹⁰,¹⁴,¹⁸,¹⁹,²⁴
The degree of injury to the AC joint, deltotrapezial fascia, and/or coracoclavicular ligaments will determine the resultant deformity.
Most low-grade injuries involve only the AC ligaments and are often self-limited.
Severe arm abduction can result in subacromial or subcoracoid displacement of the clavicle.¹⁸
Pain localized to the AC joint and a visual deformity will be present with high-grade injuries.

PHYSICAL FINDINGS

A complete physical examination of both upper extremities with the patient appropriately attired and in the upright position is critical.
Evaluation of the neck is also important as with any upper extremity examination.
Complete neurologic examination is essential as higher grade injuries may manifest brachial plexus compromise.
Low-grade injuries will be tender to palpation at the AC joint, with mild elevation possible. Increased deformity will be seen as injury grade increases, but acutely may be masked by swelling.

Classification

Rockwood (modification of Allman, Tossy, and Bannister’s work) described six types of injuries to the AC joint.¹,²,¹⁸,²⁴
This classification scheme has proven to be effective for prognosis and treatment.
- Type I: The AC and coracoclavicular ligaments are intact.
- Type II: The AC ligament is completely torn but the coracoclavicular ligaments are intact with partial subluxation of the AC joint.
- Type III: complete disruption of the AC ligaments and coracoclavicular ligaments. Degree of separation is up to 100% of the coracoclavicular interval.
- Type IV: posterior displacement of the clavicle through the trapezius muscle
- Type V: severe displacement with 100% to 300% increase in coracoclavicular interval (Bannister III-C); includes injury to the deltotrapezial fascia
- Type VI: inferior displacement of the clavicle to a subacromial or subcoracoid position