AC Joint Sprains in Rugby Union: The Shoulder Bump That Keeps Coming Back

May 21

The bump on top of the shoulder is one of the most recognisable injuries in rugby. A player falls on the tip of the shoulder, or takes a direct hit, and the acromioclavicular (AC) joint, the small joint at the top of the shoulder where the clavicle meets the acromion, is damaged.

Most players are told ‘you’ve separated your shoulder’, walk off, and then come back too early because it looks like just a bruise. The joint is more complex than it looks.

The Anatomy

The AC joint is held together by two sets of ligaments: the acromioclavicular ligaments, which stabilise the joint directly, and the coracoclavicular ligaments (the trapezoid and conoid), which suspend the clavicle from the coracoid process of the scapula below.

When the joint is loaded in a fall, the first structure to fail is the acromioclavicular ligament. If the force continues, the coracoclavicular ligaments follow. It is the status of the coracoclavicular ligaments that determines the grade of injury and drives the treatment decision.

Grading (Rockwood Classification)

Grade 1: AC ligament sprain only. No displacement. Return in 1-2 weeks. Grade 2: AC ligament rupture, intact coracoclavicular ligaments. Mild elevation of the clavicle. 3-6 weeks. Grade 3: Both sets of ligaments ruptured. Visible step deformity at the AC joint. Conservative management is often still appropriate. 6-12 weeks. Grade 4-6: Severe posterior or inferior displacement. Surgery typically indicated.

The Grade 3 Dilemma

Grade 3 AC joint injuries are controversial in rugby. The visible step deformity concerns players and parents, but the functional outcomes of conservative management versus surgery for Grade 3 injuries are similar in most studies for non-throwing athletes.

Current best practice for Grade 3 injuries in contact athletes is conservative management with structured rehabilitation in the first instance, reserving surgery for persistent instability or those with high overhead demands.

Treatment

Phase 1 (1-2 weeks): Sling for comfort, ice, gentle pendulum exercises, grip and elbow movement. Phase 2 (2-4 weeks):Progressive shoulder range of motion, rotator cuff and scapular activation below pain level. Phase 3 (4-8 weeks):Strengthening through full range, pressing and pulling progressions. Phase 4 (6-12 weeks): Rugby-specific loading: tackling technique, rucking position, overhead work.

Return to Contact

Criteria: full pain-free range of motion, symmetric strength testing, and successful completion of contact-specific drills without pain. Shoulder padding can help during the return phase by absorbing impact at the AC joint.

Preventing Recurrence

There is no strong evidence for preventing re-injury at the AC joint once it has been damaged, since the structural changes persist. Managing load, maintaining rotator cuff and scapular strength, and using appropriate shoulder protection reduces the impact forces the joint is exposed to.

Want to understand this injury at a deeper anatomical level? The Club Physio’s online anatomy course breaks down the structures, biomechanics, and load patterns behind the most common sports injuries. Built for athletes and therapists alike. [Explore the course at theclubphysio.com.au]

josh zoppo