Shoulder • Progressive Sports Medicine
AC Joint Injuries & Weight Lifter’s Shoulder
The small joint at the top of your shoulder does big work, connecting a free-hanging, mobile limb to the rest of the skeleton. Sprains, arthritis and bone stress (Weight Lifter’s Shoulder) each behave differently, and most are managed without surgery.
Anatomy
The acromioclavicular (AC) joint
The acromioclavicular joint is the joint between the end of the collar bone and the tip of the wing bone. It forms an apex at the top part of the shoulder, and it is an important connection between a free-hanging, mobile limb and the rest of the skeleton.
Inside the joint sits a fibrocartilaginous disc that normally cushions it, helping transmit and offload the forces that cross the joint every time you push, pull, carry or lift.
AC joint injuries explained ▶ Watch on YouTube
Acute injury
AC joint sprains and separations
The ligaments that hold the joint together can be damaged, often from direct trauma such as a fall onto the point of the shoulder:
Grade 1
Stable
Involves the ligaments of the AC joint itself, and the joint remains stable.
Grade 2
Partial
Additional disruption of the ligaments that hold the collarbone from lifting.
Grade 3
Unstable
Complete disruption of these ligaments, and the joint can become unstable.
Most of these injuries do not require surgery, but they can lead to long-term problems with shoulder function, and individual assessment is recommended to guide best management.
Chronic change
AC joint arthritis
In some cases, the disc inside the joint that normally cushions it will degrade, and the joint becomes arthritic, with loss of cartilage and the formation of bone spurs.
Arthritis on a scan is not a sentence. One study showed 90% of patients with asymptomatic AC joint arthritis, seen incidentally on MRI for other shoulder issues, remained symptom free at 7 years of follow-up.
Frigg A, et al. Seven-year course of asymptomatic acromioclavicular osteoarthritis diagnosed by MRI. J Shoulder Elbow Surg 2019;28:e344–e351. doi:10.1016/j.jse.2019.04.004
The bone stress injury
Weight Lifter’s Shoulder (AC joint osteolysis)
A condition that tends to be quite consistently painful, and can be very debilitating, is AC joint osteolysis, otherwise known as Weight Lifter’s Shoulder. This is where the end of the collar bone becomes painful and the inner structure of the bone starts to break down.
It is a kind of bone stress injury that happens in people who overload their shoulder in the horizontal pushing and pulling plane. However, the resorption phase seems to continue unopposed for months, and it is thought to be related to issues with limited blood flow in the area. The bone remodelling diagram below shows the normal cycle: in osteolysis, the resorption stage keeps running while formation cannot keep up.
What we see clinically is a very warm, tender edge of the collar bone, a moth-eaten appearance of the end of the clavicle on X-rays (circled in the image below), and bone bruising on MRI.
Treatment
How AC joint problems are treated
Treatment depends on which AC joint problem you have, and an accurate diagnosis comes first: examination with direct assessment of the joint, X-rays, and point-of-care ultrasound, with MRI when bone stress is suspected.
Acute sprains are managed with short-term support and pain control, then progressive restoration of strength and control of the shoulder girdle. Higher grade, unstable separations warrant an individual discussion, since decisions depend on your grade, occupation and sporting demands.
Weight Lifter’s Shoulder is treated like the bone stress injury it is: the provocative loads (heavy horizontal pressing and pulling) are modified to let the bone settle, while training continues around it. Technique and programming adjustments matter, and load is then rebuilt gradually. Because ongoing provocation can keep the resorption phase going for months, an early structured plan is the fastest way back to full training.
Symptomatic AC arthritis is managed with activity modification, strengthening, and short courses of anti-inflammatories. When pain blocks progress, a corticosteroid injection into the joint, delivered under ultrasound guidance, can settle it and open a window for rehabilitation.
Surgery is uncommon. It is reserved for recalcitrant cases that have genuinely failed non-surgical care, or for specific unstable separations, and is a decision made with a surgeon after individual assessment.
Common questions
AC joint FAQs
Usually not. Most AC joint sprains, including many higher grade injuries, are managed without surgery, though they can leave a visible bump. Because these injuries can lead to longer term problems with shoulder function, an individual assessment is recommended to guide the best management for your grade of injury and your activity demands.
Not necessarily. AC joint arthritis seen on imaging is often completely silent: one study found 90% of patients with asymptomatic AC arthritis picked up incidentally on MRI remained symptom free at 7 years of follow-up. The examination, especially direct tenderness over the joint, matters more than the scan appearance.
It is AC joint osteolysis: the end of the collar bone becomes painful and the inner structure of the bone starts to break down. It behaves like a bone stress injury, occurring in people who overload the shoulder in the horizontal pushing and pulling plane, with a warm, tender collarbone edge, a moth-eaten appearance on X-ray and bone bruising on MRI.
Training usually needs modification rather than complete rest. The provocative loads are heavy horizontal pressing and pulling, so these are reduced or adjusted while the bone settles, then reintroduced gradually. Because the bone resorption phase can continue for months if it keeps being provoked, an early, structured plan protects both your shoulder and your training continuity.
Injections are an adjunct when pain is blocking rehabilitation, delivered under ultrasound guidance for accuracy. Surgery is uncommon and reserved for recalcitrant cases, such as ongoing osteolysis or symptomatic arthritis that has failed a proper course of non-surgical care, or unstable higher grade separations in specific circumstances.
Pain at the top of your shoulder with pressing or lifting?
Our Sport and Exercise Physicians in Leichhardt can work out whether it’s a sprain, arthritis or bone stress, and build a plan that keeps you training while it settles.
This page provides general information only and is not a substitute for personalised medical advice. Please consult a qualified health practitioner for assessment of your individual circumstances.
Key references
- Frigg A, et al. Seven-year course of asymptomatic acromioclavicular osteoarthritis diagnosed by MRI. J Shoulder Elbow Surg 2019;28:e344–e351. doi:10.1016/j.jse.2019.04.004
- Mall NA, et al. Degenerative joint disease of the acromioclavicular joint: a review. Am J Sports Med 2013;41:2684–2692. doi:10.1177/0363546513485359
- Zawadsky M, et al. Osteolysis of the distal clavicle: long-term results of arthroscopic resection. Arthroscopy 2000;16:600–605. doi:10.1053/jars.2000.5875