What is the acromioclavicular joint?
The acromioclavicular (AC) joint is located on the top of the shoulder, where the acromion (top of the shoulder blade) meets the clavicle (collar bone). The joint is supported by a joint capsule and ligaments, including the acromioclavicular and coracoclavicular ligaments. These structures help to provide stability and limit movement in the joint. The AC joint is important for shoulder flexion and abduction and plays a key role in the overall structure and function of the shoulder (Wong et al 2022).
What are the causes?
The most common cause of an AC joint injury is a direct blow to the shoulder or repetitive overhead lifting. These types of injuries can occur when the acromion is pushed downwards towards the clavicle, or when an upward force is applied to the humerus. This can happen when an individual falls onto an outstretched arm with the shoulder flexed. In general, AC joint injuries are more likely to occur when the arm is close to the body and the shoulder is flexed.
AC joint symptoms
A physiotherapist may suspect an AC ligament sprain if the individual presents with a visible lump on the shoulder, swelling and tenderness over the AC joint, reduced shoulder strength and range of motion, and pain on top of the shoulder that is worsened by raising the arms overhead, moving the arm across the body, or placing the arm behind the back. These symptoms may indicate a sprain of the AC ligaments
Lump on the right AC joint indicating AC Sprain
There are six types of AC joint Injuries which vary based on the degree of injury and tissue involvement
Type 1: Partial Tear of AC ligament, with no involvement of the coracoclavicular ligament or shoulder muscles
Type 2: Complete tear of AC Ligament with a partial tear of the coracoclavicular ligament, but no muscular involvement
Type 3: Complete tear of all the involved ligaments, with no muscular involvement
Type 4: Complete tear of all the involved ligaments, with involvement of the distal end of the clavicle displaced posteriorly into or through the trapezius
Type 5: Complete tear of all the involved ligaments, but has a high chance of the deltoid and trapezius being detached from the distal clavicle
Type 6: inferior displacement of the clavicle with a range of muscular involvement
There are two main interventions for AC joint injuries: surgical and non-surgical management. The type of injury will determine which approach is best. Historically, non-surgical management was recommended for type 1 and 2 AC joint injuries. However, a study published in 2021 found that individuals with these injuries may have reduced shoulder function after seven years (Verstift et al. 2021). This finding should be interpreted with caution, as it may not be clinically meaningful.
In contrast, surgical management was typically recommended for type 4 to 6 AC joint injuries, while type 3 injuries had mixed recommendations. In 2015, the Canadian Orthopaedic Trauma Society conducted a large randomized clinical trial showing that non-surgical management had superior short-term results for the shoulder. Furthermore, there was no significant difference in the long term for type 3, 4, and 5 injuries. A study by Murray et al. in 2018 also found similar results, concluding that surgery offers no functional benefit over non-operative treatment at one year for type 3 and 4 AC joint disruptions.
A Cochrane review published in 2019 looked at the available research on this topic and concluded that “surgical intervention may have no additional benefits in terms of function, return to former activities and quality of life at one year.” The review also noted that “while these results favour a non-operative approach, the possible benefits of surgery cannot be ruled out, including for more complex, high-grade injuries.”
Based on this evidence, non-surgical management should be the first line of treatment for AC joint injuries. This approach should be followed for 4-6 months. If there is no improvement in pain or function during this time, surgical intervention may be considered
DASH Score for AC joint Injuries (Canadian Orthopaedic society. 2015)
The rehab process for an AC joint injury will typically be broken down into two phases, with a third optional phase for returning to sports.
Phase 1: Manage symptoms and regain range of motion and strength
The first phase of rehabilitation will focus on reducing pain and swelling and restoring the range of motion and strength to the injured joint. This may involve limiting activities that cause pain, modifying daily activities to decrease the demand on the shoulder, and performing exercises to improve range of motion and strength. The goal of this phase is to allow the individual to perform activities of daily living without pain or discomfort.
Phase 2: Progress range of motion and strength, and prepare for desired activities
The second phase of rehab will focus on progressing the range of motion and strength of the shoulder and preparing the individual for their desired activities. This may involve more advanced exercises, such as plyometrics or sport-specific training. The length of this phase will vary depending on the individual’s goals and progress.
Phase 3: Gradual return to sport and prepare for higher-level demands
The optional third phase of rehab is for individuals who are planning to return to high-level activities, such as sports. This phase will focus on preparing the shoulder for the increased demands of these activities, through exercises that improve power and stability. This phase will involve gradually increasing the intensity and complexity of the exercises and may include a return to sport program.
In summary, AC joint injuries, also known as shoulder separations, are injuries to the acromioclavicular joint of the shoulder. These injuries can range in severity and are typically managed conservatively with a rehab program that progresses range of motion and strength. For individuals who wish to return to high-level activities, additional exercises may be necessary to prepare the shoulder for the increased demands.
- Wong M, Kiel J. Anatomy, Shoulder and Upper Limb, Acromioclavicular Joint. [Updated 2022 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.Available from: https://www.ncbi.nlm.nih.gov/books/NBK499858/
- Verstift DE, Kilsdonk ID, van Wier MF, Haverlag R, van den Bekerom MPJ. Long-term Outcome After Nonoperative Treatment for Rockwood I and II Acromioclavicular Joint Injuries. Am J Sports Med. 2021 Mar;49(3):757-763. doi: 10.1177/0363546520981993. Epub 2021 Jan 13. PMID: 33439041.
- Canadian Orthopaedic Trauma Society. Multicenter Randomized Clinical Trial of Nonoperative Versus Operative Treatment of Acute Acromio-Clavicular Joint Dislocation. J Orthop Trauma. 2015 Nov;29(11):479-87. doi: 10.1097/BOT.0000000000000437. PMID: 26489055.
- Murray IR, Robinson PG, Goudie EB, Duckworth AD, Clark K, Robinson CM. Open Reduction and Tunneled Suspensory Device Fixation Compared with Nonoperative Treatment for Type-III and Type-IV Acromioclavicular Joint Dislocations: The ACORN Prospective, Randomized Controlled Trial. J Bone Joint Surg Am. 2018 Nov 21;100(22):1912-1918. doi: 10.2106/JBJS.18.00412. PMID: 30480595.
- Tamaoki MJS, Lenza M, Matsunaga FT, Belloti JC, Matsumoto MH, Faloppa F. Surgical versus conservative interventions for treating acromioclavicular dislocation of the shoulder in adults. Cochrane Database of Systematic Reviews 2019, Issue 10. Art. No.: CD007429. DOI: 10.1002/14651858.CD007429.pub3. Accessed 09 December 2022.