Orthopaedic Surgery - Acromioclavicular Joint Separation

Basics

Acromioclavicular joint separation is a common traumatic shoulder injury, particularly among physically active individuals who participate in contact sports. It most often results from a direct blow to the superior or superolateral aspect of the shoulder.

The injury occurs more frequently in males and may range from a mild sprain of the acromioclavicular joint capsule to complete disruption of the acromioclavicular and coracoclavicular ligaments with major displacement of the distal clavicle.

Stability of the acromioclavicular joint depends primarily on two ligamentous systems. The acromioclavicular ligaments provide mainly horizontal or anteroposterior stability, whereas the coracoclavicular ligaments provide vertical stability between the clavicle and scapula.

Rockwood Classification

The Rockwood classification is commonly used to describe acromioclavicular joint separations. It is based on the anatomical structures damaged and the degree and direction of distal clavicle displacement.

Types I and II mainly involve injury to the acromioclavicular joint capsule and ligament complex. Types III and higher involve more extensive disruption, including injury to the coracoclavicular ligaments.

Type I Injury

A type I injury consists of a sprain or partial injury of the acromioclavicular joint capsule and ligament.

There is no significant displacement of the distal clavicle, and radiographs usually appear normal.

The coracoclavicular ligaments remain intact.

Type II Injury

A type II injury involves more substantial disruption of the acromioclavicular capsule and ligament while the coracoclavicular ligaments remain intact or only mildly injured.

Radiographically, the coracoclavicular distance is increased by less than 25% compared with the opposite side.

There may be mild superior displacement of the distal clavicle, but gross deformity is uncommon.

Type III Injury

A type III injury involves complete disruption of both the acromioclavicular and coracoclavicular ligament complexes.

The distal clavicle appears displaced superiorly, with an increase in the coracoclavicular distance of approximately 25–100% compared with the contralateral side.

The apparent deformity is partly caused by the weight of the arm pulling the acromion and scapula downward relative to the clavicle.

A type III separation can usually be reduced temporarily by applying upward pressure beneath the arm.

Type IV Injury

A type IV injury is characterized by posterior displacement of the distal clavicle.

The clavicle may penetrate or become displaced through the trapezius muscle.

This injury is generally irreducible by simple upward pressure on the arm.

Posterior displacement is best appreciated clinically and on an axillary lateral radiograph.

Type V Injury

A type V injury represents a more severe version of a type III separation.

The coracoclavicular distance is increased by more than 100% compared with the opposite shoulder, sometimes reaching several times the normal distance.

There is significant disruption of the deltotrapezial fascia, and the distal clavicle may become prominent beneath the skin.

The distal clavicle may become incarcerated within the disrupted soft tissues, making the deformity irreducible.

Type VI Injury

A type VI injury is rare and involves inferior displacement of the distal clavicle.

The clavicle may become positioned beneath the acromion or coracoid.

Because of the severity and unusual direction of displacement, these injuries generally require operative treatment.

General Prevention

Complete prevention is difficult because most injuries occur suddenly during trauma.

Avoidance of high-risk contact sports or hazardous activities can reduce exposure to injury, although this is not practical for many athletes.

Appropriate protective equipment, proper tackling or falling techniques, and sports-specific conditioning may potentially reduce injury risk.

Epidemiology

Acromioclavicular joint separation occurs far more commonly in males, with a reported male-to-female ratio of approximately 8.5:1.

Around half of all injuries occur in individuals between 20 and 39 years of age.

Sporting activity is the most frequent mechanism of injury, particularly in contact and collision sports.

Among Rockwood classifications, type III injuries are among the most frequently encountered clinically significant separations.

Incidence

The overall reported incidence is approximately 1.8 injuries per 10,000 person-years.

Among athletes, the incidence is considerably higher and has been reported at approximately 9.2 per 1,000 person-years.

Rates vary depending on the type of sport and the degree of physical contact involved.

Risk Factors

The principal risk factor is participation in contact or collision sports.

Common high-risk activities include rugby, ice hockey, American football, and wrestling.

Male sex is also associated with a substantially greater incidence, likely reflecting patterns of participation in high-risk sporting activities.

Genetics

There is no recognized genetic predisposition to acromioclavicular joint separation.

The injury is traumatic and mechanical rather than inherited.

Etiology

The typical mechanism is a direct impact to the superolateral aspect of the shoulder, usually while the arm is adducted.

The force drives the acromion and scapula downward and medially while the clavicle remains relatively fixed.

Depending on the magnitude of the force, the acromioclavicular capsule, AC ligaments, coracoclavicular ligaments, and deltotrapezial fascia may fail sequentially.

Associated Conditions

ACJ separation is usually an isolated injury but may occasionally occur together with more severe injuries around the shoulder girdle.

A simultaneous sternoclavicular dislocation and ACJ injury can produce a so-called bipolar clavicle injury.

An associated scapular fracture can create a floating shoulder, particularly when disruption of the superior shoulder suspensory complex is present.

Rotator cuff contusion may also accompany the acute trauma.

Diagnosis

Signs and Symptoms

Patients usually develop immediate pain around the superior aspect of the shoulder.

Shoulder movement, particularly elevation and cross-body activity, typically increases pain.

Swelling and bruising may be present over the distal clavicle and ACJ.

Higher-grade injuries may produce an obvious deformity with prominence of the distal clavicle.

Some patients also report neck discomfort, numbness, or tingling, although major neurologic injury is uncommon.

Physical Examination

Type I and II injuries generally produce localized swelling and tenderness over the ACJ without major visible deformity.

Pain is often reproduced by cross-body adduction of the affected shoulder.

Type III and higher injuries may demonstrate obvious prominence of the distal clavicle.

The contour of the injured shoulder should always be compared with the opposite side.

Reducibility

The distinction between type III and type V injuries can be clinically important.

In a type III separation, applying upward pressure beneath the arm may temporarily reduce the deformity.

In a type V injury, reduction is usually not possible because the distal clavicle may be trapped within disrupted deltotrapezial tissue.

This distinction can influence treatment planning.

Type IV Examination Findings

A type IV injury may present with posterior prominence or protrusion of the distal clavicle.

The posterior displacement may be difficult to appreciate on a standard anteroposterior view, making clinical inspection and an axillary radiograph particularly important.

Neurovascular Examination

A complete neurovascular examination should be performed in all patients.

Although associated neurovascular injuries are uncommon, distal pulses, capillary refill, motor function, and sensation should be documented.

The remainder of the upper extremity should also be inspected and palpated to exclude additional injuries.

Stability Assessment

Anteroposterior and vertical stability of the acromioclavicular joint should be assessed gently.

The examiner should evaluate whether the distal clavicle is excessively mobile relative to the acromion.

In the acute setting, pain may make a detailed assessment of the rotator cuff, labrum, or biceps tendon difficult.

These structures may need reassessment after the acute pain subsides.

Imaging

Anteroposterior Radiographs

An anteroposterior radiograph of the affected ACJ is part of the initial evaluation.

The position of the distal clavicle relative to the acromion and the coracoclavicular distance should be assessed.

Comparison with the opposite shoulder can be particularly useful because normal anatomical measurements vary between individuals.

Zanca View

A Zanca view is commonly used for better visualization of the ACJ.

This radiograph is obtained with approximately 15° of cephalad angulation and provides a clearer assessment of the distal clavicle, acromion, and joint space.

It can help quantify superior displacement in type III and type V injuries.

Axillary Lateral View

An axillary lateral radiograph is important for identifying posterior displacement of the distal clavicle.

This view is particularly useful when a type IV injury is suspected.

Failure to obtain an axillary view can result in posterior displacement being overlooked.

Contralateral Comparison

An anteroposterior image of the opposite ACJ may be obtained to compare the coracoclavicular distance.

The coracoclavicular distance is measured from the superior surface of the coracoid to the inferior border of the clavicle.

The percentage increase compared with the uninjured side helps determine the Rockwood grade.

Additional Radiographs

Radiographs of the entire clavicle, shoulder, or scapula should be obtained when associated injury is suspected.

These images help exclude clavicle fracture, scapular fracture, coracoid fracture, shoulder dislocation, and other injuries.

A complete clavicle radiograph is particularly important when a bipolar clavicle injury is suspected.

Weighted Radiographs

Weighted stress radiographs were historically used to exaggerate displacement and distinguish lower-grade from higher-grade injuries.

However, these studies are uncomfortable and are generally not recommended routinely.

Some clinicians may still use them selectively when attempting to differentiate a type III from a type V injury.

Radiographic Appearance by Type

Type I and many type II injuries may appear normal or nearly normal on routine radiographs.

Type III injuries demonstrate approximately 25–100% increase in coracoclavicular displacement relative to the opposite side.

Type V injuries may demonstrate approximately 100–300% displacement.

Type IV injuries are defined by posterior displacement of the distal clavicle, best demonstrated on an axillary view.

CT and MRI

Computed tomography and MRI are not routinely required for an uncomplicated ACJ separation.

CT may be useful when associated fractures, complex shoulder girdle injuries, or a bipolar clavicle injury are suspected.

MRI is rarely necessary in the acute setting but may be considered when persistent symptoms suggest associated rotator cuff, labral, or other soft-tissue pathology.

Pathological Findings

Histopathological examination is not routinely required for this injury.

Diagnosis is established through clinical examination and imaging.

Differential Diagnosis

Important differential diagnoses include clavicle fracture, particularly a distal clavicle fracture, coracoid fracture, rib fracture, scapular fracture, shoulder dislocation, sternoclavicular dislocation, and proximal humeral fracture.

A coracoid fracture may mimic an ACJ separation, but the coracoclavicular relationship may remain intact.

A radiograph of the entire clavicle should be obtained when concern exists for a simultaneous sternoclavicular and acromioclavicular injury.

CT may be required when complex fracture patterns are suspected.

Treatment

General Principles

Treatment depends on the Rockwood grade, patient age, activity level, functional requirements, occupation, lifestyle, and individual goals.

Correct identification of the injury grade is important because management differs considerably between low-grade and high-grade injuries.

Type I and II Injuries

Type I and II injuries are generally treated nonoperatively.

Treatment includes short-term sling immobilization, analgesia, ice, and activity modification.

Movement is gradually restored as pain decreases.

Most patients recover good function without surgery.

Type III Injuries

Treatment of type III ACJ separation remains controversial.

Many patients can be treated successfully without surgery, especially those with lower physical demands.

Surgery may be considered in selected individuals with persistent pain, significant functional impairment, high occupational demands, cosmetic concerns, or elite athletic requirements.

The treatment decision should therefore be individualized.

Type IV to VI Injuries

Types IV, V, and VI are generally treated surgically because of marked displacement, soft-tissue disruption, instability, and difficulty obtaining or maintaining satisfactory reduction nonoperatively.

Operative stabilization aims to restore the relationship between the distal clavicle and scapula while allowing ligament healing or reconstruction.

Physical Therapy

Physical therapy is not universally required for minor injuries but may help patients regain motion, strength, and shoulder function.

For nonoperatively treated injuries, gentle range-of-motion exercises may begin approximately 2–4 weeks after injury, depending on pain and stability.

Initial exercises may include pendulum movements and pulley-assisted motion.

The program is gradually advanced toward full range of motion and strengthening over the following weeks.

Postoperative Rehabilitation

Physical therapy is routinely incorporated after surgical stabilization or reconstruction.

The exact protocol depends on the operative technique and surgeon preference.

Rehabilitation generally progresses from an initial period of protection to passive and active-assisted motion, followed by active movement, strengthening, and eventual return to sport or heavy activity.

Medication

First-line medications include nonsteroidal anti-inflammatory drugs and acetaminophen.

These medications can help control pain during the acute phase.

Short courses of stronger analgesics, including tramadol or other opioid medications, may occasionally be used for severe acute pain.

When prescribing these agents, the patient’s age, medical conditions, concurrent medications, and overall risk profile should be considered.

Sling and Local Measures

A sling is commonly used initially to support the arm and reduce traction on the injured ACJ.

Ice can help control swelling and pain during the early period.

Sleeping with the upper body elevated or in a reclined position may improve comfort during the first several days after injury.

Surgical Management

Surgery is generally recommended for type IV, V, and VI injuries, and it may be considered for selected type III injuries.

Surgery can also be performed for chronic type III or higher injuries when persistent pain, weakness, instability, or functional disability remains despite adequate nonoperative treatment.

Operative Techniques

A variety of operative methods are available.

Techniques may involve open reduction and internal fixation using plates, screws, suture-based devices, or other implants.

The objective is to restore anatomical or near-anatomical alignment and maintain stability while the damaged ligaments heal.

Some constructs permit earlier controlled shoulder motion.

Ligament Reconstruction

Modern reconstruction frequently involves restoration of the coracoclavicular ligament complex.

Autograft or allograft tendon tissue may be used to reconstruct the stabilizing ligaments.

Coracoid-based fixation devices are also commonly incorporated to restore vertical stability.

Technique selection depends on whether the injury is acute or chronic, the surgeon’s experience, and the quality of the surrounding tissues.

Chronic Injuries

Chronic ACJ separations can be more difficult to treat because the native ligaments have limited healing potential after a prolonged period.

Reconstruction may therefore require tendon graft augmentation or other biological reconstruction rather than simple fixation.

Persistent pain and instability are the most common indications for delayed surgery.

Follow-Up

Patients should be reviewed periodically to ensure that pain is improving, shoulder motion is recovering, and the alignment of the ACJ remains stable.

Although alignment usually remains unchanged after the initial injury, follow-up is important because an injury initially thought to be type I or II may occasionally prove to be of a higher grade.

Prognosis

The overall prognosis is generally good, particularly for low-grade injuries.

Athletes lose an average of approximately 18 days from sporting activity, although recovery varies significantly with injury severity.

Low-grade injuries may result in approximately 10 days of lost activity, whereas high-grade injuries may require approximately 64 days or longer before return.

Return to Sport

Return to sporting activity should be based on recovery of painless motion, strength, stability, and sport-specific function rather than on time alone.

Higher-grade injuries generally require substantially longer rehabilitation than type I or II injuries.

Some athletes with high-grade injuries elect to undergo surgical stabilization or reconstruction.

Surgical Outcomes

Good or excellent outcomes can be achieved after operative treatment when anatomical stability is restored and complications are avoided.

However, surgical treatment has a notable complication rate.

Some studies have reported overall complication rates approaching 27%, emphasizing the importance of careful patient selection and surgical technique.

Complications

Potential complications include infection, loss of reduction, clavicle fracture, graft rupture, adhesive capsulitis, implant failure, painful hardware, chronic instability, and post-traumatic ACJ arthritis.

Persistent deformity may also remain after both surgical and nonsurgical treatment, even when shoulder function is satisfactory.

Loss of Reduction

Loss of reduction is one of the more important postoperative complications.

It may result from failure of fixation, graft stretching, recurrent trauma, or inadequate biological healing.

Minor radiographic loss of alignment does not always produce symptoms, but major recurrent displacement may lead to pain or instability.

Hardware-Related Problems

Internal fixation devices may become prominent or painful, particularly in thin individuals.

Implant breakage, migration, or irritation may occasionally require additional surgery for removal.

The risk varies according to the reconstruction method used.

Chronic Instability and Arthritis

Residual horizontal or vertical instability may persist after treatment.

Abnormal joint mechanics can contribute to later development of post-traumatic acromioclavicular joint arthritis.

Some patients develop chronic pain despite satisfactory radiographic alignment.

Patient Monitoring

Patients should be followed at regular intervals during recovery.

Clinical assessment should include pain severity, shoulder range of motion, strength, joint stability, deformity, and ability to perform daily or sporting activities.

Radiographs may be repeated when there is concern about increasing displacement, loss of fixation, or an initially underestimated injury grade.

The main goals of follow-up are to ensure satisfactory pain control, progressive recovery of motion and strength, and maintenance of appropriate ACJ alignment.