Michael S. Todd and Winston J. Warme
DEFINITION
Acromioclavicular (AC) separations are relatively rare injuries that result in disruption of the AC complex.
Overall incidence of the injury is 3 to 4 per 100,000 in the general population, with up to 52% of cases occurring during sporting events.5
The degree of injury is based on the amount of force transmitted through the acromion to the distal clavicle and the surrounding deltotrapezial fascia.1,12,19
Increased force transmission leads to dissociation of the AC joint and tearing of the coracoclavicular ligaments.
Determination of the injury type will guide operative versus nonoperative management.12
ANATOMY
The AC joint is a diarthrodial joint composed of the medial acromial margin and the distal clavicle.
A fibrocartilaginous intra-articular disc between the two bony ends decreases contact stresses.12
Dynamic stability of the AC joint is provided by the trapezial fascia and the overlying anterior deltoid.
Static stability of the AC joint is provided by.
AC ligaments
The superior ligament provides the greatest restraint to anterior translation of the distal clavicle.
Anterior, posterior, and inferior ligaments add additional horizontal stability to the AC joint.
Coracoclavicular ligament.
Conoid: arises from the posteromedial aspect of the coracoid and inserts on the posteromedial clavicle
Measures about 2.5 cm long and 1 cm wide
Provides primary resistance against anterior and superior loading of the clavicle
Trapezoid: arises from the anterolateral coracoid just posterior to the pectoralis minor and attaches to the lateral or central clavicle
Measures about 2.5 cm long and 2.5 cm wide
Provides resistance against posterior loading of the clavicle
PATHOGENESIS
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).
The degree of injury to the AC joint, deltopectoral fascia, and coracoclavicular ligaments will determine the resultant deformity.
Most low-grade injuries involve only the AC joint and are often self-limited.
Severe arm abduction during the AC separation can result in subacromial or subcoracoid displacement of the distal clavicle.12
PATIENT HISTORY AND PHYSICAL FINDINGS
A complete physical examination of both upper extremities with the patient appropriately attired and in the upright position is standard.
Evaluation of the neck and a complete neurologic examination are essential, as higher-grade injuries may manifest with brachial plexus compromise.
Low-grade injuries will be tender to palpation at the AC joint, with mild elevation possible. Increased deformity is commonly seen as the injury grade increases, but acutely the deformity may be masked by swelling.
Methods for examining the AC joint include.
AC joint compression (shear) test: Isolated painful movement at the AC joint in conjunction with a history of direct trauma indicates AC joint pathology.
Cross-arm adduction test: Look for pain specifically at the AC joint. Pain at the posterior aspect of the shoulder or the lateral shoulder might indicate other pathology.
Paxino test: sometimes done in conjunction with bone scans to assess damage to AC joint
O'Brien test: Symptoms at the top of the joint must be confirmed by the examiner palpating the AC joint. Anterior glenohumeral joint pain suggests labral or biceps pathology.
Local point tenderness at the AC joint while the glenohumeral joint is kept still suggests localized AC joint pathology.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Standard shoulder radiographs can be useful for diagnosis, but overpenetrance may result in poor visualization of the AC joint.
An axillary view should be included to avoid missing a glenohumeral dislocation and to help assess anteroposterior (AP) translation of the clavicle.
FIG 1 • Zanca view of the acromioclavicular joint.
A 10- to 15-degree cephalic tilt view (Zanca) avoids superposition of the scapular spine and improves visualization of the AC joint. This also allows evaluation for loose bodies or small fractures that may be missed with standard views of the shoulder (FIG 1).12
Stress radiograph.
Standing views with 10 to 15 pounds of traction applied to the wrists are recommended by some authors to help distinguish the grade of injury because patients may guard with standard standing views.
Recent literature does not support the routine use of stress radiographs.21 They do not affect the decision-making process for operative versus nonoperative management.12,21 However, one AP view with both AC joints visible is helpful to account for normal variants and determine the degree of displacement.
DIFFERENTIAL DIAGNOSIS
Distal clavicle fracture
Acromial fracture
Glenohumeral dislocation
Sternoclavicular dislocation
Scapulothoracic dissociation
CLASSIFICATION
Rockwood (modification of Allman, Tossey, and Bannister's work) described six types of injuries to the acromioclavicular joint (Table 1).1,2,12,29
This classification scheme has proven to be effective for prognosis and treatment.
NONOPERATIVE MANAGEMENT
Types I and II
Most authors agree that nonoperative management is the treatment of choice for these incomplete injuries.1,12,16,20
A simple sling for comfort is used, with progression to range of motion as tolerated in 1 to 2 weeks.
Return to sports is authorized when the patient has painfree range of motion and normal strength.
Type III
This is more controversial, although conservative treatment is often successful.
Sling for comfort, range-of-motion exercises, and avoidance of contact sports for 6 to 8 weeks may suffice.
Padding of the residual deformity for contact athletes may be beneficial. Additional trauma may lead to the development of a higher-grade injury.
Types IV and VI are routinely treated operatively.
SURGICAL MANAGEMENT
Indication for surgery is an acute Rockwood type III or VI injury in an active patient unwilling to accept the cosmetic deformity and dysfunction of the affected shoulder.
The TightRope fixation system (Arthrex, Naples, FL) was originally designed for the treatment of syndesmotic injuries. It has two metal fixation buttons with a continuous loop of no. 5 FiberWire running between them.17
The technique allows for a quick and relatively simple arthroscopic fixation of acute, high-grade AC separations. Chronic injuries should have the coracoclavicular ligaments reconstructed with autologous or allograft tissue.
Preoperative Planning
Thorough evaluation of all radiologic studies to rule out associated fractures of the clavicle, coracoid, or glenoid is mandatory.
Films should be scrutinized and a careful physical examination performed to diagnose sternoclavicular or glenohumeral dislocations.
Positioning
Standard beach-chair position is used, with all bony and soft tissue prominences well padded.
The use of an arm positioner (McConnell Orthopaedics, Greenville, TX, or Tenet Medical Engineering, Calgary, Alberta) is optional.
Preparation is done in standard fashion. An arthroscopy drape is used.
TECHNIQUES
ESTABLISHING ANATOMY AND PORTALS
Anatomy is identified: coracoid, acromion, clavicle (length and width), AC joint.
Portals are marked: posterior, anterior inferior, and anterolateral.
The posterior portal is created for viewing 2 cm inferior and 2 cm medial to the posterolateral edge of the acromion in the “soft spot.”
Diagnostic arthroscopy with a 30-degree scope of the intra-articular space is routine.20
The subacromial space is entered from this portal using standard technique.
We do not find it necessary to move through the rotator interval to identify the coracoid base, although it is recommended in the technique guide.
A 70-degree scope may be helpful if the trans-interval technique is used.
The anterolateral portal is made using an “outside-in technique” in line with the lateral edge of the acromion and the coracoid as a working portal.
A 5- to 7-mm cannula is introduced to assist with pressure control.
CORACOACROMIAL LIGAMENT AND CORACOID PREPARATION
With the scope in the posterior portal, the anterolateral acromion and the coracoacromial (CA) ligament are identified. The CA ligament is preserved (TECH FIG 1A).
The CA ligament is followed to its attachment site on the coracoid (TECH FIG 1B).
Through the anterolateral portal an arthroscopic ablator or chondrotome is used to resect the subcoracoid bursa and allow better visualization of the inferior aspect of the coracoid and its base.
There is no need to remove soft tissue from the superior aspect of the coracoid (TECH FIG 1C).
The surgeon should be cautious when placing instruments medial to the coracoid because the scapular notch lies in close proximity. Injury to the neurovascular bundle is a possibility.
An 18-gauge spinal needle is used for localization and an “outside-in technique” is used to make the anteroinferior portal just lateral and slightly inferior to the coracoid. An 8.25-mm cannula is inserted.
The Adapteur Drill Guide C-Ring and Coracoid Drill Stop (Arthrex) is inserted through the anteroinferior portal under the base of the coracoid (TECH FIG 1D).
The surgeon should stay as far posterior, near the coracoid base, as possible, and central from a mediolateral standpoint.
A 1to 2-cm incision is made over the clavicle in line with the drill guide and the coracoid.
TECH FIG 1 • A. Coracoacromial ligament identification. B. Coracoid identification. C. Soft tissue resection of the coracoid. D. Coracoid drill stop placement. The base is hugged posterior.
GUIDE PIN PASSAGE
Under arthroscopic visualization with the clavicle reduced, a 2.4-mm guide pin is advanced through the center of the clavicle and coracoid. It is captured by the drill stop (TECH FIG 2A).
The guide pin is overreamed with a 4-mm cannulated reamer, using the drill stop to prevent plunging. The scope allows visualization of each step (TECH FIG 2B).
The guide pin is removed and the solid end of the Nitinol wire loop is passed antegrade through the cannulated reamer. It is grasped and removed out the anteroinferior portal with a push-and-pull technique (TECH FIG 2C,D).
TECH FIG 2 • A. Captured 2.4-mm guide pin. B. Captured 4-mm drill bit. C. Nitinol wire passage. D. Retrieval of Nitinol through the anteroinferior portal.
SUTURE PASSAGE
The TightRope comes fixed with two 2-0 FiberWires to lead the suture button through the bone tunnel and flip accordingly.
These are passed with the wire loop through the clavicle and coracoid and out the anteroinferior portal.
One suture strand should be colored purple with a marking pen for easier differentiation of the “lead” suture from the “flip” suture (TECH FIG 3A,B).
The TightRope button is passed and flipped when visualized with the arthroscope (TECH FIG 3C,D).
The upper extremity is then elevated and the AC joint is overreduced.
TECH FIG 3 • A. Colored “lead” suture. B. Suture button exits coracoid base. C. Button is flipped by pulling the trailing, uncolored suture. D. Reduced button on base of coracoid.
SUTURE TYING
Two or three square knots are placed over the cephalad suture button (TECH FIG 4A).
The suture ends should be left about 1 cm long to allow the knot to lie flat under the soft tissues (TECH FIG 4B).
For additional stability, the soft tissue capsule of the AC joint may be sutured, because this is an important component of AC stability.
Open versus arthroscopic AC resection should be considered, as the potential exists for the development of painful AC joint arthrosis; however, this is not routinely done.
The wounds are closed and dressed in the usual fashion.
TECH FIG 4 • A. Square knot superiorly. B. Suture ends are left long.
POSTOPERATIVE CARE
A sling is used for comfort and to slow down the patient for 4 weeks.
Range of motion of the elbow is permitted immediately, as are gentle Codman/pendulum exercises.
Gentle active motion below the shoulder level is permitted until the 6-week mark, at which time progression to full motion is authorized.
No heavy work or athletics are permitted for 3 months.
Postoperative radiographs are compared with radiographs made at the 6-week return visit.
COMPLICATIONS
Infection
Loss of reduction
Coracoid fracture11
Clavicle fracture
Suprascapular neurovascular bundle injury
OUTCOMES
The TightRope Fixation System is a relatively new system for treatment of acute AC separations. It is not intended for chronic injuries.
No long-term studies or prospective randomized trials are available.
Biomechanical data are available only for its syndesmotic use.18,19
ACKNOWLEDGMENTS
We thank John Morton, James Willobee, and Jeff Wyman from Arthrex, and the staff of the William Beaumont Army Medical Center Biomedical Research facility.
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