Approach to the Acromioclavicular Joint

Patient Position and Setup

The patient is positioned in the beach-chair or modified supine position with the head elevated 30-45 degrees. A small bump or rolled towel is placed under the ipsilateral scapula to protract the shoulder and improve access to the AC joint and coracoid. The arm is draped free to allow intraoperative stress testing of the AC joint and manipulation during reduction. The surgical field extends from the sternoclavicular joint medially to the deltoid insertion laterally and includes the coracoid process. A sterile tourniquet is rarely used for this approach. Intraoperative fluoroscopy or mini C-arm is positioned to allow AP, axillary, and Zanca views of the AC joint.

Key Landmarks

• AC joint: palpable as a step-off or tenderness point
• Distal clavicle: subcutaneous and easily palpated
• Coracoid process: palpable anteriorly approximately 2 cm inferior to the clavicle
• Acromion: lateral extension of the scapular spine
• Supraclavicular nerves: often palpable or visible through the skin in thin patients

Surface Anatomy and Incision Planning

The superior strap incision is centered directly over the AC joint and extends medially along the distal clavicle for 4-6 cm and laterally over the acromion for 2-3 cm. An alternative saber incision runs obliquely from the posterior distal clavicle anteriorly and inferiorly toward the coracoid. The incision is marked with the arm in slight abduction and forward flexion to relax the skin tension.

Bony Landmarks

• AC joint line
• Distal clavicle end
• Acromion lateral border
• Coracoid tip (anterior)

Soft Tissue Landmarks

• Supraclavicular nerve branches crossing the clavicle
• Deltoid anterior fibers
• Trapezius posterior fibers
• Pectoralis major insertion on the clavicle

The incision is made through skin and subcutaneous tissue, identifying and protecting or documenting the supraclavicular nerves as they cross the field.

Internervous Plane and Superficial Dissection

There is no true internervous plane in the superficial dissection because the deltotrapezial fascia is a confluence of the deltoid (axillary nerve) and trapezius (spinal accessory nerve) insertions. The fascia is incised in line with the skin incision, splitting the fibers rather than transecting them. This preserves the dynamic stabilizing function of the deltotrapezial complex.

Superficial Dissection Steps

1. Incise skin and subcutaneous fat
2. Identify and protect supraclavicular nerves (or document sacrifice)
3. Incise the deltotrapezial fascia in line with the incision
4. Elevate the fascia as a single layer from the clavicle and acromion
5. Tag the fascia edges with stay sutures for later repair

Deep Dissection

The AC joint capsule is opened superiorly to expose the articular disc (if present) and the distal clavicle articular surface. The capsule is elevated as a sleeve medially and laterally. To expose the coracoclavicular ligaments, the fascia is elevated from the clavicle working medially. The conoid tubercle is identified on the posterior clavicle. The trapezoid and conoid ligaments are visualized and protected unless reconstruction is planned. The coracoid base is exposed by retracting the deltoid anteriorly and the pectoralis minor medially. The lateral cord of the brachial plexus lies just medial to the coracoid and must be protected.

Danger Structures by Layer

Subcutaneous Layer

• Supraclavicular nerves (C3-C4): cross the clavicle 2-3 cm medial to AC joint. Injury causes anterior shoulder numbness. Protect when possible or document preoperative consent for sacrifice.

Fascial Layer

• Deltotrapezial fascia: the most critical structure for closure. Poor repair leads to instability.

Capsular Layer

• AC joint capsule: provides horizontal stability. Must be repaired or reconstructed.
• Articular disc: may be damaged in chronic cases.

Ligamentous Layer

• Conoid and trapezoid ligaments: exposed for reconstruction. The conoid attaches more posteriorly and medially.
• Coracoid attachments: short head of biceps, coracobrachialis, pectoralis minor - protect during coracoid exposure.

Deep Neurovascular

• Lateral cord of brachial plexus: lies medial to the coracoid base. Excessive medial retraction risks injury.
• Axillary nerve: at risk with inferior extension or coracoid drilling.
• Cephalic vein: may be encountered laterally in the deltopectoral interval if extended.

Procedures Performed Through This Approach

AC Joint Reconstruction (Acute or Chronic)

• Exposure of AC joint and CC ligaments
• Reduction of AC joint under direct vision and fluoroscopy
• CC ligament reconstruction with autograft, allograft, or synthetic device
• AC capsule repair or augmentation
• Deltotrapezial fascia closure is critical

Distal Clavicle Excision (Mumford Procedure)

• Exposure of AC joint
• Resection of 8-10 mm of distal clavicle with oscillating saw or burr
• Smooth the cut surface and confirm no residual bone
• Repair capsule and deltotrapezial fascia
• Check for residual AC joint impingement

AC Joint Fixation (Hook Plate or Other)

• Exposure for plate placement
• Reduction maintained while plate is applied
• Plate removal planned at 3-6 months to prevent acromial erosion

Extension of the Approach

Proximal Extension

• Extend medially along the clavicle for exposure of more proximal clavicle or for additional CC ligament work.

Distal Extension

• Extend laterally over the acromion or into the deltopectoral interval for combined procedures such as rotator cuff repair or shoulder arthroplasty.

Inferior Extension

• Limited inferior extension toward the coracoid is possible but the lateral cord and musculocutaneous nerve must be protected.

Closure

Meticulous layered closure is essential. The AC capsule is repaired with absorbable suture. The deltotrapezial fascia is closed with strong interrupted sutures, often reinforced with suture anchors if tissue quality is poor. Subcutaneous tissue is approximated and skin closed with absorbable or non-absorbable suture. A sling is applied postoperatively.