Shoulder — Surgical Anatomy and Approaches
Introduction
The shoulder girdle, comprising the glenohumeral joint, the acromioclavicular joint, the sternoclavicular joint, and the scapulothoracic articulation, provides the greatest range of motion of any joint in the body — a functional capacity achieved through a substantial sacrifice of bony stability in favor of soft-tissue stabilization. The surgical anatomy of the shoulder reflects this design: a relatively shallow glenoid, a generous capsule with reinforcing ligaments, the rotator cuff providing dynamic stability, and the deltoid and periscapular muscles powering motion. The orthopedic surgeon’s approaches to the shoulder must navigate this complex muscular envelope while protecting the axillary nerve (the most vulnerable nerve in shoulder surgery), the musculocutaneous nerve, and the brachial plexus and axillary vessels in the deeper structures. This chapter, drawing on Orthopaedic Surgical Approaches, Netter’s Concise Orthopaedic Anatomy, and Gray’s Anatomy, addresses the surgical anatomy and principal approaches to the shoulder.
Bony and Articular Anatomy
The glenohumeral joint is a ball-and-socket articulation between the relatively small, slightly retroverted glenoid (typical retroversion 5 to 7 degrees, with inferior tilt of about 4 to 5 degrees) and the substantially larger humeral head (covered by approximately 120 degrees of articular surface). The size mismatch produces the characteristic mobility- stability trade-off; only 25 to 30 percent of the humeral head is in contact with the glenoid at any time. The glenoid labrum is a fibrocartilaginous ring around the glenoid that deepens the socket by approximately 50 percent and provides attachment for the capsular ligaments and the long head of the biceps tendon. The acromion forms the lateral roof of the joint, with anatomical variants relevant to surgery — the acromial morphology classified as type I flat, type II curved, type III hooked (Bigliani) is associated with rotator cuff impingement, particularly in type III. The os acromiale is a failure of fusion of the acromial ossification center (occurring in 1 to 8 percent of the population), with the meso-acromion (between the middle and posterior acromial ossification centers) being the most common type and a recognized cause of impingement and rotator cuff pathology. The coracoid process projects anteriorly and provides attachment for the conjoint tendon (short head of biceps and coracobrachialis), the coracoacromial ligament, the coracoclavicular ligaments (conoid and trapezoid), and the coracohumeral ligament. The coracoid is the source of the bony graft in the Latarjet procedure for glenoid bone loss (Topic Trauma-12). The clavicle completes the shoulder girdle, articulating with the acromion laterally (AC joint) and the sternum medially (SC joint). Its anatomy and pathology were addressed in Topic Trauma-11.
Muscular Anatomy
Rotator Cuff The rotator cuff comprises four muscles forming a cuff around the humeral head: Supraspinatus: Originates from the supraspinous fossa of the scapula, passes under the acromion, and inserts on the superior facet of the greater tuberosity. Function: initial 30 degrees of abduction; participates with deltoid throughout abduction range. Most commonly torn of the rotator cuff muscles. Infraspinatus: Originates from the infraspinous fossa, inserts on the middle facet of the greater tuberosity. Function: external rotation of the shoulder. Teres minor: Originates from the lateral border of the scapula, inserts on the inferior facet of the greater tuberosity. Function: external rotation, assists infraspinatus. Subscapularis: Originates from the subscapular fossa (anterior surface of the scapula), inserts on the lesser tuberosity. Function: internal rotation; the principal anterior stabilizer of the shoulder. The rotator cuff muscles function principally to compress the humeral head into the glenoid, providing dynamic stability, while permitting the deltoid to generate the principal abduction force. Deltoid The deltoid is the principal motor of shoulder abduction beyond the initial range provided by the supraspinatus. It has three heads: Anterior (clavicular) deltoid: From the lateral third of the clavicle, producing flexion and internal rotation. Middle (acromial) deltoid: From the acromion, producing abduction. Posterior (spinous) deltoid: From the spine of the scapula, producing extension and external rotation. The deltoid inserts on the deltoid tuberosity of the humerus. The axillary nerve innervates the deltoid (and teres minor) and runs through the quadrilateral space (bounded by teres minor superiorly, teres major inferiorly, long head of triceps medially, and humeral shaft laterally) — passing approximately 5 to 7 cm distal to the acromion along the deltoid undersurface, the critical anatomical relationship that limits the size of safe deltoid-splitting incisions. Periscapular Muscles The periscapular muscles stabilize the scapula on the chest wall: Trapezius: From the occiput and spinous processes, inserting on the scapular spine, acromion, and clavicle. Provides scapular elevation, retraction, and upward rotation.
Rhomboids major and minor: From the thoracic spinous processes to the medial border of the scapula. Retract and downwardly rotate the scapula. Serratus anterior: From the ribs to the medial border of the scapula (anterior surface). Protracts and upwardly rotates the scapula; scapular winging results from serratus anterior weakness (typically from long thoracic nerve injury). Levator scapulae: From cervical transverse processes to superior medial border of scapula. Elevates the scapula.
Neurovascular Structures
Axillary Nerve (C5-C6) The axillary nerve is the principal neurological structure at risk in shoulder surgery. It branches from the posterior cord of the brachial plexus, passes posteriorly through the quadrilateral space, and then winds around the surgical neck of the humerus deep to the deltoid, dividing into branches to the deltoid and to the teres minor, with a sensory branch (superior lateral cutaneous nerve of the arm) supplying the skin over the lateral deltoid. The proximity of the axillary nerve to the surgical neck of the humerus (approximately 5 to 7 cm distal to the acromion along the deltoid undersurface) is the critical surgical anatomical fact that limits the extent of deltoid-splitting incisions. The axillary nerve is injured in approximately 10 to 20 percent of anterior shoulder dislocations and in many proximal humerus fractures (Topic Trauma-13).
Musculocutaneous Nerve (C5-C7) The musculocutaneous nerve branches from the lateral cord of the brachial plexus, pierces the coracobrachialis muscle (typically about 5 to 8 cm distal to the coracoid — the “safe zone” for retraction during anterior shoulder surgery is approximately 5 cm distal to the coracoid), and supplies the biceps brachii, brachialis, and coracobrachialis. It then continues as the lateral antebrachial cutaneous nerve. Brachial Plexus and Axillary Vessels The brachial plexus lies medial to the coracoid and posterior to the pectoralis minor. The axillary artery and vein travel with the plexus. These structures are at risk in deeper dissection medial to the coracoid and in high-energy shoulder dislocations. Suprascapular Nerve (C5-C6) The suprascapular nerve passes through the suprascapular notch (deep to the transverse scapular ligament) and supplies the supraspinatus, then continues around the spinoglenoid notch to supply the infraspinatus. Compression or traction at these notches produces suprascapular neuropathy with weakness of the supraspinatus and/or infraspinatus.
Long Thoracic Nerve (C5-C7) The long thoracic nerve runs along the lateral chest wall on the surface of serratus anterior, supplying the muscle. Injury produces scapular winging with prominence of the medial border of the scapula on forward elevation of the arm.
The Deltopectoral Approach
The deltopectoral approach is the most commonly used approach to the anterior shoulder, providing access for anterior open reduction of dislocations, open reduction and internal fixation of proximal humerus fractures, anterior glenoid procedures (Bankart, Latarjet, bone block), shoulder arthroplasty (anatomic and reverse), and tumor resections. Patient Positioning The patient is positioned in beach chair (45 to 60 degrees of trunk elevation) with the head supported in a specialized head holder; the affected arm is draped freely to permit movement during the procedure. Alternatively, the lateral decubitus position can be used for shoulder arthroscopy with the affected side up and traction applied to the arm. Surface Landmarks and Incision The incision is along the deltopectoral groove, beginning just inferior to the coracoid process and extending distally toward the deltoid insertion for approximately 10 to 15 cm. The anterior axillary fold marks the lower extent of the deltoid. Approach The deltopectoral interval between the deltoid (axillary nerve) and the pectoralis major (medial and lateral pectoral nerves) is identified — the classical landmark is the cephalic vein running in the interval. The vein is typically taken either medially (with the pectoralis) or laterally (with the deltoid); the lateral retraction may be safer with respect to vein preservation. The deltoid is then retracted laterally and the pectoralis medially. The clavipectoral fascia is incised lateral to the conjoint tendon. The conjoint tendon (coracobrachialis and short head of biceps) is identified and retracted medially with attention to the musculocutaneous nerve entering coracobrachialis approximately 5 to 8 cm distal to the coracoid (this defines the safe zone for retraction). The subscapularis is now visualized, with the anterior humeral circumflex vessels (the “three sisters”) at its inferior border. These vessels are typically ligated or coagulated. The subscapularis is then incised (with various techniques — vertical incision, lesser tuberosity osteotomy, peel from the lesser tuberosity for shoulder arthroplasty) to expose the underlying capsule and joint.
Variations The extended deltopectoral approach carries the incision more proximally and distally for extended exposure (e.g., for tumors or revision procedures). The minimally invasive deltopectoral approach uses a smaller skin incision and limited dissection for percutaneous and arthroscopically-assisted procedures.
Complications The complications of the deltopectoral approach include musculocutaneous nerve injury (rare, prevented by gentle retraction of the conjoint tendon and avoidance of vigorous retraction more than 5 cm distal to the coracoid), axillary nerve injury (rare in this approach but possible with extended distal dissection), vascular injury (rare), and subscapularis dysfunction (common after various subscapularis takedown techniques; subscapularis peel with bone block or lesser tuberosity osteotomy may produce better outcomes than the historical vertical incision).
The Posterior Shoulder Approach
The posterior approach provides access for posterior glenoid procedures (posterior Bankart, posterior bone block), posterior shoulder instability surgery, posterior reduction of locked posterior dislocations, scapular body fixation, and tumor resection of the posterior scapula. Patient Positioning The patient is positioned in lateral decubitus with the affected side up, or prone. The arm is draped freely. Surface Landmarks and Incision The scapular spine and the acromion are the principal landmarks. The incision extends from the posterolateral corner of the acromion distally over the lateral border of the deltoid for 6 to 10 cm. An alternative incision parallels the scapular spine. Approach The deltoid is split in line with its fibers between the middle and posterior heads, with the split limited to approximately 5 cm distal to the acromion to protect the axillary nerve (which runs around the surgical neck of the humerus). The posterior deltoid is reflected inferiorly. The infraspinatus and teres minor interval is identified (often by palpation of the fibers, since the interval is not as visible as the deltopectoral interval). The interval is developed, with the infraspinatus retracted superiorly and the teres minor retracted inferiorly. The posterior capsule is then exposed. Alternative techniques include the infraspinatus split approach (splitting the infraspinatus in line with its fibers, which provides direct access to the posterior capsule with preservation of the muscle but with potential for some loss of function), and the
detachment of infraspinatus from the greater tuberosity (with later repair, providing the most extensive exposure but with concern for repair healing). Complications The complications of the posterior approach include axillary nerve injury (the principal concern, prevented by limiting the deltoid split to 5 cm distal to the acromion), suprascapular nerve injury (in the spinoglenoid notch, at risk with deep dissection), and rotator cuff dysfunction (from infraspinatus disruption).
Anterior Axillary (Henry’s) Approach
The anterior axillary approach uses a more inferior anterior incision that avoids the visible anterior shoulder scar and provides access for anterior shoulder procedures with cosmetic priority (selected female patients, athletes), as well as access to certain pathologies of the anterior shoulder. Surface Landmarks and Incision The incision is in the anterior axillary skin fold, beginning approximately 1 to 2 cm distal to the coracoid and extending downward into the axilla. The incision is cosmetic when healed. Approach The dissection proceeds upward to the deltopectoral groove and proceeds in the standard deltopectoral approach. The advantage is the smaller, less visible scar; the disadvantage is the more limited proximal exposure and the somewhat more demanding orientation.
The Superior (Saber-Cut) Approach
The superior approach (also called the saber-cut approach or the superior arthroscopic-assisted approach) provides access to the superior aspect of the shoulder for distal clavicle excision, AC joint procedures, superior rotator cuff repair (open), and proximal humerus fracture access in selected cases. Surface Landmarks and Incision A small superior incision is made over the AC joint or over the greater tuberosity, depending on the desired exposure. The incision is typically 4 to 6 cm in length. Approach The deltoid is split in line with its fibers (the deltoid-splitting approach) for a maximum of approximately 5 cm distal to the acromion to protect the axillary nerve. The supraspinatus tendon and its insertion on the greater tuberosity are exposed. For AC joint procedures, the trapezoid fascia is incised over the joint and the joint capsule is opened.
For rotator cuff procedures, the tendinous insertion is identified and the repair is performed. The superior approach is largely supplanted by arthroscopic techniques for most rotator cuff and AC joint procedures, but retains a role in selected open procedures.
Shoulder Arthroscopy
Shoulder arthroscopy has largely supplanted open surgery for many shoulder pathologies and merits brief consideration in the context of surgical anatomy. The principal portals include: Posterior portal: Approximately 2 to 3 cm inferior and 1 to 2 cm medial to the posterolateral corner of the acromion. The “soft spot” between the infraspinatus and teres minor. Provides the principal viewing portal for the glenohumeral joint. Anterior portal: Established under direct vision through the rotator interval (between the supraspinatus and subscapularis). Provides the principal working portal for anterior shoulder procedures. Anterolateral portal: Inferior to the anterior acromial edge. Used for subacromial procedures and for some rotator cuff repairs. Posterolateral portal: Inferior to the posterior acromial edge. Used for subacromial procedures. Lateral portal: Through the deltoid 2 to 3 cm lateral to the acromial edge. Used for subacromial procedures and rotator cuff repair. Multiple accessory portals (e.g., 5 o’clock portal, Nevasier portal, trans-rotator cuff portal) are added as needed for specific procedures. The arthroscopic examination systematically visualizes the glenohumeral joint, with attention to the labrum (Bankart and SLAP lesions), the rotator cuff (articular-sided tears), the long head of biceps, the cartilage surfaces, and the capsule. The subacromial space is examined separately for bursal-sided cuff tears, the coracoacromial arch, and the AC joint.
Summary and Take-Home Points
The shoulder offers a substantial set of surgical approaches reflecting its mobility, complex muscular envelope, and proximity to neurovascular structures. The deltopectoral approach is the workhorse for the anterior shoulder, using the avascular plane between the deltoid (axillary nerve) and the pectoralis (pectoral nerves), with the cephalic vein as the surface landmark; the musculocutaneous nerve entering coracobrachialis approximately 5 to 8 cm distal to the coracoid limits medial retraction; the subscapularis management (vertical incision, lesser tuberosity osteotomy, or peel) is a key surgical decision in many anterior procedures. The posterior approach between infraspinatus and teres minor provides access to the posterior glenoid and capsule, with the axillary nerve running below the deltoid limiting deltoid split to approximately 5 cm distal to the
acromion. The anterior axillary approach is a cosmetic alternative to deltopectoral. The superior (saber-cut) approach with deltoid-splitting incision provides access to the superior rotator cuff and AC joint. The rotator cuff comprises four muscles (supraspinatus, infraspinatus, teres minor, subscapularis) functioning principally as dynamic stabilizers of the humeral head in the glenoid; the deltoid is the principal abductor with three heads (anterior, middle, posterior). The axillary nerve in the quadrilateral space is the critical neurological structure at risk in shoulder surgery, supplying the deltoid and teres minor and the lateral skin of the upper arm. The musculocutaneous nerve entering coracobrachialis and the suprascapular nerve in the suprascapular and spinoglenoid notches are additional neurological structures requiring protection. The long thoracic nerve along the chest wall surface of serratus anterior is at risk in lateral chest wall procedures and produces scapular winging when injured. Shoulder arthroscopy has supplanted many open procedures and uses standard posterior, anterior, anterolateral, lateral, and accessory portals to access the glenohumeral joint and subacromial space. The chapter that follows turns to the arm and humerus, continuing the systematic regional anatomy through the upper extremity.