SHOULDER ARTHROPLASTY ANATOMY
Deltopectoral Approach | Neurovascular Structures at Risk | Rotator Cuff Relationships | Glenoid Exposure
Key Anatomical Zones
Critical Must-Knows
- Axillary nerve lies 5-7 cm inferior to acromion, vulnerable during inferior capsule release
- Musculocutaneous nerve enters coracobrachialis 3-8 cm from coracoid tip
- Cephalic vein runs in deltopectoral groove - ligate laterally or retract medially
- Subscapularis can be released via tenotomy, peel, or lesser tuberosity osteotomy
- Posterior glenoid exposure requires complete anterior capsule release and careful retraction
Examiner's Pearls
- "Three critical nerves: axillary (inferior), musculocutaneous (medial), suprascapular (posterior)
- "Deltopectoral interval is internervous and intermuscular - theoretically atraumatic
- "Ascending branch of anterior humeral circumflex artery requires ligation during approach
- "Humeral version averages 30 degrees retroversion relative to transepicondylar axis
Clinical Imaging
Imaging Gallery
Critical Shoulder Arthroplasty Anatomy Exam Points
Nerve Injury Risk
Axillary nerve is most at risk during inferior capsule release and glenoid retraction. Lies 5-7 cm from acromion, travels with posterior humeral circumflex artery through quadrangular space. Test deltoid function postoperatively.
Deltopectoral Approach
Internervous plane between deltoid (axillary nerve) and pectoralis major (medial and lateral pectoral nerves). Cephalic vein marks the interval - can ligate lateral branches or retract medially with pectoralis.
Subscapularis Management
Three release techniques: subscapularis tenotomy (1 cm medial to insertion), subscapularis peel (partial thickness from tuberosity), or lesser tuberosity osteotomy (preserves tendon-bone healing). Each has specific repair requirements.
Glenoid Version
Normal glenoid retroversion 0-5 degrees. Excessive retroversion (over 10 degrees) requires reaming strategy to restore neutral version or component augmentation. Critical for implant stability and avoiding posterior instability.
Quick Decision Guide - Shoulder Arthroplasty Anatomy
| Anatomical Region | Key Structure | Clinical Significance | Protection Strategy |
|---|---|---|---|
| Deltopectoral interval | Cephalic vein | Marks surgical plane | Ligate lateral branches or retract medially |
| Subscapularis region | Musculocutaneous nerve | Enters coracobrachialis 3-8 cm from coracoid | Avoid excessive medial retraction, stay above inferior border conjoint tendon |
| Inferior capsule | Axillary nerve | Travels through quadrangular space 5-7 cm from acromion | Release capsule under direct vision, use blunt dissection inferior to subscapularis |
| Posterior glenoid | Suprascapular nerve | At spinoglenoid notch posterior to glenoid | Limit posterior retraction, avoid superior-posterior retractor placement |
Mnemonics for Shoulder Arthroplasty Anatomy
AMUSNerves at Risk During Shoulder Arthroplasty
Memory Hook:AMUS - All Must be Understood and Safe before arthroplasty proceeds!
SCARFDeltopectoral Approach Layers
Memory Hook:SCARF - Surgical Craft Achieves Reliable Function through proper layered dissection!
TOPSubscapularis Release Options
Memory Hook:TOP - Three Options for Protection and repair of subscapularis!
TILTQuadrangular Space Boundaries
Memory Hook:TILT - The space TILTs posteriorly, containing axillary nerve and posterior humeral circumflex artery!
Overview and Clinical Significance
Why Shoulder Arthroplasty Anatomy Matters
Shoulder arthroplasty demands precise anatomical knowledge due to the concentration of critical neurovascular structures within a limited surgical field. Unlike hip arthroplasty where the sciatic nerve is the primary concern, shoulder replacement requires awareness of four major nerves (axillary, musculocutaneous, suprascapular, and radial) and complex rotator cuff anatomy that must be preserved or repaired. The deltopectoral approach provides excellent exposure but requires careful dissection through multiple tissue planes. Understanding native glenoid and humeral version is essential for component positioning and preventing instability. Mastery of this anatomy reduces neurological complications (reported at 1-4 percent in most series) and improves functional outcomes.
Surgical Anatomy Goals
- Safe extensile exposure through internervous plane
- Protection of axillary nerve during capsule release
- Subscapularis preservation or secure repair
- Glenoid visualization without nerve traction injury
- Humeral canal preparation without radial nerve injury
- Restoration of anatomic version relationships
Understanding these principles guides decision-making during complex arthroplasty cases.
Clinical Impact
- Nerve injuries occur in 1-4 percent of cases
- Axillary nerve most common (0.6-4 percent)
- Musculocutaneous injury from medial retraction (0.3-1 percent)
- Subscapularis failure causes anterior instability (2-10 percent)
- Excessive glenoid retroversion leads to posterior instability
- Version restoration critical for implant longevity
Poor anatomical understanding increases complication risk significantly.
Bony Anatomy and Landmarks
Scapular Anatomy
Glenoid
- Shape: Pear-shaped, wider inferiorly
- Version: 0-5 degrees retroversion normal
- Inclination: 5 degrees superior tilt
- Depth: Shallow socket, 25-30 mm diameter
- Articular arc: 75 percent of humeral head
- Bone density: Subchondral bone critical for fixation
Glenoid morphology varies with pathology - erosion patterns guide component selection.
Coracoid Process
- Projection: Anterolateral from superior scapula
- Attachments: Conjoint tendon (short head biceps and coracobrachialis)
- Landmark: Musculocutaneous nerve enters coracobrachialis 3-8 cm from tip
- Ligaments: Coracoacromial, coracoclavicular, coracohumeral
- Importance: Reference for nerve protection, retractor placement
The coracoid is the key medial landmark during deltopectoral approach.
Humeral Anatomy
Humeral Anatomical Relationships
| Region | Key Feature | Measurement | Clinical Significance |
|---|---|---|---|
| Humeral head | Articular surface | 130-150 degree neck-shaft angle | Component position affects ROM and stability |
| Retroversion | Head relative to epicondyles | 20-40 degrees (average 30) | Restore native version to prevent instability |
| Greater tuberosity | Supraspinatus, infraspinatus, teres minor insertion | 5-8 mm superior to articular margin | Tuberosity malposition causes impingement |
| Lesser tuberosity | Subscapularis insertion | 1 cm medial width | Osteotomy site preserves tendon-bone healing |
| Bicipital groove | Long head biceps | Between tuberosities | Landmark for version, protect during exposure |
Glenoid Version Measurement
Measuring glenoid version is critical for component positioning. Use CT with Friedman or scapular body method. Normal version is 0-5 degrees retroversion. Pathologic retroversion (over 10 degrees) occurs with posterior glenoid wear from cuff tear arthropathy or longstanding posterior instability. Options to correct version: eccentric reaming (limited to 10 degrees correction), augmented components, or bone grafting. Failure to restore version leads to component failure and instability.
Rotator Cuff Anatomy
Rotator Cuff Cable System
Anterior Cuff - Subscapularis
- Origin: Subscapular fossa of scapula
- Insertion: Lesser tuberosity of humerus
- Function: Internal rotation, anterior stability
- Nerve: Upper and lower subscapular nerves (C5-C6)
- Layers: Upper third superior, middle third horizontal, lower third inferior fibers
- Release: Must be released or osteotomized for humeral exposure
The subscapularis is the most important muscle for anterior stability and internal rotation.
Superior Cuff - Supraspinatus
- Origin: Supraspinatus fossa
- Insertion: Superior facet greater tuberosity
- Function: Abduction initiation (first 15 degrees), humeral head depression
- Nerve: Suprascapular nerve (C5-C6)
- Tendon: Courses under coracoacromial arch
- Exposure: Rotator interval between subscapularis and supraspinatus
Rarely released during arthroplasty but critical for reverse shoulder function.
Posterior Cuff - Infraspinatus and Teres Minor
- Infraspinatus: Infraspinatus fossa to middle/superior greater tuberosity
- Teres minor: Lateral scapular border to inferior greater tuberosity
- Function: External rotation, posterior stability
- Nerves: Suprascapular (infraspinatus), axillary (teres minor)
- Quadrangular space: Between teres minor and major (axillary nerve)
Posterior cuff rarely requires release but can be split for posterior approach.
Rotator Interval
- Boundaries: Superior border subscapularis, anterior edge supraspinatus
- Contents: Coracohumeral ligament, superior glenohumeral ligament, long head biceps
- Floor: Anterior superior capsule
- Importance: Opened first during deltopectoral approach to access joint
- Release: Improves external rotation in stiff shoulders
The rotator interval is the key to safe joint access during anterior approach.
Subscapularis Release Techniques Comparison
| Technique | Method | Advantages | Disadvantages |
|---|---|---|---|
| Subscapularis tenotomy | Release 1 cm medial to insertion, preserve cuff on bone | Easier exposure, faster, allows repair to bone | Potential weakness, 5-10 percent failure rate |
| Lesser tuberosity osteotomy | Osteotomize tuberosity with subscapularis attached | Bone-bone healing, strongest repair, lower failure | Technical demand, tuberosity malunion/nonunion risk |
| Subscapularis peel | Partial thickness peel from tuberosity, leave capsule | Preserves some insertion, middle ground | Unclear biomechanics, healing variable |
Neurovascular Anatomy - Critical Structures
Nerves at Risk
Axillary Nerve - Highest Risk During Arthroplasty
Anatomy:
- Origin: Posterior cord of brachial plexus (C5-C6)
- Course: Exits axilla through quadrangular space with posterior humeral circumflex artery
- Quadrangular space boundaries: Teres minor (superior), teres major (inferior), long head triceps (medial), surgical neck humerus (lateral)
- Branches: Anterior (to anterior/middle deltoid), posterior (to posterior deltoid and teres minor), superior lateral cutaneous nerve of arm
Location relative to landmarks:
- 5-7 cm inferior to acromion along lateral shoulder
- Wraps around surgical neck of humerus posteriorly
- At risk during inferior capsule release and glenoid retraction
Protection strategies:
- Release inferior capsule under direct vision
- Use blunt dissection inferior to subscapularis
- Avoid inferior retractors placed blindly
- Limit inferior translation during glenoid exposure
- Test deltoid function immediately postoperatively
Injury consequences:
- Deltoid paralysis (loss of abduction beyond 15 degrees)
- Teres minor weakness (external rotation)
- Sensory loss over lateral shoulder (regimental badge area)
- Usually neurapraxia, recovers in 3-6 months
Understanding axillary nerve anatomy is mandatory for safe shoulder arthroplasty.
Nerve Injury Prevention - Golden Rules
Four golden rules to prevent nerve injury during shoulder arthroplasty:
- Axillary nerve: Release inferior capsule under direct vision, avoid blind inferior retractors, stay greater than 5 cm from acromion inferiorly
- Musculocutaneous nerve: Limit medial retraction, stay above inferior subscapularis border, avoid dissection greater than 5 cm from coracoid
- Suprascapular nerve: Minimize posterior retraction duration and force, avoid superior-posterior retractor at glenoid rim, release posterior capsule fully
- Radial nerve: Stay centered in humeral canal, protect anterior cortex, use gentle technique in osteoporotic bone
Testing nerve function immediately postoperatively identifies injury early and guides management.
Vascular Anatomy
Key Vascular Structures
| Vessel | Course | Significance | Management |
|---|---|---|---|
| Axillary artery | Medial to surgical field, behind pectoralis minor | Main blood supply to arm, rarely at risk | Avoid excessive medial dissection deep to conjoint tendon |
| Anterior humeral circumflex | Ascends in bicipital groove, gives ascending branch | Requires ligation during deltopectoral approach | Ligate ascending branch at superior border pectoralis major |
| Posterior humeral circumflex | Travels with axillary nerve through quadrangular space | At risk during inferior capsule release | Protected by protecting axillary nerve |
| Cephalic vein | Runs in deltopectoral groove | Marks surgical interval | Ligate lateral branches and retract medially, or ligate vein and retract laterally |
Deltopectoral Approach - Step by Step
Surface Anatomy and Incision Planning
Key landmarks:
- Coracoid process: Palpable anteromedial, 2-3 cm medial and inferior to AC joint
- Acromion: Lateral shoulder prominence
- Clavicle: Superior reference
- Deltopectoral groove: Visible as depression, runs from clavicle toward deltoid insertion
- Axillary fold: Inferior limit of exposure
Incision:
- Start: Coracoid process
- Direction: Oblique toward lateral edge of acromion, then distally along deltopectoral groove
- Extend: To deltoid insertion if needed (10-15 cm total length for standard arthroplasty)
- Curve: Gentle curve following natural skin lines for better scar
Skin and subcutaneous dissection:
- Incise skin and subcutaneous fat to deltopectoral fascia
- Identify cephalic vein in groove (60-70 percent of cases visible)
- Mobilize vein: Ligate lateral branches and retract medially with pectoralis OR ligate vein and retract laterally with deltoid
The deltopectoral approach is internervous and provides excellent extensile exposure.
Cephalic Vein Management Controversy
Two schools of thought on cephalic vein:
Retract medially with pectoralis (preferred by most):
- Ligate only lateral branches entering deltoid
- Preserves main vein drainage
- Reduces postoperative swelling
- Requires careful dissection
Ligate vein and retract laterally with deltoid:
- Faster, simpler dissection
- Ensures hemostasis
- Collateral drainage adequate
- Risk of increased swelling
Evidence: No significant difference in outcomes between techniques. Choose based on surgical preference and vein quality. If vein damaged during dissection, ligate completely.
Alternative Approaches
Shoulder Arthroplasty Approaches Comparison
| Approach | Indication | Advantages | Disadvantages |
|---|---|---|---|
| Deltopectoral (standard) | Most shoulder arthroplasty cases | Extensile, internervous, familiar anatomy, lower infection | Subscapularis must be released/repaired |
| Anterosuperior (Mackenzie) | Subscapularis deficiency or reverse arthroplasty | Preserves subscapularis, good superior exposure | Risk to axillary nerve, limited inferior exposure |
| Superior (Neviaser) | Selected reverse arthroplasty cases | Preserves anterior and posterior cuff | Limited exposure, supraspinatus release required, steep learning curve |
| Posterior | Posterior instability repair or revision | Direct posterior access | Requires prone position, limited anterior exposure |
When to Consider Alternative Approach
Indications for non-deltopectoral approach:
- Anterosuperior: Irreparable subscapularis deficiency, revision arthroplasty with subscapularis failure, reverse arthroplasty where subscapularis function less critical
- Superior: Primary reverse arthroplasty in hands of experienced surgeon, desire to preserve anterior structures
- Posterior: Posterior bone block for instability, posterior glenoid bone grafting, revision with posterior component removal
The deltopectoral approach remains gold standard for most cases due to extensile nature, internervous plane, familiar anatomy, and ability to extend proximally or distally as needed.
Subscapularis Repair
Subscapularis Tenotomy Repair
Repair after subscapularis tenotomy:
Preparation:
- Mobilize subscapularis tendon medially to ensure tendon reaches lesser tuberosity without tension
- Prepare bony bed on lesser tuberosity (remove soft tissue, create bleeding bone)
- Place trial components and reduce joint to assess tension
Repair technique:
-
Suture anchors (most common):
- Place 3-4 anchors in lesser tuberosity footprint
- Use knotless or traditional anchors
- Pass sutures through tendon using modified Mason-Allen or simple sutures
- Secure with arm in neutral rotation (not external rotation - creates excessive tension)
-
Transosseous tunnels (alternative):
- Drill tunnels from lesser tuberosity to lateral cortex
- Pass nonabsorbable sutures through tendon and tunnels
- Tie over bone bridge laterally
Augmentation:
- Consider pectoralis major transfer if poor tissue quality
- Use dermal allograft or synthetic patch for large defects (uncommon)
Testing:
- Belly press test: Should have resistance at 20-30 degrees external rotation
- Lag sign: Should be negative with intact repair
Tenotomy repair strength depends on bone quality and suture anchor fixation.
Anatomy
Key Anatomical Considerations for Shoulder Arthroplasty
Osseous Anatomy
- Humeral head: 40-50mm diameter, 130-145° neck-shaft angle, 20-40° retroversion
- Glenoid: Pear-shaped, 35mm height, 25mm width, 5-10° retroversion, 5° superior tilt
- Glenoid vault: Central bone stock critical for baseplate fixation (depth 15-25mm)
- Coracoid process: Reference landmark, 25mm medial to glenoid rim
Rotator Cuff Footprints
- Supraspinatus: Superior facet of greater tuberosity
- Infraspinatus: Middle facet of greater tuberosity
- Teres minor: Inferior facet of greater tuberosity
- Subscapularis: Lesser tuberosity (critical for TSA stability)
Neurovascular Structures at Risk
- Axillary nerve: 5-7cm inferior to acromion, crosses anterior to subscapularis
- Musculocutaneous nerve: Enters coracobrachialis 5-8cm distal to coracoid
- Suprascapular nerve: At spinoglenoid notch, risk with posterior glenoid exposure
Classification
Glenoid Morphology Classifications
Walch Classification (Glenoid Wear Patterns)
Walch Classification of Glenoid Morphology
| Type | Description | Implications |
|---|---|---|
| A1 | Minor central erosion, concentric humeral head | Standard glenoid component, no augment needed |
| A2 | Major central erosion, concentric humeral head | May need bone graft for central defect |
| B1 | Posterior subluxation, no erosion | Asymmetric reaming, consider RSA |
| B2 | Posterior subluxation + biconcave posterior erosion | Posterior augment or asymmetric reaming, RSA preferred |
| B3 | Monoconcave posterior erosion (retroversion greater than 15°) | Posterior augment mandatory, bone graft, or RSA |
| C | Dysplastic glenoid (retroversion greater than 25°) | RSA with augment or custom implant |
| D | Anterior subluxation/erosion | Rare, anterior augment or RSA |
Clinical Correlations - Anatomical Injury Complications
| Complication | Incidence | Cause | Prevention | Management |
|---|---|---|---|---|
| Axillary nerve injury | 0.6-4% | Inferior capsule release, retraction, traction | Careful inferior release, avoid blind retractors, limit traction | Observation 3-6 months (most recover), EMG at 6 weeks, consider exploration if no recovery |
| Musculocutaneous nerve injury | 0.3-1% | Excessive medial retraction of conjoint tendon | Limit medial retraction, stay above inferior subscapularis | Usually recovers spontaneously, splint elbow in flexion initially |
| Suprascapular nerve injury | Less than 1% | Posterior glenoid retraction, superior retractor | Limit posterior retraction force and duration, avoid superior-posterior retractors | Observation, consider decompression at notch if no recovery 6-12 months |
| Subscapularis failure | 2-10% | Poor tissue quality, inadequate repair, excessive tension, noncompliance | Secure repair technique, protect postoperatively, patient education | Revision repair if symptomatic instability, consider pectoralis major transfer |
| Vascular injury (axillary artery) | Less than 0.1% | Excessive medial dissection, fracture, cerclage wires | Stay lateral, careful medial dissection, avoid cerclage | Immediate vascular surgery consultation, repair or graft |
Immediate Postoperative Nerve Assessment
Test nerve function in recovery room before regional anesthesia wears off:
- Axillary nerve: Deltoid contraction (palpate muscle with abduction attempt), sensation over lateral shoulder
- Musculocutaneous nerve: Biceps contraction with elbow flexion
- Radial nerve: Wrist/finger extension
- Suprascapular nerve: Cannot test acutely (motor only)
Document findings and compare to preoperative examination. If new deficit detected, determine if complete or partial. Most neurapraxias recover with observation, but early recognition guides patient counseling and follow-up planning.
Investigations
Preoperative Imaging for Anatomical Assessment
Plain Radiographs (Essential)
- True AP (Grashey view): Joint space, humeral head position, glenoid wear
- Axillary lateral: Glenoid version, posterior wear, subluxation
- Scapular Y: Acromion morphology, os acromiale
- Full-length humerus: For stem sizing in revision
CT Scan with 3D Reconstruction
- Glenoid version and inclination measurement
- Walch classification determination
- Bone stock assessment for baseplate fixation
- Glenoid vault depth and screw trajectory planning
- 3D planning software for templating
MRI
- Rotator cuff integrity (determines TSA vs RSA)
- Fatty infiltration (Goutallier classification)
- Muscle atrophy assessment
Management
Management Based on Anatomical Findings
Prosthesis Selection Based on Anatomy
Arthroplasty Type Selection Based on Anatomy
| Anatomical Finding | Recommended Approach | Rationale |
|---|---|---|
| Intact rotator cuff + concentric glenoid | Anatomic TSA | Restores normal biomechanics, best ROM |
| Irreparable cuff tear + cuff arthropathy | Reverse TSA (RSA) | Deltoid-powered elevation, bypasses cuff |
| B2/B3 glenoid erosion | RSA preferred over TSA | Lower glenoid loosening with baseplate vs pegged glenoid |
| Proximal humerus fracture (elderly) | RSA preferred | No tuberosity healing required, reliable outcomes |
Glenoid Version Correction
- Retroversion less than 15°: Asymmetric reaming alone
- Retroversion 15-25°: Posterior augmented glenoid or bone graft
- Retroversion greater than 25°: Custom implant or RSA with augment
Surgical Technique
Anatomical Landmarks in Surgical Technique
Deltopectoral Approach - Key Landmarks
- Coracoid process: Central reference point
- Cephalic vein: Lateral retraction (protects vein, maintains venous drainage)
- Conjoint tendon: Medial border of exposure
- Subscapularis: Must be addressed for exposure
Subscapularis Management Options
- Lesser tuberosity osteotomy: Best healing rates, bone-to-bone healing
- Subscapularis peel: Tendon from bone, higher failure rate
- Subscapularis tenotomy: Tendon cut, poorest healing (avoid in TSA)
Glenoid Exposure Sequence
- Position arm in extension, external rotation, adduction
- Place Fukuda retractor posteriorly
- Release anterior capsule off glenoid rim
- Release inferior capsule (protect axillary nerve)
- Place blunt retractors inferiorly and superiorly
Complications
Anatomically-Related Complications
Neurovascular Injuries
- Axillary nerve: Most common (0.6-4%), from inferior capsule release or retraction
- Musculocutaneous nerve: Excessive medial retraction on conjoint tendon
- Suprascapular nerve: Posterior glenoid retraction or long superior screws
Osseous Complications
- Intraoperative fracture: Greater tuberosity (3-5%), shaft (1-2%)
- Glenoid fracture: From aggressive reaming or malpositioning
- Periprosthetic fracture: Postoperative trauma or stress risers
Soft Tissue Complications
- Subscapularis failure: 2-10% for TSA, leads to instability
- Rotator cuff tear progression: 5-10% by 10 years
- Deltoid detachment: Rare but catastrophic for RSA
Postoperative Care
Postoperative Protocols
Immobilization
- Sling immobilization: 2-4 weeks (TSA), 4-6 weeks (RSA)
- Position: Internal rotation, slight abduction on pillow
- Remove for elbow, wrist, hand exercises and hygiene
Rehabilitation Phases
Standard Rehabilitation Protocol
| Phase | Timeframe | Goals | Exercises |
|---|---|---|---|
| Protection | 0-4 weeks | Protect repair, control inflammation | Pendulums, elbow/wrist ROM, isometrics |
| Early motion | 4-8 weeks | Restore passive ROM | Passive forward flexion, external rotation |
| Active motion | 8-12 weeks | Active ROM, light function | Active assisted to active ROM |
| Strengthening | 12-16 weeks | Progressive strength | Rotator cuff, deltoid, scapular |
Outcomes
Outcomes Related to Anatomical Factors
Functional Outcomes by Prosthesis Type
Expected Functional Outcomes
| Parameter | TSA | RSA |
|---|---|---|
| Forward flexion | 140-160° | 120-140° |
| External rotation | 40-60° | 20-40° |
| Internal rotation | L1-T12 | Sacrum-L3 |
| Patient satisfaction | 85-95% | 85-90% |
| 10-year survival | 90-95% | 85-90% |
Factors Affecting Outcomes
- Glenoid morphology: B2/B3 glenoids have higher loosening rates
- Rotator cuff integrity: Intact cuff improves TSA outcomes
- Bone quality: Osteoporosis increases fracture and loosening risk
Evidence Base and Key Studies
Nerve Injuries in Shoulder Arthroplasty - Systematic Review
- Overall neurologic complication rate 1-4 percent in shoulder arthroplasty
- Axillary nerve most commonly injured (0.6-4 percent)
- Musculocutaneous nerve injury in 0.3-1 percent
- Most injuries are neurapraxias that recover in 3-6 months
- Complete nerve transections are rare (less than 0.1 percent)
Subscapularis Tendon Tears After Shoulder Arthroplasty - MRI Analysis
- MRI evaluation of 60 shoulder arthroplasty patients
- Subscapularis tears found in 30 percent on MRI
- Only 13 percent symptomatic (instability or weakness)
- Lesser tuberosity osteotomy had lower failure rate than tenotomy
- Fatty infiltration associated with tear and poor function
Musculocutaneous Nerve - Anatomic Study for Shoulder Surgery Safety
- Cadaveric study of 103 upper extremities
- Musculocutaneous nerve enters coracobrachialis 3-8 cm from coracoid tip (mean 5.4 cm)
- In 15 percent of specimens, nerve traveled outside coracobrachialis (higher risk)
- Safe zone for retraction: superior to inferior border of subscapularis
- Excessive medial retraction is primary mechanism of injury
Glenoid Version and Shoulder Arthroplasty Outcomes
- CT analysis of 113 osteoarthritic shoulders
- Three patterns of glenoid erosion (A, B, C)
- Type B glenoid (posterior wear) had mean 21 degrees retroversion
- Failure to correct version led to posterior instability and glenoid loosening
- Eccentric reaming can correct up to 10 degrees version
Axillary Nerve Anatomy and Injury Risk - Cadaveric Study
- Anatomic dissection of 10 cadaveric shoulders
- Axillary nerve consistently 5-7 cm inferior to acromion
- Nerve wraps around surgical neck within quadrangular space
- Inferior capsule release and glenoid retraction are highest risk maneuvers
- Direct visualization during release prevents injury
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Deltopectoral Approach Anatomy (2-3 min)
"You are performing shoulder arthroplasty via deltopectoral approach. Describe the key anatomical landmarks, the surgical intervals you will develop, and the nerves at risk during your dissection."
Scenario 2: Subscapularis Management (3-4 min)
"Walk me through your subscapularis management during shoulder arthroplasty. What are the different release techniques, how do you decide which to use, and what are the repair principles for each?"
Scenario 3: Axillary Nerve Injury (2-3 min)
"During shoulder arthroplasty glenoid exposure, you are concerned you may have injured the axillary nerve. Describe the anatomy of the axillary nerve, how you would assess for injury intraoperatively and postoperatively, and your management if injury is confirmed."
MCQ Practice Points
Anatomy Question
Q: What is the average distance from the tip of the coracoid process to the point where the musculocutaneous nerve enters the coracobrachialis muscle?
A: 3-8 cm, with a mean of 5.4 cm. This anatomic relationship is critical during the deltopectoral approach. Excessive medial retraction of the conjoint tendon beyond 5 cm from the coracoid tip risks musculocutaneous nerve injury. The nerve can be injured by direct trauma from retractors or by traction. In 15 percent of specimens, the nerve travels outside the coracobrachialis muscle, making it more vulnerable. Protection strategies include limiting medial retraction and staying superior to the inferior border of the subscapularis and conjoint tendon during deep dissection.
Nerve Anatomy Question
Q: What are the boundaries of the quadrangular space, and what structures pass through it?
A: Boundaries: Superior = teres minor, Inferior = teres major, Medial = long head of triceps, Lateral = surgical neck of humerus. Structures: Axillary nerve and posterior humeral circumflex artery. The quadrangular space is clinically important as the axillary nerve is vulnerable during inferior capsule release and humeral retraction for glenoid exposure. The nerve lies approximately 5-7 cm inferior to the acromion. Injury causes deltoid paralysis (loss of active abduction beyond 15 degrees), teres minor weakness, and sensory loss over the lateral shoulder (regimental badge area).
Surgical Anatomy Question
Q: What is the internervous plane for the deltopectoral approach to the shoulder?
A: Deltoid (innervated by axillary nerve from C5-C6) and pectoralis major (innervated by medial and lateral pectoral nerves from C5-T1). This is a true internervous and intermuscular plane, making it theoretically atraumatic to muscles. The interval is marked by the cephalic vein running in the deltopectoral groove. The deep layer requires release of the clavipectoral fascia and ligation of the ascending branch of the anterior humeral circumflex artery. The internervous nature is advantageous but does NOT protect deeper structures like the axillary nerve, musculocutaneous nerve, and suprascapular nerve which remain at risk during capsule release and glenoid retraction.
Subscapularis Question
Q: Compare the biomechanical strength and clinical outcomes of subscapularis tenotomy versus lesser tuberosity osteotomy repair after shoulder arthroplasty.
A: Lesser tuberosity osteotomy provides stronger healing with bone-to-bone healing interface and lower failure rates (2-3 percent) compared to subscapularis tenotomy (5-10 percent failure rate). Osteotomy can be repaired with cortical screws (biomechanically strongest), suture anchors, or heavy sutures. Tenotomy repair uses suture anchors securing tendon to bone at the lesser tuberosity footprint. However, osteotomy carries risks of tuberosity malposition (causing impingement or weakness), nonunion (2-5 percent), and increased surgical complexity. In clinical practice, both techniques can achieve good outcomes with proper technique and postoperative protection. The choice depends on tissue quality, patient factors (younger patients may benefit from osteotomy), revision versus primary surgery, and surgeon experience and preference.
Glenoid Version Question
Q: What is normal glenoid version, how is it measured, and what are the implications of pathologic retroversion for shoulder arthroplasty component positioning?
A: Normal glenoid version is 0-5 degrees retroversion (slight posterior tilt of glenoid face). It is measured on axial CT using either the Friedman method (line perpendicular to glenoid face compared to scapular body line) or the scapular body method. Pathologic retroversion (over 10 degrees) occurs with posterior glenoid wear from rotator cuff tear arthropathy, chronic posterior instability, or osteoarthritis. Excessive retroversion leads to posterior humeral subluxation, glenoid component edge loading, loosening, and instability. Correction strategies include: eccentric reaming (can correct up to 10 degrees but limited by bone stock), augmented glenoid components (metal or polyethylene wedge on posterior), posterior bone grafting (for severe defects), or accepting retroversion and using posterior augmented component. Failure to address pathologic version results in high rates of posterior instability and glenoid component failure. Preoperative CT planning is mandatory to identify and plan for version abnormalities.
Complication Question
Q: A patient develops weakness in elbow flexion and sensory loss over the lateral forearm after shoulder arthroplasty. What nerve is likely injured, what is the mechanism, and how should this be managed?
A: This presentation suggests musculocutaneous nerve injury. The musculocutaneous nerve (C5-C7 from lateral cord) innervates coracobrachialis, biceps brachii, and brachialis (elbow flexion and forearm supination) and provides sensory innervation as the lateral antebrachial cutaneous nerve (lateral forearm sensation). During shoulder arthroplasty via deltopectoral approach, the nerve is at risk from excessive medial retraction of the conjoint tendon (short head biceps and coracobrachialis). The nerve enters the coracobrachialis 3-8 cm from the coracoid tip (mean 5.4 cm), and aggressive retraction beyond this point causes traction injury or direct trauma. Management: Most musculocutaneous nerve injuries are neurapraxias that recover spontaneously in 3-6 months. Initial management includes documentation of deficit, EMG/NCS at 6 weeks for baseline and prognosis, elbow splinting in flexion initially to reduce tension, and range of motion exercises to prevent stiffness. Patient counseling about expected recovery timeline is important. If no recovery by 6 months, consider nerve exploration, although outcomes of late exploration are poor. Prevention is critical: limit medial retraction, stay superior to the inferior border of subscapularis, and avoid dissection greater than 5 cm medial to coracoid tip.
Australian Context and Medicolegal Considerations
AOANJRR Data
The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) tracks shoulder arthroplasty outcomes:
- Shoulder arthroplasty volume: Over 4,000 procedures annually in Australia
- Revision rate: 7-8 percent at 10 years for shoulder replacement
- Reverse arthroplasty: Increasing proportion (now over 60 percent of shoulder replacements)
- Infection rate: 1-2 percent deep infection requiring revision
- Nerve injury: Not specifically tracked but estimated 1-4 percent in registry centers
Registry data guides evidence-based practice and quality improvement initiatives.
Medicolegal Considerations
Informed consent must include:
- Nerve injury risk (1-4 percent overall, axillary nerve most common)
- Subscapularis failure risk and functional consequences
- Infection, stiffness, instability, component loosening
- Need for revision surgery (7-8 percent at 10 years)
- Expected recovery timeline and functional outcomes
Documentation requirements:
- Preoperative nerve examination (baseline)
- Immediate postoperative nerve examination (identify injury early)
- Operative notes detailing approach, nerve protection, subscapularis repair technique
- Discussion of complications if they occur
Neurologic injury is a common source of litigation - detailed documentation and appropriate management are essential.
Australian Guidelines and Standards
Australian Commission on Safety and Quality in Health Care (ACSQHC) guidelines:
- Surgical site infection prevention bundle (preoperative antibiotics, skin preparation, normothermia)
- Venous thromboembolism prophylaxis for all joint replacement patients
- Patient information provision and shared decision-making
- Antibiotic prophylaxis: Cefazolin 2 grams IV (or vancomycin 15 mg per kg if penicillin allergic) within 60 minutes of incision
Hospital performance metrics:
- Nerve injury rates tracked as adverse event
- Revision rates compared to registry benchmarks
- Patient-reported outcome measures (PROMs) increasingly used for quality improvement
Adherence to national guidelines reduces complications and improves outcomes.
Shoulder Arthroplasty Anatomy
High-Yield Exam Summary
Key Anatomical Relationships
- •Axillary nerve: 5-7 cm inferior to acromion, quadrangular space, at risk during inferior capsule release
- •Musculocutaneous nerve: Enters coracobrachialis 3-8 cm from coracoid (mean 5.4 cm), at risk with medial retraction
- •Suprascapular nerve: Spinoglenoid notch posteriorly, at risk during posterior glenoid retraction
- •Radial nerve: Spiral groove at mid-humerus (20 cm from acromion), at risk during humeral canal preparation
- •Cephalic vein: Marks deltopectoral interval, ligate laterally or retract medially
- •Ascending branch anterior humeral circumflex: Requires ligation at superior border pectoralis major
Deltopectoral Approach Steps
- •Internervous plane: Deltoid (axillary nerve) and pectoralis major (pectoral nerves)
- •Incision: Coracoid to lateral acromion, along deltopectoral groove distally
- •Identify cephalic vein (marks interval), ligate lateral branches and retract medially
- •Release clavipectoral fascia, ligate ascending branch anterior humeral circumflex
- •Open rotator interval (between supraspinatus and subscapularis)
- •Release subscapularis: Tenotomy (1 cm medial to insertion) OR lesser tuberosity osteotomy
Nerve Protection Strategies
- •Axillary: Release inferior capsule under direct vision, avoid blind inferior retractors, limit inferior humeral translation
- •Musculocutaneous: Limit medial retraction, stay above inferior border subscapularis/conjoint tendon, avoid dissection greater than 5 cm from coracoid
- •Suprascapular: Minimize posterior retraction force and duration, avoid superior-posterior retractor placement
- •Radial: Stay centered in humeral canal during reaming/broaching, protect anterior cortex, gentle technique in osteoporotic bone
Subscapularis Management
- •Tenotomy: Release 1-2 cm medial to insertion, repair with 3-4 suture anchors, 5-10 percent failure rate
- •Osteotomy: 1 cm bone wafer with subscapularis attached, repair with screws or anchors, 2-3 percent failure, stronger healing
- •Repair: Arm in neutral rotation (not external rotation), secure fixation, avoid excessive tension
- •Postoperative: Sling 4-6 weeks, no external rotation, gradual ROM progression, belly press test at 12 weeks
Glenoid and Humeral Anatomy
- •Normal glenoid version: 0-5 degrees retroversion, measured on CT, pathologic if over 10 degrees
- •Humeral retroversion: 20-40 degrees (average 30 degrees) relative to transepicondylar axis
- •Glenoid: Pear-shaped, 25-30 mm diameter, shallow socket (25-30 percent of sphere)
- •Quadrangular space: Teres minor (superior), teres major (inferior), triceps long head (medial), surgical neck (lateral)
- •Contains: Axillary nerve and posterior humeral circumflex artery
Key Evidence and Complications
- •Overall neurologic complication rate: 1-4 percent in shoulder arthroplasty
- •Axillary nerve most common (0.6-4 percent), most are neurapraxias recovering in 3-6 months
- •Subscapularis failure: 2-10 percent, causes anterior instability and internal rotation weakness
- •Immediate postoperative nerve exam before regional anesthesia wears off - document findings
- •EMG/NCS at 6 weeks if nerve injury suspected, observation for 3-6 months (most recover)
- •AOANJRR: 7-8 percent revision rate at 10 years, nerve injury not tracked but estimated 1-4 percent