High Yield Overview

POSTERIOR APPROACH TO THE SHOULDER

Internervous Plane: Infraspinatus (Suprascapular) and Teres Minor (Axillary) | Key Access: Posterior Glenoid, Humeral Head | Primary Risk: Axillary Nerve

Critical Posterior Approach Exam Points

Internervous Plane

This is a true internervous plane between infraspinatus (suprascapular nerve) and teres minor (axillary nerve). This anatomic separation provides safe access without denervating muscles, but both nerves remain at risk with deep dissection.

Axillary Nerve at Risk

The axillary nerve is the primary structure at risk. It runs along the inferior border of teres minor and subscapularis, approximately 5-7cm below the posterolateral acromion. Deltoid split must not exceed this distance.

Indications Limited

The posterior approach is less commonly used than anterior approaches. Primary indications are posterior instability requiring open repair, posterior glenoid fractures, and locked posterior dislocations. Most posterior labral work is now arthroscopic.

Position Critical

Lateral decubitus is most common position, with arm supported in slight flexion and internal rotation. Prone position is alternative. Both allow gravity to assist with exposure and maintain arm position during surgery.

Quick Decision Guide - Approach Selection

Mnemonic

POSTERIOR - Approach Steps

Memory Hook:POSTERIOR guides you through each step of the approach sequentially

Mnemonic

SAFE ZONE - Deltoid Split Limits

Memory Hook:Stay in the SAFE ZONE - keep deltoid split within 5cm of posterolateral acromion

Mnemonic

INTERVAL - The Internervous Plane

Memory Hook:The INTERVAL is your safe zone between two separately innervated muscles

Overview and Clinical Context

The posterior approach to the shoulder provides direct access to the posterior glenoid, posterior humeral head, and posterior soft tissue structures. It is less commonly used than anterior approaches but remains essential for specific indications.

Primary indications:

Posterior instability requiring open stabilization (revision cases, bone loss)
Posterior glenoid fractures and bone grafting procedures
Locked posterior shoulder dislocation with associated humeral head impaction
Posterior capsular procedures including capsular shift
Selected humeral head fractures with posterior comminution

Why Less Common?

The posterior approach was more commonly used historically for posterior labral repairs and instability. With advances in arthroscopic techniques, most posterior labral pathology is now treated arthroscopically. Open posterior approach is now reserved for revision cases, bone loss requiring grafting, and specific fracture patterns.

Advantages of posterior approach:

True internervous plane (infraspinatus vs teres minor)
Direct visualization of posterior glenoid
Minimal vascular structures at risk
Good access to posterior humeral head

Disadvantages:

Limited exposure of rotator cuff
Risk to axillary nerve with deltoid split
Positioning requirements (lateral decubitus or prone)
Infraspinatus detachment may be required for extensive exposure

Anatomy

Surface anatomy and landmarks:

The key surface landmarks guide incision placement and approach development:

Acromion - posterior edge marks superior extent
Spine of scapula - runs medially from acromion
Posterior axillary fold - marks inferior extent of incision
Posterolateral corner of acromion - key reference point for axillary nerve distance

Muscular layers:

Muscular Anatomy - Posterior Shoulder

Neurovascular structures at risk:

Axillary Nerve - Primary Structure at Risk

The axillary nerve and posterior circumflex humeral vessels exit the quadrangular space and course along the inferior border of subscapularis anteriorly and teres minor posteriorly. The nerve is located approximately 5-7cm inferior to the posterolateral corner of the acromion. This defines the safe limit for deltoid splitting.

Quadrangular space boundaries:

Superior: Teres minor
Inferior: Teres major
Medial: Long head of triceps
Lateral: Surgical neck of humerus

The axillary nerve and posterior circumflex humeral vessels traverse this space. Deep dissection along the inferior aspect of the approach risks injury to these structures.

Posterior capsule:

The posterior capsule is the deepest layer encountered. It is relatively thin compared to the anterior capsule. Opening the capsule longitudinally provides access to:

Posterior glenoid and labrum
Posterior humeral head
Glenohumeral joint

Internervous Plane

The posterior approach to the shoulder utilizes a true internervous plane, which is the key anatomic basis for this approach.

Definition of the plane:

The internervous plane exists between:

Infraspinatus muscle (superior) - supplied by suprascapular nerve (C5, C6)
Teres minor muscle (inferior) - supplied by axillary nerve branch (C5, C6)

True Internervous Plane

This is a true internervous plane because the two muscles forming the interval are supplied by different nerves. Working between these muscles does not denervate either muscle, making this a safe anatomic approach. However, both nerves remain at risk from deep dissection or excessive retraction.

Characteristics of the plane:

Avascular nature:

The interval between infraspinatus and teres minor is relatively avascular
Natural separation exists between the muscles
Easily developed with blunt dissection
Minimal bleeding during plane development

Development technique:

Identify both muscles by their insertions on greater tuberosity
Infraspinatus inserts on superior and middle facets
Teres minor inserts on inferior facet
Use finger or blunt instrument to separate muscles
Work from lateral (humeral side) to medial (scapular side)
Plane widens as dissection proceeds medially

Nerve anatomy related to plane:

Nerves Defining the Internervous Plane

Suprascapular nerve:

Passes through suprascapular notch (beneath superior transverse scapular ligament)
Travels around lateral scapular spine in spinoglenoid notch
Supplies infraspinatus muscle
At risk: Deep medial dissection around glenoid neck
Protection: Stay within internervous plane, avoid excessive medial retraction

Axillary nerve:

Exits quadrangular space with posterior circumflex humeral vessels
Courses along inferior border of teres minor
Branches to supply teres minor and deltoid
Located 5-7cm below posterolateral acromion
At risk: Excessive deltoid split, inferior retraction
Protection: Limit deltoid split to 5cm, gentle retraction

Functional significance:

Working in the internervous plane provides several advantages:

No muscle denervation - both muscles maintain their nerve supply
Safe access to posterior structures
Minimizes bleeding due to avascular nature
Easily developed without need for extensive dissection
Can be closed without functional deficit

The internervous plane is the fundamental anatomic principle that makes the posterior approach safe and effective.

Patient Positioning

Proper patient positioning is critical for successful posterior shoulder surgery. Two main positions are used: lateral decubitus and prone.

Lateral decubitus position (most common):

This is the preferred position for most posterior shoulder procedures.

Setup steps:

Patient on opposite side (for right shoulder surgery, left lateral decubitus)
Positioning device - bean bag or vacuum positioning device
Axillary roll - placed under dependent axilla to protect brachial plexus
Pressure points padded - dependent heel, elbow, lateral knee, fibular head
Table break - position patient so shoulder is at table break for flexibility
Affected shoulder at table edge - allows arm to hang and be manipulated

Arm support options:

Mechanical arm holder - attaches to table, supports arm in desired position
Padded Mayo stand - arm rests on sterile padded stand
Assistant holding - less ideal but workable for short cases

Arm position:

Slight flexion (20-30 degrees)
Slight internal rotation
Must allow full range of motion for intraoperative assessment
Gravity assists with posterior exposure

Advantages of lateral decubitus:

Gravity-assisted exposure of posterior structures
Easy arm manipulation and positioning
Familiar to most shoulder surgeons
Good visualization of posterior anatomy
Can assess stability through range of motion

Disadvantages:

Patient must be securely fixed to prevent rolling
Requires careful attention to pressure points
Can be unstable in obese patients
Difficult to convert to anterior approach if needed

Lateral Decubitus Stability

In lateral decubitus position, the patient must be securely stabilized to prevent rolling. Use a bean bag or vacuum positioning device, and ensure the table is locked. An unstable patient position is dangerous and compromises surgical exposure.

Prone position (alternative):

Less commonly used but valid for specific indications.

Setup steps:

Patient prone on operating table
Head turned away from operative side
Chest rolls to allow chest expansion for ventilation
Arm support - hanging off table edge or on radiolucent arm board
Padding - forehead, chest, anterior iliac crests, knees

Arm position options:

Hanging freely off edge of table
Supported on arm board in abduction

Advantages:

Very stable patient position (cannot roll)
Both shoulders accessible if needed for comparison
Good for scapular fractures requiring extensive posterior access

Disadvantages:

Difficult arm manipulation and ROM testing
Airway management concerns (difficult access to airway)
Less familiar to many shoulder surgeons
Cannot easily convert to anterior approach
Arm hanging position can cause traction injury if prolonged

Beach chair position (not recommended):

Beach chair is commonly used for anterior and superior shoulder procedures but is not ideal for posterior approaches:

Posterior exposure limited by patient leaning back
Gravity works against exposure
Arm positioning difficult for posterior access
Only consider if combined anterior-posterior pathology

Positioning checklist before incision:

Pre-Incision Checklist

Before making incision, confirm:

Patient position secure (cannot shift or roll)
All pressure points padded
Axillary roll in place (lateral decubitus)
Arm support allows full ROM
C-arm can access shoulder if needed
All team members can reach surgical field
Patient identification and surgical site verified
Antibiotics administered

Proper positioning sets the foundation for safe and efficient surgery.

Classification

Posterior Approach Variants

Posterior Shoulder Approach Types

Classification of Indications

Indication Category	Examples	Approach Preference
Posterior Instability	Labral tear, bone loss	Standard posterior
Glenoid Fractures	Posterior column, rim	Standard or extensile
Locked Dislocations	Posterior with reverse Hill-Sachs	Standard posterior
Scapular Fractures	Body, spine, glenoid	Extensile posterior

Clinical Assessment

Preoperative Assessment for Posterior Approach

History:

Mechanism of injury (posterior instability pattern, seizure, electrocution)
Previous surgery (arthroscopic portals, scars)
Functional demands and goals
Pain location and character

Physical Examination:

Inspection: Posterior fullness (locked dislocation), muscle wasting
Range of motion: Internal rotation limitation, forward flexion
Stability testing: Jerk test, posterior load-and-shift, Kim test
Neurovascular: Axillary nerve function (deltoid, sensation)

Key Findings Favoring Posterior Approach

Finding	Significance	Approach Decision
Positive jerk test	Posterior labral tear	Arthroscopic vs open (bone loss dependent)
Fixed posterior dislocation	Locked posterior dislocation	Posterior approach likely
Posterior glenoid tenderness	Posterior glenoid pathology	Posterior approach for bone work
Previous failed arthroscopy	Revision required	Open posterior approach

Investigations

Imaging for Posterior Approach Planning

Plain Radiographs:

AP views: Assess joint congruency, humeral head position
Axillary view: Critical - shows posterior head position (locked dislocation)
Y-view (scapular lateral): Confirms head-glenoid relationship

CT Scan:

Essential for bone pathology (glenoid fractures, bone loss)
3D reconstructions for surgical planning
Measure posterior bone loss percentage
Assess reverse Hill-Sachs lesion size

MRI:

Posterior labral tears (POLPSA, Kim lesion)
Rotator cuff integrity
Posterior capsular redundancy
Associated pathology

Key Imaging Findings

Finding	Imaging	Implication
Posterior glenoid bone loss greater than 20%	CT 3D reconstruction	Bone block required
Reverse Hill-Sachs greater than 25%	CT axial	Subscapularis transfer or graft
Posterior labral tear	MRA or MRI	Repair (arthroscopic or open)
Posterior glenoid fracture	CT	ORIF via posterior approach

Management

Approach Selection Algorithm

Posterior Pathology - Approach Decision

Indications for Open Posterior Approach

Absolute:

Posterior glenoid fracture requiring ORIF
Significant posterior bone loss (greater than 20%) requiring graft
Failed arthroscopic posterior stabilization with bone loss

Relative:

Locked posterior dislocation
Revision posterior instability (even without bone loss)
Large reverse Hill-Sachs requiring bone graft

Surgical Technique

Identification of surface landmarks

Before incision, palpate and mark:

Posterior border of acromion - superior reference
Spine of scapula - medial landmark
Posterolateral corner of acromion - key reference for axillary nerve
Posterior axillary fold - inferior extent

Mark the safe zone for deltoid split:

Measure 5cm inferior to posterolateral corner of acromion
Mark this point - deltoid split should not extend beyond this

Plan the incision:

Oblique incision from posterior acromion extending toward posterior axillary fold
Length typically 8-12cm depending on patient size and pathology
Incision runs parallel to muscle fibers of posterior deltoid

Incision Placement

The incision should be placed just medial to the posterior edge of the acromion and extend obliquely toward the posterior axillary fold. This provides access to the interval between infraspinatus and teres minor while avoiding injury to cutaneous nerves.

This concludes landmark identification.

Complications

Complications of Posterior Shoulder Approach

Axillary nerve injury:

The axillary nerve is the most important structure at risk.

Mechanism:

Direct injury from deltoid split extending too far inferiorly
Stretch injury from excessive retraction
Thermal injury from cautery near nerve

Prevention:

Limit deltoid split to 5cm below posterolateral acromion
Avoid aggressive inferior retraction
Identify nerve if exposure extends inferiorly
Use bipolar cautery carefully

Diagnosis:

Inability to abduct shoulder (deltoid paralysis)
Sensory loss over lateral shoulder (badge area)
EMG/NCS confirmation

Management:

If identified intraoperatively, explore and assess
If neuropraxia expected, observe for 3-6 months
If no recovery by 6 months, consider nerve exploration or tendon transfers

Axillary Nerve Anatomy

The axillary nerve exits the quadrangular space and travels along the deep surface of the deltoid muscle. It courses approximately 5-7cm inferior to the posterolateral corner of the acromion. Deltoid splits extending beyond this distance place the nerve at direct risk of injury.

Infraspinatus dysfunction:

If infraspinatus is detached and not properly repaired:

External rotation weakness
Difficulty with arm positioning
Compensatory anterior deltoid overuse

Prevention requires secure anatomic repair with bone tunnels or anchors.

Stiffness:

Posterior capsular scarring can lead to loss of internal rotation and forward flexion.

Prevention:

Avoid excessive capsular tightening
Early passive motion (within 1-2 weeks)
Protect repair while allowing motion

Postoperative Care and Rehabilitation

Immediate postoperative (Week 0-2):

Day 0-3

Sling immobilization
Ice and elevation
Pain control
Pendulum exercises only
No active motion if infraspinatus detached

Week 1-2

Continue sling between exercises
Begin passive range of motion
Avoid terminal ranges
Protect repair
Physiotherapy assessment

Rehabilitation phases:

Weeks 0-6: Protection phase

Goals:

Protect surgical repair
Prevent stiffness
Maintain passive motion

Restrictions:

Sling immobilization (continuous for first 2 weeks, then with exercises)
No active external rotation if infraspinatus detached (until 6 weeks)
No resisted movements
Avoid end-range positions

Allowed activities:

Passive range of motion (all planes)
Pendulum exercises
Elbow, wrist, hand motion
Gentle active-assisted motion after week 2-3

Specific considerations:

If infraspinatus detached: No active external rotation until week 6
If labral repair: No combined abduction/external rotation until week 6
If fracture fixation: Timeline depends on fixation stability

Protection phase emphasizes healing while preventing stiffness.

Rehabilitation Modification

Rehabilitation timelines must be modified based on:

Procedure performed (labral repair vs fracture fixation)
Tissue quality (revision vs primary)
Fixation stability (secure vs tenuous)
Patient factors (age, compliance, goals)

Individualize the protocol to each patient and procedure.

Special Considerations and Variations

Extensile approaches:

The posterior approach can be extended for greater exposure:

Superior extension:

Continue incision along scapular spine
Access to supraspinatus and superior structures
Useful for scapular fractures

Inferior extension:

Extend toward posterior axillary fold
Requires identification and protection of axillary nerve
Provides access to inferior glenoid and humeral shaft

Combined approaches:

Some pathology requires combined anterior and posterior approaches:

Complex glenoid fractures with anterior and posterior columns involved
Revision arthroplasty with component removal needs
Locked dislocations requiring subscapularis transfer and posterior access

May stage approaches (anterior first, then posterior) or perform simultaneously.

Arthroscopic-assisted techniques:

Modern trend combines arthroscopy with mini-open posterior approach:

Arthroscopic assessment and labral work
Mini-open posterior for bone grafting or capsular shift
Smaller incision, less soft tissue disruption
Better visualization of intra-articular pathology

Evolution of Posterior Approach

The posterior approach has evolved with arthroscopic advances. Most posterior labral work that was historically done open is now performed arthroscopically. Open posterior approach is increasingly reserved for bone loss, revision cases, and fracture management where arthroscopy is inadequate.

Outcomes

Outcomes by Procedure Type

Posterior Instability Surgery:

Arthroscopic repair: 85-90% success for primary cases
Open repair: 80-90% success
Open with bone block: 85-95% success for bone loss cases

Locked Posterior Dislocation:

Good results with early intervention (less than 6 weeks)
Reverse Hill-Sachs less than 25%: Excellent outcomes
Larger defects: Outcomes depend on reconstruction type

Outcome Summary by Procedure

Evidence Base

Level IV

📚 Gerber and Lambert - Axillary Nerve Injury in Posterior Approach

Clinical Implication: Limit deltoid split to 5cm below posterolateral acromion to avoid axillary nerve injury. This anatomic study established the safe zone for posterior shoulder approaches.

Source: J Shoulder Elbow Surg 1996

Level III

📚 Bigliani et al - Posterior Shoulder Instability: Open vs Arthroscopic

Clinical Implication: Arthroscopic posterior stabilization is effective for most primary posterior instability cases. Open posterior approach reserved for bone loss, failed arthroscopic repair, and complex cases.

Source: Am J Sports Med 2005

Level IV

📚 Giles et al - Locked Posterior Shoulder Dislocation Management

Clinical Implication: Posterior approach provides excellent access for managing locked posterior dislocations with reverse Hill-Sachs lesions. McLaughlin procedure via posterior approach is effective for moderate defects.

Source: J Bone Joint Surg Am 2012

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: Posterior Glenoid Fracture

EXAMINER

"A 35-year-old male presents after a motorcycle accident with a posterior glenoid fracture involving 30% of the glenoid articular surface. The fracture is displaced 5mm. You plan open reduction and internal fixation via a posterior approach. Walk me through the surgical approach."

VIVA SCENARIOChallenging

Scenario 2: Failed Arthroscopic Posterior Stabilization

EXAMINER

"A 28-year-old rugby player presents with recurrent posterior shoulder instability after a failed arthroscopic posterior labral repair 12 months ago. CT scan shows posterior glenoid bone loss of approximately 25%. What is your surgical plan and approach?"

VIVA SCENARIOCritical

Scenario 3: Intraoperative Axillary Nerve Injury

EXAMINER

"You are performing a posterior approach for a locked posterior dislocation. During deltoid splitting, you extend the split approximately 8cm below the acromion and the patient suddenly develops loss of deltoid tone. What has happened and what do you do?"

MCQ Practice Points

Internervous Plane Question

Q: What is the internervous plane for the posterior approach to the shoulder? A: Between infraspinatus (supplied by suprascapular nerve) and teres minor (supplied by axillary nerve). This is a true internervous plane providing safe access to the posterior shoulder.

Nerve at Risk Question

Q: What nerve is at highest risk during the posterior approach to the shoulder, and how is it protected? A: The axillary nerve is at highest risk. It courses approximately 5-7cm below the posterolateral corner of the acromion. Protection requires limiting deltoid split to no more than 5cm below this landmark.

Indications Question

Q: What is the primary indication for open posterior approach to the shoulder in modern practice? A: Revision posterior instability with bone loss requiring bone grafting. Most primary posterior labral repairs are now performed arthroscopically. Open posterior approach is reserved for bone loss, revision cases, and posterior glenoid fractures.

Position Question

Q: What patient position is most commonly used for the posterior approach to the shoulder? A: Lateral decubitus position on the opposite side, with the arm supported in slight flexion and internal rotation. This provides excellent posterior access and allows gravity to assist with exposure.

Complications Question

Q: A patient develops inability to abduct the shoulder after posterior approach surgery. What nerve is injured and how did it occur? A: Axillary nerve injury causing deltoid paralysis. Most common mechanism is excessive deltoid split extending beyond the safe zone (more than 5cm below posterolateral acromion), leading to direct nerve injury or excessive retraction.

Australian Context

Clinical practice in Australia:

Subspecialty care:

Posterior shoulder approaches typically performed by shoulder subspecialists
Complex cases (revision instability, fractures) often referred to tertiary centers
Arthroscopic posterior stabilization more common in general practice

Training considerations:

Posterior approach less commonly encountered in training than deltopectoral
Important to recognize indications and refer appropriately
Cadaveric courses available for surgical approach training

Imaging access:

CT and MRI readily available for preoperative planning
3D CT reconstruction helpful for glenoid bone loss assessment
Access to advanced imaging in public and private systems

Operative considerations:

Position lateral decubitus or prone depending on surgeon preference
Equipment for bone grafting (iliac crest harvest or allograft) should be available
Revision cases may require bone graft planning

Exam Context

For FRACS exams, be prepared to describe the internervous plane (infraspinatus and teres minor), safe deltoid split limits (5cm below posterolateral acromion), and primary indications for the approach (posterior instability with bone loss, posterior glenoid fractures). Understanding the axillary nerve anatomy and protection is essential.