Shoulder Arthrodesis

Indications for Shoulder Arthrodesis

Primary Indications

1. Brachial Plexus Palsy (Most Common Indication)

• Complete or near-complete brachial plexus injury affecting C5–C6 (deltoid and rotator cuff)
• Flail, painful, unstable glenohumeral joint
• Prerequisite: functioning serratus anterior (long thoracic nerve, C5–C7) and trapezius (accessory nerve, CN XI)
• Elbow and hand function should ideally be preserved to benefit from shoulder positioning
• Chammas 2004 (PMID 15274265): Comparative series of 27 patients (11 upper palsy with a functional hand, 16 total palsy with a flail hand). Both groups gained function after glenohumeral fusion; a flail hand did NOT compromise the post-operative active range of movement, and pectoralis major strength was the key prognostic factor for hand excursion and shoulder strength. Prerequisite in every case was restored active elbow flexion before fusion.

2. Failed Shoulder Arthroplasty

• Failed TSA or RSA with irreparable glenoid bone loss, periprosthetic infection, or multiple revision failures
• Requires functioning serratus anterior and trapezius
• More complex due to bone loss — may require structural allograft

3. Irreparable Rotator Cuff Tear with Deltoid Loss

• Combined loss of both deltoid AND rotator cuff — neither TSA nor RSA is possible
• Classic scenario: prior deltoid detachment failure plus irreparable cuff
• RSA requires functioning deltoid; TSA requires intact cuff — if BOTH lost, arthrodesis is the only reconstructive option

4. Infection / Septic Arthritis / Chronic Osteomyelitis

• Uncontrolled septic glenohumeral joint where arthroplasty is contraindicated
• May be performed as a salvage once infection eradicated
• Higher non-union risk in previously irradiated or infected tissue

5. Flail Shoulder — Various Causes

• Tumour resection (proximal humerus or scapula with glenohumeral involvement)
• Paralytic conditions (poliomyelitis, upper motor neuron lesion)
• Severe post-traumatic bone and soft tissue loss

6. Recurrent Glenohumeral Instability with Severe Bone Loss

• Bipolar bone loss (humeral and glenoid) where instability surgery is not feasible
• Rare indication — most instability managed by soft tissue or bone procedures

When NOT to Perform Arthrodesis

Absolute Contraindications:

• Bilateral shoulder disease (patient cannot use crutches or perform personal hygiene)
• Non-functioning scapular muscles (fusion achieves nothing without scapulothoracic motion)
• Active uncontrolled infection at the operative site

Relative Contraindications:

• Significant contralateral shoulder disease
• Severe osteoporosis (fixation may fail)
• Charcot arthropathy (high non-union risk)
• Patient unable to comply with prolonged post-op immobilisation

Key Evidence

Rowe CR (1974) — PMID 4847239 (J Bone Joint Surg Am 1974;56(5):913-22). Classic re-evaluation of arm position in shoulder arthrodesis. Rowe argued AGAINST the historically high abduction angles then in use and advocated comparatively modest abduction (measured from the side of the body, NOT from the scapular plane), with the central message that excessive abduction leaves the arm protruding and impairs comfort and crutch use.

Cofield RH, Briggs BT (1979) — PMID 457712 (J Bone Joint Surg Am 1979;61(5):668-77). Seventy-one shoulders, mean follow-up nine and a half years, all with internal fixation. The achieved mean position was approximately 45° abduction, 25° flexion and 25° rotation; relief of pain was adequate in three-quarters and 82% felt they had benefited. Importantly, in this series the exact position of fusion had little effect on outcome — three-quarters could reach the trunk, half could reach the head, one-quarter could do light work at shoulder level.

Modern consensus position — Contemporary teaching favours a lower-profile position than the older 45° abduction, commonly summarised as the "rule of 30s" (approximately 30° abduction, 30° flexion, 30° internal rotation) or the slightly modified range used here (15–30° abduction, 15–25° flexion, 40–50° internal rotation). The unifying principle, not the precise degrees, is examinable: enough abduction/flexion for the hand to reach the face via scapular rotation, and enough internal rotation to reach the perineum and midline.

Chammas M et al. (2004) — PMID 15274265 (J Bone Joint Surg Br 2004;86(5):692-5). Comparison of 27 patients (upper vs total brachial plexus palsy). Glenohumeral arthrodesis improved function in both groups; a flail hand did not reduce post-operative range of movement, and pectoralis major strength was the significant prognostic factor for hand excursion and shoulder strength. Confirms brachial plexus palsy as a core indication, with restored elbow flexion as the prerequisite.

Anatomy Relevant to Shoulder Arthrodesis

Glenohumeral Joint

Articular Surfaces to be Prepared:

• Humeral head: Spherical articular surface, covered by hyaline cartilage 1–2mm thick. Must be fully denuded to bleeding cancellous bone for fusion.
• Glenoid: Slightly concave pear-shaped articular surface. Cartilage denuded entirely; subchondral bone prepared to bleeding cancellous bone.
• Acromion undersurface: Also prepared and incorporated into the fusion mass in many techniques — acromial contact with the humeral head provides additional surface area.

Bone Quality Concerns:

• In brachial plexus palsy: bone quality may be reduced from disuse; adequate but reduced
• In failed arthroplasty: significant bone stock deficiency — may need allograft
• In infection: bone quality may be compromised

Posterior Approach to the Glenohumeral Joint

Incision: Longitudinal incision along the spine of scapula extending laterally to the posterior deltoid.

Internervous Plane:

• Teres minor above (axillary nerve) and infraspinatus (suprascapular nerve)
• In brachial plexus palsy these muscles are denervated — the interval still used but muscles not functional
• Posterior capsule and residual cuff identified and reflected

Key Posterior Structures at Risk:

• Axillary nerve: exits the quadrangular space posteriorly, winds around the surgical neck. In brachial plexus cases, may already be injured. Identify and protect during dissection.
• Suprascapular nerve: deep in supraspinatus fossa and spinoglenoid notch. At risk from deep retractor placement posteriorly.
• Posterior circumflex humeral artery: accompanies axillary nerve.

Deltoid in Shoulder Arthrodesis

Denervated deltoid (brachial plexus):

• Not functional but present as a biological tissue envelope
• Preserved as soft tissue coverage over the plate
• Cannot use deltoid as a motor postoperatively

Intact deltoid (other indications):

• Must be protected during dissection
• Posterior approach splits the deltoid posteriorly — enter the posterior deltoid fibres from the posterior acromion, taking care not to detach it anteriorly
• Deltoid-splitting approaches risk denervating the anterior deltoid if the axillary nerve is not identified

Scapulothoracic Anatomy — The Functional Motor After Fusion

Serratus Anterior (Long Thoracic Nerve, C5–C7):

• Origin: lateral surfaces of ribs 1–9
• Insertion: costal (anterior) surface of scapula, medial border
• Function: protracts scapula, rotates scapula upward (inferior angle rotates laterally/anteriorly)
• CRITICAL for elevation post-fusion — rotates the glenoid upward so the fused arm elevates

Trapezius (Accessory Nerve, CN XI):

• Upper: elevates scapula; Middle: retracts scapula; Lower: depresses scapula, rotates upward
• Lower trapezius works synergistically with serratus anterior for scapular upward rotation
• Must be functioning for adequate post-fusion elevation

Clinical Test Preoperatively:

• Ask patient to attempt elevation — if scapular rotation visible (scapular rotation with inferior angle moving laterally), serratus and trapezius are functioning
• Winging of scapula (serratus palsy) = CONTRAINDICATION to arthrodesis

Surgical Technique — Shoulder Arthrodesis

Patient Position

Lateral decubitus or beach chair, with arm draped free.

• Lateral decubitus preferred by many for posterior approach — gravity assists in positioning the arm
• Ensure ability to manipulate the arm intraoperatively to confirm and set fusion position
• Image intensifier (fluoroscopy) available for intraoperative position confirmation

Setting the Fusion Position

The most important step — plan before making incisions.

Target Position (Cofield Modified Standard):

• Abduction: 15–30° (arm away from body in coronal plane)
• Forward Flexion: 15–25° (arm slightly anterior to coronal plane)
• Internal Rotation: 40–50° (forearm parallel to floor with elbow at 90°, or slightly internally rotated)

Practical intraoperative assessment:

1. With elbow flexed to 90°, the forearm should point toward the face and downward to the perineum when the shoulder is in the planned position
2. Confirm hand can reach the mouth (combined forward elevation via scapular rotation)
3. Confirm hand can reach the lower back and perineum
4. Mark the intended position with a temporary wire or confirm with fluoroscopy before definitive fixation

Step 1: Approach

Posterior approach to the glenohumeral joint:

1. Longitudinal incision along scapular spine, curving laterally over the posterior deltoid
2. Elevate posterior deltoid from the spine of scapula to expose the posterior scapula and proximal humerus
3. Identify the teres minor and infraspinatus interval (or go through the infraspinatus in brachial plexus cases where it is denervated)
4. Expose the posterior glenohumeral joint capsule
5. Open capsule and enter the joint

In brachial plexus palsy: The denervated muscles (infraspinatus, teres minor, supraspinatus) are swept aside. The posterior capsule is incised. The humeral head and glenoid are identified.

Step 2: Joint Surface Preparation

This is the most critical step for achieving union.

1. Denude the humeral head of all articular cartilage down to bleeding cancellous bone — use sharp curette, osteotome, or burr
2. Denude the glenoid articular surface completely to bleeding cancellous bone
3. Create flat opposing surfaces to maximise bone contact
4. Prepare the acromion undersurface similarly — the humeral head will be placed in contact with the underside of the acromion as part of the fusion mass in many techniques
5. Multiple drill holes into both surfaces to encourage vascular ingrowth

Key principle: Maximum bone contact surface area is the single most important technical factor for union. Inadequate preparation is the most preventable cause of non-union.

Step 3: Bone Grafting

Iliac crest autograft is the gold standard.

1. Harvest cancellous and corticocancellous bone from the ipsilateral or contralateral iliac crest
2. Pack graft into any gaps between the humeral head and glenoid
3. Place additional graft around the fusion site superiorly to the acromion contact

When additional graft is required:

• Failed arthroplasty with bone loss — structural allograft (femoral head allograft) may be needed
• Large bone defects from tumour or infection

Step 4: Plate Fixation

A long contoured reconstruction plate is the workhorse.

Plate configuration:

1. A 3.5mm or 4.5mm pelvic reconstruction plate (or dedicated shoulder arthrodesis plate) is contoured to span from the scapular spine/acromion, across the glenohumeral joint, down to the proximal to mid-humerus
2. The plate lies on the posterior-superior surface of the shoulder
3. Proximal fixation: screws into the scapular spine or base of acromion (3–4 screws)
4. Glenohumeral screws: 2–3 screws across the glenohumeral joint, compressing the prepared surfaces
5. Distal fixation: 3–4 screws into the proximal humeral shaft

Why long plate? The weight of the arm generates an enormous bending moment at the fusion site. Short plates fail. The plate must act as a long-moment-arm device, anchored both proximally (scapula) and distally (humerus).

Supplementary fixation:

• Some techniques use additional screws from the humerus into the acromion
• Intramedullary fixation (rarely used, technically demanding)
• External fixation (rarely used in adults)

Step 5: Position Confirmation

Before closing:

1. Confirm fusion position with fluoroscopy — check abduction angle on AP view
2. Check that arm hangs comfortably at side (not excessively abducted)
3. With elbow at 90°, forearm should be in appropriate internal rotation
4. Confirm arm can swing freely without catching

Step 6: Closure

1. Repair posterior deltoid back to scapular spine fascia
2. Layered closure over deep drain
3. Compressive dressing
4. Apply spica cast or orthosis in the fusion position for 6–12 weeks

Complications of Shoulder Arthrodesis

Post-operative Protocol

Immobilisation Phase (0–12 weeks)

External immobilisation in fusion position is mandatory until radiological evidence of early union.

Options:

• Shoulder spica cast: traditional, effective, poorly tolerated
• Custom thoracohumeral orthosis (brace): better tolerated, allows hygiene, preferred in most modern centres
• Duration: 6–12 weeks depending on fusion progress and patient compliance

Monitoring:

• X-rays at 6 weeks and 12 weeks — look for early bridging callus
• If non-union suspected: CT at 3–6 months (more sensitive than X-ray)

Rehabilitation Phase (Weeks 12+)

Once early union confirmed:

• Remove immobilisation
• Begin scapulothoracic physiotherapy — train serratus anterior and trapezius to use the fused shoulder for elevation
• The patient must LEARN to use scapulothoracic motion to position the arm — this is a re-education process
• Progressive loading: light activities from 12 weeks, heavy activities from 6 months

Return to Function:

• Light activities of daily living: 3–4 months
• Heavy manual work: 6 months
• Driving: typically 6 months (varies by jurisdiction and arm dominance)

Expected Functional Outcomes

Strength: Lifting strength: approximately 50–70% of the contralateral arm after successful fusion. Significantly superior to a flail, unstable shoulder.

Rowe 1974 (PMID 4847239) and Cofield & Briggs 1979 (PMID 457712) outcomes: These classic series established that a broad, sensible fusion position combined with rigid internal fixation gives durable pain relief and useful function. Cofield notably found that the exact position had little effect on outcome, while gross malposition (especially insufficient internal rotation, leaving the patient unable to reach the perineum) remains a genuine cause of dissatisfaction.