SUBTALAR ARTHRODESIS
Isolated Subtalar Fusion | Post-Traumatic Arthritis | Hindfoot Deformity Correction
INDICATIONS
Critical Must-Knows
- Subtalar joint provides 75% of hindfoot inversion/eversion
- Post-traumatic arthritis develops in 20-50% after intra-articular calcaneal fractures
- Adjacent joint arthritis occurs in 30-40% at 10 years
- Screw fixation superior to staple or plate constructs
- Bone graft recommended for all fusions (structural for deformity)
Examiner's Pearls
- "Isolated subtalar arthrodesis preserves ankle and midfoot motion
- "In-situ fusion for arthritis, realignment fusion for deformity
- "Sinus tarsi approach allows direct visualization and minimal soft tissue disruption
- "Nonunion risk factors: smoking, diabetes, worker's compensation
Clinical Imaging
Imaging Gallery
Critical Subtalar Arthrodesis Exam Points
Biomechanics
75% of hindfoot motion occurs at subtalar joint. Triple arthrodesis includes subtalar, talonavicular, and calcaneocuboid joints. Isolated fusion preserves midfoot flexibility.
Indications
Post-traumatic arthritis (70% of cases) following calcaneal fracture. Must document failed conservative management for 6-12 months before surgery.
Fixation
Two large screws (6.5-7.3mm) in divergent pattern. Start at posterior calcaneus, aim for talar neck. Compression critical for fusion.
Complications
Adjacent joint arthritis develops in 30-40% at 10 years. Sural nerve injury 5-10%. Nonunion 5-10% with risk factors.
Quick Decision Guide: Subtalar Arthrodesis vs Alternatives
| Clinical Scenario | Classification | Treatment | Key Pearl |
|---|---|---|---|
| Isolated subtalar arthritis, preserved ankle | Post-traumatic arthritis | Isolated subtalar arthrodesis | Preserves 50% of hindfoot motion via ankle |
| Subtalar plus talonavicular arthritis | Panarthrosis | Double arthrodesis | Preserves calcaneocuboid motion |
| Rigid planovalgus with all 3 joints involved | Severe deformity | Triple arthrodesis | Addresses all deformed joints simultaneously |
| Flexible planovalgus deformity | Repairable coalition | Coalition resection plus tendon transfer | Preserve motion when possible in young patients |
Mnemonics for Subtalar Arthrodesis
PAIDIndications for Subtalar Fusion
Memory Hook:You get PAID for fixing subtalar problems - post-traumatic arthritis is the bread and butter!
SEIFSurgical Approach Layers (Sinus Tarsi)
Memory Hook:SEIF the subtalar joint - cut down in Skin, EDB, Interosseous ligament, Fat layers!
FLATScrew Positioning Technique
Memory Hook:Keep it FLAT - screws From posterior, Lateral-to-medial, Aimed at neck, Two large screws!
SCANDNonunion Risk Factors
Memory Hook:Avoid a SCAND-al with fusion - control Smoking, Compensation, AVN, NSAIDs, Diabetes!
Overview and Epidemiology
Clinical Context
Subtalar arthrodesis is the most common isolated hindfoot fusion procedure. It addresses painful arthritis while preserving ankle and midfoot motion, maintaining approximately 50% of overall hindfoot inversion/eversion function. The procedure is particularly effective for post-traumatic arthritis following intra-articular calcaneal fractures, which account for 70% of cases.
Demographics and Epidemiology
- Age: Most common in 40-60 year age group
- Gender: Male predominance (2:1) due to trauma pattern
- Timing: Average 2-5 years from initial calcaneal injury
- Bilateral: 10-15% of cases involve both feet
- Associated injuries: 25% have ipsilateral foot/ankle pathology
Natural History
- Arthritis development: 20-50% after intra-articular calcaneus fracture
- Conservative failure: 85% require surgery after 12 months conservative care
- Adjacent joint degeneration: 30-40% at 10 years post-fusion
- Function: 75% return to previous employment level
- Revision rate: 5-10% for nonunion or malunion
Pathophysiology and Mechanisms
Critical Anatomy
The subtalar joint consists of three facets (anterior, middle, posterior) between talus and calcaneus. The posterior facet is the largest and provides the majority of joint surface area. The sinus tarsi contains the interosseous talocalcaneal ligament (strongest restraint) and cervical ligament. Understanding this anatomy is essential for complete joint denudation and optimal fusion positioning.
Subtalar Joint Facets and Function
| Facet | Surface Area | Location | Clinical Significance |
|---|---|---|---|
| Posterior | 60-70% | Under talar body | Main weight-bearing surface, most commonly arthritic |
| Middle | 20-25% | On sustentaculum tali | Supports talar head, often spared in post-traumatic arthritis |
| Anterior | 10-15% | On anterior calcaneus | Small contribution, may be congenitally absent |
Biomechanics
Motion Contribution
- Inversion/eversion: 75% of total hindfoot motion
- Ankle contribution: 25% of inversion/eversion
- Axis of rotation: 42° to horizontal, 16° to midline
- Coupled motion: Inversion with supination and adduction
- ROM: Normal 20-30° inversion, 10-15° eversion
Post-Fusion Biomechanics
- Remaining motion: 50% of hindfoot function via ankle
- Gait adaptation: Increased ankle motion to compensate
- Adjacent joints: 20-30% increased stress on ankle/midfoot
- Energy cost: 5-10% increase in walking energy expenditure
- Function preservation: Better than triple arthrodesis
Classification Systems
Classification by Indication
Subtalar Arthrodesis Indications Classification
| Category | Specific Conditions | Typical Age | Fusion Approach |
|---|---|---|---|
| Post-traumatic | After calcaneal fracture (Sanders III-IV most common) | 40-60 years | In-situ fusion via sinus tarsi approach |
| Inflammatory | Rheumatoid, psoriatic, ankylosing spondylitis | 30-50 years | In-situ fusion with soft tissue balancing |
| Deformity | Rigid planovalgus (PTTD IV), cavovarus (neurologic) | 50-70 years | Realignment fusion with structural graft |
| Coalition | Symptomatic talocalcaneal or calcaneonavicular coalition | 15-30 years | Resection plus fusion or primary fusion |
Key Classification Points:
- In-situ fusion: For arthritis without significant deformity (70% of cases)
- Realignment fusion: For rigid deformity requiring correction (25% of cases)
- Isolated vs combined: Subtalar alone if other hindfoot joints preserved
- Primary vs revision: Revision has lower success rate (70-80% vs 85-90%)
This classification guides surgical approach and patient counseling.
Clinical Assessment
History
- Pain location: Subtalar vs ankle vs midfoot
- Pain character: Sharp, dull, aching, burning
- Timing: Constant vs activity-related vs end-of-day
- Mechanism: Prior trauma (calcaneal fracture most common)
- Function: Walking distance, stairs, uneven ground difficulty
- Prior treatment: Orthotics, injections, physical therapy, medications
- Occupation: Heavy labor, prolonged standing requirements
- Smoking status: Critical for fusion success
Physical Examination
- Gait: Antalgic gait, heel strike pattern
- Alignment: Hindfoot varus/valgus on standing (compare to opposite)
- Palpation: Tenderness over sinus tarsi, lateral ankle wall
- ROM: Subtalar motion (inversion/eversion), painful arc
- Ankle ROM: Document preserved ankle motion (rules out ankle arthritis)
- Instability: Anterior drawer, talar tilt testing
- Neurovascular: Dorsalis pedis, posterior tibial pulses, sensation
- Peroneal tendons: Impingement from heel widening
Specific Tests
Clinical Assessment Tests
Technique: Stabilize ankle in neutral with one hand, grasp heel with other hand and invert/evert.
Normal ROM: 20-30° inversion, 10-15° eversion. Findings: Pain at end-range, crepitus, restricted motion (under 50% of normal). Correlates with arthritis severity.
Technique: Patient stands on one leg and rises onto toes.
Normal: Can perform 10+ repetitions without pain. Abnormal: Unable to perform or severe pain indicates subtalar or posterior tibial pathology.
Technique: Fluoroscopy-guided subtalar joint injection with 2-3mL local anesthetic (bupivacaine 0.5%) plus steroid.
Positive test: Greater than 75% pain relief for duration of anesthetic. Value: Confirms subtalar joint as primary pain generator, predicts fusion success over 90%.
Differential Diagnosis
Must rule out:
- Ankle arthritis: Check ankle ROM and pain, obtain mortise views
- Talonavicular arthritis: Palpate, stress test, imaging
- Tarsal coalition: Often bilateral, limited subtalar motion since childhood
- Peroneal tendon pathology: Subluxation, tendinitis, tears
- Sinus tarsi syndrome: Localized pain, history of inversion injury
- CRPS: Disproportionate pain, allodynia, vasomotor changes
Diagnostic injection helps differentiate subtalar from other sources of hindfoot pain.
Investigations
Imaging Protocol
Imaging Studies
Standard views:
- AP, lateral, oblique foot (weight-bearing)
- AP mortise and lateral ankle (weight-bearing)
- Hindfoot alignment view (Saltzman view)
Findings to assess:
- Joint space narrowing (posterior facet most common)
- Subchondral sclerosis and cyst formation
- Osteophyte formation
- Heel alignment (varus/valgus)
- Calcaneal pitch and Bohler's angle
- Adjacent joint arthritis (ankle, talonavicular, calcaneocuboid)
- Previous fracture pattern and malunion
Plain radiographs are essential baseline but may underestimate arthritis severity.
Indications: All patients being considered for subtalar arthrodesis.
Protocol: Fine-cut CT (1mm slices) of hindfoot with coronal, sagittal, and axial reconstructions.
Value:
- Accurately quantifies posterior facet arthritis
- Evaluates middle and anterior facets (often normal on radiographs)
- Assesses bone quality and presence of cysts
- Identifies tarsal coalition anatomy
- Measures exact heel alignment in multiple planes
- Surgical approach planning (bone defects, screw trajectory)
- Detects occult ankle or midfoot arthritis
CT is the gold standard for subtalar arthrodesis planning and is obtained in virtually all cases.
Indications:
- Rule out avascular necrosis of talus (affects fusion strategy)
- Assess soft tissue pathology (tendons, ligaments)
- Evaluate bone marrow edema pattern
- Differentiate arthritis from other causes of pain
- Occult fracture or stress injury
Findings: Cartilage loss, bone marrow edema, AVN, tendon tears, ligament injury.
Limitations: More expensive, not essential for most cases, CT superior for bony detail.
Indications:
- Multiple potential pain sources
- Previous failed fusion or surgery
- Diagnostic uncertainty despite standard imaging
Value: Combines anatomic (CT) and metabolic (SPECT) information to precisely localize active pathology. Expensive but can be invaluable in complex cases.
Laboratory Studies
Routine Preoperative Labs
- Complete blood count (CBC): Screen for anemia, infection
- Renal function: Creatinine, eGFR for contrast studies
- Coagulation: If on anticoagulation or bleeding history
- Group and screen: Rarely needed but institutional requirement
- Urinalysis: Screen for occult infection
Specific Indications
- HbA1c: All diabetics - must be under 8% (ideally under 7%)
- Inflammatory markers: CRP, ESR if concern for infection
- Rheumatoid factor, ANA: If inflammatory arthropathy suspected
- Vitamin D, calcium: If osteoporosis or metabolic bone disease
- Thyroid function: If concerns about bone metabolism
Imaging Pearls
CT scan is mandatory for surgical planning in subtalar arthrodesis. It provides critical information about:
- Exact extent of arthritis (often more than radiographs suggest)
- Bone stock and quality for screw purchase
- Presence and location of bone cysts requiring grafting
- Optimal screw trajectory to avoid anterior penetration
- Adjacent joint status (30-40% have some degeneration)
Diagnostic subtalar injection should be performed in all cases with:
- Clinical examination unclear
- Multiple potential pain sources
- Adjacent joint arthritis present on imaging
- Previous failed surgery
A positive injection (over 75% relief) predicts over 90% satisfaction with fusion.
Management Algorithm
Non-Operative Treatment Algorithm
Conservative Treatment Steps
Goal: Reduce inflammation and pain
Interventions:
- Activity restriction (avoid impact, prolonged standing)
- NSAIDs for 2-4 weeks (if no contraindications)
- Ice application after activity
- Gentle ROM exercises for ankle (maintain motion)
- Patient education about condition
Goal: Optimize foot mechanics and reduce subtalar stress
Interventions:
- Custom foot orthoses with medial or lateral posting
- Rocker-bottom shoe modifications
- Ankle-foot orthosis (AFO) for severe cases
- Lace-up ankle brace for additional support
- Heel cushions for shock absorption
Goal: Provide temporary symptom relief and diagnostic information
Protocol:
- Fluoroscopy-guided subtalar joint injection
- Corticosteroid (40mg triamcinolone or equivalent) plus local anesthetic
- May repeat once at 3-month interval
- Document pain relief percentage and duration
Success: 30-50% achieve lasting relief (over 6 months) with 1-2 injections.
Decision point: Determine if conservative management has failed
Criteria for surgical consideration:
- Persistent pain limiting function despite 6-12 months conservative care
- Failed injection therapy (relief under 6 weeks)
- Progressive deformity
- Inability to work or perform desired activities
- Patient motivated for surgical intervention and prolonged recovery
Approximately 50-60% of patients ultimately require surgery after failed conservative care.
Conservative management is effective in 40-50% of cases, particularly for mild-moderate arthritis.
Algorithm Pearl
The diagnostic subtalar injection is both therapeutic and prognostic. Patients who achieve over 75% pain relief with injection have over 90% probability of good outcome with fusion. Those with under 50% relief may have concurrent ankle or midfoot pathology and should be further investigated before proceeding with isolated subtalar arthrodesis.
Indications and Patient Selection
Post-Traumatic Arthritis (70% of Cases)
Typical Presentation Timeline
Intra-articular calcaneal fracture (Sanders Type III-IV most common). Primary injury includes posterior facet disruption, heel widening, varus/valgus malalignment.
Shoe modifications, orthotics, activity modification, NSAIDs, intra-articular steroid injections. Conservative management successful in 40-50% of cases.
Pain with weight-bearing, hindfoot stiffness, difficulty on uneven ground, peroneal impingement from heel widening. Failed conservative management indicates surgery.
Surgical Indications:
- Painful arthritis limiting function
- Failed 6-12 months conservative management
- Radiographic evidence of joint space loss
- Absence of significant ankle or midfoot arthritis
- Patient motivated for prolonged non-weight-bearing
Isolated subtalar arthrodesis is the preferred treatment for post-traumatic arthritis confined to the subtalar joint.
Contraindications
Absolute Contraindications:
- Active infection in foot or ankle
- Severe peripheral vascular disease (ABI under 0.5)
- Charcot neuropathy (relative if can offload)
- Uncontrolled diabetes (HbA1c over 8%)
Relative Contraindications:
- Significant ankle arthritis (consider ankle fusion first)
- Pan-hindfoot arthritis (consider triple arthrodesis)
- Severe osteoporosis (augment with bone graft)
- Smoking (absolute cessation required)
- Worker's compensation claims (worse outcomes)
Preoperative Assessment
History
- Pain location: Subtalar vs ankle vs midfoot
- Mechanism: Trauma history, fracture pattern
- Function: Walking distance, terrain limitations
- Prior treatment: Injections, orthotics, shoe modifications
- Occupation: Heavy labor, prolonged standing
- Goals: Realistic expectations for return to activity
Physical Examination
- Gait: Antalgic, heel varus/valgus alignment
- Hindfoot alignment: Neutral, valgus, varus deformity
- Subtalar motion: Pain at extremes, crepitus, ROM
- Ankle ROM: Preserved motion rules out ankle arthritis
- Peroneal tendons: Impingement from heel widening
- Neurovascular: Posterior tibial, dorsalis pedis pulses
Imaging Protocol
Imaging Studies
Standard views:
- AP, lateral, oblique foot
- Mortise and lateral ankle
- Hindfoot alignment view (Saltzman view)
Findings: Joint space narrowing, subchondral sclerosis, osteophytes, heel alignment, fracture malunion.
Indications: All surgical candidates for fusion planning.
Value: Evaluates posterior facet arthritis, quantifies bone loss, identifies coalition anatomy, assesses heel alignment in coronal/axial planes, surgical approach planning.
Indications: Rule out AVN, assess soft tissue, evaluate adjacent joints.
Findings: Bone marrow edema, cartilage loss, ligament integrity, tendon pathology.
Diagnostic Injection Test
Subtalar Joint Injection: Fluoroscopy-guided injection of local anesthetic (and steroid) into the subtalar joint. Positive test = greater than 75% pain relief for duration of anesthetic. This confirms subtalar joint as primary pain generator and predicts fusion success. Perform if clinical examination unclear or multiple joint involvement suspected.
Surgical Technique
Patient Positioning and Setup
Operating Room Setup
Lateral decubitus position (most common) or supine with bump under ipsilateral hip.
- Operative side up if lateral
- Hip and knee flexed to relax Achilles tension
- Beanbag or supports for stability
- Opposite leg well-padded
Critical pressure points:
- Axillary roll under dependent axilla (check radial pulse)
- Pillow between knees
- Padding of dependent fibular head (common peroneal nerve)
- Heel protection with foam padding
Thigh tourniquet application:
- Well-padded high on thigh
- Inflate to 100mmHg above systolic (typically 250-300mmHg)
- Limit tourniquet time to under 120 minutes
- Consider exsanguination with Esmarch bandage
Surgical field preparation:
- Circumferential prep to mid-calf
- Foot free to allow manipulation
- C-arm positioned for AP, lateral, and Broden views
- Confirm fluoroscopy images before draping complete
Positioning Pearl
Lateral decubitus positioning provides excellent visualization of the sinus tarsi approach and allows gravity to assist with retraction. The foot should be free to manipulate into various positions to assess alignment. Always confirm C-arm can obtain AP and lateral views before starting the procedure.
Proper positioning is critical for surgical exposure and optimal screw trajectory.
Intraoperative Troubleshooting
Common Intraoperative Problems and Solutions
| Problem | Cause | Solution |
|---|---|---|
| Cannot achieve adequate exposure | Inadequate EDB mobilization or sinus tarsi dissection | Detach EDB more extensively, excise all fat and ligament |
| Bone loss prevents adequate contact | Prior trauma, cystic degeneration, osteoporosis | Use structural autograft to fill defect, consider BMP augmentation |
| Cannot correct heel varus/valgus | Soft tissue contracture, midfoot stiffness | Consider Achilles lengthening, midfoot osteotomy, or accept slight residual deformity |
| Screw penetrates anterior cortex | Trajectory too anterior, inadequate length measurement | Redirect starting point more posterior, measure carefully, use fluoroscopy |
Complications
Complications: Incidence, Risk Factors, and Management
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Nonunion | 5-10% | Smoking, diabetes, inadequate fixation, poor bone prep | Revision fusion with bone graft and rigid fixation |
| Malunion (varus/valgus) | 5-8% | Poor alignment assessment, inadequate correction | May require revision osteotomy if symptomatic |
| Sural nerve injury | 5-10% | Inferior incision placement, excessive retraction | Neurolysis if identified, desensitization therapy, rarely excision |
| Superficial peroneal nerve injury | 3-5% | Superior incision placement, excessive traction | Similar to sural nerve management |
| Wound complications | 5-8% | Diabetes, smoking, tension, infection | Local wound care, antibiotics if infected, rarely debridement |
| Adjacent joint arthritis | 30-40% at 10 years | Altered biomechanics, pre-existing degeneration | Conservative care initially, may require fusion extension |
| Persistent pain | 10-15% | Incomplete fusion, nerve injury, adjacent joint | Identify source with exam and imaging, treat accordingly |
Preventing Nonunion
Most critical modifiable factors:
- Smoking cessation - absolute requirement for minimum 6 weeks before and 12 weeks after surgery
- Complete cartilage removal - inadequate denudation is leading technical cause
- Rigid fixation - two large divergent screws superior to alternatives
- Bone graft use - routine grafting improves fusion rate by 10-15%
- Glycemic control - HbA1c under 7% before surgery in diabetics
Nonunion is the most devastating complication and requires revision surgery in most cases.
Postoperative Care and Rehabilitation
Standard Postoperative Rehabilitation
Postoperative Timeline
Hospital care:
- Posterior splint maintained
- Elevation above heart level
- Ice application (20 min on/off cycles)
- DVT prophylaxis (mechanical and chemical per protocol)
- Pain management (multimodal analgesia)
- Strict non-weight-bearing with crutches or walker
Wound check:
- Remove splint and inspect incision
- Suture removal if non-absorbable used
- Apply short leg non-weight-bearing cast or removable boot
- Continue strict non-weight-bearing
- Radiographs (AP, lateral, oblique) to assess alignment
First radiographic assessment:
- AP, lateral, oblique radiographs
- Look for early bridging bone, no lucency around screws
- If early fusion signs: transition to weight-bearing as tolerated in boot
- If no fusion signs: continue non-weight-bearing for 6 more weeks
- Begin ankle and toe range of motion exercises
Primary fusion endpoint:
- Radiographs to confirm fusion (bridging bone on 3 views)
- CT scan if radiographs equivocal
- If fused: progress to full weight-bearing in supportive shoe
- If not fused: continue protected weight-bearing, repeat imaging at 16 weeks
- Begin proprioception and strengthening exercises
Progressive rehabilitation:
- Full weight-bearing in regular shoes
- Physical therapy for gait training and strengthening
- Gradual return to work (light duty at 3-4 months, heavy at 6 months)
- Low-impact activities (swimming, cycling) at 4 months
- Impact activities (running, jumping) not before 6 months
Surveillance:
- Annual radiographs for first 2 years
- Monitor for adjacent joint symptoms
- Functional outcome scores (AOFAS, SF-36)
- Return to pre-injury activity level in 75% of patients
Standard protocol achieves 80-90% fusion rate at 12 weeks with low complication rate.
Weight-Bearing Criteria
- Radiographic fusion: Bridging bone on 3 views
- Clinical fusion: No pain with palpation at fusion site
- CT confirmation: Bridging in 2+ planes (if radiographs equivocal)
- Time: Minimum 6 weeks for standard risk, 8 weeks for high risk
- Progression: Gradual increase over 2-4 weeks to full weight-bearing
Red Flags Requiring Assessment
- Increasing pain: May indicate hardware failure or nonunion
- Wound drainage: Infection until proven otherwise
- Loss of correction: Hardware failure or bone resorption
- Persistent swelling: DVT, infection, or CRPS
- New neurologic symptoms: Nerve compression from hardware
Outcomes and Prognosis
Outcomes by Indication
| Indication | Fusion Rate | Patient Satisfaction | Notes |
|---|---|---|---|
| Post-traumatic arthritis | 85-90% | 85-90% | Best outcomes in isolated subtalar disease |
| Inflammatory arthritis | 80-85% | 80-85% | Higher complication rate but good pain relief |
| Deformity correction | 75-85% | 75-85% | Success depends on maintenance of correction |
| Coalition | 85-90% | 85-90% | Outcomes similar to post-traumatic cases |
Functional Outcomes
Positive Outcomes
- Pain relief: 80-90% significant or complete relief
- Function: AOFAS hindfoot score improves 40-50 points
- Gait: Normalized in 70-80% of patients
- Activity: 75% return to previous employment level
- Sports: Low-impact sports achievable in 80%
- Satisfaction: 85-95% satisfied or very satisfied
Limitations
- Motion loss: 50% reduction in hindfoot motion
- Gait changes: Subtle limp in 20-30%
- Footwear: May require supportive shoes long-term
- High-impact: Running, jumping limited in 40-50%
- Energy cost: 5-10% increase in walking energy
- Adjacent joints: Progressive arthritis risk
Prognostic Factors
Predictors of Better Outcomes:
- Isolated subtalar arthritis (vs pan-hindfoot disease)
- Non-smoker status
- Normal BMI
- No worker's compensation claim
- Successful fusion at 12 weeks
- Neutral heel alignment achieved
Predictors of Poorer Outcomes:
- Smoking (even with cessation)
- Obesity (BMI over 30)
- Worker's compensation involvement
- Diabetes mellitus
- Pre-existing adjacent joint arthritis
- Delayed union or nonunion requiring revision
Evidence Base and Key Studies
Biomechanical Study: Adjacent Joint Stress After Subtalar Arthrodesis
- Finite element analysis of ankle arthrodesis effects on subtalar joint
- 20-30% increase in stress on talonavicular and calcaneocuboid joints
- Gait analysis showed compensatory increased ankle motion
- Plantar pressure patterns significantly altered, especially forefoot loading
- Provides biomechanical explanation for adjacent joint degeneration
Systematic Review: Screw vs Staple Fixation for Subtalar Arthrodesis
- Meta-analysis of 23 studies, over 1000 patients
- Screw fixation: 88% fusion rate vs 78% for staples
- Two screws superior to single screw (90% vs 82% fusion)
- Large diameter screws (6.5-7.3mm) better than small (4.0mm)
- Divergent screw pattern provides rotational stability
Prospective Study: Bone Graft Augmentation in Subtalar Fusion
- Prospective cohort: 150 patients, randomized to autograft vs no graft
- Autograft group: 92% fusion at 12 weeks vs 78% without graft
- Iliac crest harvest resulted in donor site pain in 15%
- Local calcaneal graft equally effective without donor site morbidity
- BMP augmentation showed promise in high-risk patients (off-label use)
Long-Term Outcomes Study: 10-Year Follow-Up After Subtalar Arthrodesis
- Retrospective review of 178 patients with minimum 10-year follow-up
- 85% patient satisfaction maintained at 10 years
- Adjacent joint arthritis: 38% at ankle, 32% at midfoot
- 21% required additional surgery (9% for adjacent joint, 6% for nonunion, 6% hardware removal)
- AOFAS scores declined slightly after 5 years but remained improved vs pre-op
Australian Registry Data: Subtalar Fusion Techniques and Outcomes
- 1,247 subtalar arthrodesis procedures from 2018-2023
- Sinus tarsi approach used in 85%, medial approach 10%, combined 5%
- Average age 52 years, 60% male, 70% for post-traumatic arthritis
- Revision rate 8.2% at 2 years (6.1% for nonunion, 2.1% for malunion)
- Infection rate 2.1%, lower than triple arthrodesis (4.3%)
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Post-Traumatic Arthritis Presentation (2-3 min)
"A 45-year-old male presents 3 years after a Sanders Type III calcaneal fracture treated nonoperatively. He complains of lateral hindfoot pain, difficulty on uneven ground, and pain with prolonged standing. Conservative management including orthotics, NSAIDs, and 2 steroid injections has failed. Weight-bearing radiographs show complete loss of subtalar joint space with subchondral sclerosis. Ankle and midfoot joints appear preserved. What is your assessment and management plan?"
Scenario 2: Surgical Technique Deep Dive (3-4 min)
"You are performing a subtalar arthrodesis via the sinus tarsi approach. Walk me through the key steps of the procedure, focusing on achieving successful fusion. What are the critical technical points at each stage?"
Scenario 3: Nonunion Management (2-3 min)
"A 52-year-old diabetic smoker underwent subtalar arthrodesis 6 months ago. Despite initial compliance with non-weight-bearing, he has persistent pain at the fusion site. CT scan shows nonunion with lucency around both screws and no bridging bone. How do you manage this complication?"
MCQ Practice Points
Anatomy Question
Q: What percentage of hindfoot inversion and eversion occurs at the subtalar joint? A: 75% of hindfoot inversion/eversion occurs at the subtalar joint, with the remaining 25% contributed by the ankle joint. After subtalar arthrodesis, approximately 50% of overall hindfoot motion is preserved through compensatory ankle motion. This is a key point when counseling patients.
Indication Question
Q: What is the most common indication for isolated subtalar arthrodesis? A: Post-traumatic arthritis following intra-articular calcaneal fracture accounts for approximately 70% of cases. This typically develops in 20-50% of patients 2-5 years after initial injury, particularly after Sanders Type III and IV fractures treated nonoperatively or with residual joint incongruity.
Fixation Question
Q: What is the optimal screw configuration for subtalar arthrodesis and why? A: Two large (6.5-7.3mm) partially threaded cannulated screws in a divergent pattern from the posterolateral calcaneus into the talar neck. This configuration provides: (1) compression of the fusion site (partially threaded design), (2) rotational stability (divergent trajectory), and (3) superior fusion rates (88-90%) compared to single screw (82%), staples (78%), or plates. Biomechanical studies confirm this as the gold standard.
Complication Question
Q: What is the incidence and time course of adjacent joint arthritis after subtalar arthrodesis? A: 30-40% of patients develop adjacent joint arthritis within 10 years after subtalar fusion. This affects primarily the ankle (38%) and talonavicular/calcaneocuboid joints (32%). Biomechanical studies show 20-30% increased stress on these joints due to altered load distribution. This is an important counseling point and requires long-term surveillance.
Technique Question
Q: What is the most common technical cause of nonunion in subtalar arthrodesis? A: Incomplete cartilage removal is the leading technical cause of nonunion. Complete denudation of all three facets (posterior, middle, anterior) down to bleeding cancellous bone is essential. Supplementing with fish-scale drilling and bone graft enhances the biological environment. Studies show 10-15% improvement in fusion rates with meticulous technique and bone graft use.
Outcome Question
Q: What are the strongest modifiable risk factors for nonunion in subtalar arthrodesis? A: Smoking is the most significant modifiable risk factor, increasing nonunion risk 3-5 fold. Diabetes with poor glycemic control (HbA1c over 8%) also significantly increases risk. Inadequate fixation (single screw, small screws) and incomplete denudation are technical factors. NSAIDs in the perioperative period may impair bone healing. Absolute smoking cessation for 6 weeks pre-op and 12 weeks post-op is essential.
Australian Context and Medicolegal Considerations
Australian Registry Data
- Volume: 1,247 subtalar arthrodesis procedures (2018-2023)
- Indication breakdown: 70% post-traumatic, 18% inflammatory, 12% deformity/other
- Approach: Sinus tarsi 85%, medial 10%, combined 5%
- Revision rate: 8.2% at 2 years (6.1% nonunion, 2.1% malunion)
- Infection: 2.1% (lower than triple arthrodesis at 4.3%)
- Average age: 52 years, male predominance 60%
PBS and Therapeutic Guidelines
- Antibiotic prophylaxis: Cephalexin 2g IV or vancomycin 1.5g IV (penicillin allergy)
- DVT prophylaxis: LMWH for 2 weeks or until mobile (eTG recommendation)
- Analgesia: Multimodal approach per Acute Pain Management guidelines
- Bone stimulator: Not currently PBS-listed, patient cost AU$800-1200
- BMP use: Off-label, not PBS-listed, AU$4000-6000 per use
Medicolegal Considerations
Key Documentation Requirements:
Informed Consent Must Include:
- Fusion rate 80-90% with need for extended non-weight-bearing (6-12 weeks)
- Loss of 50% of hindfoot motion (permanent)
- Adjacent joint arthritis risk 30-40% over 10 years
- Nonunion risk 5-10%, higher in smokers (15-20%) and diabetics
- Nerve injury risk 5-10% (sural, superficial peroneal)
- Infection risk 2-5%, wound complications 5-8%
- Alternative treatments: continued conservative care, ankle arthrodesis, amputation (severe cases)
- Recovery timeline: 3-4 months to walking, 6 months to impact activities
Common Litigation Issues:
- Failure to adequately counsel about adjacent joint arthritis risk
- Operating on actively smoking patients without documentation of cessation attempts
- Inadequate preoperative workup (missing ankle or midfoot arthritis)
- Failure to use diagnostic injection to confirm subtalar pain source
- Inadequate technique (incomplete denudation, poor fixation) leading to nonunion
- Nerve injury without documentation of careful dissection and protection
Protective Documentation:
- Detailed preoperative counseling note including risks and alternatives
- Smoking cessation counseling and patient's response (documented refusal or compliance)
- Diagnostic injection results confirming subtalar joint as pain generator
- Operative note detailing complete denudation, bone graft use, screw trajectory
- Postoperative instructions emphasizing non-weight-bearing compliance
- Regular follow-up with radiographic documentation of fusion progress
Private Hospital Typical Costs (2024):
- Subtalar arthrodesis procedure: AU$8,000-12,000
- Includes surgeon fee, assistant, anaesthetist, hospital, implants
- Bone graft harvest (iliac): Add AU$1,500-2,000
- Revision surgery: 1.5x primary surgery costs
SUBTALAR ARTHRODESIS
High-Yield Exam Summary
Key Anatomy
- •Subtalar joint = 3 facets (posterior 60-70%, middle 20-25%, anterior 10-15%)
- •75% of hindfoot inversion/eversion occurs at subtalar joint
- •Sinus tarsi contains interosseous talocalcaneal ligament (strongest) and cervical ligament
- •Sural nerve at risk inferiorly, superficial peroneal nerve superiorly
- •Post-fusion: 50% of hindfoot motion preserved via compensatory ankle motion
Indications
- •Post-traumatic arthritis (70% of cases) - most common after Sanders III-IV calcaneal fractures
- •Inflammatory arthritis - rheumatoid, psoriatic, ankylosing spondylitis
- •Rigid deformity - planovalgus (PTTD Stage IV) or cavovarus (neurologic)
- •Symptomatic coalition - after failed conservative care or prior resection
- •Must have failed 6-12 months conservative management and confirmed by diagnostic injection
Surgical Technique
- •Sinus tarsi approach (85% of cases) - oblique incision from fibula to 4th MT base
- •Complete denudation of all 3 facets to bleeding bone (critical for fusion)
- •Fish-scale drilling and bone graft application enhance biology
- •Two 6.5-7.3mm partially threaded screws in divergent pattern from posterolateral calcaneus to talar neck
- •Starting point 1-2cm posterior to posterior facet, avoid anterior penetration into talonavicular joint
- •Achieve compression without gapping, confirm position with AP and lateral fluoroscopy
Postoperative Protocol
- •Strict non-weight-bearing 6 weeks (standard risk) to 8 weeks (high risk) in cast or boot
- •Radiographs at 6 and 12 weeks to assess fusion (bridging bone on 3 views)
- •CT scan at 12 weeks if radiographs equivocal or high-risk patient
- •Progress to weight-bearing only after fusion confirmed clinically and radiographically
- •Return to full activity 4-6 months, impact activities not before 6 months
- •High-risk patients (smokers, diabetics): extended protocol, consider bone stimulator
Complications and Management
- •Nonunion 5-10% (15-20% in smokers) - requires revision with structural graft and BMP
- •Malunion 5-8% - varus/valgus deformity may need osteotomy if symptomatic
- •Nerve injury 5-10% (sural, superficial peroneal) - careful dissection essential
- •Adjacent joint arthritis 30-40% at 10 years - counsel preoperatively, long-term surveillance
- •Infection 2-5% - prophylactic antibiotics, meticulous wound care
- •Most critical prevention: smoking cessation, complete denudation, rigid fixation, bone graft use
Key Evidence and Outcomes
- •Fusion rate 80-90% at 12 weeks with two large divergent screws
- •Patient satisfaction 85-95%, AOFAS score improves 40-50 points
- •75% return to previous employment, 80% achieve low-impact sports
- •Screw fixation superior to staples (88% vs 78% fusion rate)
- •Bone graft improves fusion by 10-15%, local calcaneal graft avoids donor site morbidity
- •Adjacent joint arthritis 38% ankle, 32% midfoot at 10 years - requires counseling