Isolated Subtalar Fusion | Post-Traumatic Arthritis | Hindfoot Deformity Correction
- 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)
- “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
75% of hindfoot motion occurs at subtalar joint. Triple arthrodesis includes subtalar, talonavicular, and calcaneocuboid joints. Isolated fusion preserves midfoot flexibility.
Post-traumatic arthritis (70% of cases) following calcaneal fracture. Must document failed conservative management for 6-12 months before surgery.
Two large screws (6.5-7.3mm) in divergent pattern. Start at posterior calcaneus, aim for talar neck. Compression critical for fusion.
Adjacent joint arthritis develops in 30-40% at 10 years. Sural nerve injury 5-10%. Nonunion 5-10% with risk factors.
- Classification
- Post-traumatic arthritis
- Treatment
- Isolated subtalar arthrodesis
- Key Pearl
- Preserves 50% of hindfoot motion via ankle
- Classification
- Panarthrosis
- Treatment
- Double arthrodesis
- Key Pearl
- Preserves calcaneocuboid motion
- Classification
- Severe deformity
- Treatment
- Triple arthrodesis
- Key Pearl
- Addresses all deformed joints simultaneously
- Classification
- Repairable coalition
- Treatment
- Coalition resection plus tendon transfer
- Key Pearl
- Preserve motion when possible in young patients
Overview and Epidemiology
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.
- 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
- 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
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.
- 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%)
- 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
- 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
- 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
- AP, lateral, oblique foot
- Mortise and lateral ankle
- Hindfoot alignment view (Saltzman view)
Joint space narrowing, subchondral sclerosis, osteophytes, heel alignment, fracture malunion.
All surgical candidates for fusion planning.
Evaluates posterior facet arthritis, quantifies bone loss, identifies coalition anatomy, assesses heel alignment in coronal/axial planes, surgical approach planning.
Rule out AVN, assess soft tissue, evaluate adjacent joints.
Bone marrow edema, cartilage loss, ligament integrity, tendon pathology.
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.
Pathophysiology and Mechanisms
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.
- Surface Area
- 60-70%
- Location
- Under talar body
- Clinical Significance
- Main weight-bearing surface, most commonly arthritic
- Surface Area
- 20-25%
- Location
- On sustentaculum tali
- Clinical Significance
- Supports talar head, often spared in post-traumatic arthritis
- Surface Area
- 10-15%
- Location
- On anterior calcaneus
- Clinical Significance
- Small contribution, may be congenitally absent
Biomechanics
- 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
- 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
- Specific Conditions
- After calcaneal fracture (Sanders III-IV most common)
- Typical Age
- 40-60 years
- Fusion Approach
- In-situ fusion via sinus tarsi approach
- Specific Conditions
- Rheumatoid, psoriatic, ankylosing spondylitis
- Typical Age
- 30-50 years
- Fusion Approach
- In-situ fusion with soft tissue balancing
- Specific Conditions
- Rigid planovalgus (PTTD IV), cavovarus (neurologic)
- Typical Age
- 50-70 years
- Fusion Approach
- Realignment fusion with structural graft
- Specific Conditions
- Symptomatic talocalcaneal or calcaneonavicular coalition
- Typical Age
- 15-30 years
- Fusion Approach
- 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
- 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
- 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
Stabilize ankle in neutral with one hand, grasp heel with other hand and invert/evert.
20-30° inversion, 10-15° eversion. Findings: Pain at end-range, crepitus, restricted motion (under 50% of normal). Correlates with arthritis severity.
Patient stands on one leg and rises onto toes.
Can perform 10+ repetitions without pain. Abnormal: Unable to perform or severe pain indicates subtalar or posterior tibial pathology.
Fluoroscopy-guided subtalar joint injection with 2-3mL local anesthetic (bupivacaine 0.5%) plus steroid.
Greater than 75% pain relief for duration of anesthetic. Value: Confirms subtalar joint as primary pain generator, predicts fusion success over 90%.
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
- AP, lateral, oblique foot (weight-bearing)
- AP mortise and lateral ankle (weight-bearing)
- Hindfoot alignment view (Saltzman view)
- 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.
All patients being considered for subtalar arthrodesis.
Fine-cut CT (1mm slices) of hindfoot with coronal, sagittal, and axial reconstructions.
- 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.
- 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
Cartilage loss, bone marrow edema, AVN, tendon tears, ligament injury.
More expensive, not essential for most cases, CT superior for bony detail.
- Multiple potential pain sources
- Previous failed fusion or surgery
- Diagnostic uncertainty despite standard imaging
Combines anatomic (CT) and metabolic (SPECT) information to precisely localize active pathology. Expensive but can be invaluable in complex cases.
Laboratory Studies
- 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
- 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
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.
Differential Diagnosis
- Key Features
- Lateral hindfoot pain, painful restricted inversion/eversion, prior calcaneal fracture
- Discriminating Test
- Greater than 75% relief with image-guided subtalar injection; CT shows posterior facet loss
- Implication for Fusion
- Primary indication for isolated subtalar arthrodesis
- Key Features
- Anterior ankle pain, restricted/painful dorsiflexion-plantarflexion
- Discriminating Test
- Weight-bearing mortise view; negative or partial response to subtalar injection
- Implication for Fusion
- Isolated subtalar fusion will not relieve pain; consider ankle fusion/replacement
- Key Features
- Dorsomedial midfoot pain, pain on forefoot abduction
- Discriminating Test
- Focal tenderness and imaging at talonavicular joint
- Implication for Fusion
- May need double/triple fusion rather than isolated subtalar
- Key Features
- Long-standing stiff hindfoot since adolescence, often bilateral, peroneal spasm
- Discriminating Test
- CT/MRI showing osseous or fibrous bar
- Implication for Fusion
- Resection if no arthritis; fusion if arthritic or rigid deformity
- Key Features
- Lateral/retromalleolar pain, subluxation, worse on resisted eversion
- Discriminating Test
- MRI/US of peroneal tendons; pain not abolished by subtalar injection
- Implication for Fusion
- Treat tendon disease; fusion alone will not address it
- Key Features
- Focal sinus tarsi pain after inversion injury, or disproportionate burning pain with allodynia
- Discriminating Test
- Localised injection (sinus tarsi syndrome); clinical diagnosis for CRPS
- Implication for Fusion
- CRPS is a relative contraindication; optimise before any fusion
Management Algorithm
Non-Operative Treatment Algorithm
Conservative Treatment Steps
Reduce inflammation and pain
- 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
Optimize foot mechanics and reduce subtalar stress
- 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
Provide temporary symptom relief and diagnostic information
- 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
30-50% achieve lasting relief (over 6 months) with 1-2 injections.
Determine if conservative management has failed
- 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.
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.
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
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
- Cause
- Inadequate EDB mobilization or sinus tarsi dissection
- Solution
- Detach EDB more extensively, excise all fat and ligament
- Cause
- Prior trauma, cystic degeneration, osteoporosis
- Solution
- Use structural autograft to fill defect, consider BMP augmentation
- Cause
- Soft tissue contracture, midfoot stiffness
- Solution
- Consider Achilles lengthening, midfoot osteotomy, or accept slight residual deformity
- Cause
- Trajectory too anterior, inadequate length measurement
- Solution
- Redirect starting point more posterior, measure carefully, use fluoroscopy
Distraction Bone-Block Subtalar Arthrodesis (for Calcaneal Malunion)
The deformity table lists "heel height loss / calcaneal fracture malunion → large structural graft to restore height" and the technique calls to "restore calcaneal pitch and Bohler's angle", but the specific named procedure - the distraction bone-block arthrodesis (Carr, Bohlman) - is never described.
- The problem it solves. A malunited intra-articular calcaneal fracture does not just cause subtalar arthritis - it loses calcaneal height, flattens the talar declination and widens the heel. The resulting dorsiflexed (horizontalised) talus produces anterior ankle (tibiotalar) impingement and loss of ankle dorsiflexion, the lost height shortens the heel lever arm, and the widened heel causes lateral wall and peroneal impingement. A simple in-situ fusion cements these problems in place.
- The operation. Through a lateral (or extensile lateral) approach the subtalar joint is prepared and then distracted, and a structural (tricortical) bone block - iliac-crest autograft or femoral-head allograft - is interposed into the posterior facet. This restores calcaneal height and the talar declination (re-tilting the talus back towards normal and relieving the anterior ankle impingement), lengthens the heel lever, and is held with large compression screws.
- Adjuncts and caveats. A lateral wall exostectomy (with peroneal tenolysis) addresses the widened heel and peroneal impingement; the graft must be large enough to restore height without overdistracting. It is technically demanding with a higher nonunion rate than an in-situ fusion (a large graft-host interface to heal), so meticulous preparation and rigid fixation are essential.
Q: What is a distraction bone-block subtalar arthrodesis and when is it used? A: A subtalar fusion for symptomatic calcaneal-fracture malunion with lost heel height. The subtalar joint is distracted and a structural (tricortical) bone block is interposed in the posterior facet to restore calcaneal height and the talar declination angle - re-tilting the horizontalised talus and relieving the anterior ankle impingement and loss of dorsiflexion that a simple in-situ fusion would leave. A lateral wall exostectomy and peroneal tenolysis address the widened heel; nonunion risk is higher than an in-situ fusion.
Arthroscopic Subtalar Arthrodesis
The Controversies section names "arthroscopic (posterior or sinus-tarsi portal) subtalar arthrodesis" as an alternative to the open sinus-tarsi fusion, but the technique, indications and evidence are never developed.
- Rationale and portals. For an in-situ fusion of a well-aligned, arthritic subtalar joint (no significant deformity to correct), the posterior facet can be prepared and fused arthroscopically - either through two posterior portals with the patient prone (the standard posterior hindfoot arthroscopy portals, on either side of the Achilles) or through sinus-tarsi/lateral portals. The joint is denuded with a shaver and burr and fixed percutaneously with the same one-to-two large compression screws as the open technique.
- Advantages. Minimal soft-tissue stripping means fewer wound complications and less sural-nerve morbidity, less pain, and some series report faster union - attractive in the patient with a poor soft-tissue envelope (diabetic, smoker) for whom a large open lateral wound is risky.
- Limits. It cannot correct significant deformity (a realignment fusion still needs an open approach with wedge resection or a structural bone block), it has a real learning curve, and the comparative evidence is limited and largely single-centre. Open sinus-tarsi fusion therefore remains the default, with arthroscopic fusion reserved for the in-situ, well-aligned, at-risk-wound case.
Q: When would you choose an arthroscopic subtalar arthrodesis over the open sinus-tarsi approach? A: For an in-situ fusion of a well-aligned but arthritic subtalar joint - especially in a poor soft-tissue envelope (diabetic, smoker). Through posterior (prone, either side of the Achilles) or sinus-tarsi portals the posterior facet is denuded arthroscopically and fixed percutaneously with the same large compression screws, giving fewer wound and sural-nerve complications and potentially faster union. It cannot correct significant deformity (which still needs open realignment) and has a learning curve, so open sinus-tarsi fusion remains the default.
Complications
- Incidence
- 5-10%
- Risk Factors
- Smoking, diabetes, inadequate fixation, poor bone prep
- Management
- Revision fusion with bone graft and rigid fixation
- Incidence
- 5-8%
- Risk Factors
- Poor alignment assessment, inadequate correction
- Management
- May require revision osteotomy if symptomatic
- Incidence
- 5-10%
- Risk Factors
- Inferior incision placement, excessive retraction
- Management
- Neurolysis if identified, desensitization therapy, rarely excision
- Incidence
- 3-5%
- Risk Factors
- Superior incision placement, excessive traction
- Management
- Similar to sural nerve management
- Incidence
- 5-8%
- Risk Factors
- Diabetes, smoking, tension, infection
- Management
- Local wound care, antibiotics if infected, rarely debridement
- Incidence
- 30-40% at 10 years
- Risk Factors
- Altered biomechanics, pre-existing degeneration
- Management
- Conservative care initially, may require fusion extension
- Incidence
- 10-15%
- Risk Factors
- Incomplete fusion, nerve injury, adjacent joint
- Management
- Identify source with exam and imaging, treat accordingly
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.
- 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
- 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
- Fusion Rate
- 85-90%
- Patient Satisfaction
- 85-90%
- Notes
- Best outcomes in isolated subtalar disease
- Fusion Rate
- 80-85%
- Patient Satisfaction
- 80-85%
- Notes
- Higher complication rate but good pain relief
- Fusion Rate
- 75-85%
- Patient Satisfaction
- 75-85%
- Notes
- Success depends on maintenance of correction
- Fusion Rate
- 85-90%
- Patient Satisfaction
- 85-90%
- Notes
- Outcomes similar to post-traumatic cases
Functional 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
- 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
- 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
- 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
Guidelines, Registries & Global Practice
- Dominant indication: Post-traumatic arthritis after displaced intra-articular calcaneal fractures, the most common tarsal fracture
- Demographics: Typically men in the 4th-6th decades; high-energy and occupational/fall mechanisms predominate worldwide
- Pipeline from injury: Nonoperatively managed displaced calcaneal fractures require later subtalar fusion more often than operatively fixed ones (Luo 2016)
- Inflammatory burden: In settings with high rheumatoid prevalence, inflammatory hindfoot disease is a larger share of fusions
- Coalition/deformity: Younger cohorts in tarsal coalition and neuromuscular (CMT) deformity
- AO Foundation: Emphasises complete joint preparation to bleeding cancellous bone, divergent/compression screw fixation, and structural graft to restore height in calcaneal malunion
- AAOS (US): Evidence-based calcaneal fracture guidance notes operative fixation may reduce later subtalar fusion in selected displaced fractures
- BOA / BOFAS (UK): Support shared decision-making after the UK Heel Fracture trial showed no functional benefit of routine ORIF for most displaced fractures
- EFORT / European consensus: Endorse isolated fusion when disease is confined to the subtalar joint, reserving double/triple fusion for multi-joint involvement
- Common ground: All stress smoking cessation, confirming the subtalar joint as pain generator, and protecting adjacent joints
- No dedicated international subtalar-fusion registry exists; evidence comes from cohort series and meta-analyses
- Hindfoot/foot-and-ankle modules in national registries (e.g. national audit data in the UK and trauma registries in Europe) increasingly capture calcaneal fracture pathways
- Pooled cohort data: nonunion ~12% in low-risk patients rising to ~24% with multiple risk factors (Ziegler 2017)
- Construct trends: shift toward divergent and three-screw or variable-pitch compression fixation in higher-risk cases (Wirth 2019)
- Imaging: CT is standard for planning in high-resource settings; weight-bearing radiographs and image-intensifier-guided diagnostic injection carry much of the workload where CT access is limited
- Fixation: Cannulated compression screws are the global workhorse; staples or non-cannulated lag screws are used where cannulated systems are unavailable
- Graft: Local calcaneal autograft is universally accessible and avoids donor-site morbidity; structural allograft and BMP are restricted by cost and availability
- Adjuncts: Bone stimulators and BMP are largely confined to well-resourced, high-risk practice
- Rehab: Prolonged protected weight-bearing demands social support that is harder to deliver in lower-resource settings
- Fusion rate generally 80-90% with extended protected/non-weight-bearing (6-12 weeks)
- Permanent loss of roughly half of hindfoot inversion/eversion
- Adjacent joint arthritis as a recognised long-term sequela
- Nonunion risk (~12% low-risk, rising to ~24% with multiple risk factors; markedly higher in smokers)
- Nerve injury risk (sural, superficial peroneal), infection and wound complications
- Alternatives: continued conservative care, double/triple fusion, and salvage options in severe disease
- Recovery timeline: months to comfortable walking, longer to impact activity
- Smoking-cessation counselling and the patient's response (compliance or documented refusal)
- Diagnostic injection result confirming the subtalar joint as the pain generator
- Operative note detailing complete denudation, graft used, and screw configuration/trajectory
- Structured follow-up with radiographic (and CT if equivocal) documentation of union
Controversies and Areas of Uncertainty
Traditional teaching favours two large divergent screws. However, a retrospective series (Wirth 2019) reported substantially lower nonunion (14% vs 35%) and revision (8% vs 38%) with three screws, while cadaveric work (Riedl 2017) found a third anterior screw mainly improves internal-rotation resistance without changing overall torsional stiffness. There is no randomized trial; many surgeons reserve a third screw for high-risk or revision cases.
Arthroscopic (posterior or sinus tarsi portal) subtalar arthrodesis may reduce wound complications and speed union in selected in-situ cases, but it cannot correct significant deformity and has a learning curve. Comparative evidence is limited and largely from single-centre series; open sinus tarsi fusion remains the global default.
Local calcaneal autograft is widely used, but the marginal benefit of routine grafting in clean in-situ fusions is not established in high-quality trials. Freeze-dried iliac crest as an interpositional graft was an independent nonunion risk factor in one series (Kang 2022), and BMP use remains off-label with cost and safety questions.
Radiographs over-call union; CT detects incomplete fusion that plain films miss. There is no consensus threshold for how much CT bridging defines union, which contributes to the wide reported nonunion range (roughly 5-25%) across series with different definitions and risk profiles.
Mnemonics for Subtalar Arthrodesis
PAIDIndications for Subtalar Fusion
Hook:You get PAID for fixing subtalar problems - post-traumatic arthritis is the bread and butter!
SEIFSurgical Approach Layers (Sinus Tarsi)
Hook:SEIF the subtalar joint - cut down in Skin, EDB, Interosseous ligament, Fat layers!
FLATScrew Positioning Technique
Hook:Keep it FLAT - screws From posterior, Lateral-to-medial, Aimed at neck, Two large screws!
SCANDNonunion Risk Factors
Hook:Avoid a SCAND-al with fusion - control Smoking, Compensation, AVN, NSAIDs, Diabetes!
MCQ Practice Points
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.
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.
Q: What is the optimal screw configuration for subtalar arthrodesis and why? A: Two large (6.5-7.3mm) partially threaded or variable-pitch 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), and (2) rotational stability — a divergent (angulated) construct allows significantly less rotational micromotion than a parallel one, and parallel screws are an independent nonunion risk factor (OR 5.70). A third anterior screw can be added in high-risk patients, where it has been associated with lower nonunion and revision rates.
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.
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.
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.
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“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?”
“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?”
“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?”
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 typically 80-90%; nonunion ~12% in low-risk vs ~24% with multiple risk factors (Ziegler 2017)
- Divergent screws reduce rotational micromotion vs parallel; parallel config independent nonunion risk (OR 5.70, Kang 2022)
- Three-screw fixation reduced nonunion (14% vs 35%) and revision (8% vs 38%) vs two screws in one series (Wirth 2019)
- Smoking independently raises nonunion risk ~3.6-fold; prior infection strongest predictor (OR 4.33)
- Operative calcaneal fracture fixation lowers later subtalar fusion rate vs nonoperative (Luo 2016 meta-analysis)
- Adjacent joint arthritis is a recognised long-term sequela - counsel and provide long-term surveillance
Evidence Base and Key Studies
Nonunion Risk Factors After Post-Traumatic Subtalar Arthrodesis
- Retrospective review of 165 post-traumatic subtalar arthrodeses after displaced intra-articular calcaneal fracture
- Overall nonunion rate 13.3% (22 of 165), diagnosed at 6 months by clinical, radiographic and CT criteria
- Smoking independently raised nonunion risk (OR 3.64, 95% CI 1.23-10.75)
- Parallel screw configuration raised nonunion risk (OR 5.70, 95% CI 1.62-20.06) versus divergent
- Freeze-dried iliac crest interpositional graft also raised nonunion risk (OR 9.16)
Prospective Cohort: Nonunion and Functional Outcome of Subtalar Fusion for Post-Traumatic Arthrosis
- Prospective comparative cohort: 214 patients, 267 subtalar fusions, mean age 49 years, 83% male, 59% calcaneal fracture
- Nonunion 23.8% across the whole cohort but only 12% in patients with no risk factors
- Prior infection in the operative field was the strongest negative predictor (OR 4.33)
- Summation of risk factors (smoking, diabetes, obesity, alcohol, infection) compounded nonunion risk
- Mean post-fusion AOFAS hindfoot score ~49 (primary) and ~46 (secondary) arthrodesis
Two-Screw versus Three-Screw Fixation for Isolated Subtalar Fusion
- Retrospective comparison of 113 isolated subtalar fusions (36 three-screw, 77 two-screw)
- Nonunion 14% with three screws versus 35% with two screws
- Revision arthrodesis required in 8% (three-screw) versus 38% (two-screw), both statistically significant
- BMI of 30 or above, prior ankle fusion and diabetes independently raised revision risk
- Authors recommend three-screw fixation for more reliable union
Biomechanics: Angulated versus Parallel Screw Configuration
- Eight paired cadaveric hindfeet fixed with parallel versus angulated (divergent) two-screw constructs
- After cyclic loading, angulated construct allowed less internal/external rotation (3.3° vs 8.8°, p=0.006)
- Angulated construct also reduced inversion/eversion motion (1.9° vs 3.9°, p=0.017)
- No significant difference in sagittal-plane (dorsiflexion/plantarflexion) motion
- Divergent screws provide superior rotational stability of the fusion construct
Biomechanics: Two-Screw versus Three-Screw Headless Compression Fixation
- Ten paired cadaveric subtalar joints fixed with two posterior divergent versus two posterior plus one anterior headless compression screws
- Internal rotation was significantly lower with the three-screw (added anterior) construct
- No difference in external rotation or overall torsional stiffness between two and three screws
- Variable-pitch headless screws outperformed historical conventional lag-screw constructs
- An anterior third screw mainly resists internal rotation
Meta-Analysis: Operative versus Nonoperative Calcaneal Fracture and Late Subtalar Fusion
- Meta-analysis of 7 randomized controlled trials, 824 patients with displaced intra-articular calcaneal fractures
- Rate of late subtalar arthrodesis significantly lower after operative than nonoperative treatment
- Complication rate higher with operative treatment (25.0% vs 16.6%, RR 1.53)
- No significant difference in pooled functional scores between operative and nonoperative groups
- Evidence remains insufficient to declare operative treatment definitively superior