SINUS TARSI SYNDROME
Post-Traumatic Lateral Hindfoot Pain | Sinus Tarsi Tenderness | Conservative First
Clinical Severity Classification
Critical Must-Knows
- Sinus Tarsi Anatomy: Conical tunnel between talus and calcaneus, contains interosseous talocalcaneal ligament, cervical ligament, fat, and mechanoreceptors
- Post-Traumatic Etiology: 90% follow ankle inversion injury - disrupts ligaments and fat pad
- Clinical Triad: Lateral hindfoot pain, sinus tarsi tenderness, sensation of hindfoot instability
- MRI Findings: High signal in sinus tarsi on T2, ligament disruption, fat pad edema
- Conservative First: 70-80% respond to physiotherapy, injections, and proprioceptive training
Examiner's Pearls
- "Sinus tarsi is anterior and lateral to lateral malleolus
- "Pain worse on uneven ground and lateral movements
- "Single-leg stance reveals hindfoot instability
- "Diagnostic injection provides immediate but temporary relief
Critical Sinus Tarsi Syndrome Exam Points
Anatomy Location
Sinus tarsi is a cone-shaped tunnel located between the talus superiorly and calcaneus inferiorly, opening laterally anterior to the lateral malleolus. Contains the interosseous talocalcaneal ligament (ITCL), cervical ligament, inferior extensor retinaculum, fat pad, and rich mechanoreceptors. Injury disrupts proprioception.
Post-Traumatic Origin
90% follow ankle inversion injury. The mechanism is forceful inversion that crushes the lateral structures of the sinus tarsi, disrupting ligaments and fat pad. Chronic inflammation, synovitis, and adhesions develop. Often associated with lateral ankle instability.
Clinical Diagnosis
Triad: Vague lateral hindfoot pain, point tenderness over sinus tarsi, and sensation of instability on uneven ground. Pain reproduced by forced inversion and eversion. Negative anterior drawer (unless coexisting ATFL injury). MRI confirms with high T2 signal in sinus tarsi.
Conservative First
70-80% respond to non-operative treatment. Physiotherapy with proprioceptive training is key. Diagnostic and therapeutic corticosteroid injection into sinus tarsi provides temporary relief and confirms diagnosis. Surgery reserved for refractory cases after 6 months.
Quick Decision Guide - Management Based on Duration and Severity
| Phase | Clinical Features | Management | Key Pearl |
|---|---|---|---|
| Acute (under 3 months) | Recent inversion injury, lateral pain | Rest, NSAIDs, physiotherapy, ankle brace | Most resolve with conservative treatment |
| Subacute (3-6 months) | Persistent pain, sinus tarsi tenderness | Corticosteroid injection, proprioceptive training | Injection confirms diagnosis if relief obtained |
| Chronic (over 6 months) | Failed conservative, MRI shows synovitis | Arthroscopic sinus tarsi debridement | Exclude subtalar arthritis before surgery |
SINUSSinus Tarsi Contents
Memory Hook:The SINUS contains five key structures - disruption causes pain and instability!
TENDERClinical Features of Sinus Tarsi Syndrome
Memory Hook:The sinus tarsi is TENDER to palpation - this is the pathognomonic clinical sign!
LATERALDifferential Diagnosis
Memory Hook:LATERAL foot pain has many causes - exclude these before diagnosing sinus tarsi syndrome!
Overview and Epidemiology
Clinical Significance
Sinus tarsi syndrome is an underdiagnosed cause of chronic lateral ankle pain following inversion injury. The syndrome was first described by O'Connor in 1958 as a clinical entity distinct from lateral ankle ligament injury. It represents chronic inflammation and scarring within the sinus tarsi following disruption of its contents. The vague nature of symptoms and lack of specific tests lead to delayed diagnosis averaging 6-12 months from injury.
Epidemiology
- Incidence: 1-2% of all chronic ankle sprains develop sinus tarsi syndrome
- Post-inversion: 30-50% after severe ankle inversion injury if untreated
- Age: Peak 20-40 years (active population)
- Sex: Equal male and female distribution
- Athletic: Common in runners, soccer players, basketball
- Bilateral: 10-15% have bilateral involvement
Young active individuals with history of ankle sprains are typical.
Risk Factors
Predisposing factors:
- Previous ankle inversion injury (90% of cases)
- Chronic lateral ankle instability
- Repetitive microtrauma (running, jumping)
- Hindfoot valgus alignment
- Generalized ligamentous laxity
- Inflammatory arthropathy (RA, seronegative)
Protective factors:
- Proper ankle rehabilitation after sprains
- Proprioceptive training
- Ankle bracing during sports
History of inadequately rehabilitated ankle sprain is almost universal.
Anatomy and Pathophysiology
Sinus Tarsi Anatomy
Sinus Tarsi Boundaries
The sinus tarsi is a cone-shaped tunnel between the talus and calcaneus. The wide opening faces laterally (anterior and inferior to lateral malleolus). The narrow apex points medially and becomes the tarsal canal (containing posterior tibial neurovascular bundle). Boundaries: Superior - neck and body of talus. Inferior - superior surface of calcaneus. Medial - tarsal canal. Lateral - opens between anterior process of calcaneus and talar neck.
Sinus Tarsi Contents:
| Structure | Anatomy | Function | Injury Effect |
|---|---|---|---|
| Interosseous talocalcaneal ligament (ITCL) | Strong ligament in tarsal canal, two bands | Primary stabilizer of subtalar joint | Disruption causes subtalar instability |
| Cervical ligament | Oblique ligament from talar neck to calcaneus | Restricts inversion, secondary stabilizer | Injury common in inversion sprains |
| Inferior extensor retinaculum | Crosses lateral opening of sinus tarsi | Restrains extensor tendons | Thickening contributes to stenosis |
| Fat pad | Adipose tissue filling the sinus | Shock absorption, gliding surface | Inflammation, fibrosis after trauma |
| Mechanoreceptors | Dense proprioceptive nerve endings | Proprioception for hindfoot position | Loss causes instability sensation |
| Synovial tissue | Extension of subtalar joint synovium | Joint lubrication | Chronic synovitis, adhesions |
Clinical Relevance:
- The sinus tarsi is palpable anterior to the lateral malleolus
- Depth: approximately 1-2 cm from skin surface
- Width at lateral opening: 1-2 cm diameter
- Rich vascular and nerve supply explains pain severity
Pathophysiology
Acute Injury Phase
Initial trauma (ankle inversion):
- Forced inversion crushes lateral sinus tarsi structures
- Disruption of cervical and interosseous ligaments
- Fat pad contusion and hemorrhage
- Synovial membrane inflammation
- Nerve ending trauma
This acute phase lasts 2-6 weeks.
Chronic Phase
Chronic inflammation develops:
- Persistent synovitis
- Fibrosis and adhesions
- Scar tissue formation
- Fat pad degeneration
- Loss of proprioceptive function
- Secondary subtalar instability
Chronic changes perpetuate symptoms beyond 3-6 months.
Proposed Mechanisms:
- Mechanical compression: Inversion crushes lateral sinus tarsi contents between talus and calcaneus
- Ligamentous disruption: Cervical and ITCL partial tears lead to microinstability
- Proprioceptive loss: Mechanoreceptor damage causes subjective instability and poor proprioception
- Inflammatory cascade: Chronic synovitis perpetuates pain
- Scar tissue stenosis: Adhesions narrow the sinus tarsi, causing impingement
Classification Systems
Classification by Duration
Temporal Stages
| Stage | Duration | Pathology | Treatment Approach |
|---|---|---|---|
| Acute | Under 3 months | Acute inflammation, edema | Conservative - rest, NSAIDs, physio |
| Subacute | 3-6 months | Persistent synovitis, early fibrosis | Injection therapy, proprioceptive training |
| Chronic | Over 6 months | Fibrosis, adhesions, stenosis | Consider surgical debridement |
Stage determines management approach and prognosis.
Clinical Assessment
History
Classic presentation:
- Pain location: Vague lateral hindfoot pain anterior to lateral malleolus
- Character: Deep, aching, poorly localized
- Onset: Gradual after ankle inversion injury (weeks to months)
- Aggravating factors: Uneven ground, stairs, slopes, lateral movements
- Associated symptoms: Sensation of instability, giving way
- Previous injury: 90% report ankle sprain 3-12 months prior
The triad of lateral pain, sinus tarsi tenderness, and instability sensation is pathognomonic.
Examination
Key findings:
- Inspection: Usually normal, may have mild lateral swelling
- Palpation: Exquisite point tenderness over sinus tarsi (anterior to lateral malleolus)
- Range of motion: Subtalar motion painful at extremes of inversion and eversion
- Forced inversion test: Reproduces pain in sinus tarsi
- Forced eversion test: Also reproduces pain
- Anterior drawer: Usually negative unless coexisting ATFL injury
- Single-leg stance: Reveals proprioceptive deficit, hindfoot instability
Sinus tarsi point tenderness is the most reliable clinical sign.
Special Tests
Clinical Tests for Sinus Tarsi Syndrome
| Test | Technique | Positive Finding | Sensitivity/Specificity |
|---|---|---|---|
| Sinus tarsi palpation | Press 1 cm anterior and inferior to lateral malleolus | Exquisite point tenderness | High sensitivity (over 90%), moderate specificity |
| Forced inversion | Passively invert hindfoot, apply axial pressure | Pain reproduced in sinus tarsi | Moderate sensitivity and specificity |
| Forced eversion | Passively evert hindfoot | Pain in sinus tarsi (compression of lateral contents) | Lower sensitivity than inversion |
| Single-leg stance | Stand on affected leg 30 seconds | Difficulty maintaining balance, subjective instability | Reflects proprioceptive deficit |
| Diagnostic injection | Inject 2 mL lidocaine into sinus tarsi | Immediate pain relief confirms diagnosis | High specificity (over 90%) |
Differential Diagnosis
Must exclude:
- Lateral ankle instability: Positive anterior drawer, talar tilt. May coexist with sinus tarsi syndrome.
- Subtalar arthritis: Older age, crepitus, reduced subtalar motion. X-ray shows joint space narrowing.
- Peroneal tendinopathy: Tenderness posterior to lateral malleolus, pain with resisted eversion.
- Stress fracture: Calcaneus, talus. High index of suspicion in athletes. MRI shows bone marrow edema.
- Tarsal coalition: Rigid flat foot, usually younger age. CT diagnostic.
- L5-S1 radiculopathy: Back pain, dermatomal sensory loss, weakness.
Coexisting lateral ankle instability is found in 30-40% and should be addressed surgically if present.
Investigations
Investigation Algorithm
Diagnosis is primarily clinical based on history (post-inversion lateral hindfoot pain) and examination (sinus tarsi point tenderness). No investigations required if typical presentation and good response to initial conservative treatment.
Weight-bearing AP, lateral, and mortise ankle views:
- Usually normal in sinus tarsi syndrome
- Exclude fractures, arthritis, tarsal coalition
- Assess hindfoot alignment (valgus, varus)
- Check for talar tilt (lateral instability)
Findings: Normal in isolated sinus tarsi syndrome. May show signs of chronic lateral instability.
Gold standard for diagnosis:
T2-weighted sequences show:
- High signal intensity in sinus tarsi (edema, inflammation)
- Fat pad signal changes
- Disruption of cervical ligament
- ITCL abnormalities
- Synovitis, fluid in subtalar joint
- Exclude subtalar arthritis
Sensitivity 80-90% for sinus tarsi pathology.
Ultrasound or fluoroscopy-guided injection:
- 2 mL 1% lidocaine into sinus tarsi
- Immediate pain relief confirms diagnosis
- Can combine with corticosteroid for therapeutic effect
Specificity over 90% - positive response confirms sinus tarsi syndrome as pain source.
MRI Findings
Typical findings:
- High T2 signal in sinus tarsi (greater than 90%)
- Fat pad edema and inflammation
- Cervical ligament disruption or thickening
- ITCL signal abnormality
- Subtalar joint effusion
- Synovial thickening
Sensitivity: 80-90% for diagnosis
Ultrasound
Dynamic assessment:
- Evaluate sinus tarsi soft tissues
- Assess cervical ligament integrity
- Identify fluid collections
- Guide injection placement
Advantages: Dynamic, real-time, cost-effective. Operator-dependent.
Management Algorithm
Conservative Management (First-Line)
Initial Management (Under 3 Months)
Goal: Reduce inflammation, restore proprioception, prevent chronicity
Conservative Protocol
- Reduce impact activities
- Avoid uneven surfaces
- Use lateral ankle brace or taping
- Continue non-impact exercise (swimming, cycling)
Relative rest allows acute inflammation to settle.
- NSAIDs: Regular dosing for 3-4 weeks
- Ice therapy: 15 minutes 3-4 times daily
- Compression: Ankle sleeve or wrap
Controls acute inflammatory response.
Key interventions:
- Range of motion: Subtalar joint mobility exercises
- Strengthening: Peroneal and tibialis posterior strengthening
- Proprioceptive training: Balance board, single-leg stance (critical)
- Manual therapy: Soft tissue mobilization
Proprioceptive retraining is the most important component.
- Lateral wedge: Reduces inversion stress
- Cushioned heel: Shock absorption
- Arch support: Controls excessive pronation
Biomechanical support reduces sinus tarsi loading.
Expected outcome: 50-60% improve with conservative treatment alone within 3 months.
Surgical Technique - Arthroscopic Sinus Tarsi Debridement
Indications for Surgery
Strict Criteria for Surgical Intervention
All of the following must be met:
- Minimum 6 months failed conservative treatment
- Documented compliance with physiotherapy and proprioceptive training
- Failed injection therapy (at least one corticosteroid injection)
- MRI confirms sinus tarsi pathology (synovitis, adhesions)
- Pain significantly limiting activities
- Exclusion of subtalar arthritis (poor surgical outcomes)
Contraindications:
- Active infection
- Subtalar arthritis (consider arthrodesis instead)
- Inadequate conservative trial
- Inflammatory arthropathy (higher failure rate)
- Unrealistic expectations
Arthroscopic Sinus Tarsi Debridement
Advantages over open:
- Smaller incisions
- Less soft tissue disruption
- Faster recovery
- Better visualization
- Lower complication rate
Surgical Steps
- Lateral decubitus position with affected side up
- Beanbag or lateral positioning device
- Thigh tourniquet applied
- Ankle and foot prepped free
- C-arm available for portal placement
Anterolateral portal:
- Just anterior to tip of lateral malleolus
- At level of ankle joint
- For visualization
Sinus tarsi portal:
- 1-2 cm anterior and inferior to lateral malleolus
- Directly into sinus tarsi opening
- For instrumentation
Mark portals before inflation to identify landmarks.
- Insert 2.7 mm 30-degree arthroscope via anterolateral portal
- Navigate to sinus tarsi
- Inspect contents: Synovitis, adhesions, scar tissue
- Switch to sinus tarsi portal for direct access
- Debride inflamed synovium with shaver
- Remove scar tissue and adhesions
- Preserve cervical and ITCL ligaments (do not excise)
- Irrigate thoroughly
Goal is debridement of pathologic tissue while preserving ligamentous stability.
- View subtalar joint through sinus tarsi
- Assess for articular cartilage damage
- If significant arthritis, reconsider surgical plan
- May require arthrodesis instead
- Irrigate portals
- Close skin only with nylon suture
- Soft compressive dressing
- Non-weight bearing for first week in boot
Minimal closure required for arthroscopic technique.
Key technical points:
- Preserve ligaments - debride synovium and scar only
- Thorough debridement of all inflamed tissue
- Assess subtalar joint for arthritis
- Gentle technique to avoid iatrogenic damage
These steps ensure optimal outcomes while preserving stability.
Complications
Surgical Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Persistent pain (incomplete relief) | 20-30% | Subtalar arthritis, inflammatory arthropathy, inadequate debridement | Reassess for missed pathology, consider subtalar arthrodesis |
| Superficial peroneal nerve injury | 5-10% | Open technique, inadequate visualization | Numbness dorsum of foot. Usually recovers 3-6 months. Desensitization if persistent |
| Wound complications | 5% | Open surgery, smoking, diabetes | Wound care, antibiotics if infection. Delayed healing common with open technique |
| Subtalar stiffness | 10-15% | Aggressive debridement, prolonged immobilization | Physiotherapy, mobilization. Rarely clinically significant |
| Recurrence | 10-20% | Incomplete debridement, untreated instability | Revision debridement or consider arthrodesis |
| Iatrogenic instability | Rare (under 5%) | Excessive ligament excision | Prevention: Preserve cervical and ITCL. Treatment: Lateral ligament reconstruction |
Preventing Persistent Pain
Most common cause of surgical failure is unrecognized subtalar arthritis. Preoperative MRI must assess subtalar joint cartilage. If arthritis present, counsel patient that debridement alone has 40-60% failure rate, and subtalar arthrodesis may be necessary.
Other causes of persistent pain:
- Incomplete debridement of pathologic tissue
- Coexisting lateral ankle instability not addressed
- Inflammatory arthropathy (RA, seronegative)
- Wrong diagnosis (L5-S1 radiculopathy, peroneal pathology)
Postoperative Care and Rehabilitation
Rehabilitation After Arthroscopic Debridement
- Below-knee boot or CAM walker
- Non-weight bearing first week
- Partial weight-bearing week 2 (if minimal pain)
- Elevate, ice, analgesia
- Ankle pumps and toe exercises
- Sutures removed at 2 weeks
- Weight-bearing as tolerated in boot
- Begin gentle range of motion exercises
- Subtalar mobilization (plantarflexion-inversion, dorsiflexion-eversion)
- Proprioceptive training: Balance board, single-leg stance
- Continue ice and elevation
Proprioceptive retraining is critical to prevent recurrence.
- Wean from boot to supportive shoes
- Progressive strengthening: Peroneal, tibialis posterior
- Advance proprioception: Unstable surfaces, eyes closed
- Start low-impact activities (swimming, cycling)
- Gradual return to walking, then light jogging
Most patients return to full activity by 3 months.
- Sport-specific training from month 3
- Continue proprioceptive maintenance
- May require ankle brace initially for high-risk sports
- Full return to sport 4-6 months typically
Athletes return to competitive sport by 4-6 months in most cases.
Expected Outcomes
Success rates:
- Arthroscopic debridement: 70-80% good to excellent
- Open debridement: 65-75% good to excellent
- Best outcomes: Post-traumatic, no arthritis
- Poorer outcomes: Inflammatory arthropathy, subtalar arthritis
Return to activity:
- Walking: 6-8 weeks
- Running: 3-4 months
- Full sports: 4-6 months
Red Flags Post-op
Contact surgeon if:
- Increasing pain after initial improvement
- Signs of infection (fever, drainage, erythema)
- No improvement by 3 months
- New instability or giving way
- Numbness or tingling (nerve injury)
- Unable to bear weight by 6 weeks
Early identification prevents complications.
Outcomes and Prognosis
Prognostic Factors
Predictors of Outcome
| Good Prognosis | Poor Prognosis |
|---|---|
| Post-traumatic etiology | Inflammatory arthropathy (RA, seronegative) |
| Early diagnosis and treatment (under 6 months) | Chronic symptoms (over 12 months) |
| MRI shows isolated sinus tarsi inflammation | Subtalar arthritis on MRI |
| Good response to diagnostic injection | No response to injection |
| Compliance with physiotherapy | Poor compliance, inadequate rehab |
| Young age (under 40) | Older age (over 50) |
Key Prognostic Indicators
Best outcomes:
- Post-traumatic sinus tarsi syndrome without arthritis
- Early treatment (within 6 months of symptom onset)
- Good compliance with proprioceptive training
- Positive response to diagnostic injection
Worst outcomes:
- Concomitant subtalar arthritis (consider arthrodesis instead)
- Inflammatory arthropathy as underlying cause
- Chronic symptoms over 12 months
- Failed multiple injection attempts
The presence of subtalar arthritis on MRI is the single strongest predictor of poor outcome with debridement alone.
Evidence Base and Key Studies
Sinus Tarsi Syndrome: MRI Findings and Clinical Correlation
- MRI study of 50 patients with clinically diagnosed sinus tarsi syndrome
- Sensitivity of MRI for sinus tarsi pathology: 84%
- Commonest finding: High T2 signal in fat pad (92%)
- Cervical ligament abnormalities in 68% of cases
- Subtalar joint effusion in 56%
Arthroscopic Treatment of Sinus Tarsi Syndrome
- Case series of 49 patients undergoing arthroscopic sinus tarsi debridement
- Mean follow-up 3.2 years
- Good to excellent results in 74% of patients
- Best results in post-traumatic etiology (85% success)
- Poor results if subtalar arthritis present (40% success)
- Complication rate 8% (nerve injury, persistent pain)
Conservative vs Surgical Treatment for Sinus Tarsi Syndrome
- Retrospective comparison of 30 patients conservative vs 35 surgical
- Conservative treatment: 70% good results at 2 years
- Surgical debridement: 77% good results at 2 years
- No statistically significant difference in outcomes
- Surgery recommended only after failed conservative treatment
- Mean time to surgery: 11 months from injury
Corticosteroid Injection for Sinus Tarsi Syndrome
- Prospective case series of 42 patients receiving corticosteroid injection
- Ultrasound-guided injection technique
- Good to excellent response in 64% at 6 months
- Mean duration of symptom relief: 5.2 months
- Positive response to injection predicted good surgical outcome (88% correlation)
- No complications from injection
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Initial Presentation and Diagnosis
"A 28-year-old recreational soccer player presents with 4 months of lateral ankle pain following an inversion injury. He describes vague pain anterior to the lateral malleolus, worse on uneven ground. He feels his ankle gives way occasionally. On examination, you find exquisite point tenderness over the sinus tarsi. Anterior drawer is negative. How do you diagnose and initially manage this patient?"
Scenario 2: Refractory Case - Injection and Surgical Decision
"The same patient returns after 5 months of comprehensive conservative treatment including physiotherapy with proprioceptive training, bracing, and orthotics. He remains significantly symptomatic with persistent sinus tarsi pain limiting his soccer. MRI shows high T2 signal in sinus tarsi with cervical ligament disruption but no subtalar arthritis. What are your next steps?"
Scenario 3: Surgical Technique and Complications
"You are planning arthroscopic sinus tarsi debridement for a patient who has failed 8 months of conservative treatment and two corticosteroid injections. Walk me through your surgical technique. What would you do if you encounter significant subtalar arthritis during the arthroscopy? What are the potential complications?"
MCQ Practice Points
Anatomy Question
Q: What is the most important ligament within the sinus tarsi for subtalar joint stability?
A: The interosseous talocalcaneal ligament (ITCL) is the primary stabilizer of the subtalar joint. It is located in the medial aspect of the sinus tarsi (tarsal canal) and has two bands. The cervical ligament is located more laterally in the sinus tarsi and is a secondary stabilizer. During surgical debridement, both ligaments must be preserved to maintain subtalar stability. Excessive excision of these ligaments can lead to iatrogenic subtalar instability.
Clinical Diagnosis Question
Q: What is the pathognomonic physical examination finding for sinus tarsi syndrome?
A: Exquisite point tenderness over the sinus tarsi (located anterior and inferior to the lateral malleolus) is the most reliable clinical sign. This is present in over 90% of cases. The sinus tarsi is palpable approximately 1-2 cm anterior to the lateral malleolus. Other findings include pain with forced inversion and eversion, and subjective instability, but sinus tarsi point tenderness is the hallmark finding that differentiates it from other causes of lateral ankle pain.
Imaging Question
Q: A patient with suspected sinus tarsi syndrome undergoes MRI. What is the characteristic finding?
A: High T2 signal intensity within the sinus tarsi (fat pad edema and inflammation) is seen in 80-90% of cases. Additional findings may include disruption or signal changes in the cervical ligament, interosseous talocalcaneal ligament abnormalities, synovitis, and subtalar joint effusion. Plain radiographs are usually normal. The most important MRI assessment is to exclude subtalar arthritis, which is a poor prognostic indicator for surgical debridement and may require arthrodesis instead.
Treatment Question
Q: What is the most important component of conservative treatment for sinus tarsi syndrome?
A: Proprioceptive training with balance exercises and single-leg stance work is the most critical component. The sinus tarsi contains dense mechanoreceptors that provide proprioceptive feedback for hindfoot position. Injury disrupts this proprioceptive function, leading to the sensation of instability. Rehabilitation must include balance board exercises, single-leg stance on unstable surfaces, and sport-specific proprioceptive drills. This is combined with activity modification, NSAIDs, ankle bracing, and orthotics. Approximately 70-80% of patients respond to conservative treatment over 3-6 months.
Surgical Question
Q: During arthroscopic sinus tarsi debridement, what is the most important technical point?
A: Preserve the cervical ligament and interosseous talocalcaneal ligament while debriding synovium and scar tissue. The goal of surgery is to remove inflamed synovium, scar tissue, and adhesions that are causing pain and impingement. However, the ligaments provide essential subtalar joint stability and must be preserved. Complete excision of these ligaments can lead to iatrogenic subtalar instability. The surgical principle is debridement of pathologic soft tissue while maintaining ligamentous integrity.
Prognosis Question
Q: Which MRI finding predicts the poorest outcome with arthroscopic sinus tarsi debridement?
A: Subtalar arthritis (joint space narrowing, cartilage loss, subchondral changes) is the strongest predictor of poor outcome. Debridement alone in the presence of subtalar arthritis has only a 40-60% success rate compared to 70-80% without arthritis. If significant arthritis is present, the patient should be counseled that subtalar arthrodesis may be necessary for definitive pain relief. Preoperative MRI assessment of the subtalar joint is essential to identify arthritis and set realistic expectations.
Australian Context and Medicolegal Considerations
PBS and Healthcare
Funded treatments:
- Corticosteroid injection: PBS-funded
Not PBS-funded (out-of-pocket):
- Platelet-rich plasma injection: 500-800 AUD
- Custom orthotics: 300-600 AUD (some private health rebate)
Counsel patients about costs before recommending non-PBS treatments.
Australian Guidelines
Best Practice Recommendations:
- Minimum 6 months conservative trial before surgery
- Proprioceptive training essential component
- Preoperative MRI to assess subtalar joint
- Informed consent including 20-30% persistent pain risk
Workers' Compensation:
- Common in occupations requiring walking on uneven ground
- Document conservative compliance thoroughly
- Early return to modified duties improves outcomes
Medicolegal Considerations
High-risk areas for litigation:
-
Inadequate conservative trial: Document minimum 6 months comprehensive conservative treatment including physiotherapy with proprioceptive training, bracing, and injection therapy before recommending surgery.
-
Missed subtalar arthritis: Preoperative MRI must assess subtalar joint. Performing debridement in presence of arthritis leads to high failure rate. Document discussion of findings and potential need for arthrodesis.
-
Nerve injury: Superficial peroneal nerve at risk. Informed consent must include numbness risk (5-10%). Document protection of nerve during surgery.
-
Persistent pain: 20-30% have incomplete relief. Set realistic expectations preoperatively. Document that surgery is not guaranteed cure.
-
Wrong diagnosis: Exclude lateral ankle instability, peroneal pathology, subtalar arthritis, stress fracture before diagnosing sinus tarsi syndrome. Consider diagnostic injection to confirm.
Documentation requirements:
- Timeline of conservative treatment and compliance
- Injection response (diagnostic confirmation)
- MRI findings especially subtalar joint assessment
- Informed consent discussion including complications and incomplete relief risk
- Surgical findings (presence of arthritis, extent of debridement)
Sinus Tarsi Syndrome
High-Yield Exam Summary
Key Anatomy
- •Sinus tarsi: Cone-shaped tunnel between talus (superior) and calcaneus (inferior)
- •Location: Opens laterally anterior to lateral malleolus, palpable 1-2 cm anterior to tip
- •Contents: Interosseous talocalcaneal ligament (ITCL - main stabilizer), cervical ligament, fat pad, mechanoreceptors
- •Function: Subtalar stability, proprioception for hindfoot position
Clinical Features
- •Triad: Lateral hindfoot pain, sinus tarsi point tenderness, instability sensation
- •History: 90% follow ankle inversion injury, pain worse on uneven ground
- •Examination: Exquisite sinus tarsi tenderness (pathognomonic), pain with forced inversion/eversion
- •Negative anterior drawer unless coexisting lateral ankle instability (30-40%)
Investigations
- •Clinical diagnosis: Based on history and examination
- •X-rays: Usually normal, exclude fracture and arthritis
- •MRI: High T2 signal in sinus tarsi (80-90% sensitivity), assess subtalar joint for arthritis
- •Diagnostic injection: 2 mL lidocaine, immediate relief confirms diagnosis (over 90% specificity)
Conservative Management
- •First-line: 70-80% respond to conservative treatment over 3-6 months
- •Proprioceptive training: Most important component - balance exercises, single-leg stance
- •Activity modification: Avoid uneven surfaces, lateral ankle brace
- •Injection: Corticosteroid if failed 3 months conservative, 60-70% temporary relief
- •Limit 2 corticosteroid injections maximum
Surgical Technique
- •Indication: Over 6 months failed conservative including injection therapy
- •Arthroscopic debridement: Lateral decubitus, anterolateral and sinus tarsi portals
- •Key technical point: Debride synovium and scar, PRESERVE cervical and ITCL ligaments
- •Assess subtalar joint: If arthritis present, may require arthrodesis instead
- •Success: 70-80% good to excellent results without arthritis, 40-60% if arthritis present
Complications and Outcomes
- •Persistent pain: 20-30% most common, often due to unrecognized arthritis
- •Nerve injury: 5-10% superficial peroneal nerve, numbness dorsum of foot
- •Recurrence: 10-20%, incomplete debridement or untreated instability
- •Best prognosis: Post-traumatic, no arthritis, good injection response
- •Worst prognosis: Subtalar arthritis (consider arthrodesis), inflammatory arthropathy