High Yield Overview
Tarsal Coalition
Peroneal Spastic Flatfoot
CN / TCMost Common (90%)
ADInheritance
CTGold Std Imaging
ResectionSurgical Rx
Types by Location
Calcaneonavicular (CN)
PatternOssifies 8-12 yrs. Anteater Nose sign.
TreatmentResection + Interposition (EDB)
Talocalcaneal (TC)
PatternOssifies 12-16 yrs. C-Sign. Middle facet usually.
TreatmentResection (if under 50%) or Fusion
Critical Must-Knows
- Definition: Abnormal connection between two tarsal bones (Fibrous, Cartilaginous, or Osseous).
- Presentation: Rigid flatfoot, frequent ankle sprains, 'Peroneal Spastic Flatfoot'.
- Onset: Symptoms start when the coalition ossifies (stiffens). 8-12y for CN, 12-16y for TC.
- X-ray Signs: Anteater Nose (CN), C-Sign (TC), Talar Beaking (Dorsal).
- Treatment: Conservative (Rest/Cast) → Resection (if under 50% of joint) → Fusion (Triple/Subtalar).
Examiner's Pearls
- "CN coalition ossifies FIRST (8-12y), TC coalition LATER (12-16y).
- "Anteater Nose Sign = CN Coalition (elongated anterior calcaneus).
- "C-Sign = TC Coalition (continuity of talus/calcaneus on lateral).
- "Resection of TC coalition is only viable if under 50% of the joint is involved and no arthrosis.
- "Bilateral in 50% of cases.
Clinical Imaging
Imaging Gallery
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Coalition Pitfalls
Missed Diagnosis
'Ankle Sprains'. Recurrent ankle sprains in an adolescent with a flat foot → Think Coalition.
Talar Beak
Not the Coalition. Talar beak is a traction spur from abnormal motion/stress. It is NOT the coalition itself.
TC Resection Limit
The 50% Rule. Do not resect TC coalitions if over 50% of the middle facet is involved. Outcome is poor. Fuse instead.
Peroneal Spasm
Not True Spasm. It is adaptive shortening of the peroneals due to the valgus deformity.
At a Glance: CN vs TC Coalition
| Feature | Calcaneonavicular (CN) | Talocalcaneal (TC) |
|---|---|---|
| Frequency | Common (45%) | Common (45%) |
| Age of Onset | 8 - 12 years | 12 - 16 years |
| Location | Anterior Calcaneus - Navicular | Middle Facet (Sustentaculum) |
| X-ray Sign | Anteater Nose | C-Sign |
| View | Oblique Foot | Lateral Foot / Harris Axial |
| Surgical Outcomes | Excellent (Resection) | Variable (Resection vs Fusion) |
Mnemonic
CN-TCCoalition Onset Age
C
Calcaneo
Navicular
N
Nine
~9-12 years (Earlier)
T
Talo
Calcaneal
C
College
~12-16 years (Later)
Memory Hook:CN = 9-12. TC = Teens.
Mnemonic
Ant-CX-ray Signs
Ant
Anteater
CN Coalition (process of calcaneus)
C
C-Sign
TC Coalition (halo around sustenaculum)
Memory Hook:Anteater for CN, C for TC.
Mnemonic
RICEResection Steps
R
Resect
Generous block (greater than 1cm)
I
Interpose
EDB (CN) or Fat (TC) to prevent regrowth
C
Check
Verify motion intra-op
E
Early Motion
Cast 2 weeks then ROM
Memory Hook:RICE for Resection success.
Overview and Epidemiology
Definition: A failure of segmentation between two or more tarsal bones, producing a fibrous (syndesmosis), cartilaginous (synchondrosis), or osseous (synostosis) bridge.
Epidemiology:
- Incidence: Less than 1% of population.
- Genetics: Autosomal Dominant with variable penetrance.
- Laterality: Bilateral in 50% of cases.
- Types: CN and TC make up greater than 90% of all coalitions.
Pathophysiology:
- Congenital problem, but asymptomatic in young children because the coalition is cartilaginous/fibrous and allows motion.
- Symptoms start when the coalition ossifies (turns to bone) and becomes rigid, restricting subtalar motion.
- Peroneal Spastic Flatfoot: Rigid valgus foot causes shortening/tightness of peroneal tendons (not true spasm).
Pathophysiology and Mechanisms
Key Anatomy: Understanding the relevant anatomy is crucial for diagnosis and management. The structures involved include the osseous architecture and surrounding soft tissues.
Pathomechanics: The injury mechanism often involves specific loading patterns that disrupt the structural integrity.
Classification Systems
- Calcaneonavicular (CN): Ossifies 8-12 yrs. Anteater Nose sign.
- Talocalcaneal (TC): Ossifies 12-16 yrs. C-Sign. Middle facet usually.
Clinical Assessment
History:
- Pain: Vague hindfoot/midfoot pain, worse with activity.
- Stiffness: "My foot doesn't move right."
- Sprains: Recurrent ankle sprains (rigid hindfoot can't accommodate uneven ground).
- Deformity: Progressive flatfoot.
Physical Examination:
- Inspection: Rigid Flatfoot (Pes Planus). Valgus heel.
- Motion:
- Restricted Subtalar Motion (Inversion/Eversion).
- Locking: Foot may be locked in valgus.
- Tender:
- Sinus Tarsi (CN).
- Medial Malleolus/Sustentaculum (TC).
- Toe Raise Test: Heel remains in valgus (does not invert) → Indicates RIGID flatfoot.
Investigations
X-ray:
- Lateral:
- C-Sign: Continuous C-shaped line from talar dome to sustentaculum tali (TC coalition).
- Talar Beak: Dorsal spur on talar head (sign of increased stress, not the coalition).
- Anteater Nose: Elongated anterior process of calcaneus (CN coalition).
- Oblique (Slanted): Best for CN coalition.
- Harris Axial: Can show TC coalition (middle facet angulation).
CT Scan (Gold Standard):
- Confirms diagnosis.
- Defines location and extent.
- Assesses % of joint involvement (Critical for TC).
- Look for degenerative changes.
MRI:
- Useful for fibrous/cartilaginous coalitions (non-ossified) if CT negative but high suspicion.
Management Algorithm
📊 Management Algorithm
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Conservative Management
- Indication: Initial presentation, Mild symptoms.
- Modalities:
- Activity Modification: Avoid uneven ground.
- Immobilization: Short leg walking cast (3-6 weeks) to settle inflammation.
- Orthotics: UCBL or medial arch support (rigid support).
- Success: ~30% may resolve or become manageable without surgery.
Surgical Technique
CN Coalition Resection
- Incision: Ollier's (Lateral oblique over sinus tarsi).
- Identify: EDB muscle belly. Reflect it.
- Excise: Identify the coalition bar (calcaneus to navicular). Excise a generous rectangular block (1cm minimum) to prevent regrowth.
- Check: Verify navicular and calcaneus surfaces are clear. Check motion.
- Interpose: Sew EDB muscle origin into the defect (anchored to deep tissue/plantar aspect).
- Post-op: Cast 2 weeks then early ROM.
Complications
Complications of Surgery
| Complication | Cause | Prevention |
|---|---|---|
| Recurrence | Inadequate resection (greater than 50% remaining) | Resect greater than 1cm block, Interposition (EDB/Fat) |
| Persistent Pain | Degenerative changes, Missed double coalition | Pre-op CT calc, Triple Fusion if arthrosis |
| Sural Nerve Injury | Lateral approach incision | Identify nerve, careful retraction |
| Wound Dehiscence | Medial approach tension | Gentle retraction |
Complications of Non-Treatment
- Progressive Valgus deformity.
- Peroneal tendon contracture/shortening.
- Subtalar and TN joint arthritis.
Postoperative Care
Protocol:
- Immobilization: Initial splinting/casting to protect the repair/fracture.
- Rehabilitation: Gradual Range of Motion (ROM) and strengthening as healing progresses.
- Weight Bearing: Progression depends on stability of fixation and healing.
Outcomes
- CN Resection: Usually very successful. Pain relief and improved motion.
- TC Resection: success depends on size (less than 50%). If greater than 50%, consider primary fusion.
- Recurrence: Bone can regrow. Interposition material helps prevent this.
Evidence Base
Resection of TC Coalition
Key Findings:
- Resection of TC coalition yields good results if:
- Coalition area less than 50% of posterior facet.
- No degenerative changes.
- Heel valgus is mild.
Clinical Implication: Measure the % involvement on CT.
Limitation: Retrospective
Anteater Nose Sign
Key Findings:
- Describes the anterior calcaneal process enlargement in CN coalition.
- Looks like an anteater's nose on lateral X-ray.
Clinical Implication: Classic sign for CN coalition.
Limitation: Diagnostic
Long-term CN Resection
Key Findings:
- Excellent function maintained at long-term follow-up (mean 13 years).
Clinical Implication: Resection is a durable solution for CN.
Limitation: Retrospective
Triple Arthrodesis Outcomes
Key Findings:
- Long term follow up of triple arthrodesis.
- Good pain relief and deformity correction.
- High rate of adjacent joint ankle arthritis (OA) at 20-40 years.
- Fusion is a salvage, not primary choice if resection possible.
Clinical Implication: Fusion has a shelf life (Ankle OA).
Limitation: Long term follow up
Conservative Treatment
Key Findings:
- 30% of tarsal coalitions can be managed non-operatively.
- Casting for 6 weeks settled symptoms in many adolescents.
- Some stiff feet become painless stiff feet with time.
Clinical Implication: Always try non-op first.
Limitation: Case Series
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
The Rigid Flatfoot
EXAMINER
"What is the diagnosis and workup?"
EXCEPTIONAL ANSWER
**Tarsal Coalition (Likely CN given sinus tarsi pain).**
1. **Clinical Signs**: Rigid Pes Planus (No heel inversion on toe raise). Restricted subtalar motion.
2. **Age**: 13 fits with onset of ossification.
3. **Imaging**:
- X-ray: Oblique foot (best for CN). Look for Anteater Nose.
- CT: Confirm diagnosis and rule out TC coalition (often coexist or confused).
4. **Management**:
- Initial: trial of casting (4-6 weeks) or orthotics.
- If fails: Surgical Resection + EDB interposition.
KEY POINTS TO SCORE
Rigid Flatfoot
Peroneal Spastic Flatfoot
X-ray: Oblique
CT confirmation
COMMON TRAPS
✗Diagnosing flexible flatfoot
✗Missing the second coalition
LIKELY FOLLOW-UPS
"What muscle do you interpose?"
"Why does it present at age 13?"
VIVA SCENARIOStandard
The TC Coalition
EXAMINER
"Can you resect this?"
EXCEPTIONAL ANSWER
**No - Resection Contraindicated.**
1. **Rule**: Resection is generally contraindicated if over 50% of the facet is involved or if there is heel valgus over 16-20 degrees.
2. **Reason**: Instability and poor outcomes after removing such a large stabilizer.
3. **Management**: Subtalar Fusion (Arthrodesis).
- Corrects the deformity.
- Relieves pain.
- Sacrifices motion (which is already lost).
KEY POINTS TO SCORE
50% Rule for TC
Fusion if large
Fusion if arthrosis
COMMON TRAPS
✗Resecting a large coalition (failure)
✗Ignoring alignment
LIKELY FOLLOW-UPS
"What if it was 30% size with arthrosis?"
"What is the C-Sign?"
MCQ Practice Points
Onset Age
Q: Which coalition presents earlier? A: Calcaneonavicular (8-12 years). Talocalcaneal presents later (12-16 years).
Radiographic Sign
Q: What is the 'Anteater Nose' sign? A: Elongation of the anterior process of the calcaneus, seen on lateral X-ray, indicated Calcaneonavicular coalition.
C-Sign
Q: What does the C-Sign indicate? A: Talocalcaneal coalition. A continuous C-shaped line formed by the medial outline of the talar dome and inferior outline of the sustentaculum tali on lateral X-ray.
Resection Contraindication
Q: What is the size cutoff for resecting a TC coalition? A: 50%. If over 50% of the facet is involved, resection has poor outcomes. Fusion is preferred.
Toe Raise Test
Q: What happens to the heel during a toe raise test in tarsal coalition? A: The heel stays in Valgus (does NOT invert). This indicates a RIGID flatfoot. (In flexible flatfoot, the heel inverts).
Australian Context
- Terminology: Often called "Peroneal Spastic Flatfoot" historically, though "Rigid Flatfoot" is more accurate.
- CT: Low dose CT protocols usually used for pediatric foot assessment.
High-Yield Exam Summary
Key Features
- •Rigid Flatfoot
- •Age 8-16 (Ossification)
- •Bilateral 50%
- •Recurrent Sprains
CN Coalition
- •8-12 years
- •Anteater Nose
- •Oblique View
- •Resection Excellent
TC Coalition
- •12-16 years
- •C-Sign
- •CT Essential
- •Less than 50% to Resect
Management
- •Cast 4-6wks first
- •Resect CN + EDB
- •Resect TC (Small)
- •Fuse TC (Large)