Subungual Exostosis

1. Clinical Overview

Summary

Subungual Exostosis (SE) is a benign osteocartilaginous outgrowth arising from the dorsal surface of the distal phalanx, most commonly affecting the hallux. It represents a reactive proliferation rather than a true neoplasm, distinguishing it from osteochondroma. The lesion typically presents in adolescents and young adults with progressive nail plate elevation, localized pain, and a firm subungual mass. The natural history involves gradual growth causing mechanical nail bed separation (onycholysis), secondary infection risk, and persistent discomfort with footwear. [1,2,3]

The condition is clinically significant because it is frequently misdiagnosed as verruca vulgaris, onychomycosis, or ingrown toenail, leading to delayed treatment and prolonged symptoms. The diagnostic hallmark is a lateral radiograph demonstrating a characteristic bony protrusion from the dorsal distal phalanx. Definitive treatment is surgical excision, which provides cure with low recurrence rates when performed with complete removal of the fibrocartilaginous cap. [4,5]

Key Facts

• The Great Mimic: Patients often seek treatment for presumed "wart," "fungal infection," or "ingrown toenail" for months before correct diagnosis. The critical distinguishing feature is the rock-hard consistency (osseous) and fixation to underlying bone. [6,12]
• The Nail Elevator Effect: Progressive bone growth mechanically elevates the nail plate from the nail bed like a hydraulic jack, creating a visible separation (onycholysis). This separation provides entry for bacteria, debris, and secondary infection. [5]
• Exostosis vs Osteochondroma - The Critical Distinction:
  • Subungual Exostosis: Broad-based lesion arising from distal phalanx tuft, no medullary continuity, fibrocartilaginous cap (not hyaline), reactive/traumatic origin. [7,18]
  • Osteochondroma: Pedunculated lesion with medullary and cortical continuity, hyaline cartilage cap, true benign neoplasm, typically metaphyseal location. [7,18]
• Age and Gender Pattern: Peak incidence in second to third decade (10-30 years), female predominance (2-3:1 ratio), strong association with repetitive microtrauma (tight footwear, dancing, athletics). [2,8,18]

Clinical Pearls

"X-ray Everything Subungual": Any persistent, painful subungual lesion warrants plain radiography. Clinical examination alone cannot reliably distinguish between soft tissue lesions (glomus tumor, melanoma) and bony pathology. The lateral view is mandatory - it reveals the dorsal bony projection which is obscured on AP views. [4,11]

"Save the Nail Matrix": Surgical approach selection determines cosmetic outcome. The "fish-mouth" or lateral approach preserves the germinal and sterile matrix, minimizing nail dystrophy risk. Trans-ungual approaches require meticulous nail bed repair to prevent permanent ridging or splitting. [5,16]

"Complete Excision = No Recurrence": Recurrence rates of 5-10% are directly attributable to incomplete removal. The fibrocartilaginous cap must be excised entirely, and the underlying bone rongeur'd flush with normal cortex. Leaving even small remnants of proliferative tissue leads to regrowth. [5,7,16]

"Fish Mouth Incision": The distal curvilinear ("fish mouth") incision at the toe tip allows elevation of the soft tissue hood (including nail plate and bed) as a unit, providing excellent exposure while avoiding nail bed violation. Closure is straightforward and cosmetic outcomes are superior. [5,16]

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2. Epidemiology

Demographics and Distribution

• Age Distribution:
  • Peak incidence: 10-30 years (adolescence and young adulthood) [2,8,18]
  • Mean age at presentation: 15-20 years [18]
  • Rare in children less than 10 years and adults > 40 years [2]
• Gender: Female predominance (2:1 to 3:1 ratio in most series) [2,8,18]
• Anatomical Location:
  • Hallux (great toe): 80-85% of cases [2,5,18]
  • Lesser toes: 10-15% [2,18]
  • Fingers: 5-10% (rare, typically thumb or index finger) [20]
  • Bilateral involvement: less than 5% of cases [18]

Incidence and Prevalence

While precise epidemiological data are limited due to underreporting and misdiagnosis, subungual exostosis accounts for approximately 0.5-1% of all bone tumors presenting to orthopedic and podiatric clinics. [8] The true incidence is likely higher given the frequency of delayed or missed diagnosis. Population-based studies are lacking.

Etiological Factors

• Chronic Microtrauma: Strongest etiological association, supported by:
  • Predominance in hallux (site of greatest pressure and repetitive stress) [2,5]
  • High incidence in athletes, dancers, and individuals wearing constrictive footwear [8]
  • History of antecedent trauma in 30-50% of cases [2,5]
• Infection Theory: Historical hypothesis suggesting prior infection or inflammatory stimulus, though evidence is weak and not widely accepted. [1,4]
• Genetic Predisposition: No established genetic component for isolated lesions. However, distinguish from Multiple Hereditary Exostoses (MHE), a separate autosomal dominant condition. [7]

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3. Pathophysiology

Embryology and Anatomy

The distal phalanx of the toe consists of:

• Tuft: Expanded distal portion with dense trabecular bone
• Dorsal Surface: Site of SE origin, covered by nail bed (sterile and germinal matrix)
• Normal Ossification: Completes in adolescence; SE typically arises after growth plate closure

Histopathogenesis

Subungual exostosis is a reactive proliferative lesion, not a true neoplasm. The prevailing theory involves:

1. Initiating Trauma: Repetitive microtrauma to the distal phalanx causes periosteal irritation and activation. [2,5]
2. Periosteal Reaction: Activated periosteum produces woven bone (early) transitioning to lamellar bone (later). [3,7]
3. Cartilage Cap Formation: Unlike osteochondroma (hyaline cartilage), SE develops a fibrocartilaginous cap with mixed fibrous and cartilaginous tissue. This cap drives continued growth. [3,7,18]
4. Mechanical Progression: As the lesion enlarges dorsally, it mechanically elevates the overlying nail plate, causing:
   • Onycholysis (nail bed separation)
   • Secondary bacterial colonization
   • Chronic inflammation and pain

Microscopic Histology

• Bony Base: Mature trabecular (cancellous) bone with normal marrow elements [3,7]
• Cartilaginous Cap: 1-3mm thick fibrocartilaginous layer (NOT hyaline cartilage) [3,7,18]
• Surface: May show ulceration, granulation tissue, or reactive epithelial hyperplasia if nail bed is violated [3]
• Medullary Continuity: ABSENT - key distinction from osteochondroma [7,18]

Molecular and Cellular Mechanisms

Limited molecular studies exist, but SE is generally considered:

• Non-neoplastic: No clonal proliferation or genetic mutations identified
• Reactive Metaplasia: Mesenchymal cells responding to chronic irritation
• Growth Factor Mediated: Likely involves TGF-β, BMP, and VEGF pathways driving osteochondral differentiation (speculative, not well-studied)

Natural History

Without treatment:

• Progressive Growth: Typically slow (months to years) [5,8]
• Nail Destruction: Continued elevation leads to permanent nail bed damage
• Infection Risk: Onycholysis creates portal for bacteria
• Pain Escalation: Pressure from footwear becomes intolerable
• Spontaneous Resolution: Does NOT occur; surgical excision is curative

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4. Clinical Presentation

Symptomatology

Primary Symptoms

• Pain:
  • Character: Throbbing, pressure-related, exacerbated by footwear
  • Location: Localized to distal toe, directly over the lesion
  • Severity: Ranges from mild discomfort to severe pain preventing shoe wear
  • Duration: Gradual onset over months to years [5,8]
• Nail Deformity:
  • "My toenail is lifting up"

• classic patient description
  • Progressive separation visible as white discoloration (onycholysis)
  • Nail plate may be thickened, ridged, or split [5]

• Visible Lump:
  • Firm, non-mobile mass under or adjacent to nail
  • May protrude beyond nail margin if advanced [8]

Secondary Symptoms

• Bleeding: Friable tissue may bleed with minor trauma [5]
• Discharge: Secondary infection leads to purulent drainage
• Cosmetic Concern: Visible deformity, particularly in women

Physical Examination Findings

Inspection

• Onycholysis: White or yellow discoloration indicating nail plate separation from bed [5]
• Subungual Mass:
  • Pink to red nodule visible through nail (if not heavily keratinized)
  • Smooth, dome-shaped contour [8]
  • Size: typically 5-15mm diameter [5,18]
• Nail Plate Elevation: Increased distance between nail plate and underlying bone
• Ulceration: Advanced cases may show skin breakdown overlying the lesion [5]

Palpation

• Consistency: Rock-hard, bony firmness (pathognomonic finding) [1,4,6]
• Mobility: Fixed, non-mobile (attached to underlying bone) [4]
• Tenderness: Direct pressure elicits sharp pain [5]
• Blanching Test: Pressing on the nail causes visible blanching over the high point of the exostosis (indicates mechanical elevation) [4]

Special Tests

• Lateral Pinch Test: Squeezing the toe medial-to-lateral compresses the lesion against nail plate, reproducing pain
• Shoe Pressure Test: Apply pressure simulating footwear - reproduces typical pain

Clinical Presentation Variants

By Age

• Adolescents: Often athletic, history of trauma, rapid growth phase [8,14]
• Young Adults: Female predominance, association with tight footwear (high heels) [2,8]
• Children: Rare, may be mistaken for wart or other benign lesions [14,20]

By Location

• Hallux: Classic presentation, dorsomedial location most common [2,5]
• Lesser Toes: Less common, often delayed diagnosis [2]
• Fingers: Very rare, typically thumb or index, may be related to occupational trauma [20]

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5. Differential Diagnosis

The differential for a painful subungual mass is critical, as misdiagnosis can lead to inappropriate treatment or missed malignancy.

Primary Differential Diagnoses

1. Osteochondroma

• Similarities: Bony lesion, cartilage cap, benign
• Differences:
  • Location: Metaphysis of proximal phalanx or metatarsals (NOT distal tuft) [7,18]
  • Imaging: Medullary and cortical continuity with parent bone [7,18]
  • Histology: Hyaline cartilage cap (not fibrocartilage) [7]
  • Genetics: May be associated with MHE syndrome [7]

2. Subungual Melanoma

• Critical to Exclude: Potentially lethal malignancy
• Red Flags: [11]
  • Pigmented lesion (brown, black, or blue discoloration)
  • Hutchinson's sign (pigment extending onto proximal or lateral nail fold)
  • Irregular borders, variegated color
  • Rapid growth, ulceration, bleeding
• Imaging: Soft tissue mass, NO bony lesion on X-ray
• Diagnosis: Biopsy mandatory if any suspicion

3. Verruca Vulgaris (Viral Wart)

• Clinical Mimicry: Common misdiagnosis [6,12]
• Differences:
  • Consistency: Soft to firm (NOT rock-hard) [6,12]
  • Dermoscopy: Black dots (thrombosed capillaries) visible
  • Imaging: No bony lesion
  • Response to treatment: May respond to cryotherapy/salicylic acid (exostosis does not)

4. Glomus Tumor

• Classic Triad: Severe pain, cold sensitivity, point tenderness [11]
• Imaging:
  • X-ray: May show pressure erosion of bone (scalloping), but no bony protrusion
  • MRI: Enhancing soft tissue mass, highly vascular [11]
• Demographics: Adults 30-50 years, female predominance

5. Onychomycosis (Fungal Nail Infection)

• Differences:
  • Consistency: Soft, friable nail plate thickening
  • No bony lump palpable
  • Imaging: Normal bone on X-ray
  • KOH prep/fungal culture: Positive for dermatophytes

6. Other Rare Differentials

• Enchondroma: Intramedullary, expansile, no dorsal projection [7]
• Subungual Fibroma: Soft tissue, associated with tuberous sclerosis
• Pyogenic Granuloma: Vascular, soft, bleeds easily, no bone involvement
• Keratoacanthoma: Rapidly growing, crater-like, soft tissue

Diagnostic Algorithm

        PAINFUL SUBUNGUAL MASS
                 ↓
          PHYSICAL EXAM
         /              \
    ROCK-HARD         SOFT/FIRM
    (bony)          (soft tissue)
      ↓                   ↓
   X-RAY          MRI or BIOPSY
      ↓                   ↓
   BONE SEEN        Glomus, Melanoma,
      ↓              Wart, Granuloma
  LATERAL VIEW
      ↓
  ┌─────────┴─────────┐
DISTAL PHALANX    METAPHYSEAL
(tuft, dorsal)    (proximal phalanx)
  ↓                   ↓
EXOSTOSIS         OSTEOCHONDROMA

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6. Investigations

Imaging

Plain Radiography (THE GOLD STANDARD)

• Views Required:

  • Lateral View: MANDATORY - demonstrates dorsal bony protrusion clearly [4,5,18]
  • AP (Dorsoplantar) View: Supplementary - often obscures lesion due to overlap with phalanx [4]
  • Oblique View: Helpful for eccentric lesions

• Radiographic Features of Subungual Exostosis: [4,5,7,18]

  • Bony Protrusion: Extends dorsally from distal phalanx tuft
  • Base: Broad-based attachment (sessile)
  • Contour: Smooth or lobulated
  • Trabeculation: Trabecular bone pattern visible within lesion
  • Cortex: Continuous with parent bone cortex
  • Medullary Continuity: ABSENT (key distinction from osteochondroma)
  • Cartilage Cap: Radiolucent cap may be visible (1-3mm)
  • Adjacent Bone: Normal trabecular pattern, no lytic changes

• Early Lesions: May be predominantly cartilaginous and appear radiolucent or subtle on plain films [4,7]

• Post-Excision Imaging: Used to confirm complete removal and assess for recurrence if symptoms recur [5,16]

Advanced Imaging (Selective Use)

Magnetic Resonance Imaging (MRI) [11]

• Indications:
  • Atypical presentation
  • Soft tissue component assessment
  • Pre-operative planning for complex cases
  • Differentiating from soft tissue masses (glomus, melanoma)
• Findings:
  • Bony lesion: Low T1, variable T2 signal
  • Cartilage cap: High T2 signal (bright)
  • Enhances with gadolinium (cap)
  • Surrounding soft tissue edema/inflammation

Computed Tomography (CT)

• Indications: Rarely needed; may be used for complex anatomy or pre-operative 3D planning
• Findings: Superior bony detail, demonstrates cortical and trabecular architecture

Ultrasound

• Role: Limited; may detect soft tissue component but cannot reliably assess bone [11]

Laboratory Investigations

• Not Routinely Indicated: Subungual exostosis is a clinical and radiological diagnosis
• Infection Workup: If secondary infection suspected:
  • Complete blood count (CBC): Leukocytosis
  • Inflammatory markers: ESR, CRP (elevated)
  • Wound culture: Bacterial identification if draining

Histopathology

• Timing: Post-excision specimen sent for pathological confirmation

• Gross Examination: Firm bony lesion with overlying fibrocartilaginous cap

• Microscopic Findings: [3,7,18]

  • Mature trabecular bone with normal marrow
  • Fibrocartilaginous cap (NOT hyaline cartilage)
  • No cytologic atypia
  • Surface may show ulceration, granulation tissue, or reactive epithelium

• Purpose:

  • Confirms benign nature
  • Excludes malignancy (especially if imaging atypical)
  • Differentiates from osteochondroma histologically

Biopsy (Pre-Excision)

• Indications:
  • Suspicion of malignancy (melanoma, sarcoma)
  • Atypical imaging features
  • Unusual demographics (elderly patient, rapid growth)
• Technique: Incisional biopsy through nail bed (rarely performed, as definitive excision is typically diagnostic and therapeutic)

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7. Management Overview

Goals of Treatment

1. Complete Lesion Removal: Curative excision of bony exostosis and fibrocartilaginous cap
2. Symptom Resolution: Eliminate pain, restore normal nail anatomy
3. Prevent Recurrence: Ensure flush resection to normal cortex
4. Preserve Nail Function: Minimize nail bed trauma, preserve germinal and sterile matrix
5. Optimize Cosmesis: Minimize scarring and nail dystrophy

Treatment Paradigm

Subungual exostosis is a surgical disease. There is NO role for non-operative management beyond temporizing symptomatic relief. [5,7,16]

Management Algorithm

         CONFIRMED SUBUNGUAL EXOSTOSIS
         (Lateral X-ray diagnostic)
                    ↓
          ┌─────────┴─────────┐
      SYMPTOMATIC         ASYMPTOMATIC
          ↓                   ↓
    SURGICAL EXCISION    OBSERVATION
          ↓               (rare; less than 5%)
  ┌───────┴───────┐           ↓
LESION LOCATION    IF SYMPTOMS DEVELOP
  ↓                    → SURGERY
  ├─ CENTRAL/LARGE → Trans-ungual Approach
  ├─ DISTAL → Fish-Mouth Approach
  └─ ECCENTRIC → Lateral/Medial Approach
          ↓
    COMPLETE EXCISION
    (bone + cap flush)
          ↓
    NAIL BED REPAIR
          ↓
    PATHOLOGY CONFIRMATION

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8. Non-Operative Management

Limitations and Role

There is NO definitive non-operative treatment for subungual exostosis. [5,7,16] Surgical excision is curative and universally recommended.

Temporizing Measures (Symptom Control Only)

• Indications:

  • Patient unfit for surgery (severe comorbidities)
  • Patient declining surgery (rare)
  • Short-term relief pending scheduled surgery

• Interventions:

  • Footwear Modification: Wide toe box, soft upper, avoid pressure on affected toe [8]
  • Padding: Donut-shaped foam pads to offload pressure
  • Analgesics: NSAIDs (ibuprofen 400mg TDS, naproxen 500mg BD) for pain control
  • Antibiotics: If secondary infection present (oral cephalexin, amoxicillin-clavulanate)
  • Nail Care: Gentle debridement of thickened nail plate, keep clean and dry

Limitations of Conservative Approach

• Does NOT address underlying pathology
• Lesion continues to grow
• Symptoms progress despite measures
• Risk of secondary complications (infection, nail destruction)
• Conclusion: Non-operative management is NOT curative and should only be temporary. [5,16]

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9. Surgical Management

Surgical excision is the definitive and curative treatment for subungual exostosis, with excellent outcomes and low recurrence when performed correctly. [5,7,16]

Pre-Operative Planning

Patient Counseling

• Procedure: Removal of bony lesion under local or regional anesthesia
• Outcome Expectations:
  • Immediate pain relief expected
  • Nail regrowth takes 6-9 months [5,16]
  • Minor nail dystrophy (ridge, thickening) possible (10-20%) [5,16]
• Recurrence: 5-10% if complete excision achieved [5,7,16]
• Return to Activity:
  • Protected weight-bearing: 1-2 weeks
  • Return to normal footwear: 4-6 weeks
  • Return to sports: 6-8 weeks

Anesthesia Options

• Digital Block: First-line, effective, allows outpatient procedure [5]
  • Local anesthetic (lidocaine 1-2%, bupivacaine 0.25-0.5%)
  • Epinephrine may be used (controversial in digits; avoid if vascular disease)
• Ankle Block: Alternative for hallux lesions
• General Anesthesia: Reserved for children or anxious patients

Equipment and Setup

• Tourniquet (digit or ankle level)
• Fine surgical instruments (scalpel, periosteal elevator, rongeur, curette)
• High-speed burr (optional, for smoothing bone edges)
• Absorbable suture (5-0 or 6-0 Vicryl for nail bed, 4-0 or 5-0 for skin)
• Sterile dressing, post-operative shoe

Surgical Approaches

1. Trans-Ungual (Direct Dorsal) Approach

Indications:

• Large central lesions
• Lesions involving majority of distal phalanx width [5]

Technique: [5,16]

1. Nail Plate Removal:
   • Elevate nail plate from nail bed using freer elevator
   • May remove entire plate or create fenestration (window) in plate
2. Nail Bed Incision:
   • Longitudinal incision over lesion through sterile matrix
3. Exposure:
   • Elevate nail bed flaps laterally to expose underlying bone
4. Lesion Excision:
   • Remove exostosis using rongeur, curette, or osteotome
   • Resect fibrocartilaginous cap completely
   • Burr bone flush with normal cortex
5. Nail Bed Repair:
   • Meticulous repair of nail bed with 6-0 absorbable suture
   • Minimize tension, avoid strangulation
6. Nail Plate Replacement:
   • Replace nail plate as splint (or use foil/silicone conformer)
   • Suture nail plate proximally to prevent displacement

Advantages:

• Direct visualization of lesion
• Complete excision possible [5]

Disadvantages:

• Highest risk of nail dystrophy (permanent ridging, split nail) [5,16]
• Nail bed scarring common (10-30%) [5,16]
• Requires precise nail bed repair technique

2. Fish-Mouth (Distal/Tip) Approach

Indications:

• Distal lesions
• Desire to preserve nail bed integrity [5,16]

Technique: [5,16]

1. Incision:
   • Curvilinear (U-shaped) incision at distal tip of toe
   • Extends from one lateral edge to other, just distal to hyponychium
2. Flap Elevation:
   • Elevate soft tissue hood (including nail plate and nail bed) as single unit
   • Reflect proximally to expose distal phalanx dorsal surface
3. Lesion Excision:
   • Remove exostosis completely
   • Burr bone flush with cortex
4. Closure:
   • Return soft tissue hood to anatomic position
   • Close skin with interrupted or continuous suture

Advantages:

• BEST for nail preservation [5,16]
• Avoids nail bed incision
• Excellent cosmetic outcomes
• Lower nail dystrophy rate (5-10%) [5,16]

Disadvantages:

• Limited to distal lesions
• Requires careful flap elevation to avoid nail matrix injury

3. Lateral or Medial Approach

Indications:

• Eccentric lesions (laterally or medially located) [5]

Technique: [5]

1. Incision: Longitudinal incision along lateral or medial nail fold
2. Dissection: Elevate soft tissue laterally, expose lateral phalanx
3. Excision: Remove lesion, burr bone
4. Closure: Close skin primarily

Advantages:

• Avoids central nail bed
• Good for eccentric lesions

Disadvantages:

• Limited exposure for central lesions
• Risk of nail fold scarring

Excision Technique - Key Principles

Complete Removal is CRITICAL: [5,7,16]

• Remove ALL fibrocartilaginous cap tissue
• Rongeur bone down to healthy cancellous bone
• Create smooth, flush contour with normal cortex
• NO residual bony prominence should remain
• Send specimen for histopathology

Recurrence Prevention: [5,7,16]

• Incomplete excision is the PRIMARY cause of recurrence (5-10%)
• Visual and tactile confirmation of flush resection
• Use burr to smooth sharp edges
• Ensure no cartilaginous remnants at base

Post-Operative Care

Immediate (0-2 Weeks)

• Dressing: Soft bulky dressing, non-adherent layer over nail bed [16]
• Weight-Bearing: Protected weight-bearing in post-operative shoe
• Elevation: Elevate foot to reduce swelling
• Analgesia: Oral NSAIDs, paracetamol
• Antibiotics: Prophylactic oral antibiotics (cephalexin) if nail bed violated (controversial; not universally recommended)

Early (2-6 Weeks)

• Suture Removal: 10-14 days
• Wound Care: Keep clean and dry, simple dressing changes
• Footwear: Transition to wide, soft shoes
• Activity: Gradual increase in walking

Late (6 Weeks to 9 Months)

• Nail Regrowth: Monitor for nail plate regrowth (6-9 months to full growth) [5,16]
• Follow-Up: Clinical examination at 6 weeks, 3 months, 6 months
• Imaging: Repeat X-ray if pain recurs (assess for recurrence)

Surgical Outcomes and Evidence

Success Rates: [5,7,16]

• Symptom resolution: 90-95%
• Recurrence: 5-10% (primarily due to incomplete excision)
• Nail dystrophy: 10-30% (trans-ungual approach), 5-10% (fish-mouth approach)

Comparative Studies:

• Suga et al. (2005) [5]: Retrospective review of 16 cases. Fish-mouth and lateral approaches had significantly fewer nail deformities than trans-ungual approach. Recommended preserving nail bed when possible.
• Pascoal et al. (2020) [16]: Study of 12 pediatric cases with nail bed preservation techniques. No recurrences, minimal nail dystrophy. Advocated for approaches avoiding nail bed incision.
• Göktay et al. (2018) [18]: Series of 25 cases. Recurrence rate 8%, all due to incomplete excision. Emphasized importance of complete cap removal and flush bone resection.

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10. Complications

Intra-Operative Complications

• Nail Matrix Injury: Damage to germinal or sterile matrix during dissection → permanent nail dystrophy
• Incomplete Excision: Failure to remove entire lesion → recurrence
• Excessive Bone Resection: Over-resection → weakened phalanx, fracture risk (rare)
• Vascular Injury: Damage to digital arteries (rare with proper technique)
• Nerve Injury: Digital nerve injury → numbness, neuroma

Post-Operative Complications

Recurrence (5-10%) [5,7,16]

• Cause: Incomplete removal of fibrocartilaginous cap or bony base
• Presentation: Return of pain, visible or palpable lump, 6-24 months post-op
• Diagnosis: Lateral X-ray shows bony regrowth
• Management: Revision surgery with meticulous complete excision
• Prevention: Ensure flush resection, remove all cap tissue, confirm smooth contour intra-operatively

Nail Dystrophy (10-30%) [5,16]

• Types:
  • Longitudinal ridging (most common)
  • Nail plate splitting
  • Onycholysis (persistent separation)
  • Thickened, irregular nail
• Cause: Scar formation in nail matrix (germinal or sterile)
• Risk Factors: Trans-ungual approach, poor nail bed repair, infection
• Prevention: Preserve nail bed when possible, meticulous repair with fine suture, avoid tension
• Management: Typically permanent; cosmetic concern rather than functional limitation

Infection (2-5%) [16]

• Presentation: Wound erythema, purulent discharge, pain, fever
• Organisms: Staphylococcus aureus, Streptococcus species (most common)
• Management:
  • Superficial: Oral antibiotics (cephalexin, amoxicillin-clavulanate)
  • Deep/Osteomyelitis: IV antibiotics, possible surgical debridement
• Prevention: Sterile technique, prophylactic antibiotics if high risk

Delayed Wound Healing

• Risk Factors: Diabetes, peripheral vascular disease, smoking
• Management: Extended dressing care, offloading, optimize comorbidities

Chronic Pain

• Causes: Neuroma formation, inadequate bone resection, scar tissue
• Management: Analgesia, physiotherapy, rarely revision surgery

Cosmetic Concerns

• Scar: Hypertrophic scar, keloid (rare)
• Nail Appearance: Dystrophic nail may be cosmetically unacceptable to patients
• Management: Patient counseling pre-operatively, realistic expectations

Rare Complications

• Fracture: Distal phalanx fracture if excessive bone removed (extremely rare)
• Complex Regional Pain Syndrome (CRPS): Rare, reported in case reports
• Radiation for Recurrent Lesions: One case report of electron beam irradiation for refractory recurrent SE [17] (experimental, not standard practice)

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11. Prognosis and Long-Term Outcomes

Overall Prognosis

Excellent with appropriate surgical management. [5,7,16,18]

• Symptom Resolution: 90-95% of patients experience complete pain relief post-excision [5,16]
• Recurrence: 5-10% (primarily incomplete excision) [5,7,16,18]
• Functional Outcome: Return to normal activities including sports in 6-8 weeks [16]
• Quality of Life: Significant improvement in pain, footwear tolerance, and cosmesis

Factors Affecting Prognosis

Positive Prognostic Factors

• Complete surgical excision (flush resection, cap removal) [5,7,16]
• Fish-mouth or lateral approach (nail bed preservation) [5,16]
• Experienced surgeon
• Early diagnosis and treatment
• Absence of secondary infection

Negative Prognostic Factors

• Incomplete excision → recurrence [5,7,16,18]
• Trans-ungual approach → higher nail dystrophy [5,16]
• Chronic infection → wound healing complications
• Delayed diagnosis → advanced nail bed destruction

Long-Term Follow-Up

• Clinical Surveillance: 6 weeks, 3 months, 6 months, 12 months
• Recurrence Monitoring: Any return of symptoms warrants lateral X-ray
• Nail Growth Monitoring: Full nail regrowth expected by 6-9 months [5,16]
• Lifetime Risk: No malignant transformation reported; benign natural history [7,18]

Malignant Transformation

Extremely rare to non-existent. [7,18] Subungual exostosis is a benign reactive lesion with NO documented cases of malignant transformation in literature. However, critical to distinguish from:

• Subungual melanoma (pre-operative)
• Osteosarcoma (atypical imaging, rapid growth)

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12. Special Populations

Pediatric Patients [14,16,20]

• Presentation: Often younger (10-16 years), may be related to sports trauma
• Diagnosis: Same radiographic criteria as adults
• Surgical Approach: Fish-mouth approach preferred to minimize nail dystrophy [16,20]
• Outcomes: Excellent, recurrence rates similar to adults (5-10%) [16,20]
• Anesthesia: General anesthesia often preferred in young children

Pregnant Patients

• Timing: Elective surgery deferred until post-partum if possible
• Anesthesia: Local/regional anesthesia safe during pregnancy if urgent
• Imaging: Plain X-rays safe with abdominal shielding

Diabetic Patients

• Pre-Operative Optimization: Glycemic control critical (HbA1c less than 7-8%)
• Infection Risk: Higher risk of wound infection and osteomyelitis
• Prophylactic Antibiotics: Consider extended course
• Wound Healing: May require prolonged offloading and dressing care

Immunocompromised Patients

• Infection Risk: Prophylactic antibiotics recommended
• Wound Healing: Delayed, may require extended follow-up

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13. Mimics and Diagnostic Pitfalls

Common Misdiagnoses and How to Avoid Them

1. Verruca Vulgaris (Wart) [6,12]

• Why Confused: Both present as subungual/periungual lesions
• Key Distinguishing Features:
  • SE: Rock-hard, fixed, bony on X-ray
  • Wart: Soft to firm, may have black dots (dermoscopy), NO bone on X-ray
• Pitfall Prevention: X-ray every persistent subungual lesion

2. Ingrown Toenail

• Why Confused: Both cause toe pain, nail deformity
• Key Distinguishing Features:
  • SE: Dorsal/distal location, hard lump, nail elevation
  • Ingrown: Lateral nail fold, soft tissue swelling, nail spicule
• Pitfall Prevention: Palpate for hard lump, obtain X-ray

3. Fungal Nail Infection (Onychomycosis)

• Why Confused: Both cause nail plate separation, thickening
• Key Distinguishing Features:
  • SE: Localized hard lump, bony on X-ray
  • Fungal: Diffuse nail thickening, friable, KOH positive
• Pitfall Prevention: Palpate, X-ray, KOH prep

4. Subungual Melanoma [11]

• Why Critical: Potentially lethal malignancy
• Key Distinguishing Features:
  • SE: Bony lesion on X-ray, non-pigmented (typically)
  • Melanoma: Soft tissue, pigmented, Hutchinson's sign, NO bone on X-ray
• Pitfall Prevention: Biopsy ANY pigmented lesion. Do NOT assume exostosis without X-ray confirmation.

Red Flags Requiring Biopsy Before Excision

• Pigmented lesion
• Rapid growth over weeks
• Age > 50 years with new lesion
• Irregular borders, ulceration
• Soft tissue mass on MRI with normal bone
• History of melanoma or skin cancer

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14. Evidence Synthesis and Guidelines

Systematic Reviews and Meta-Analyses

No systematic reviews or meta-analyses exist specifically for subungual exostosis management (limited by rarity and case series literature). Evidence is primarily derived from retrospective case series and cohort studies. [5,7,16,18]

Landmark Studies

Suga et al. (2005) [5]

• Study: Retrospective review of 16 cases of subungual exostosis
• Findings:
  • Approaches preserving nail bed (fish-mouth, lateral) resulted in significantly fewer nail deformities than trans-ungual approach
  • Recurrence in 1/16 (6.3%), due to incomplete excision
• Conclusion: Recommended nail bed preservation techniques when feasible
• Impact: Shifted practice toward fish-mouth approach for distal lesions

Pascoal et al. (2020) [16]

• Study: Retrospective study of 12 pediatric cases with nail bed preservation
• Findings:
  • No recurrences at mean 24-month follow-up
  • Minimal nail dystrophy
  • Excellent functional and cosmetic outcomes
• Conclusion: Nail bed preservation is safe and effective in children
• Impact: Supported fish-mouth approach in pediatric population

Göktay et al. (2018) [18]

• Study: Descriptive study of 25 cases of subungual exostosis and osteochondroma
• Findings:
  • Recurrence rate 8% (2/25)
  • All recurrences due to incomplete excision of fibrocartilaginous cap
  • Histologic distinction: SE has fibrocartilage, osteochondroma has hyaline cartilage
• Conclusion: Complete excision critical for cure
• Impact: Reinforced importance of thorough surgical technique

Dąbrowski et al. (2023) [7]

• Study: Analysis of clinical factors affecting recurrence in surgically treated SE and osteochondroma
• Findings:
  • Incomplete excision = strongest predictor of recurrence
  • Surgical approach selection influences nail dystrophy rates
• Conclusion: Complete lesion removal and approach selection are key determinants of outcome
• Impact: Evidence-based guidance on surgical technique

Societal Guidelines

No formal society guidelines exist for subungual exostosis management (too rare for guideline development by AAOS, BOFAS, etc.). Management is based on:

• Expert opinion
• Case series evidence
• Surgical principles for benign bone tumors

Current Best Practice Consensus [5,7,16,18]

1. Diagnosis: Lateral X-ray is gold standard
2. Treatment: Surgical excision is curative
3. Approach Selection: Fish-mouth approach preferred for distal lesions (nail bed preservation)
4. Excision Technique: Complete removal of lesion and fibrocartilaginous cap, flush resection to normal cortex
5. Recurrence Prevention: Meticulous surgical technique, ensure no residual tissue
6. Follow-Up: Clinical and radiographic surveillance for recurrence

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15. Patient Education and Counseling

What is Subungual Exostosis?

"You have a small bone spur growing out of the tip of your toe bone. It's pushing your toenail up from underneath, which is causing your pain and the nail lifting you've noticed. This is a benign (non-cancerous) condition caused by repeated pressure or minor injuries to the toe over time." [2,5]

Why Did This Happen?

"We don't know the exact cause, but it's likely related to repetitive pressure on your toe from tight shoes, sports, or activities like dancing. It's NOT caused by infection or cancer, and it's NOT hereditary (your children won't get it)." [2,5,8]

Do I Need Surgery?

"Yes, surgery is the only way to permanently fix this. The bone spur won't go away on its own, and it will continue to grow and cause pain if we don't remove it. The good news is that the surgery is straightforward and very effective." [5,7,16]

What Does the Surgery Involve?

"We'll give you a local anesthetic (numbing injection) in your toe so you won't feel anything during the procedure. Then we'll make a small incision at the tip of your toe, lift up the soft tissue and nail, and shave off the bony spur so it's flush with the normal bone. We'll stitch everything back together, and you'll go home the same day." [5,16]

What Happens to My Toenail?

"Your toenail will grow back, but it takes time - usually 6 to 9 months for a full nail. Sometimes the new nail has a small ridge or bump, but most people have a normal-looking nail. We'll do our best to preserve your nail bed to minimize this risk." [5,16]

What is Recovery Like?

• Pain: Moderate pain for 2-3 days, managed with over-the-counter painkillers (ibuprofen, paracetamol)
• Walking: You can walk in a special shoe right away, but avoid tight shoes for 4-6 weeks
• Work: Desk job: 1-2 weeks off. Physical job: 4-6 weeks off
• Sports: 6-8 weeks [16]

What are the Risks?

• Recurrence: 5-10% chance the bone spur grows back (if we don't get it all out) [5,7,16]
• Nail Problems: 10-30% chance of a ridge or thickened nail [5,16]
• Infection: 2-5% chance, treated with antibiotics [16]
• Scar: Small scar at the tip of your toe

Will It Come Back?

"If we remove all of the bone spur completely, the chance of it coming back is very low (5-10%). If it does come back, it's usually because a tiny piece was left behind, and we can do the surgery again." [5,7,16]

When Should I Call the Doctor After Surgery?

• Severe pain not controlled by painkillers
• Redness, swelling, or pus from the wound
• Fever (temperature > 38°C)
• Numbness or tingling that doesn't go away

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16. Examination Focus (Viva Vault)

Core Questions for Postgraduate Examinations (FRCS, FRACS)

Q1: What is the key difference between Subungual Exostosis and Osteochondroma?

A: [7,18]

Q2: Why is the Lateral X-ray view critical for diagnosis?

A: [4,5] The lateral view is essential because:

• Dorsal Projection: The exostosis arises from the dorsal surface of the distal phalanx and projects upward. This is clearly visible on lateral view.
• AP View Limitation: On the AP (dorsoplantar) view, the exostosis is superimposed over the phalanx and may be completely obscured or appear as subtle increased density, leading to missed diagnosis.
• Diagnosis Made on Lateral: The characteristic "beak" or "thorn" of bone projecting dorsally is pathognomonic on lateral radiograph.

Q3: Does the nail plate always need to be removed during surgery?

A: [5,16] No, not always. The surgical approach depends on lesion location:

• Fish-Mouth Approach (preferred for distal lesions): The nail plate and nail bed are lifted together as a soft tissue hood, allowing bone removal without nail bed incision or nail plate removal.
• Trans-Ungual Approach (for central/large lesions): Nail plate is removed (or fenestrated) to access the lesion directly. Nail bed must be incised and repaired.
• Rationale: Preserving nail bed integrity (avoiding incision) minimizes risk of permanent nail dystrophy (ridging, splitting). Fish-mouth approach has superior cosmetic outcomes.

Q4: What is the cause of nail dystrophy after surgery?

A: [5,16] Scar formation in the nail matrix (germinal or sterile).

• Mechanism: The germinal matrix (proximal) produces the nail plate. The sterile matrix (distal) is the nail bed to which the plate adheres. Incision, trauma, or infection to these structures causes scarring.
• Result: Scar tissue disrupts normal nail plate production and adherence, leading to:
  • Longitudinal ridging (most common)
  • Nail splitting
  • Onycholysis (separation)
  • Thickened, irregular nail
• Prevention: Preserve nail bed when possible (fish-mouth approach), meticulous repair with fine absorbable suture (6-0 Vicryl), avoid excessive tension or strangulation.

Q5: What is the most common cause of recurrence?

A: [5,7,16,18] Incomplete excision of the lesion.

• Specifically, failure to remove:
  1. The entire fibrocartilaginous cap
  2. The bony base down to flush, smooth cortex
• Prevention:
  • Visual confirmation of complete cap removal
  • Rongeur/burr bone until flush with normal phalanx
  • Palpate resection bed to ensure smooth contour
  • No residual bony prominence should remain
• Recurrence Rate: 5-10% overall; virtually all due to incomplete excision [5,7,16,18]

Q6: What are the differential diagnoses for a painful subungual mass?

A: [6,11,12]

1. Benign Bony: Subungual exostosis, osteochondroma, enchondroma
2. Benign Soft Tissue: Glomus tumor, pyogenic granuloma, subungual fibroma, verruca vulgaris (wart)
3. Malignant: Subungual melanoma, squamous cell carcinoma, bone sarcoma (rare)
4. Infectious/Inflammatory: Onychomycosis, ingrown toenail with granulation tissue

Key Discriminator: Imaging

• Bony lesion on X-ray → Exostosis, osteochondroma, enchondroma
• Soft tissue on X-ray → Glomus, melanoma, wart
• Pigmented lesion → Biopsy to exclude melanoma

Q7: Describe the surgical technique for the Fish-Mouth approach.

A: [5,16]

1. Anesthesia: Digital block with local anesthetic (lidocaine 1-2% ± epinephrine)
2. Tourniquet: Apply digit tourniquet for hemostasis
3. Incision: Curvilinear (U-shaped or "fish-mouth") incision at the distal tip of the toe, just distal to the hyponychium, extending from one lateral edge to the other
4. Flap Elevation: Using sharp and blunt dissection, elevate the entire soft tissue hood (including nail plate, nail bed, and hyponychium) as a single unit, reflecting it proximally to expose the dorsal surface of the distal phalanx
5. Lesion Identification: Identify the exostosis arising from the dorsal phalanx
6. Excision:
   • Remove the exostosis using rongeur, curette, or osteotome
   • Ensure complete removal of fibrocartilaginous cap
   • Burr or rongeur bone down flush with normal cortex
   • Palpate to confirm smooth contour
7. Hemostasis: Achieve hemostasis, release tourniquet briefly to check
8. Closure:
   • Return soft tissue hood to anatomic position
   • Close skin with interrupted or continuous suture (4-0 or 5-0 absorbable or non-absorbable)
9. Dressing: Apply non-adherent dressing, bulky soft dressing
10. Specimen: Send excised tissue for histopathology

Advantages: Avoids nail bed incision, lowest nail dystrophy rate, excellent cosmetic outcome [5,16]

Q8: What is the histologic appearance of subungual exostosis?

A: [3,7,18]

• Gross: Firm bony lesion with overlying cartilaginous cap
• Microscopic:
  • Bone: Mature trabecular (cancellous) bone with normal marrow elements, continuous trabecular pattern
  • Cartilage Cap: 1-3mm thick fibrocartilaginous layer (mixed fibrous and cartilaginous tissue), NOT hyaline cartilage (key distinction from osteochondroma)
  • Surface: May show ulceration, granulation tissue, or reactive squamous epithelium if nail bed involved
  • Cellularity: Normal cellularity, no cytologic atypia
• No Medullary Continuity: Bone does not communicate with parent bone marrow (unlike osteochondroma)

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17. Clinical Pearls Summary

1. "X-ray Everything": Lateral X-ray is diagnostic gold standard; AP view misses the lesion. [4,5]
2. "Rock-Hard = Bone": Palpation distinguishing SE (osseous) from soft tissue lesions (wart, glomus, melanoma). [1,4,6]
3. "Save the Matrix": Fish-mouth approach preserves nail bed, minimizes dystrophy. [5,16]
4. "Complete Excision = Cure": Flush resection, remove cap completely, prevent recurrence. [5,7,16]
5. "Fibrocartilage vs Hyaline": SE has fibrocartilage cap; osteochondroma has hyaline - key histologic distinction. [7,18]
6. "Pigment = Biopsy": ANY pigmented subungual lesion requires biopsy to exclude melanoma. [11]
7. "No Medical Treatment": Surgery is the ONLY curative option. [5,7,16]
8. "Nail Regrows in 6-9 Months": Counsel patients pre-operatively. [5,16]
9. "Recurrence = Incomplete Excision": Technical failure, not biological recurrence. [5,7,16,18]
10. "Adolescent + Hallux + Trauma History": Classic presentation triad. [2,5,8]

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18. References

1. Landon GC, Johnson KA, Dahlin DC. Subungual exostoses. J Bone Joint Surg Am. 1979;61(2):256-259. PMID: 422608.

2. DaCambra MP, Gupta SK, Ferri-de-Barros F. Subungual exostosis of the toes: a systematic review. Clin Orthop Relat Res. 2014;472(4):1251-1259. doi:10.1007/s11999-013-3345-4. PMID: 24186470.

3. Woo TY, Rasmussen JE. Subungual osteocartilaginous exostosis. J Dermatol Surg Oncol. 1985;11(5):472-476. doi:10.1111/j.1524-4725.1985.tb01379.x. PMID: 3998266.

4. Cohen HJ, Frank SB. Subungual exostoses. Arch Dermatol. 1973;107(3):431-432. doi:10.1001/archderm.1973.01620160061020. PMID: 4692133.

5. Suga H, Mukouda M, Mii Y, Yamamoto Y. Subungual exostosis: a review of 16 cases focusing on postoperative deformity of the nail. Ann Plast Surg. 2005;55(3):272-275. doi:10.1097/01.sap.0000171681.29147.16. PMID: 16106166.

6. Gruzmark FS, Zimmerman LM, Cheng N. A Case of Subungual Exostosis Mimicking Verruca Vulgaris. Cureus. 2024;16(12):e75445. doi:10.7759/cureus.75445. PMID: 39881924.

7. Dąbrowski M, Rusek D, Woś H, Czajka-Jakubowska A. The Influence of Clinical Factors on Treatment Outcome and a Recurrence of Surgically Removed Protruded Subungual Osteochondroma and Subungual Exostosis. J Clin Med. 2023;12(19):6413. doi:10.3390/jcm12196413. PMID: 37835058.

8. Anderson DJ. Subungual exostosis. J Am Podiatr Med Assoc. 1990;80(3):130-133. doi:10.7547/87507315-80-3-130. PMID: 2332834.

9. Haneke E. Nail surgery. Clin Dermatol. 2013;31(5):516-525. doi:10.1016/j.clindermatol.2013.06.001. PMID: 24079580.

10. Chesler SM, Basler RS. Subungual exostosis. J Am Podiatry Assoc. 1978;68(10):651-654. doi:10.7547/87507315-68-10-651. PMID: 690386.

11. Baek HJ, Lee SJ, Cho KH, et al. Subungual tumors: clinicopathologic correlation with US and MR imaging findings. Radiographics. 2010;30(6):1621-1636. doi:10.1148/rg.306105514. PMID: 21071379.

12. Tritto M, Mirkin G, Reyzelman A. Subungual Exostosis on the Right Hallux. J Am Podiatr Med Assoc. 2022;112(4):20-306. doi:10.7547/20-306. PMID: 35294159.

13. Ardebol J, Mubarak A, Butt S, Cullen N. Subungual exostosis recurrence in a 16-year-old athletic male. Oxf Med Case Reports. 2020;2020(5):omaa025. doi:10.1093/omcr/omaa025. PMID: 32577292.

14. Yousefian F, Davis BM, Brodell RT. Pediatric Subungual Exostosis. Cutis. 2021;108(5):255-257. doi:10.12788/cutis.0381. PMID: 35100532.

15. Vaccaro M, Bartolomeo LD, Borgia F, Guarneri F, Cannavo SP. Dupuytren Subungual Exostosis. Indian Pediatr. 2021;58(2):188. PMID: 33632969.

16. Pascoal D, Balacó I, Cardoso R, Cabral R. Subungual exostosis - treatment results with preservation of the nail bed. J Pediatr Orthop B. 2020;29(4):392-396. doi:10.1097/BPB.0000000000000652. PMID: 32195759.

17. Sakamoto K, Ishii N, Nakajima H. Postoperative electron beam irradiation to prevent recurrence of refractory subungual exostosis: a case report. AME Case Rep. 2024;8:57. doi:10.21037/acr-24-69. PMID: 39091543.

18. Göktay F, Atış G, Aytekin S. Subungual exostosis and subungual osteochondromas: a description of 25 cases. Int J Dermatol. 2018;57(7):848-853. doi:10.1111/ijd.13985. PMID: 29704255.

19. Ghosh SK, Bhunia D, Bandyopadhyay D, Barua JK. Subungual exostosis. Indian Pediatr. 2013;50(8):800. doi:10.1007/s13312-013-0233-5. PMID: 24036655.

20. Womack ME, Fisher OJ, Nwawka OK, Abzug JM. Subungual Exostosis of the Hand: A Case Report in a 5-Year-Old Boy and Literature Review. J Am Acad Orthop Surg Glob Res Rev. 2022;6(3):e21.00299. doi:10.5435/JAAOSGlobal-D-21-00299. PMID: 35315793.

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19. Related Topics and Further Reading

Essential Related Topics

• Osteochondroma: True benign bone neoplasm with medullary continuity and hyaline cartilage cap
• Subungual Melanoma: Malignant tumor requiring early recognition and biopsy
• Glomus Tumor: Painful vascular lesion with classic triad (pain, cold sensitivity, tenderness)
• Multiple Hereditary Exostoses (MHE): Autosomal dominant condition with multiple osteochondromas
• Nail Anatomy and Physiology: Understanding matrix function for surgical planning

Advanced Reading

• Nail bed repair techniques in hand and foot surgery
• Benign bone tumors of the hand and foot
• Differential diagnosis of subungual lesions
• Pediatric bone tumors
• Surgical approaches to the distal phalanx

Examination Resources

• FRCS (Tr & Orth) viva questions on bone tumors
• FRACS oral examination cases in foot and ankle surgery
• Radiology interpretation: lateral foot and toe X-rays
• Histopathology: distinguishing benign bone tumors

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