Bunion Deformity | Osteotomy Selection | First MTP Joint Arthritis
- Hallux valgus angle (HVA): Normal under 15 degrees; mild 15-25, moderate 25-40, severe over 40 degrees
- Intermetatarsal angle (IMA): Normal under 9 degrees; key determinant of osteotomy type
- Chevron osteotomy: Distal, for mild-moderate deformity with IMA under 13 degrees
- Scarf osteotomy: Mid-shaft, for moderate-severe with IMA 13-20 degrees, most versatile
- Lapidus procedure: TMT arthrodesis for severe deformity, hypermobility, or IMA over 20 degrees
- “IMA over 13 degrees typically requires proximal or scarf osteotomy, not distal chevron
- “First TMT hypermobility is an indication for Lapidus fusion over osteotomy
- “Congruent vs incongruent MTP joint determines if distal soft tissue release needed
- “Hallux valgus interphalangeus (distal phalanx deviation) may require Akin osteotomy
IMA determines procedure. Under 13 degrees: chevron. 13-20 degrees: scarf. Over 20 degrees or hypermobility: Lapidus. Examiners expect precise thresholds.
Congruent joint = parallel articular surfaces on AP stress. Incongruent = subluxation requiring lateral release. Determines soft tissue procedure.
Undercorrection of IMA is the leading cause of recurrence. Must correct to under 9 degrees. Other factors: hypermobility, insufficient fixation, obesity.
Avoid overcorrection. First ray shortening over 3mm or excessive dorsiflexion causes transfer of load to lesser metatarsals. Balance is critical.
- HVA / IMA
- HVA 15-25° / IMA under 13°
- Procedure
- Chevron (distal metatarsal)
- Key Pearl
- Inherently stable, minimal shortening
- HVA / IMA
- HVA 25-40° / IMA 13-20°
- Procedure
- Scarf (mid-shaft) + lateral release
- Key Pearl
- Most versatile, corrects IMA and HVA
- HVA / IMA
- HVA over 40° / IMA over 20°
- Procedure
- Lapidus (TMT fusion)
- Key Pearl
- Addresses instability at source
- HVA / IMA
- Variable, often IMA still high
- Procedure
- Lapidus or MTP fusion
- Key Pearl
- Salvage when soft tissue depleted
Overview and Epidemiology
Definition and Pathoanatomy
Hallux valgus is a complex deformity characterized by:
- Lateral deviation of the hallux at the first metatarsophalangeal (MTP) joint
- Medial deviation of the first metatarsal (metatarsus primus varus)
- Medial prominence of the first metatarsal head (bunion)
- Progressive subluxation of the first MTP joint
The deformity involves bony malalignment, soft tissue contracture (lateral structures), and attenuation of medial capsule and ligaments.
Normal first ray function: The first metatarsal and hallux bear 50% of forefoot load during gait. Hypermobility of the first tarsometatarsal (TMT) joint allows progressive varus drift of the metatarsal, creating a vicious cycle of worsening deformity with each step.
Risk Factors
- Genetics: Familial in 60-70%, autosomal dominant with incomplete penetrance
- Gender: Female predominance (hormonal influence on ligament laxity)
- Foot shape: Pes planus, first ray hypermobility, long first metatarsal
- Neuromuscular: CP, CMT, stroke (muscle imbalance)
- Footwear: High heels, narrow toe box (exacerbate, not cause)
- Inflammatory arthritis: RA, psoriatic arthritis
- Hypermobility syndromes: Ehlers-Danlos, Marfan syndrome
- Obesity: Increased forefoot loading
Examiners will ask: Do high heels cause bunions? Answer: No. Footwear can exacerbate symptoms in predisposed individuals but does not cause the deformity. Genetic and biomechanical factors are primary. Societies with barefoot populations have similar prevalence.
Pathophysiology and Mechanisms
First Ray Anatomy
- First metatarsal: Thicker, shorter than lesser metatarsals
- Proximal phalanx: Articulates at MTP joint
- Sesamoids: Medial (tibial) and lateral (fibular) within FHB tendon
- TMT joint: Between first metatarsal and medial cuneiform
- Medial capsule: Attenuates with progressive deformity
- Adductor hallucis: Lateral pull on proximal phalanx
- Abductor hallucis: Medial stabilizer, becomes plantarflexor
- Plantar plate: Sesamoid sling, acts as windlass
Blood Supply to First Metatarsal Head
Vascular anatomy: First metatarsal head supplied by:
- Dorsal metatarsal artery: Enters dorsomedially
- Plantar metatarsal artery: Enters plantarly
- Nutrient artery: Mid-shaft
Risk of AVN: Extensive soft tissue stripping, especially combined dorsal and plantar dissection, can devascularize the metatarsal head. Limit dissection, preserve periosteum.
Biomechanical Pathology
The deformity progresses through a vicious cycle:
- Initial subluxation: First TMT hypermobility or pes planus causes metatarsus primus varus
- Soft tissue imbalance: Adductor hallucis pulls hallux laterally; medial capsule stretches
- Sesamoid subluxation: Sesamoids remain fixed to lesser metatarsals; first metatarsal drifts medially
- Progressive deformity: Each step increases valgus force; abductor hallucis becomes plantarflexor
BUNIONSCauses of Hallux Valgus
Hook:BUNIONS = Bunions Usually Need Investigation Of Natural Structure - genetic and biomechanical factors dominate!
Classification Systems
Radiographic Classification (Gold Standard)
Measured on weight-bearing AP foot radiograph:
- HVA
- Under 15°
- IMA
- Under 9°
- DMAA
- Under 10°
- Sesamoid Subluxation
- Grade 0-1
- HVA
- 15-25°
- IMA
- 9-13°
- DMAA
- 10-15°
- Sesamoid Subluxation
- Grade 1-2
- HVA
- 25-40°
- IMA
- 13-20°
- DMAA
- 15-25°
- Sesamoid Subluxation
- Grade 2-3
- HVA
- Over 40°
- IMA
- Over 20°
- DMAA
- Over 25°
- Sesamoid Subluxation
- Grade 3-4
Key Measurements:
- HVA (Hallux Valgus Angle): Angle between first metatarsal and proximal phalanx axes
- IMA (Intermetatarsal Angle): Angle between first and second metatarsal axes
- DMAA (Distal Metatarsal Articular Angle): Angle of first metatarsal articular surface to metatarsal axis
- Sesamoid Position: Grade 1 (normal) to 4 (complete lateral subluxation)
IMA over 13 degrees typically requires proximal or mid-shaft osteotomy (scarf) rather than distal (chevron). IMA is the primary determinant of procedure selection. Know the thresholds: under 13 = distal; 13-20 = scarf; over 20 = proximal or Lapidus.
The IMA determines the osteotomy type needed for correction.
Clinical Assessment
- Pain location: Medial bunion, MTP joint, IPJ, lesser toes (transfer)
- Functional limitation: Shoe wear, walking distance, sports
- Progression: Rate of worsening, previous treatments
- Footwear: Heel height, toe box width
- Occupation: Standing, walking demands
- Medical history: Inflammatory arthritis, neuromuscular disease
- Look: Bunion prominence, callus, lesser toe deformity
- Feel: Medial tenderness, first TMT mobility, MTP crepitus
- Move: MTP ROM (normal 70-80° dorsiflexion), IPJ alignment
- Special tests: First ray mobility test, Coleman block test (if pes planus)
- Gait: Pronation, hallux push-off
- Neurovascular: Sensation, pulses (important for diabetics)
First Ray Mobility Assessment
First Ray Mobility Test
Grasp metatarsal heads 2-5 with one hand, dorsal and plantar.
With other hand, dorsiflex and plantarflex the first metatarsal head. Compare to contralateral foot.
Normal: 5-8mm of motion. Hypermobile: Over 10mm (consider Lapidus). Stiff: Under 5mm (arthritis or compensation).
Clinical pearl: If first TMT hypermobility is present, osteotomy alone will fail. The instability at the TMT joint will cause recurrence. Lapidus procedure (TMT fusion) is the appropriate choice to address the pathology at its source.
Sesamoid Assessment
- Palpation: Tenderness suggests sesamoiditis or arthritis
- Position: Grade subluxation (radiographic correlation)
- Movement: Sesamoids should reduce with manual hallux varus stress (if fixed, indicates severe soft tissue contracture)
Differential Diagnosis
Not every painful medial forefoot is a simple bunion. Distinguish hallux valgus from conditions that change management:
- Key Distinguishing Features
- Lateral hallux deviation, medial eminence, increased HVA/IMA on weight-bearing AP
- Discriminator
- Deformity is correctable/reducible early; HVA over 15 degrees
- Key Distinguishing Features
- Dorsal osteophyte, painful/limited MTP dorsiflexion, no significant valgus
- Discriminator
- Loss of dorsiflexion and dorsal pain; HVA near normal
- Key Distinguishing Features
- Global joint-line pain, crepitus, joint-space narrowing on radiograph
- Discriminator
- Pain through arc of motion, not just at the eminence
- Key Distinguishing Features
- Acute red, hot, exquisitely tender first MTP; raised urate; rheumatoid pattern in RA
- Discriminator
- Acute inflammatory onset, systemic features, joint aspirate crystals
- Key Distinguishing Features
- Plantar first MTP pain, tender sesamoids, pain on hallux dorsiflexion
- Discriminator
- Plantar (not medial) tenderness; sesamoid views/MRI
- Key Distinguishing Features
- Deviation at the IP joint with relatively normal MTP alignment
- Discriminator
- Increased IP angle; correction needs Akin osteotomy
MAIDSAssessment of Hallux Valgus Deformity
Hook:MAIDS = Metatarsal Alignment Is Decision-maker for Surgery - measure all angles before choosing procedure!
Investigations
Imaging Protocol
Views: AP, lateral, oblique. Must be weight-bearing for accurate measurement.
Measure:
- HVA (hallux valgus angle)
- IMA (intermetatarsal angle)
- DMAA (distal metatarsal articular angle)
- Sesamoid position (grade 1-4)
- Joint congruity
- MTP and TMT arthritis
Assess: First metatarsal length relative to second (normal is equal or 1-2mm longer). Metatarsus elevatus (indicates transfer metatarsalgia risk). Pes planus, midfoot arthritis.
Indications: Suspected AVN, sesamoid pathology (bipartite vs fracture), plantar plate tear, MTP arthritis assessment. Not routine for hallux valgus.
Indications: Complex revision cases, TMT arthritis assessment pre-Lapidus, postoperative nonunion evaluation.
Radiographic Pitfalls
Common mistake: Measuring angles on non-weight-bearing radiographs underestimates deformity severity. IMA and HVA both decrease by 20-30% when non-weight-bearing. Always obtain weight-bearing films for surgical planning.
Non-Operative Management
Conservative Treatment Algorithm
- Wide toe box to accommodate bunion
- Low heel (under 2cm) to reduce forefoot pressure
- Soft uppers to minimize friction
- Avoid pointed toes and constrictive shoes
- Bunion pads over medial eminence
- Toe spacers to separate hallux from second toe
- Metatarsal pads if transfer metatarsalgia
- Custom orthotics for pes planus, pronation control
Important counseling point: Orthoses, toe spacers, and bunion pads can relieve symptoms but do not correct or prevent progression of the deformity. Set realistic expectations. Surgery is the only corrective treatment.
These measures provide symptomatic relief and may delay surgery.
Indications for Surgery
Surgery is indicated when:
- Pain refractory to conservative measures (minimum 3-6 months)
- Functional limitation affecting daily activities or employment
- Progressive deformity with difficulty wearing any shoes
- Secondary pathology: Transfer metatarsalgia, lesser toe deformity, intractable plantar keratosis
Not indicated for:
- Cosmetic concerns alone (high complication risk, patient dissatisfaction)
- Asymptomatic deformity (even if severe radiographically)
- Unrealistic expectations for shoe wear
Management Algorithm
Chevron Osteotomy Algorithm
Patient Profile: HVA 15-25 degrees, IMA under 13 degrees, congruent joint
Treatment Pathway
Wide toe box shoes, bunion pads, NSAIDs for 3-6 months. If symptoms persist despite optimal conservative care, offer surgery.
Weight-bearing radiographs confirm IMA under 13 degrees. Assess joint congruity (if congruent, lateral release may not be needed). Plan chevron osteotomy with 3-5mm lateral translation.
Chevron osteotomy (distal metatarsal V-shaped cut), translate laterally to correct IMA. Fixation with screw. Add lateral release if incongruent. Medial eminence resection.
Heel weight-bearing in postoperative shoe for 6 weeks. Progress to regular shoes at 6 weeks. Return to full activity at 3 months.
Advantages: Fast recovery, inherently stable, minimal shortening
Expected Outcome: 85-90% satisfaction, recurrence 5-10%
This algorithm is ideal for mild to moderate deformity with good bone quality.
Hallux valgus in the skeletally immature is a distinct problem and a classic exam trap. It is more often familial, frequently bilateral and congruent, and characteristically has a high DMAA (the deformity lies in the orientation of the distal metatarsal articular surface rather than at a subluxed joint). The cardinal rule is to delay surgery until skeletal maturity wherever possible: operating across an open physis risks growth disturbance, and — more importantly — recurrence rates are far higher in juveniles than in adults. Conservative measures and reassurance are first-line, with surgery reserved for genuinely painful, functionally limiting deformity. When surgery is required, the plan must correct the DMAA (a distal medial closing-wedge / biplanar osteotomy such as a Reverdin-type cut or a biplanar chevron) rather than simply reducing the IMA — correcting the IMA on a congruent joint with a high DMAA creates an incongruent joint and drives recurrence. Address true first-ray hypermobility on its merits, but be cautious about TMT fusion before the physis has closed.
Surgical Technique
Chevron (Distal Metatarsal) Osteotomy
Indications: Mild to moderate deformity with IMA under 13 degrees, congruent joint.
Advantages: Inherently stable (V-shape), minimal shortening, fast recovery.
Surgical Steps
Position: Supine, thigh tourniquet. Draping: Lower leg free, ankle block or GA.
Incision: 4-5cm longitudinal incision over medial MTP joint, centered on metatarsal head. Dissection: Deepen to capsule, identify and protect medial dorsal cutaneous nerve (runs just dorsal to incision).
Capsule: Longitudinal capsulotomy preserving dorsal and plantar flaps. Expose: Metatarsal head and medial eminence. Measure: Depth of osteotomy (aim for 60-70° V-shape).
Resect: Medial prominence with sagittal saw, flush with medial metatarsal shaft (avoid over-resection). Smooth: Edges with rongeur.
Apex: Place apex at center of metatarsal head (plantar view). Arms: 60-70° V-shape, equal dorsal and plantar arms. Cut: Complete osteotomy with sagittal saw, irrigate to prevent thermal necrosis.
Translate: Distal fragment laterally 3-5mm (aim for IMA under 9 degrees). Avoid: Excessive translation (risk of metatarsal head fracture). Check: Sesamoid reduction under fluoroscopy.
K-wire: Temporary fixation with 1.6mm K-wire from medial eminence into metatarsal shaft. Screw: 2.0-2.7mm cannulated or solid screw, perpendicular to osteotomy. Check: Stability, no rotation.
If incongruent: Separate 1cm incision in first web space. Tenotomy: Adductor hallucis tendon (identified by pulling hallux medially). Release: Lateral capsule with beaver blade. Confirm: Hallux reduces to neutral.
Capsule: Close medial capsule with 2-0 absorbable suture (slight plication to tighten). Skin: 3-0 nylon interrupted or subcuticular. Dressing: Soft bandage, toe in neutral alignment.
Why chevron is stable: The V-shape creates inherent interlocking stability. Translation should be limited to 50% of metatarsal width (3-5mm) to prevent fracture. Over-translation risks AVN and metatarsal head fracture.
This technique is ideal for mild to moderate deformity with good bone quality.
Percutaneous/minimally invasive surgery (MIS) has become a mainstream alternative to open osteotomy, and examiners increasingly ask about it. The dominant modern technique is the MICA (Minimally Invasive Chevron-Akin): through tiny stab incisions a high-torque low-speed burr makes an extra-articular distal metatarsal osteotomy, the capital fragment is translated laterally and held with percutaneous screws, and a percutaneous Akin addresses the phalangeal component. MIS has evolved through generations — early (first/second-generation) techniques were unfixed or held with a buried K-wire and had higher recurrence, whereas current third/fourth-generation, screw-fixed techniques are stable and reproducible. Advantages are small scars, less soft-tissue stripping, less stiffness and good early pain scores, with RCT and meta-analysis data showing radiographic correction and patient outcomes broadly comparable to open chevron/scarf. Caveats: a genuine learning curve, thermal necrosis if the burr is not irrigated/cooled, hardware-related symptoms, and the same recurrence drivers (under-correction of the IMA, unaddressed hypermobility). MIS does not abolish the algorithm — gross first-ray hypermobility or a very high IMA still points toward a Lapidus.
Complications
- Incidence
- 5-15% at 5 years
- Risk Factors
- Undercorrection of IMA, hypermobility, obesity
- Management
- Revision with proximal osteotomy or Lapidus
- Incidence
- 5-30%
- Risk Factors
- First ray shortening over 3mm, excessive dorsiflexion
- Management
- Offloading orthoses, lesser metatarsal osteotomy if severe
- Incidence
- 2-10%
- Risk Factors
- Excessive lateral release, over-translation of osteotomy
- Management
- Observation if mild, tendon transfer or fusion if severe
- Incidence
- 1-3% (chevron)
- Risk Factors
- Excessive soft tissue stripping, thermal necrosis
- Management
- Observation (may revascularize), arthroplasty or fusion if collapse
- Incidence
- 5-10% (Lapidus)
- Risk Factors
- Smoking, poor fixation, non-compliance
- Management
- Bone graft, revision fixation if symptomatic
- Incidence
- 10-20% (numbness)
- Risk Factors
- Iatrogenic during incision or retraction
- Management
- Usually resolves (neuropraxia), neuroma excision if persistent
- Incidence
- 5-15%
- Risk Factors
- Aggressive rehabilitation, MTP arthritis
- Management
- Physiotherapy, intra-articular injection, fusion if disabling
Key principles to avoid recurrence:
- Correct IMA to under 9 degrees (most important factor)
- Assess and address TMT hypermobility (Lapidus if hypermobile)
- Lateral soft tissue release if incongruent joint
- Avoid under-correction (better to slightly overcorrect than undercorrect)
- Patient compliance with postoperative immobilization and weight-bearing restrictions
TRANSFERComplications of Hallux Valgus Surgery
Hook:TRANSFER = Transferring load away from first ray is the hallmark complication - avoid shortening!
Postoperative Care and Rehabilitation
Rehabilitation Timeline
Dressing: Soft bandage, change at 2 weeks. Weight-bearing: Heel weight-bearing in postoperative shoe (stiff-soled). Elevation: Keep foot elevated above heart to reduce swelling. Ice: 20 minutes every 2 hours. DVT prophylaxis: Aspirin 100mg daily or LMWH if high risk.
Wound: Sutures removed at 2 weeks. Weight-bearing: Progress to full weight-bearing in postoperative shoe. ROM: Gentle passive MTP dorsiflexion exercises (avoid forceful). Radiographs: At 6 weeks to assess healing. Footwear: Transition to wide, soft shoes at 6 weeks.
Activity: Gradual increase in walking distance. Physiotherapy: Active ROM, strengthening (intrinsic muscles). Footwear: Regular shoes with wide toe box. Return to work: Sedentary at 6 weeks, standing/walking at 8-12 weeks.
Sports: Return to impact sports at 3-4 months (running, jumping). Swelling: May persist for 6-12 months (normal). Outcome: Most patients (80-90%) satisfied at 6 months.
This protocol applies to distal and mid-shaft osteotomies.
Outcomes and Prognosis
Predictors of Poor Outcome
Poor outcomes associated with:
- Unrealistic expectations (cosmetic surgery mentality)
- Undercorrection of IMA (leads to recurrence)
- Overcorrection (hallux varus, transfer metatarsalgia)
- Pre-existing lesser toe deformity (not addressed at surgery)
- Poor bone quality (osteoporosis, metabolic bone disease)
- Smoking (nonunion, wound complications)
Procedure-Specific Outcomes
- Satisfaction
- 85-90%
- Recurrence
- 5-10% at 5 years
- Key Outcome Measure
- AOFAS score improvement 30-40 points
- Satisfaction
- 85-95%
- Recurrence
- 5-15% at 5 years
- Key Outcome Measure
- Greater IMA correction than chevron
- Satisfaction
- 80-90%
- Recurrence
- Under 5% (lowest recurrence)
- Key Outcome Measure
- Fusion rate 90-95%, longer recovery
- Satisfaction
- 85-90%
- Recurrence
- No recurrence
- Key Outcome Measure
- Loss of MTP motion but pain-free
Guidelines, Registries & Global Practice
Global Epidemiology
- Pooled Prevalence
- 19% (95% CI 13-25%)
- Source
- Cai 2023, PMID 37726760
- Pooled Prevalence
- 23%
- Source
- Nix 2010, PMID 20868524
- Pooled Prevalence
- 35.7%
- Source
- Nix 2010, PMID 20868524
- Pooled Prevalence
- 30% vs 13% (Nix); 23.7% vs 11.4% (Cai)
- Source
- Nix 2010 / Cai 2023
- Pooled Prevalence
- 29.3%
- Source
- Cai 2023, PMID 37726760
Hallux valgus is among the most common forefoot deformities worldwide, with a consistent female predominance and a strong rise in prevalence with age. Regional differences (highest in Oceania and Asia, lowest reported in Africa) reflect both true variation and heterogeneity in diagnostic criteria.
Guidelines & Consensus, Side by Side
There is no single high-level international clinical guideline that mandates a specific osteotomy; major bodies converge on principles rather than a named procedure, reflecting the Cochrane finding that no technique is uniformly superior.
- Core Position
- Surgery (osteotomy) superior to orthoses/no treatment; no osteotomy superior to another
- Evidence Level
- Level 1 (systematic review)
- Core Position
- Match procedure to deformity (HVA/IMA), joint congruity and first-ray stability; surgery for symptoms not cosmesis
- Evidence Level
- Expert consensus
- Core Position
- Exhaust conservative care first; surgery for pain/function, not appearance; offer minimally invasive options where expertise exists
- Evidence Level
- Consensus / Level 1-2 RCTs
- Core Position
- Algorithm by IMA: distal osteotomy for low IMA, scarf/proximal for higher, Lapidus for hypermobility/severe
- Evidence Level
- Consensus / Level 1-2
Registry & Procedure-Volume Evidence
Unlike hip and knee arthroplasty, hallux valgus correction is osteotomy- or fusion-based and is not tracked by the national joint registries (NJR, AJRR, AOANJRR, SHAR). Evidence therefore comes from RCTs, meta-analyses and national administrative/HES-type datasets rather than implant survival data. Quoted recurrence and revision rates derive from cohort and trial follow-up, not registry implant-survival curves.
Global Practice Variation
- Scarf and distal chevron remain the workhorse osteotomies across most high-income systems
- Minimally invasive (percutaneous) chevron/Akin has expanded rapidly in Europe and Australasia with RCT-level support
- Lapidus favoured where first-TMT hypermobility or severe IMA predominates
- First MTP fusion reserved for arthritis, salvage and neuromuscular cases
- High-resource: weight-bearing radiographs, intra-operative fluoroscopy, locking-plate fixation standard
- Limited-resource: greater reliance on clinical grading and simpler fixation (K-wire, single screw)
- Access: long elective waiting lists in many publicly funded systems, as hallux valgus is classed as low-priority/elective
- Day-case surgery with regional/ankle block is the global norm for primary osteotomy
Peri-operative Standards (Globally Accepted)
- Antibiotic prophylaxis: single pre-operative dose of a first-generation cephalosporin (e.g. cefazolin) at induction for clean forefoot surgery
- VTE prophylaxis: routine pharmacological prophylaxis not indicated for isolated forefoot osteotomy in low-risk patients; risk-stratify and consider it for prolonged immobilisation/non-weight-bearing regimens (e.g. Lapidus)
- Surgical-site infection target under 2% for clean elective foot surgery
Document, in any jurisdiction:
- Conservative treatment trial (typically 3-6 months) before surgery
- Realistic expectations - correction of pain/function, not a cosmetic guarantee; shoe-wear may still be restricted
- Specific complications disclosed: recurrence (5-15%), transfer metatarsalgia, medial dorsal cutaneous nerve injury, stiffness, AVN, and nonunion (Lapidus 5-10%)
- Smoking status - increases nonunion and wound complications
Common litigation themes: undisclosed recurrence/transfer metatarsalgia, unrealistic cosmetic expectation, and procedure-deformity mismatch (e.g. distal chevron for a high IMA).
MCQ Practice Points
Q: What is the primary blood supply to the first metatarsal head? A: The dorsal metatarsal artery (branch of dorsalis pedis) and plantar metatarsal artery. Risk of AVN with extensive soft tissue stripping, especially combined dorsal and plantar dissection.
Q: What is the normal intermetatarsal angle (IMA) and what threshold typically requires proximal osteotomy? A: Normal IMA is under 9 degrees. IMA over 13 degrees typically requires proximal or scarf osteotomy rather than distal chevron. IMA over 20 degrees often requires Lapidus procedure.
Q: What is the primary indication for Lapidus procedure over standard osteotomy? A: First TMT hypermobility (over 10mm of dorsoplantar motion). Lapidus arthrodesis addresses the instability at source and prevents recurrence. Also indicated for severe deformity (IMA over 20 degrees) or TMT arthritis.
Q: What is the most common cause of hallux valgus recurrence after osteotomy? A: Undercorrection of the intermetatarsal angle (IMA). Must correct IMA to under 9 degrees. Other causes: first TMT hypermobility not addressed, inadequate lateral release, poor fixation, patient non-compliance.
Q: What is the nonunion rate for Lapidus procedure and how can it be reduced? A: Nonunion rate is 5-10% with modern fixation. Risk reduced by: smoking cessation, plantar plate fixation (lower nonunion than crossed screws alone), adequate compression at fusion site, bone grafting if poor quality bone.
Q: What is troughing in scarf osteotomy and how is it prevented? A: Troughing is fracture of the plantar cortex during the horizontal saw cut, causing instability. Prevention: Use oscillating saw carefully, ensure plantar cortex remains intact, check before completing cuts. If occurs, add plantar screw or convert to different procedure.
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 45-year-old woman presents with painful bunion for 5 years, worsening over the past year. She has tried wide shoes and orthotics without relief. On examination, there is a prominent medial bunion, hallux deviates laterally, and the second toe overlaps slightly. Weight-bearing AP radiograph shows HVA 30 degrees, IMA 16 degrees, DMAA 12 degrees. The MTP joint is incongruent with subluxation. What is your assessment and management?”
“Walk me through the scarf osteotomy technique. A 50-year-old patient with moderate hallux valgus (HVA 28 degrees, IMA 15 degrees, incongruent joint). Describe your surgical approach, key steps, fixation, and how you avoid complications.”
“A 52-year-old woman had scarf osteotomy 3 months ago. She now complains of worsening pain under the second and third metatarsal heads that she did not have preoperatively. She can barely walk. On examination, there are tender calluses under the second and third metatarsal heads. Radiographs show well-healed scarf osteotomy, but the first metatarsal appears shorter than the second by 5mm. How do you manage this?”
Key Measurements
- Normal HVA under 15°, IMA under 9°, DMAA under 10°
- Mild: HVA 15-25°, Moderate: 25-40°, Severe: over 40°
- IMA under 13° = chevron; 13-20° = scarf; over 20° = Lapidus
- Sesamoid grade 1-4 (4 = complete lateral subluxation)
Osteotomy Selection
- Chevron: IMA under 13°, congruent joint, inherently stable
- Scarf: IMA 13-20°, most versatile, corrects HVA and IMA
- Lapidus: IMA over 20°, TMT hypermobility, recurrence, arthritis
- MTP fusion: Severe MTP arthritis, salvage, neuromuscular
Surgical Pearls
- Protect medial dorsal cutaneous nerve (dorsal to incision)
- Lateral release for incongruent joint (adductor tenotomy, capsule)
- Scarf: avoid troughing (plantar cortex fracture), use two screws
- Lapidus: 6 weeks non-weight-bearing, fusion rate 90-95%
- First ray length critical: avoid shortening over 3mm (transfer metatarsalgia)
Complications
- Recurrence 5-15%: undercorrection of IMA, hypermobility
- Transfer metatarsalgia 10-30%: first ray shortening, elevation
- AVN 1-3% (chevron): excessive soft tissue stripping
- Nonunion 5-10% (Lapidus): smoking, poor fixation
- Nerve injury 10-20%: medial dorsal cutaneous (numbness)
Postoperative Care
- Chevron/Scarf: heel weight-bearing postop shoe, 6 weeks
- Lapidus: non-weight-bearing 6 weeks, boot for 12 weeks
- Return to regular shoes at 6-12 weeks
- Sports at 3-4 months (osteotomy), 4-6 months (Lapidus)
Evidence Base and Key Trials
Prevalence of Hallux Valgus in the General Population (Nix Meta-analysis)
- Systematic review and meta-analysis of 76 surveys (496,957 participants)
- Pooled prevalence 23% in adults aged 18-65 and 35.7% in those over 65
- Prevalence higher in females (30%) than males (13%)
- Prevalence increases progressively with age
Global Prevalence and Incidence of Hallux Valgus (Cai Meta-analysis)
- Meta-analysis of 45 studies (over 186 million individuals)
- Overall global pooled prevalence 19% (95% CI 13-25%)
- Regional variation: Asia 22.0%, Europe 18.4%, Oceania 29.3%, North America 16.1%, Africa 3%
- Female prevalence 23.7% versus male 11.4%; highest in those over 60 (22.7%)
Cochrane Review: Interventions for Treating Hallux Valgus and Bunions
- Review of 21 randomised or quasi-randomised trials of conservative and surgical treatment
- Chevron osteotomy improved all outcomes versus orthoses or no treatment
- No single osteotomy shown superior to any other osteotomy
- Orthoses and night splints no better than no treatment for the deformity
- Dissatisfaction remained high (25-33%) even when angles and pain improved
Distal Chevron versus Other Procedures for Hallux Valgus: Meta-analysis
- Meta-analysis of 10 RCTs (985 patients)
- Distal chevron gave greater HVA correction than scarf
- Scarf corrected IMA a mean 2.18 degrees more than distal chevron
- Proximal chevron corrected IMA a mean 1.08 degrees more than distal chevron
Lapidus Arthrodesis: Fixation and Nonunion Meta-analysis
- Systematic review and meta-analysis of 16 studies (1,176 participants)
- Nonunion: 0.7% plantar plating, 1.4% dorsomedial plating, 5.3% screw-only
- Overall complication rate lowest with plantar plating (13%)
- Longer time to full weightbearing correlated with nonunion (r=0.376, p=0.009)
- No difference in HVA/IMA correction or AOFAS between fixation constructs
Chevron Osteotomy in Hallux Valgus: Ten-Year Results
- Prospective cohort of 112 feet (73 patients), mean follow-up 12.7 years
- Mean AOFAS improved from 46.5 to 88.8 points
- IMA improved from 13.8 to 8.7 degrees; HVA/MTP angle from 27.6 to 14.0 degrees
- Only one foot required revision for recurrence; radiographic correction maintained
- First MTP joint arthritis progressed significantly without affecting clinical result