Scarf and Akin Osteotomy for Hallux Valgus

Indications

Absolute Indications

• Moderate to severe hallux valgus with HVA 20-40°, IMA 13-20°
• Symptomatic bunion with pain limiting function after failed conservative management (minimum 6 months orthotics, footwear modification, analgesia)
• Congruent MTPJ on weight-bearing radiographs (critical - subluxed joint requires different approach)

Relative Indications

• Younger patients (age <60 years) with higher functional demands
• Patients requiring cosmetic improvement with functional symptoms
• Combined first-second intermetatarsal angle widening with stable TMT joint
• Transfer metatarsalgia requiring metatarsal length preservation (versus Chevron which shortens)
• Revision surgery after failed distal osteotomy (Chevron, Mitchell)

Contraindications

• Severe deformity with IMA >20° or HVA >40° (consider Lapidus)
• TMT joint hypermobility >9mm translation (Lapidus preferred)
• Incongruent MTPJ (subluxed joint) - requires realignment, not osteotomy alone
• Active infection or soft tissue compromise
• Peripheral vascular disease (assess pulses, consider vascular studies)
• Severe osteoporosis or bone quality concerns (risk of fixation failure)
• Inflammatory arthropathy with severe MTPJ arthritis (arthrodesis preferred)

Exam Key Points

• Conservative management prerequisites: 6 months trial of wide toe box footwear, orthotics with bunion pad, activity modification, NSAIDs
• Radiographic assessment: weight-bearing AP and lateral foot radiographs mandatory - assess HVA, IMA, DMAA, MTPJ congruency, sesamoid position, first metatarsal length
• TMT stability testing: clinical examination with TMT joint translation - passive dorsoplantar motion >9mm suggests hypermobility
• Patient selection: motivated patients with realistic expectations, understand recovery time 12-16 weeks to normal footwear

Surgical Anatomy

First Metatarsal

• Shaft morphology: Oval cross-section with thicker plantar cortex (weight-bearing surface) and thinner dorsal cortex
• Metaphyseal flare: Head-shaft junction is transition zone - distal scarf limb exits here to avoid intra-articular violation
• Blood supply: Dominant nutrient artery enters mid-diaphysis medially, metaphyseal branches enter plantarly at neck - subperiosteal dissection critical to preserve
• Sesamoid articulation: Plantar surface has medial and lateral facets - lateral sesamoid position correlates with deformity severity

First MTPJ Joint

• Capsule structure: Thickened medially (becomes attenuated with chronic valgus), tight laterally (requires release), plantar plate with sesamoids
• Ligaments: Collateral ligaments (medial stretched, lateral contracted), transverse metatarsal ligament (connects to second metatarsal, may require release)
• Congruency assessment: Joint surfaces parallel on weight-bearing radiographs indicates congruent joint - prerequisite for osteotomy success

Neurovascular Structures

• Dorsomedial cutaneous nerve: Superficial branch of superficial peroneal nerve, crosses dorsomedial aspect of foot at MTPJ level, 15-20% injury rate if not protected
• Medial plantar proper digital nerve: Branch of medial plantar nerve, runs plantar to metatarsal head deep to capsule, supplies medial hallux sensation
• First dorsal metatarsal artery: Branch from dorsalis pedis, courses in first intermetatarsal space dorsally, at risk with deep dorsal dissection
• Lateral sesamoid blood supply: Lateral plantar artery branches, disrupted by aggressive lateral release, AVN risk if over-released

Soft Tissue Deforming Forces

• Adductor hallucis: Attaches to lateral sesamoid and proximal phalanx base, primary deforming force pulling hallux laterally
• Abductor hallucis: Displaced plantarly with chronic deformity, loses mechanical advantage as deforming force
• Extensor hallucis longus: Bowstrings laterally over prominent medial eminence, contributes to valgus and pronation
• Flexor hallucis brevis: Two heads with sesamoids, lateral head pulls hallux into valgus, medial head weakened

Operative Technique

Step 1: Patient positioning and marking

Patient positioning and marking: Supine with bump under ipsilateral hip, thigh tourniquet applied but not inflated. Mark medial eminence, metatarsal shaft, osteotomy site (mid-diaphysis), check contralateral for symmetry goals. EXAM KEY: Proper positioning allows ankle rotation for fluoroscopy without leg holder interference.

Step 2: Inflate tourniquet and prep

Inflate tourniquet and prep: Inflate thigh tourniquet to 100mmHg above systolic (typically 250-300mmHg). Prep entire foot and ankle. Drape foot free. EXAM KEY: Tourniquet allows bloodless field for accurate osteotomy cuts and hardware placement.

Step 3: Medial incision and superficial dissection

Medial incision and superficial dissection: 3-4cm medial longitudinal incision centred over mid-shaft 1st metatarsal, extending from proximal third to metatarsal head. Identify and protect dorsomedial cutaneous nerve (2-3mm dorsal to incision). Deepen through subcutaneous tissue. EXAM KEY: Nerve injury causes dorsal numbness - most common complaint.

Step 4: Capsular incision and periosteal elevation

Capsular incision and periosteal elevation: Longitudinal capsular incision along medial metatarsal shaft. Elevate capsule and periosteum as continuous layer. Expose medial eminence and metatarsal shaft from head to base. Insert Hohmann retractors dorsally and plantarly. EXAM KEY: Subperiosteal dissection protects vascular supply to metatarsal head.

Step 5: Lateral release assessment and execution

Lateral release assessment and execution: Assess MTPJ congruency and lateral deviation. If passive correction inadequate, perform lateral release through same medial incision (inside-out technique) or small lateral stab incision. Release: (1) lateral capsule, (2) adductor hallucis from lateral sesamoid, (3) transverse metatarsal ligament if tight. EXAM KEY: Adequate lateral release essential to prevent undercorrection.

Step 6: Scarf osteotomy planning and marking

Scarf osteotomy planning and marking: Mark osteotomy on bone with sterile marker or electrocautery: (1) Horizontal cut through mid-diaphysis (parallel to ground), (2) Proximal limb 60° angle directed dorsal-proximal (exits 10-12mm distal to TMT joint), (3) Distal limb 60° angle directed plantar-distal (exits at junction of metatarsal head and shaft). EXAM KEY: Z-shaped cut provides large surface area (30-35mm) and intrinsic stability.

Step 7: Execute scarf osteotomy cuts

Execute scarf osteotomy cuts: Use sagittal saw with fine blade (0.4-0.6mm). First cut: horizontal longitudinal cut in sagittal plane, mid-diaphysis, dorsal cortex to plantar cortex (do NOT penetrate plantar cortex completely - leave 2-3mm hinge). Second cut: proximal limb 60° angle. Third cut: distal limb 60° angle. Complete plantar cortex cut gently with osteotome. EXAM KEY: Incomplete plantar cortex cuts prevent propagation fracture and troughing.

Step 8: Mobilize osteotomy fragments

Mobilize osteotomy fragments: Use small osteotome to gently mobilize capital fragment. Avoid excessive force or levering. If tight, complete cuts under direct vision with saw. EXAM KEY: Gentle mobilization prevents comminution and maintains cortical contact.

Step 9: Translate capital fragment laterally

Translate capital fragment laterally: Displace metatarsal head fragment laterally 3-5mm (typically 50-75% metatarsal width for moderate deformity). Use ruler to measure translation. Maintain parallel alignment of fragments. EXAM KEY: Lateral translation corrects IMA by 1.5° per millimeter translated.

Step 10: Rotational and sagittal plane correction (if required)

Rotational and sagittal plane correction (if required): If DMAA elevated (>10°), rotate capital fragment medially (pivot point at distal plantar corner). If transfer metatarsalgia present, plantarflex capital fragment 2-3mm. EXAM KEY: Rotation corrects pronation and DMAA. Plantarflexion unloads lesser metatarsals.

Step 11: Provisional fixation and correction check

Provisional fixation and correction check: Hold reduction with pointed reduction forceps or 1.6mm K-wire. Check alignment clinically: (1) hallux alignment straight, (2) no rotation, (3) length compared to contralateral. Fluoroscopy: (1) sesamoids centred under metatarsal head, (2) IMA <9°, (3) HVA <15°, (4) DMAA <10°. EXAM KEY: This is correction confirmation before definitive fixation.

Step 12: Definitive fixation with compression screws

Definitive fixation with compression screws: Two headless compression screws required for stability. First screw: 2.0-2.7mm headless screw (depending on bone size), proximal fragment into distal fragment, angled 15-20° from horizontal to engage thick dorsal cortex of capital fragment. Second screw: distal to first, parallel orientation. Lag technique for compression. EXAM KEY: Compression at osteotomy site essential for healing.

Step 13: Medial eminence resection

Medial eminence resection: Resect medial eminence with sagittal saw. Cut line from dorsal to plantar, parallel to medial shaft cortex. Avoid excessive resection (weakens fixation construct, causes flat-top deformity). Smooth with rongeur/rasp. EXAM KEY: Conservative resection sufficient after lateral translation.

Step 14: Akin osteotomy assessment

Akin osteotomy assessment: Assess hallux alignment after scarf correction and provisional capsule closure. If hallux valgus interphalangeus present (HVI angle >10°) or residual hallux valgus despite corrected IMA, perform Akin osteotomy. EXAM KEY: Akin addresses phalangeal component of deformity that scarf cannot correct.

Step 15: Akin osteotomy execution (if indicated)

Akin osteotomy execution (if indicated): Separate medial incision over proximal phalanx base (2cm longitudinal). Elevate periosteum circumferentially. Medial-based closing wedge osteotomy at base of proximal phalanx (apex lateral). Remove 2-3mm wedge. Close osteotomy with pointed clamp, creates varus correction. Fix with single headless screw (lag technique) or staple. EXAM KEY: Closing wedge more stable than opening wedge.

Step 16: Capsular repair and closure

Capsular repair and closure: Repair medial capsule with 2-0 absorbable sutures in vest-over-pants technique (overlapping imbrication). Avoid excessive tension. Close subcutaneous layer with 3-0 absorbable suture. Skin closure with 3-0 or 4-0 nylon or monocryl subcuticular. Apply sterile dressing and post-operative shoe. EXAM KEY: Capsular imbrication provides additional stability.

Complications

Additional Complications

• Dorsomedial cutaneous nerve injury: 15-20% incidence (usually transient neuropraxia). Prevention: identify and protect nerve during superficial dissection, gentle retraction, avoid skin retractor pressure over nerve course. Management: transient neuropraxia resolves 3-6 months with reassurance, permanent numbness usually small area and well tolerated, desensitization techniques if bothersome.

• Stiffness/reduced MTPJ ROM: 10-15% incidence (usually mild <10° loss). Prevention: early protected ROM exercises from 2 weeks, avoid overcorrection creating joint tension, preserve capsule for anatomic closure, address intra-articular pathology if present. Management: physiotherapy with passive ROM exercises, manipulation under anaesthesia if severe and within 12 weeks, arthrofibrosis requiring late MUA or arthroscopic adhesiolysis rarely needed.

• Infection: <2% incidence. Prevention: perioperative antibiotics (cefazolin 2g IV within 60 minutes), sterile technique, minimize tourniquet time, atraumatic tissue handling. Management: superficial infection with cellulitis: oral antibiotics; deep infection: operative debridement, hardware retention if stable and within 4 weeks, hardware removal if loose or infection >4 weeks postop, IV antibiotics 6 weeks.

Postoperative Management

Immediate Postoperative (0-2 weeks)

• Weight bearing: Heel weight bearing in postoperative shoe, crutches for balance
• Elevation: Foot elevated above heart level majority of time to reduce swelling
• Ice: 20 minutes every 2-3 hours for first 48-72 hours
• Dressing: Bulky dressing maintained for 2 weeks, kept clean and dry
• Analgesia: Multimodal - paracetamol, NSAIDs (controversial first 6 weeks due to bone healing concerns), opioids short-term if needed
• VTE prophylaxis: Risk assessment, aspirin 100mg daily for 2 weeks if low risk, LMWH if high risk factors

Early Rehabilitation (2-6 weeks)

• Wound care: Suture removal at 2 weeks, wound check for healing
• Weight bearing: Progress to forefoot weight bearing in postoperative shoe, wean crutches as tolerated
• Exercises: Active and passive MTPJ ROM exercises, start gentle (5-10° initially, increase gradually)
• Swelling management: Compression stocking, continued elevation when resting
• Radiographs: First postoperative radiographs at 2 weeks to assess alignment and hardware position

Intermediate Phase (6-12 weeks)

• Weight bearing: Transition to supportive athletic shoe at 6 weeks (wide toe box, rigid sole initially)
• Radiographs: 6-week radiographs to assess healing progression
• Exercises: Progressive MTPJ ROM, strengthening exercises (toe curls, marble pickup)
• Activity: Return to sedentary work at 2-4 weeks, light duty work at 6-8 weeks, avoid impact activities until 12 weeks
• Footwear: Gradual transition to normal shoes 8-12 weeks based on swelling and comfort

Advanced Rehabilitation (3-6 months)

• Radiographs: 12-week radiographs to confirm union
• Activity progression: Return to impact activities (running, jumping) at 12-16 weeks if radiographic union confirmed
• Footwear: Return to fashion footwear (including heels) at 4-6 months, gradual progressive wear
• Final assessment: 6-month clinical and radiographic assessment of final alignment and function

Long-term Follow-up

• Monitoring: Annual follow-up first 2 years to detect early recurrence
• Patient education: Appropriate footwear selection (wide toe box, adequate depth), avoid excessive heel heights (>5cm), maintain healthy weight
• Complication surveillance: Monitor for late complications (recurrence, arthritis, hardware symptoms)