Lapidus Procedure (1st TMT Arthrodesis for Hallux Valgus)

Anatomical Considerations

First TMT Joint Anatomy

• Joint configuration: First metatarsal base articulates with medial cuneiform
• Shape: Medial cuneiform is trapezoid - wider DORSALLY (12-15mm) than plantarly (8-10mm) - predisposes to dorsiflexion malposition
• Orientation: Joint line oriented 45° dorsomedial to plantar lateral
• Stability: Stabilized by capsule, plantar and dorsal ligaments (Lisfranc ligament attaches C1 to M2 base, not M1)
• Blood supply: Dorsalis pedis (lateral), medial plantar artery (plantar), periosteal vessels

Surface Anatomy & Approach

• Palpable landmarks: Navicular tuberosity 3cm proximal, 1st metatarsal base 3-4cm distal to navicular
• EHL tendon: Critical landmark - stays LATERAL to it for safety
• Dorsalis pedis: Palpable between EHL and EHB, 15-20mm lateral to incision line
• Incision position: Dorsomedial 4-5cm longitudinal centered over TMT joint

Biomechanical Pathology

• Hypermobility: Normal TMT translation <5mm; pathologic >9mm dorsoplantar translation
• Deformity mechanism: Hypermobile TMT allows 1st metatarsal to drift into varus (increased IMA), hallux compensates into valgus
• Force transmission: 50% body weight through 1st ray during push-off - hypermobility allows progressive deformity
• Recurrence mechanism: Distal procedures in hypermobile patients fail because apex of deformity (TMT) remains mobile

Indications

Primary Indications

1. Severe hallux valgus with hypermobility

   • IMA >18-20° (severe intermetatarsal angle)
   • HVA >40° (hallux valgus angle)
   • TMT hypermobility >9mm dorsoplantar translation

2. Metatarsus primus varus

   • Structural varus of 1st metatarsal
   • Fixed deformity at TMT level

3. Revision bunion surgery

   • Failed chevron, scarf, or other distal procedures
   • Recurrent deformity due to unaddressed TMT instability

4. Younger active patients

   • Age <50 years requiring definitive correction
   • High activity demands precluding nonunion risk of osteotomy

5. Degenerative TMT arthritis with hallux valgus

   • Concurrent arthritis and deformity - corrects both

Relative Indications

• Moderate hallux valgus (IMA 15-18°) with clear hypermobility
• Rheumatoid arthritis affecting first ray
• Neuromuscular deformity with dynamic component

Contraindications

Absolute:

• Active infection at surgical site
• Severe peripheral vascular disease (non-palpable pedal pulses, ABI <0.5)
• Charcot neuropathy with active inflammation
• Non-ambulatory patient

Relative:

• Heavy smoker (>1 pack/day) - nonunion risk 20-30%
• Uncontrolled diabetes (HbA1c >8%) - infection and nonunion risk
• Severe osteoporosis - fixation failure risk
• Spastic neuromuscular disorder - deforming forces persist
• Mild deformity (IMA <15°) - distal procedures preferable

Clinical Assessment

History

• Deformity progression: Rate of worsening, prior failed procedures
• Shoe wear: Wide toe box, difficulty with shoe fit
• Pain location: MTP joint medially, lesser metatarsals (transfer), TMT midfoot
• Functional limitation: Walking distance, footwear restrictions
• Medical optimization: Smoking cessation, diabetic control, vascular status

Physical Examination

1. Deformity assessment

   • HVA measurement clinically (angle between hallux and 1st metatarsal)
   • IMA assessment (medial prominence, widened forefoot)
   • Lesser toe deformities (crossover 2nd toe, hammer toes from transferred load)

2. TMT hypermobility testing - CRITICAL for surgical decision

   • Stabilize hindfoot and midfoot with one hand
   • Grasp 1st metatarsal head with other hand
   • Dorsally and plantarly translate
   • Measure displacement: <5mm normal, 5-9mm borderline, >9mm pathologic
   • Compare with contralateral side

3. MTP joint assessment

   • ROM: normal 65-75° dorsiflexion, 15° plantarflexion
   • Sesamoid position: subluxation indicates severe deformity
   • Hallux pronation (rotation into valgus)

4. Vascular examination

   • Palpate dorsalis pedis and posterior tibial pulses
   • Capillary refill <2 seconds
   • Ankle-brachial index if any concern

5. Neurology

   • Sensation intact (diabetic neuropathy assessment)
   • Motor function (EHL, FHL strength)

Imaging

Weight-bearing AP foot radiograph - MANDATORY

• Measure IMA (intermetatarsal angle): Normal <9°, mild 9-13°, moderate 13-18°, severe >18°
• Measure HVA (hallux valgus angle): Normal <15°, mild 15-30°, moderate 30-40°, severe >40°
• Assess TMT joint: arthritis, subluxation
• Assess sesamoid position (subluxation indicates soft tissue imbalance)
• Distal metatarsal articular angle (DMAA): >10° suggests intra-articular deformity

Weight-bearing lateral foot radiograph

• 1st metatarsal declination angle: normal 15-25° below horizontal
• Check for TMT arthritis
• Assess medial arch

Stress radiographs (optional)

• Lateral stress view with dorsal force on 1st metatarsal
• Demonstrates >9mm translation = hypermobility

Advanced imaging (selective)

• MRI: Not routine, consider if concern for AVN, occult fracture, soft tissue pathology
• CT: For revision cases with complex anatomy or to assess TMT arthritis severity

Surgical Planning

Correction goals

• IMA: Correct to <10° (aim 5-8°)
• HVA: Correct to <15°
• Sesamoid reduction: Subluxation corrected
• Sagittal alignment: NEUTRAL or slight plantarflexion (avoid dorsiflexion)
• Length: Minimize shortening (<5mm) to prevent transfer metatarsalgia

Fixation planning

• Preferred: Dorsomedial locking plate (low-profile, anatomic) + lag screw
• Alternative: Plantar plate (biomechanically superior but technically demanding)
• Avoid: Crossed lag screws alone (higher nonunion 12-15%)

Adjunct procedures consideration

• Akin osteotomy: If residual hallux valgus interphalangeus (DMAA >10°)
• Medial eminence: Resection usually not needed if deformity fully corrected
• Lateral soft tissue release: Usually not needed with Lapidus (correction at TMT eliminates tension)

Patient consent - key points

• Union time: 10-12 weeks until full consolidation
• Nonunion risk: 5-8% with plate, higher in smokers
• NWB period: 6 weeks strict non-weight bearing, then gradual progression
• Transfer metatarsalgia: 10-15% if excessive shortening or dorsiflexion
• Hallux varus: 2-5% if overcorrection
• Nerve injury: 5-10% superficial sensory (dorsomedial cutaneous)
• Hardware removal: 10-15% require removal for prominence
• Return to activities: 4-6 months for full unrestricted activities

Positioning and Preparation

Patient Position: Supine with small bump under ipsilateral hip for 15-20° external rotation. Foot at end of table for intraoperative imaging access. Radiolucent table and triangle positioning aid optional.

Anesthesia: General or regional (ankle block). Popliteal block provides excellent postoperative analgesia.

Tourniquet: Ankle tourniquet (250mmHg) or thigh tourniquet (300mmHg based on limb circumference formula). Exsanguinate with Esmarch or elevation.

Preparation: Prep circumferentially to mid-calf. Drape to allow full foot exposure and fluoroscopy access.

Equipment Check:

• Fluoroscopy (AP, lateral, oblique views)
• Dorsomedial locking plate system (TMT-specific, low-profile)
• 3.5mm or 4.0mm lag screw instrumentation
• Sagittal saw with narrow blade
• Smooth K-wires for provisional fixation
• Small bone curettes and rongeurs

Surgical Technique

Step 1: Incision and Superficial Dissection

Incision: Dorsomedial longitudinal incision 4-5cm centered over 1st TMT joint. Start 2cm proximal to joint, extend 2-3cm distal. Stay centered over metatarsal shaft medially.

Subcutaneous dissection: Carefully incise subcutaneous tissue. CRITICAL: Identify dorsomedial cutaneous nerve branches - typically 2-3 branches crossing dorsally within 2-3mm of incision. Use loupe magnification. Gently retract branches medially or laterally with vessel loops.

Fascial layer: Incise fascia longitudinally. Identify EHL tendon coursing distally and laterally - this is your KEY anatomical landmark.

Step 2: Deep Dissection and Joint Exposure

Interval development: Develop plane MEDIAL to EHL tendon. Retract EHL laterally with small Hohmann retractor. This protects dorsalis pedis artery and deep peroneal nerve which are lateral to EHL.

Capsulotomy: Identify TMT joint line - typically at proximal extent of medial eminence but variable. Confirm with fluoroscopy if uncertain. Incise capsule longitudinally along dorsal and medial aspects. Then make transverse capsular incisions creating T-shaped or H-shaped capsulotomy for maximal exposure.

Exposure: Place small Hohmann retractors medially and laterally (staying medial to EHL). Plantarly directed retractors risk medial plantar neurovascular bundle - avoid excessive plantar retraction. Expose entire TMT joint dorsally and medially.

Synovectomy: Remove synovium from joint to improve visualization of cartilage surfaces.

Step 3: Joint Preparation - Cartilage Removal

Preparation philosophy: Goal is flat, parallel, congruent surfaces with healthy bleeding cancellous bone contact.

Technique options:

Option A: Flat cut technique (preferred)

• Use sagittal saw with narrow blade
• Make perpendicular cut to metatarsal removing 2-3mm from metatarsal base surface
• Make corresponding perpendicular cut removing 2-3mm from cuneiform surface
• Maintain surfaces parallel and flat
• Most stable configuration, easiest to achieve correct position

Option B: Curved/concave-convex technique

• Create slight concavity in one surface, convexity in other
• Theoretically increases surface area
• More technically demanding, risk of instability if surfaces non-congruent

Cartilage removal: After bone cuts, use small curettes to remove all remaining cartilage fragments. Use rongeur or burr to fenestrate subchondral plate exposing cancellous bone. Avoid thermal necrosis - intermittent burr use with irrigation.

Surface preparation goals:

• Complete cartilage removal (any retained cartilage = nonunion risk)
• Exposed bleeding cancellous bone (multiple punctate bleeding points)
• Minimal bone resection (excessive shortening >5mm = transfer metatarsalgia)
• Parallel surfaces (non-parallel = malposition)

Step 4: Provisional Reduction and Deformity Correction

Reduction maneuvers:

1. Grasp 1st metatarsal distally
2. Translate metatarsal LATERALLY toward 2nd metatarsal (narrows IMA)
3. Derotate - correct pronation (hallux should point straight, not rotated)
4. Sagittal plane - ensure NEUTRAL or slight plantarflexion (NOT dorsiflexion)
5. Length - minimize shortening, maintain contact with lesser metatarsals

Provisional fixation: Hold reduction with 1-2 smooth K-wires:

• Insert K-wire from dorsal metatarsal into cuneiform, aiming plantar-proximal
• Check does not penetrate plantar cortex (risk to neurovascular bundle)
• Second K-wire for rotational control if needed

Reduction assessment checklist:

• IMA: Narrowed to <10° (aim 5-8°) - check AP fluoroscopy
• Rotation: Hallux aligned, no pronation
• Sagittal: NO dorsiflexion - neutral or 5° plantarflexion - check LATERAL fluoroscopy
• Length: Metatarsal head aligned with lesser metatarsals, <5mm shortening

Step 5: Fluoroscopic Confirmation - MANDATORY

Imaging protocol: AP, lateral, and oblique views with K-wires in place BEFORE plating.

AP view assessment:

• IMA corrected to <10° (measure angle between 1st and 2nd metatarsals)
• Alignment: metatarsal base centered on cuneiform
• No varus overcorrection
• K-wire position appropriate

LATERAL view assessment - CRITICAL:

• NO DORSIFLEXION: 1st metatarsal should align with or be slightly below (plantarflexed to) 2nd-5th metatarsals
• Check declination angle if able to measure
• K-wire trajectory acceptable

Oblique view:

• Joint reduction confirmed
• No interposition

Correction of malposition: If ANY malposition identified, remove K-wires and reposition BEFORE plating. Much harder to correct after plate fixation.

Step 6: Definitive Fixation - Plate Application

Plate selection: Dorsomedial locking plate (TMT-specific, anatomic, low-profile)

• Typical size: 6-hole plate (3 screws proximal in cuneiform, 3 screws distal in metatarsal)
• Pre-contoured to anatomic shape
• Locking screws provide angular stability

Plate positioning:

• Position plate on dorsomedial surface spanning TMT joint
• Ensure plate sits flush on bone (may need minor contouring)
• Avoid overhang medially (painful prominence)
• Center plate so equal screw distribution proximal and distal to joint

Screw insertion sequence:

1. First screw in cuneiform (proximal fragment) - typically non-locking
2. Check fluoroscopy - any position adjustment needed
3. First screw in metatarsal (distal fragment) - typically non-locking
4. Check fluoroscopy - final adjustment opportunity
5. Remaining locking screws alternating proximal/distal
6. Check each screw does not penetrate adjacent joints (2nd TMT, intercuneiform, naviculocuneiform)

Screw length:

• Proximal screws: 16-22mm typically (through cuneiform, may engage opposite cortex)
• Distal screws: 18-24mm (through metatarsal base)
• Measure carefully - penetration of plantar cortex risks neurovascular bundle

Step 7: Supplemental Lag Screw Fixation

Lag screw rationale: Provides interfragmentary compression supplementing plate neutralization. Biomechanical studies show improved stability.

Lag screw technique:

1. Drill hole from dorsal metatarsal base toward plantar cuneiform
2. Trajectory: Aim from dorsolateral to plantarmedial (perpendicular to fusion plane)
3. Overdrill near cortex (metatarsal side) with larger diameter to create lag effect
4. Measure depth carefully
5. Insert 3.5mm or 4.0mm partially threaded screw
6. Tighten to achieve compression (feel resistance increase, see surfaces approximate)
7. Check fluoroscopy for screw position and compression

Screw position:

• Outside plate if possible for independent fixation
• If through plate, ensure compatible with plate hole design
• Avoid intra-articular penetration of naviculocuneiform or intercuneiform joints

Alternative: Plantar plate

• Biomechanically superior (tension side fixation)
• Requires separate plantar incision and more extensive dissection
• Higher technical difficulty
• Consider for revision cases or if dorsal plate undesirable

Step 8: Bone Grafting (Selective)

Indications for bone graft:

• Revision surgery with bone defect
• Osteoporotic bone
• Smokers (>10 cigarettes/day)
• Large surfaces with gap >2mm after compression
• Diabetes or other nonunion risk factors

Graft options:

Local bone (most common):

• Use bone resected from TMT joint preparation
• Morselized into small fragments
• Pack around fusion site peripherally
• No additional incision required

Iliac crest autograft:

• Gold standard for biology
• Harvest from anterior or posterior iliac crest
• Cancellous or corticocancellous
• Donor site morbidity (pain, hematoma, nerve injury)

Allograft:

• Cancellous chips or demineralized bone matrix
• No donor site morbidity
• Potential for disease transmission (very low with modern screening)

Bone substitutes:

• Calcium phosphate or sulfate
• Osteoconductive scaffolds
• Expensive, mixed evidence

Application technique:

• Pack bone graft around periphery of fusion site AFTER fixation
• Avoid interposition between fusion surfaces (prevents compression)
• Does not replace adequate preparation and stable fixation

Step 9: Distal Adjunct Procedures (Selective)

Assessment for distal procedures: After TMT fusion, assess residual hallux valgus at MTP joint. Usually Lapidus corrects entire deformity. Consider distal procedures if:

• Residual HVA >15° after TMT correction
• DMAA >10° (intra-articular deformity)
• Hallux valgus interphalangeus

Akin osteotomy (most common adjunct):

• Medial closing wedge osteotomy of proximal phalanx
• Corrects hallux valgus interphalangeus
• Separate 2-3cm medial incision over proximal phalanx
• Remove medial wedge, close with screw or K-wire

Medial eminence resection:

• Usually not needed if deformity corrected
• If medial prominence persists: limited resection through TMT incision or separate MTP incision
• Avoid excessive resection weakening medial column

Lateral soft tissue release:

• Rarely needed with Lapidus (correction at TMT eliminates tension)
• If severe contracture: release adductor hallucis and lateral capsule through separate incision
• Risk of AVN to metatarsal head if combined with extensive medial dissection

Step 10: Final Imaging and Wound Closure

Final fluoroscopy - 3 views:

• AP: IMA <10°, hardware well-positioned, no intra-articular screws
• Lateral: NO dorsiflexion, 1st ray aligned with or plantar to lesser rays, appropriate hardware position
• Oblique: Joint reduction confirmed, compression achieved, no interposition

Closure sequence:

1. Copious irrigation (3L normal saline minimum)
2. Deflate tourniquet and achieve hemostasis (bipolar cautery)
3. Repair capsule with 2-0 or 3-0 absorbable suture (Vicryl) - provides additional stability
4. Close subcutaneous layer with 3-0 absorbable (reduces dead space)
5. Skin: 4-0 or 5-0 monofilament interrupted or subcuticular (nylon or Monocryl)
6. Sterile dressing with gentle compression
7. Apply posterior splint or CAM boot maintaining alignment

Dressing technique:

• Adaptic or non-adherent layer over incision
• Fluffed gauze for gentle compression
• Webril wrap from toes to mid-calf
• Posterior splint with ankle at neutral, foot at neutral or slight plantarflexion
• Overwrap with elastic bandage
• Alternative: Removable CAM boot for compliant patients

Additional Complications

Recurrent Deformity (<5% with proper technique)

• Rare if TMT fusion eliminates hypermobility
• Usually indicates nonunion (continued mobility) or concurrent untreated pathology
• Management: Assess for nonunion (CT scan), address underlying cause, revision if needed

DVT/PE (1-3%)

• Risk from prolonged immobilization and non-weight bearing
• Prevention: Chemical prophylaxis in high-risk patients (consider aspirin 325mg daily or LMWH), early ankle ROM exercises, calf pumps, compression stockings
• Management: Standard anticoagulation protocols

Infection - Deep (1-2%)

• Presentation: Persistent pain, fever, elevated inflammatory markers, drainage, radiographic changes
• Prevention: Appropriate antibiotic prophylaxis (cefazolin), sterile technique, minimize operative time
• Management: Surgical debridement, culture-directed IV antibiotics 6 weeks, retain hardware if fusion incomplete, remove hardware if fusion solid and infection persistent

Complex Regional Pain Syndrome (1-2%)

• Severe pain, vasomotor changes, trophic changes, functional impairment
• Prevention: Minimize surgical trauma, early mobilization of uninvolved joints, multimodal analgesia
• Management: Multidisciplinary - physical therapy, sympathetic blocks, medications (gabapentin, tricyclics), psychology referral

Adjacent Joint Arthritis (Long-term concern)

• Intercuneiform, naviculocuneiform, or 2nd TMT arthritis from altered mechanics
• Develops over years to decades
• Usually asymptomatic or mild
• Management: Conservative initially (orthotics, NSAIDs), fusion extension if severe symptomatic

Immediate Postoperative Period (0-2 weeks)

Immobilization: Well-padded posterior splint or removable CAM boot in neutral ankle position, neutral or slight plantarflexion of forefoot

Weight bearing: STRICT non-weight bearing (NWB) - crutches or walker, no weight on operative foot

Elevation: Keep foot elevated above heart level 23 hours/day for first 2 weeks to minimize swelling

Ice: Ice packs 20 minutes on, 20 minutes off while awake

Pain management:

• Multimodal analgesia: scheduled acetaminophen 1000mg TDS
• Opioids: Short course (5-7 days) oxycodone 5-10mg PRN, minimize use
• Gabapentin 300mg TDS for neuropathic component
• NSAIDs: Avoid first 6 weeks (impair bone healing) unless low-dose aspirin for DVT prophylaxis

DVT prophylaxis:

• Low-risk patients: Mechanical (calf pumps, ankle ROM exercises, compression stockings)
• High-risk patients (obesity, smoking, prior DVT, prolonged surgery): Consider aspirin 325mg daily or LMWH

First post-op visit (10-14 days):

• Remove surgical dressing
• Assess wound healing
• Remove sutures if non-absorbable (typically 14 days)
• Apply new dressing and splint or CAM boot
• Continue NWB

Weeks 2-6: Protected Healing Phase

Immobilization: Transition to removable CAM boot if not already (allows hygiene)

Weight bearing: Continue STRICT NWB - fusion site is healing but not strong enough for load

Wound care: Once sutures removed and wound sealed, allow gentle washing (soap and water), pat dry, keep dressing

Exercises:

• Ankle ROM exercises (gastrocnemius stretching, ankle pumps) - prevents stiffness
• Knee and hip ROM
• NO hallux or forefoot ROM (fusion site)

Radiographs: At 6 weeks - AP, lateral, oblique

6-week assessment - CRITICAL decision point:

• Clinical exam: Tenderness at TMT fusion site (less expected as healing), wound healed, neurovascular status
• Radiographs: Evidence of early union (bridging trabeculae, callus formation, no lucency progression)
• CT scan: If radiographs equivocal - shows trabecular bridging better than X-ray

Decision:

• If progressing to union: Advance to protected weight bearing
• If questionable: Extend NWB 2-4 more weeks, repeat imaging
• If nonunion concern: Consider CT scan, may need extended NWB or bone stimulator

Weeks 6-12: Progressive Weight Bearing Phase

Weight bearing progression (if union progressing at 6 weeks):

• Weeks 6-8: Partial weight bearing (25-50% body weight) in CAM boot with crutches
• Weeks 8-10: Weight bearing as tolerated (50-75%) in boot with 1 crutch
• Weeks 10-12: Full weight bearing in boot, wean crutches

Immobilization: Continue CAM boot until 12 weeks

Exercises:

• Continue ankle ROM
• Begin gentle hallux ROM (passive) at 8-10 weeks
• Toe curls, marble pickup for intrinsic strength
• Stationary bike (no resistance) from 8 weeks

Radiographs: At 12 weeks - assess union

12-week assessment:

• Clinical exam: Pain-free weight bearing expected, no tenderness at TMT
• Radiographs: Solid union (bridging trabeculae 3+ cortices, no lucency, callus maturation)
• CT scan: If radiographs equivocal

Decision:

• If solid union: Transition to supportive shoes, gradual return to activities
• If incomplete union but progressing: Continue boot 2-4 more weeks, repeat imaging
• If nonunion: See complications section - may need revision surgery

Months 3-6: Return to Activities

Footwear: Transition from boot to supportive athletic shoes or walking shoes (wide toe box, rigid sole initially)

Weight bearing: Full weight bearing in shoes

Exercises:

• Progress strengthening (resistance band, heel raises)
• Proprioception (single leg balance, wobble board)
• Gradual return to impact activities (walking → jogging → running)
• Swimming/cycling excellent during this phase

Activity restrictions:

• No high-impact activities until 4 months (running, jumping)
• No sports until 6 months
• Individual progression based on symptoms and radiographic union

Radiographs: At 6 months - confirm solid union and alignment maintenance

6-month assessment:

• Expected outcome: Solid fusion, full pain-free weight bearing, return to regular shoes, minimal activity limitations
• Alignment maintained (IMA <10°, no dorsiflexion)
• No hardware complications

Long-term Follow-up (>6 months)

Return to full activities: Unrestricted activities at 6 months if solid union and asymptomatic

Hardware removal: Consider at 12-18 months if symptomatic prominence (10-15% require removal)

Annual radiographs: First 2 years to monitor for late complications (adjacent joint arthritis, hardware issues)

Long-term outcomes:

• Union rate: 92-95% with modern fixation
• Patient satisfaction: 85-90%
• Recurrence: <5% (fusion eliminates TMT hypermobility)
• Return to sports: 90% return to pre-injury level by 12 months

Troubleshooting Common Post-op Issues

Persistent pain at 6 weeks:

• Normal to have some tenderness
• Concerning if sharp pain with weight bearing, night pain, or worsening pain
• Consider delayed union or nonunion - obtain CT scan
• May need extended NWB, bone stimulator, or revision

Transfer metatarsalgia developing 3-6 months:

• Suggests dorsiflexion malunion or excessive shortening
• Obtain weight-bearing lateral radiograph
• Conservative management initially (metatarsal pads, orthotics)
• May require surgical correction if severe

Wound issues:

• Dehiscence: Local wound care, exclude infection
• Persistent drainage: Concern for deep infection - labs (CBC, CRP, ESR), consider aspiration
• Early recognition and treatment crucial

Numbness:

• Dorsomedial cutaneous nerve neuropraxia common (5-10%)
• Usually improves over 3-6 months
• Desensitization techniques if dysesthetic
• Neuroma excision if painful persistent neuroma