AN

Lapidus Bunionectomy (McGlamry Ch 13)

Definition & Historical Evolution

  • Original concept
    • 1st tarsometatarsal joint (1st TMT) is the anatomic apex of hallux valgus (HAV) deformity.
    • True Lapidus = arthrodesis of 1st TMT plus fusion (or rigid screw fixation) between bases of 1st & 2nd metatarsals.
  • Key milestones
    • 1911 Albrecht – first 1st TMT arthrodesis.
    • 1925 Truslow – term “metatarsus primus varus” (transverse-plane adduction of 1st MT).
    • 1934 Lapidus – recommended fusion at metatarsocuneiform joint “mechanically sound apex.”
  • Why popularity increased
    • Better fixation hardware, faster bone healing, 3-D anatomical understanding.
    • Ability to correct triplanar deformity, not just transverse inter-metatarsal angle.

Classical (Severity-Based) Indications

  • Reserved for severe IM angle deformity:
    • Condon 2002: severe = IMA\ge 16^{\circ}.
    • Coughlin & Jones 2007 followed same.
  • Other classic triggers
    • Symptomatic osteoarthritis at 1st TMT (uncommon in HAV).
    • First-ray elevation / hypermobility (aka “functional instability”).
    • Root 1977: hypermobility = excessive equal dorsal & plantar displacement compared to 2nd ray.
    • Dynamic Hicke test (Roukis & Landsman 2003).
    • Windlass engagement loss documented by Rush 2000.
  • Sagittal signs: 2nd-ray stress fractures, plantar gapping at 1st TMT (Fig 13.1).
  • Transverse signs: positive “splay test” (Weber 2006), 73.8 % transverse instability in HAV (Fleming 2015).

Triplane Classification & Modern Indications

  • Concept shift: anatomic-based, no longer severity-based.
    • 1st TMT is CORA (center of rotation & angulation) for HAV (Paley 2002).
    • Majority of HAV feet show frontal-plane valgus rotation (14.5° vs 3.1° normals – Scranton 1980; 12.7° – Mortier 2012).
  • Hatch et al. 2018 Triplane HAV Classification (Table 13.1)
    • Class 1 → increased HVA & IMA, no MT pronation.
    • Class 2A/2B → MT pronation ± sesamoid subluxation.
    • Class 3 → IMA>20^{\circ} + metatarsus adductus.
    • Class 4 → DJD at 1st MTP.
    • Treatment algorithms add “first-met inversion” & sesamoid release when pronation present.
  • Current indications
    • Any HAV with IM increase and/or frontal-plane rotation.
    • Anatomic apex accessible at 1st TMT; allows simultaneous transverse/sagittal/frontal correction.
    • Adjacent-ray fusion (MC–2MT or IC joints) when first–second ray instability exists.

Radiographic & Clinical Planning

  • Weight-bearing AP
    • Measure IMA, HVA; both reproducible.
    • DMAA/PASA unreliable; changes with MT rotation.
    • Tibial sesamoid position (TSP) appears worse with MT pronation; rely on axial view/CT.
  • Weight-bearing axial sesamoid view
    • Quantifies MT eversion & true sesamoid displacement (Fig 13.2).
  • Lateral view
    • Assess Meary angle, Seiberg index; note first-ray elevation.
  • Philosophy: do NOT rigidly follow numeric cut-offs; evaluate full 3-D relationships.

Anatomy & Biomechanics

  • 1st ray – inherently unstable; stabilizers:
    • Static: 1st TMT surfaces, intercuneiform, MC–2MT base, plantar 1MT–MC ligament.
    • Dynamic: plantar aponeurosis (windlass); peroneus longus (locks ray in eversion & elevates talus).
  • Medial cuneiform obliquity not correlated with HAV (Vyas 2010 plus others).
  • Doty cadaver metrics:
    • 1st TMT depth 28.3\pm? mm, width 13.1\pm? mm; lateral inclination 26.5^{\circ}.
  • Windlass & peroneus longus function improve after Lapidus (Bierman 2001).

Surgical Technique Highlights

  • Incision choices:
    • Long dorsal (favours 3-D visualisation) vs medial cosmetic approach.
  • Sequence (multiplanar philosophy)
    1. Fully mobilise 1st TMT; release any lateral MTP ankylosis.
    2. Use joystick pins / jigs; simultaneously correct
    • Transverse (reduce IMA → target \le 4^{\circ}),
    • Sagittal (neutralise elevation/depression),
    • Frontal (derotate until sesamoids collinear; abolish “lateral round sign”).
    1. Confirm under fluoroscopy; anatomical landmarks > arbitrary angles.
  • Sesamoid management
    • If axial view shows displacement, perform lateral capsular/sesamoid release (Fig 13.3).
  • Adjacent fusions (Fig 13.5)
    • MC–2MT base or IC joints for residual transverse/sagittal instability.
  • Bone preparation
    • Preferred: complete removal of cartilage & subchondral plate with low-heat saw + drill-bit fenestration → autogenous chips retained (Fig 13.8).
    • Curettage alone may leave \approx 50\% calcified cartilage (↓ surface area).
    • Aim ≤ 3\,\text{mm} shortening.
  • Fixation constructs
    • Traditional: 2!\text{–}3 crossed compression screws → need 6 wk NWB.
    • Plate + screw combos permit earlier WB.
    • Biplanar locked plates (Dayton 2018): biologic micromotion (Perren 2002) → callus, stable union; protected WB within 1 wk (Fig 13.9).
    • Immediate WB achievable with robust constructs (Basile 2010; Prissel 2016 level-III no union difference early vs delayed).

Post-operative Protocol (typical modern)

  • Day 1–7: Bulky dressing, partial WB in CAM boot as tolerated.
  • Week 1–6: Protected WB boot, active ROM exercises to minimise stiffness/DVT.
  • Week 6+: Transition to regular shoe if radiographic union progressing.
  • Emphasise patient factors: smoking, diabetes, metabolic bone disease must be optimised.

Complications & Recurrence Drivers

  • Shortening, dorsiflexion elevation, non-union, neuropraxia (medial dorsal cutaneous nerve), recurrence.
  • Non-union rates
    • Literature 5\%!\text{–}!10\%; meticulous prep + shear-strain graft 2.7\% (Mani 2015).
  • Recurrence predictors
    • Inadequate sesamoid reduction (Okuda 2009, Shibuya 2018).
    • Undercorrected IMA / 1–2 MT angle (should be \le4^{\circ}).
  • Mitigation
    • Ensure triplanar correction; consider adjacent fusion when instability; verify neutral sagittal alignment intra-op.

Surgical Pearls & Pitfalls

  • “Correct first, cut second” – apply jig only after provisional triplanar reduction.
  • Always release sesamoids if subluxed on axial imaging.
  • Multiplanar locking plates = less intra-fusion bone sacrifice, better surface area.
  • Avoid excess soft-tissue stripping; maintain full-thickness flaps for blood supply (Fig 13.7).

Summary Take-Home Messages

  • 1st TMT fusion (Lapidus) now viewed as primary HAV correction because it sits at anatomic CORA and permits comprehensive 3-D realignment.
  • Indications focus on anatomy (IMA increase, MT pronation, instability), not degree severity charts.
  • Radiographs must include weight-bearing axial view or CT; AP alone is misleading for sesamoids & DMAA.
  • Modern technique = minimal dissection, full cartilage removal, fenestration, locking biplanar plate fixation, early protected weight bearing.
  • Success hinges on:
    • Complete multiplanar correction (target IMA\le4^{\circ} & collinear sesamoids),
    • Stable fixation allowing biologic micromotion,
    • Recognition/management of first–second ray instability.

Selected Numerical / Formula Review

  • Severe deformity historical cutoff: IMA\ge 16^{\circ}.
  • Triplane class 3 criterion: HVA+IMA>20^{\circ} with metatarsus adductus.
  • Average valgus rotation in HAV: \approx 12!\text{–}!15^{\circ} (various CT studies).
  • Desired postoperative IMA\le 4^{\circ}.
  • Cadaveric 1st TMT dimensions: depth 28.3\,\text{mm}, width 13.1\,\text{mm}, lateral inclination 26.5^{\circ}.

Quick Reference Connections

  • Windlass mechanism → plantar aponeurosis; restored by sesamoid realignment.
  • Peroneus longus → improved lever arm after Lapidus, enhancing first-ray stability.
  • Biologic fixation philosophy → Perren 2002: controlled micromotion fosters callus; applied via biplanar plates.