Introduction / Definition

Hallux valgus (HV) is a progressive, triplanar subluxation of the first metatarsophalangeal (MTP) joint characterised by lateral deviation and axial pronation of the hallux accompanied by medial deviation (varus) of the first metatarsal. Although colloquially termed a 'bunion' (referring to the prominent medial exostosis and overlying adventitious bursa), the condition is a multifactorial structural malalignment involving transverse, sagittal, and coronal planes rather than simple isolated lateral drift.

Epidemiology

Hallux valgus is among the most prevalent forefoot pathologies encountered in orthopaedic practice. Population-based epidemiological studies indicate a pooled overall prevalence of approximately 23% in adults aged 18–65 years, escalating to over 35% in individuals aged 65 and older. It demonstrates a marked female predilection (female-to-male ratio ranging between 2:1 and 4:1), predominantly attributable to footwear factors, ligamentous laxity, and anatomical variations.

Etiology

• Extrinsic Factors: Constrictive footwear (narrow toe boxes, elevated heels) exacerbates deformities by loading the forefoot and forcing the hallux laterally. High heels transfer up to 75% of body weight across the forefoot.
• Intrinsic Factors:
  • Genetic predisposition (strong familial clustering; maternal transmission often reported).
  • Ligamentous laxity (e.g. generalised hypermobility, Marfan syndrome, Ehlers-Danlos syndrome).
  • Anatomical variants: pes planovalgus (loss of the medial longitudinal arch leading to dynamic metatarsus primus varus), tight gastrocnemius/Achilles complex, long first metatarsal relative to the second, rounded first metatarsal head (inherently less stable than a flat articular surface), and metatarsus adductus.
  • Inflammatory arthropathies (rheumatoid arthritis leading to capsular destruction and joint subluxation).
  • Neuromuscular imbalance (cerebral palsy, stroke, Charcot-Marie-Tooth disease).

Relevant Anatomy & Pathophysiology

Bony & Capsular Architecture

The first ray consists of the medial cuneiform, first metatarsal, proximal phalanx, distal phalanx, and two sesamoids within the flexor hallucis brevis (FHB) tendons. The head of the first metatarsal normally articulates with the proximal phalanx and the sesamoid apparatus, separated plantarly by a longitudinal osseous ridge called the crista.

Pathomechanics of Deformity Evolution

1. Capsuloligamentous Attenuation: Attenuation and attenuation of the medial collateral ligament and medial MTP capsule permit the first metatarsal head to drift medially off the sesamoid sling.
2. Sesamoid Subluxation: The sesamoids are anchored firmly to the second metatarsal via the transverse intermetatarsal ligament. Consequently, as the first metatarsal head migrates medially, the sesamoid complex appears relatively displaced laterally into the intermetatarsal space on standard AP radiographs (with the tibial sesamoid eroding or subluxing over the crista).
3. De-centring of Dynamic Tendon Vectors:
   • Adductor Hallucis: Inserts into the lateral sesamoid and base of the proximal phalanx, exerting an unopposed lateral and pronatory pull.
   • Extensor Hallucis Longus (EHL) & Flexor Hallucis Longus (FHL): Shift laterally to the centre of rotation, bowing laterally and functioning as pathological adductors (bowstring effect), worsening the deformity.
   • Abductor Hallucis: Shifts plantarly beneath the metatarsal head, losing its capacity to resist valgus drift and instead contributing to hallux pronation.
4. First Ray Hypermobility & Transfer Metatarsalgia: Incompetence of the first ray reduces plantar load transmission beneath the first metatarsal head, redistributing excessive ground reaction forces laterally across the lesser metatarsal heads (transfer metatarsalgia, intractable plantar keratoses, and secondary clawing or hammer toes).

Classification & Radiological Parameters

Clinical grading is guided by standardised weight-bearing radiographs. The widely adopted Coughlin and Mann classification stratifies hallux valgus into mild, moderate, and severe categories:

| Severity | Hallux Valgus Angle (HVA) | 1st–2nd Intermetatarsal Angle (IMA) | Sesamoid Subluxation (Tibial Sesamoid) | MTP Joint Congruence | | :--- | :--- | :--- | :--- | :--- | | Mild | < 20° | ≤ 11° | < 50% displacement | Usually congruent | | Moderate| 20°–40° | 12°–16° | 50%–75% displaced | Incongruent / subluxated | | Severe | > 40° | > 16° | > 75% subluxated / displaced | Incongruent / subluxated |

Essential Angular Measurements

• Hallux Valgus Angle (HVA): Angle subtended by the long axis of the first metatarsal shaft and the proximal phalanx (Normal: < 15°).
• Intermetatarsal Angle (IMA): Angle between the longitudinal axes of the first and second metatarsals (Normal: < 9°).
• Distal Metatarsal Articular Angle (DMAA): Angle between the perpendicular to the first metatarsal longitudinal axis and a line traversing the distal articular surface (Normal: < 10°). An elevated DMAA denotes intrinsic articular tilt requiring an intra-articular corrective cut (e.g. biplanar chevron).
• Hallux Valgus Interphalangeus (HVI): Angle between the long axes of the proximal and distal phalanges (Normal: < 10°).
• Metatarsus Adductus Angle (MAA): Axis of the lesser tarsus relative to the second metatarsal (Normal: < 15°–20°). Severe adductus falsely masks true metatarsus primus varus and significantly increases the risk of recurrence following isolated distal corrections.

Clinical Presentation & Examination

History

• Symptoms: Localised medial bunion pain aggravated by shoe contact; footwear restriction; difficulty finding accommodating footwear.
• Associated Pain: Plantar forefoot pain beneath the second and third metatarsal heads (transfer metatarsalgia); dorsal pain over contracted lesser toes.
• Functional Goals: Ambulation distance, employment requirements, and sporting expectations.
• Past Medical History: Diabetes, peripheral vascular disease, inflammatory arthritides, smoking, and connective tissue disorders.

Physical Examination (Standing & Seated)

• Standing Assessment: Evaluate overall foot posture (pes planus, hindfoot valgus, Achilles tightness with the Silfverskiöld test), toe alignment, and clawing/hammering of the second ray.
• Medial Eminence: Inspect for ulceration, erythema, bursitis, and the status of the dorsomedial cutaneous nerve (often irritated or compressed).
• MTP Joint Evaluation:
  • Assess active and passive range of motion in sagittal and coronal planes (pain through mid-arc indicates articular degenerative change/osteoarthritis).
  • Passive reducibility of the hallux to neutral position (assesses whether the deformity is fixed or flexible).
  • Joint stability and assessment of first carpometatarsal (TMT-1) sagittal hypermobility.
• Lesser Rays: Palpate for plantar callosities (calluses under the second metatarsal head), assess transverse arch tenderness (Morton neuroma), and examine lesser MTP instability (vertical drawer / Lachman test of the second MTP joint for plantar plate insufficiency).
• Vascular & Neurological Exam: Distal pulses (dorsalis pedis, posterior tibial), capillary refill, and protective sensation (10 g monofilament).

Investigations

• Weight-Bearing Plain Radiographs (Mandatory Standard):
  • AP, Lateral, and Oblique views of the foot: Weight-bearing is obligatory; non-weight-bearing radiographs significantly underestimate both HVA and IMA.
  • Sesamoid Axial View: Evaluates sesamoid subluxation, crista erosion, and osteoarthritic changes in the articulation between the first metatarsal head and sesamoids.
• Advanced Imaging:
  • Weight-Bearing CT (WBCT): Increasingly utilised to objectively quantify the 3D coronal rotation (pronation) of the first metatarsal and precise sesamoid positioning.
  • MRI / Ultrasound: Reserved for suspected plantar plate ruptures of the lesser toes, osteonecrosis of the metatarsal head, or interdigital neuromas.

Management

Non-Operative Management

Conservative treatment represents the primary initial approach for all patients, as surgery is purely elective and contraindicated for cosmetic desires alone.

• Footwear Modification: Shoes with a wide, deep toe-box, soft leather uppers, low heels, and seamless construction over the bunion.
• Orthoses: Medial arch supports to manage concurrent flexible planovalgus; metatarsal pads or dome bars placed proximal to the lesser metatarsal heads to offload transfer metatarsalgia.
• Splints & Spacers: Silicone interdigital toe spacers and dynamic night splints can alleviate soft-tissue tension and bursal pain, though they do not permanently halt or correct structural osseous progression.
• Analgesia & Activity Modification: Simple analgesics (paracetamol, topical/systemic NSAIDs) and avoidance of provocative high-impact loading.

Operative Management

Surgical intervention is indicated when conservative measures fail to provide adequate pain relief and the deformity interferes significantly with activities of daily living. Operative choice is governed by severity, joint congruency, articular cartilage status, and first TMT joint stability.

1. Distal Metatarsal Osteotomies

• Indications: Mild to moderate hallux valgus (HVA < 30°–35°, IMA < 13°–15°).
• Distal Chevron (Austin) Osteotomy: A 60° V-shaped horizontal osteotomy in the metatarsal head with lateral translation of the capital fragment (usually up to 30%–50% of the bone width) and rigid screw fixation. Can incorporate a wedge resection (biplanar chevron) to correct an elevated DMAA.
• Distal Soft-Tissue Release (Silver / Modified McBride): Performed in conjunction with osteotomies; involves medial capsulorraphy, lateral capsular release, adductor hallucis tenotomy, and lateral sesamoid suspensory ligament release (avoiding complete lateral sesamoid excision to prevent hallux varus).

2. Diaphyseal & Midshaft Metatarsal Osteotomies

• Indications: Moderate to severe hallux valgus (IMA 14°–20°).
• Scarf Osteotomy: A longitudinal Z-step osteotomy of the metatarsal shaft allowing substantial lateral translation, slight plantarflexion/shortening, and coronal rotation. Inherently stable due to broad cancellous contact surfaces; typically secured with two small-fragment cannulated compression screws.
• Mau / Ludloff Osteotomies: Oblique shaft osteotomies designed to rotate and translate the distal fragment, indicated for wide IMAs.

3. Proximal Metatarsal Osteotomies

• Indications: Severe deformities (IMA > 16°–18°) with a congruent or reducible MTP joint.
• Techniques: Proximal crescentic, proximal closing wedge, or proximal opening wedge osteotomies. Because proximal osteotomies yield a significant corrective leverage arm, small shifts dramatically diminish the IMA. However, they carry an elevated risk of first-ray elevation (dorsiflexion nonunion/malunion), necessitating meticulous rigid plate or screw fixation.

4. First Tarsometatarsal (Lapidus) Arthrodesis

• Indications: Severe hallux valgus (IMA > 18°–20°), significant first-ray hypermobility/instability, generalised ligamentous hyperlaxity, recurrent hallux valgus, or coexistent severe planovalgus.
• Technique: Articular preparation of the first TMT joint, triplanar correction (adduction, plantiflexion, and supination to derotate the pronated metatarsal), and stable compression plating or crossed-screw fixation. Often combined with a distal soft-tissue release.

5. First MTP Joint Arthrodesis

• Indications: Severe hallux valgus with established first MTP osteoarthritis (hallux rigidus), inflammatory arthritis (rheumatoid arthritis), severe salvage/recurrence, or severe fixed deformities in elderly or low-demand patients.
• Target Position for Fusion:
  • 10°–15° of valgus.
  • 15°–20° of dorsiflexion relative to the plantar aspect of the foot (or 5–10 mm clearance from the ground with the foot flat).
  • Neutral rotation (parallel to lesser nail plates).
• Fixation: Cup-and-cone reamer preparation secured with a dorsal low-profile locking plate and an interfragmentary lag screw.

6. Phalangeal Osteotomy (Akin Osteotomy)

• Indications: Medial closing wedge osteotomy of the proximal phalanx base. Never indicated as an isolated procedure for hallux valgus; used purely as an adjunct to correct persistent distal hallux valgus interphalangeus (HVI > 10°) or residual valgus after correction of the IMA.

7. Minimally Invasive Surgery (MIS / PECA)

• Technique: Percutaneous Endosteal Chevron Akin (PECA) and 3rd-generation MIS utilize high-torque, low-speed burrs under fluoroscopy through stab incisions, fixed with percutaneous cannulated screws.
• Evidence: Demonstrated equivalent mid-term clinical outcomes and faster initial soft-tissue recovery compared to open surgery in experienced hands, though accompanied by a distinct technical learning curve.

Complications

• Recurrence (Under-correction): The most common complication (occurring in 5%–15% of cases). Caused by failing to address a wide IMA, ignoring an elevated DMAA or metatarsus adductus, or unrecognised first-ray hypermobility.
• Over-correction (Hallux Varus): Arises from excessive lateral release, over-resection of the medial eminence (staking the metatarsal head), or over-translation of the osteotomy.
• Avascular Necrosis (AVN) of the Metatarsal Head: Risk is accentuated by aggressive lateral capsular stripping combined with distal osteotomy cuts that compromise the dorsolateral nutrient vessels (branches of the first dorsal metatarsal artery and deep plantar arch). Reported rates with modern technique remain < 2%.
• Transfer Metatarsalgia: Occurs if the first metatarsal is excessively shortened or elevated (dorsiflexion malunion), transferring load to the second metatarsal head.
• Nerve Injury: Entrapment, neuroma, or transection of the dorsomedial cutaneous branch of the superficial peroneal nerve or terminal branches of the deep peroneal nerve, resulting in medial numbness or painful neuroma.
• Nonunion / Malunion: Most common after Lapidus arthrodeses (nonunion rate ~5%–10%) and proximal metatarsal osteotomies.
• Stiffness: Arthrofibrosis of the first MTP joint, typically mitigated by early active rehabilitation post-fixation.

Exam Pearls for Fellowship Vivas

• Cosmesis is Never an Indication: Operating purely for cosmetic reasons is universally penalised in FRCS/EBOT vivas due to unpredictable satisfaction and the risk of chronic post-surgical pain.
• Never Akin Alone: An Akin osteotomy corrects hallux valgus interphalangeus, not metatarsus primus varus. If performed alone in primary hallux valgus, recurrence and rapid joint decompensation are inevitable.
• Beware of Metatarsus Adductus: Always assess the metatarsus adductus angle. An unrecognised adducted lesser tarsus will push the first metatarsal into apparent relative varus; performing standard distal translation without factoring this in leads to early recurrence.
• The Staked Head: Resecting the medial prominence past the sulcus (over-resection of the sagittal groove) disrupts joint mechanics, causing medial subluxation of the proximal phalanx and iatrogenic hallux varus.
• Position of First MTP Fusion: State the numbers precisely: 10°–15° valgus, 15°–20° dorsiflexion to the plantar ground plane (or 25°–30° relative to the first metatarsal shaft), and neutral axial rotation with the pulp resting ~5 mm clear of the floor.