Foot & Ankle — Hallux Valgus

Hallux valgus (HV) is the most common forefoot deformity, characterised by lateral deviation of the great toe at the first metatarsophalangeal (MTP) joint, medial prominence of the first metatarsal head (the `bunion`), and progressive deformity of the first ray. It is a complex three-dimensional deformity involving not just the MTP joint but the entire first ray — including pronation of the hallux, sesamoid subluxation, and frequently a widened first-second intermetatarsal angle. Understanding the radiological measurements, surgical thresholds, and the growing role of correction of pronation are essential for the practising orthopaedic surgeon.

• Epidemiology: prevalence approximately 23% in adults; female predominance (10:1); strongly associated with wearing narrow-toed shoes (exacerbates but does not cause the deformity); familial predisposition (autosomal dominant with variable penetrance); bilateral in approximately 70% of cases; incidence increases with age
• Pathoanatomy: the deformity begins with hypermobility of the first tarsometatarsal (TMT) joint or intrinsic ligamentous laxity; the first metatarsal drifts medially (increased intermetatarsal angle — IMA); the hallux deviates laterally (increased hallux valgus angle — HVA); the medial capsule of the MTP joint stretches while the lateral structures (lateral capsule, adductor hallucis, fibular sesamoid) tighten; the sesamoids sublux laterally relative to the first metatarsal head; the hallux pronates (the nail rotates medially); the plantar plate and collateral ligaments are progressively disrupted; the deformity becomes self-perpetuating
• Associated conditions: metatarsus primus varus (increased IMA, often structural); hypermobile first TMT joint (Lapidus procedure indicated); first MTP joint OA (bunion arthritis); lesser toe deformities (hammer toes, crossover second toe from the hallux pushing laterally); transfer metatarsalgia (overloading of the lesser metatarsals after first ray deformity)

• Radiographs: weight-bearing AP and lateral views of the foot; weight-bearing is essential — non-weight-bearing views underestimate the deformity; the sesamoid position is assessed on the AP view (Grade 1–7 sesamoid subluxation — the lateral sesamoid`s position relative to the crista of the first metatarsal head indicates the degree of deformity)
• Metatarsus adductus: if the lesser metatarsals angle medially (metatarsus adductus, Engel angle >15°), correction of the hallux valgus alone without addressing the adductus will leave residual forefoot deformity; metatarsus adductus is an important concomitant finding to assess pre-operatively

• Non-operative treatment does not correct or halt the deformity but may relieve symptoms: wide-toed footwear; toe spacers/separators; bunion pads for medial prominence; night splints (do not correct the deformity); custom orthotics (to offload the medial border and correct flexible flat foot contributing to the deformity); activity modification
• Indications for surgery: symptomatic hallux valgus that has failed non-operative management for at least 3–6 months; the deformity itself is not an indication — the patient must have functional impairment or pain; surgery is generally deferred until skeletal maturity in adolescents (operating on an immature skeleton has high recurrence rates); asymptomatic hallux valgus in an elderly patient with minimal footwear issues rarely requires surgery

• Hallux valgus pronation and the TMIC concept: modern understanding of hallux valgus recognises that the deformity is three-dimensional; in addition to the lateral deviation (HVA) and IMA, the hallux pronate (the nail faces medially rather than dorsally); this pronation is driven by the pronated first metatarsal at the TMT joint (the metatarsal rotates into pronation as it deviates medially); the Tibial sesamoid position (the relationship of the tibial sesamoid to the first metatarsal head) reflects the pronation; correction of pronation is now incorporated into modern osteotomies (the Scarf osteotomy can be rotated to depronated the metatarsal); the Lapidus procedure directly corrects pronation at the TMT joint; failing to address pronation is a cause of `under-corrected` hallux valgus
• Hallux varus — the over-correction complication: iatrogenic hallux varus (medial deviation of the great toe) is the most feared complication of hallux valgus surgery; it occurs when the lateral release is too aggressive (overcorrecting the lateral structures), the osteotomy over-corrects the IMA, or the medial capsule is over-tightened; results in a cosmetically unacceptable deformity and may impair weight-bearing; mild hallux varus can be treated by extensor hallucis brevis tendon transfer; severe hallux varus may require MTP arthrodesis
• Minimally invasive surgery (MIS) for hallux valgus: percutaneous and minimally invasive osteotomy techniques (e.g., MICA — minimally invasive chevron Akin; Bösch technique) are increasingly popular; the burr is used percutaneously to create the osteotomy through stab incisions; preliminary evidence shows equivalent deformity correction to open techniques with potentially faster recovery and lower wound complication rates; the learning curve is significant and fluoroscopic guidance is required; this is an active area of development in foot and ankle surgery

• HVA normal <15°; IMA normal <9°; mild HV: HVA 15–20°; moderate: HVA 20–40°, IMA 11–16°; severe: HVA >40°, IMA >16°
• Weight-bearing X-rays mandatory — non-weight-bearing underestimates deformity
• Chevron: mild-moderate HV (HVA <30–35°, IMA <13°); distal V osteotomy; +/- Akin; most common procedure
• Scarf: moderate-severe (HVA <40°, IMA <16–18°); Z diaphyseal; corrects rotation (DMAA); troughing complication = metatarsal fracture/subluxation
• Lapidus (1st TMT arthrodesis): IMA >16°; hypermobile 1st ray; recurrent HV; most powerful IMA correction; corrects pronation; 6 weeks NWB; non-union risk
• Akin: proximal phalanx closing wedge; corrects hallux valgus interphalangeus (HIPA); NEVER standalone — always adjunct to metatarsal osteotomy
• 1st MTP arthrodesis: for OA, inflammatory arthropathy, neuromuscular deformity, failed previous surgery; fused at 10–15° valgus + 20–25° dorsiflexion; most reliable long-term result
• Hallux varus: over-correction complication; too aggressive lateral release + over-correction osteotomy; EHB tendon transfer (mild) or MTP arthrodesis (severe)
• Pronation correction: 3D nature of HV — pronation of hallux; Lapidus corrects at TMT level; Scarf can de-pronate; failure to address pronation = under-correction
• Surgery indication: SYMPTOMS failing non-operative treatment; not the deformity alone; defer until skeletal maturity in adolescents