Surgical Correction of Juvenile Bunion

B. David Horn

DEFINITION

Adolescent bunion is a multifactorial, complex deformity consisting of medial deviation of the first metatarsal (metatarsus primus varus), lateral deviation of the great toe through the first metatarsophalangeal joint (hallux valgus), and enlarged medial eminence of the distal first metatarsal.²^, ³^, ⁴^, ⁶
Other findings include contracted lateral and lax medial soft tissues of the first metatarsophalangeal joint, lateral subluxation of the sesamoids, pronation of the great toe, plantar subluxation of the abductor hallucis muscle, and generalized ligamentous laxity, flexible pes planus, and gastrocnemius contracture.

ANATOMY

Metatarsus primus varus resulting in increased intermetatarsal (IM) angle²^, ³
Obliquity of the medial cuneiform-first metatarsal joint²^, ³
Medial prominence of the first metatarsal head
Valgus angulation through the first metatarsophalangeal joint²^, ³
Minimal or no deformity through the first interphalangeal joint
Lateral translation of sesamoids
Plantar-lateral positioning of the abductor hallucis with unopposed pull of the adductor hallucis muscle
Lateral subluxation of the extensor hallucis longus and flexor hallucis longus tendons
Pronation (internal rotation) of the first toe
Differs from an adult bunion
- Physis of the first metatarsal and proximal phalanx are located proximally (this limits ability to perform proximal osteotomies in skeletally immature patients).
- The first metatarsophalangeal joint does not have osteoarthrosis.
- The medial eminence is less prominent in adolescent bunions than in adult bunions.

PATHOGENESIS

Multiple theories exist; it is difficult to differentiate primary findings from secondary ones.²^, ³^, ⁶
Extrinsic and intrinsic factors contribute to formation of adolescent bunions.
Intrinsic
- Metatarsus primus varus
- Obliquity of the medial cuneiform-first metatarsal joint
- Long first metatarsal
- Ligamentous laxity
- Heel cord contracture causes foot pronation, which in turn places a valgus force on the hallux while walking
Extrinsic
- Shoe wear, particularly those with a narrow toe and elevated heel

NATURAL HISTORY

Natural history is believed to be favorable. Most patients with adolescent bunions can be treated nonoperatively.²^, ⁵

PATIENT HISTORY AND PHYSICAL FINDINGS

Patients typically present in late childhood or adolescence.²^, ³
Complaints about appearance of foot
Complaints of pain over the medial exostosis or about the first metatarsophalangeal joint
Pain is exacerbated by shoe wear.
Complaints about finding shoes that are comfortable
Physical examination²^, ³
- Areas of tenderness: first metatarsophalangeal joint, medial prominence
- Alignment when standing and walking
- Mobility of first metatarsophalangeal joint
- Skin condition: the clinician should search for calluses, areas of irritation
- Foot and ankle range of motion
Careful neurologic examination