Juvenile Hallux Valgus

Juvenile Hallux Valgus is defined as the onset of hallux valgus deformity before skeletal maturity (usually less than 14-16 years).

• Epidemiology: Distinct from congenital hallux valgus (present at birth) and adult acquired hallux valgus.
• Genetics: High familial penetrance (Autosomal dominant with incomplete penetrance). 70% of patients have an affected mother.
• Pathomechanics: Often related to Metatarsus Primus Varus (medial deviation of the first metatarsal) and a sloping distal articular surface (High DMAA). Ligamentous laxity allows the first ray to drift medially while the toe stays laterally.

Key Deforming Forces:

1. Metatarsus Primus Varus: The primary deformity is the varus of the first metatarsal.
2. DMAA (Distal Metatarsal Articular Angle): This defines the orientation of the cartilage of the metatarsal head relative to the shaft. In juveniles, this is often "dysplastic" (tilted laterally).
3. Congruency: Because the articular surface is tilted, the joint surfaces remain parallel (congruent) despite the valgus appearance.
4. Pes Planus: Pronation of the foot unlocks the midtarsal joint, increasing mobility of the first ray and effectively increasing the IMA.

Growth Plates:

• The first metatarsal physis is PROXIMAL.
• The proximal phalanx physis is PROXIMAL.
• Distal metatarsal osteotomies (Chevron/Mitchell) are performed distal to the physis, but care must be taken not to violate it if still open.

History:

• Pain: Is it over the bunion (medial eminence) or inside the joint?
• Cosmesis: Often the driving factor for parents/teenagers. Manage expectations firmly.
• Family Hx: "Does your mum have bunions? How did her surgery go?"

Physical Exam:

1. Standing: Assess hindfoot valgus and arch height. Correct the heel valgus - does the bunion improve?
2. First Ray Mobility: Check for hypermobility (sagittal plane motion).
3. Congruency Test: Reduce the HVA to neutral. Does the toe rotate? Does the ROM decrease? If motion is blocked when straight, the joint is Congruent (High DMAA).
4. Grind: Check for crepitus/arthritis (rare).

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Plain Radiographs (Weightbearing is Mandatory):

• IM Angle (Intermetatarsal): Separation between 1st and 2nd metatarsal shafts.
• HV Angle (Hallux Valgus): Angle between 1st metatarsal and proximal phalanx.
• DMAA: Angle between the articular surface of the head and the shaft axis. Normal is less than 10 degrees. In Juvenile HV, often 20-30 degrees.
• Physeal Status: Are the growth plates open or closed?

Sesamoid View:

• Check for subluxation and rotation of the metatarsal head (Crista erosion is rare in kids).

1. Respect the Physis If performing a distal chevron osteotomy in a child with an open physis:

• The cut must remain DISTAL to the physis (which is proximal in the metatarsal, but wait - the metatarsal head physis is PROXIMAL? No, 1st Metatarsal physis is PROXIMAL. The Head physis is in the lesser metatarsals. This is a common exam trap).
• Correction: 1st Metatarsal Physis is PROXIMAL. Lesser Metatarsals are DISTAL.
• So a Distal Chevron is SAFE from the physis.
• However, a PROXIMAL osteotomy (Scarf/Base Wedge) puts the physis at risk.

2. The DMAA Correction How to correct a high DMAA intra-operatively?

• Biplanar Chevron: Instead of just shifting the head lateral, you must tilt it medially (take a wedge out of the medial side of the chevron limb) to reorient the cartilage.
• Reverdin Procedure: A specific wedge osteotomy behind the articular surface to correct DMAA.

3. Modified McBride

• Avoid extensive lateral release in congruent joints. It causes instability.
• Avoid excision of the lateral sesamoid.

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• Immobilization: Heel-wedge shoe or Cast for 6 weeks.
• Weightbearing: Heel weightbearing allowed usually (if stable osteotomy).
• X-rays: Check at 2 weeks (position) and 6 weeks (union).
• Return to Sport: 3-4 months.

• Satisfaction: Generally lower than adults due to unrealistic cosmetic expectations and stiffness.
• Long Term: Recurrence is the major issue. Many require revision in adulthood.
• Function: Most return to sport, but range of motion is often permanently reduced compared to normal.

• Referral: Most GPs refer these to Orthopaedic Surgeons, not Podiatrists, due to the complexity of open growth plates.
• Waitlists: Public hospital waitlists can be long; often the child matures while waiting, which simplifies the surgical decision making.

The Silent Killer of Success The Distal Metatarsal Articular Angle (DMAA) represents the "tilt" of the cartilage on the metatarsal head.

• Normal: less than 10 degrees (Cartilage faces straight).
• Abnormal: greater than 15-20 degrees (Cartilage faces lateral).
• Mechanism: If you act like a carpenter and just straighten the shaft (move the head lateral), but don't change the TILT, the toe will point medial but the joint will be crooked (incongruent). The toe will naturally drift back into valgus to make the joint happy (congruent).
• Solution: You must cut a wedge out of the bone to rotate the articular surface back to neutral (Reverdin or Biplanar Chevron).

Measuring DMAA

1. Draw the axis of the first metatarsal.
2. Draw a line connecting the medial and lateral margins of the articular surface.
3. The angle should be less than 10 degrees. If it is 20-30 degrees, it is dysplastic.

The Historical Answer to DMAA Described by Jacques Reverdin in 1881, long before the Chevron.

• Concept: A closing wedge osteotomy of the metatarsal HEAD (sub-capital).
• Goal: Solely changes the orientation of the articular surface (DMAA). It does NOT correct the IMA.
• Modern Use: Rarely used in isolation. Often combined with a shaft osteotomy (double osteotomy) or modified (Reverdin-Laird) to shift the head as well.
• Technique: Remove a medial wedge of bone just behind the cartilage. Close it down. This rotates the cartilage to face medially.