What is the likely cause and recommended management for a prominent left ankle roll in a 9‑month‑old infant who crawls and pulls to stand, with no hip abnormalities?

Prominent Left Ankle Roll in a 9-Month-Old Infant

This is most likely a normal physiological variant related to asymmetric fat distribution or early developmental positioning, and reassurance with observation is the appropriate management at this age.

Clinical Assessment

At 9 months, this infant is demonstrating age-appropriate motor milestones (crawling and pulling to stand). The unilateral "prominent leg roll" at the ankle requires systematic evaluation to distinguish normal developmental variation from pathological deformity.

Key Clinical Features to Assess

Immediate evaluation should focus on:

• Foot progression angle during crawling and standing – observe whether the left foot turns inward, outward, or maintains neutral alignment
• Ankle joint range of motion – assess dorsiflexion, plantarflexion, inversion, and eversion symmetry between sides
• Thigh-foot angle – measure tibial torsion by positioning the infant prone with knees flexed to 90 degrees
• Hip rotation – internal and external rotation in prone position to evaluate femoral anteversion
• Actual bony deformity versus soft tissue prominence – palpate to distinguish adipose tissue from structural ankle abnormality
• Weight-bearing alignment – when pulling to stand, observe whether the ankle demonstrates varus, valgus, or neutral alignment 1

Normal Developmental Context

At 9 months, infants commonly have:

• Asymmetric fat distribution that creates apparent "rolls" or fullness, particularly around joints
• Physiological genu varum (bowlegs) that typically persists until approximately 18-24 months before transitioning to neutral alignment 1
• Variable rotational alignment that evolves predictably with growth 2

Differential Diagnosis

Most Likely (Reassurance Appropriate)

• Normal asymmetric adipose tissue distribution – common in healthy infants
• Positional molding from intrauterine positioning – self-correcting postural deformity 3

Requires Further Evaluation

• Unilateral structural deformity – if true bony abnormality is palpable
• Metatarsus adductus – forefoot adduction with heel in neutral position
• Tibial torsion abnormality – excessive internal or external rotation of the tibia 2
• Ankle instability or ligamentous laxity – though extremely rare at this age

Red Flags Requiring Specialist Referral 4

Refer to pediatric orthopedic surgery if:

• Rigid, fixed deformity that does not correct with passive manipulation
• Progressive worsening of asymmetry over serial examinations
• Associated pain, swelling, or functional limitation during weight-bearing activities
• Inability to bear weight or refusal to pull to stand
• Signs of underlying metabolic bone disease (though hip examination was normal, ruling out developmental dysplasia)
• Neuromuscular abnormalities affecting gait or motor development

Management Algorithm

Initial Approach (Primary Care)

1. Perform focused physical examination as outlined above
2. Document baseline measurements of thigh-foot angle, foot progression angle, and ankle range of motion
3. Photograph the finding for comparison at follow-up visits

If Examination Shows Soft Tissue Prominence Only

Reassure parents that asymmetric fat distribution is normal and self-resolving. Schedule follow-up at 12-month well-child visit to reassess. No imaging or intervention needed 3.

If Examination Reveals Structural Abnormality

• Flexible deformity (corrects passively): Observe with serial examinations every 2-3 months. Most resolve spontaneously by age 2 years 1, 3
• Rigid deformity (does not correct passively): Refer to pediatric orthopedic surgery for evaluation 4
• Progressive deformity on serial examinations: Refer to pediatric orthopedic surgery 4

Imaging Considerations

Radiographs are NOT indicated at 9 months for isolated soft tissue prominence without functional impairment, as tarsal bones are largely cartilaginous and poorly visualized 5.

Ultrasound may be useful if structural ankle abnormality is suspected, as it visualizes cartilaginous structures and permits dynamic assessment 5.

Common Pitfalls to Avoid

• Over-imaging infants with normal developmental variants – most "deformities" at this age are physiological and self-correcting
• Prescribing corrective shoes or braces – current evidence does not support their use for physiological variants, and they do not improve outcomes beyond natural correction 3
• Delaying referral for truly rigid or progressive deformities – early specialist evaluation is appropriate when red flags are present 4
• Confusing adipose tissue prominence with structural deformity – careful palpation distinguishes these

Prognosis

If this represents normal asymmetric fat distribution or flexible postural deformity, complete spontaneous resolution is expected as the infant grows and motor development progresses. The achievement of motor milestones (crawling, standing) at appropriate ages is reassuring and suggests no underlying neuromuscular or structural pathology 6.