Proximal medial tibial metaphyseal bump-a normal variant.

Background: Skeletal abnormalities are important to recognize in the workup of physical child abuse. Normal variants can simulate child abuse and cause incorrect diagnosis and management. An osseous protuberance of the proximal medial tibial metaphysis, "the tibial bump," is a normal variant that is important to recognize.

Objective: To determine the prevalence of a tibial bump in infants undergoing a skeletal survey for a child abuse evaluation.

Materials and methods: A retrospective study of initial and follow-up child abuse skeletal surveys at a tertiary center was conducted to assess for the presence of a tibial bump on the proximal medial tibial metaphysis. The presence or absence of fracture healing changes around the tibial bump was recorded.

Results: Twenty of two hundred sixty cases showed a tibial bump on the initial skeletal survey, estimating a prevalence of 7.7%. Fourteen of these twenty cases (70%) demonstrated a persistent tibial bump unchanged in appearance on the follow-up skeletal survey. None of the tibial bumps demonstrated findings of a healing fracture on the initial or follow-up skeletal survey. In cases with a tibial bump present, 10 (50%) were bilateral and 10 were unilateral (50%). The mean (median) age of a child with a tibial bump was 3.5 (2.9) months with a range from 1 to 8 months, and there was a statistically significant association between age and the presence of a bump, supporting that this is a finding of infancy (P = 0.04).

Conclusion: A tibial bump on the proximal medial tibial metaphysis was a relatively common finding in infants undergoing workup for child abuse and not radiographically consistent with a fracture. It is a normal variant and should not be confused with a traumatic finding.