Congenital bilateral agenesis of the tibialis anterior muscles: a rare case report

Congenital bilateral agenesis of the tibialis anterior muscles is a rare condition. We present a case of congenital absence of bilateral tibialis anterior muscles in a 6-year-old boy who presented with an abnormal gait. He was previously diagnosed to have bilateral congenital talipes equinovarus (CTEV) deformity for which he underwent corrective surgery two times. However, he still had a residual foot problem and claimed to have difficulty in walking. On examination, he walked with a high stepping gait and muscle power of both lower limbs was 5/5 on the medical research council scale (MRCS) except for both ankle dorsiflexors and long toe extensors. The sensation was intact. Magnetic Resonance Imaging (MRI) study of both legs revealed that tibialis anterior muscles were not visualized on both sides suggestive of agenesis of the tibialis anterior muscles. The rest of the muscles appeared mildly atrophied. The electrophysiological study showed normal motor and sensory conduction in both upper and lower limbs. Electromyographic (EMG) study of the vastus medialis was within normal limit and no response could be elicited for EMG of tibialis anterior muscles suggesting possible absence of tibialis anterior muscles, bilaterally. The patient underwent split tibialis posterior tendon transfer to achieve a balanced and functional foot and was well on discharge. The present case describes the normal anatomy and embryology of tibialis anterior muscles as well as possible causes of its agenesis along with its clinical implications.