Anomalous plantar intrinsic foot muscle attaching to the medial longitudinal arch: possible mechanism for medial nerve entrapment: a case report

BACKGROUND: Muscular variations are potentially symptomatic and may complicate imaging interpretation. Intrinsic foot musculature and extrinsic tendon insertion variations are common. Distinct supernumerary muscles are rare. We report a novel anomalous intrinsic foot muscle on the medial longitudinal arch. CASE PRESENTATION: An accessory muscle was encountered on the medial arch of the right foot of a 78-year-old white male cadaver, between layers two and three of the foot intrinsics. It did not appear to be a slip or variant of a known foot muscle. This muscle consisted of two slips that ran transversely on the plantar aspect of the medial arch, crossing the medial transverse tarsal joint and attaching to the tuberosity of the navicular, the short and long plantar ligaments, and spring ligament. CONCLUSIONS: The medial plantar vessels and nerve passed from deep to superficial between the two slips, and this suggests a possible location for medial nerve entrapment.