Cadaveric study of zone 2 flexor hallucis longus tendon sheath

Purpose: The purpose of this study was to investigate the anatomy of the zone 2 flexor hallucis longus (FHL) tendon sheath.

Methods: Dissection of the zone 2 FHL tendon sheath was performed in 12 feet of 6 cadavers. The tendon sheath was subdivided into proximal fibrous (zone 2A) and distal fascial (zone 2B) parts. The lengths of the zone 2A and 2B FHL tendon were measured and represented the length of the corresponding tendon sheaths, and the relation of the medial plantar nerve to each part of the zone 2 FHL tendon sheath was studied.

Results: In all specimens there were fibrous and fascial components of the zone 2 FHL tendon sheath. The medial plantar nerve crossed the zone 2B tendon sheaths and then became plantar lateral to the sheath in 7 specimens. The distance between the medial plantar nerve and the orifice of the zone 2A tendon sheath averaged 7.6 mm. The distance between the medial plantar nerve and the junction between zones 2A and 2B averaged 3.2 mm. The distance between the medial plantar nerve and the distal end of the zone 2B tendon sheath averaged 4.2 mm. The mean length of the zone 2A tendon sheath was 35.9 mm, and the mean length of the zone 2B tendon sheath was 30.5 mm.

Conclusions: The zone 2 FHL tendon sheath can be subdivided into a proximal fibrous zone (2A) and a distal fascial zone (2B). Because of the close proximity of the medial plantar nerve to the tendon sheath, there is a significant risk of iatrogenic nerve injury when surgical procedures are performed in zone 2B.

Clinical relevance: An understanding of the anatomy of the zone 2 FHL tendon sheath is useful for the safe practice of zone 2 FHL tendoscopy.