Classification system for flexor digitorum accessorius longus muscle variants within the leg: clinical correlations

Area of Science:

• Anatomy
• Orthopedics
• Surgical Anatomy

Background:

• The flexor digitorum accessorius longus (FDAL) is an accessory muscle in the leg.
• This variant muscle can cause tarsal tunnel syndrome by compressing the tibial nerve.

Purpose of the Study:

• To classify anatomical variants of the FDAL.
• To correlate these variants with clinical presentations of tarsal tunnel syndrome.
• To elucidate the topographical relationship between the FDAL and the posterior tibial neurovascular bundle (PTNV).

Main Methods:

• Dissection of 80 embalmed Korean cadaver lower limbs.
• Classification of FDAL variants based on origin and relationship to the PTNV.
• Correlation of dissection findings with MRI from two clinical tarsal tunnel syndrome cases attributed to FDAL.

Main Results:

• The FDAL was present in 11.3% of specimens.
• Three types of FDAL were identified: Type I (origin in leg, superficial to PTNV), Type II (origin in tarsal tunnel).
• Clinical cases correlated with Type Ia and Type II FDAL variants.

Conclusions:

• The FDAL, in its various forms, can cause tibial nerve compression in the tarsal tunnel or distal leg.
• Understanding the anatomical variations and spatial relationship of the FDAL to the PTNV is crucial for surgical management of FDAL-induced tarsal tunnel syndrome.