Flexor accessorius longus: A rare variationof the deep extrinsic digital flexors of the leg and its phylogenetic significance

ABSTRACT

Anomalies of the calf muscles are rare. One such anomalous muscle, known as the Muscle Flexor accessorius longus (also named accessorius ad accessorium, accessorius secondus, accessory flexor digitorum longus or pronator pedis) is of morphological significance. When present, this originates in the deep fascia of the tibia or fibula and inserts in the foot either into the flexor digitorum accessorius or into the tendons of the flexor digitorum longus. In this report we present a discussion of the morphological significance and phylogenetic history of one such muscle observed. In this case report we describe an anomalous calf muscle which extends from the popliteal region, runs along the posterior compartment of the leg, reaches the sole and is inserted to the flexor digitorum longus muscle. This kind of muscle variations are considered to be the higher origin of the flexor digitorum accessorius muscle of the sole. Here we discuss the phylogenetic history of this muscle as this muscle variant is present in some primitive mammals, absent in apes and in this particular case appeared as one of the muscles of the flexor compartment of the leg.

KEY WORDS

Flexor accessorius longus - flexor digitorum accessorius - foot - muscular variations

• 1 Macalister A. Additional observations on muscular anomalies in human anatomy (3rd series) with a catalogue of the principal muscular variations hitherto published. Trans Royal Ir Acad 1875; 25: 1-134
• 2 Testut L. Les anomalies musculaires chez I’homme. Masson Paris: 1884: p. 688-94
• 3 Le AFDouble. Traitι des variations du systθme musculaire de I’homme et de leur signification an point de I’ anthropologie zoologique. vol Librarie W, Reinwald C. Schleicher Frθres; Paris: 1897: p. 402-6
• 4 Wood J. Variations in human myology observed during the winter session of 1867-68 at King’s College. London: Proc Roy Soc. 1868. (; 16). 483-525
• 5 Bergman RA, Thompson SA, Afifi AK, Saadeh FA. Compendium of human anatomic variation. Urban and Schwarzenberg; Baltimore: 1988: p. 27-8
• 6 Resser LA, Susman RL, Stern J. Electgromiographyic studies of the human foot: Experimental approaches to hominid evolution. Foot and Ankle 1983; 3: 391-407
• 7 Wood JF. Structure and Function as seen in the Foot. 2nd ed. Bailliere, Tindall and cox; London, England: 1949: p. 157 (; 188). 225
• 8 Nathan H, Gloobe H, Yosipovitch Z. Flexor digitorum accessorius longus. Clin Orthop Relat Res 1975; 113: 158-61