Takaya Ishii1,2, Kyutaro Kawagishi3,4, Shogo Hayashi5, Shinnosuke Yamada2, Hirotaka Yoshioka2, Yoshiharu Matsuno6, Yasutake Mori1,2, Jun Kosaka1,2. 1. Department of Basic Medical Science, Graduate School of Medicine, International University of Health and Welfare, 4-3 Kozunomori, Narita, Chiba, 286-8686, Japan. 2. Department of Anatomy, Faculty of Medicine, School of Medicine, International University of Health and Welfare, 4-3, Kozunomori, Narita, Chiba, 286-8686, Japan. 3. Department of Basic Medical Science, Graduate School of Medicine, International University of Health and Welfare, 4-3 Kozunomori, Narita, Chiba, 286-8686, Japan. kyutaro@iuhw.ac.jp. 4. Department of Anatomy, Faculty of Medicine, School of Medicine, International University of Health and Welfare, 4-3, Kozunomori, Narita, Chiba, 286-8686, Japan. kyutaro@iuhw.ac.jp. 5. Department of Anatomy, Division of Basic Medical Science, Tokai University School of Medicine, 143, Shimokasuya, Isehara, Kanagawa, 259-1193, Japan. 6. Center for Basic Medical Research, International University of Health and Welfare, 4-3 Kozunomori, Narita, Chiba, 286-8686, Japan.
Abstract
PURPOSE: An extra muscle was observed on both sides of the popliteal fossa in the cadaver of a 78-year-old Japanese male during dissection. The aim of this case report was to identify whether this variant is a double plantaris or a third head of the gastrocnemius according to its morphological characteristics and innervation. METHODS: The muscles were displayed by careful dissection and delineation of surrounding structures. The size of each of the muscle bellies and tendons of those extra muscles were measured manually by the vernier caliper. RESULTS: The origin of each extra muscle was lateral to the tibial nerve and superior to the plantaris, and each extra muscle which transitioned to a descending tendon parallel to the plantaris had a cone-shaped belly. However, the tendon of the extra muscles was fused into the investing fascia of the gastrocnemius with a tendon length of 4.5 cm on the left and 4.6 cm on the right. The extra muscles were innervated by the branch of the tibial nerve to the medial head of the gastrocnemius on both sides. CONCLUSION: Although they had an origin and shape similar to that of the plantaris, we identified the extra muscles in this case as a third head of the gastrocnemius, because of innervation to the plantaris arises directly from the tibial nerve. This case highlighted that the innervation is essential to understanding the myogenesis of extra muscles, especially in cases which are difficult to categorize based on the morphological features of the muscle.
PURPOSE: An extra muscle was observed on both sides of the popliteal fossa in the cadaver of a 78-year-old Japanese male during dissection. The aim of this case report was to identify whether this variant is a double plantaris or a third head of the gastrocnemius according to its morphological characteristics and innervation. METHODS: The muscles were displayed by careful dissection and delineation of surrounding structures. The size of each of the muscle bellies and tendons of those extra muscles were measured manually by the vernier caliper. RESULTS: The origin of each extra muscle was lateral to the tibial nerve and superior to the plantaris, and each extra muscle which transitioned to a descending tendon parallel to the plantaris had a cone-shaped belly. However, the tendon of the extra muscles was fused into the investing fascia of the gastrocnemius with a tendon length of 4.5 cm on the left and 4.6 cm on the right. The extra muscles were innervated by the branch of the tibial nerve to the medial head of the gastrocnemius on both sides. CONCLUSION: Although they had an origin and shape similar to that of the plantaris, we identified the extra muscles in this case as a third head of the gastrocnemius, because of innervation to the plantaris arises directly from the tibial nerve. This case highlighted that the innervation is essential to understanding the myogenesis of extra muscles, especially in cases which are difficult to categorize based on the morphological features of the muscle.