Analysis of fibularis tertius muscle in terms of frequency, morphology and morphometry in a Scottish population

Abstract

Fibularis tertius (FT) is a muscle of medical and academic interest, characterised by its great variability. Despite its importance, there are no publications related to its anatomical features in Scottish people. The current work aims to investigate the morphological characteristics of FT in the aforementioned population. Forty-four Thiel-embalmed cadavers (19 females, 25 males; age at death: 81.8 ± 11.2 years) of Scottish origin were dissected. For each cadaver, its presence or absence was determined and if present, its origin, insertion and morphometric measurements were assessed. This muscle was found to be absent in 6.8% of the lower limbs, with no difference between sexes. In 80% of cases, the absence was unilateral. Regarding the origin, in 95.1% of the cases there was no clear separation between the muscle bellies of FT and the extensor digitorum longus. In 88.6% of the lower limbs the origin was in the distal third of the fibula, while in 11.4% of the cases the insertion extended to the lower half of this bone. The length and width of the origin averaged 72.8mm and 23.3mm respectively, with no differences between sexes or sides of the body. Tendon length and width averaged 70.4mm and 3.2mm respectively, with no differences between sexes or sides of the body. The insertion of the tendon showed substantial inter- and intra-individual variations, in both type and morphological variants. Contrary to what is mentioned in currently used anatomy textbooks, in 67% of the cases some kind of insertion was found at the level of the 4th metatarsal bone, in addition to the insertion at the 5th metatarsal bone usually described. Almost half of the cadavers (48.7%) had different insertion sites when comparing the two sides of the body. The fan-shaped insertion variant was observed in the majority of cases (83%). In the present study, the significant variability of the anatomical characteristics of FT, outlined in the scientific literature, was confirmed for the Scottish population. In addition, several variations were identified that are not mentioned in current anatomy textbooks, something that should be taken into account in anatomy and surgical training courses. Further studies of Scottish and other populations are required.