Author(s): MANTECON TAGARRO, C.J., TAKAHASHI, K., TOMARI, K., SHIOTANI, H., MAAS, H., KAWAKAMI, Y., Institution: WASEDA UNIVERSITY , Country: JAPAN, Abstract-ID: 1175

INTRODUCTION:
The Biceps Femoris Long Head (BFlh) has a high injury risk due to its complex architecture, with an intramuscular aponeurosis (IntApo) where fascicles from each region (e.g. proximal, middle and distal) attach. Previous studies using ultrasound (US) methodology have primarily assessed fascicle length (FL) differences among these regions, however, the interindividual variation between regions remains unclear. Additionally, fascicles are often assumed as straight-line (e.g. running in a single plane) (1). Novel techniques like Diffusion Tensor Imaging (DTI) enable tracking of fascicles and the observation of their orientation changes and curvature. While DTI has been applied effectively to muscles like the Medial Gastrocnemius (2), its application to the BFlh remains largely unexplored. This study aims to employ DTI analysis to observe fascicle characteristics between different regions of the BFlh.
METHODS:
Eight healthy subjects (four males and four females, 24.7 ± 2.3 years, 167.5 ± 7.2 cm, 62.8 ± 10.8 kg), without lower extremity injuries in the past year, participated in this study. Magnetic Resonance diffusion tensor imaging scans were taken with the subjects positioned prone and knee fully extended. Prior to imaging, subjects lay prone for 20 minutes to mitigate fluid content shifts, followed by pre-conditioning trials 50% MVC of knee flexion for five seconds. Segmentation of the BFlh muscle and IntApo was conducted utilizing 3DSlicer software, and tractography was performed by dsi_studio software. Fascicles attaching to the IntApo and intersecting at 30%, 50% and 70% of aponeurosis lengths (e.g. proximal, middle and distal regions) were selected. FL was defined as the length between muscle surface to the IntApo and calculated by multiplying the number of coordinates within the fascicle by the distance between these coordinates. Fascicle curvature (FC) was expressed as the ratio of its length to the straight-line distance between its endpoints.
RESULTS:
No significant changes in FL (proximal: 113.03 ±17.455 (95% CI [95.575 – 130.485]) , middle: 117.80 ±15.938 (95% CI [101.862 – 133.738]) , distal: 112.11 ±13.845 (95% CI [98.265 – 125.955])) or FC (proximal: 2.76 ±0.194 (CI 95% [2.566 – 2.954]), middle: 2.78 ±0.249 (CI 95% [2.531 – 3.029]) , distal: 2.92 ±0.284 (CI 95% [2.636 – 3.204])) were observed within regions. However, fascicles were shown to change its orientation along its length, elucidating that the fascicles run in the sagittal and coronal planes.
CONCLUSION:
DTI tractography allows to observe differences in FL and FC between regions of the BFlh. Additionally, it demonstrated that BFlh runs along the sagittal and coronal planes rather than just a single plane, which can lead to measurement errors when measuring FL using two-dimensional US methods.

References
Franchi MV et al. Med Sci Sports Exerc. 2020 Jan;52(1):233-243
Takahashi, K et al. J Anat, 2022 Aug; 241, 1324–1335.