Morphometric Analysis of the Filum Terminale and Conus Medullaris: A Cadaveric Study

Introduction The filum terminale (FT) is a fibrous continuation of the spinal cord that anchors the conus medullaris to the coccyx. Variations in the termination level of the conus medullaris and morphometry of the FT are clinically relevant in the evaluation of tethered cord syndrome. However, comprehensive morphometric correlations between total spinal cord length (TLSC), vertebral column length, and FT dimensions remain limited in the literature. Methods Thirty formalin-fixed adult cadavers (15 males and 15 females) were dissected from C1 to Co1. Measurements included TLSC, length up to the conus medullaris (LSCCM), total filum terminale length (FT-L), internum (FTI-L) and externum (FTE-L) lengths, segmental diameters, vertebral column length (VCL), and cadaver height (CH). Vertebral termination levels of the conus medullaris and FT-dural sac (DS) fusion were documented. Statistical analysis was performed using independent t-tests, Pearson correlation, and multiple linear regression. Results The conus medullaris most frequently terminated at the lower third of L1. The FT fused with the DS predominantly at the upper third of S2. The mean FT length was 221.83 ± 24.90 mm, with all segmental diameters remaining below the pathological 2 mm threshold. Significant positive correlations were observed between the VCL and TLSC (p < 0.001), TLSC and LSCCM (p < 0.001), and FT-L and proximal intradural diameter (p < 0.001). CH was strongly correlated with TLSC length and selected FT parameters. Significant sex differences were identified in the TLSC, LSCCM, selected diameter measurements, CH, and VCL. Conclusion This study establishes normative cadaveric morphometric data for the conus medullaris and FT. The novel integration of TLSC, VCL, CH, and detailed FT morphometry demonstrates proportional anatomical scaling. These findings enhance anatomical understanding and provide clinically relevant reference values for distinguishing physiological variations from pathological tethering in tethered cord syndrome.