The purpose of this study was to reveal the influence of the morphological variations of the Blumensaat’s line on antero-medial(AM), postero-lateral(PL) femoral tunnel position in anatomical double-bundle anterior cruciate ligament (ACL) reconstruction.
Forty-eight subjects undergoing anatomical double-bundle ACL reconstruction were included in this study (22 male, 26 female: median age 26.9:14-50). Using an inside-out trans-portal technique, the PL tunnel placement was made on a line drawn vertically from the bottommost point of the lateral condyle at 90° of knee flexion, spanning a distance of 5 to 8 mm, to the edge of the joint cartilage. AM tunnel placement was made 2 mm distal to the PL bundle tunnel placement. Following Iriuchishima’s classification, the morphology of the Blumensaat’s line was classified into straight and hill types (large and small hill type). AM, PL femoral ACL tunnel position was evaluated using the Quadrant method. When the Quadrant method grid was applied, the baseline of the grid was matched to the anterior part of the Blumensaat’s line, without considering the existence of a hill. Using post-operative 3D-CT data, the axial and sagittal morphology of the knee was also compared, establishing straight and hill types.
There were 17 straight type knees and 31 hill type knees (11 small hill and 20 large hill type knees). The AM, PL femoral tunnel placement in straight type knees was 22.4 ± 6.9%, 34.3 ± 10.3% in the shallow-deep direction, and 41.6 ± 11.2%, 71.9 ± 8.7% in the high-low direction, respectively. In hill type knees, the AM, PL femoral tunnel position was 20.8 ± 5.0%, 36.7 ± 6.3% in the shallow-deep direction, and 44.7 ± 10.7%, 72.5 ± 9.9% in the high-low direction, respectively. No significant difference in AM, PL femoral tunnel position was observed between straight type and hill types.
The most important finding of this study was that no significant difference in AM, PL femoral tunnel position was observed between straight type and hill types. Iriuchishima et al. reported the single-bundle ACL reconstruction femoral tunnel was placed significantly difference when compared with straight type and hill types knees. In this study, there may not have been a significant difference because the operative method was to determine the AM, PL femoral tunnel position on the index from the bottommost point of the lateral condyle to the edge of the joint cartilage.
AM, PL femoral ACL tunnel placement was not influenced by the morphological variations of the Blumensaat’s line. As detecting morphological variation in arthroscopic surgery is difficult. The surgeon may not be influenced by the Blumensaat’s line if the AM, PL femoral tunnel position is indexed from the bottommost point of the lateral condyle.