Blumensaat’s Line as a Prediction of Native Anterior Cruciate Ligament Length
F. Baker Mills IV, MS, James R. Andrews, MD, Charles A. Roth, MD, Patrick W. Joyner, MD, MS
Graft-tunnel mismatch (GTM) is a condition in which the anterior cruciate ligament (ACL) graft is either too long or short. GTM is particularly problematic when bone-patellar ligament-bone (BPTB) grafts are used, due to a potential compromise in fixation of the bone plug on the tibia. It is hypothesized that Blumensaat’s line (BL), a radiographic landmark representing the roof of the intercondylar fossa, will accurately approximate the native ACL (nACL) length and may aid in the prevention of GTM.
Methods:
A total of 130 patients (66 male and 64 female) underwent direct measurement of their nACL during knee arthroscopy. The length of the nACL and patellar ligament (PL) were measured intra-operatively and BL length was measured on lateral knee radiographs. nACL length was compared with PL and BL length to calculate absolute difference (AD). Mean AD was calculated and utilized to determine mean percent difference (MPD). Pearson’s correlation coefficients (CC) between BL, PL, and nACL length were calculated, along with inter- and intra-observer reliability coefficients for the measurement of BL.
Results:
For males, the average length of the ACL was 32.5mm, BL 30.4mm, and the PL 49.2mm. The AD between BL and the native ACL was 2.4mm ± 1.3mm, MPD 3.7% ± 1.9, and CC 0.88. The CC between the PL and nACL was 0.08. For females, the average length of the ACL was 30.2mm, BL 27.5mm, and PL 44.4mm. The AD between BL and nACL was 2.7mm ± 1.7mm, MPD was -4.5% ± 2.4, and CC was 0.93. The CC between the PL and nACL was 0.1. The inter- and intra-observer reliability coefficients for the measurement of BL was 0.86 and 0.83, respectively.
Conclusion:
A strong correlation was found between Blumensaat’s Line and the native ACL with a high inter- and intra-observer reliability. This correlation provides the first simple and reliable method to closely approximate native ACL length, prior to reconstruction, and may aid in the prevention of graft-tunnel mismatch.