Tibial ACL insertion site length: correlation between preoperative MRI and intra-operative measurements

Abstract

Purpose: This study was undertaken primarily to identify the tibial insertion site length of ruptured ACL fibres in patients undergoing primary ACL reconstruction. A secondary aim was to evaluate the correlation of pre- and intra-operative measurements.

Methods: In 146 patients undergoing primary ACL reconstruction, a preoperative measurement on MRI of the tibial ACL insertion site length was taken by two raters and then compared with single surgeon's intra-operative measurements using a specialized ruler. Inclusion criteria were primary ACL reconstruction and MRI performed within 3 months prior to surgery on one specific MRI machine at the study centre. Inter-rater and intra-rater reliability based on intra class correlation (ICC) was calculated. Additionally, correlation between preoperative and postoperative measurements and the anthropometric data was assessed using Pearson correlation.

Results: The tibial ACL insertion site had a mean length of 16.6 ± 1.6 mm (11.9-21.0) as measured by MRI, and 16.4 ± 1.6 mm (11.0-20.0) as measured intra-operatively. The ICCs for intra- and inter-rater reliability of the MRI measurements were 0.99 (95 % CI 0.97; 0.99; p < 0.001) and 0.81 (95 % CI 0.75; 0.86; p < 0.001), respectively. Regression analysis demonstrated, after controlling for subject height and weight, that the MRI measurements significantly predicted intra-operative measurement of tibial insertion site length (β = 0.796; R (2)-change 0.77; p < 0.001).

Conclusion: Preoperative measurement of the tibial ACL length is possible using MRI and can be a valuable aid in more efficient preoperative planning given the knowledge of expected dimensions of special knee structures.

Level of evidence: III.

Keywords: Anterior cruciate ligament reconstruction; Insertion site; Inter-rater reliability; Length; MRI.