Summary

If preoperative magnetic resonance imaging of anterior cruciate ligament injury reveals lateral meniscus extrusion (LME) over 2.2 mm, there is a high possibility of complete lateral meniscus posterior root tear (LMPRT) complications. This LME cut-off value had a sensitivity of 78% and specificity of 71% for complete LMPRT.

Abstract

Background

Lateral meniscus posterior root tears (LMPRTs) have been identified as a combined injury with anterior cruciate ligament (ACL) rupture in 6.7–20.4% of patients in previous studies. Because LMPRT is associated with meniscal extrusion and rotational instability and has been linked to degenerative changes in the knee, complete LMPRT repair is recommended. However, it is difficult to diagnose complete LMPRT based on magnetic resonance imaging (MRI) findings alone. In addition, even with an intact meniscal root, various degrees of LM extrusion (LME) are usually observed in association with ACL tears. Therefore, LME has not been demonstrated as an indicator of LMPRT.
Objectives
The purpose of this study was to investigate the relationship between preoperative LME, provide an arthroscopic evaluation of LMPRT in ACL-injured knees, and determine the complete LMPRT cut-off value from preoperative LME.
We hypothesized that preoperative LMEs would be larger in patients with complete LMPRTs associated with ACL injuries than those with partial LMPRTs with ACL deficiency.
Study Design & Methods
Four hundred four patients who underwent ACL reconstruction at our hospital between February 2011 and July 2021 were retrospectively evaluated. A total of 45 patients were included in the study, 35 with LMPRTs with concomitant ACL injuries and 10 with intact lateral menisci with ACL injuries.
The most widely used classification of La Prade divides the LMPRTs into five types. Using this classification, 35 patients were divided into two groups, partial (type 1) and complete (types 2–5) LMPRTs, based on arthroscopic findings at the time of ACL reconstruction. LME was measured using MRI as the distance from the lateral edge of the tibial plateau cartilage to the outer border of the LM. Results
A total of 35 LMPRTs were classified using the morphological classification system; 17 knees (10 males and 7 females; mean ± SD age 23.5 ± 11.6 years) were classified into the partial LMPRT group and 18 (9 males and 9 females; mean ± SD age 20.4 ± 6.7 years) into the complete LMPRT group. Patients in the complete LMPRT group had 3 radial tears (type 2), 11 bucket-handle tears (type 3), and 4 oblique tears (type 4). There were no cases of avulsion fractures (Type 5). 20 knees (10 males and 10 females; mean ± SD age 20.7 ± 2.7 years) were classified into the intact lateral meniscus group. There were no significant differences between the three groups in terms of the relevant characteristics of the participants.
On MRI evaluations, preoperative LMEs were larger in complete LMPRTs associated with ACL injuries than that in intact lateral menisci with ACL injuries and partial LMPRTs with ACL injuries. The ROC analysis identified the optimal cut-off point of the preoperative LME as 2.2 mm, which had a sensitivity of 78% and specificity of 71% for complete LMPRT.

Conclusion

When a preoperative MRI of ACL injury reveals LME over 2.2 mm, there is a high possibility of complete LMPRT complications.