Summary

Associations between lateral meniscus posterior root tear and knee stability in ACL injured patients were investigated. Lateral meniscus posterior root tear was associated with anterolateral rotational instability in ACL injured patients, whereas it did not seem to be associated with anteroposterior instability.

Abstract

Introduction

Importance of meniscus posterior root tear has been recognized; however, its contribution on knee stability has not been thoroughly investigated. The purpose of this study was to investigate meniscus status and clinical findings in anterior cruciate ligament (ACL) injured patients, in order to clarify associations between lateral meniscus posterior root tear (LMPRT) and knee instability in ACL injured patients.

Methods

Patients who underwent primary anatomic double-bundle ACL reconstruction between May 2012 and April 2016 were included and retrospectively reviewed. Exclusion criteria included knees with locked meniscus, history of injuries in the ipsilateral knee, history of ligamentous injuries in the contralateral knee, and knees with osteoarthritis. Positive rate of LMPRT in magnetic resonance imaging (MRI) (coronal, sagittal and axial views) was retrospectively reviewed using arthroscopic findings as gold standard. Patients with LMPRT (LMPRT group) were then compared with patients with no meniscus tear (control group) in terms of 1) number of giving way, 2)presence of bone bruise, 3) extrusion width of lateral meniscus in coronal view of MRI, 4) preoperative KT-1000 measurement and 5) preoperative pivot shift test grading.

Results

Three hundred and seventeen patients were included according to inclusion and exclusion criteria. They comprised of 171 males and 146 females with an average age of 25 years at the time of surgery. Among them, 39 patients (12.3 %) had LMPRT, whereas 117 patients had no meniscus tear. Positive rate of LMPRT in at least one view of MRI was 71.8 %, with the coronal view showing the highest positive rate (69.2 %). In the LMPRT group, 48.7 % of the patients showed meniscus extrusion of 1mm and more, and 12.8 % showed meniscus extrusion of 3 mm and more. The LMPRT group showed greater meniscus extrusion than the control group (average: 1.3 mm in the LMPRT group vs. 0.5 mm in the control group, p < 0.001). Preoperative pivot shift test grading in the LMPRT group was significantly greater than that in the control group (p < 0.001). There were no differences in number of giving way, presence of bone bruise and preoperative KT measurements.

Discussion

LMPRT was identified in a certain number of ACL injured patients as previously reported. Coronal view of MRI was the most useful to identify LMPRT, although its sensitivity was not as high as expected. Meniscus extrusion has been reported to be associated with progression of osteoarthritis; the current study suggests that LMPRT causes meniscus extrusion, which would lead to osteoarthritis. A recent cadaveric study has shown that release of the lateral meniscus posterior root increases anterolateral rotational instability in ACL resected knees. The current study also showed that LMPRT was associated with anterolateral rotational instability in ACL injured patients, whereas LMPRT did not seem to be associated with anteroposterior instability.