Summary

This study evaluated by MRI in contralateral knee and assessed predictive factors with the bilaterality and tear of patients in a symptomatic discoid lateral meniscus. Our study revealed that discoid lateral meniscus commonly occurs bilaterally and combines the presence of discoid pathology that was significantly associated with characteristic x-ray findings.

Abstract

Purpose

Although the incidence of bilateral discoid lateral meniscus (DLM) has been reported to range between 5-20% traditionally, recent reports demonstrated bilateral DLM in 70-90% was diagnosed by magnetic resonance imaging (MRI) or arthroscopic evaluation of bilateral sides. However, very little has been known about which prognostic factors could influence the bilaterality and tear of contralateral side. The purposes of this study were to assess which predictive factors could influence on the bilaterality and tear of patients with a symptomatic DLM. We hypothesized that there would be a correlation between the younger ages or severe tear pattern in symptomatic DLM and the associated tear imaged by MRI in contralateral knee.

Methods

This prospective diagnostic study included 76 consecutive patients who underwent arthroscopic surgery for a unilaterally symptomatic DLM. All patients’ contralateral knees were checked with simple X-rays and MRI scans. Mean age at operation was 32.1 years (range, 3–59 years), 32 knees were male and 40 knees were right knees. Based on the MRI findings, DLM was categorized into three type (normal, incomplete discoid and complete discoid) and the tear patterns and the associated chondral lesions were analyzed by consensus in the bilateral knees. The characteristic radiographic findings (0/1/more than 2) in the bilateral knees were analyzed by agreement. Age, sex, preoperative symptom period, pre-injury activity, MRI type of DLM, combined chondral lesion, tear-pattern of operative side and operative technique were investigated to find a correlation with the associated tear in contralateral knee.

Results

MRI in the contralateral knee revealed 43 (57%) complete discoid type, 25 (33%) incomplete discoid type, and 8 (11 %) normal meniscus. Meniscus tears and chondral lesion were diagnosed in the contralateral knee with incidences of 29 (38%) and 6 (8%) in patients, respectively. On plain radiograph of the contralateral knee, 27 (36%) had one characteristic radiologic finding, and 24 (32%) had more than two characteristic radiologic findings. DLM type in contralateral side was significantly different in knees with presence of characteristic X-ray finding (P=0.004). Combined meniscus tear in contralateral side was significantly higher in knees with presence of characteristic X-ray finding (P<0.0001). Associated chondral lesion in contralateral side was not correlated with all variables. Based on logistic regression analysis, combined meniscus tear in contralateral side was associated with one characteristic finding (adds ratio [OR], 16.5; P=0.01) and more than two characteristic findings (OR, 264.0; P=0.000). The other variables were not found to be a significant predictive factor.

Conclusion

Among the predictive factor variables, characteristic x-ray findings in contralateral knee was only significant predictive factors for type of DLM and tear of DLM in contralateral side. The possibility of bilateral DLM with combined meniscus tear should prompt orthopaedic surgeon to evaluate the careful characteristic X-ray with or without MRI study of contralateral knee in patients with symptomatic, unilateral surgical DLM even though there is no clinical evidence.
Level of Evidence: Level I diagnostic study of consecutive patients