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Association between discoid lateral meniscus and medial meniscus posterior root tear: A retrospective cohort study

Ryosuke Yamashita^1,2, Yuki Okazaki¹, Keisuke Kintaka³

¹Department of Orthopaedic Surgery Okayama University Hospital Okayama Japan.

Journal of Experimental Orthopaedics

|February 20, 2026

Abstract

Purpose:

Medial meniscus (MM) posterior root tear (PRT) has gained increasing attention because of its biomechanical impact and rapid progression to osteoarthritis. Identifying the risk factors for MMPRT is essential for early diagnosis. Although the discoid lateral meniscus (DLM) is a common congenital variant, no studies have reported on the relationship between MMPRT and DLM. This study aimed to examine the relationship between MMPRT and DLM.

Methods:

This retrospective cohort study included 94 matched knees that underwent arthroscopic surgery between 2015 and 2021 (58 with MMPRT and 36 with other MM injuries). The matching was performed according to age and sex. Morphological analysis of the lateral meniscus (LM) was performed using coronal magnetic resonance imaging (MRI). DLM was defined as an LM ratio (LM width/tibial width) > 0.20. LM width, LM ratio and DLM prevalence were compared between the two groups. In the MMPRT group, subgroup analysis compared the preoperative and 1-year postoperative clinical outcomes between patients with and without DLM.

Results:

The PRT group showed significantly greater LM width (12.6 ± 3.1 mm vs. 11.1 ± 2.2 mm; p = 0.03) and LM ratio (0.18 ± 0.04 vs. 0.16 ± 0.03; p = 0.01) compared with the other group. The incidence of DLM was also significantly higher in the PRT group (29.3% vs. 8.3%; p = 0.02). No significant differences in clinical scores were observed between the two subgroups either preoperatively or 1 year postoperatively. However, both groups demonstrated significant improvement in all clinical outcomes 1 year postoperatively (p < 0.01).

Conclusions:

DLM was significantly more prevalent in patients with MMPRT than in those with other MM injuries. Favourable clinical outcomes were achieved following pullout repair in MMPRT knees regardless of the presence of DLM.

Level Of Evidence:

Level III, retrospective cohort study.

Insights

Discoid lateral meniscus (DLM) is more common in patients with medial meniscus posterior root tears (MMPRT). MMPRT repair outcomes are favorable, irrespective of DLM presence.

Area of Science:

Orthopedics
Sports Medicine
Knee Surgery

Background:

Medial meniscus posterior root tears (MMPRT) significantly impact knee biomechanics and can accelerate osteoarthritis.
Early diagnosis of MMPRT is crucial, necessitating identification of associated risk factors.
Discoid lateral meniscus (DLM) is a common congenital anomaly, but its association with MMPRT remains unexplored.

Purpose of the Study:

To investigate the relationship between medial meniscus posterior root tears (MMPRT) and discoid lateral meniscus (DLM).
To determine if DLM is a risk factor or associated condition for MMPRT.

Main Methods:

A retrospective cohort study compared 58 knees with MMPRT to 36 knees with other medial meniscus injuries, matched for age and sex.
Coronal MRI was used for morphological analysis of the lateral meniscus (LM), defining DLM by an LM ratio > 0.20.
LM width, LM ratio, and DLM prevalence were compared; clinical outcomes were assessed preoperatively and postoperatively in MMPRT subgroups with and without DLM.

Main Results:

The MMPRT group exhibited significantly greater LM width and LM ratio compared to the control group.
Prevalence of DLM was significantly higher in the MMPRT group (29.3%) versus the other medial meniscus injury group (8.3%).
No significant differences in clinical outcomes were found between MMPRT subgroups with or without DLM, with both groups showing significant postoperative improvement.

Conclusions:

Discoid lateral meniscus (DLM) is significantly more prevalent in knees with medial meniscus posterior root tears (MMPRT).
Arthroscopic pullout repair yields favorable clinical outcomes for MMPRT, regardless of the presence of DLM.
DLM may be an associated finding in MMPRT, but does not appear to negatively impact surgical outcomes.

Read full analysis

Keywords:

clinical outcome discoid lateral meniscus medial meniscus morphology posterior root tear

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