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Discoid lateral meniscus and the frequency of meniscal tears
E M Rohren1, F J Kosarek, C A Helms
1Department of Radiology, Duke University, Durham, NC 27710, USA.
Objective:
To use MRI to determine the incidence of discoid lateral menisci in a large study population, and to compare those patients with those without a discoid meniscus in order to assess the impact of a discoid lateral meniscus on the frequency of meniscal tears.
Design And Patients:
Results of 1,250 knee MRI studies were retrospectively reviewed. Using the criterion of three or more meniscal body segments on sequential sagittal images, 56 patients were found to have a discoid lateral meniscus. After exclusion of patients with prior knee surgery, 49 patients with a discoid lateral meniscus were compared with 1,146 patients without a discoid meniscus. Patients were categorized as having tears of the medial meniscus, lateral meniscus, or both menisci.
Results:
In our study population, there was a 4.5% incidence of discoid lateral meniscus. Seventy-one percent of patients with a discoid lateral meniscus had one or more meniscal tears, compared with 54% of the comparison group (P=0.01). The frequency of solitary lateral meniscal tears in the discoid group was also higher than in the comparison group: 20%.versus 11% (P=0.03). The frequency of solitary medial meniscal tears and concomitant tears of both menisci were not significantly different between the two groups.
Conclusions:
The discoid lateral meniscus is an uncommon variant, but not as rare as once believed. Compared with the normal semilunar meniscus, the discoid lateral meniscus has a higher frequency of meniscal tears, and solitary tears of the lateral meniscus are more common in the discoid variant. The frequency of medial meniscal tears is not altered by the presence of a discoid lateral meniscus.
Insights
The discoid lateral meniscus, a knee variant, is more common than previously thought and significantly increases the risk of meniscal tears, particularly isolated lateral tears.
Area of Science:
- Orthopedics
- Radiology
- Sports Medicine
Background:
- The discoid meniscus is a congenital anomaly of the knee.
- Its exact incidence and association with meniscal tears require further investigation.
Purpose of the Study:
- To determine the incidence of discoid lateral meniscus (DLM) in a large population using MRI.
- To compare meniscal tear frequency in patients with and without DLM.
Main Methods:
- Retrospective review of 1,250 knee MRI studies.
- Identified 56 cases of DLM using specific imaging criteria.
- Compared 49 DLM patients with 1,146 controls, analyzing tear locations.
Main Results:
- The incidence of DLM was 4.5%.
- Patients with DLM had a higher rate of meniscal tears (71% vs. 54%, P=0.01).
- Solitary lateral meniscal tears were more frequent in the DLM group (20% vs. 11%, P=0.03).
Conclusions:
- Discoid lateral meniscus is an uncommon but significant knee variant.
- DLM is associated with an increased risk of meniscal tears, especially isolated lateral tears.
- Medial meniscal tear frequency is not affected by the presence of a DLM.
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