Etiology of posterior meniscus root tears: medial vs. lateral.

PURPOSE: The aim of this study was to generate more information on the etiology and pathogenesis of medial (MM) and lateral (LM) meniscus root tears. Our hypothesis was that root tears of the MM predominantly result from degenerative damage, whereas root injuries of the LM are mainly of traumatic origin.

METHODS

Consecutively, 53 patients with a root tear of the medial meniscus (MMRT) and 51 patients with a root tear of the lateral meniscus (LMRT) were included in this study. The diagnosis was confirmed radiologically by MRI as well as arthroscopically. In addition to patient-specific data such as age, BMI and trauma history, the leg axis was determined and accompanying injuries (ligamentous and chondrogenic) were documented.

RESULTS

The mean age of the MMRT group was 57.2 (± 11.2) years, and that of the LMRT group 33.9 (± 11.4) years. The BMI was significantly higher in the MMRT group compared to the LMRT (30.5 vs. 25.1). 82.4% of patients in the LMRT group demonstrated an accompanying anterior cruciate ligament (ACL) rupture, whereas only 5.7% of the MMRT were associated with an ACL injury. A trauma was described in only 13.2% of patients of the MMRT group in contrast to 88.2% of the LMRT group. An extrusion > 3 mm of the MM in the coronal plane of MRI images could be detected in 86.8% of patients, whereas in the LMRT group, it was 15.7%. The mechanical varus angle was 5.6° in the MMRT group and 2.4° in the LMRT group. The rate and degree of concomitant cartilage damage in the affected compartment was significantly higher in the group with medial root injuries than in the group with lateral root tears.

CONCLUSIONS

The root injuries of the MM and LM show significant differences in terms of patient age, etiology and accompanying injuries. Root injuries to the medial meniscus are mostly of non-traumatic origin and more likely to occur in the context of medial osteoarthritis and varus deformity of the knee. Lateral root tears tend to be predominantly traumatic and are frequently associated with ACL ruptures. However, in the MMRT group, a small subgroup with a traumatic etiology and in the LMRT group a small subgroup of patients with non-traumatic etiology could be identified.

LEVEL OF EVIDENCE: III.