Risk factors for medial meniscus posterior root tear.

BACKGROUND: Medial meniscus posterior root tears (MMPRT) have a different clinical effect from other types of meniscal tears. These tears are very common among Asian people and may be related to the frequent use of postures such as the lotus position or squatting.
PURPOSE: The present study was designed to identify the risk factors for MMPRT among an Asian sample. STUDY
DESIGN: Cohort study; Level of evidence, 3.
METHODS: An observational study was performed of 476 consecutive patients undergoing an arthroscopic procedure on their medial meniscus from January 2010 to December 2010. One hundred four patients had MMPRT (group 1), and the other patients had other types of medial meniscal tears (group 2). Demographic characteristics (age, sex, body mass index [BMI]), radiographic features (mechanical axis angle, tibia vara angle, tibial slope angle, Kellgren-Lawrence grade [KLG]), and environmental factors (occupation, trauma history, sports activity level, table use or not, bed use or not-variables that are representative of the oriental lifestyle of lotus position and squatting) were surveyed. We assessed the relation of these risk factors to the type of meniscal tear (group 1 or 2).
RESULTS: In group 1, there were 7 male and 97 female patients, with an average age of 58.2 years (range, 39-78 years) and BMI of 26.7 ± 3.4 kg/m2. In group 2, there were 136 male and 236 female patients (P < .01 compared with group 1), with an average age of 54.3 years (range, 17-77 years; P < .01) and a BMI of 24.9 ± 3.1 kg/m2 (P < .01). With regard to radiographic features, the mechanical axis angle demonstrated a significantly increased varus alignment in group 1 (4.5° ± 3.4°) compared with group 2 (2.4° ± 2.7°; P < .01), and the KLG was 1.4 ± 0.8 in group 1 and 0.9 ± 0.6 in group 2 (P < .01). Environmental factors showed no differences in occupation, table use or not, and bed use or not, except sports activity level. There were 41 patients (42.7%) in group 1 and 77 patients (20.6%) in group 2 who did not participate in any recreational activity (P < .01). Multiple logistic regression analysis showed that female sex was associated with a 5.9-fold increase in risk (95% confidence interval [CI], 2.138-16.575), a varus mechanical axis angle with a 3.3-fold increase (95% CI, 1.492-7.153), a BMI more than 30 kg/m2 with a 4.9-fold increase (95% CI, 1.160-20.955), and lower sports activity level with a 2.7-fold increase (95% CI, 1.011-7.163) for MMPRT.
CONCLUSION: Persons with MMPRT had significantly increased age, female sex predominance, higher BMI, increased KLG, greater varus mechanical axis angle, and lower sports activity level compared with persons with other types of meniscal tear. After adjusting for other factors, sex, BMI, mechanical axis angle, and lower sports activity level remained strong determinants of MMPRT. Interestingly, oriental postural positions including the lotus position and squatting showed no contribution to increased risk of MMPRT. This suggests that intrinsic risk factors (similar to those that predispose to osteoarthritis) predispose to MMPRT.