Association of internal rotation of the knee joint with recurrent subluxation of the lateral meniscus.

PURPOSE: To compare the arc of rotation of the knee joint at 90° of flexion in control knee joints and those affected by recurrent subluxation of the lateral meniscus (RSLM), in determining whether rotatory instability of the knee joint is a risk factor for RSLM.

METHODS

Knee joints were diagnosed with RSLM when there was a history of mechanical locking episodes and when subluxation of the lateral meniscus with the peripheral margin of the posterior segment moving anteriorly beyond the lateral femoral condyle was recognized on arthroscopy. In this study 288 knee joints in 270 subjects were evaluated. The joints were classified into a control group (252 joints), an RSLM group (24 joints), and a contralateral RSLM group (12 joints). The arcs of external and internal rotation at 90° of flexion of the knee joint induced by 7 Nm of torque under non-weight-bearing conditions were measured with a Biodex System 3 (Biodex Medical Systems, Shirley, NY).

RESULTS

There were no significant differences in mean values of external rotation among the 3 groups. The mean values of internal rotation of both the RSLM and contralateral RSLM groups were significantly larger than that of the control group, by about 15° (P < .0001). The mean value of internal rotation was slightly higher than that of external rotation in the RSLM and contralateral RSLM groups, although the mean value of internal rotation was smaller than that of external rotation by 10.1° in the control group.

CONCLUSIONS

RSLM was found to be strongly related to bilateral increase in the arc of internal rotation at 90° of flexion of the knee joint, suggesting that internal rotatory instability of the flexed knee joint can be considered one of the risk factors for and diagnostic parameters of RSLM.

LEVEL OF EVIDENCE: Level III, diagnostic study of nonconsecutive patients.