This study was conducted in healthy adults using special upright magnetic resonance imaging to understand the dynamics of the meniscus under the weight-loading condition. The medial meniscus showed significant medial meniscal shift, and the lateral meniscus showed significant meniscal shift in lateral, anterior and posterior directions in single- and double-leg weight-loading conditions.
Meniscal morphology under the weight-loading condition remains unknown because weight loading during magnetic resonance imaging (MRI) is rarely performed. We focused on the weight-loading condition and developed special upright MRI. This study aimed to investigate the meniscal shift of the medial and lateral meniscus in healthy adults under full weight loaded and unloaded conditions using both supine and upright MRI.
Eighteen volunteers (13 men and 5 women) without previous knee complaints underwent MRI of the right knee. The mean age was 21.8±3.1 years. The examination was performed in three positions: supine, double-leg upright (DLU) and single-leg upright (SLU). The knees were fully extended in each position. For supine and upright examination, we used a special MRI apparatus (Gravity MRI, Hitachi, Japan) that is capable of imaging in any position with a static magnetic field strength of 0.4 T. T1-weighted images in the coronal and sagittal planes with a slice thickness of 2 mm were obtained. The medial or lateral and anterior and posterior shifts of the medial and lateral meniscus against the tibial wedge were measured. The medial and lateral meniscal shift rates were measured as assessment items under each condition. The shift rate was defined as the proportion of the measured amount of the meniscal shift to the measured overall width of the medial and lateral meniscus. The MRI reference section on the sagittal plane was the midpoint of the medial or lateral femoral condyle, and on the coronal plane, the reference point was the midpoint of the medial and lateral tibial condyle. Analysis of variance and multiple comparison test were performed to compare the three imaging positions for all measurement items, with statistical significance set at P < 0.05.
The difference among the three conditions for medial shift rate of the medial meniscus was significant. The medial shift rate was significantly greater in DLU and SLU positions than in the supine position (supine: 7.3±5.8% vs. DLU: 20.0±8.8 %. P<0.01, supine vs. SLU: 21.5±7.6%. P<0.01, DLU vs. SLU. P=0.7). No significant differences were observed for the anterior and posterior shift rates of the medial meniscus (anterior: P=0.6, posterior: P=0.4). In the lateral meniscus, the lateral shift rate was significantly greater in the SLU position than in the supine position, but no significant difference was observed in the DLU position (supine: -1.2±11.8% vs. DLU: 2.7±11.1 %. P=0.2, supine vs. SLU: 4.5±10.8%. P=0.04, DLU vs. SLU. P=0.7). Anterior and posterior shift rates in the lateral meniscus were significantly greater in DLU and SLU positions than in the supine position (anterior; supine: -20.6±14.3% vs. DLU: -14.7±12.2%. P<0.01, supine vs. SLU: -8.9±14.9%. P<0.01, DLU vs. SLU. P=0.3, posterior; supine: -78.0±19.6% vs. DLU: -63.7±18.7 %; P<0.01, supine vs. SLU: -57.8±19.2%; P<0.01, DLU vs. SLU; P=0.4).
In the upright weight-loading condition, the medial meniscus showed only medial shift, and the lateral meniscus showed meniscal shift in lateral, anterior and posterior directions.
No significant difference was observed between the DLU and SLU shift rates in both medial and lateral meniscus in healthy adults.