変形性膝関節症の発症と進行のメカニズムに関する研究

―形態学的, 筋電図学的検討―

抄録

The aim of this study was to clarify the relationship between the changes of alignment of the lower extremity in the coronal and horizontal planes at the level of the knee, and the imbalance of muscle strength in primary osteoarthritis (OA) of the knee.
Sixty patients of primary OA of the knee were graded according to the CIOMS radiographic system. Femorotibial angle (FTA) and joint space angle (JA) were measured with X-rays of the whole limb in standard position. The rotational deformities were assessed by computerized axial tomography. The rotational change of the tibia against the femur on quadriceps contraction was also measured. Muscle activities were estimated from electromyographic measurement of muscle contraction during walking using surface electrodes.
In the early stage of OA, a decrease of external rotation of the tibia without any change in FTA and JA was demonstrated, and it was well correlated with the decreased activity of the vastus medialis muscle. Relative increase in the activities of the lateral supporting muscles of the knee was also observed with the progression of OA, and this finding could be understood to indicate the role of the lateral supporting muscles in withstanding varus deformity of the knee. But in advanced OA, it was estimated that this mechanism was not sufficient to stop the progression of the varus deformity.
From these results, we concluded that disturbance of the screw-home movement due to the relative decrease of activity of the vastus medialis muscle should be considered one of the most important factors in the onset of OA of the knee.