[A roentgenographic study of extension movements in osteoarthritic knees].

Serial lateral roentgenographs were taken of extension movements in 120 normal knees and 153 osteoarthritic knees, and analysis was made of both gliding and rolling movements of the medial femoral condyle with respect to the tibia. In normal knees, the medial femoral condyle showed a smooth forward shift with respect to the tibia in their extension movements from flexion 90 degrees to maximum extension, made gliding movements from flexion 90 degrees to 60 degrees, and then, added with an element of rolling movements, took its final extension position. Index of contact for flexion 90 degrees and maximum extension position was 40.94 +/- 4.87% and 54.38 +/- 6.55%, respectively, and index of shift was 14.33 +/- 4.66%, with no differences by age. In osteoarthritic knees, with the grade of disease, the alteration on the cartilaginous surface of the medial femoral condyle progressed and a rhythm disturbance occurred between gliding and rolling movements; from flexion 90 degrees to 60 degrees gliding movements were made similarly to normal knees, from flexion 60 degrees rolling movements increased, and further from flexion 30 degrees to the final extension position, rolling movements rather than gliding movements played the leading role, with observed strong forward shift of the medial femoral condyle and extension disturbance of the knee joint. Index of contact for 90 degrees and maximum extension position was 40.41 +/- 6.71% and 60.80 +/- 9.52%, respectively, and index of shift was 23.39 +/- 9.94% with an index of rearward shift of over 5% on the way to extension observed in 39 joints (25%). According to the above result, it was concluded that the aggravation of osteoarthritic knees could be partly due to abnormal gliding and rolling of the medial femoral condyle in knee extension movements.