Femur movement on the tibial plateau during kneeling
From 90º to 150º of knee flexion (upright kneeling to full flexion), there is an average femoral posterior translation of 36 mm. During this movement, there is also 8º of external rotation, accompanied by lower values of abduction and lateral translation.
At full flexion, the femoral condyles rest on the posterior rim of the tibial plateau and external rotation allows for the alignment of the popliteal fossa with the posterior margin of the medial tibial plateau.
Kneeling is an important movement for functional, cultural, religious and social activities. Various routine activities, such as stair climbing and rising from a chair, require a degree of knee flexion. However, people over the age of 45 may lose this ability due to osteoarthritis, joint stiffness or pain.
Twenty-five patients between 45 and 85 years old with no history of knee pain, injury or disease participated in the study. Participants knelt in a cushioned box with the feet free, sat on their heels, and returned to the upright position. Fluoroscopy and CT were used to obtain images of femoral movement.
There was a linear and significant relation between knee flexion and femur posterior translation and external rotation from 90º to 150º of knee flexion.
Traditionally, the concave-convex rule states that the tibia should be moved posteriorly to treat knee stiffness limiting full flexion. However, this study provides video evidence that the femur needs to translate posteriorly in order to achieve full flexion.
The findings of this study put this rule into question and prompt changes in manual therapy approaches.
Expert opinion by José Pedro Correia
This study shows not only maintainted knee accessory motion in subjects over 45 years old but, perhaps more importanty, that traditional and established manual therapy approaches taught and practiced by physiotherapists worldwide may actually not be supported by video evidence.
This study is in line with others that have questioned the validity of the concave-convex rule in other joints such as the shoulder.
> From: Scarvell et al., Phys Ther 99 (2019) 311-318 (Epub ahead of print). All rights reserved to American Physical Therapy Association. Click here for the online summary.