Loading on the knee joint during kneeling and squatting

Status:

completed 01/2009

Aims:

In the scientific reasoning for the new occupational disease of gonarthrosis, the cause is stated to be increased contact force upon the joint cartilage during occupational activity performed in a kneeling position or during comparable loading upon the knee. Biomechanical studies into the level of loading on the knee joint in such situations are not yet available, however. The objective of the project was therefore to perform preliminary biomechanical analyses of the level of knee joint forces during occupational tasks performed in a kneeling or squatting position. For this purpose, it was first necessary to develop a special biomechanical analysis model of the knee joint for squatting and kneeling postures, in order for analyses of the loading to be performed under laboratory conditions.

Activities/Methods:

The biomechanical knee model was developed based upon existing knee models and biomechanical and anatomical findings described in the literature. Its objective was to extend the scope to include squatting and kneeling postures. The model required the entire flexion and extension apparatus of the knee joint, including its tendons and the knee-cap, to be modelled in terms of its kinematics. The focus upon the flexion and extension apparatus enabled the joint forces in the joint portion between the femur and the tibia and on the rear of the knee-cap to be analysed in accordance with the laws of mechanics. In this way, example contact forces in the knee joint were determined under laboratory conditions from combined motion and force measurements in selected forms of squatting and kneeling. Tests were performed on 13 persons in total, including five tilers and five heating system fitters. Tasks specific to particular occupations, i.e. tile-laying and radiator installation, could therefore be studied at the same time.

Results:

The (tibio-femoral) knee joint forces attained uniform values of around 50% body weight (BW) in symmetrical squatting and kneeling postures. The contact force on the knee-cap lay between 80 and 100% BW. During kneeling on one knee, the joint force attained values of between 100 and 140% BW, the force on the patella values of between 170 and 200% BW. Conversely, during kneeling down and standing up, joint forces of between 250 and over 300% BW – around 400% BW on the patella – were measured. For the purpose of comparison, knee-joint forces of between 170 and 250% BW on the leg under load may be anticipated during standing and walking.

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