Stresses and strains in hip joint cartilage during occupational activities

Status:

completed 04/2015

Aims:

Hip osteoarthritis is a disorder of high socio-economic relevance. Besides having a considerable impact upon the health and financial situation of the affected individuals, its impact upon the health system and the economy must also be considered. For example, hip osteoarthritis was the cause of approximately 2.6 million working days lost due to unfitness for work and approximately 1.600 cases of early retirement in Germany in 2011 (source: Robert Koch-Institut 2013. Arthrose. Gesundheitsberichterstattung des Bundes, Vol. 54). The causes of hip osteoarthritis are multifactorial; however, the epidemiological literature regularly cites occupational tasks, such as heavy lifting and carrying, as a risk factor. The level of stresses upon the hip joint caused by occupational tasks, and in particular their possible influence upon the incidence of arthritis, remain largely unclear, however.

Activities/Methods:

Conducted with the cooperation of the Berufsgenossenschaftliche Unfallklinik Murnau (BGUM) and the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA), this project sought to quantify the level of mechanical stresses upon the hip joint during occupational tasks associated with risk. For the purposes of comparison, corresponding stresses arising during everyday activities, such as walking, were determined.

Sectors and occupational activities presenting a high potential for stress upon the hip joint were identified by means of a survey conducted among the accident insurance institutions. Lifting, carrying and load transfer (25 to 50 kg), ladder climbing and stair climbing (without additional load and with an additional load of 25 kg) were selected from among these sectors and activities for the purpose of the study. Laboratory measurements were performed in which motion capturing and a range of force measurement apparatus were used to record and evaluate the performance of the selected tasks by 12 skilled workers from a number of sectors. multi-body simulation was used to calculate the stress in the form of hip-joint contact forces. The contact pressures and their geometric distribution on the cartilage surfaces of the hip joint were then calculated from these results by means of finite-element analysis. This produced an indicator for the strain upon the hip joint.

Results:

The highest hip-joint forces, at (637±148)% of the body weight, occurred during handling of the 50 kg load. This corresponded to 1.7 times the stress arising during walking, at (368±78)% of the body weight. Significantly higher hip-joint forces compared to those arising during walking were observed for the carrying of loads of 40 kg and 50 kg, the handling of loads of 25 kg, 40 kg and 50 kg, and stair climbing with an additional load of 25 kg. Maximum contact pressures of 24.1 MPa were computed during the finite-element analysis (lifting of 50 kg); only very small regions of the joint surface were however affected by these high pressures. During walking, the maximum pressure reached 15 MPa.

The results obtained provide a quantitative overview of the stresses upon the hip joint during occupational and everyday tasks. They constitute an aid to future quantitative exposure assessments in a range of sectors and occupational fields, and thus contribute to improving estimation of the relevance of stresses of occupational origin to the incidence of hip osteoarthritis.

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