Exercise and Functional Performance in Middle-aged Patients with Knee Osteoarthritis

The overall purpose of this thesis was to explore the impact of exercise and functional performance on development and treatment of knee osteoarthritis in the middle aged. In this thesis, I have studied a population based cohort of middle-aged subjects (35-54 years, 42 % women) with chronic knee pain at baseline, to evaluate the longitudinal effect of muscle weakness on knee osteoarthritis development, the relationship between muscle function and joint load and the effects of exercise on joint load. I have also studied the effect of exercise on pain and function in another middle-aged cohort (36-65 years, 51 % women) with moderate to severe knee osteoarthritis, and explored their conceptions of exercise as treatment. In the first study, 148 subjects with chronic knee pain underwent radiographic examination and tests of functional performance at baseline. 94 of them had no radiographic signs of knee osteoarthritis. Five years later they had new radiographs taken and 41/94 (44 %) had developed incident knee osteoarthritis. I found that reduced functional performance, assessed by maximum number of one-leg rises from a stool, predicted knee osteoarthritis development. The result was controlled for the previously known risk factors of age, BMI and pain. In the second study, I used 3-dimensional motion analysis to explore the possibility of altering joint load by exercise. The medial compartment joint load (peak adduction moment) during maximum number of one-leg rises was assessed in 13 subjects with early radiographic signs of knee osteoarthritis from the cohort in study one, before and after 8 weeks of exercise. Two subjects were lost to follow up for reasons not related to the knee. The peak adduction moment could be reduced by exercise, and a high maximum number of one-leg rises was associated with lower levels of peak adduction moment. The third study included 61 subjects with moderate to severe radiographic knee osteoarthritis. They were randomized to 6 weeks of intensive exercise or to a control group. The effects of exercise were assessed using questionnaires. No effects were seen on pain or self estimated function, however, the quality of life improved. The individual response to exercise ranged from clinically significant improvement to clinically significant worsening. As an attempt to understand this large inter individual response to exercise, I designed the fourth study, where I interviewed 16 of the 30 patients in the exercise group about their conceptions of exercise as treatment. The interviews were analysed using qualitative methodology, and it was revealed that all patients were aware of the general health benefits of exercise, but had doubts about exercise as treatment of osteoarthritis even if they had perceived pain relief and improvement in physical function from the exercise intervention. The pain experienced during exercise caused the patients to believe that exercise was harmful to their knees, and some of them would prefer not to exercise at all. They thought that exercise should be introduced early during the course of the disease, and all of them expressed the need of continuous encouragement and support to adhere to exercise. From this thesis I conclude that reduced muscle function is a risk factor of knee osteoarthritis development among middle aged subjects with knee pain. Reduced muscle function is associated with increased joint load, which seem to be modifiable by exercise. Initial pain when starting exercise, or occasional pain from exercise, should be treated by combining exercise with pain relief such as analgesics or acupuncture. Pain contributes to the difficulty patients have determining the degree of benefit or damage related to exercise, and thus causes feelings of anxiety and helplessness (paper IV). Pain also seems to interfere with the possibility of achieving increased functional performance (paper II, III, IV)