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Many variables have retrospectively been associated with the presence of anterior knee pain. Very few prospective data exist, however, to determine which of these variables will lead to the development of anterior knee pain. It was our purpose in this study to determine the intrinsic risk factors for the development of anterior knee pain in an athletic population over a 2-year period. Before the start of training, 282 male and female students enrolled in physical education classes were evaluated for anthropometric variables, motor performance, general joint laxity, lower leg alignment characteristics, muscle length and strength, static and dynamic patellofemoral characteristics, and psychological parameters. During this 2-year follow-up study, 24 of the 282 students developed patellofemoral pain. Statistical analyses revealed a significant difference between those subjects who developed patellofemoral pain and those who did not concerning quadriceps and gastrocnemius muscle flexibility, explosive strength, thumb-forearm mobility, reflex response time of the vastus medialis obliquus and vastus lateralis muscles, and the psychological parameter of seeking social support. However, only a shortened quadriceps muscle, an altered vastus medialis obliquus muscle reflex response time, a decreased explosive strength, and a hypermobile patella had a significant correlation with the incidence of patellofemoral pain. We concluded that the latter four parameters play a dominant role in the genesis of anterior knee pain and we therefore deem them to be risk factors for this syndrome.

fear-related avoidance of activities may have negative effects on physical abilities and may also be predictive for future falls. Avoidance of activities is therefore an important additional psychological variable in the development of physical frailty and falling in community-living elderly.

Heterotopic ossification is defined as the presence of lamellar bone at locations where bone normally does not exist. The condition must be distinguished from metastatic calcifications, which mainly occur in hypercalcaemia, and dystrophic calcifications in tumours. It is a frequent complication following central nervous system disorders (brain injuries, tumours, encephalitis, spinal cord lesions), multiple injuries, hip surgery and burns. In addition to this acquired form, hereditary causes also exist, such as fibrodysplasia ossificans progressiva, progressive osseous heteroplasia and Albright's hereditary osteodystrophy. Although these conditions are extremely rare, they can provide useful information on the physiopathology of heterotopic ossification, and thus lead to novel and causal treatment modalities. Heterotopic ossification is no trivial complication. A limitation of the range of joint motion may have serious consequences for the daily functioning of people who are already severely incapacitated because of their original lesion. Increased contractures and spasticity, pressure ulcers and increasing pain further compromise the patient's capabilities. Consequently, we feel that attention should be paid to the pathogenesis and particularly the prevention and treatment of this disorder.

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