Is anterior knee pain a predisposing factor to patellofemoral osteoarthritis?
Introduction
Adolescent anterior knee pain has traditionally been considered a benign self-limiting disease with no long-term sequelae [1]. Few studies have charted the natural history of idiopathic anterior knee pain, but Nimon et al. [2] in a 20 year follow up study have shown one in four patients continuing to have significant symptoms over this period of time. They were however unable to identify any factors predicting those patients in whom symptoms would persist. Stathopulu and Baildam in a shorter follow up of 22 anterior knee pain patients between 4 and 18 years after their initial presentation found 91% still having knee pain of varying frequency and intensity although 45% were later diagnosed with other arthritic conditions [3]. These studies may suggest that anterior knee pain main not be the benign entity that it is traditionally considered.
In middle aged and elderly patients with anterior knee pain, patellofemoral arthritis is a relatively commonly encountered problem, with 13.6% women and 15.4% of men greater than 60 years of age having radiological evidence of isolated patellofemoral arthritis [4], [5]. As yet, no causal link has been identified between idiopathic adolescent anterior knee pain and patellofemoral osteoarthritis. The aim of this study was to examine this possible link by means of a comparative study of two patients groups, one who had undergone patellofemoral arthroplasty for isolated patellofemoral arthritis, and a control group who had undergone medial unicompartmental arthroplasty for isolated medial compartment arthritis. Both groups were surveyed as to whether they had suffered with anterior knee pain, knee injury and patellar instability.
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Patients and methods
150 patients who had undergone isolated patellofemoral arthroplasty were identified from the Bristol Knee Arthroplasty Database. The criteria for the operation included severe patellofemoral osteoarthritis and an absence of changes in the tibiofemoral compartment. These patients were assessed for precipitating factors and particularly for a history of anterior knee pain. Each patient was sent a postal questionnaire relating to their past experiences of patellofemoral problems. The questionnaire
Results
Almost 80% of both groups returned their questionnaire. The demographic data for the two groups were similar (Table 1). Mean age at operation was similar for both groups. The number of patellofemoral arthroplasty patients who had suffered with adolescent anterior knee pain (22%) was much higher than in the medial unicompartmental arthroplasty group (6%). This difference was statistically significant (p<0.001).
Patients who underwent isolated patellofemoral replacement recalled suffering from
Discussion
A significant number of patients who have isolated patellofemoral arthritis suffered with anterior knee pain in their adolescent or early adult life and many report having symptoms 20 years prior to their arthroplasty thus suggesting that the problem has been more or less continuous throughout their life and that adolescent anterior knee pain or “chondromalacia patellae” may have lead to isolated patellofemoral osteoarthritis. Ficat has described in his classification of chondromalacia patellae
Acknowledgements
We would like to thank Sue Miller for her help in running the Bristol knee database and sending out the questionnaires and Dr. Paul Ewings for providing statistical expertise.
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