Factors Affecting Wear. Patient Activity Level

, Paul D. Siney¹ and Patricia A. Fleming¹

(1)

The John Charnley Research Institute Wrightington Hospital, Wigan, Lancashire, UK

… wear is related more to the grade of functional activity than the weight of the subject. (1973).

It was clear that any study of factors affecting wear of the UHMWPE cup had to take patient activity level into account. Although there is agreement as to its importance, translating “activity level” into some standard and uniformly acceptable form has proved more difficult. Other than enumerating some common activities often related to sport or employment, the tendency has often been to present anecdotal, single case successes.

Theoretical Considerations

We set out to assess patients’ activity level as expressed in terms of load and sliding distance at the level of articulation.

It was assumed that walking is the main activity and the highest load to which the hip joint is subjected, other than occasionally. If leg length, stride length and the time taken to walk a measured distance were known, then the sliding distance at the level of the articulation could be calculated as a simplified to and fro linear motion.¹

Clinical Assessment of Activity Levels [1]

Patients selected for the study fulfilled two set criteria: the follow-up was not less than 8 years and patients considered the outcome a success. Seventy nine patients, 109 Charnley LFAs, were included in the study.

A detailed questionnaire, completed at an interview, was used as an indication of activities over a typical 1 week period. As a result each patient was assigned to a one of five activity grade based on the estimated distance walked during 1 week (The distance walked during 1 week varied from 1 km to more than 25 km). In order to validate the estimates, as recorded in questionnaires, 21 patients were selected for pedometer studies. Their leg and stride length, as well as the time to walk a measured distance, were recorded.

Detailed statistical analysis has shown that: