Comparative study of the activity of total hip arthroplasty patients and normal subjects

The walking activity of normal subjects and total hip arthroplasty (THA) pa tients from the Wrightington Hospital for Joint Disease and The General Inf irmary at Leeds was assessed by means of electronic pedometers. The princip al objectives were to establish the extent to which joint arthroplasty pati ents recover their activity relative to normal subjects and to establish th e number of loading cycles to which prostheses should be subjected in joint simulator Studies of implant performance. A further objective was to estab lish an experimental procedure for the assessment of the role of activity i n contributing to the well-known scatter in the measurements of femoral hea d penetration into acetabular cups in in vivo studies of implant performanc e. The last-mentioned issue is addressed in another article [1]. The walkin g activity of 2 normal subjects of disparate ages was assessed during I ful l year. It was concluded that fair estimates of activity could be achieved by recording pedometer readings during successive 2- to 4-week periods. Thi s approach was adopted in the full assessment of the walking activity of co horts of normal subjects and THA patients. Linear regression expressions re lating the number of steps taken daily and the annual number of loading cyc les on each leg to age are presented for normal subjects and THA patients. In all cases, activity declines with age, but it is shown that total joint arthroplasty is not at all restrictive on walking activity-a remarkable tes timony to the efficacy of total joint arthroplasty. Attention is drawn, how ever, to different levels of activity of THA patients recorded in the prese nt United Kingdom study and a similar survey conducted in California.