Duration and frequency of every day activities in total hip patients

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Abstract

Little knowledge about frequency and duration of daily activities in patients after total hip arthroplasty is available. Such information is required for the definition of realistic load collectives for pre-clinical testing of prostheses. It could also be helpful for the quantitative evaluation of surgery outcome with different prosthesis types. The purpose of this study was to develop and apply a system for the determination of frequency and duration of patient activities in their habitual environment and to compare the results to a clinical outcome score (Harris hip score).

A portable activity monitoring system (weight 1.6 kg including batteries) was designed using a Palmtop computer, 2 inclination sensors for the thigh and calf and one goniometer positioned at the knee joint. An algorithm was developed to identify frequency and duration of the activities lying, sitting, standing, walking and stair climbing from the signals of the 3 sensors. 42 patients participated in the study and were equipped with the system in the morning at their home. Datasets of 31 patients (age 62.5±11.5 y) covered more than 6 h (9.8±1.6 h) and were included in the analysis. Prosthesis specific data as well as the Harris hip score were collected.

The most frequent patient activity was sitting (44.3% of the time), followed by standing (24.5%), walking (10.2%), lying (5.8%) and stair climbing (0.4%). The median number of steps/stairs was 6048/164. The number of step cycles representing one year in vivo use should, consequently, be increaesed to 1.1 million. The Harris hip score (91.4±9.8) correlated significantly with the number of stairs (r2=0.26, p=0.003) and showed a positive tendency with the number of steps per day. No differences in activity levels between prosthesis specific factors were found.

Introduction

Testing procedures for artificial joints (Scheller et al., 1999; Brummitt and Hardaker, 1996; Saikko, 1996; Bragdon et al., 1996; Mejia and Brierley, 1994) are based on model calculations (Ramamurti et al., 1996; van den Bogert et al., 1999), in vivo measurements (Bergmann et al., 1993; Bergmann et al., 1997; Kotzar et al., 1991) and rather general estimations of the frequency of loading situations in situ. These are presently restricted to the number of walking steps per year (Schmalzried et al., 1998; Schmalzried et al., 1996). In order to develop, test and optimize total joint replacements in a more realistic manner, a detailed profile of the duration and frequency of the most common daily activities of patients after total hip arthroplasty (THA) is required.

Furthermore, the outcome of THA is typically assessed using several different hip score systems (Bryant et al., 1993; Kilgus et al., 1991; Garellick et al., 1998; Lieberman et al., 1997). The relation between hip scores and the activity level of patients has been established for the UCLA activity rating (Zahiri et al., 1998) but not for the commonly used Harris hip score (HHS) (Harris et al., 1988). It is hypothesized that a higher HHS should be reflected by a more active daily profile. The purpose of this study was to develop and apply a system for the monitoring of total hip patient activities over whole day periods and to evaluate the relation between the individual activity profiles and the Harris hip score.

Section snippets

Methods and material

The frequency and duration of daily activities were determined based on the assumption that the activity of a patient can be identified from the inclinations of the calf and the thigh of one leg. The system was designed to be easy to use, robust and to interfere as little as possible with the normal life of the patient. Consequently the patient was visited at her/his home and equipped with the system there.

Verification measurements

Identification of the defined activities from the video recordings proved to be more difficult as expected, especially regarding the numbers of sequences of walking, stair climbing and standing (Table 4). The deviation of walking and standing sequences were due to problems in differentiating walking movements during standing periods. The deviation of stair climbing sequences were caused by a dog-legged stair with a half-pace: the classifying program identified sometimes only one instead of two

Discussion

Realistic pre-clinical testing of artificial joints is an important aspect in the improvement of durability and survival times of these implants. The data presented in this study together with information regarding in vivo hip joint forces during different activities (Bergmann et al., 1997; Bergmann et al., 1999) allow to define realistic load collectives. This concerns the number of steps walked, the number of stairs de- or ascended and the frequencies of sitting down re. getting up from a

Acknowledgements

This study was supported in part by the European Community, Contract No. SMT4-CT96-2076.

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