VALIDATION OF AN ACCELERATION BASED GAIT TEST

Abstract

In joint arthroplasty and in knee replacement in particular, the currently used patient assessment scores like KSS, are characterized by subjective ceiling effects. To monitor patients accurately in time, objective function assessment is required which is impossible with the classic scores. A single time point comparison study showed that an acceleration based gait test is reliable to analyze gait and to distinguish between knee pathologies. How-ever the use of an accelerometer to monitor functional changes over time is never reported before and will be investigated in this study. A representative group of 29 TKP patients (11 men, mean age 72yrs, weight 85kg, height 1.68m) operated for osteoarthritis receiving unilateral TKP (Stryker Scorpio) were monitored for 3 months. Classic scores (ROM, KSS, WOMAC, VAS, PDI) and the gait test was performed pre, 2 and 6 weeks and 3 months postoperative. Gait was analyzed using a triaxial accelerometer fixed to the sacrum while walking 6 times 20meters at preferred speed. Movement parameters like step frequency, step time, step length, speed and up/down displacement were calculated based on a peak detection algorithm. The gait test was compared with the classic scores using Pearson correlation. The paired t-test was used to investigate the changes after surgery (p< 0.05). Significant correlations were shown between all classic scores and all movement parameters (except up/down displacement and step length). The function KSS and PDI showed significant correlations with most gait parameters, while all Womac scores did not. Two weeks after surgery, the classic scores reached the preoperative scores. For instance function KSS was 57.21 preoperative and reached a score of 59.75 at 2 weeks postoperative. No significant changes were shown between preoperative and 2 weeks postoperative for the VAS, KSS and PDI. In contrast all gait parameters were significantly impaired at 2 weeks postoperative (step time of 0.63s) compared to preoperative (step time of 0.72s) and reached the preoperative functional abilities only at 6 week follow up or still later (step time of 0.64s). Between the 2nd and 6th week postoperative, significant changes were shown in all classic scores, ROM and in speed, up/down displacement. After 6 weeks postoperative KSS, PDI, ROM and the frequency improved significantly. The correlations between all movement parameters and function KSS and PDI indicates that these scores are more function based due to inclusion of objective function measures like ROM, while the Womac contains only questions about ADLs. According to the classic scales, patients show at 2 weeks similar skills as preoperative, while the gait test shows that patients are performing less at 2 weeks and reach the pre operative ability at 6 weeks. This suggest that the addition of the gait test give more information about the functional changes a patient experiences after surgery.