Influence of the test duration in Posturography performed by healthy adults, THA and TKA patients

The balance control after total hip and knee arthroplasty could be evaluated by means of Orthostatic Posturography. Unfortunately, there is a lack of standardization concerning the test protocol adopted for elderly subjects and arthroplasty patients. The aim of the present study is to analyze the influence of test duration on the posturographic parameters. Two 120 seconds long trials were performed by 220 subjects (47 healthy subjects; 74 total hip and 99 total knee arthroplasty patients), with eyes open and closed, respectively. The test were executed before surgery, and 6 and 12 months after surgery. The statokinesigram was subdivided into eight non-overlapping time windows (15 seconds each), calculating for each window: mean velocity; root-mean-square amplitude of the centre of pressure (resultant, antero-posterior and medio-lateral components); sway area; band of frequencies accounting for 95% of the power (antero-posterior and medio-lateral components). Results in the eyes closed test in healthy subjects and hip arthroplasty patients were significantly higher in the first time window (between 120% and 400% of the value over the whole record). One 60 seconds long test is sufficient to provide a reliable evaluation of balance control in healthy elderly subjects and total hip or knee replacement patients. The higher results obtained in the first 15 seconds suggest that this time window should be excluded from the analysis, to avoid bias due to delayed stabilization.