Assessment of objective ambulation in lower extremity sarcoma patients with a continuous activity monitor: Rationale and validation

In addition to patient reported outcome measures, accelerometers may provide useful information on the outcome of sarcoma patients treated with limb salvage. The StepWatch (SW) Activity Monitor (SAM) is a two-dimensional accelerometer worn on the ankle that records an objective measure of walking performance. The purpose of this study was to validate the SW in a cross-sectional population of adult patients with lower extremity sarcoma treated with limb salvage. The main outcome was correlation of total steps with the Toronto Extremity Salvage Score (TESS). In a sample of 29 patients, a mean of 12 days of SW data was collected per patient (range 6-16), with 2767 average total steps (S.D. 1867; range 406-7437). There was a moderate positive correlation between total steps and TESS (r=0.56, P=0.002). Patients with osseous tumors walked significantly less than those with soft tissue sarcoma (1882 versus 3715, P<0.01). This study supports the validity of the SAM as an activity monitor for the objective assessment of real world physical function in sarcoma patients.