Sarcoma, Bone

The goal of DEEPGAIT study is to determine how serious walking problems are for pediatric cancer patients who have had orthopedic surgery, how they change over time, and what can be done to help. Healthy participants without cancer will also be included in this study in order to better understand the difference in walking problems between the 2 groups. DEEPGAIT is a long term study that uses advanced tools-including 3D motion capture, muscle sensors, force plates, and wearable devices-to take a detailed look at how these patients move. Their results are compared to healthy children of the same age and sex. PRIMARY OBJECTIVES * Characterize gait deficits in pediatric cancer patients 1 year following orthopedic surgery for lower limb bone sarcoma, soft tissue sarcoma, or steroid-induced avascular necrosis. * Identify personal, disease, treatment and environment risk factors for gait deficits in pediatric cancer patients 1 year following orthopedic surgery for lower limb bone sarcoma, soft tissue sarcoma, or steroid-induced avascular necrosis. SECONDARY OBJECTIVES * Build a library of broadly representative normative reference values to generate age- and sex-matched z-scores to quantify frequency, severity and progression of gait deficits among pediatric cancer patients in relation to healthy controls. * Characterize the changes of gait parameters in pediatric cancer patients with or without gait deficits 1 year after orthopedic surgery for lower limb bone sarcoma, soft tissue sarcoma, or steroid-induced avascular necrosis, up to 5 years after surgery. * Identify personal, disease, treatment and environment risk factors for trajectories of gait deficits in pediatric cancer patients with or without gait deficits 1 year after orthopedic surgery for lower limb bone sarcoma, soft tissue sarcoma, or steroid-induced avascular necrosis, up to 5 years after surgery.