Bone sarcomas are the fourth most common cancer in individuals under 25 years. Limb salvage procedures are popular for the treatment of osteosarcomas as they have functional and physiological benefits over traditional amputative procedures. The objective of this study was to apply disease specific measures to a group of intra-articular knee osteosarcoma patients and to evaluate structural and treatment variables predictive of the functional outcome scores. Twenty patients (10 female, 10 male) treated with tumour resection and endoprosthetic knee arthroplasty took part in the study. The Musculoskeletal Tumour Society (MSTS) rating scale and the Toronto Extremity Salvage Score (TESS) were used to assess impairment and disability respectively. Impairment was recorded as 83% and disability was recorded as 86% suggesting moderate to high function following limb salvage surgery. Task difficulty was shown to increase for activities requiring large knee flexion angles, presumably due to increased patellofemoral forces. Bivariate correlations revealed that loss of quadriceps musculature, knee extension strength and knee flexion range of motion were parameters moderately associated with the assessment instruments. ANOVA revealed no significant differences in impairment (P=0.962) or disability (P=0.411) between the differing types of prostheses. In conclusion clinicians and therapists should emphasise restoration of post-surgical range of motion and strength in order to enhance functional recovery.