Can we quantify a safe margin to reduce local recurrence in parosteal osteosarcomas around the distal femur? A cohort study based on 27 patients

BACKGROUND AND PURPOSE: Parosteal osteosarcoma of the distal femur usually presents as a posteriorly outgrowing tumor that lies close to the popliteal neurovascular bundle, making resection with a wide margin difficult. Tumors are often lower grade meaning surgery often forms the mainstay of treatment. We aimed to evaluate resection margins on local recurrence (LR) and metastasis-free survival rates of patients undergoing surgery for parosteal osteosarcoma of the distal femur. METHODS: This retrospective study evaluated patients with histologically confirmed parosteal osteosarcoma of the distal femur at a single institution between 2000 and 2022, with at least 2 years of follow-up. Patients undergoing primary amputation, those with distant metastases at diagnosis, and those with insufficient clinical information were excluded from the study. Data such as postoperative margins, tumor grade, LR, and metastasis was collected and analyzed. RESULTS: 27 patients were included. Involved margin at resection was recorded in 4 patients: a closest margin of < 1 mm in 14 and ≥ 1 mm in 9. Local recurrence (LR) occurred in 8 patients. Compared with ≥ 1 mm margins, the risk of LR was higher for involved margins (risk difference [RD] 0.75, 95% confidence interval [CI] 0.21-0.95; relative risk [RR] 14.0, CI 0.88-222) and for < 1 mm margins (RD 0.36, CI 0.00-0.61; RR 7.33, CI 0.45-119). Metastasis-free survival showed similar trends. Compared with ≥ 1 mm margins, the risk of metastasis was higher for involved margins (RD 0.25, CI -0.11 to 0.70; RR 6.0, CI 0.29-122) and for < 1 mm margins (RD 0.36, CI 0.00-0.61; RR 7.33, CI 0.45-119). There was no significant difference between the tumor grade and rate of LR. CONCLUSION: A margin greater than or equal to 1 mm showed reduced LR and less metastasis in patients with parosteal osteosarcoma of the distal femur.