Insufficiency fractures in patients with sacral chordoma treated with high-dose radiation therapy with and without resection.

Objectives: Determine the incidence, location, and features of insufficiency fractures (IFs) in sacral chordoma patients treated with high-dose radiation therapy (HDR) with(out) resection, relative to radiation therapy type and irradiation plans.

Methods: Clinical data, including details of all surgical procedures and radiotherapies of patients histologically diagnosed with sacral chordoma between 2008 and 2023 available at our database, were retrospectively reviewed. Inclusion criteria were as follows: availability of diagnostic, treatment planning and follow-up magnetic resonance and/or computed tomography scans, and completed treatment. Scans were re-evaluated for the presence and location of IF defined as linear abnormalities with(out) bone marrow oedema (BME)-like changes.

Results: From 48 included patients (29 male, median age 66, range 27-85), 22 were diagnosed with 56 IF (45.8%). IF occurred 3-266 months following the treatment. All sacral and iliac bone IF had vertical components parallel to the SI joint. Twenty patients had bilateral and 16 unilateral IF. BME-like changes were visible in 46 IF (82.1%, 0.80, P ≤ .001). In 13/56 IF (23.2%), BME-like changes were seen prior to IF diagnosis; in only 1 patient, BME-like changes did not develop into an IF. Thirty-nine IF (84.7%) occurred within low-dose volume and 7 (15.3%) outside of irradiated volume in 16/44 irradiated patients. Six IF occurred in 1 patient treated with surgery only.

Conclusions: Pelvic IFs are common in sacral chordoma patients treated with definitive or (neo)adjuvant HDR, occurring months to years following treatment. Not all IF occur in the irradiated volume.

Advances in knowledge: When present, BME-like changes indicate risk of IF developing. IF do not heal over time.