Sacral Insufficiency Fractures are Common After High-dose Radiation for Sacral Chordomas Treated With or Without Surgery.

Background: Surgery with high-dose radiation and high-dose radiation alone for sacral chordomas have shown promising local control rates. However, we have noted frequent sacral insufficiency fractures and perceived this rate to be higher than previously reported.
Questions/purposes: We wished (1) to characterize the incidence of sacral insufficiency fractures in patients with chordomas of the sacrum who received high-dose radiation, and (2) to determine whether patients treated with surgery plus high-dose radiation or high-dose radiation alone are more likely to experience a sacral fracture, and to compare time to fracture in these groups.
Methods: Sixty-two patients who received high-dose radiation for sacral chordomas with (n = 44) or without surgical resection (n = 18) between 1992 and 2013 were included in this retrospective study. At our institution, sacral chordomas generally are treated by preoperative radiotherapy, followed by en bloc resection, and postoperative radiotherapy. Radiation alone, with an intent to cure, is offered to patients who otherwise are not good surgical candidates or patients who elect radiotherapy based on tumor location and the anticipated morbidity after surgery (such as sexual, bowel, or bladder dysfunction). MRI and CT scans were evaluated for evidence of sacral insufficiency fractures. Complete followup was available at a minimum of 2 years (or until fracture or death) for all 18 patients who underwent radiation alone, whereas 14% (six of 44 patients) in the surgery plus radiation group (9% [three of 33] after high sacrectomy and 27% [three of 11] after low sacrectomy) were lost to followup before 2 years.
Results: Sacral insufficiency fractures occurred in 29 of the 62 patients (47%). A total of 25 of 33 patients (76%) with high sacrectomy had fractures develop compared with zero of 11 (0%) after low sacrectomy, and four of the 18 patients (22%) who had high-dose radiation alone (p < 0.001). The fracture rate was greater in the high sacrectomy group than in the low sacrectomy group (p < 0.001) and the radiation only group (p < 0.001). There was no difference with the numbers evaluated in fracture probability between patients in the low-sacrectomy group and those treated with radiation alone (p = 0.112). The fracture-free survival probability was 0.99 for the low sacrectomy group at all times as there were no insufficiency fractures in this group; the 1-year fracture-free survival probability was 0.53 (95% CI, 0.35-0.69) after high sacrectomy, 0.83 (95% CI, 0.57-0.94) after radiation alone; the 2-year fracture-free survival probability was 0.36 (95% CI, 0.19-0.52) after high sacrectomy and 0.77 (95% CI, 0.50-0.91) after radiation alone; and the 5-year fracture-free survival probability was 0.14 (95% CI, 0.04-0.30) after high sacrectomy and 0.77 (95% CI, 0.50-0.91) after radiation alone.
Conclusions: Acknowledging the limitations of potential differences in baseline and followup among treatment groups in our study, we found that almost ½ of our patients experienced an insufficiency fracture. We found that the fracture rate was greater in the surgery group compared with the radiation alone group and that high sacrectomy accounted for all fractures in the surgery group. These findings can be used to inform patients and also support the need for further research to elucidate the influence of high-dose radiation on bone quality.
Level of Evidence: Level III, therapeutic study.