Using data that are nationally representative of the Medicare fee for service population of older Americans, we found that approximately 50% of vertebral fractures and 3% of hip fractures were coded as pathologic fractures. For only approximately 25% of persons with vertebral fractures identified using a “pathologic fracture” ICD-9 code, but 66% of persons with pathologic hip fractures, there was evidence of a possible cancer diagnosis.
The underlying explanations for why a fracture that is solely due to osteoporosis would be coded as a pathologic fracture are unclear but could relate to the amount of trauma associated with the fracture, administrative coding ambiguities or even to reimbursement advantages. A vertebral fracture may occur spontaneously and thus be more easily identified as occurring due to a disease (e.g. osteoporosis) and, therefore, coded as a pathologic fracture (ICD9 733.13). In contrast, a hip fracture usually occurs in association with a fall, even though the fracture may have caused the fall. Perhaps for this reason, hip fractures may be more likely to be coded as traumatic fractures (ICD9 800-829), and we found that a code for a pathologic hip fracture is considerably more likely to suggest underlying malignancy than for a vertebral fracture. Consistent with this explanation, women and younger persons were significantly more likely to have a pathologic fracture diagnosis of the spine but not the hip. This suggests the possibility that osteoporosis (rather than cancer) was more easily recognized as being responsible for the vertebral fracture. Additionally, for a hospitalized vertebral fracture in the U.S., a pathologic fracture diagnosis (ICD9 733.13) generates a higher-weighted Diagnosis Related Group (DRG) and thus higher reimbursement to the facility than a non-pathologic fracture diagnosis (ICD9 805.X). This circumstance does not extend to other fractures that require surgical management since reimbursement for the procedure will generally be equivalent regardless of the fracture diagnosis code used.
The results of our study must be interpreted in light of its methodologic design. We used administrative claims data and did not have access to medical records, so we could not confirm incident fractures or cancer diagnoses. However, we used claims-based fracture identification algorithms that have been shown to perform well in prior validation studies that did have access to medical records (5
). Administrative claims data have also been shown to identify malignancies with high validity (8
). The definition of malignancy that we used intentionally maximized sensitivity over specificity; we did not, for example, require treatment with radiation or chemotherapy as might be expected for many incident cancers that had skeletal complications. Therefore, our estimates of the prevalence of cancer are likely too high. Moreover, even among persons with both a pathologic fracture and cancer, one cannot assume that the fracture was due to the cancer. Finally, we acknowledge that patterns of fracture care and administrative coding in the U.S. may be different than in other countries with different reimbursement structures and administrative data coding, and thus our results may not be generalizable to these settings.
In conclusion, we found that a large proportion of vertebral fracture cases is coded as pathologic, yet only in a minority of these is there evidence of a malignancy. In contrast, the majority of hip fractures coded as pathologic seem to be associated with cancer diagnoses. Future studies of the epidemiology and outcomes associated with fractures should be explicit about how they handle pathologic fractures, since excluding them may substantially underestimate the burden of fractures due to osteoporosis.