AUA 2018: Risk of Bone Fractures Following Urinary Intestinal Diversion: A Population-Based Study

San Francisco, CA ( Urinary diversion is an integral part of the management of muscle-invasive bladder cancer; often, the removal of the bladder is the less involved portion of the case. Urinary diversion comes in many forms, and while different segments of bowel can be used, ileum is used most often as it has been shown to have the least consequences from a post-operative metabolic standpoint. Even in patients with an incontinent ileal conduit, metabolic complications still occur – most often, metabolic acidosis. These metabolic changes can have theoretical implications for patient care, independent of cancer outcomes. One such theoretical risk is that of bone fractures due to calcium resorption, yet this has never been demonstrated – indeed, bone fractures may also occur due to disease progression instead.

To answer this question, the authors used administrative databases in Ontario, Canada – leveraging the strength of a fully government-run healthcare system – to identify all patients who underwent a urinary intestinal diversion between 1994 and 2014. Patients were categorized as being diverted for BC or non-BC (other malignancy, benign etiologies) and matched 4:1 to a control cohort (4x as many controls at their tested cohort) who had no history of malignancy or urinary diversion. Diversion in the setting of BC and non-BC were assessed independently to distinguish pathologic fractures from bone metastases versus acidosis-induced fractures, respectively.

  • Patients were matched on age, gender, Charlson comorbidity score, neighborhood income quartile, area of residency, history of chemotherapy, CKD, prior fractures, era and type of urinary diversion
4301 BC patients and 907 non-BC patients underwent a urinary intestinal diversion during the study period. The incidence rate of fracture was significantly greater in the BC and non-BC cohorts when compared to their respective matched-controls [6.05 vs. 3.83 fractures per 100 persons-years (p<0.01) for the BC cohort and their matched-controls; and 5.67 vs. 3.51 fractures per 100-persons-year (p<0.01) for the non-BC cohort and their matched-controls, respectively]. Time to first fracture was also shorted in the patients treated with urinary diversion. 

On multivariable analysis, patients that had undergone a urinary diversion (be it for BC or non-BC reasons) had significantly shorter fracture-free survival compared to their respective matched-cohorts [HR:1.6 (1.4-1.8) and HR:1.36 (1.1-1.7), respectively].

Based on this, the authors conclude that patients who underwent a urinary intestinal diversion are at increased risk of bone fractures compared to the general population. However, it should be noted that association doesn’t mean causation – other confounders may account for increased risk of pathologic fractures. Unknown confounders, which may not have been matched for, may contribute.

Regardless, as preventative measures such as calcium and Vit D supplementation, carry minimal risk, it is worth improving patient and physician education in patients undergoing intestinal diversion.

Limitations / Discussion Points:
1. Patients in the non-BC category had diversions for many causes – including non-BC malignancy. Therefore, these patients may also have had pathologic fractures from other diseases, which can’t be accounted for.

Presented by: Patrick O. Richard, the University of Toronto and University of Sherbrooke, Canada
Co-Authors: Shaheena Bashir, Amit Gupta, Neil Fleshner, Alexandre Zlotta, Roselyne Choinière, Aza Mohammed, Girish Kulkarni

Written by: Thenappan Chandrasekar, MD, Clinical Fellow, University of Toronto, @tchandra_uromd at the 2018 AUA Annual Meeting - May 18 - 21, 2018 – San Francisco, CA USA