Temporal trends in the incidence, treatment and outcomes of hip fracture after first kidney transplantation in the United States

Abstract

It is currently unknown whether any secular trends exist in the incidence and outcomes of hip fracture in kidney transplant recipients (KTR). We identified first-time KTR (1997-2010) who had >1 year of Medicare coverage and no recorded history of hip fracture. New hip fractures were identified from corresponding diagnosis and surgical procedure codes. Outcomes studied included time to hip fracture, type of surgery received and 30-day mortality. Of 69,740 KTR transplanted in 1997-2010, 597 experienced a hip fracture event during 155,341 person-years of follow-up for an incidence rate of 3.8 per 1000 person-years. While unadjusted hip fracture incidence did not change, strong confounding by case mix was present. Using year of transplantation as a continuous variable, the hazard ratio (HR) for hip fracture in 2010 compared with 1997, adjusted for demographic, dialysis, comorbid and most transplant-related factors, was 0.56 (95% confidence interval [CI]: 0.41-0.77). Adjusting for baseline immunosuppression modestly attenuated the HR (0.68; 95% CI: 0.47-0.99). The 30-day mortality was 2.2 (95% CI: 1.3-3.7) per 100 events. In summary, hip fractures remain an important complication after kidney transplantation. Since 1997, case-mix adjusted posttransplant hip fracture rates have declined substantially. Changes in immunosuppressive therapy appear to be partly responsible for these favorable findings.

Keywords: Bone disease; fracture; kidney transplant; mortality; outcomes.

Figure 1

Flow diagram of cohort derivation.

Figure 2. Comparisons of estimated categorical and linear trends in the incidence of hip fracture in recipients of a first kidney transplant

(A) Unadjusted. (B) Adjusted for age, sex, race and Hispanic ethnicity (Model 1). Exact numbers for hazard ratios and 95% confidence intervals are available in Tables S3 and S4.

Figure 3. Temporal trends in the incidence of hip fracture in recipients of a first kidney transplant

Note: Model 1 is adjusted for demographic variables (age, sex, race, Hispanic ethnicity); Model 2 is additionally adjusted for all comorbidities, dialysis-related and healthcare utilization variables in Table 1 and for BMI; Model 3 is additionally adjusted for all transplant variables in Table 1; Model 4 is additionally adjusted for induction and baseline immunosuppression. p-Values for linear year in Models 1–3 were <0.001. Exact numbers for hazard ratios and 95% confidence intervals are available in Table S4.

Figure 4

Three-year cumulative hip fracture incidence in recipients of a first kidney transplant, stratified by age and sex.

Figure 5. Trends in the surgical treatment received for hip fracture

(A) Number of hip fracture treatments, by category and year. (B) Proportion of hip fracture treatments, by category and year. Note: Other includes reduction and repair not otherwise specified. Tests for trend of the use of internal fixation versus other treatment were not significant in unadjusted or any of the adjusted models.