Discussion:
In this retrospective study, vertebral fragility fractures were detected in 56.4% (n=114) of the patients. Forty-six (40.3%) patients with VF had normal DEXA. Osteoporosis and osteopenia were observed in 20% and 35.6% of the whole study group. Diabetic patients had lower BMD levels and Z scores both in the femoral neck and lumbar spine.
Age and BMI, which have already known as predictive factors of osteoporosis in the general population, were found as the factors associated with femoral neck BMD scores in renal transplant recipients in our study. Techawathanawanna et al. also stated that the decreasing BMI and increasing age were correlated with osteoporosis of the hip region [3].
The standardized incidence ratio of vertebral fractures was 23.1% in Vautour et al.’s study [24]. Vertebral fractures were detected in 1.8% of patients in the O’Shaughnessy et al. study [25]. On the other hand, in Nam et al., Durieux et al., Vautour et al., Schreiber et al., Patel et al., and Pichette et al. study the prevalence of VF was 38.5%, 28.8%, 15.1%, 14.3%, 9.1%, and 5.7%, respectively [4, 17, 18, 23, 24, 27]. While Nam et al. [23] and Patel et al. [18] evaluated VF respectively with X-ray morphometric criteria and semiautomated method, the rest of the studies used a semiquantitative method. This wide distribution rate among studies on vertebral fracture frequency can be attributed to different definition criteria in the fracture decision.
Increased fracture risk was associated with diabetes mellitus in previous reports [25, 28]. In Vautour et al. study [24], increasing age and diabetes as the cause of end-stage renal disease were found as independent predictors of overall fracture risk. While the standardized incidence ratio of vertebral fracture was 33.5% in the diabetic patient, it was 21.2% in the non-diabetic group [24]. While the presence of diabetes was not associated with vertebral fractures in our study, diabetic patients had lower BMD levels both in the femoral neck and lumbar spine.
Low BMD in the femoral neck and lumbar spine was associated with an increased risk of vertebral fractures [23]. In our study, femoral neck Z scores were found to be associated with vertebral fractures.
In a study with 238 kidney transplant recipients, patients with osteoporosis were found to have a 3.5-fold increased risk of fracture than patients with normal BMD [5]. Contrary to Nam et al. study [23], BMD levels showed no significant differences between patients with VF and without VF in our study. In the Marcel et al. study, vertebral fractures were primarily observed in osteoporotic patients, but 43% of patients with VF had normal lumbar BMD [6]. In our study, the VF ratio in patients with normal BMD was 40.3%. Although our osteopenia and osteoporosis rate is lower than most previous reports, lower prevalences have been reported [5, 17]. This difference between studies may be attributed to false signals from extra‐osseous calcifications or falsely high values obtained from unrecognized mechanical bone deformation or pre‐existing renal osteodystrophy.
Lumbar BMD losses have been reported as 3–10% in the first six months following kidney transplantation [9]. Although there are no well-established therapeutic approaches to prevent early post-transplantation bone loss, the most recommended manners to provide bone anabolic effects in renal transplant recipients are; minimizing the dose of corticosteroids and using vitamin D supplements, active vitamin D (calcitriol or alfacalcidol), or bisphosphonates [29-31]. In addition, determining the high-risk group for fractures with routine vertebral radiological imaging can be helpful to decide giving treatment to renal transplant recipients in the early period.
The major limitation of this study is that the evaluation of vertebral fractures was made using a semiquantitative method. Secondly, we evaluated retrospectively, limiting our ability to determine the exact timing of the occurrence of VF, whether it had occurred before transplantation. To determine the occurrence time of VF, prospective studies with long-term follow-up with a routine evaluation of spine X-rays at regular intervals before and after transplantation are needed.
In this study, a high vertebral fracture prevalence was found regardless of osteoporosis and CRF duration. Vertebral fractures were observed more frequently in patients with normal BMD. Besides the BMD evaluation, vertebral fracture evaluation may help a proper therapy decision for metabolic bone disease in kidney transplant recipients.
Funding: This study did not receive any specific grants from any funding agencies in the public, commercial, or not-for-profit sector.
Conflict of interest: Dilek Gogas Yavuz, Kadriye Aydin, Tugce Apaydın, Arzu Velioglu, Meral Mert, Zafer Pekkolay, Ergun Parmaksiz, Meral Mese, Ayse Esen Pazir, Emre Aydın, Onur Bugdayci, Serhan Tuglular declare that they have no conflict of interest.