Background/Purpose: Tibia/Fibula (Tib/Fib) fractures are one of osteoporotic fragility fractures. They have been suggested to be more likely to occur secondary to osteoporosis (OP) than any other fracture (1).  Furthermore, as they are more likely to be open fractures, are more prone to infections and other co-morbidities. It is known that body mass index (BMI) is a protective factor in fragility fractures whilst low Bone Mineral Density (BMD) is known to be predictor of fragility fractures. However the specific predisposing factors for Tib/Fib fragility fractures are not known. Furthermore risk of factues is determined using the femoral neck in the FRAX ™ tool. Use of lumbar spine BMD has not been examined as a specific predictor.  We aimed to use a Case-Control approach to examine these predictors for Tib/Fib fractures.  

 Methods: A cohort of patients referred after a Tib/Fib fragillity fracture for a DEXA scan in the North West of England between 2004 and 2011 were identified, and were age and sex matched with scanned controls that had no indications for a scan. Students T-Test and Chi 2 test were used to test for any differences between the groups in terms of continuous and categorical variables respectively.  Logistic models were fitted examining the contribution of risk factors to tib/fib using BMD in the femoral neck and the lumbar spine.

Results: 797 patients were matched to 797 controls, 679 (85%) were female. Mean age in both cases and controls was 64.3years (SD11.3). Surprisingly, mean BMI  was higher in the fracture group 28.3 kg/m2 vs 26.7 kg/m2 (p<0.01). This was mostly due to the fracture group being heavier (74.6kg vs 69.7 kg p<0.01)  Univariate analysis showed an unadjusted odds ratio of  1.06 (95%CI 1.04,1.08) , after adjustment for the lumbar spine BMD , the difference persisted (OR 1.06 95%CI 1.04,1.08) and after adjusting for femoral neck BMD this also persisted (OR 1.05 95%CI 1.02,1.09).  This would suggest that that BMI does not influence the risk of developing Tib/Fib fragility fractures. This is contrary to what is stated in literature in relation to fragility fractures.

Conclusion: This study would seem to indicate that people with higher BMI values tend to get Tib/Fib fragility fractures compared to a control population. this persisted after adjusting for BMD, an obvious confounder. This suggests that other factors are involved in increasing the risk of Tib/Fib fractures. Further work is therefore needed to assess other predictors for Tib/Fib fractures.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/osteoporotic-fragility-tibiafibula-fractures-are-not-asociated-with-a-low-body-mass-index-an-observational-study/