Can femoral neck-shaft angle predict timing of contralateral second hip fracture? A 7-year retrospective cohort study at a tertiary referral centre for trauma.

Introduction: Previously published literature from our institution found that patients with a fragility hip fracture were estimated to have a 4-10% risk of sustaining a second contralateral hip fracture. A follow-up, multi-centre study found that 1 in 11 (9.1%) patients sustained a contralateral hip fracture within three years of index hip fracture. Previous studies have examined the anatomic geometry of the hip joint as a risk factor for hip fractures. Our study aimed to establish a relationship between the neck-shaft angle (NSA) of the contralateral hip in patients who had already suffered a hip fragility fracture in terms of timing to second hip fracture.

Methods: A 7-year, single-institution, retrospective cohort study of patients that presented with a second contralateral fragility hip fracture from 2013 to 2019 were reviewed. Inclusion criteria were all patients 60 years old and above who suffered a second contralateral hip fracture. Exclusion criteria were all patients who were aged less than 60 years old, high-energy injuries or those who suffered peri-prosthetic fractures. The NSA was calculated by measuring the intersection of the femoral neck axis and the femoral shaft axis of the hip. Age, gender, surgery type and American Society of Anaesthesiologists Physical Status Classification (ASA) score were also examined.

Results: Ninety-four patients were suitable for analysis. NSA ranged from 113 to 146.5 degrees with an average of 130.2 degrees. Female patients had an average NSA of 129.7 degrees compared to 131.3 degrees in male patients. Average time to second hip fracture was 3.5 years, ranging from 0.08 years (29 days) to 20 years (7326 days). There was a 2.3:1 ratio of female-to-male presentations. Patient age ranged from 60 to 100 years old. The largest age group included patients aged 80-89 years, with 38 patients (28 females and 10 males). Correlation analysis performed showed no statistical significance between NSA and timing of second contralateral hip fracture with a p value of 0.235. There was an association between fracture type, specifically intracapsular hip fractures, and time to second hip fracture, but this was not statistically significant (p value 0.052).

Conclusion: There is no statistically significant association between femoral NSA and time to second fragility hip fracture. As we have excluded NSA as an independent risk factor, further studies may now be carried out to look for other potential predictors of timing to second hip fracture.