Is there a femoral morphology at risk of a cervical or pertrochanteric fracture? Description and validation of the “Neck shaft ratio” and the “Intertrochanteric distal ratio” after analyzing a continuous cohort of 126 bilateral fractures of the proximal femur

Background

Proximal femur fractures constitute a public health concern given their high frequency and the aging population. The frequency of a contralateral fracture occurring can reach up to 15% of cases. Certain historical or demographic factors constitute risk factors for refracture, but the type of fracture, either of the femoral neck (FN) or pertrochanteric (PT), cannot be predicted. The objectives of this retrospective study were: firstly, to analyze several anatomical markers in order to determine whether they predispose to a certain type of fracture in the event of contralateral refracture, and secondly, to determine the predictive power of these possible radiological markers for the type of contralateral fracture.

Hypothesis

The hypothesis was that the “Neck shaft ratio” (NSR) and the “Intertrochanteric distal ratio” (ITDR) made it possible to determine a proximal femoral morphology at risk of FN and/or PT fracture in the event of a second fracture.

Material and methods

This continuous retrospective single-center series from January 2011 to December 2019 of patients who presented with bilateral fractures of the proximal femurs was analyzed. Radiographs, taken after the first fracture, of the contralateral femur were studied. Morphological measurements previously described in the literature were carried out as well as the NSR (ratio of the medial cortical thicknesses of the femoral neck at its narrowest and basicervical level) and the ITDR (ratio of the medial diaphyseal cortical thicknesses at 5 mm and 20 mm from the distal portion of the lesser trochanter). One hundred and twenty-six patients were included: 46/126 (36.5%) had bilateral FN, 50/126 (39.7%) bilateral PT and 30/126 (23.8%) one of each.

Results

Only NSR and ITDR were significant predictive measures for FN or PT fracture type [0.54 ± 0.11 vs. 0.81 ± 0.16 (p < 0.0001) and 0. 85 ± 0.1 vs. 0.68 ± 0.1 (p < 0.0001), respectively]. These two ratios had an excellent predictive value for the type of fracture occurring on the contralateral side [NSR: AUC ROC = 0.91 (95% CI; 0.86–0.96); ITDR: AUC ROC = 0.81 (95% CI; %, 0.74–0.89)]. The NSR had excellent intra- and inter-observer reproducibility with an interclass correlation coefficient of 0.93 [95% CI: 0.86–0.97] and 0.91 [95% CI: 0.82–0.96] respectively, the same also applied for the ITDR with interclass correlation coefficient values of 0.93 [95% CI: 0.87–0.97] and 0.86 [95% CI: 0.73–0.93] respectively.

Discussion

The NSR and ITDR ratios offer a simple and reproducible means to predict a morphological predisposition to a certain fracture type, respectively an FN and PT on the side contralateral to an initial osteoporotic proximal femur fracture. A prospective cohort study would be useful in defining a possible prognostic nature on the occurrence and/or time until refracture.

Level of evidence

III; retrospective control case.