Malalignment is the most important risk factor for fixation failure after intertrochanteric fracture treated with a cephalomedullay nail (CMN). Malalignment continues to occur despite advances in surgical techniques.

We hypothesized that small femur canal size causes intra-operative reduction loss during cephalomedullary nail insertion.

A retrospective study was performed from 2014 to 2017. Patients with acute intertrochanteric fracture implanted with the same sized CMN (Stryker, Mahwah, NJ, USA, diameter: 10mm, length: 170mm, degree 130) were included. Evaluated radiographic parameters included femoral canal size, corrected neck-shaft angle, and calcar reduction.

The study totally included and analyzed the data from 108 patients. Patients with smaller femoral canal size tended to have increased calcar distance according to Pearson's correlation coefficient analysis (r(106)=−0.805, p<0.001). Patients with calcar mal-reduction had higher corrected neck-shaft angle post-operatively. This observed correction tended to be lost during follow up.

Small femoral canal size resulted in poorer reduction quality. Reduction loss during nail insertion may be due to the whole proximal fragment instead of the superolateral femoral neck. Reaming the isthmus before nail insertion or choosing a smaller sized CMN is indicated in this patient population to prevent intra- or post-operative loss of reduction.

III; retrospective study.