The Bock Effect

Background:
Trochanteric fractures are among the common fractures admitting to the ER. The treatment of choice is internal fixation using an intramedullary nail(IMN). The surgical technique mandates an anatomical reduction followed by insertion of the nail. Often a varus malalignment after nail insertion can be noticed.

Hypothesis:
A sub optimal anatomical reduction will lose alignment after nail insertion in fixation of trochanteric fractures by a block to reduction – “block effect”.

Materials and Methods:
A retrospective study of thirty consecutive patients who underwent a 125 degrees Proximal Femoral Nail procedure during 2020. A radiographic comparison of the images obtained intraoperatively after anatomical reduction, during and after nail insertion was performed using Traumacad©. The Neck shaft angle(NSA) was examined and compared to follow up images.

Results:
The average NSA prior to nail insertion was 130.6 degrees (range 120-140), SD 6.2013. After nail insertion the NSA average was 129.94(range 117-137), SD 5.71. There was a correlation with statistically significance(p=0.029) between the change in the NSA after reduction and after nail insertion.

Discussion:
The presented study is considered a pilot for a larger study. In our study we have demonstrated the relation between primary reduction and final result in terms of NSA. We believe that the results are affected by errors in the surgical technique. Following studies isolating each component affecting the NSA and examine them separately should be conducted.