Abstract
Purpose
Incidence of malrotation of femoral fractures after intramedullary nailing is as high as 28%. Prevention of malrotation is superior to late derotation osteotomy. The lesser trochanter (LT) profile has been in use for some time as a radiographic landmark of femoral rotation. One of the authors has previously described a linear regression model that describes the relationship of the LT to rotation. This paper aims to validate the use of this equation in predicting femoral rotation.
Method
A survey was created and circulated online. Twenty images of cadaveric femurs of known rotation were chosen randomly from a large series. Thirty individuals with varying degrees of orthopaedic experience were invited to participate. Participants were asked to take measurements of the LT in a standardized fashion. Inter-observer variation for predicted rotation and the precision of predicted rotation was calculated. Results were grouped into those with the LT readily visible and those with the LT hidden by the femoral shaft.
Results
A pilot study found the standard deviation for films with the LT hidden was 10.8 degrees, and only 6.0 degrees for films with the LT visible. The mean difference between the predicted and actual rotation was equally high in both groups (18.3 and 17.3 degrees respectively).
Conclusion
Preliminary results found that the LT must be clearly visible to predict femoral rotation. This suggests that the surgeon should place the femur in a neutral or externally rotated position. In a favourable position most predictions were within a 6.0 degree spread, which would be sufficient to prevent a fifteen degree malrotation. Predicted rotation was however not precise enough to prevent a fifteen degree malrotation, regardless of LT visibility.
The precision of predicted rotation may be improved by using a non-linear model. Such a model has recently been designed by a group of engineers at the University of Manitoba. The r squared value of the non-linear model was 0.88, in comparison to 0.78 for the linear equation. Precision may be further improved by using the contra-lateral LT for comparison.
