Abstract
The principle of the sliding hip screw is to provide a controlled collapse at the fracture site. It is during the screw insertion that clockwise rotational torque is imparted to the head and neck
In right-sided fractures the screw causes the head fragment to rotate clockwise leading to apposition or flexed position of the fracture site. In Left sided fractures the clockwise rotation leads to the head and neck fragment into extension of the fracture site leading to a potentially unstable construct.
All intertrochanteric fractures treated over a 12-month period were assessed. 75 fractures were included in the study. The fractures were classified according to Tronzo’s classification (Grades I & II – stable; Grades III & IV – unstable). Intraoperative and postoperative films were assessed for rotational abnormalities in the form of an anterior spike of the proximal fragment in left-sided fractures and a flexed position of reduction in right-sided fractures.
There were 39 Left sided fractures and 36 Right sided fractures.
A rotational abnormality was seen in 11 Left sided fractures compared with none on the right side. All 11 abnormalities were seen in Grade III and IV fractures (2 and 9 respectively). Analysis of results using the Chi-Square test revealed a significant difference (p < 0.001). 3 out the 11 fractures with rotational anterior spike had an implant cut out which needed revision surgery.
Compared to stable fractures, the accuracy of reduction determines the final stability in unstable fractures. In these fractures the rotational torque imparted to the proximal head and neck fragment can cause loss of reduction leading to potential failures of fixation. This appears to be greater in left sided fractures where the rotational torque causes the anterior spike which when not butressed inferiorly and medially can lead to a state where the implant cannot control the shear forces at the fracture site. This can then lead to failure of fixation.
In right-sided fractures the rotational torque often causes compression of the head and neck fragment into the distal fragment with the creation of an infero- medial butress.
The methods of overcoming this problem are with modifications in the technique. Untwisting the last few threads of the screw after insertion could reduce the anterior spike. The application of digital pressure along the anterior neck or the application of a reduction clamp at screw insertion provides counter rotation.
The results of this study confirm that the problem of torque at the fracture site is not of considerable importance in stable fractures but is significantly so in unstable left sided fractures. This results in a greater predisposition for potential failure of fixation
The abstracts were prepared by Mr Simon Donell. Correspondence should be addressed to him at the Department of Orthopaedics, Norfolk & Norwich Hospital, Level 4, Centre Block, Colney Lane, Norwich NR4 7UY, United Kingdom.
