Sliding characteristics of compression hip screws in the intertrochanteric fracture: a clinical study

Sliding of compression hip screws (CHS) is advantageous when it allows for controlled collapse of a hip fracture and progressive stabilization. A retrospective review was performed on 47 intertrochanteric (IT) fractures treated with a Zimmer CHS. Previous studies had identified certain parameters as being important to CHS sliding characteristics in vitro. Using conventional diagnostic material (radiographs), we sought to use these parameters as clinically useful tools. Screw sliding, as well as geometric parameters of CHS that relate to screw sliding, such as barrel engagement in relation to screw extension and screw-plate angle, were measured and calculated from serial radiographs. Almost all screw sliding occurred within 30 days postoperation. Fracture stability and quality of reduction were two main factors relating to screw sliding (p < 0.01). High screw-plate angle and longer screw-barrel engagement had no correlation with screw sliding even in unstable fractures. All five failures were due to cut-out after complete or almost complete collapse of the sliding mechanism in non-anatomically reduced fractures in osteoporotic females. Unstable fractures in osteoporotic bone do seem to require supplementary fixation beyond sliding screw fixation alone. None of the mechanical parameters (as judged from plane radiographs) that control the tendency of the CHS to slide could be statistically correlated with incidence or degree of sliding. Therefore, it was concluded that it is impractical to attempt to predict sliding tendency from plane radiograph measurements.