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 stabilizati on. A retrospective review was performed on 47 intertrochanteric (IT) fractures treated with a Zimmer CHS. Previous studies had identified c ertain parameters as being important to CHS sliding characteristics in vitro. Using conventional diagnostic material (radiographs), we sough t to use these parameters as clinically useful tools. Screw sliding, a s well as geometric parameters of CHS that relate to screw sliding, su ch as barrel engagement in relation to screw extension and screw-plate angle, were measured and calculated from serial radiographs. Almost a ll screw sliding occurred within 30 days postoperation. Fracture stabi lity and quality of reduction were two main factors relating to screw sliding (p < 0.01). High screw-plate angle and longer screw-barrel eng agement had no correlation with screw sliding even in unstable fractur es. All five failures were due to cut-out after complete or almost com plete collapse of the sliding mechanism in non-anatomically reduced fr actures in osteoporotic females. Unstable fractures in osteoporotic bo ne do seem to require supplementary fixation beyond sliding screw fixa tion alone. None of the mechanical parameters (as judged from plane ra diograph s) that control the tendency of the CHS to slide could be sta tistically 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.