Failure of fixation of trochanteric femur fractures: Clinical recommendations for avoiding Z-effect and reverse Z-effect type complications

The paper describes three cases of pertrochanteric fractures that were treated with PFN with two interlocking screws that evolved to either Z-effect or reverse Z-effect. Literature-based explanations for this phenomenon are provided together with recommendations of how to avoid such complications.Although intramedullary fixation is an established method of treatment of femoral intertrochanteric and subtrochanteric fractures, the evolution of the procedure may include complications associated with the migration of the interlocking head screws. The occurrence of Z-effect and reverse Z-effect has not been completely elucidated, but the main causes of such complications are probably fracture fixation in varus position, severe medial comminution, inappropriate entry point of the nail and poor bone quality.The incidence of fractures of the proximal femur has increased considerably over the last few decades as a consequence of the greater longevity of the population [1]. Femoral pertrochanteric fractures (FPF) typically occur in patients presenting diverse types of comorbidities and are associated with a high rate of mortality in the first year after the event [2].In the present paper, we describe the complications observed in three patients arising from surgical treatment of FPF with proximal femoral nails (PFN) comprising two interlocking head screws that migrated in opposite directions (Z-effect and reverse Z-effect). The possible causes of these complications and relevant preventive methods are discussed.A 44-year old male doctor (with no comorbidities), who had been injured in a car accident, presented subtrochanteric fracture (AO/OTA 32-B1) of the right femur and was submitted to osteosynthesis with PFN (Hexagon？, Campinas, SP, Brazil) one day after the trauma. The femur fracture was classified as level 3 on the abbreviated injury scale (AIS), whereas the injury severity score (ISS) was level 9 without any associated injuries. After 10 months, the patient evolved wit