title: Failure of fixation of trochanteric femur fractures: Clinical recommendations for avoiding Z-effect and reverse Z-effect type complications.
abstract: BACKGROUND
  Z-effect and reverse Z-effect are complications that arise from the surgical treatment of pertrochanteric fractures of the femur with proximal femoral nails (PFN) comprising two interlocking head screws. Such complications are induced by the migration of screws in opposite directions, which may lead to failure of the osteosynthesis.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Hospital Felício Rocho, Av, do Contorno 9790, 30110-060, Belo Horizonte, MG, Brasil. robinsonesteves@ig.com.br.
authors.forename: Robinson Esteves Santos
authors.initials: RE
authors.lastname: Pires
authors.forename: Egídio Oliveira
authors.initials: EO
authors.lastname: Santana
authors.forename: Leandro Emílio Nascimento
authors.initials: LE
authors.lastname: Santos
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Giordano
authors.forename: Daniel
authors.initials: D
authors.lastname: Balbachevsky
authors.forename: Fernando Baldy
authors.initials: FB
authors.lastname: Dos Reis