Implants failure in Hip with Intarmedullary Devices

Complications arising from fixation of unstable proximal femur fracture with PFN having 2 screws .


1.Z-effect


  lateral migration of caudal screw , varus collapse and perforation of femoral head by superior screw




2. Reverse Z-effect


  lateral  migration of superior screw , varus collapse and femoral head cut by inferior screw






Causes


 varus fixation of fractures , severe medial communition , inappropriate entry point and poor bone


  quality.




Intaoperative Procedures to stabilize unstable IT fractures


 Osteotomies and fixed with nail plate


  Design (Smith -Peterson nail plate  )


    e.g. 1. Dimon  -Hughston medial displacement Osteotomy


           2. Sarmiento Valgus Osteotomy


           3. Wayne -County lateral displacement Osteotomy


No evidence are there to support these osteotomies combined with sliding hip screw fixation .

Intramedullary Implants in Hip

Advantages

1.Ability to fix majority of fractures

2. Short surgical time and less blood loss

  for unstable Intertrochanteric fractures , (no difference compare to DHS fixation for stable IT fracture

3. smaller moment arm - to bear tensile forces and lesser calcar strain

 DHS - produces 1.5 times calcar strain of a normal femur

 IM < 10 percent of strain

4.Better controlled collapse as bending moment at lag screw for nail is lesser than DHS .

5. Biomechanically nail construct are more stiff so more stable than DHS for torsion and bending
 
    stress.


Disadvantages

  1. Abductor injury while insertion

  2. difficult revision by arthroplasty if it fails

   3. anterior thigh pain due  to impingement of nail tip

  4. curative mismatch of nail and femora produces iatrogenic fractures

  5. stress concentration at nail tip leads to fracture

  6. implants are costlier .