Abstract
Introduction:Medial migration is the paradoxical migration of the femoral neck element (FNE) superomedially against gravity with respect to the intramedullary component of the cephalomedullary device, increasingly seen in the management of pertrochanteric hip fractures with the intramedullary nail. We postulate that the peculiar anti-gravity movement of the FNE in the medial migration phenomenon stems from a ratcheting mechanism at the intramedullary nail-FNE interface, which should inadvertently produce unique wear patterns on the FNE that can be seen with high-powered microscopy. By examining the wear patterns on retrieved implants from patients with medial migration, our study aims to draw clinical correlations to the ratcheting mechanism hypothesis.Material and Methods:Four FNEs were retrieved from revision surgeries of four patients with prior intramedullary nail fixation of their pertrochanteric hip fractures complicated by femoral head perforation. The FNEs were divided into two groups based on whether or not there was radiographic evidence of medial migration prior to the revisions. Wear patterns on the FNEs were then assessed using both scanning electron microscopy and light microscopy.Results:Repetitive, linearly-arranged, regularly-spaced, unique transverse scratch marks were found only in the group with medial migration, corresponding to the specific segment of the FNE that passed through the intramedullary component of the PFNA during medial migration. These scratch marks were absent in the group without medial migration.Conclusion:Our findings are in support of a ratcheting mechanism behind the medial migration phenomenon with repetitive toggling at the intramedullary nail-FNE interface and progressive propagation of the FNE against gravity.
Highlights
Medial migration is the paradoxical migration of the femoral neck element (FNE) superomedially against gravity with respect to the intramedullary component of the cephalomedullary device, increasingly seen in the management of pertrochanteric hip fractures with the intramedullary nail
Medial migration is a phenomenon seen almost exclusively in the management of pertrochanteric hip fractures with the intramedullary nail (Fig. 1). This is the paradoxical migration of the femoral neck element (FNE) superomedially against gravity with respect to the intramedullary component of the cephalomedullary device, first seen in the description of the Z-effect by WernerTutschcku et al in their series of 70 proximal femur fractures managed with the Proximal Femoral Nail (PFN)[8]
There were unique wear patterns present only on the FNEs from the group with medial migration corresponding to the segment of the FNE that has passed through the intramedullary component of the Proximal Femoral Nail Antirotation (PFNA) during medial migration (Fig. 2)
Summary
Medial migration is the paradoxical migration of the femoral neck element (FNE) superomedially against gravity with respect to the intramedullary component of the cephalomedullary device, increasingly seen in the management of pertrochanteric hip fractures with the intramedullary nail. Medial migration leads to complications with considerable morbidity including femoral head perforation, penetration into the acetabulum, destruction of the hip joint, and in some cases, migration into the pelvic cavity (Table I) This is a poorly understood phenomenon increasingly reported in the literature in the last decade with limited studies investigating the biomechanics of the phenomenon to date (Table I)
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