"Cut-in" Phenomenon – The Rare and Secret Complication of Proximal Femoral Nails – A Retrospective Analysis from the Soroka University Medical Center 2009-2015

Introduction: The use of intramedullary devices to fix intertrochanteric NOF fractures is an internationally well-established fixation method which demonstrated mechanical and biological advantages, especially in the treatment of unstable fractures patterns. Despite the biomechanically proved advantages of the proximal femoral nails, some complications had occurred over the years. A very rare type of complication was sporadically reported over the last few years, and was termed "Cut-in" or "medial migration" of the blade.

Methods: This is a retrospective study taking place at the Soroka University Medical Center, Israel. We have looked at all our NOF fractures between the years 2009-2015 and isolated the ones operated using the PFNA implant. Data was collected from the electronic patients’ files and included demographics and post operative complications mandating a second operation.

Results: 1775 patients were operated for their extracapsular NOF fracture between the years 2009-2015 in our institution. 785 of them were operated using the PFNA device. The overall incidence of complications mandating a second operation was 3.82% (30 patients). 12 patients suffered from infections, 2 patients developed non-union and 3 patients developed AVN of the femoral head. 6 patients suffered a periprosthetic femur fracture - all after a secondary fall. 7 patients were diagnosed with secondary displacement; 5 patients (0.63%) demonstrated the "classic" cut-out, and they were all treated successfully with a total hip replacement surgery. 2 patients (0.25%) developed the very rare Cut-in pattern with medial migration of the PFNA blade into the acetabulum. Both patients had their blades removed, and went on to good healing.

Conclusion: The “cut-in” phenomenon is a very rare but potentially very dangerous complication. This complication is most probably inherent to most of the proximal femur nail designs, and must be recognized by orthopaedic trauma surgeons dealing with these injuries.