INTRODUCTION: Total hip arthroplasty (THA) and total knee arthroplasty (TKA) are common procedures in the increasing older population. According to the AAOS, approximately 19,200 Americans are actually living with ipsilateral prosthetic hip and knee leading to 240 interprosthetic fractures annually. Few reviews and case reports give an idea of the obvious problem to achieve consolidation in interprosthetic fractures. Preconfigured plates have been shown to be superior compared with other treatments in patients with stable components. Utilization of internal fixators for interprosthetic fractures might be advantageous. The purpose of this study was to evaluate interprosthetic femoral fractures with polyaxial locking plate treatment in regard to surgical procedure, complications, and clinical outcome. METHODS: Between 2005 and 2012, 143 patients underwent surgical treatment for periprosthetic femur fractures. Thirty-two fractures were identified as interprosthetic fractures. Five patients were excluded. Fractures were classified according to OTA/AO system, Vancouver, Rorabeck, Soenen and Pires. Trauma fellowship trained orthopaedic surgeons performed the surgeries using a NCB-construct (Zimmer Inc., Warshaw, IN). Plate choice was determined according to radiographic classification. Submuscular plate insertion was performed if possible. Complications were recorded concerning infection, union, fixation failure, and revision surgery. RESULTS: Twenty-seven patients were identified. There were 92.6% females. Follow-up by regular outpatient clinic visits was 24 months. Surface replacements were found in 18 TKA. Nine patients had a stemmed femur component of their TKA. 89% healed after the index procedure. Three patients developed a nonunion with 1 construct leading to hardware failure. Previous revision THA or Pires/modified Vancouver classification did not influence nonunion formation, but all patients with nonunion formation were classified as AO/OTA type B (p=0.001). These fractures were treated with longer plates (p=0.015), but with similar working length (p=0.400). Plate design, additional cerclages, or submuscular insertion did not influence nonunion formation. CONCLUSION: Interprosthetic fracture treatment remains challenging. NCB-locked plating can achieve satisfactory results. Additional soft tissue damage can be prevented by submuscular plate insertion. Treatment of type B fractures resulted in significantly greater nonunion rate. Therefore, consideration of the individual fracture type is essential to determine plate length, plate type, and additional bone grafting or BMP supplementation.