Interprosthetic femoral fractures, ones occurring between ipsilateral total hip and total knee arthroplasties, are an increasingly common and challenging problem for orthopaedic surgeons. The purpose of this study was to report specific fracture locations and treatment outcomes associated with a protocol of femoral plate fixation that spanned the interprosthetic zone applied with modern soft tissue preserving reduction techniques without adjuvant bone grafts.Retrospective cohort study.One Level I and one Level II trauma center.A consecutive cohort of 25 patients with 26 interprosthetic femur fractures surgically treated by one of four orthopaedic traumatologists were retrospectively reviewed. There were nine fractures of the femoral shaft (Orthopaedic Trauma Association [OTA] 32) about hip arthroplasty prostheses and 17 supracondylar fractures (OTA 33) about total knee prostheses. Five patients with six fractures were excluded as a result of lack of follow up (n = 4) or deviation from the treatment protocol (n = 2). The remaining 20 fractures were all low-energy closed injuries in elderly patients (average age 80 years; range, 56-98 years; 14 females and six males).A common surgical treatment protocol included plate fixation that spanned the entire interprosthetic zone (overlapping the stem proximally and knee component distally) and the use of biologic tissue-preserving plating techniques without use of supplemental bone grafts of any kind.Fracture healing, time to full weightbearing, malunion, nonunion, and the presence of any hardware failure.Supracondylar interprosthetic fracture patterns (OTA 33A) were two times more common than proximal diaphyseal fractures (OTA 32) (Vancouver B), 65% versus 35%. All 20 fractures healed after the index procedure. The average time to weightbearing as tolerated was 13 weeks (range, 6-22 weeks). There were three malunions (one 10° valgus, one 9° extension, and one 10° flexion), two cases of painful implants (one required removal), and one loose long-stem revision hip prosthesis (required total femur replacement). All other implants remained well-fixed. All complications occurred in patients with supracondylar fracture patterns. There were no additional associated peri-implant fractures.Interprosthetic femoral fractures tend to occur more frequently in the supracondylar region about total knee arthroplasty components than in the diaphysis about hip stems. Modern biologic plating techniques that span the entire interprosthetic zone to eliminate additional stress risers show reliable union rates without the use of adjuvant bone graft while maintaining limb alignment and implant survivorship.