Valgus osteotomy for atypical interprosthetic femoral fracture with lateral bowing of the femur

INTRODUCTION: In recent years, it has been reported that periprosthetic femoral fractures in the form of atypical femoral fractures (AFFs) are found occasionally as difficult-to-treat conditions. To date, there have been no reports of interprosthetic femoral fractures (IPFFs) having the form of AFFs. We report a case of an atypical IPFF with breakage of the plate due to abnormal femoral alignment. CASE REPORT: A 70-year-old woman was admitted. She underwent left knee replacement and left hemi-arthroplasty at ages 61 and 60. And she had been taking bisphosphonate for 5 years. A plain X-ray revealed IPFF. The fracture was a complete transverse fracture with circumscribed thickening of the lateral cortical bone (“beak sign”) at the fracture site. She underwent surgery. A reversed condylar locking compression plate (LCP) was used for internal fixation. Subsequently, she could walk without particular pain. Five months after the operation, she heard the snap of a bone breaking, and had difficulty walking. Plain X-ray revealed a re-fracture of the fracture site and breakage of the plate at the same high position. She underwent re-operation. A valgus osteotomy was performed at an angle of 15°. A reversed condylar LCP was used on the lateral side of the femur. A bone grafting was performed focusing on the fracture site. In addition, a short-LCP was fixed anteriorly to the femur. The bone union 1 year and 6 months postoperatively. She could walk, with no impairment being noted regarding ADL. CONCLUSIONS: We performed osteosynthesis for an IPFF having the characteristics of AFF, but the patient suffered breakage of the plate and re-fracture. Bone union was achieved as a result of re-operation that consisted of valgus osteotomy of the fracture site in combination with autologous bone grafting and double orthogonal plating.