• Michael Yam, Benjamin Joseph Kang, Anuj Chawla, Wei Zhang, Law Gin Way, Rex Premchand Antony Xavier, Derek Howard Park, N E M Yeo, T S Howe, and E B K Kwek.
• Tan Tock Seng Hospital, Singapore, Singapore. Michael.yam@mohh.com.sg.
• Arch Orthop Trauma Surg. 2020 Dec 1; 140 (12): 1939-1945.

ObjectivesProximal femoral nail antirotation (PFNA) cut-in is a unique phenomenon seen in pertrochanteric hip fractures treated with the PFNA. Cut-in refers to the superomedial migration of the proximal femoral blade into the femoral head and hip joint. We recognize that cut-in is a completely separate entity from the well-described cut-out failure. This study assesses relevant radiological and patient risks factors for cut-in.DesignRetrospective multicenter study looking at patients with pertrochanteric hip fractures managed with the Synthes PFNA SETTING: Four tertiary hospitals over 7 years.PatientsPatients with cut-ins were identified.Outcome MeasurementThe radiological appearance of this mode of failure was assessed and compared to cut-outs. Patient demographics, fracture configuration, time to implant failure (cut-in), bone mineral density, tip-apex distance, neck-shaft angle and position of the tip of the helical blade in the femoral head were collected.ResultsThere was a total of 1027 patients across 4 institutions with 23 patients with cut-in. Average neck-shaft angle was 133 degrees. 16 out of 19 patients had severe osteoporosis with BMD < - 2.5. 14 of 23 patients had poor placement of the blade. 13 of 23 had a tip-apex distance of more than 20 mm.ConclusionWe propose a standardized nomenclature of "cut-in" for the phenomenon of superomedial migration of the proximal femoral blade. An anatomical neck-shaft reduction, accurate blade placement and increased surveillance for patients with severe osteoporosis are required to reduce the incidence and morbidity of cut-in.

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