Study settings
A retrospective multicenter cohort study was performed including patients ≥ 60 years with an MRI verified FNF treated with IF between January 2003 and October 2018 at four orthopedic departments in Sweden: Umeå University Hospital (2003–2018) a third-level university hospital with a catchment area of about 160,000 inhabitants, Danderyd Hospital (2010–2018) a third-level university hospital with a catchment area of about 500,000 inhabitants, Skåne University Hospital in Malmö (2005–2014) a third-level university hospital with a catchment area of about 450,000 inhabitants and Skellefteå Hospital (2004–2018) a first-level hospital with a catchment area of about 80,000 inhabitants.
Patients and data collection
A consecutive series of patients ≥ 60 years with an MRI verified FNF were included. Only patients treated with IF by either cannulated screws or pins were included and followed until death or December 2020. Patient demographics were collected by a review of the surgical and medical charts. We collected data including age, sex, ASA classification, cognitive impairment (diagnosis in medical records prior to fracture), use of a walking aid prior to fracture, admission from sheltered housing or a nursing home, the use of MRI for diagnosis, method of surgical treatment, reoperation, treatment failure and date of death.
Radiographic assessment
The plain anteroposterior (AP) radiographs were used to classify fractures according to the Garden classification system (Fig. 1 a, b) [14]. The pre- and postoperative tilt of the femoral head was measured on a lateral radiograph of the hip using the method described by Palm et al. [10, 11, 15]. If a postoperative lateral radiograph was missing, the postoperative tilt was measured on the intraoperative image documentation. For implant inclination we performed measurements on the inferior pin or screw on the postoperative AP radiograph [16]. Three raters (JS, PS, AP), who were not blinded, performed all measurements. At the time of the study no national guidelines on diagnosing fractures with MRI were present, however, in most cases T1, T2 and STIR weighted sequences were used (Fig. 2a, b). All images were digitally acquired using a Picture Archiving and Communication System (PACS, Impax, Agfa, Antwerp, Belgium).
Internal fixation
IF was performed according to the same principles at the 4 hospitals. With the patient on a fracture table and under intra operative imaging 2 or 3 pins/screws were placed along the femoral neck transfixing the fracture. Either Hansson Pins; Swemac Orthopaedics AB, Sweden or Olmed Screws; DePuy/Johnson & Johnson, Sollentuna, Sweden were used.
Outcome measurements
The primary end-point was a major reoperation due to avascular necrosis (AVN), fixation failure, posttraumatic osteoarthritis or nonunion. Major reoperation was defined as hip arthroplasty, excision arthroplasty or re-osteosynthesis due to peri-implant fractures. The definition of minor reoperation was removal or adjustment of implant.
Statistical analysis
Variables are presented as proportions of all fractures. Nominal variables are presented as proportions of all fractures and scale variables as means ± standard deviation (± SD) and range. We used SPSS (IBM SPSS Statistics for Mac, Version 26.0, Armonk, NY: IBM Corp. USA) for statistical analyses.