Occult periprosthetic femoral fractures occur frequently during a long, trapezoidal, double-tapered cementless femoral stem fixation in primary THA.

The present study aimed to investigate the prevalence and clinical consequences of occult intra-operative periprosthetic femoral fractures in total hip arthroplasty (THA). Between 2012 and 2017, a total of 113 primary THAs were enrolled. The mean age of the patients was 66.4 ± 7.6 years. We assessed occult intra-operative periprosthetic femoral fractures with the use of computed tomography (CT) and risk factors, including age, sex, body mass index, diagnosis, stem size, and radiographic parameters of proximal femoral geometry were analyzed. We also assessed the differences in thigh pain and stem subsidence and alignment between the patients with and without occult periprosthetic femoral fracture. Occult intra-operative periprosthetic femoral fractures were found in 13 of 113 hips (11.5%). In 9/13 (69.2%) of occult fractures, fracture lines were started from the region below the tip of the lesser trochanter. Six periprosthetic femoral fractures (5.3%) were found during the operation. Out of the five hips that had detected femoral fractures around the lesser trochanter intra-operatively, four hips (80%) showed concurrent occult fractures on different levels. The female sex (P = .01) and canal filling ratio at 7 cm below the tip of the lesser trochanter (P = .01) were significantly different between the patients with and without occult periprosthetic femoral fracture. The sex was significantly associated with an increased risk in predicting an occult intra-operative periprosthetic femoral fracture (odds ratio of male, 0.25 compared with the female; 95% CI, 0.08-0.85; p = .02). There was a significant difference in the incidence of thigh pain between occult fracture group and non-occult fracture group (P < .05). There were no significant differences in stem subsidence and alignment between the patients with and without occult periprosthetic femoral fracture. All 13 cases of occult intra-operative periprosthetic femoral fractures were healed at the final follow-up. Occult periprosthetic femoral fractures are common during a long, trapezoidal, double-tapered cementless femoral stem fixation in primary THA, that CT scans are helpful to identify them, and that these fractures do not adversely affect the implant's survival if a rigid fixation of the implants has been achieved.