MRI Can Detect “Invisible” Femoral Neck Fractures in Patients with Shaft Fractures

For more than 40 years, orthopaedic trauma surgeons have been interested in this fairly common fracture combination, which is often seen in polytrauma patients. We have long hypothesized that much of the energy that fractures the femoral shaft is dissipated, leaving many ipsilateral neck fractures nondisplaced and difficult to recognize on plain radiographs.

But the consequences of missing a femoral neck fracture can be devastating. For example, because the neck fracture pattern is often vertical (Pauwels type III), the risk of displacing the neck fracture during intramedullary nailing is very high. Achieving reduction and fixation of a displaced neck fracture near an intramedullary nail—either intraoperatively or postoperatively—is extremely challenging.

Because of these issues, some authors recommend a thin-cut CT series to identify nondisplaced ipsilateral neck fractures preoperatively, and this protocol has been shown to significantly reduce the delay in identifying such fractures. In the February 19, 2020 issue of The Journal, Rogers et al. from UTHealth in Houston show that even with thin-cut CT, the crack can be missed. These authors added to the protocol limited-sequence MRI that identifies these fractures with very high sensitivity and takes <10 minutes to perform.

In this study, among 39 acute, high-energy femoral shaft fractures, the authors identified 4 ipsilateral neck fractures with MRI that were not seen on CT. Despite exhibiting polytrauma, 89% of all indicated patients in this study were evaluated preoperatively with the limited-sequence MRI protocol, including those in traction and those treated initially with external fixation.

The findings from this study should prompt trauma surgeons practicing in high-volume centers to develop similar MRI protocols. It may also be possible to develop such protocols in lower-volume centers, but in those settings it is especially incumbent on the surgical team to recognize that this fracture combination occurs in a fairly high percentage of cases and to carefully scrutinize plain radiographs and consider thin-cut CT scanning of the ipsilateral hip. In addition, the potential for an ipsilateral nondisplaced femoral neck fracture should trigger increased use of fluoroscopy during intramedullary nailing of shaft fractures, so that concomitant neck fractures can be recognized and stabilized with screws before they become displaced.

Marc Swiontkowski, MD
JBJS Editor-in-Chief

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