by Elizabeth Hofheinz, M.P.H., M.Ed.
“Can you obtain a quality image with a lower dose CT scan,” asked researchers in new work funded by The Orthopaedic Research and Education Foundation. The multicenter study, “Standard Versus Low-Dose Computed Tomography for Assessment of Acetabular Fracture Reduction,” appears in the September 2020 edition of the Journal of Orthopaedic Trauma.
Co-author Geoffrey Marecek, M.D. is an orthopaedic surgeon at Cedars-Sinai Medical Center in Los Angeles. He told OSN, “Postoperative CT is important for checking the quality of your work and ensuring that the fixation is safe – and it’s especially important when educating residents and fellows as it provides valuable feedback. However, patients with pelvic and acetabular fractures have typically had multiple CT scans prior to surgery, so additional scans need to be justified or be done with minimal radiation. Some other authors have reported good results with low dose CT in other regions of the body so we wanted to see if it could be a useful tool for minimizing the downside to postop CT.”
“We created posterior wall acetabular fractures in 8 fresh-frozen cadaver hips and reduced them with varying combinations of step and gap displacement,” wrote the authors. “The insertion of an intra-articular screw was randomized. Each specimen had a CT with standard (120 kV), intermediate (100 kV), and low-dose (80 kV) protocols, with and without metal artifact reduction post- processing. Reviewers quantified gap and step displacement, overall reduction, quality of the scan, and identified intra- articular implants.”
Reviewing the CT scans were five fellowship-trained orthopedic trauma surgeons. The researchers established four separate viewing sessions so that “no 2 scans of the same hip (eg, the standard-dose and low-dose scans of the same hip specimen) were contained in one session.”
The surgeon reviewers assessed gap displacement, step displacement, and overall displacement (Matta criteria) as anatomic (0–1 mm displacement), imperfect (2–3 mm displacement), or poor (.3 mm dis- placement). They were asked to identify intra-articular implants (yes or no), and to rate the subjective quality of the CT scan (from useless to excellent on a 4-point scale).
Dr. Marecek: “There were no differences between low dose CT and standard dose CT with respect to identifying the quality of reduction or presence of intra-articular implants. Even with standard dose CT, the surgeons only identified the intra-articular implants in about 2/3 of the cases. Since this is one of the main reasons given for use of postop CT, it was a surprising finding. It was probably in part due to the fact that the reviewers were not the ones placing the implant, and so didn’t have a ‘suspicious’ place to look but is surprising nonetheless.”
“A low dose (80 kVp) scan is as effective as a standard dose scan, and only amounts to the same radiation as 5 chest x-rays. Using a low-dose protocol may be helpful in obtaining the useful information from a postop CT without the high radiation dose.”