Novel Use of the O-Arm Following Open Reduction of a Dislocated Hip for a Walking Age Patient Provides a Low-Radiation Alternative to CT.

Background: Surgical treatment of a dislocated hip at walking age includes open reduction (OR) with or without osteotomies of the pelvis and/or femur. Three-dimensional imaging, such as computerized tomography (CT), can be utilized postoperatively to determine femoral head position following cast placement. Alternatively, intraoperative 3D imaging (O-arm) may be used for the same purpose. Disadvantages of CT include limited access to the patient's airway and high radiation dose. The current study aimed to determine the ability of O-arm imaging to visualize femoral head position following surgical treatment of a dislocated hip, and compare radiation dosage between CT and O-arm.

Methods: Thirteen patients (16 hips) with a dislocated hip at walking age who underwent OR with pelvic ± femoral osteotomies at a single institution were retrospectively reviewed. All patients underwent CT or O-arm evaluation following surgery and spica cast application. Total radiation dose per kilogram was compared between the CT (n=8 hips) and O-Arm 14 (n=8 hips) groups. Radiographic parameters and complication rates were analyzed. Image quality was blindly assessed by 3 fellowship-trained pediatric orthopedic surgeons with hip expertise.

Results: The mean age was 4.68 years (range: 3.1-7.8) in the CT group and 4.31 (range: 1.2-7.5) in the O-Arm group. The average radiation dose from the O-arm was lower than CT (4.51 19 mGy/kg vs. 6.12 mGy/kg, P =0.37). Five hips in the CT cohort were scanned post-extubation. All surgeons agreed that femoral head position was adequately visualized in all images from both groups. No patient in either group required a cast change post-scanning due to a malpositioned femoral head.

Conclusion: The O-arm is a reasonable alternative to CT following surgical treatment of a dislocated hip. It may decrease radiation dose and provides adequate visual information to determine femoral head position following surgical intervention and casting. Utilization of the O-arm keeps the patient in the operating room during the study, allowing for immediate revision of the cast position or revision reduction if necessary, while maximizing access to the patient's airway and minimizing risk for adverse anesthetic events.

Level of evidence: Level III, retrospective comparative study.