Preclinical evaluation of a prototype freehand drill video guidance system for orthopedic surgery.

Purpose: Internal fixation of pelvic fractures is a challenging task requiring the placement of instrumentation within complex three-dimensional bone corridors, typically guided by fluoroscopy. We report a system for two- and three-dimensional guidance using a drill-mounted video camera and fiducial markers with evaluation in first preclinical studies. Approach: The system uses a camera affixed to a surgical drill and multimodality (optical and radio-opaque) markers for real-time trajectory visualization in fluoroscopy and/or CT. Improvements to a previously reported prototype include hardware components (mount, camera, and fiducials) and software (including a system for detecting marker perturbation) to address practical requirements necessary for translation to clinical studies. Phantom and cadaver experiments were performed to quantify the accuracy of video-fluoroscopy and video-CT registration, the ability to detect marker perturbation, and the conformance in placing guidewires along realistic pelvic trajectories. The performance was evaluated in terms of geometric accuracy and conformance within bone corridors. Results: The studies demonstrated successful guidewire delivery in a cadaver, with a median entry point error of 1.00 mm (1.56 mm IQR) and median angular error of 1.94 deg (1.23 deg IQR). Such accuracy was sufficient to guide K-wire placement through five of the six trajectories investigated with a strong level of conformance within bone corridors. The sixth case demonstrated a cortical breach due to extrema in the registration error. The system was able to detect marker perturbations and alert the user to potential registration issues. Feasible workflows were identified for orthopedic-trauma scenarios involving emergent cases (with no preoperative imaging) or cases with preoperative CT. Conclusions: A prototype system for guidewire placement was developed providing guidance that is potentially compatible with orthopedic-trauma workflow. First preclinical (cadaver) studies demonstrated accurate guidance of K-wire placement in pelvic bone corridors and the ability to automatically detect perturbations that degrade registration accuracy. The preclinical prototype demonstrated performance and utility supporting translation to clinical studies.

Image guided percutaneous spine procedures using an optical see-through head mounted display: proof of concept and rationale.

BACKGROUND AND PURPOSE: Optical see-through head mounted displays (OST-HMDs) offer a mixed reality (MixR) experience with unhindered procedural site visualization during procedures using high resolution radiographic imaging. This technical note describes our preliminary experience with percutaneous spine procedures utilizing OST-HMD as an alternative to traditional angiography suite monitors. METHODS: MixR visualization was achieved using the Microsoft HoloLens system. Various spine procedures (vertebroplasty, kyphoplasty, and percutaneous discectomy) were performed on a lumbar spine phantom with commercially available devices. The HMD created a real time MixR environment by superimposing virtual posteroanterior and lateral views onto the interventionalist's field of view. The procedures were filmed from the operator's perspective. Videos were reviewed to assess whether key anatomic landmarks and materials were reliably visualized. Dosimetry and procedural times were recorded. The operator completed a questionnaire following each procedure, detailing benefits, limitations, and visualization mode preferences. RESULTS: Percutaneous vertebroplasty, kyphoplasty, and discectomy procedures were successfully performed using OST-HMD image guidance on a lumbar spine phantom. Dosimetry and procedural time compared favorably with typical procedural times. Conventional and MixR visualization modes were equally effective in providing image guidance, with key anatomic landmarks and materials reliably visualized. CONCLUSION: This preliminary study demonstrates the feasibility of utilizing OST-HMDs for image guidance in interventional spine procedures. This novel visualization approach may serve as a valuable adjunct tool during minimally invasive percutaneous spine treatment.

Diagnosis of femoral neck fracture associated with femoral shaft fracture: blinded comparison of computed tomography and plain radiography.

OBJECTIVE: Femoral neck fractures that are associated with femoral shaft fractures have historically been associated with high rates of missed diagnosis. Despite the potentially serious consequences of a missed femoral neck fracture, little work has been conducted to rigorously evaluate the ability of commonly used imaging studies to detect such fractures. Our hypothesis was that axial-view computed tomography is superior to plain radiography at detecting femoral neck fractures. DESIGN: Blinded assessment of a randomized image set that included axial-view computed tomographic scans of the pelvis, anteroposterior-view radiographs of the pelvis, and anteroposterior-view radiographs of the femur. SETTING: Academic trauma center. PATIENTS: Twenty-eight patients who had femoral shaft fractures with femoral neck fractures and 60 patients who had femoral shaft fractures without femoral neck fractures. INTERVENTION: Images that were stripped of demographic data were independently viewed in random order on computer workstations by 5 trauma fellowship-trained orthopaedic surgeons who were blinded to treatment and diagnosis. MAIN OUTCOME MEASUREMENTS: Sensitivity, specificity, positive post-test probability, and 1 minus negative post-test probability were calculated for diagnosing femoral neck fracture based on each image type. RESULTS: Interobserver reliability showed "substantial agreement" (kappa > 0.65) for all imaging modalities, indicating that the surgeons had a high level of agreement. All 3 imaging sets had high specificity (>94%) and 1 minus negative post-test probability (>95%) but had poor sensitivity (<65%) and positive post-test probability (<58%). False positives and false negatives were equally likely for all imaging modalities (P > 0.2). CONCLUSIONS: Plain radiography and computed tomography have rates of missed femoral neck fractures that are similar and substantial, with a sensitivity of only 56%-64%. Our data emphasize the importance of intraoperative and postoperative imaging in detecting nondisplaced femoral neck fractures in association with femoral shaft fractures.