Extremity cone-beam CT for evaluation of medial tibiofemoral osteoarthritis: Initial experience in imaging of the weight-bearing and non-weight-bearing knee
Introduction
Osteoarthritis (OA) of the knee is the most common chronic joint disease, with a rising prevalence of about 15% [1]. Currently, weight bearing plain radiography is the most common imaging modality to monitor the severity and progression of knee OA by demonstrating the narrowing of joint space width (JSW). Accurate and reproducible JSW evaluation using plain radiography requires careful positioning of both the X-ray system and the patient [2] and does not provide information on soft tissue structures or 3D orientation of osseous structures. Multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) provide detailed assessment of cartilage disease and other structural damage in patients with knee OA, such as meniscal or ligamentous injuries [3], which can contribute to joint space narrowing and progression of disease. For example, in addition to cartilage damage, the presence of meniscal extrusion (ME) can contribute to narrowing of knee JSW [4], [5] and is a strong predictor of further cartilage loss in patients with knee OA [6].
Cone-beam computed tomography (CBCT) uses a large-area detector (>1000 detector rows covering ∼30 × 30 cm2) and a pyramid-shaped X-ray beam to acquire a volumetric image in a single rotation. A CBCT system for extremity imaging has been recently developed [7] and translated to a clinical prototype with the ability to acquire both weight bearing (WB) and non-weight bearing (NWB) exams of the lower extremities. Feasibility of CBCT scanning in either configuration was recently confirmed [8], and initial results demonstrated reduced radiation exposure, soft tissue image quality sufficient for visualization of ligaments, cartilage, and menisci, and bone visualization meeting or exceeding the performance of high-resolution MDCT [9], [10]. Other work also demonstrates the ability to acquire images of the lower extremities in a physiologic WB setup, which may improve diagnosis and management of certain pathologies in WB joints, like the ankle and the knee [11].
The purpose of the current study was to test the hypothesis that there is a significant difference in measurements of JSW and ME between NWB and WB examinations of the knee joints with known medial compartment OA using a dedicated CBCT extremity system.
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Patient population
Institutional review board approval was obtained for this prospective study. Informed consent was obtained from 17 symptomatic patients (11 females, 6 males; age range: 31–78 years, mean age: 56 years) with diagnosis of OA in their medial tibiofemoral compartment, independent of the CBCT studies reported below, as per the clinical symptoms and findings in plain radiographs. The severity of OA was classified in plain radiographs using a previously described grading classification system [3]
Result
A summary of measurements for JSW and ME is presented in Table 1, Table 2. Disease severity in the OA subjects was graded using radiographs for each subject acquired as part of the standard of care. Of the 17 symptomatic subjects with OA, 3 (17.6%) were severe, 12 (70.6%) were moderate, and 2 (11.8%) were mild in the severity of disease in the medial compartment according to the previously described grading system based on plain radiographs [3]. Additionally, OA severity was graded according to
Discussion
In this study, we demonstrated that the medial tibiofemoral JSW and ME change significantly in patients with OA between a WB and NWB setup using a CBCT extremity scanner. CBCT images provide image data with isotropic spatial resolution, which can be reconstructed in any plane in support of accurate measurements of JSW, as opposed to plain radiographs, where JSW measurements can be highly dependent on the positioning of the patient and X-ray beam [16]. Plain standing radiographs require precise
Conflict of interest
None.
Funding
This project was funded by Carestream Health Inc. and NIH Grant No.R21-AR-062293.
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