Three‐dimensional ultrasound to investigate synovitis in first carpometacarpal osteoarthritis: A feasibility study
Authors: du Toit Carla , Dima Robert , Papernick Samuel , Jonnalagadda Melanie , Tessier David , Fenster Aaron , Lalone Emily 
Published: July 2023

Background

Synovitis is one of the defining characteristics of osteoarthritis (OA) in the carpometacarpal (CMC1) joint of the thumb. Quantitative characterization of synovial volume is important for furthering our understanding of CMC1 OA disease progression, treatment response, and monitoring strategies. In previous studies, three‐dimensional ultrasound (3‐D US) has demonstrated the feasibility of being a point‐of‐care system for monitoring knee OA. However, 3‐D US has not been tested on the smaller joints of the hand, which presents unique physiological and imaging challenges.

Purpose

To develop and validate a novel application of 3‐D US to monitor soft‐tissue characteristics of OA in a CMC1 OA patient population compared to the current gold standard, magnetic resonance imaging (MRI).

Methods

A motorized submerged transducer moving assembly was designed for this device specifically for imaging the joints of the hands and wrist. The device used a linear 3‐D scanning approach, where a 14L5 2‐D transducer was translated over the region of interest. Two imaging phantoms were used to test the linear and volumetric measurement accuracy of the 3‐D US device. To evaluate the accuracy of the reconstructed 3‐D US geometry, a multilayer monofilament string‐grid phantom (10 mm square grid) was scanned. To validate the volumetric measurement capabilities of the system, a simulated synovial tissue phantom with an embedded synovial effusion was fabricated and imaged. Ten CMC1 OA patients were imaged by our 3‐D US and a 3.0 T MRI system to compare synovial volumes. The synovial volumes were manually segmented by two raters on the 2D slices of the 3D US reconstruction and MR images, to assess the accuracy and precision of the device for determining synovial tissue volumes. The Standard Error of Measurement and Minimal Detectable Change was used to assess the precision and sensitivity of the volume measurements. Paired sample t‐tests were used to assess statistical significance. Additionally, rater reliability was assessed using Intra‐Class Correlation (ICC) coefficients.

Results

The largest percent difference observed between the known physical volume of synovial extrusion in the phantom and the volume measured by our 3D US was 1.1% (p‐value = 0.03). The mean volume difference between the 3‐D US and the gold standard MRI was 1.78% (p‐value = 0.48). The 3‐D US synovial tissue volume measurements had a Standard Error Measurement (SEm) of 11.21 mm3 and a Minimal Detectible Change (MDC) of 31.06 mm3, while the MRI synovial tissue volume measurements had an SEM of 16.82 mm3 and an MDC of 46.63 mm3. Excellent inter‐ and intra‐rater reliability (ICCs = 0.94–0.99) observed across all imaging modalities and raters.

Conclusion

Our results indicate the feasibility of applying 3‐D US technology to provide accurate and precise CMC1 synovial tissue volume measurements, similar to MRI volume measurements. Lower MDC and SEm values for 3‐D US volume measurements indicate that it is a precise measurement tool to assess synovial volume and that it is sensitive to variation between volume segmentations. The application of this imaging technique to monitor OA pathogenesis and treatment response over time at the patient's bedside should be thoroughly investigated in future studies.