Extremity cone-beam CT for evaluation of medial tibiofemoral osteoarthritis: Initial experience in imaging of the weight-bearing and non-weight-bearing knee

• The medial tibiofemoral joint space width (JSW) and meniscal extrusion (ME) exhibit measurable change in patients with OA, imaged using a dedicated cone-beam CT (CBCT) scanner in weight bearing (WB) and non-weight bearing (NWB) configurations.
• There is weak association between the ME measured in a NWB scan and the change in ME exhibited between WB and NWB scans. This suggests that ME measurements obtained in conventional NWB studies (such as MDCT and MRI acquired with the patient in decubitus) are limited in the ability to predict the extent of ME in the WB knee.
• A dedicated CBCT extremity scanner capable of imaging the WB knee could provide increased functional information relevant to OA compared to plain radiography or NWB imaging.

PurposeTo investigate differences in joint space width (JSW) and meniscal extrusion (ME) between non-weight bearing (NWB) and weight bearing (WB) examinations of knee joints with medial compartment osteoarthritis (OA) using a cone-beam CT (CBCT) extremity imaging system.Materials and methodsIn this IRB approved prospective study, informed consent was obtained for 17 patients symptomatic for OA (11 F,6 M; 31–78 years, mean 56 years) and 18 asymptomatic controls (0 F,18 M; 29–48 years, mean 38.5 years) enrolled for CBCT exams in NWB and WB positions. Three independent observers measured medial tibiofemoral JSW and ME. Measurements were compared between NWB and WB images using paired Wilcoxon signed-rank sum test.ResultsOA subjects exhibited a statistically significant reduction in JSW between NWB and WB scans (average JSWNWBOA = 2.1 mm and JSWWBOA = 1.5 mm, p = 0.016) and increase in ME (average MENWBOA = 6.9 mm and MEWBOA = 8.2 mm, p = 0.018)). For non-OA subjects, the change in JSW and ME between NWB and WB exams was reduced (average JSWNWBnonOA = 3.7 mm and JSWWBnonOA = 3.4 mm; average MENWBnonOA = 2.6 mm and MEWBnonOA = 2.7 mm) and was not statistically significant. Inter-observer agreement was evaluated using Bland–Altman limits of agreement, with good agreement for all measurements (correlation coefficient 0.89–0.98).ConclusionThe ability to conduct NWB and WB exams in CBCT with a dose profile that is favorable in comparison to multidetector CT (MDCT) and with image quality sufficient for morphological analysis of joint space narrowing and meniscal extrusion could provide a valuable tool for OA diagnosis and treatment assessment.