Ultrasound-detected accelerated fat deposition in the vastus medialis as a marker for early knee osteoarthritis
Authors: Hoki Atsushi , D’Amico Ella , Ambrosio Fabrisia , Matsuda Yoshikazu , Iijima Hirotaka 
Published: April 2023

ABSTRACTImportanceThe absence of a reliable marker of early-stage knee osteoarthritis (KOA) represents a missed opportunity to develop interventions that restore joint integrity. The use of ultrasonography (US) to measure fat infiltration of muscle, which has been associated with incidence and progression of KOA, is one possible solution. Summarizing the trajectory of fatty infiltration during natural aging and KOA processes and establishing US-implementation as a tool for the early diagnosis of KOA represent essential first steps.Objective(1) To summarize the alterations in quadriceps muscle quality during healthy aging (young vs. older) and in the setting of KOA (older vs. KOA) using computational approaches, and (2) to validate and translate these findings by applying US assessment of muscle quality in a clinical setting.Design, Setting, ParticipantsSystematic review with network meta-analysis integrated with a subsequent case-control validation study in an orthopedic clinic. Both analyses evaluated three groups: healthy young, healthy older, and individuals with KOA.Main outcome and MeasuresQuadriceps muscle quality assessed by US.ResultsData from a total of 718 healthy aging individuals (young, n = 336; old, n = 382) and 1,046 individuals with KOA (old, n = 625; KOA, n = 421) were synthesized for meta-analyses. As determined by US, older adults displayed poor quadriceps muscle quality compared to young; this decline was significantly exacerbated when individuals had KOA. The network meta-analysis revealed that the presence of KOA significantly accelerated muscle fatty infiltration compared to natural aging. Notably, US findings were comparable to gold-standard imaging modalities of both MRI and CT for fat infiltration in skeletal muscle. The findings from these computational analyses were supported by an US-implemented validation study in a clinical setting, which also identified the vastus medialis as the most sensitive quadricep muscle to predict both the onset and development of KOA.Conclusions and RelevanceThis study established accelerated fat deposition in the vastus medialis as a distinct marker for early KOA, as reliably identified by US. These findings expand opportunities for the early diagnosis and treatment for KOA in a clinical setting given the increased cost-efficiency and accessibility of the US system compared to MRI or CT.Trial registrationPROSPERO Identifier: CRD 42022380856KEY POINTSQuestionDoes ultrasonography identify distinct declines in quadriceps muscle quality related to age and knee osteoarthritis (KOA)?FindingsA hybrid approach of network meta-analysis (1,794 participants) followed by ultrasound assessment revealed that KOA significantly accelerated aging-induced fat infiltration in muscle. This study suggests that the 10-year rate of decline in quadriceps muscle quality in KOA is greater than in healthy aging. Furthermore, these changes can sensitively be assessed by ultrasonography.MeaningFatty infiltration in the quadriceps muscle over the course of natural aging is accelerated in the setting of KOA. Such trajectories are assessable using ultrasonography, a valuable approach to identify adults at risk for KOA.