Background Knee osteoarthritis (KOA) is the most prevalent musculoskeletal degenerative disease worldwide. Periarticular muscle abnormalities are considered closely associated with its pathogenesis, yet the relationships between various muscle parameters and KOA remain controversial. Objective To clarify the correlations of thigh muscle quantity, muscle quality, and muscle strength with KOA through a systematic review and meta-analysis, and to provide evidence-based support for the risk screening and early intervention of KOA in high-risk populations. Methods Relevant cross-sectional, cohort, and case-control studies published up to March 2026 were searched in PubMed, Embase, and MEDLINE (accessed via the Ovid). Methodological quality was assessed using the AHRQ scale for cross-sectional studies and the Newcastle-Ottawa Scale for cohort and case-control studies. Meta-analyses were performed using RevMan 5.3 software, and subgroup analyses stratified by study design were conducted to explore sources of heterogeneity. Results A total of 24 studies involving 10,300 participants were included. Patients with KOA showed significantly increased cross-sectional areas of sartorius muscle (SMD = 0.09, P = 0.002) and flexor muscles (SMD = 0.09, P = 0.0008), and markedly reduced thickness of vastus lateralis muscle (SMD=-0.61, P = 0.03). Intermuscular adipose tissue content was significantly higher in KOA patients than in healthy controls (SMD = 0.35, P = 0.001). For muscle strength, KOA patients exhibited significant reductions in knee extensor torque (SMD=-1.09, P = 0.0001), extensor strength (SMD=-0.16, P = 0.0002), knee extensor relative strength (SMD=-0.15, P = 0.04), flexor torque (SMD=-0.95, P = 0.04), and flexor strength (SMD=-0.12, P = 0.004). Substantial heterogeneity was observed in key outcomes including knee extensor torque (I²=97%), knee flexor torque (I²=99%) and intermuscular adipose tissue (I²=72%). Low knee extensor strength was associated with a 1.45-fold increased odds of KOA (OR = 1.45, P = 0.01), and this association was more prominent in women (OR = 1.54, P = 0.0006). Conclusion Alterations in thigh muscle quantity, quality and strength are significantly associated with KOA, particularly increased intermuscular adipose tissue infiltration and decreased knee extensor strength. Current evidence is predominantly derived from cross-sectional and case-control studies, and causal inferences cannot be established. These muscle parameters may serve as potential indicators for KOA risk stratification, and their predictive value and clinical utility require further verification in large-scale prospective cohort studies. Systematic Review Registration https://www.crd.york.ac.uk/PROSPERO/view/CRD420261350323 , identifier CRD420261350323.