The study compared knee range of motion and muscle strength in patients with symptomatic knee osteoarthritis and healthy controls and assessed the influence of Kellgren-Lawrence grade and measurement protocols. 30 studies identified in PubMed, Scopus and Web of Science databases were included. Osteoarthritis patients had significantly reduced knee flexion of 16.30° (95% CI: 11.40–21.21) and extension of 4.25° (95% CI: 2.30–6.19), with the loss of flexion greater in advanced degrees of KL. Muscle strength was lower in all types: isometric in extensors (SMD = 0.86, 95% CI: 0.57–1.14) and flexors (SMD = 0.52, 95% CI: 0.30–0.74), concentric in extensors (SMD = 1.07, 95% CI: 0.65–1.50) and flexors. (SMD = 0.77, 95% CI: 0.43–1.12) and eccentric in the extensors. Force deficits were similar across all degrees of KL, angles, and speeds of testing. Disease severity affects range of motion but not strength deficits. The results have very low to low certainty of evidence and should therefore be interpreted with caution.