The sitting active and prone passive lag test: a validity study in a symptomatic knee population.

[Purpose] This study aimed to determine the diagnostic utility of the sitting active and prone passive lag test in identifying terminal extension lag in unilaterally symptomatic knees. The lack of full extension at the knee leads to greater force of quadriceps activation, overloading of the weight bearing joints, abnormal gait mechanics, resulting in pain and dysfunction. [Participants and Methods] Participants were randomly assigned and evaluated by two blinded examiners, to determine the presence of extension lag at the knee.