Clarke's Sign / Patellar Grind Test for Patellofemoral Pain The Clarke's Sign is a common test that is used in the diagnosis of patellofemoral pain syndrome (PFPS) as it is reasoned to stress the patellar cartilage. However, Cook et al. (2012) did a systematic review on various tests and clinical findings and found a variable sensitivity of 39-49% and a variable specificity of 67-95%. For this reason, Clarke's Sign does not seem to be able to add much value to the diagnosis of PFPS. | Physiotuto