Participants will undergo knee aspirations. During a knee aspiration, the investigator will remove fluid from the space around the knee using a needle and syringe. This is usually performed under a local anesthetic to either relieve swelling or to obtain fluid for analysis to diagnose a joint disorder and/or problem. Knee aspirations after ACL tear with a painful effusion are a common orthopaedic practice and standard of care in at the UK Medical Center. Thus they are not considered additional interventions with regard to this study unless the participant has no fluid in the knee.