Rotator cuff tears are a common injury that lead to pain and loss of function for those who suffer from it. Treatment includes the use of arthroscopic surgery to return function to the patient and reduce their pain. This study is interested in a technique that has the potential to improve patient outcomes in terms of less pain and better function after their surgery. Autologous Conditioned Plasma (ACP) or Platelet Rich Plasma (PRP) is the intervention of interest, which is simply the patient's own blood that is withdrawn and spun down to obtain a high concentration of cells called platelets. Platelets release growth factors important for healing, as well as fibrin, which acts like a biological glue. The PRP is then re-injected into the shoulder at the time of surgery and again at 4 weeks. It has been shown to accelerate healing in other studies for injuries such as chronic elbow tendinopathy, but there is no randomized controlled trial that evaluates the effect of PRP in rotator cuff tears. It is on this basis that the study is being performed. Participating patients will receive either a PRP injection or a placebo (normal saline) and the effects will be compared at 2 weeks, 4 weeks, and 6 weeks based on a pain score and return to function questionnaires. The primary hypothesis for this study is that ACP compared with placebo is effective in reducing pain at the site of a rotator cuff injury that has undergone arthroscopic repair. It is expected that ACP administered during surgery and 4 weeks post-surgery will reduce 6-week pain scores compared to the placebo group.