Use of Corticosteroid in Intraopertive Injections in Total Knee Replacement Surgery.

The goal of this clinical trial is to find out which type of steroid medicine, when added to a standard pain-control injection during total knee replacement surgery, works best at reducing pain, limiting opioid use, and improving recovery in adults undergoing surgery for severe knee arthritis or injury. The main questions it aims to answer are: Does adding a steroid to the injection improve pain control and reduce opioid use after surgery? Is the newer extended-release steroid (Zilretta) more effective and safer-especially for patients with diabetes-than the traditional steroid (methylprednisolone)? Researchers will compare: Standard pain-control injection alone Standard injection plus methylprednisolone Standard injection plus Zilretta to see which option provides better pain relief, less opioid use, and improved knee function. (Patients with diabetes or prediabetes will only be in the standard injection or Zilretta groups so researchers can study whether Zilretta is safer for blood sugar control.) Participants will: Be randomly assigned to one of the study groups during their total knee replacement surgery Receive the assigned pain-control injection around the knee joint Be followed after surgery to measure: Pain levels Opioid pain medication use Knee movement (range of motion) Whether another procedure (such as manipulation under anesthesia) is needed if the knee becomes too stiff Patient-reported outcome surveys about pain and function

Inclusion Criteria: * Patients within the MHS who are DEERS eligible undergoing primary TKA at Walter Reed National Military Medical Center (WRNMMC), Surgery Center of Chevy Chase or District Surgery Center * Age 18 or older * successful surgical intervention Exclusion Criteria: * Unicompartmental knee arthroplasty (UKA) * Revision total knee arthroplasty (rTKA) * Females who are pregnant or nursing * Allergic to ingredients in PAI or previous adverse reaction to steroids being used in this study * Diabetics will be excluded from Group 2 (standard PAI + methylprednisolone)