Spinal Anesthetic for Hip and Knee Replacement Surgery - Intrathecal Morphine or Hydromorphone

In the current healthcare system, a short length of stay is paramount, for medical, functional, and financial reasons. Most patients undergoing hip and knee replacement at Hôpital Montfort institution receive spinal anesthetic, with intrathecal morphine for enhanced analgesia. However, morphine can cause urinary retention, nausea or vomiting resulting in increased length of stay (LOS). Based mainly on local experience, The investigators believe hydromorphone may be a good alternative (1). According to the literature review, no adult study compares morphine and hydromorphone. QUESTIONS Does intrathecal hydromorphone lead to equal or better pain control/post-operative function, with fewer side effects than morphine? OBJECTIVES. Primary objective: to demonstrate that hydromorphone is the choice narcotic for spinal anesthesia for arthroplasty patients. Secondary objectives: * increased patient satisfaction * decreased hospital length of stay METHODOLOGY The investigators propose a prospective randomized double-blind trial with three groups of 155 patients each undergoing total hip arthroplasty (THA), total knee arthroplasty (TKA), or unicompartmental knee arthroplasty (UKA), striving for similar proportions of each procedure in all three groups. * Group 1: spinal anesthetic with standard painkillers, without intrathecal narcotics (ie "placebo" group) * Group 2: spinal anesthetic with intrathecal morphine * Group 3: spinal anesthetic with intrathecal hydromorphone The primary outcome measure will be urinary retention. Secondary outcome measures will be nausea/vomiting, pain control, post-operative function and length of stay. RESULTS The investigators expect to show that intrathecal hydromorphone will provide the best combination of post-operative patient pain control and function, with diminished negative side effects. They hope to extrapolate this to a potential out-patient arthroplasty program.