Post-Operative Urinary Retention on Revision Knee Arthroplasty: the Role of Intrathecal Morphine

Introduction Total knee arthroplasties (TKA) are among the most performed surgeries worldwide(1). In Canada, between 2020 and 2021, 55,285 TKAs were performed, with 4179 (7.56%) being revision total knee arthroplasties (rTKA). The main reasons for rTKAs are infection (35.6%), aseptic loosening (18.0%) and instability (3.6%)(2). Most TKA are done under a neuraxial anesthetic technique alongside a multimodal approach to postoperative pain management. The approach to postoperative pain management comprises combining intrathecal opioids like morphine, fentanyl; IPACK (interspace between the popliteal artery and the posterior knee capsule) block; adductor canal block (ACB), single shot or continuous with catheters; local infiltration analgesia (LIA) and systemic administration of paracetamol and non-steroid anti-inflammatory drugs (NSAIDs). Oral and intravenous (IV) opioids are usually reserved as rescue medications(3).

In many types of surgeries (lower limbs and abdominal surgeries), intrathecal morphine (IM) administration has been shown to significantly reduce pain scores and postoperative opioid requirements within the first 24 hours. However, its administration has potential side effects, which includes respiratory depression, pruritus, nausea, vomiting and postoperative urinary retention (POUR)(4-7). POUR may require bladder catheterization and can result in delayed hospital discharge and poor patient satisfaction. Ultimately, the need for bladder catheterization increases the risk of periprosthetic infection in hip and knee arthroplasties surgeries(8, 9).

Among primary TKA surgery, there is fair amount of evidence demonstrating equivalence of IM to femoral nerve block or ACB for postoperative analgesia, but at the cost of side effects when IM is used(10, 11). Therefore, for primary TKA surgery, when the proper peripheral nerve blocks are performed, IM is often not used.

A limitation of most of the existing literature focusing on postoperative analgesia in TKA is the exclusion of rTKA surgeries. Consequently, there are very few studies to guide analgesic management specific to rTKA. One study demonstrates that, when a multimodal protocol including continuous ACB (CACB) was performed, patients who underwent rTKA experienced a similar postoperative analgesic course as primary TKA patients(12). Regardless the benefits of peripheral nerve blocks and the potential side effects of IM, the latter is still commonly used for rTKA perioperative management. To the best of our knowledge, there is no prospective study assessing the real analgesic role and potential side effects of IM in addition to peripheral nerve blocks in rTKAs.

Significance Revision TKAs are on a rise following primary TKA. It is a more costly procedure than primary TKA and tends to be more painful. In our institution (Mount Sinai Hospital - Sinai Health System - Toronto, Ontario, Canada), most rTKAs are done under neuraxial anesthesia with IM to achieve optimal pain control. Peripheral nerve blocks (single shot and CACB and IPACK block) are done depending on the presence or absence of contra-indications (anatomy abnormalities, infection on block site). The usage of IM has been shown to be a risk factor for POUR(4, 6), which may require bladder catheterization for its management. This increases the risk for urinary tract infections and subsequently periprosthetic joint infection(8, 9). Despite of the potential side effects, IM is still fairly used for postoperative management in rTKA surgeries.