What will be done about the pain after my joint replacement, and will I need strong painkillers?
It is one of the questions asked at almost every consultation before a hip or knee replacement, and it deserves a straight answer. A knee replacement in particular is a painful operation. The modern answer is not one strong drug but several smaller measures layered on top of each other, each working in a different way, so that the opioid tablets do a smaller share of the work. This entry reads the guideline that sets that regimen out, and three papers that explain why it is built the way it is.
What the study looked at
PROSPECT (PROcedure SPEcific Postoperative Pain ManagemenT) is a working group of anaesthetists and surgeons within the European Society of Regional Anaesthesia and Pain Therapy. Rather than writing general advice on pain, it writes a recommendation for one operation at a time, judged only on the trials for that operation. This paper is its 2022 update for primary total knee replacement.
The method was to find every systematic review and meta-analysis of pain relief after knee replacement published between 2014 and 2020, 151 of them, and then go back to the individual randomised trials inside them. A trial counted only if it met the group’s standards, and 106 did. Three rules shaped what followed. A difference in pain had to reach at least one point on a ten-point scale to count as real. Each intervention was judged against a background of paracetamol and an anti-inflammatory, because that is what patients should be getting anyway, not against nothing. And the side effects of each measure, and its effect on walking in the first day or two, were weighed as carefully as its effect on the pain score.
The guideline deliberately left out the choice of anaesthetic, spinal or general, which is why a second paper below is needed to cover it.
What they found
The recommended regimen for a primary knee replacement:
- Paracetamol and an anti-inflammatory (a conventional NSAID or a COX-2 inhibitor), started before or during the operation and continued afterwards. In all six trials of COX-2 inhibitors that met the criteria, pain at rest and on movement fell and opioid use fell, even when patients were already receiving paracetamol or local infiltration.
- A single-shot adductor canal block given before surgery, combined with local infiltration analgesia, meaning local anaesthetic injected into the tissues around the joint by the surgeon during the operation. The combination is preferred over either alone. The adductor canal block numbs the front and inner knee without weakening the thigh muscle, so patients can stand and walk; the older femoral nerve block gave the same pain relief but weakened the quadriceps.
- One intravenous dose of dexamethasone during the operation, a steroid that reduced pain, opioid use and nausea in every single-dose trial.
- Opioids reserved as rescue, for the pain that comes through the layers, rather than as the foundation.
The interventions the group recommended against are as telling as the ones it recommended for. Epidurals gave good pain relief but more nausea, low blood pressure, urinary retention and slower mobilisation. Femoral and sciatic nerve blocks weakened the leg. Gabapentin and pregabalin, once popular, added nothing clinically useful on top of the basic regimen and carry sedation and dizziness. Ketamine and continuous nerve-block catheters had inconsistent evidence. Morphine in the spinal injection was kept only for the rare patient in whom neither a block nor infiltration is possible.
What the companion papers add
The hip guideline from the same group, published the year before, reaches the same backbone: paracetamol, an NSAID or COX-2 inhibitor, 8 to 10 mg of intravenous dexamethasone, and either local infiltration or a fascia iliaca block, with opioids for rescue. Epidurals, femoral and lumbar plexus blocks and gabapentinoids are again not recommended. It adds one point the knee paper left out: the choice between a spinal and a general anaesthetic has only a minor effect on pain, so that decision should be made on other grounds.
Those other grounds are the subject of the ICAROS consensus, a systematic review of 94 studies comparing spinal (neuraxial) with general anaesthesia for hip and knee replacement. Spinal anaesthesia was associated with lower odds of nearly every complication recorded: for hip replacement, death within the study periods (odds ratio 0.67, 95% CI 0.57 to 0.80), chest complications (0.65), deep vein thrombosis (0.52), infection (0.73) and transfusion (0.85), with similar or smaller differences for knees. Urinary retention was the one exception. The group recommends spinal anaesthesia for hip replacement and prefers it for knee replacement, while grading the evidence as low to moderate because most of it is observational.
The population-based study supplies what a guideline cannot: outcomes across whole health systems. In 512,393 hip and 1,028,069 knee replacements in American hospitals between 2006 and 2016, 85.6% of patients received more than opioids alone. Hip patients given more than two additional modes of pain relief had, after adjustment, 19% lower odds of a respiratory complication (odds ratio 0.81, 95% CI 0.70 to 0.94), 26% lower odds of a gastrointestinal complication (0.74, 0.65 to 0.84), an 18.5% lower opioid prescription (median 205 against 300 oral morphine equivalents) and a 12.1% shorter stay (median two days against three). The knee results followed the same pattern, and anti-inflammatories looked like the most effective single addition.
Local infiltration itself has an Australian origin. It was described in 2008 by Kerr and Kohan in New South Wales, in a series of 325 hip and knee patients of whom two-thirds needed no morphine at all and 71% went home after a single night. The PROSPECT paper credits that description as the start of the technique.
What it means for you
Put together, the four papers describe a pattern rather than a single drug: a spinal anaesthetic where it is safe for you, local anaesthetic infiltrated around the joint during the operation, a nerve block chosen for the joint, and then regular paracetamol and an anti-inflammatory at home with a short supply of a stronger tablet for the pain that comes through and for the night. Each layer lets the next one do less. That is the regimen this practice works to, with the anaesthetist deciding the anaesthetic and block for each patient.
It does not mean no pain. The guideline itself notes that 15 to 20% of knee replacement patients report some persistent pain, and real, medication-needing pain usually lasts two to three weeks after a knee and less after a hip. What the layers change is how much of that early period is carried by opioid tablets, and the evidence is that fewer opioids mean fewer of the complications that go with them. The chapter on what to expect of the pain and the section on pain after surgery set out the timeline; the anaesthetist’s assessment before surgery is where the plan for you is settled.
A caveat worth knowing
A guideline built from reviews is only as good as the trials underneath, and the group says so. Many of the trials did not give their control patients the basic paracetamol and anti-inflammatory, which flatters whatever was being tested; infiltration mixtures and volumes varied so much that nothing could be pooled; and the trials were mostly in hospital patients, not day-surgery pathways. Patients with long-standing pain or already taking opioids, the group most likely to struggle afterwards, were largely excluded. The population-based study is observational: hospitals that layer their pain relief may differ from those that do not in ways the adjustment cannot capture. And the ICAROS evidence for the spinal anaesthetic is graded low to moderate for the same reason. The direction of all four papers is consistent, which is the reassurance; the size of each effect for an individual patient is not something any of them can give.