We have found that a useful technique is a local anaesthetic block injected into the damaged tissues in the last stages of the operation. Our technique was developed from that of Kerr and Kohan (2008).
Ropivacaine 300 mg, ketorolac 30 mg, and epinephrine 0.5 mg are made up to a total volume of 100 ml with normal saline. Adrenaline is added to a ratio of 1:200,000. The mixture is put into two 50-ml syringes. Before the components are implanted, the mixture is injected through a 19 gauge spinal needle into any tissue that was damaged during the operation. This is done methodically so that no area is missed, with particular attention being paid to the posterior capsule , the periosteum around the implant, and the margins of the incision in the quadriceps muscle. The skin is infiltrated up to 3 cm from the margins of the wound and 10 ml is reserved until the end of the procedure to inject around the drain site, if a drain is used.
This treatment usually results in very little pain when the patient wakes from the anaesthetic, allowing immediate resumption of knee flexion and walking. Occasionally, however, the local anaesthetic is slow to work and patients awake with severe pain. Pain immediately after the operation can be more reliably avoided by regional nerve blocks given at the beginning of the procedure. They have the additional advantage of minimising the dose of general anaesthetic required, which helps with more rapid recovery. However, femoral and sciatic nerve blocks with bupivacaine, and epidural anaesthesia, may have motor effects that delay mobilisation. Therefore, we now use prilocaine nerve blocks or a short-acting spinal anaesthetic. The effects of these have usually worn off 2–3 hours after the operation when the patients start to walk.
Severe pain may occur on the second day when all these drugs have ceased to act (so called ‘rebound pain’). This can be controlled by instilling local anaesthetic into the joint through a fine (epidural) catheter inserted into the knee before wound closure. The catheter should be fitted with a bacterial filter to minimise the risk of infection. The morning after surgery, 20 ml of 0.5% bupivacaine is instilled into the joint. (If a suction drain was used it should be clamped.) The catheter (and drain) are then removed. In a randomised controlled trial, we found that this technique can provide good pain relief for a further 24 hours (Weston-Simons et al,, 2012).
In recent years, long acting local anaesthetic (liposomal bupivacaine) has been used for pain relief after UKA. It is reported to last for up to 72 hours, allowing UKA to be performed as a day case in the majority of cases (J Barrington – personal communication). We do not have experience with the use of liposomal bupivicaine as it is not licensed for use in the UK.
In addition to the local anaesthetic, we use high doses of oral non-steroidal anti-inflammatory drugs with a gastroprotective agent such as ranitidine or omeprazole.