Navigation in total knee replacement is now used more frequently. The proven benefits in comparison to a conventional knee replacement include reduced hospital stay, reduced blood loss, and improved component alignment. A retrospective study was carried out to evaluate the difference in post-operative pain outcomes between conventional and computer-assisted navigation knee arthroplasty in a high volume setting. Computer-assisted surgery may be more painful because of the extra pin holes required for the navigation. The amount of anti-emetic use between the two groups was also looked at as evidence exists that greater anti-emetic is used if pain levels are greater. All the navigated arthroplasty operations were performed by one of two surgeons in a single hospital using a uniform surgical approach and navigation system. A single type of prosthesis was used in the conventional group. In the first part of the study, the navigated group consisted of 87 patients and the conventional group of 40 patients (total = 127 cases). In the second ‘antiemetic use’ study, the navigated group consisted of 71 patients and the conventional group of 39 (total = 110). The analgesic and anti-emetic use was collated for the 72-hour post-operative period. This was chosen so that any analgesic influence of the anesthetic would have been negated over this period. Pain scores were measured over the 72 hour period at regular intervals using a visual analogue scale. Patients in the navigated group seemed to report less pain in the first 24 hours but this was later reversed. Interestingly, their pain scores were more constant during this period, whilst the conventional group exhibited greater variability. The actual difference in pain scores between the two groups was however not significant (p=0.33). The amount of opioid used by patients in each group was the primary factor used to see if a difference exists between the two procedures. The assumption was made that a correlation exists between opioid usage and pain. The total opioid usage was calculated by using referenced opioid conversion calculations for intravenous and oral forms of morphine including weaker opioids such as codeine and tramadol. The average opioid used in the conventional group was 164.8 mg whilst in the navigated it was 173.7mg. However using the Student’s t-test this difference was not significant with a p value = 0.69. The percentage of patients requiring opioid greater than 300mg in 72 hours was actually greater in the conventional group (15% vs 12.6%). The average antiemetic use looking initially at cyclizine was 57.7mg in conventional and 50.4mg in the navigated. This difference was also not significant (p=0.59). On analysis of the tourniquet times between the groups it was noted that the average time for a conventional operation was 89.6 minutes whilst it was 88.6 minutes in the other. This is in contrast to previous findings and it seems that the learning curve is improving at least in this high volume setting. This paper suggests that there is no difference between the two groups with respect to pain experienced in the post-operative period.
