SKIN TEMPERATURE FOLLOWING TOTAL KNEE ARTHROPLASTY: A LONGITUDINAL OBSERVATIONAL STUDY

Total knee arthroplasty (TKA) is the most effective method of pain relief and increased functional status for end stage knee arthritis. Shared by both surgeons and patients, infection is one of the most feared complications. Due to this fear, patients constantly present to physicians complaining of increased temperature on the operated knee. This common clinical observation can be mistaken as a sign for infection leading to unnecessary investigations or the inappropriate use of antibiotics. We aimed to assess in patients undergoing unilateral, primary total knee arthroplasty, whether the temperature of the operated limb, compared to the non-operative limb, remains elevated up to one year post-operatively using a large prospective, longitudinal observational study design. A prospective longitudinal observational study performed in a single center clinical setting (Alberta Hip and Knee Clinic) with patients undergoing operations at three academic hospitals within Calgary, Alberta. These included the Peter Lougheed Center, Rockyview General Hospital and Foothills Medical Center. Fifteen arthroplasty-trained surgeons participated. Patients were Included if they were having an elective primary total knee arthroplasty. Exclusion criteria included patients who have undergone revision TKA, previous major infection, post-traumatic arthritis with previous hardware, previous major operation on the knee including high tibial osteotomy, open reduction internal fixation or major open ligamentous repair excluding arthroscopic ACL reconstruction. Skin temperatures were taken in 4 quadrants using infrared thermometer on the operated and non-operated knees pre-op, 2 weeks, 6 weeks, 3 months and at one year post-operatively. Subgroup analysis was performed in the patients deemed to have a superficial or deep infection. A total of 1094 patients were enrolled in the research study. 889 patients completed a minimum of 4 out of 5 follow-up appointments. Follow-up was impacted due to the COVID-19 pandemic. 864 patients had a normal post-operative course while 25 were deemed to have either superficial or deep infection. Within primary total knee patients, there was a statistically significant increase in skin temperature in the operated versus non-operated knee at every follow-up including the one year follow-up with p<0.001. However, the effect size was small at one-year follow-up with a mean difference in skin temperature of only 0.3oC. In the infected subgroup, there was also a statistically significant difference in skin temperature at 2, 6 and 12 weeks, with a greater difference in skin temperature between operated and non-operated knees (4.05 degrees versus 3.78 degrees in non-infected). However, there was little clinical difference (0.27 degrees) at two weeks between patients who were infected versus not infected. This study has a direct impact to improve the post-operative interaction between patients and surgeons. It is normal for skin temperature post TKA to increase initially and improve over time but can take up to a year before there is little clinical difference. Because of the small difference in the rise of skin temperature between those infected and not infected, there is little indication that skin temperature is a reliable indicator for infection.