Regional differences in temperature course after knee arthroplasty.

PURPOSE: During wound healing after surgery, physiological inflammation leads to an increase in soft tissue perfusion. This is reflected by a characteristic temperature course in the skin. Although local surgical trauma also influences soft tissue perfusion, no data have been available on the regional temperature distribution after knee arthroplasty to date. This study aims at testing the hypothesis that the greatest regional difference in the temperature course is on the site of the maximum surgical trauma (medially) after knee arthroplasty implantation. This is to our knowledge the first study to present regional differences in the temperature course after TKA which would limit the diagnostic value of thermography.
METHODS: Forty-two subjects who were to receive a surface replacement of the knee joint due to primary varus gonarthrosis were included in the study. In all cases, a medial parapatellar approach was chosen. Patients who underwent lateral release or a release of the lateral ligament structures were excluded. In all patients, a thermographic temperature determination was carried out on the operated knee joint every day up to the seventh post-operative day.
RESULTS: On the medial side, there was no significant change in temperature between day one 34.9° ± 0.2° (34.6-35.3 °C) and seven after surgery. Thereafter, the temperature remained constant here up to the seventh day after the operation. In contrast to this, on the lateral side there was an increase in skin temperature from the second 35.0 ± 0.2 °C (34.7-35.4 °C) to the fifth 34.6° ± 0.2° (34.1-34.9 °C) post-operative day (p = 0.002). Thereafter, the temperature remained constant here up to the seventh day after the operation.
CONCLUSION: This study refutes the hypothesis that the greatest regional difference in the temperature course is on the site of maximum surgical trauma (medially) after knee arthroplasty implantation. It is shown to the contrary that there is the least regional difference in the temperature course on the site of maximum surgical trauma (medially) after total knee arthroplasty implantation. It is on the site of the minimal trauma (laterally) where marked differences in the temperature course appeared. The normal temporary temperature increase typical of physiological wound healing could only be shown at a distance from the site of soft tissue preparation. This may be the result of a local compromise of perfusion. Consequently, the post-operative diagnostic application of thermography remains limited to regions distant from the surgical site. This may prevent misinterpretation of post-operative thermographic measurements for scientific or clinical reasons. LEVEL OF EVIDENCE: II.