Decreased oxygenation and delayed wound healing may negate the advantages of using a medial parapatellar incision in Total Knee Replacement. Tissue biochemical and blood flow data are not currently available in the literature. 20 patients were included in the study and randomised to midline or medial parapatellar skin incision groups, being supervised by one of 3 Consultant surgeons. Cutaneous blood flow was measured using a Speckle Contrast Blood Perfusion Imager at pre-operative and Days 1 & 3 post-operative intervals. Interstitial fluid measurements for lactate, pyruvate, lactate/pyruvate ratio and glucose were obtained from subcutaneous catheters with a dialysis membrane. Pre-operative samples were obtained from a catheter inserted into the prospective lateral wound edge. A catheter inserted after wound closure supplied dialysates at 0.5, 1, 2, 4, 6, 12 and 24-hour intervals. One catheter was corrupted on insertion; therefore the patients with biochemical data numbered 19. Cutaneous blood flow improved over the 3 post-operative days in both types of incision and both sides, the medial retaining comparatively better flow. At Day 3, the parapatellar incision group displayed better flow on both sides of the wound. The concentration of lactate was highest in the parapatellar incision group of patients at all intervals. Pyruvate concentrations did not appear to differ across the incision types. Similarly, glucose concentrations did not appear to differ until after 4 hours, when higher concentrations were recorded in the midline group. Lactate/pyruvate ratio appeared to be notably greater in the parapatellar incision group. Plotting change in blood flow relative to change in lactate concentration demonstrated an increase in lactate as flow deteriorates. The study findings suggest medial parapatellar incisions have increased anaerobic metabolites due to tissue hypoperfusion. Previous studies have demonstrated decreased oxygen tension in lateral based flaps and more recently the medial to lateral arterial anatomy has been demonstrated.
