BACKGROUND: Robotic-assisted total knee arthroplasty (TKA) platforms require tibial and femoral pins to support rigidly fixed navigation arrays. These pins can be placed inside or outside the primary incision. We sought to compare 90-day complication rates between three different pin configurations: all-outside, intra-incisional femur/extra-incisional tibia, and all-inside. METHODS: A retrospective cohort study of 2,880 patients undergoing robotic primary TKA was performed, including 1,004 patients (35%) with all-outside pins, 1,056 patients (37%) with intra-incisional femur/extra-incisional tibia pins, and 820 patients (29%) with all-inside pins. The primary outcomes were primary wound complications and pin-site wound complications within 90 days. Secondary outcomes were manipulations under anesthesia (MUAs) and complex regional pain syndrome (CRPS). RESULTS: There were 41 (2.0%) tibial pin-site wound complications and three (0.3%) femoral pin-site wound complications. There were 109 (3.8%) wound complications involving the primary incision. There was no difference in primary wound complication rates between the all-outside, intra-incisional femur/extra-incisional tibia, and all-inside groups (3.3 versus 3.9 versus 4.3%, P = 0.54). There were 18 major wound complications requiring reoperation or readmission
13 of these involved the primary incision only, three involved the primary incision and tibial pin sites, and two involved the tibial pin sites only. There were no differences between the three groups in the rates of MUAs (4.1 versus 2.4 versus 3.4%, P = 0.09) or CRPS (0.1 versus 0.1 versus 0.6%, P = 0.06), respectively. There were no intraoperative or postoperative periprosthetic pin-related fractures in the study sample. CONCLUSIONS: Primary wound complication rates were similar in patients who had pins placed outside or within the primary incision during robotic TKA. However, among patients who had extra-incisional tibial pins, there was an additional 2.0% risk of tibial pin site-related wound complications. All-inside pin placement did not lead to an increased risk of CRPS or MUAs compared to extra-incisional tibial pins.