A comparison of pin site complications between large and small pin diameters in robotic-assisted total knee arthroplasty

PURPOSE: Robotic-assisted total knee arthroplasty typically necessitates use of tracking pins, which can vary in diameter. Complications such as infections and fractures at the pin-site have been observed, but clarification of the effect of pin diameter on complication is needed. The aim of this study is to compare the pin-related complication rates following robotic-assisted total knee arthroplasty between 4.5 mm and 3.2 mm diameter pins. METHODS: In this retrospective cohort study, 90-day pin-site complication rates after robotic-assisted total knee arthroplasty were compared between 4.5 mm diameter and 3.2 mm diameter groups. In total, 367 patients were included: 177 with large pin diameter and 190 with small pin diameter. All four pin sites were evaluated using postoperative radiographs. Cases without orthogonal views or visualization of all four pin tracts were noted. Multivariate logistic regression was used to control for age, which differed between the two cohorts. RESULTS: The rate of pin-site complications was 5.6% in the large pin diameter cohort and 2.6% in the small pin diameter cohort, with no statistically significant difference between the groups. The adjusted odds ratio for complications in small compared to large diameter group was 0.48, with a p-value of 0.18. The most common pin-site complication was infection/persistent drainage, found in 1.9% of patients, followed by intraoperative fracture of the second cortex in 1.4%. Intraoperative fracture could not be ruled out in 96 cases due to inadequate radiographic visualization of all pin sites. There was one postoperative pin-site fracture in the large diameter cohort, which required operative fixation. CONCLUSION: This study demonstrates no statistically significant difference in pin-site complication rates after robotic-assisted total knee arthroplasty between 4.5 mm and 3.2 mm pin diameter cohorts, although there was a trend towards increased intraoperative and postoperative pin-site fractures in the 4.5 mm group.