Is bicortical femoral pin insertion safe for image-based robotic knee arthroplasty surgery? A comparative complications analysis in 970 consecutive cases

Objectives: Limited data exists on complications associated with robotic image-based system in knee arthroplasty. This study aims to document complications in robotic arm-assisted knee arthroplasties and evaluate the system's safety by comparing two femoral pin insertion methods: bicortical diaphyseal with additional stab wounds, and unicortical metaphyseal placement through the main incision. Methods: All patients undergoing primary knee arthroplasty with the image-based robotic system (Mako, Stryker, Mako Surgical Corp., Fort Lauderdale, FL, USA) from 1st March 2021 to 31st January 2024 with a minimum followup of 2 months were included. Demographics, system and non-system-related complications, as well as outcomes were recorded. Complications were categorized as either major (requiring a second surgical intervention) or minor. Results: A total of 970 consecutive cases (median age 69.3 years) were analyzed. The unicortical group comprised 651 cases, while the bicortical group 319. The incidence of non-system-related complications was 2.37%, with the most common being joint stiffness (10 cases; 1.03%), followed by lateral femoral condyle fracture (4; 0.41%). The overall incidence of system-specific complications was 1.03%. Pin-related femoral fractures occurred in 0.2% of cases, all postoperatively and in the unicortical group. There was no statistically significant difference between the femoral pin insertion- related complication rates among the two groups (0.3% in the unicortical, compared to 0% in the bicortical group; p-value = 0.3). Complications included tibia fracture (0.1%), delayed wound healing (0.2%), superficial wound infection (0.1%), tibia osteomyelitis (0.1%), and "exostosis" (0.2%). The major complications rate was 0.3% and minor 0.7%. Conclusions: Minimal system-specific overall complications indicate that robotic arm-assisted surgery is safe. The bicortical diaphyseal femoral pin insertion method does not increase the complication rates compared to the unicortical metaphyseal method. Level of evidence: III.