Biomechanical Assessment of Pin-Site Fractures in Intra- Versus Extraincisional Pinning Technique for Robotic Total...

Robotic-assisted total knee arthroplasty offers enhanced precision, but introduces new challenges, including pin-site fracture risk from tracker fixation, with incidence rates of 0.06 to 4.8%. This study aimed to evaluate the effects of intra- versus extra-incisional pin placement on torsional rigidity to fracture failure in cadaver specimens.

Twenty matched cadaver femora and tibiae were randomized to undergo either intraincisional/metaphyseal or extraincisionalincisional/diaphyseal pinning. Specimens were cemented into jigs and subjected to torsional load-to-failure in two stages, first at 100 Nm, then 300 Nm, with two separate machines, with continuous monitoring of torque, rotation, and time. Fracture documentation and trendline analysis were performed to calculate torsional rigidity and coefficient of determination (R2). Fracture characteristics, including pin-site involvement, and fracture patterns were also recorded.

Mean torsional rigidity was significantly higher for intraincisional femora at both 100 Nm (14.03 versus 10.91 Nm/degree, P = 0.048) and 300 Nm (14.46 versus 10.91 Nm/degree, P = 0.048). 80% of extraincisional femora fractured when subjected to 100 Nm of torsion, than 20% of intraincisional femora (P = 0.058). Mean torsional rigidity was 8.24 Nm/degree for intraincisional compared to 6.35 Nm/degree for extraincisional pinning for tibiae (P = 0.2), although this did not reach statistical significance. There were 80% of extraincisional tibiae that fractured when subjected to 100 Nm of torsion, compared to 40% of intraincisional tibiae. Overall, 80% of extraincisional specimens fractured, compared to a significantly lower 30% of intraincisional specimens (P = 0.025). There were half of the extraincisional specimens had fractures that involved the pin site(s), compared to none in intraincisional specimens.

Intraincisional pin placement confers biomechanical advantages by having significantly higher torsional rigidity and reduced fracture risk, particularly of pin-site failures, in both femora and tibiae compared to extraincisional pin placements. Patients who are encouraged to ambulate immediately after robotic-assisted total knee arthroplasty operations may have a better safety profile by using intraincisional pinning techniques.