ERS3063. Safe Zones and Trajectory of Femoral Pin Placement in Robotic Total Knee Arthroplasty
Authors * Denotes Presenting Author
  1. Jaime Carvajal Alba; University of Miami
  2. David Constantinescu; University of Miami/Jackson Health System
  3. Juan Lopez; University of Miami/Jackson Health System
  4. Victor Hernandez; University of Miami
  5. Michele D'Apuzzo; University of Miami
  6. Joseph Villavicencio *; University of Miami/Jackson Health System
  7. Jean Jose; University of Miami
The emerging popularity of robotic-assisted total knee arthroplasty (TKA) comes with unique complications compared to conventional instrumentation. Limited knowledge of ideal pin placement leads to varied insertion and trajectory, largely based on surgeon preference. The risk to surrounding neurovascular structures has yet to be determined. Therefore, the primary aim of our study was to measure the proximity of surrounding neurovascular structures to the projected femoral pin placement throughout the femur. Our secondary aim included analyzing the difference between sexes. Our hypothesis was that increased risk to vascular structure is present proximally on the femur and in females.

Materials and Methods:
The study included 10 femur MRI’s, comprising of 5 age matched pairs of males and females. In order to standardize measurements across varied heights, the femur was divided into 3 equal zones by drawing a line from the greater trochanter to the knee joint on the coronal MRI. These zones were further subdivided into 3 sections to create 6 total zones of study. For each zone of study that was produced on a coronal MRI of the femur, the correlating axial image was produced using scout mode technique. From the corresponding axial image, the femur was divided into quadrants. Consistent with manufacturer technique, femoral pin placement was replicated by drawing a line angled 45 degrees from the anterior to posterior reference in the anteromedial quadrant. In order to most accurately depict the risk that femoral pin placement poses, this line was extended beyond bicortical limits. The distance to identified neurovascular structures was then measured.

Of the 10 MRI’s reviewed, the mean age was 72.2. Laterality consisted of 6 right femurs and 4 left femurs. The popliteal artery and vein, as well as tibial and common peroneal nerves were within proximity in zone 1A. Proximally to the bifurcation, in Zones 1C – 2C, the femoral artery as well as sciatic nerve were in proximity to the proposed femoral pin path. Most proximally, at Zone 2C, the profunda femoris becomes an additionally present vascular structure. The closest neurovascular structure to the proposed femoral pin path differed according to Zone along the femur. In 4 out of 6 of the Zones, females had a statistically significant lesser distance to neurovascular structures than males.

Our proposed classification system for safe zones and trajectory of femoral pin placement in robotic total knee arthroplasty demonstrates that proximally the profunda femoris and femoral artery/vein are at risk of injury, while distally the common peroneal nerve and popliteal artery/vein are at risk. Caution should be exercised particularly if femoral pins are inserted with an angle less than 45 degrees, especially in females. In adopting this classification system, radiologists can provide increased clinical value by evaluating whether safe pin placement was achieved. In cases of post-operative complications, radiologists will be critical in helping determine whether the complication may be attributable to pin placement.