Accuracy of anterior cruciate ligament tunnel placement with an active robotic system: a cadaveric study

The objective of this study was to evaluate the accuracy of tunnel placement for ACL reconstruction performed with an active robotic system.

Cadaveric analysis.

A reference screw containing 4 fiducials was placed in the femur and tibia of 13 fresh-frozen cadaveric knees. A preoperative plan was developed using images from 3-dimensional computed tomography reconstructions of the knee. The active robotic system then drilled the tunnels. The location and direction of each planned tunnel in the femur and tibia were determined from the preoperative plan. To compare these parameters postoperatively, a mechanical digitizer and a tunnel plug were used. The deviation in location and direction between the planned and drilled tunnel was determined.

In preliminary trials, the tibial tunnel was located inaccurately because slippage of the drill bit occurred on the bone at the start of tunnel drilling. This was minimized by decreasing the feed rate of the robot by 75%. For the remaining 10 knees, deviations with respect to the preoperative plan were found of 2.0 +/- 1.2 mm and 1.1 degrees +/- 0.7 degrees for the intra- articular tibial tunnel location and direction, respectively. For the femur, the deviations were 1.3 +/- 0.9 mm for the tunnel location (intra-articular) and 1.0 degrees +/- 0.6 degrees for the tunnel direction.

The active robotic system is highly accurate for tunnel placement during ACL reconstruction, meaning that the robot drills the tunnels very close to the surgeon's plan. Comparison to a control group of surgeons could not be made because no preoperative plan is usually created in traditional surgery. However, accuracy values in this study were found to be below the values for precision of repeated tunnel placements reported in the literature.