Image guidance systems offer better tunnel placement in ACL reconstruction

Differences seen between computerized systems and standard approach are small but significant.

Computer-assisted image-guided techniques for ACL reconstruction can make tunnel placement more efficient, decreasing anterior translation and internal rotation compared with the standard transtibial technique. However, one group of investigators question whether the lessons learned from the image-guided systems may allow improved ACL reconstructions even without use of the system.

Todd C. Battaglia, MD, of department of orthopedic surgery, New England Baptist Hospital in Boston, and colleagues compared the two ACL reconstruction methods in terms of tunnel placement and knee kinematics. They found advantages to the computer-assisted image guidance (IG) systems in both areas.

"Obviously, it remains to be seen whether these small differences that we saw in our study in terms of translation and rotation are clinically relevant," he said. "We certainly know that the clinical results with the transtibial technique have been very good."

The study did not compare the financial or practical aspects of the two systems. Battaglia said the IG systems increased surgical time, morbidity and radiation exposure. "Ultimately, it is not known whether we will need such a technology if we can use the information that we get from studies here and apply that to our tunnel placement using anatomy we can already see through the arthroscopes."

The researchers used 10 pairs of cadaveric knees. One knee in each pair was randomly chosen to receive the transtibial method for ACL reconstruction; the other received the reconstruction with an IG system (BrainLab, Vector Vision). The investigators used the IG system on all knees to assess translational and rotational kinematics with the intact ACL, after resection and post reconstruction.

"In the transtibial group we used previously published tunnel guidelines by Morgan," Battaglia said. "The IG system accepts bony landmarks which are put into the computer, and gives you tunnel placements based on defaults in the system." On the tibia, the default tunnel position is 44% over from the medial tibia and 43% back from the anterior tibia. The femoral tunnel is based on Bernard's Quadrant System and is near the superior-most quadrant.

Following the reconstructions, they found that on the tibia, the transtibial group had the tunnels placed in the posterior footprint, whereas the IG knees were placed more anterior in the footprint. On the femur the transtibial tunnels were placed in the superior most aspect of the footprint and in many cases missed the footprint entirely. In the IG group, the tunnels were centrally placed in the footprint.

"Interestingly, we found that it was impossible to hit the computer-prompted tunnel position on the femoral side when going through the tibial tunnel," Battaglia said. "We had to use a low anteromedial portal to reach that target."

He said, "In terms of kinematics, as one might expect, we found the translation increased significantly after the ACL was cut, but then after reconstruction by the two different methods, only the image-guided technique restored translation back to baseline levels. In the transtibial technique, translation remained elevated from baseline, although it was significantly decreased from the transected ACL situation." He said the results were similar for rotation. "There were small differences, only a couple of degrees, but they were statistically significant." Rotational control was better restored after IG reconstruction vs. transtibial techniques.

Battaglia's comments were presented at the American Orthopaedic Society for Sports Medicine 2006 Annual Meeting.

For more information:
Battaglia TC. Tunnel placement and knee kinematics after standard versus computer-assisted ACL reconstruction. Presented at the American Orthopaedic Society for Sports Medicine 2006 Annual Meeting. June 29-July 2, 2006. Hershey, Pa.