Issue: May 2006
May 01, 2006
9 min read

Knee surgeons report increased tunnel accuracy with navigated ACL reconstruction

One skeptic says the technology will fail to catch on without a standard for optimal tunnel placement.

Issue: May 2006
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Emerging research indicates that computer navigation for ACL reconstruction aids in tunnel placement and provides real-time data on stability. Yet, it remains unclear if these advances produce better results.

Accurate tunnel placement remains a significant obstacle in ACL reconstruction. Of the 175,000 procedures performed in the United States each year, 10% to 20% of patients will require revision. The main reason for revision: improper tunnel placement.


 Blaine L. Warkentine, MD [photo]
Blaine L. Warkentine

“Problems with tunnel positioning can cause problems with range of motion in the knee, stability in the knee, synovitis, inflammation, pain impingement and graft failure,” Jason L. Koh, MD, an orthopedist at Northwestern University Medical School in Chicago, said during an industry-sponsored presentation at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting.

Even in experienced hands, tunnel position remains an issue.

“How good are we at doing this?” Koh said. “I think that the answer is, we’re not really as good as we think we are or hope we are.”

He cited research presented by Christopher D. Harner, MD, at the European Society of Sports Traumatology, Knee Surgery and Arthroscopy Congress, which showed that 43% of his cases required tibial guide pin repositioning.

“What’s happening now is that we’re so concerned about getting impingement on the intercondylar notch from the two anterior tunnels that the error that an experienced ACL surgeon may make is [putting] the tunnel too posterior, which can cause additional problems,” Koh said.

Erring is easy

A study performed by F. Picard, MD, and Anthony M. DiGioia III, MD, found that the two experienced surgeons misplaced the tibial and femoral tunnels on 20 foam models.

“The femoral tunnel was off by an average of 4.2 mm from where they wanted it to be, and the tibial tunnel was off by an average of 4.9 mm of the intended location,” Koh said.

He also pointed to a cadaver study led by Dieter M. Kohn, MD, of Homburg/Saar, Germany, which revealed that surgeons drilled femoral tunnels in unintended locations 50% of the time. The same 24 surgeons who participated in the trial also incorrectly predicted tibial tunnel placement in 25% of cases.

Computer navigation can help surgeons with tunnel positioning by projecting results before drilling. “ACL navigation can give you precise positioning of your tunnel, calculate the isometry of the graft, provide a projection of the intercondylar notch onto the tibial plateau so that you can avoid impingement, and it delivers, essentially, the third dimension to otherwise monocular vision from arthroscopy,” Koh said.

Andrew D. Pearle performs a navigated reconstruction. He uses Praxim Medivision’s Surgetics Station.

Courtesy of Andrew D. Pearle

Navigated ACL surgery requires surgeons to attach reflective markers to the tibia, femur and a probe.

Courtesy of Jason L. Koh

Universal use

Researchers have found that surgeons improved tunnel positioning with navigation across surgical skill levels. Jürgen Eichhorn, MD, an orthopedist at the Orthopädische Gemeinschaftspraxis in Straubing, Germany, examined cadaveric reconstructions performed by five fellows with an “average knowledge of arthroscopic surgery,” he told Orthopedics Today. Eichhorn found little intrapersonal differences between navigated attempts, which he said illustrates improved accuracy with limited skill.

Eichhorn said that the technology could also aid inexperienced surgeons.

“The problem in Germany and the United States is that 70% of the ACLs are done by surgeons who perform fewer than 20 a year,” he said. “They need guidance because the main reason for revision surgery is tunnel placement. With this navigation system, you cannot miss the right tunnel.”

Eichhorn added that the navigation system is especially useful at helping “young and intermediate surgeons become much more precise.”

Like a speedometer to a driver, navigation can alert the expert surgeon to small, consistent errors.

“You drive all the time, but still look at the speedometer,” Koh told Orthopedics Today. “I think that most people can detect the difference between going 35 mph and 55 mph, but what about between 35 mph and 40 mph? Maybe not, and small differences are quite important.”

Koh compared his navigated and non-navigated tunnels and found a repeated tendency or bias.

“The tibial tunnel was consistently more posterior than I would have wanted,” he said. “That’s similar to what’s been seen with total knee replacement, where experienced surgeons tend to be very consistent. They might make consistent small errors in one direction.” He now makes his tunnels more anterior.

Navigated vs. non-navigated

Results from a recent randomized trial in France suggest that navigation increases surgical accuracy, but it may also provide reproducible outcomes.

Researchers from Grenoble University Hospital found less laxity and variability in International Knee Documentation Committee (IKDC) laxity scores for knees with navigated tunnel placement vs. non-navigated knees.

“The variability of laxity in the navigated group was significantly less than in the conventional group, with the standard deviation of the navigated group being smaller than that in the conventional group (P=.0003 at 150 N and P=.0005 at 200 N Telos),” the researchers wrote in their study.

The investigators studied 60 patients who underwent ACL reconstruction and were placed in navigated or conventional tunnel drilling groups. The researchers discovered that 97% of the navigated knees had less than 2 mm of laxity while 83% of the conventional group showed similar graft tension.

The experimental cohort also displayed a significantly higher ATB value (P=.03), which is defined as the distance between the projection of the Blumensaat line on the tibial plateau and the anterior edge of the tibial tunnel.

“In the conventional group, the mean ATB was —0.2 (range, —5 to +4), whereas it was 0.04 (range, 0 to 3) in the navigated patients,” the authors wrote. “There were no negative ATB values in the navigated group.”

In a preliminary study, Yasuyuki Ishibashi, MD, an associate professor from the Hirosaki University School of Medicine in Japan, found similar results comparing non-navigated and conventional double-bundle reconstruction.

“[Our] study shows that tunnel position is more precise and [there is] low variation in navigated double-bundle surgery compared to non-navigated surgery,” he told Orthopedics Today.

Navigation systems detail the isometry profile while alerting surgeons to impingement conflicts for planned tunnels.

Courtesy of Andrew D. Pearle

Stability testing

Navigation systems also provide surgeons with isometric data, real-time stability testing and rotational stability, a measurement unattainable by other measures. Andrew D. Pearle, MD, the clinical director of the Hospital for Special Surgery’s Computer-Assisted Surgery Center, discovered that navigated tests provided results as accurate as those of a 6°-of-freedom robot for detecting rotational and translational changes.

Stability exams allow surgeons to compare preop and immediate postop differences.

“[Without navigation], we sort of go at the end of the case and say, ‘Well this feels right,’” Koh said during his presentation. “Well, this feels fairly stable. But we have no information actually on the absolute numbers of anterior posterior translation and particularly not any information on rotational stability. There is no KT-1000 for rotational stability or pivot shift at this point in time.”

Learning curve

Most of the surgeons interviewed agreed that the learning curve for navigation and amount of additional operating time depends on the type of system selected. Pearle uses Praxim Medivision’s Surgetics Station.

“It’s certainly not a turnkey operation,” Pearle told Orthopedics Today. “It takes quite a bit of time. Really, you need to do it in a lab-type setting or a saw-bone-type setting, and then you need to do it clinically. The reality is that you can use the same workflow but, when you use the navigation, you have to be cognizant of where you’re placing the pins and where the cameras are so they don’t interfere with the line of sight of the rigid bodies. That is not something that’s intuitively obvious; you have to play around with it before you get facile with it.”

Koh uses the image-free OrthoPilot (B. Braun/Aesculap) and said surgeons can gain ease with the navigation after three cases.

“The difference between this and navigation for total knee is that we’re only navigating two pins as opposed to multiple cuts for a knee replacement,” he said. “So, it’s much faster than navigation for the knee replacement.” Registering landmarks and setting up the system can add five to 10 minutes.

Surgeons can expect longer preparation times with fluoroscopic systems, said Blaine L. Warkentine, MD, who is studying surgical navigation applications at Long Beach Memorial Center in California. He uses a system from BrainLab.

“In our experience with fluoro-based [systems], because of the operative set-up time, we’re spending about 15 to 20 extra minutes placing the pins into the bone and setting up the C-arm and registering the anatomy,” he said. “It’s a time commitment, but it’s well worth it in terms of having this data available.”


Even proponents of computer-assisted surgery acknowledge the potential pitfalls inherent in systems that depend on input supplied by users. If surgeons fail to match patient coordinates with entered computer points, registration errors occur.

“I think with any sort of system, it’s ‘garbage in, garbage out,’” Koh said. “If you choose points without thinking about it, the results that you’ll get may not match what you think you have.”

Similarly, mechanical errors result when markers attached to patients shift and alter computer calculations.

“It’s particularly problematic, because the computer gives you very, very precise data,” Pearle said. “It’s much more precise data than you’ve ever had before, and you tend to trust numbers, but those numbers can be off.”

Navigation provides additional visualization, but surgeons should be extra vigilant of components during double-bundle techniques

“If a surgeon uses the transtibial technique for femoral tunnel creation of the posterolateral bundle, direction of the tibial transmitter is important,” Ishibashi said. “It is relatively difficult for the navigation camera to catch both the tibial transmitter and tibial guide transmitter at the same time. The tibial guide transmitter should be placed more anterior.”

Improved results?

Despite increasing the amount of data available to surgeons, it remains unclear if computer navigation leads to better outcomes. The key to this puzzle: defining a standard tunnel placement.

“Until we know exactly where we want to put things, it’s going to be difficult for navigation to appeal to the masses,” Warkentine said. “It will probably [need] a year or so of more research to really define where these tunnels should be placed, whether isometry really makes a difference, whether these biomechanical parameters are really tracked and how they’re changed with this process that will help us define better tunnel placements for the standard ACL.”

Once researchers address these issues, navigated studies may help settle longstanding debates.

“I think the jury’s still out as to whether the whole double-bundle technique is superior or not, but with this technology, we can at least assess what results we’re getting when we do this type of technique,” Koh said.

Ishibashi has already begun to use navigation to weigh in on this controversy. In his recent research, Ishibashi and his colleagues used navigation to examine 32 double-bundle procedures performed with an endoscopic technique and fixed with hamstring tendon grafts. The researchers also assessed the individual functions of the anteromedial bundles (AMB) and posterolateral bundles (PLB).

They found that double-bundle techniques provided less anterior-posterior displacement than AMB or PLB fixation alone.

“Although the posterolateral bundle has an important role in the extension position, posterolateral bundle function significantly decreases in the flexion position,” the researchers wrote. “The anteromedial bundle has an important role in a flexed position, and the function is relatively constant from extension to flexion, compared to posterolateral bundle function. Thus, traditional single-bundle reconstruction, which reproduces the anteromedial bundle, is a reasonable procedure.

“However, double-bundle ACL reconstruction, which reproduces the posterolateral bundle and anteromedial bundle, resulted in improved knee stability and biomechanical advantages of the procedure in this study,” they added.

Kinematic information

New navigated devices may also provide long-term kinematic data.

“The ideal is if you could have implantable dynamic reference frames so that you could interrogate the knee yearly and get the same quantitative data that you got intraoperatively,” Pearle said. “Then, you have this longitudinal way to quantify the kinematics or behavior of the knee postoperatively. That would be a tremendous asset to really refine the surgical techniques.”

Today, ACL navigation remains in its infancy, but some researchers say that the technology could revolutionize the procedure.

“In the end, it makes more sense to be accurate,” Warkentine said. “We just need to know where this [tunnel] accuracy needs to be placed.

“There are a few more steps in the research in terms of getting the information available. The exciting part is this is the tool that will get us there, because we can start to close the loop.”

For more information:
  • Ishibashi Y, Tsuda E, Tazawa K, et al. Intraoperative evaluation of the anatomical double-bundle anterior cruciate ligament reconstruction with the OrthoPilot Navigation System. Orthopedics. 2005;28:1277.
  • Koh JL. Computer assisted navigation and anterior cruciate ligament reconstruction: Accuracy and outcomes. Orthopaedics 2005 Oct. 28 (10 suppl): s1283-7.
  • Kohn D, Beusche T, Caris J. Drill hole position in endoscopic anterior cruciate ligament reconstruction: Results on an advanced arthroscopy course. Knee Surg Sports Traumatol Arthrosc. 1998;6:13-S15 (suppl 1).
  • Picard F, DiGioia AM, Moody J, et al. Clinical paper: Accuracy in tunnel placement for ACL reconstruction. Comparison of traditional arthroscopic and computer-assisted navigation techniques. Comp Aided Surg. 2001;6:279-289.
  • Plaweski S, Cazal J, Rosell P, et al. Anterior cruciate ligament reconstruction using navigation: A comparative study on 60 patients. Am J Sports Med. 2006;34:542-552.