Navigating through ACL reconstruction

Technology may improve tunnel placement in this emerging field.

As navigation becomes more popular in total hip and knee procedures, researchers are beginning to adopt the technology in the performance of ACL reconstruction.

“Navigation has had encouraging results in its early applications for ACL surgery. It is giving the ability to understand where your selected tunnel placements are in space throughout the surgical process,” said Blaine L. Warkentine, MD, currently studying surgical navigation applications at Long Beach Memorial Center in California.

Navigation may help surgeons avoid the most common pitfalls of ACL reconstruction — such as tunnel misplacement. Different authors have reported misplacement rates without using navigation as high as 40%. Other studies cite incorrect tunnel placement as the major cause of revision in 73.5% of cases. “It is reported as the most common reason for failure in ACL reconstruction surgeries to date,” Warkentine said during his presentation at Orthopedics Today NY 2005 — a comprehensive CME course.

Navigation provides surgeons with three-dimensional, real-time images to guide tunnel placement. “It gives you the ability to mark key parameters during surgery that you can use throughout the surgical process to assist in the reconstruction,” he said. The technology also provides surgeons with improved anatomical views and allows them to assess and avoid graft impingement.

Selecting tunnel placement

In order to navigate, the surgeon must first rigidly place percutaneous reference arrays that the computer can track into both the femur and the tibia. The anatomy of the knee is then registered with the computer. This can either be done through landmark acquisition of critical surgical landmarks (known as image free) or by taking multiple fluoroscopic images of the involved extremity, Warkentine said. These landmarks and/or images allow the surgeon to virtually on the computer screen plan tunnel placement, perform real-time impingement analysis, and isometric calculations, and lastly track and record key kinematic parameters such as anterior tibial translation both before and after reconstruction. This affords for the first time the ability for the intraoperative quality control in the field of orthopedic surgery as opposed to a week later with postoperative radiography in clinic.

Additionally, visualization is likely the number one reason for tunnel misplacement and these images from the software help guide the placement of your drill guide to your preferred intraarticular location with confidence, as the systems have an accuracy of nearly 0.5° and 0.5 mm, Warkentine said.

Ultimately, this all adds up to a lot more information for the surgeon to sift through during surgery and in most hands requires a few extra minutes to perform, Warkentine explaind. But the data output from the computer is essentially limitless and will lead to a huge expansion in the number of research studies with quantified information to back up study designs.

A key issue remains currently in navigating for ACL reconstructions. That is, even if you can put the tunnel in the right place 100% of the time, “ ... do we necessarily know where that placement should be?” Warkentine asks. “There are a lot of studies out there that try and answer this question, and are currently used to attempt to help guide the surgeon in the right direction. Precise navigation has potential applications for double-bundle reconstructions and patient-specific tunnel placements. Future studies will explore both rotational or translatory laxity through this technology.”

For the short term, there may actually be more confusion than revelation from this new type of information and, as an early adopter, it will be important for the system to be adaptable to current treatment preferences and techniques, and involves the need for further documentation of its potential benefits to patients, Warkentine said.

Nonetheless widespread adoption will likely occur over the ensuing years as patients begin to demand some form of quality control for their surgical corrections. “When you’re talking about a 27-year-old athlete, quality control is of paramount importance, especially when you consider failure likely results in early arthritis of the knee,” Warkentine said.

Warkentine is working with Douglas W. Jackson, MD, chief medical editor of Orthopedics Today on using preoperative MRI to mark patient-specific remnant positions allowing perhaps a more customized tunnel placement for each patient. “Utimately, navigation has the potential to play an important role in the next generation of ACL treatment.”

For more information:
Warkentine BL. Surgical navigation for ACL and HTO. Presented at Orthopedics Today NY 2005 - A comprehensive CME course. Nov. 19-20, 2005. New York.