January 22, 2018
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Customized total knee implants may restore neutral coronal mechanical axis in patients

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Results published in the Journal of Knee Surgery showed customized total knee implants individually made with patient-specific cutting jigs accurately restored neutral coronal mechanical axis in most patients.

“My concern was ... whether CT-based cutting instruments were as accurate as they were purported to be,” Gary A. Levengood, MD, of Gwinnett Medical Center, told Healio.com/Orthopedics. “There were some studies out of Australia with MRI-based cutting instruments that showed that they were not as accurate as they were supposed to be. I had been doing a lot of computer navigation and so I decided, since there was already a study out there looking at MRI-based [cutting instruments], I would look at the CT-based cutting block[s] to see if they were accurate. What we found was that they showed great accuracy in recreating the coronal alignment.”

Using preoperative CT scans, Levengood and colleagues created patient-specific instruments and implants (ConforMIS Inc.) for 63 patients undergoing total knee arthroplasty. The investigators used a computer-assisted system (Aesculap) to determine mechanical alignment in all patients. They also used patient-specific instruments to make bone cuts, and recorded both bone cuts and final coronal mechanical alignment using a navigation system.

Results showed 53 patients experienced perfect neutral coronal mechanical alignment, while the remaining 10 patients had a postoperative alignment within 2°of neutral. Researchers found an average deformity of 5.57° preoperatively vs. 0.18° postoperatively, as well as a mean correction angle of 5.68°. The computer-assisted system revealed no postoperative extension deficits in any patient, according to results.

“We have done a lot with custom cutting blocks and the custom knee that it has changed the whole paradigm on total knee arthroplasty in the sense that now ... you actually have to do minimal soft-tissue balancing with this prosthesis because of the fact that we are cutting into a neutral alignment,” Levengood said. “We are restoring the patient’s normal kinematics and that is extremely important in not only performance, but longevity of the prosthesis.” – by Casey Tingle

Disclosure s : Levengood reports he receives teaching and consulting fees from ConforMIS Inc. Please see the full study for a list of all other authors’ relevant financial disclosures.