Most total knee arthroplasties (TKAs) for end-stage knee arthritis are successfully performed using standard instruments, with patients reporting significant pain relief and enhanced mobility. Newer patient-specific instrumentation (PSI) is designed to further improve TKA by enabling orthopaedic surgeons to customize surgery to a patient’s individual anatomy. The goal is a faster procedure that reduces the risk of implant malpositioning, increases alignment accuracy, and improves patient outcomes. According to a review article in the September 2013 issue of the Journal of the American Academy of Orthopaedic Surgeons (JAAOS), however, additional data are needed before widespread use of these instruments can be recommended.

“It’s important to analyze the costs and benefits before adopting any new technology,” said coauthor Paul F. Lachiewicz, MD, of the Durham Veterans Affairs Medical Center, Durham, N.C., and Duke University Medical Center. “We wanted to objectively evaluate the purported benefits of PSI. Does the data justify their use? We found that they do not.”

Dr. Lachiewicz admitted that because PSI for TKA is a fairly new technology, the literature on it is not very extensive. “The studies we reviewed, however, showed very little evidence of improved implant alignment and patient outcomes with the use of these instruments,” he said.

Preoperative computer navigation
PSI uses advanced imaging to generate one-time-use instruments specific to each patient. Several weeks prior to surgery, a computed tomography (CT) or magnetic resonance imaging (MRI) scan is taken of the patient’s leg. Using a manufacturer-specific protocol, the surgeon sends the scan and preliminary surgical preferences for overall alignment, femoral and tibial resection angles, and default component sizes to the implant manufacturer.

An engineer uses the data to identify specific anatomic landmarks and create a computer-generated customized surgical plan. Once the plan is approved by the surgeon, the manufacturer fabricates a corresponding set of disposable cutting blocks or pin guides designed to help the surgeon position and align the implant during surgery.

“Before performing a knee replacement, a surgeon will typically take a standard radiograph of the patient’s leg. With PSI, an additional CT or MRI scan is required. When these costs are added to the expense of making the instruments, TKA with PSI can run thousands of dollars more than TKA with conventional instruments,” Dr. Lachiewicz explained.

“PSI also increases the time to surgery; the time from surgeon approval of the plan to delivery of the instruments is typically 3 to 6 weeks,” he continued. “We found no data to justify the expense nor the time involved with using these instruments.”

The authors also noted the “possibility of alignment error or component size mismatch between the bone resections suggested by these instruments and that desired intraoperatively,” which would cause the surgeon to make changes during surgery. In addition, they pointed out that conventional techniques are still needed to perform tibial component rotation, implant fixation, and patella preparation and that PSI cannot be used to perform ligament balancing and releases in knees with fixed deformities.

Dr. Lachiewicz likens PSI to the computer-assisted TKA surgeries popular in the late 1990s, in which computers were used in the operating room to guide the surgeon in making cuts. “Computer-assisted TKA became very popular, but it’s not used anymore. That’s because when it was studied analytically it was found to be costly, time-intensive, and ineffective in improving results,” Dr. Lachiewicz explained. “PSI’s use of CT or MRI before surgery shifts computer navigation for bony landmark registration and implant positioning from the intraoperative to the preoperative setting.”

Additional data needed
The value of any medical technology depends on whether or not it improves clinical outcomes for patients. “The studies we reviewed showed that PSI for TKA had very little impact on improving the surgical procedure, and no studies have assessed whether the use of PSI results in improved implant survival, patient satisfaction, or function,” Dr. Lachiewicz said.

He concluded, “PSI may have a small and specific role in very complex knee replacements, but additional data are required before they can be justified for routine use. These instruments should continue to be studied on a research basis only to evaluate whether or not they provide any benefit to the patient.”

Dr. Lachiewicz’s coauthor is Robert A. Henderson, MD, MSc.

Disclosure information: Dr. Lachiewicz—Innomed; Cadence; Allergan; Center for Healthcare Education & Research; Gerson Lehrman Group; Global Guidepoint Advisors; GlaxoSmithKline; Zimmer; Slack Inc.; Journal of Arthroplasty; Journal of Surgical Orthopaedic Advances; Hip Society; Orthopaedic Surgery & Trauma Society. Dr. Henderson—no conflicts.

Maureen Leahy is assistant managing editor of AAOS Now. She can be reached at leahy@aaos.org

Bottom Line

• Patient-specific instrumentation (PSI) claims to reduce the risk of implant malpositioning, increase alignment accuracy, and improve patient outcomes.
• However, a literature review found little data to support these claims.
• Because additional preoperative imaging is required and instruments are custom-made, using PSI for TKA delays time to surgery and substantially increases costs.
• Although PSI may be useful in complex cases, additional research is necessary to justify routine use.