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Modes of failure can predict outcomes after revision TKA

By Annie Hayashi

Evidence-based study on knee arthroplasty shows correlation

As the American population ages, the demand for total knee arthroplasty (TKA) continues to increase, and so does the rate of TKA revision. In fact, the TKA revision rate of 19.3 percent is the highest of all joint replacement revisions.

Retrospective studies have shown that specific failure modes affect the outcomes of revision TKA (RTKA), but until recently, no prospective studies have been conducted. Yesterday, Khaled J. Saleh, MD, MSc, FRCSC, FACS, reported on the results of the North American Knee Arthroplasty Revision Study, which examined factors that predict outcomes after RTKA.

“The results of this prospective study provide the first evidence-based information on caring for the knee revision population,” he said.

Instability, tibial bone lysis primary factors for failure

Patients who had experienced failure of primary TKA and were candidates for revision surgery were recruited for this prospective study.

Of 308 participants, 221 patients completed 2-year follow-up. The reasons for RTKA included instability (28.9 percent); tibial bone lysis (27.5 percent); polyethylene wear (24.5 percent); femoral bone lysis (22.5 percent); tibial loosening (22.5 percent); and infection (18 percent). More than one cause of failure was noted in almost two thirds (64.4 percent) of the patients.

“Overall, 82 percent of the pa­tients had aseptic failure, while 18 per­cent had septic failure,” said Dr. Saleh.

The investigators also divided the patients based on when the failure occurred. The “early group” had their implant less than two years; the “late group” had their implant for more than two years. Among the “early group,” one in four patients (25.4 percent) had infection as a cause for failure (P < 0.001). The infection rate in the “late group” was just 6.9 percent.

The mean time from the primary implant procedure to RTKA was 7.9 years (range: 6 months to 27 years); the median time to revision (7.15 years) was also consistent with other studies of RTKA that showed “an alarmingly high rate of revision within 5 years of the primary TKA,” he noted.

Improvement wanes at 1-year mark

Researchers also measured the impact of revision surgery on patients’ quality of life and function. At 6 months, all patients demonstrated considerable improvement. Between 6 months and 1 year, however, most patients realized only limited improvement, and very few experienced any improvement on these assessments at their 18- and 24-month follow-up visits.

This pattern, according to Dr. Saleh, “reflects what has previously been reported in the literature but adds the troubling component of the continued fall-off of functional improvement 12 months postsurgery.”

“Gains in functional ability were mostly achieved during the first year after RTKA as demonstrated by statistically significant slopes of both general health scores—as measured by the Short Form (SF)-36 Physical Component Score (PCS), SF-36 Mental Component Score (MCS), and Lower Extremity Activity Scale (LEAS)—and the knee-specific scores—as measured by the Western Ontario and McMaster University (WOMAC) Osteoarthritis Index.

“In the second year, the gains either leveled off or started to decline,” he noted.

Factors for worse outcomes

When the outcomes of revisions performed for infection were compared to those performed for aseptic causes, investigators found that patients who had an infection also had much lower (P < 0.001) Knee Society Score (KSS) Objective and Function, WOMAC Pain and Function, and LEAS scores at baseline. These patients continued to report poorer outcomes at 6 months and at follow-up visits. Infection was also a predictor of increased pain.

Patients with a higher number of comorbidities and patients with tibial bone lysis also had poorer outcomes than patients whose implants failed for other reasons.

Word of caution

“This early onset of deterioration at 12 months following surgery is of great concern and further emphasizes the need to closely monitor patients who undergo RTKA to understand their functional survivorship,” Dr. Saleh said.

Coauthors of “Failure mode as a predictor of outcomes in RTKA: A prospective multi-center study” are Wendy Novicoff, PhD; William Michael Mihalko, MD, PhD; Thomas E. Brown, MD; Quanjun Cui, MD; and Kevin James Mulhall, MD.

The authors report the following disclosures: Dr. Saleh—Aesculap/B. Braun, Stryker, OMNI, Kimberly Clark; Dr. Novicoff—Smith and Nephew, Aesculap, Stryker, and EKR Therapeutics; Dr. Brown—DePuy, a Johnson & Johnson Company, Acumed, LLC,

Smith & Nephew; Dr. Cui—Synthes, Smith & Nephew; Dr. Mulhall—Sisk Healthcare, Ireland; Dr. Mihalko—Aesculap/B. Braun, Johnson & Johnson, Stryker.

Annie Hayashi is the senior science writer for AAOS Now. She can be reached at hayashi@aaos.org

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