December 2010

Good to go? Testing key after TKA

By Barbara Boughton

Recent published studies suggest that patient-reported outcomes after total knee arthroplasty (TKA) don’t actually reflect performance on functional tests. So, although patients may be reporting significant improvement in their ability to walk, climb stairs, and function overall, their Timed Up and Go Test results may actually tell a different story.

Why does this matter? One reason is that being able to accurately assess a patient’s ability to perform functional tasks is important in assessing his or her overall health outcomes after TKA. Another is that rehabilitation after TKA presents a “window of opportunity” to get patients with knee osteoarthritis into the habit of exercise—and knowing their actual strengths and limitations is crucial in prescribing an exercise program.

“Patients’ perceptions of what they can do versus what we find with performance-based tests don’t necessarily correspond,” says Ryan Mizner, PT, PhD, an assistant professor in the school of physical therapy and rehabilitation science at the University of Montana. “By using just patient self-reports, you really don’t get the entire picture of the patient’s ability to move and function.”

In a study of 100 patients e-published in The Journal of Arthroplasty in September, Mizner and fellow researchers found that outcomes measures such as the SF-36 and the Knee Outcomes Survey-Activities of Daily Living Scale did not correlate with patients’ performance on tests such as Timed Up and Go, stair climbing, and the six-minute walk test. In general, patients tended to overestimate their ability to function even one month postsurgery—when they were also likely to be experiencing the acute after-effects of their procedure. Even if they were unable to bear weight on the affected limb, and were using assistive devices to walk and climb stairs, many patients rated their function as improved.

“What knee replacement does really well is relieve patients’ pain. So patients are very satisfied afterward. If they can walk or sit down in a chair or go up stairs without pain or with relatively little exertion, they perceive that they’re doing very well,” Mizner said.

Patients also overestimated their ability to perform functional tasks as much as one year after surgery, the same study found.

Although self-reported assessments are relatively easy to perform, they’re also more likely than performance-based tests to be influenced by patients’ perceptions of reduced pain after surgery, researchers say.

“Once the pain is gone, that change is so profound that it trumps everything else,” said Lynn Snyder-Mackler, PT, ScD, alumni distinguished professor of physical therapy at the University of Delaware and a co-author of the Journal of Arthroplasty study.

She and Mizner agree that the best ways to assess patients’ ability to function is with a combination of self-reports and functional tests. Accurate assessments are especially important in the acute phase after surgery because it’s then that patients can be encouraged to work on their functional deficits through regular exercise.

“The idea is to figure out what’s really going on with these folks, and to encourage them in the short time after surgery when they’re in the healthcare system to make changes in their lives,” Snyder-Mackler said. “Most of the residual functional problems that persist after total knee replacement are things that can be fixed, and they need to be addressed.”

Unfortunately, many patients—after years of knee pain that kept them sedentary—are  not inclined to commit to the exercises that will continue to enhance their function even after their formal rehabilitation is over.

“It’s crucial to address physical impairments such as restricted range of motion and muscle strength, and to be aware of and preserve the health of the leg that did not undergo surgery after TKA. Take advantage of the opportunity provided by the resurfacing of the joint to help patients become stronger and more fit,” Mizner said. “I think we can achieve much more with total knee arthroplasty besides just great pain relief.”

Sponsored by an educational grant from Elite Seat

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