Abstract

Total knee arthroplasty (TKA) is the most common management for end-stage knee osteoarthritis that does not respond to nonoperative management. TKA is also the most common elective surgical procedure performed in the United States. The University of Delaware recently completed a clinical trial of outcomes after unilateral TKA. At one year after TKA, persons after TKA continue to be weaker, and move more slowly, compared to persons without osteoarthritis.

The first goal of this project was to assess persons 2 and 3 years after unilateral TKA. Many individuals who undergo unilateral TKA often have bilateral osteoarthritis; therefore the purpose was to assess changes in the nonoperated limb 3 years after unilateral TKA. Analysis of individuals tested annually at 1, 2, and 3 years after TKA report greater pain in the nonoperated limb compared to the operated limb and compared to controls; the nonoperated limb weakens significantly from 1 to 2, and from 2 to 3 years after TKA, and greater knee pain is reported. However, tests of functional performance, such as a 6-minute walk test and a stair climbing test, are consistent with time, albeit slower compared to controls at all intervals. Hierachical regressions indicate that nonoperated knee pain has become the primary contributor to the variance in the results of the stair climbing test (45%) and the 6 minute walk (44%), at 3 years after unilateral TKA.

Given the shift of the nonoperated limb is weakening and becoming more painful over the 3 years since the index unilateral TKA, the next step is to investigate movement patterns—do persons with TKA have a pattern that over loads the nonoperated limb? Sit-to-stand, return-to-sit, and stair ascent and descent were investigated, as all of these tasks are more demanding than walking.

Sit-to-stand and return-to-sit analysis was done in persons 3 months (n=26) and 1 year (n=23) after unilateral TKA, and compared to age-, gender-, and size-matched controls (n=26) without a history of osteoarthritis. Persons 3 months after TKA stand up using greater hip flexion and larger hip extensor moments compared to controls; by 1 year, the extensor moments increase further in persons with TKA. This pattern transfers demand away from the knee extensors, to the hip extensors. This pattern, albeit different compared to controls, may act to spare the nonoperated knee. When it comes to the return-to-sit, a similar movement strategy was adopted; using greater hip flexion with larger hip extensor moments. Persons with TKA sit down using higher muscle co-contractions around the knees, particularly 3 months after TKA. The knee flexors aid the extensors to control the descent, likely because the knee extensors are not strong enough to eccentrically control descent.

Stair ascent and descent are more demanding than getting in and out of a chair. Persons 1 year after TKA (n=15) were weaker compared to controls (n=15), and during stair ascent, are slower. Persons 1 year after TKA ascend stairs with lower moments at the knee and ankle, and higher muscle co-contractions at the knee, when compared to controls. The difference found in the movement pattern during ascent is that persons with TKA place their foot flat on the step, which provides more stability for the prolong stance times found. They then lift their leg to the next step, rather than pushing off with their plantarflexors. During descent, the eccentric control required appears to be taken up at the hip, as persons with TKA have altered moments at the hip, but no differences at the knee between limbs or compared to controls. Few differences when compared to controls were likely affected by the highly functioning persons with TKA that participated in this study—the ability to ascend and descend stairs without the use of a railing is uncommon in this population.

Overall, persons with TKA demonstrate altered movement patterns during STS, RTS, and stair ascent and descent. These patterns are different, but it is not clear of their impact: it is possible altered patterns will act to spare the contralateral knee, which is at a high risk of having osteoarthritis; it is also possible that the contralateral knee is still at risk.