Endurance Sports After Total Knee Replacement: A Biomechanical Investigation
Abstract & Commentary
Synopsis: Cycling and power walking appear to be acceptable and preferable to running and downhill walking in patients following total knee replacement.
Source: Kuster MS, et al. Endurance sports after total knee replacement: A biomechanical investigation. Med Sci Sports Exerc 2000;32:721-724.
The majority of investigations on the effect of physical activity on joint stresses following hip and knee arthroplasty have considered walking on level ground. Kuster and colleagues sought to determine the contact stress distribution and contact area of three different knee joint designs during four common recreational activities. The simulated recreational activities included cycling, power walking, hiking, and jogging. The total knee designs consisted of a flat, curved, and mobile bearing tibial inlay. For all designs, a medium-sized prosthesis was used. All designs were cemented into a metal block and mounted on a material testing system. Pressure-sensitive films were inserted between the femoral component and the inlay, scanned, and analyzed using an image analysis system to obtain total contact area and the area overloaded beyond the yield point of the polyethylene. The test positions simulated power walking (4 ´ BW at 20° simulated knee flexion), downhill walking (8 ´ BW at 40° flexion), jogging (9 ´ BW at 50° flexion), and cycling (1.2 ´ BW at 80° flexion).
Results demonstrated that during cycling, the area of stress levels above the yield point of polyethylene was less than 15 mm2 for each design. During power walking, the mobile design showed no overloaded area, whereas it was less than 50 mm2 for the flat and curved designs. During downhill walking and jogging, more than 140 mm2 was overloaded for each of the three designs.
COMMENT BY DAVID H. PERRIN, PhD, ATC
The benefits of physical activity are well known, and it behooves surgeons and therapists to recommend modifications so that patients undergoing arthroplasty of the hip or knee can continue to experience the benefits of regular exercise. Kuster et al surmise that it is important to distinguish between suitable activities after arthroplasty because of different implant geometries, and that many total knee replacements result in a mismatch between the femoral and tibial radius with high peak pressures on the polyethylene inlay. These high pressures could lead to increased wear and resultant destruction of the inlay. As such, they emphasize that both the load and knee flexion angle of the peak load should be considered when recommending physical activities. Kuster et al conclude that 40-70% of the overall contact area was stressed above the yield point during jogging and downhill walking, and that these activities may endanger the inlay of most total knee prostheses. Power walking produced overload areas three times smaller than jogging or downhill walking, and they thus recommend that power walking can be permitted. They further reported that the tibiofemoral load was small during cycling, and that cycling can be performed after total knee replacement, although patients should place the bicycle seat as high as possible. They recommend an optimal exercise protocol based on these findings that alternates between cycling and power walking following total knee replacement, because these activities load different parts of the tibial inlay and thus ensure a more even wear pattern.
The obvious limitation of this study was that the joint stresses during the physical activities of power walking, jogging, downhill walking, and cycling were based on a simulated biomechanical model. Nevertheless, the study reminds us of the importance of modifying and recommending activities that reduce the stress to joints following arthroplasty so that patients can experience the benefits of physical activity. Further research models should determine joint stresses during a variety of physical activities following arthroplasty and other surgical and bracing procedures for lower extremity degenerative joint conditions.
Following total knee replacement, the most desirable form of exercise with the most equal distribution of joint stress appears to be:
a. hiking that includes downhill walking.
b. a combination of cycling and power walking.
c. power walking.
d. jogging.
e. cycling.
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