KUSTER M, S., E. SPALINGER, B. A. BLANKSBY, and A. GÄCHTER. Endurance sports after total knee replacement: a biomechanical investigation. Med. Sci. Sports Exerc., Vol. 32, No. 4, pp. 721–724, 2000.
Purpose: No biomechanical evaluation of total knee designs exists for loads occurring during sports activities. It was the purpose of the present study to evaluate the contact stress distribution and contact area of different knee joint designs for loads that occur during four common recreational endurance activities.
Methods: Three different total knee designs were evaluated for loads occurring during cycling (1.2 body weight (BW) at 80° of knee flexion), power walking (4 BW at 20°), hiking (8 BW at 40°), and jogging (9 BW at 50°) using Fuji pressure-sensitive film. The designs consisted of a flat tibial inlay, a curved inlay, and an inlay with mobile bearings. Five measurements were conducted for each load. The pressure sensitive films were scanned and analyzed using an image analysis program.
Results: During cycling, the area with stress levels above the yield point of polyethylene (overloaded area) was below 15 mm2 for each design. During power walking, the mobile bearing design showed no overloaded area, whereas it was below 50 mm2 for the flat and curved design. During downhill walking and jogging, more than 140 mm2 were overloaded for each design.
Conclusions: It was concluded that patients after total knee replacement should alternate activities such as power walking and cycling. For mountain hiking, patients are advised to avoid descents or at least use ski poles. Jogging or sports involving running should be discouraged after total knee replacement.
Regular exercise has been shown to reduce all-cause mortality, anxiety, and depression, and improve cardiovascular health (3,19). Other beneficial effects of physical fitness are weight loss, increased bone density, and improved muscle coordination. The American College of Sports Medicine recommends endurance exercise such as jogging, cycling, swimming, power walking, or hiking for 20–60 min, 3–5 times a week, in order to develop and maintain cardiorespiratory and muscular fitness (1). There are few studies which address sports participation after total hip replacement (11,13,15,18,23,25) or total knee replacement (16,18) despite the increasing numbers of total joint replacements performed. Furthermore, most biomechanical evaluations of total knee replacements have considered only level walking with loads of 3–4 body weight (BW) (4–6,9,21,24,26).
Mountain hiking involves ascending and descending steep trails. Walking uphill has been shown to produce tibiofemoral compressive forces of 4–5 BW (17). However, during downhill walking tibiofemoral loads as high as 8 BW have been recorded at knee flexion angles of 40° (14).
During slow jogging (9.7 km·h (1), an extension moment of 2.9 Nm·kg−1 BW was found at 50° of knee flexion (27). A similar value of 2.7 Nm·kg−1 BW at 40° was recorded for downhill walking (14). Hence, tibiofemoral compressive loads of 8–9 BW at 50° of knee flexion can be assumed during slow jogging.
It has been reported that walking speeds of 6–7 km·h−1 are necessary to obtain and maintain aerobic fitness (26). Tibiofemoral loads as high as 4 BW at 20° of knee flexion at a speed of 5.3 km·h (1 (14) or 7.2 km·h−1 (20) have been recorded.
Extensive investigations of cycling have demonstrated tibiofemoral compressive loads of 1.2 BW at 80–90° of knee flexion while subjects pedaled at 60 cycles·min−1 and a 120-W load (12).
Contact area and stress evaluations of total knee replacements for loads that occur during these sport activities are not available in the current literature. Therefore, physicians are forced to make recommendations based on subjective opinion rather than scientific evidence (18). This study sought to evaluate the contact stress distribution and contact area of different knee joint designs for loads which occur during four common recreational activities. The purpose was to enable objective postoperative recommendations regarding sport participation after total knee replacement.