Aim: Cycling is a common activity after TKA and it has been shown that up to 50 % of the TKA patients are riding a bike and 25 % think that cycling has an important place in their life. The specific contact mechanics of tibiofemoral joint is well known during walking, however, there is little data during cycling for TKA patients. The purpose of this study was to determine the tibiofemoral contact mechanics during cycling for TKA patients.
Methods: We recruited 10 patients implanted with a mobile bearing and 10 patients with a fixed bearing posterior stabilized prosthesis. An age-matched, asymptomatic control group consisted of 10 subjects. The patients were physically examined, and WOMAC index and knee society score were taken. Motion analysis was performed using a retroreflective marker based technique called “PCT”. Forces and moments during cycling were recorded with load cells at the crank shafts of the bike. Motion and load data were synchronized.
Results: Resultant pedal forces showed no significant differences between study groups but the generated impulse was higher in the mobile bearing group. Patients with contra-lateral osteoarthritis showed higher forces and impulse at the operated leg. The motion analysis showed the following mean values ±SD for TKA patients/Normals: maximum flexion angle 132.5° ±16.0°/131.5° ±18.3°, minimum flexion angle 41.4° ±12.0°/40.3° ±15.7°, range of rotation in transversal plane 12.6° ±4.7°/9.9° ±3.6° and range of anterior-posterior translation 5.3 mm ±5.1 mm/2.7 mm ±0.4 mm. There were no significant differences between study groups.
Discussion: In this study, force and impulse of TKA patients with contemporary prostheses were comparable to healthy subjects indicating functional restoration of the joint. Contralateral osteoarthritis may cause higher forces at the operated leg and thus, relatively higher stresses at the artificial articulation.
As expected, the generated forces at the bike pedal were low (20–25% body-weight) calling for little muscle activity and low compressive joint forces. However, with a mean maximum flexion angle of 131.5°, the observed motion ranges were higher than expected. Prostheses not designed for high flexion activities could lose tibio-femoral contact during cycling with detrimental effects on wear. Still, the measured range of rotation in the transverse plane indicates that despite its posterior-stabilized design rotation is taking place with approximately the same amount as it occurs in normal subjects. This may have detrimental effects on the post at the tibial plateau and could explain the previously observed rotational damage patterns on retrieved posterior stabilized TKA specimens.
Data are suggesting that leisure activities should be considered to determine the appropriate TKA design. This study will provide useful data for future design and wear testing scenarios.
