Age has a minimal effect on knee kinematics: A cross-sectional 3D/2D image-registration study of kneeling

Kneeling is an activity of daily living which becomes difficult with knee pathology and increasing age. This study aimed to capture kneeling kinematics in six-degrees-of-freedom in healthy adults as a function of age.

67 healthy knee participants aged from 20 to 90 years were categorised into four 20-year age-groups. 3D knee kinematics were captured using 3D/2D image-registration of CT scan and fluoroscopy during kneeling. Kinematic variables of position, displacement and rate-of-change in six-degrees-of-freedom were compared between age-groups while controlling for University of California Los Angeles activity scale and the Assessment of Quality of Life physical score.

Over the entire kneeling cycle there were few differences between the age-groups. Results are reported as pairwise contrasts. At 110° flexion, 80+ knees were more varus than 20-39 and 40-69 (4.9° (95%CI: 0.6°, 9.1°) and 6.4° (2.1°, 10.7°), respectively). At 120° flexion, the 80+ age-group femur was 5.5 (0.0, 11.0) mm more anterior than 20-39. Between 120° to maximum flexion, 80+ knees rotated into valgus more than 20-39, 40-59 and 60-79 (5.5° (1.2°, 9.8°); 5.5° (1.1°, 9.8°); and 4.5° (0.9°, 7.5°), respectively).

This is the first study to report kneeling knee kinematics of ageing using 3D/2D image registration. We found that ageing does not change knee kinematics under 80 years, and there are minimal changes between 120° and maximum flexion between the younger and 80+ age-groups. Thus, difficulty kneeling should not be considered to be an inevitable consequence of ageing.