Lifelong physical activity and knee osteoarthritis development in mice

AimTo examine the effect of lifelong physical activity on the development of knee osteoarthritis (OA). MethodsFifteen C57Bl/6J mice (8 male and 7 female) were individually caged with a running wheel, magnetic sensor and digital odometer, and 15 mice (7 male and 8 female) were individually housed without a running wheel. Each mouse was provided with standard chow and water ad libitum. Running wheel distance, duration and speed were recorded daily. A diagnostic ultrasound (SONOS 5500 Ultrasound and 15-6L ultrasound probe) was used to measure medial and lateral knee joint space in both hind limbs every month until the end of the mice's lifespans. ResultsRight medial (P=0.002), right lateral (P<0.0001), left medial (P=0.01), and left lateral (P=0.007) knee joint spaces were significantly larger from months 3 to 12 in the physically active C57Bl/6J mice. However, there was no significant difference between all knee joint spaces of the running and sedentary C57Bl/6J mice throughout the remainder of the lifespan. All hindlimb knee joint spaces significantly declined with aging (P<0.0001). ConclusionsDuring the first 12months of the lifespan, physical activity seemed to protect the joint from degeneration; however; after that there was no protective benefit. This may be due to the fact that C57Bl/6J mice are genetically known to develop OA at 9months of age. Physical activity may have no impact on this genetic predisposition. Further study in mice not genetically predisposed to develop OA is needed.