To examine the effect of lifelong physical activity on the development of knee osteoarthritis (OA).
Fifteen 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.
Right 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).
During the first 12 months 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 9 months of age. Physical activity may have no impact on this genetic predisposition. Further study in mice not genetically predisposed to develop OA is needed.