Achilles tendon healing in rats is improved by intermittent mechanical loading during the inflammatory phase

Tendons adapt to changes in mechanical loading, and numerous animal studiesshow that immobilization of a healing tendon is detrimental to the healingprocess. The present study addresses whether the effects of a few episodes ofmechanical loading are different during different phases of healing. Fifty femalerats underwent Achilles tendon transection, and their hind limbs were unloadedby tail suspension on the day after surgery. One group of 10 rats was taken downfrom suspension to walk on a treadmill for 30 minutes per day, on days 2-5 aftertransection. They were euthanized on day 8. Another group underwent similartreadmill running on days 8-11 and was euthanized on day 14. Completelyunloaded groups were euthanized on day 8 and 14. Tendon specimens were thenevaluated mechanically. The results showed that just 4 loading episodesincreased the strength of the healing tendon. This was evident irrespective of thetime-point when loading was applied (early or late). The positive effect on earlyhealing was unexpected, considering that the mechanical stimulation was appliedduring the inflammatory phase, when the calluses were small and fragile. Ahistological study of additional groups with early loading also showed someincreased bleeding in the loaded calluses. Our results indicate that a smallamount of early loading may improve the outcome of tendon healing. This couldbe of interest to clinical practice.
funding agencies|Swedish National Centre for Research in Sports||Swedish Research Council| VR 2009-6725 |Ostergotland County Council