Prolonged immobilization compromises up-regulation of repair genes after tendon rupture in a rat model

It was hypothesized that mobilization vs immobilization after injury would promote tissue healing by regulating gene expression for molecules associated with repair. Cast immobilization vs free mobilization was studied after rat Achilles tendon rupture. Reverse transcriptase-polymerase chain reaction was performed at 8 and 17 days post-rupture to assess different growth factors [brain-derived neurotrophic factor (BDNF), basic fibroblast growth factor (bFGF), nerve growth factor (NGF) and insulin-like growth factor-1 (IGF-1)] and inflammatory mediators [cyclooxygenase 1 and 2 (COX 1 and COX 2), inducible nitric oxide synthase and hypoxia-inducible factor-1 alpha (HIF-1 alpha)] in the healing region. At 8 days post-injury, tendon mRNA levels were comparable in both groups. However, by day 17, the mRNA levels for BDNF, bFGF, COX 1 and HIF-1 alpha in the mobilized group had increased significantly. Corresponding mRNA levels in the immobilized group decreased during the same period. There were no significant differences in the expression of NGF, IGF-1 or COX 2 between the different groups, indicating that injury-associated expression of these molecules is not overtly influenced by loading. This study supports the notion that prolonged immobilization post-rupture hampers the healing process by compromising the up-regulation of repair gene expression in the healing tendon. It might be speculated that a shorter period of immobilization, i.e. 1 week, would not impair the healing process significantly. The findings support the current development of earlier and more active rehabilitation programs after tendon injuries.