Botulinum toxin combined with static progressive stretching improves fibrous stiffness of knee joint in rats through TGF-β1/Smad pathway.

Joint stiffness and fibrosis are common complications that affect mobility and quality of life, necessitating effective therapeutic strategies to alleviate these issues. The study aimed to observe the therapeutic effect of static progressive stretching (SPS) combined with botulinum toxin type A (BTX-A) on knee joint stiffness in rats and its effect on the transforming growth factor beta 1 (TGF-β1)/small mother against decapentaplegic (Smad) pathway in the development of joint capsule fibrosis. Forty Sprague Dawley rats were randomly divided into the blank control group, model control group, SPS intervention group, BTX-A intervention group, and SPS combined with BTX-A intervention group. Except for the blank control group, the right knee joints of the other rats were surgically fixed with Kirschner wire internal immobilization in full flexion for four weeks to form joint flexion contracture and cause fibrotic stiffness of the joint. The therapeutic effect of each intervention was assessed by the range of motion (ROM) of the knee joint, joint stiffness, the number of total cells, and collagen deposition in the posterior joint capsule, as well as the protein level expressions of  TGF-β1, Smad2, Smad3, Smad4, p-Smad2/3, collagen I and III, and alpha smooth muscle actin (α-SMA) in the posterior joint capsule in the TGF-β1/Smad pathway. SPS combined with BTX-A was more effective in relieving joint fibrosis stiffness, improving the histopathological changes in the posterior joint capsule, and suppressing the high expression of target proteins and the overactivated TGF-β1/Smad pathway. The overactivated TGF-β1/Smad pathway was involved in the formation of knee joint fibrosis stiffness in rats. SPS combined with BTX-A was effective in relieving joint flexion contracture and fibrosis of the joint capsule. Moreover, the inhibition of the overactivated TGF-β1/Smad pathway may be the potential molecular mechanism for its therapeutic effect.