Objective  To investigate the effect and mechanism of static progressive stretching (SPS) in different durations on traumatic knee contracture in rats.

  Methods  Seventy male Wistar rats were randomly divided into three groups, including surgical modeling group (n=50), control group (CON, no surgery, no treatment, n=10) and trauma without immobilization group (TRA, no treatment, n=10). The knee contracture model was established, and 50 surgical modeling rats were randomly divided into five groups including static progressive stretching treatment for 20 minutes group (S20 min, n=10), treatment for 30 minutes group (S30 min, n=10), treatment for 40 minutes group (S40 min, n=10), untreatment group (UNT, no SPS, n=10) and modeling group (MOD, n=10, euthanized after immobilization for histological staining and Western blot). Individuals in the S20 min, S30 min, and S40 min groups were anesthetized and submitted to SPS. One treatment session took place every other day. A total of 8 sessions were given till the final treatment session on the day 16. On the day 0, 8, and 16 of intervention, the range of joint motion (ROM) and gait analysis were measured and compared. After the ROM measurements and gait analysis, the rats were euthanized on the day 16 and the samples were stained with HE and Masson methods. The changes of pathological organization were observed. Western blot was used to detect the expressions of transforming growth factor-β1 (TGF-β1) and interleukin-6 (IL-6).

  Results  ① ROM: the ROM of S30 min group recovered similar to that of the S20 min and S40 min groups after 8 days of treatment (P>0.05), and was the best among all the surgical modeling groups after 16 d of treatment (P<0.05). The ROM of S20 min, S30 min and S40 min groups significantly improved on the day 8 and day 16 comparing with that on day 0 (P<0.01). ② Gait analysis: the stands in the S30min group improved best on the day 8 and day 16 (P<0.05) , and better than that on day 0 (P<0.05). The stride length of the S30 min group progressed similar to that of the S40 min group on the day 8 (P>0.05), and there was no difference among three groups on the day 16 (P>0.05). The stride length of the S30 min group appeared to recover more quickly on the day 8 (P<0.05), and those of S20 min and UNT groups recovered significantly on the day 16 (P<0.05). In addition, the swings in the S30 min group improved best (P<0.05), and it appeared to recover better on the day 16 (P<0.05). There was no statistical difference in terms of the swing speed among the four surgical modeling groups on the day 8 (P>0.05). The swing speed of the S30min group increased most than those of the other three groups (P<0.05), and it was much better on the day 8 and day 16 comparing with that on the day 0 (P<0.05 ). ③ HE and Masson staining: the fibrosis and inflammation of the S30min group were significantly suppressed comparing to the other groups on the day 16. ④ Western blot: The protein expression levels of TGF-β1 and IL-6 were significantly lower than those in the other intervention groups including the S20 min, S40 min and UNT groups on the day 16 (P<0.05).

  Conclusion  Static progressive stretching treatment for 30 min could significantly improve the traumatic knee contracture in rats. The mechanism may be that the SPS decreased the expressions of TGF-β1 and IL-6, reduced the adhesion and inflammation of joint capsule. Therefore it relieved the pain and increased the joint mobility by reconstructing the structure of the capsule and suppressing the fibrotic changes.