A rat model of arthrofibrosis developed after anterior cruciate ligament reconstruction without rigid joint immobilization

<b>Purpose</b>: Complications including arthrofibrosis have been reported after anterior cruciate ligament reconstruction (ACLR) even under accelerated rehabilitation. To overcome this, we developed an animal model of ACLR-induced arthrofibrosis without immobilization. <b>Materials and Methods</b>: Thirteen male Wistar rats were divided into ACL transection (ACLT) and ACLR groups. Surgery was performed in the right knees and untreated left knees were used as controls. After surgery, rats could move freely without joint immobilization. <b>Results</b>: One week after surgery, flexion contracture represented by passive ROM reduction was 49 ± 5° and 21 ± 6° in ACLR and ACLT groups, respectively. Thereafter, flexion contractures were gradually reduced to 21 ± 8° and 12 ± 6° after 12 weeks, respectively. Fibrosis, which is characterized by significant upregulation of fibrosis-related genes, thickening, and adhesion in the posterior joint capsule, was observed in the ACLR group after 12 weeks of surgery. Nociceptive behavior and joint swelling were more apparent in the ACLR group than in the ACLT group, especially after 1 week of surgery. <b>Discussions</b>: We developed a rat model of ACLR-induced joint contracture due to arthrofibrosis without rigid immobilization. Joint contracture was also observed in the ACLT group, but to a considerably milder degree than in the ACLR group. Thus, signs of inflammation as a result of reconstruction surgery, rather than ACL transection, play an important role in the formation of joint contracture after ACLR. Our animal model is suited to examine the mechanisms and efficacy of therapeutic strategies for arthrofibrosis following ACLR treated without rigid joint immobilization.

**研究目的**：即便采用加速康复方案，前交叉韧带重建术（anterior cruciate ligament reconstruction, ACLR）后仍可出现包括关节纤维化（arthrofibrosis）在内的多种并发症。为解决这一问题，本研究构建了无需制动的前交叉韧带重建术后关节纤维化动物模型。
**材料与方法**：将13只雄性Wistar大鼠分为前交叉韧带切断术（ACL transection, ACLT）组与ACLR组。以右侧膝关节作为手术侧，左侧膝关节不予处理作为对照。术后大鼠可自由活动，无需进行关节制动。
**研究结果**：术后1周，ACLR组与ACLT组以被动活动度（passive ROM）降低为表征的屈曲挛缩分别为49±5°与21±6°；至术后12周时，两组屈曲挛缩分别逐渐降至21±8°与12±6°。术后12周，ACLR组可见以纤维化相关基因显著上调、后方关节囊增厚及粘连为特征的纤维化病变。ACLR组的痛觉行为与关节肿胀表现较ACLT组更为显著，尤以术后1周时为甚。
**讨论**：本研究构建了无需刚性制动的前交叉韧带重建术后关节纤维化所致关节挛缩的大鼠模型。ACLT组亦可观察到关节挛缩，但程度显著轻于ACLR组。由此可见，前交叉韧带重建术引发的炎症反应而非单纯的前交叉韧带切断，在前交叉韧带重建术后关节挛缩的形成中发挥关键作用。本动物模型适用于探究无需刚性关节制动的前交叉韧带重建术后关节纤维化的发病机制与治疗策略的有效性。