Allocation of rats into groups.

In this study, a novel rat model of knee joint adhesion was developed, and its formation was analyzed quantitatively over time. Thirty-nine Wistar rats were randomly divided into intact control (n = 3) and experimental (n = 36) groups. The latter was equally divided into three groups according to the experimental intervention: fixed with deep bending of the knee joint (group I), fixed after incision of the capsule (group II), and fixed after exposure of the patellofemoral joint to artificial patellar subluxation (group III). All rats were subdivided according to their joint immobilization period (1, 2, or 4 weeks). Thereafter, the limited range of motion of the knee joint with (limited knee range of motion) and without (limited knee joint intrinsic range of motion) skin and muscles were measured. The lengths of adhesions of the anterior knee joint and posterior capsules were evaluated histologically. The limited intrinsic range of motion of the knee joint was found to be increased in groups II and III compared to that in group I 4 weeks after immobilization. Adhesions were confirmed within 1 week after immobilization in groups II and III. The length of the adhesions in group III was significantly longer than in other groups at 2 weeks and remained longer than in group I at 4 weeks. This model may contribute to the assessment of the adhesion process and development of new therapeutic avenues following trauma or surgical invasion.</div

Raw data of a limited range of motion of maximum knee extension after immobilization.

Raw data of a limited range of motion of maximum knee extension after immobilization.</p

Knee joint angle at the point in each evaluation period.

(a) Restriction of extension range of motion (ROM) involving the skin and muscles. A two-way ANOVA revealed significant effects by group (F[4, 31]: 56.18; p (b) Restriction of extension ROM excluding the skin and muscles. Two-way ANOVA revealed significant effects by group (F[4, 31]: 26.67; p p p p p <0.05 (vs. group II).</p

Length of knee adhesions and posterior capsule.

(a) Adhesion length. Two-way ANOVA revealed significant intergroup effects (F[4, 31]: 7.71; p = 0.0002). (b) Suprapatellar bursa adhesion length. Two-way ANOVA revealed no significant intergroup effects (F[4, 31]: 1.99; p = 0.12). (c) Patellofemoral joint adhesion length. Two-way ANOVA revealed no significant intergroup effect (F[4, 31]: 2.24; p = 0.09). (d) Distal length of patellar adhesion. Two-way ANOVA revealed significant intergroup effects (F[4, 31]: 4.31; p = 0.0069). Data are expressed as mean ± standard error (n = 4 in each group). †p p p p (e). Posterior capsule length after immobilization. Two-way ANOVA revealed significant intergroup effects (F[4, 31]: 61.66; p p p p p <0.05 (vs. group II).</p

Fig 3 -

a. Adhesion sites of the anterior knee joint. Hematoxylin and eosin (H&E), picrosirius red staining, and scanning electron microscopy (SEM) images of adhesion sites. Upper panels: In the control group (13-week-old), the images show a well-organized structure with an articular cavity. Lower panels: In the experimental groups (picrosirius red staining: 4 weeks group III, SEM: 1 week group III), the images show disorganized dense collagen fiber structure (arrowheads) between the patella and femur. Scale bar: H&E staining, 100 μm; picrosirius red staining, 100 μm; SEM, 10 μm. b. Changes in the histologic appearance of the adhesion of the knee joint with H&E staining. The arrowheads show adhesion sites. P, patella; F, femur. Scale bar: 1,000 μm.</p

Surgical procedures.

(a) Rat knee joint fixed with deep bending using Kirschner wire and resin; (b) fixed after incision of the inner joint capsule; (c) fixed after dislocation of the patella from the femoral pulley groove for 5 min. A line drawing of the surgical fixation method. (d) Insertion of K-wire into the femur (e) Insertion of K-wire into the tibia (f) Fixation using resin. (g). Assessment regions of the adhesion length of the anterior knee joint in the histological image of a standard sagittal section with hematoxylin and eosin staining. (A) The suprapatellar bursa. (B) The patellofemoral joint. (C) The distal part of the patella. P, patella; F, femur. Scale bar: 1000 μm. (h). Microphotograph of the sagittal section of the medial region of the rat knee joint. (D) Posterosuperior capsule length. (E) Posteroinferior capsule length. Hematoxylin and eosin staining. Scale bar: 1,000 μm.</p