A Simplified Murine Model to Imitate Flexor Tendon Adhesion Formation without Suture

Abstract

Peritendinous adhesion (PA) around tendons are daunting challenges for hand surgeons. Tenotomy with various sutures are considered classical tendon repair models (TRM) of tendon adhesion as well as tendon healing. However, potential biomimetic therapies such as anti-adhesion barriers and artificial tendon sheaths to avoid recurrence of PA are sometimes tested in these models without considering tendon healing. Thus, our aim is to create a simplified model without sutures in this study by using three 6 mm longitudinal and parallel incisions called the longitudinal incision model (LCM) in the murine flexor tendon. We found that the adhesion score of LCM has no significant difference to that in TRM. The range of motion (ROM) reveals similar adhesion formation in both TRM and LCM groups. Moreover, mRNA expression levels of collagen I and III in LCM shows no significant difference to that in TRM. The breaking force and stiffness of LCM were significantly higher than that of TRM. Therefore, LCM can imitate flexor tendon adhesion formation without sutures compared to TRM, without significant side effects on biomechanics with an easy operation.

Keywords: biomechanics; collagen deposition; flexor tendon; tendon adhesion.

Figure A1

The processing of longitudinal incision model. T: tendon, ST: surround tissue. Yellow arrow shows the incision. (A–C) To make the LCM, the flexor digitorum longus (FDL) tendon in the right hind-paw was surgically exposed through a posterior midline incision. The FDL tendon was then cut along three 6 mm longitudinal plantar incisions. (A) is enlarged 4 times under the microscope. (B) is enlarged 8 times and (C) is enlarged 10 times, which are both the same figure. But (C) was marked with the incision (yellow arrow). (D) To create the TRM, the FDL tendon was transected and repaired using a Kessler suture in the right hind-paw. (D) is enlarged 8 times.

Figure A2

The histological evaluation standards for tendon adhesion. The histological scoring system of adhesions was scored in grades 0–10. The area was divided into 5 parts on both side of the tendon (yellow line). Every area with adhesion equals one score, and the cumulative score is the final result. For example, the score of the figure is 8. Scale bar, 200 μm.

Figure A3

The histological evaluation standards for tendon healing. (A) Score of cellularity. Score 0: marked; Score 1: moderated; Score 2: mild; Score 3: minimal. (B) Score of parallel fibers. Score 0: less than 25% of fibers oriented parallel to the longitudinal axis; Score 1: 25–50% of fibers oriented parallel to the longitudinal axis; Score 2: 50–75% of fibers oriented parallel to the longitudinal axis; Score 3: more than 75% of fibers oriented parallel to the longitudinal axis. (C) Score of fiber continuity. Score 0: less than 25% of fibers showing continuity; Score 1: 25–50% of fibers showing continuity; Score 2: 50–75% of fibers showing continuity; Score 3: more than 75% of fibers showing continuity. Scale bars, 200 μm.

Figure A4

Equipment for ROM. (A,B) The injured hind-limb was harvested and fixed in a custom apparatus where the tibia was rigidly gripped to prevent rotation.

Figure 1

The schematic diagram of the longitudinal incision model and classical tendon repair model. It includes anesthesia and exposure of the FDL tendon. Three 6 mm longitudinal plantar incisions were made on the LCM. Yellow arrow shows the incision. TRM consists of tenotomy and Kessler suture.

Figure 2

The evaluation of tendon adhesion and healing in the three groups. (A–C) The H&E staining showing space between the tendon and its surrounding tissue. (D) Tendon adhesion score. (E–G) Tendon healing scores including the cellularity score, parallel fiber score and fiber continuity score. n = 6 mice for all groups. Scale bars, 200 μm. Mean ± SD, * p < 0.05; ** p < 0.01; *** p < 0.001; **** p < 0.0001; ns, no significance.

Figure 3

The range of motion in the three groups. (A,B) The range of motion (ROM) and gliding coefficient. (C–E) The Schematic diagram of measuring ROM. (C–E) The representative measurement of ROM in the LCM, TRM and control group, respectively. Two different loadings (0 g/19 g) were respectively suspended on the proximal end of FDL statically (upper subfigures were 0 g and middle subfigures were 19 g). The difference of MTP joint angles between the two images (0 g/19 g) was the range of motion (ROM) as the lower subfigures showed; green line was the reference, red line and yellow line were MTP joint angles under two different loadings, respectively. The angle made by the red and yellow line was the ROM. The examples of the ROM in (C–E) were 44.1°, 46.4° and 57.7°. Mean ± SD, ** p < 0.01; *** p < 0.001; ns, no significance.

Figure 4

Relative mRNA expression of collagens related to tendons in the three groups. (A,B) Relative mRNA expression of collagen I and III. Mean ± SD, * p < 0.05; ** p < 0.01; ns, no significance.

Figure 5

Biomechanics of the three groups. (A–C) Representative force-displacement curve. Breaking force and stiffness were recorded by the testing system automatically. The diagrams were copied from the testing system by the Engauge Digitizer and Prism, software. Red lines show the slope of the linear region of the documented curve. (D) Breaking force. (E) Stiffness. Mean ± SD, *** p < 0.001; **** p < 0.0001; ns, no significance.