A model of anterior cruciate ligament injury in cynomolgus monkeys developed via arthroscopic surgery

Abstract

The anterior cruciate ligament (ACL) is an important structure that maintains the stability of knee joints. Animal models of ACL injury are helpful to explore its underlying mechanisms, and strategies for prevention, treatment and rehabilitation. Therefore, the aim of the present study was to develop an efficient model of ACL injury in cynomolgus monkeys via arthroscopic techniques. In the present study, 18 cynomolgus monkeys were randomly divided into a model group (n=6), a sham operation group (n=6) and a blank control group (n=6). One-quarter of the ACL was removed under arthroscopy in the model group. In the sham operation group, only arthroscopic exploration was performed as a control. In the blank control group, monkeys were housed under the same conditions for the same length of time. Magnetic resonance imaging examination was performed pre- and post-operatively, as well as measurements of the circumference of the thigh and calf, and of the maximum flexion degree of the knee. Anterior drawer test, Lachman test and pivot-shift tests were also performed. The results revealed that the injured side of the knees in the model group became unstable, as determined from evaluation of the physical tests. In conclusion, based on these findings, the modeling method of ACL injury was effective, and may contribute to the associated research concerning ACL injury.

Keywords: animal model; anterior cruciate ligament; arthroscopic; cynomolgus monkeys; injury.

Figure 1.

Daily activity conditions of cynomolgus monkeys and the Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC) accreditation. (A) The monkeys were housed in several stable cages during periods of sleeping, feeding and rest. Additionally, all animals were moved out of the cages to another spacious activity room, equipped with resting shelves, a small rockery, wooden branches and a swing, for 6–8 h of free time per day. (B) Accreditation of the animal research facilities by the AAALAC.

Figure 2.

Development of animal models under arthroscopy. (A) Marking the incision for arthroscopic approaches before surgery; (B) after all preparations, the anterior medial and anterior lateral approaches of the knee joint were performed with 0.5-cm long incisions to explore the knee joint, via arthroscopy in the cavity of the knee; (C) exploration indicated that the articular cartilage, anterior cruciate ligament (ACL), posterior cruciate ligament and meniscus were intact, specifically, the normal and smooth ACL was observed under arthroscopy, the white arrow pointed to the normal ACL; (D) One-quarter of the ACL was transversely cut using a hook knife under a clear arthroscopic visual field, the white arrow pointed to the injured ACL.

Figure 3.

Observation of animal physiology. (A) Measurement of the circumference of the thigh. The thigh circumference of humans is usually measured at the suprapatellar 10–15 cm point. As the thigh segment of the cynomolgus monkeys is shorter than that of humans, thigh circumference was tested at 5 cm above the patella on the monkeys. (B) Measurement of the circumference of the calf. Calf circumference was measured at the widest position on the calf. (C) Measurement of the maximum flexion degree of the knee. In the state of anesthesia, the position of the knee joint was flexed maximally in the supine position, and the angle was measured. (D) Evaluation of the anterior drawer test. Under anesthesia, monkeys were fixed in a supine position, with the hips passively flexed to 45 degrees, the knee passively flexed to 90 degrees and the feet flat on the table. With the distal side of the leg fixed, the proximal side of the leg was pulled forward by the examiner using both hands, and the degree of movement of the tibia was observed. (E) Evaluation of the Lachman test. The distal side of the leg was held in one hand and the proximal side of the calf was held with the other under anesthesia in a supine position, so as to observe the movement by reverse force of both hands. (F) Evaluation of the pivot-shift test. In a supine position, monkeys were anesthetized before inspection with full extension of the knee joint. One hand of the examiner was placed on the outside of the knee, and the other held the foot to make the calf rotate. The knee was gradually flexed from 0 degrees, and the tibial plateau began to gradually move forward toward subluxation when the knee was removed from the ‘lock’ position. When the knee was flexed to 20 degrees, instability appeared as a positive result.

Figure 4.

Magnetic resonance imaging observation of the knee joints. (A) The normal ACL on T1W was continuous and uniform, and the tension was good. (B) Tension and continuity of the injured ACL on T1W were poor. ACL, anterior cruciate ligament; T1W, T1-weighted.