Abstract: BACKGROUND: Internal tension-reduction technique is to reconstruct the anterior cruciate ligament through high-strength suture system combined with tendon. It can effectively reduce graft relaxation and frets by sharing the internal load of the knee joint, and has achieved good biomechanical results and clinical efficacy. However, whether it can reduce cartilage degeneration after anterior cruciate ligament reconstruction through stress sharing reduction has not been studied.
OBJECTIVE: To investigate the effect of internal tension-reduction technique on articular cartilage degeneration in southern Yunnan small-ear pigs undergoing anterior cruciate ligament reconstruction.
METHODS: Ten adult female Yunnan small-ear pigs were selected, and the ipsilateral knee Achilles tendon was taken from the left knee joint for anterior cruciate ligament reconstruction (normal group, n=10), and the ipsilateral knee Achilles tendon from the right knee joint combined with internal tension-reduction and augmentation system for anterior cruciate ligament reconstruction (tension-reduction group, n=10). One year after surgery, the experimental pigs were sacrificed, and the left and right knee cartilage was taken for hematoxylin-eosin staining, Safranin O-fast green staining, Osteoarthritis Research Society International scoring, and immunohistochemistry staining of type II collagen, interleukin-1β, and tumor necrosis factor-alpha in the cartilage.
RESULTS AND CONCLUSION: Hematoxylin-eosin staining showed that in the tension-reduction group, there were mild pathologic changes of osteoarthritis, with a low number of empty bone lacunae and no obvious pathological changes such as fibrosis or cell layer breakage; in the normal group, more severe cartilage damage, with an increased number of empty bone lacunae, loss of chondrocytes near the bone and even the formation of fissures. Safranin O-fast green staining indicated that the tension-reduction group had normal cartilage tissue thickness, flat cartilage surface, a neat cell arrangement in a polar pattern, and no swelling or apoptosis, while in the normal group, the thickness of cartilage tissue was obviously thinner, the cell arrangement was disordered with no polarity, the number of cells was reduced, obvious cartilage fractures and cartilage vacuoles formed, and the absence of cells near the central bone was obvious. The Osteoarthritis Research Society International score was significantly lower in the tension-reduction group than in the normal group (P < 0.05).  Immunohistochemical findings showed that the protein expression of type II collagen in cartilage tissue of the tension-reducing group was higher than that of the normal group (P < 0.05), and the protein expression of interleukin 1β and tumor necrosis factor ɑ in cartilage tissue was lower than that of normal group (P < 0.05). To conclude, internal tension-reduction technique can delay the degeneration of articular cartilage in Yunnan small-eared pigs following anterior cruciate ligament reconstruction.

Key words: anterior cruciate ligament, anterior cruciate ligament reconstruction, animal model, osteoarthritis, internal reduction technique, articular cartilage