The Healing of Cartilage Injuries Under the Influence of Joint Immobilization and Repeated Hyaluronic Acid Injections:An Experimental Study

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Abstract
In an experimental animal model the influence of intraarticularly injected high-molecular hyaluronic acid on the healing of superficial and deep lesions of the articular cartilage in freely mobile and immobilized joints was investigated. In the right knee joint in 42 adult rabbits two intracartilaginous lesions were produced in one of the femoral condyles and an osteochondral lesion in the other. In half of the animals the injured knee joint was immobilized in plaster of Paris, while the other half were allowed to move the joint freely. Half of the injured joints in each group were then injected with high-molecular hyaluronic acid once a week for 8 weeks. After 2 months the knee joints were examined histologically, histochemically and microangio-graphically and the water content of the articular cartilage was determined. The intracartilaginous lesions remained unchanged in all knee joints. The wound margins of the osteochondral lesions showed better closure in the immobilized animals. As a rule the osteochondral lesion healed with fibrous connective tissue. In a few joints, however, hyaline cartilage, with production of chondroitin sulphate, developed during healing of the osteochondral lesion. In the vicinity of the joint surface this tissue was transformed into fibrocartilage. Immobilization of the joint invariably led to pannus formation. The hyaluronic acid injections appeared to have no effect, either positive or negative, on the healing of intracartilaginous and osteochondral joint lesions. In mobile joints, however, these injections prevented a reduction of the water content of the articular cartilage, which was regarded as favourable.