Intra-articular hyaluronic acid following knee immobilisation for 6 weeks in rabbits

Thirty-two mature female New Zealand White rabbits were immobilised in an aluminium splint on one knee, using the contralateral non-treated knee as control. After 6 weeks the splints were removed and the rabbits allowed unrestricted movement. On a random basis, 16 rabbits were given an intra-articular injection of 5 mg in 0.5 ml of hyaluronic acid (HA) in the knee of the immobilised hindlimb at weekly intervals for 6 weeks, starting 1 week after the joint had been remobilised, for a total of six injections. In the other 16 rabbits no further intervention was conducted. At the end of the experiment the rabbits were killed, the area of degenerated joint surface of the distal femur, and water and proteoglycan content were measured, and the articular cartilage stained with haematoxylin and eosin and safranin O. Remobilisation without HA administration resulted in a significantly larger degenerated joint surface area. By the end of the experiment both remobilisation and remobilisation and intra-articular HA injections had produced a greater but non-significant water cartilage content compared to the control side. The average cartilage glycosaminoglycan content of the remobilisation and intra-articular HA injection group was significantly greater than in the remobilisation group. In conclusion, in the rabbits with one knee immobilised for 6 weeks, 6 weeks of remobilisation alone are not sufficient to recover from the moderate articular surface changes produced, and the intra-articular administration of HA may produce a morphologically and biochemically more normal cartilage. More extensive animal and human studies should be performed before the routine use of intra-articular administration of HA following musculoskeletal injuries that required immobilisation can be recommended.