Using tritiated glycine (glycine 3H) as an indicator of amino acid incorporation in protein synthesis in cartilage matrices, Mankin and Conger injected hydrocortisone acetate into rabbit knees. Their data showed a rapid and profound decrease in glycine incorporation that appeared to depend on dosages. Maximum decline was seen six hours after the injection. 28 They did a similar experiment using glycine 14C as the radiotracer, which showed a definite decrease in the rate of protein synthesis within two hours of the injection. They noted that the rate of the inhibitory effect of intraarticular hydrocortisone on cartilage protein synthesis was about twice that of the observed rate for corticosteroids given by intramuscular route. 29 One year later, researchers injected hydrocortisone into normal rabbit knees and produced thinning of the cartilage, and the development of fissures and fibrillations in the articular cartilage. They also found multiple small white deposits within the substance of the articular cartilage, which were found to represent cystic areas of degeneration within the middle zone of the cartilage matrix. These effects were most marked in the animals which had the greatest number of injections. 30 Deleterious effects of cortisone were reported by some researchers who noted that the drug inhibited the synthesis and deposition of chondroitin sulfate in cartilage. 31-33
Although epidural steroid injections (also called epidural corticosteroid injections) may be helpful to confirm a diagnosis, they should be used primarily after a specific presumptive diagnosis has been established. Also, injections should not be used in isolation, but rather in conjunction with a program stressing muscle flexibility, strengthening, and functional restoration.
Epidural injections and intradiscal injections have been used in the treatment of non-radicular degenerative disc disease with limited success. Proper follow-up after injections to assess the patient's treatment response and ability to progress in the rehabilitation program is essential. A limited number of injections can be tried to reduce pain, but careful monitoring of the response is required prior to a second or third injection.