The significance of implant shape in experimental testing of biological materials: Disc vs. Rod

Adult albino rabbits were implanted with 304 stainless steel discs and cylinders (rods) in the following sites: beneath periosteum of the anterior calvarium, under the masseter muscle of the left mandibular ramus and in the body of the sacrospinalis muscle. (1) The tissue reaction around the disc implants was compared with that observed around the cylinder implants through the study of histological sections. (2) The degree of reactions observed at the various sites was contrasted with that seen at the other sites. In all cases the muscle implants showed the greatest reaction. Discs showed many micro areas of tissue reaction randomly around their periphery. In contrast all the rod shaped implants in muscle showed a greater reaction towards the ends than in the mid portion of the shaft (clubbing) but rods implanted at other sites did not show this phenomenon. The results show that much of the histological tissue reaction seen around muscle implants is really caused by mechanical trauma which must be differentiated from a non-compatibility reaction. It is important to choose a test site where mechanical trauma will be minimal (submasseteric site) and use an implant shape (discs) which will not produce clubbing.