Abstract

The new endoprosthesis system SHEP (Spongiosa Hip Endo-Prosthesis) developed by the author and manufactured by Howmedica has been in clinical use since October 1987. This system comprises a hollow-stem prosthesis with a microporous surface and a straight, collarless stem with circular and oval perforations in the anterior and posterior surfaces. The conical threaded acetabular component is doublewalled. In primary operations endogenous spongiosa is packed into the spaces in the acetabulum and the cavity of the stem, and in exchange procedures the spaces are packed with homologous spongiosa preserved under cold storage. The prosthetic components are implanted cement-free. The system is indicated in all forms of osteoarthritis of the hip. To date more than 360 SHEPs have been implanted by the author and at other clinics, 1/3 of which were exchange prostheses. The biomechanical properties of the prosthesis have undergone endurance tests and far exceed the statutory values. The SHEP system is made of Vitallium, the inlay is polyethylene, and the head is ceramic. Scintiscans initially show raised counting rate quotients compared with the healthy side. Video film reveals impressive bony regeneration and peg-shaped bony bridges between the inner cortical bone and the prosthesis. Microscopic examination shows lamellar bone, rich in osteocytes and osteoblasts. Microscopic investigation of samples from inside the prosthesis (after 5, 9 and 12 months) shows transformation of foreign spongiosa and substitution by endogenous spongiosa or spongy bone with lamellar stratification and good microvascularization.