Mechanical characteristics of impacted morsellised bone grafts used in revision of total hip arthroplasty

The use of impacted, morsellised bone grafts has I become popular in revisi on total hip arthroplasty (THA), The initial stability of the reconstructio n and the effectiveness of any subsequent pr(,cess of revitalisation and in corporation will depend on the mechanical integrity of the graft. Our aim i n this study was to document the time-dependent mechanical properties of th e morsellised graft. This information is useful in clinical application of the graft, in studies of migration of the implant and, in the design of the joint. We used 16 specimens of impacted, morsellised cancellous bone from the ster num of goats to assess the mechanical properties by confined compression cr eep tests, Consideration of the graft material as a porous, permeable solid , filled with fluid, allowed determination of the compressive modulus of th e matrix, and its permeability to fluid flow. In all specimens the compression tests showed large, irreversible deformati ons, caused by how-independent creep behaviour as a result of rolling and s liding of the bone chips. The mean permeability was 8.82 *10(-12) m(4)/Ns ( sD 43%), and the compressive modulus was 38.7 MPa (sD 34%). No correlation was found between the apparent density and the permeability or between the apparent density and the compressive modulus. The irreversible deformations in the graft could be captured by a creep law for which the parameters wer e quantified. We conclude that ire clinical use the graft is bound to be subject to perma nent deformation after operation, The permeability of the material is relat ively high compared with, for example, human cartilage, The confined compre ssion modulus is relatively low compared wills cancellous bone of the same apparent density, Designs of prostheses used in revision surgery must accom modate the viscoelastic and permanent deformations in the graft without cau sing loosening at the interface.