|Title: ||Bone ingrowth in total knee arthroplasty: the impact of HA-coatings and the relationship with mechanical stability|
|Authors: ||Labey, L. ×|
Van Campenhout, H.
Van der Sloten, J.
Van Audekercke, R.
Van der Perre, G.
Fabry, G. #
|Issue Date: ||1998 |
|Publisher: ||Pergamon Press|
|Series Title: ||Journal of Biomechanics vol:31 pages:26|
One of the prerequisites for a long lasting functionality of prostheses is the existence of a mechanically sound interface between the implant and bone. Bone ingrowth into porous surfaces is a way to achieve this in cementless prostheses. The amount of bone ingrowth seems to be determined by geometrical as well as material considerations. In order to evaluate the performance of an integrally cast woven mesh with and without a vacuum plasma sprayed hydroxyapatite (HA) coating, an animal study was carried out in our institution. Although this has been investigated previously, a functional implant has not yet been used for this purpose in an animal study.
The sheep knee joint was selected for our purpose. 40 adult Suffolk ewes of moderate weight received a total knee replacement. Three surface variants were investigated: the cast woven mesh (16 sheep), the cast woven mesh with HA coating (16 sheep) and a sintered beads surface (8 sheep). The animals were sacrificed at three, six, twelve and twenty-four months after implantation. Every three months, clinical performance of the knee joint was evaluated and a clinical score was assigned, based on parameters such as alignment, mobility, patellar tracking, stability and functionality during standing and running. At the same time röntgen stereophotogrammetric analysis (RSA) pictures were made. After sacrifice both hindlimbs were resected, the soft tissues were removed and the tibia was exposed. A non-destructive measure-ment of the load-induced displacements of the tibial plateau was then carried out. More details about this mechanical test can be found elsewhere . Further evaluation of implant performance was carried out by means of histological and histomorphometrical analysis of the soft tissues and the bone-implant interfaces and a wear analysis of the polyethylene inserts.
RESULTS AND DISCUSSION:
The clinical scores were almost constant throughout the whole study and the mean clinical score for all implant types was equal (7,5/10). The wear analysis showed that all implants were functionally loaded. The HA-coated implants migrated significantly less after two years than both other types (0,3 mm vs. 6 mm, p<0,05). This is probably due to the better interface quality. The load-induced displacements of the HA-coated implants were smaller for all but the three months group of sheep. Histomorphometry was the most powerful technique to differentiate between the three different types. The amount of direct bone contact on a light microscopic level was 1,6% for the sintered beads, 2,1% for the mesh and 39,6% for the HA-coated mesh. The difference was highly significant (p=3.10-5). There is a significant inverse correlation between the amount of bone ingrowth and load-induced displacements (R2=0,81, p<0,01).
We conclude from this study that HA-coatings enhance the performance of prostheses in terms of bone contact and ingrowth as well as the mechanical quality of the interface. The geo-metry of the mesh alone does not improve bone integration compared to a sintered beads surface.
|Publication status: ||published|
|KU Leuven publication type: ||IT|
|Appears in Collections:||Orthopaedics Section (-)|