Osseo-mechanical induction of extra-cortical plates with reference to their surface properties and geometric designs

The purpose of this investigation was to determine which geometric and surf ace properties encouraged optimal ingrowth and bonding of bone to an extra- cortical plate. Forty-eight titanium extra-cortical plates were attached on to the left and right femora of adult rabbits. The plates were of six diffe rent designs and the osseoconductive effects of four surfaces were examined . A roughened titanium surface, a plasma sprayed HA coating of low crystall inity (57%) and a solution precipitated calcium phosphate coating were comp ared with a plasma sprayed crystalline hydroxyapatite coating (crystallinit y 85%). Thin sections were prepared by grinding and polishing. Bone formati on and the interface around the plates were investigated histologically and computer and morphometric analyses were used to quantify new bone formatio n, bone apposition onto the plate, bone porosity and the condition of the H A coating. The study found that a hydroxyapatite coating (with the exceptio n of the solution precipitated coating) had significantly greater interfaci al contact with bone when compared to a roughened titanium surface, and tha t significantly more bone attached to a crystalline HA coating compared wit h the HA coating of lower crystallinity although significantly more bone fo rmed in the vicinity of the lower crystalline HA coating. Differences in th e bony reaction induced by the various geometric designs were evident and t he optimal plate design requires either holes or slots along its length as this encouraged bone ingrowth into the plate. (C) 1999 Elsevier Science Ltd . All rights reserved.