BONE PLATE FIXATION ITS RELATIONSHIP WITH IMPLANT INDUCED OSTEOPOROSIS

The use of internal fixation devices for fracture repair induces profo und changes in the affected bone. The factors implicated in the develo pment of implant induced osteoporosis have been extensively studied. T he processes following bone plate fixation which results in vascular a nd structural changes to the bone have not been accurately described. There are many inconsistencies in the design of experimental studies a nd in data interpretation which confound the issue. Implant induced os teoporosis appears to be a biphasic phenomenon following the applicati on of rigid internal fixation, with an early-onset osteonecrosis (8-12 weeks) elicited through cortical vascular insufficiency, followed by osteoporosis (24-36 weeks) induced by stress redistribution. The devel opment of implant induced osteoporosis appears to involve mechanical f actors (surgical trauma, screw placement, rigidity of the fixation dev ice), acting in conjunction with vascular insufficiencies related to t he bone-plate interface contact area and pressure distribution. Whatev er the pathogenesis, the end result is a thinning of the diaphyseal co rtices. Should implant removal be deemed necessary such osteoporosis i s a cause for concern in view of the bones predisposition to refractur e following plate removal. The degree of cortical osteoporosis observe d appears to be time-dependent following internal fixaton and as such the clinical outcomes, after implant removal, are also related to the timing of removal.