Coathup, Melanie Jean; (1999) Fixation of uncemented implants. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

My thesis postulates that bone ingrowth and direct bone apposition combined with implants engineered to produce interfacial strains lead to beneficial bone remodelling which may result in fixation of joints that will last for the patients life-time. The concept of extra-cortical plate fixation was investigated by assessing the bony response to plates of different design and surface coating. The study found that only one geometric design (holes) significantly increased bone ingrowth into the plate when compared with the control (p=0.01). A crystalline HA coating encouraged significantly greater interfacial contact when compared with a roughened titanium surface (p=0.01), a HA coating of lower crystallinity (p=0.004) and a solution precipitated HA coating (p=0.02). No significant differences were found when bone ingrowth into the plates were compared, except significantly more bone had grown into plates coated with a HA coating of lower crystallinity (p=0.036). Differences in bony reaction induced by the plates of different design were evident and therefore a combination of the correct design and surface coating are required for optimal bone attachment and ingrowth to extra-cortical plates. An experimental goat model was developed to investigate hydroxyapatite coated extra-cortical plate fixation in massive segmental bone tumour replacements. On retrieval, all of the plates were securely fixed by new bone. Bone apposition had occurred through a combination of periosteal bone production, invasion of bone through slots and bone growth over the ends of the plate. It was concluded that due to both mechanical and biological effects, extra-cortical plate fixation generated new bone growth that enhanced fixation and encouraged plate integration into cortical bone. The importance of the implant surface was demonstrated in a series of human autopsy retrieved hip implants. The proximal region of each implant was coated with either a plasma sprayed porous ingrowth surface (plain porous), a HA coated porous surface (porous HA) or a grit blasted surface. Significantly more bone ingrowth (p=0.012) and bone attachment (p<0.05) was measured to the porous HA surface when compared with the plain porous surface. There was no significant difference in bone attachment between the plain porous and grit blasted surfaces. A combination of a HA surface combined with extra-cortical plate fixation has been used to treat a number of bone tumour patients.

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