CHAPTER 5 R eplacing Organs with Permanent Prostheses 5.1 Defining the Clinical Problem 5.2 Anatomica l Considerations 5.3 Biomechanical Considerations 5.4 Functional Requirements 5.5 Goodness of Fit 5.6 Fixation 5.1 ABSORBABLE VERSUS PERMANENT DEVICES/IMPLANTS Absorbable Goal Regeneration Function Template for regeneration. Tempo rary replacement of key function(s) until regeneration occurs Materials "Absorbable, resorbable, biodegradable" polymers (synthetic or natural) and certain calcium compounds Incorporation of "Tissue engineering" Cells Permanent Replacement of Function: Temporary or permanent ("prosthesis" - "artificial organ") Replicate/approximate key function(s) of the organ Metals, nondegradable polymers, and ceramics Hybrid artificial organs Requirements Potential for tissue regeneration: Benefit/risk ration regenerate organelles for Use 1) ability of cells to divide or 2) Integration into the organ system Limitations Limitations in regeneration 1) size of defect, 2) number of tissues involved, 3) controlling mechanical and chemical environment during regeneration. Implications in Incomplete regeneration of F alling S h ort of reparative tissue Goal (accelerated degeneration) Adverse Effects of P remature degradation the Body on the Implant (c hemical and m echanical e nvironment) Adverse Effects Local response: of the Implant o n degradation products cause the Body cell toxicity or inflammation, ("Biocompatibility") or alteration in strain distribution Systemic response: 1) m igra tion of material to distant organs with effects, 2) immune response Complications Bacterial infection (lower incidence than with permanent devices) Imperfect adaptation to changing demands of human activity. Inability to adequately duplicate function (need for revision with additional loss of tissue) Fracture, wear, and corrosion (polymer degradation) S ame Infection: bacteria colonize implant surface