Austin Classification of Middle Ear Prostheses
Classification System Overview
The Austin classification system categorizes ossicular chain defects to guide selection of appropriate prostheses for ossicular reconstruction surgery. 1, 2
The Austin classification (also known as Austin-Kartush classification) defines specific patterns of ossicular pathology:
Austin Type A Defects
- Type A defects are characterized by erosion of the incus with an intact malleus handle and intact stapes superstructure. 1, 2
- This represents the most common pattern requiring ossicular reconstruction in chronic ear disease. 1
- Both PORP (partial ossicular replacement prosthesis) and TORP (total ossicular replacement prosthesis) can be used for Type A defects, though traditionally PORP is selected when the stapes superstructure is intact. 1, 3
Prosthesis Selection for Type A Defects
- Recent evidence suggests TORP may provide superior long-term stability compared to PORP even when the stapes superstructure is intact in Type A defects. 1
- Hearing outcomes are comparable between TORP and PORP, with air-bone gap closure of approximately 17-23 dB achievable with either prosthesis. 1
- TORP reconstruction (malleus to footplate) provides more favorable mechanical results than PORP reconstruction (malleus to stapes superstructure) based on laser interferometer studies. 1
Expected Outcomes
- With PORP reconstruction in Type A defects, approximately 55% of patients achieve postoperative air-bone gap within 10 dB, and 85% achieve air-bone gap within 20 dB. 2
- With TORP reconstruction, 67% of patients achieve air-bone gap closure to within 20 dB. 4
- Outcomes are significantly better when the tympanic membrane is intact preoperatively and when cholesteatoma is not present. 3
Clinical Considerations
- The choice between autologous ossicle grafts, homografts, and alloplastic prostheses depends on availability and surgical experience, as hearing results are comparable. 5, 2
- Autologous ossicle or cortical bone grafts maintain their integrity for over 25 years, making them a reliable long-term option. 5
- Alloplastic prostheses (porous polyethylene) have extrusion rates that can be minimized with proper placement and interposition of tragal cartilage. 4