Types of Middle Ear Prostheses for Ossicular Reconstruction
Middle ear prostheses for ossicular reconstruction are classified into two main types: Partial Ossicular Replacement Prosthesis (PORP) and Total Ossicular Replacement Prosthesis (TORP), with the choice traditionally determined by the presence or absence of an intact stapes superstructure.
Primary Classification System
Partial Ossicular Replacement Prosthesis (PORP)
- PORP is used when the stapes superstructure remains intact, bridging from the tympanic membrane (or malleus handle if present) to the head of the stapes 1, 2.
- This prosthesis is indicated for Austin Type A ossicular defects with an intact stapes superstructure 1.
- PORP provides hearing improvement with mean postoperative air-bone gap (ABG) closure of approximately 17-18 dB 1.
Total Ossicular Replacement Prosthesis (TORP)
- TORP is used when only the stapes footplate remains, with complete absence of the stapes superstructure 1, 2.
- This prosthesis extends from the tympanic membrane (or malleus) directly to the stapes footplate 1.
- TORP achieves mean ABG closure of approximately 20-23 dB 1.
Material Composition Options
Titanium Prostheses
- Titanium is the most widely used material for middle ear prostheses due to excellent biocompatibility and mechanical properties 2, 3.
- Titanium prostheses are available in five different sizes for both PORP and TORP configurations, allowing customization without time-consuming intraoperative shaping 3.
- Success rates (postoperative ABG ≤20 dB) range from 68-79% with titanium prostheses 2, 3.
- Extrusion rates are minimal, and biologic fixation occurs between the prosthesis and native structures 2, 3.
Polycel® (Hydroxyapatite) Prostheses
- Polycel® represents an alternative synthetic material for ossicular reconstruction 4.
- This material has been used historically but shows higher complication rates compared to newer alternatives 4.
Autologous Bone-Cartilage Composite Graft (BCCG)
- BCCG represents a novel autologous technique with the lowest extrusion rate (0%) among all prosthesis types 4.
- This method uses the patient's own tissue, eliminating biocompatibility concerns 4.
- BCCG shows satisfactory hearing outcomes comparable to synthetic materials 4.
Critical Decision-Making Algorithm
Traditional Approach
The conventional algorithm bases prosthesis selection solely on stapes superstructure integrity: intact superstructure → PORP; absent superstructure → TORP 1, 5.
Contemporary Evidence-Based Modification
- Recent mechanical studies suggest TORP may provide superior long-term stability even with intact stapes superstructure (Austin Type A defects) 1.
- Laser interferometer studies demonstrate that malleus-to-footplate reconstruction (TORP) produces more favorable mechanical results than malleus-to-stapes-superstructure reconstruction (PORP), even when the superstructure is intact 1.
- Both PORP and TORP achieve comparable hearing outcomes (ABG closure 18 dB at late follow-up) when the stapes superstructure is intact 5.
Clinical Outcomes and Success Factors
Hearing Improvement Expectations
- Approximately 90% of patients achieve mild hearing loss (26-30 dB) or better postoperatively with either prosthesis type 1.
- Overall success rates (ABG ≤20 dB) range from 68-79% across different prosthesis materials 2, 3.
Factors Influencing Outcomes
- Preoperatively intact tympanic membrane significantly improves outcomes 5.
- Absence of cholesteatoma predicts better hearing results 5.
- Prosthesis type (PORP vs. TORP) does not significantly influence outcomes when the stapes superstructure is intact 5.
- Primary versus revision surgery status does not significantly affect audiological outcomes 5.
Common Pitfalls and Technical Considerations
Prosthesis Stability
- TORP demonstrates increased mechanical stability compared to PORP, making it preferable for long-term outcomes in Austin Type A defects 1.
- Using cartilage between the prosthesis and tympanic membrane graft helps prevent extrusion 2.
Material Selection
- Titanium prostheses are delicate, easy to handle, and require no intraoperative trimming, reducing operative time 2, 3.
- Autologous BCCG should be considered in patients at high risk for extrusion or with concerns about foreign body implantation 4.