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TORP - Total Ossicular Replacement Prosthesis
Definition
A TORP (Total Ossicular Replacement Prosthesis) is an alloplastic implant used in ossiculoplasty to restore sound conduction when the entire ossicular superstructure is absent - i.e., the malleus, incus, and stapes crura are all missing, leaving only the stapes footplate (mobile or fixed).
It bridges the gap between the stapes footplate and the tympanic membrane (TM), acting as a single column to transmit vibratory energy.
- PORP (Partial Ossicular Replacement Prosthesis) = used when stapes superstructure (head + crura) is intact - bridges stapes head to TM
- TORP = used when stapes superstructure is absent - bridges stapes footplate to TM
In Wullstein's classification, TORP placement corresponds to a Type IIIc (major columella) tympanoplasty.
Indications
- Chronic otitis media with total ossicular chain erosion/destruction
- Cholesteatoma with absent superstructure
- Traumatic ossicular disruption with absent crura
- Previous failed ossiculoplasty with complete ossicular loss
- Congenital ossicular anomalies
Anatomy of the TORP
A TORP has two main components:
| Component | Function |
|---|
| Footplate platform / base | Sits on the stapes footplate; transmits vibration into the oval window |
| Shaft / strut | Vertical column transmitting sound energy upward |
| Head plate | Upper surface that contacts the TM (via a cartilage interposition graft) |
Adjustable TORPs allow the shaft length to be modified intraoperatively to fit the exact middle ear dimensions. Fixed-length TORPs come in standard sizes and must be selected to match the measured distance.
TORP in situ - Diagrams
TORP positioned between stapes footplate and tympanic membrane (intraoperative view)
Schematic of TORP - cartilage interposed between prosthesis head and TM
Materials Used
Historical (now less favored)
| Material | Issue |
|---|
| Polyethylene / Teflon | High extrusion rate |
| Proplast / Plasti-Pore | Improved biocompatibility but poor extrusion + hearing results |
| Ceravital / Bioglass (glass ceramics) | Extrusion issues |
Current Standard
| Material | Advantages | Disadvantages |
|---|
| Titanium | Lightweight (~4 mg), high rigidity, closest mass to native ossicles, excellent visualization during insertion (open headplate design), claw-like base for secure footplate contact, easy handling, low extrusion rate | Cost |
| Hydroxyapatite (HA) | Can integrate with bone without encapsulation; bonds to tissue | Brittle, hard to sculpt intraoperatively |
| Hydroxyapatite + Plasti-Pore composite | HA platform (low extrusion, tissue bonding) + Plasti-Pore shaft (easily trimmed to length) | Combined manufacturing complexity |
Key: Multiple RCTs and a meta-analysis of 12 studies (1388 patients) found no significant difference in stability or hearing outcomes between titanium and non-titanium prostheses. The underlying middle ear pathology has more influence on outcome than prosthesis material.
Surgical Technique - Key Principles (TRACS Mnemonic)
- T - Tension: The prosthesis must be placed under appropriate minimal tension from the TM. Too lax = sound energy loss. Too tight = TM erosion and extrusion. The prosthesis should spontaneously return to position when displaced with gentle pressure.
- R - Rigidity: Higher rigidity = better high-frequency transmission. Titanium is optimal.
- A - Angulation: The TORP must be placed as close to perpendicular to the stapes footplate as possible. Angulation reduces efficiency of piston motion.
- C - Contact: The base must maintain secure stable contact with the footplate center.
- S - Surface (Cartilage interposition): A 0.5-0.7 mm conchal or tragal cartilage graft is always interposed between the TORP headplate and the TM undersurface. This:
- Prevents direct TM-prosthesis contact
- Reduces TM erosion and implant extrusion
- Has minimal acoustic transmission effect when matched to prosthesis head diameter (shown in cadaver studies)
Placement Requirements for TORP
- Mobile footplate preferred - TORP on a fixed footplate gives worse results
- Healthy, well-aerated middle ear mucosa
- Normal middle ear pressure / functional Eustachian tube
- Stable tympanic membrane graft (second-stage TORP placement recommended if TM graft done simultaneously to reduce displacement risk)
Outcomes
| Measure | PORP | TORP |
|---|
| Air-bone gap < 20 dB | 50-85% of cases | 40-50% of cases |
| 5-year success rate | ~2/3 (67%) | ~1/3 (33%) |
| Extrusion rate (Kurz titanium, 5-yr) | ~5% | ~5% |
TORP outcomes are consistently inferior to PORP because:
- Longer column = less stable; more likely to displace
- No stapes superstructure to provide medial support
- Greater distance to bridge = harder to achieve optimal tension
- Relies entirely on the footplate as the medial anchor
Factors Affecting TORP Success
- Eustachian tube dysfunction (major risk for displacement)
- Chronic infection / mucosal adhesions
- Atelectasis of the middle ear
- Intraoperative stability at time of surgery
- Open vs. closed mastoidectomy technique
- Cartilage cap size and placement
Sources:
- Cummings Otolaryngology Head and Neck Surgery (9780323612173), pp. 2733-2773 - Materials and TORP outcomes
- Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol. 2 (9781138094634), p. 1076 - TORP terminology and technique