TORP and PORP in Ossiculoplasty

Introduction

Definition and Distinction

A PORP is used when the stapes superstructure is intact; a TORP is used when the superstructure is absent.

Pathophysiology Requiring Ossiculoplasty

Ossicular Discontinuity

Ossicular Fixation

Classification of Ossicular Defects (Austin–Kartush System)

Materials Used in Ossiculoplasty

1. Autografts

• Incus interposition (sculpted native incus): historically the gold standard
  • Advantages: biocompatible, low cost, immediately available, low extrusion rate
  • Disadvantages: risk of cholesteatoma recurrence from residual matrix; requires time and skill to sculpt; may be demineralized or eroded
• Cartilage (tragal, conchal, or costal): used primarily as an interposition layer between the prosthesis head and the TM to reduce extrusion

2. Alloplastic (Allograft) Prostheses

Hydroxyapatite (HA)

• Undergoes osseointegration — bonds to bone without fibrous encapsulation
• Available in porous and dense forms
• Disadvantage: brittle, difficult to sculpt; top-heavy designs tend to tilt
• Often combined with Plastipore shaft (HA platform + Plastipore body) to exploit bone-bonding while enabling easy length adjustment

Titanium

• Currently the most widely used material
• Low mass (≤4 mg), high rigidity — closest in mass to the ossicles being replaced
• Reduces acoustic impedance and sound damping, particularly at high frequencies
• Open headplate design allows superior intraoperative visualization
• Claw-like medial design grips the stapes head (PORP) securely
• Not top-heavy → stays upright without propping
• Surgeon-friendly: reduced learning curve

PORP — Surgical Details

1. After disease clearance, the stapes capitulum and malleus handle are exposed.
2. A PORP of appropriate length is selected or adjusted (adjustable vs. fixed-length designs available).
3. A 0.5–0.7 mm conchal or tragal cartilage cap is fitted over the prosthesis head. The perichondrium is stripped from the prosthesis-contact surface and left intact on the TM-contact surface.
4. The prosthesis is placed perpendicular to the TM, in a vertical plane from the center of the stapes footplate.
5. Stabilized with minimal tension from the drum.
6. Silastic sheeting or hyaluronic acid sheets may be placed on the promontory to prevent adhesions.

TORP — Surgical Details

1. The stapes footplate is identified and confirmed to be mobile (a fixed footplate significantly worsens outcome).
2. A TORP of appropriate length spans from the stapes footplate to the TM (or malleus handle).
3. A cartilage cap is interposed between the prosthesis head and the TM — essential to prevent extrusion.
4. The TORP must be placed in parallel piston motion to the footplate — perpendicular orientation is critical.
5. Length matters: a short TORP fails to transmit high frequencies and risks dislodgement; a long TORP over-tensions the TM, dampens low frequencies, and risks footplate fracture, subluxation, or perilymph fistula.

Factors Determining Prosthesis Length and Position

• Favorable geometry: Narrow anteroposterior distance with deeper middle ear → prosthesis lies in a more vertical position → optimal energy transfer
• Unfavorable geometry: Wide AP distance, shallow middle ear → prosthesis lies more horizontally → poor hearing result

Factors Affecting Surgical Outcome (Cummings)

1. Mucosal fibrosis in middle ear
2. Revision ear surgery
3. Absence of the malleus
4. Removal of ear canal wall (open cavity)

Staging: Simultaneous vs. Delayed Ossiculoplasty

1. Status of middle ear mucosa — if thickened, infected, or bleeding, delay is prudent
2. Cholesteatoma operations — some surgeons prefer to place a Silastic/Gelfilm spacer at the first operation to "set" the TM level on the promontory, then perform ossiculoplasty at the second stage when anatomy is stable and predictable
3. Economic/access constraints — if a second-look is not feasible, simultaneous ossiculoplasty is justifiable, keeping in mind that cholesteatoma eradication always takes priority over hearing restoration

Results

• PORP: ABG <20 dB in 82% at 5 years
• TORP: ABG <20 dB in 63% at 5 years
• Extrusion rate: 5%

• A 2012 meta-analysis (Zhang et al., 12 studies, n=1388): no significant difference in stability or sound transmission
• The only RCT (94 patients, 24-month follow-up): no significant difference in extrusion rates or hearing gain
• A 2018 systematic review (14 studies): incus interposition and allograft PORPs produce similar hearing improvement (allograft PORP: 71% ABG closure; incus interposition: 64%)
• The severity of middle ear pathology has more influence on outcome than material choice

Complications

Role of Implantable Devices (Bone-Anchored and Middle Ear Implants)

Key Points for PG Exam

1. PORP = stapes superstructure present (stapes crura intact); TORP = stapes superstructure absent
2. Both require a cartilage cap to prevent extrusion; cartilage equal in size to the prosthesis head does not impair acoustic transmission
3. Titanium is the most widely used material — low mass, rigid, closest to native ossicle mass, MRI-compatible, user-friendly
4. ABG <20 dB is the standard for surgical success
5. Success rates: PORP > TORP (2:1 at 5 years by Yung & Vowler)
6. Titanium vs. non-titanium: no significant difference in RCTs or meta-analyses — disease severity matters more than material
7. Malleus absence is a major independent predictor of poor outcome
8. Prosthesis must be placed perpendicular to the footplate (parallel piston motion)
9. Long-term progressive hearing deterioration occurs regardless of material
10. Austin–Kartush classification guides prosthesis selection intraoperatively

Non-Titanium Materials for TORP and PORP in Ossiculoplasty

I. Autografts

1. Autograft Ossicles (Incus / Malleus Head)

2. Autograft Cartilage

• Source: tragus (most common), conchal bowl, costal cartilage
• Not used as a primary PORP/TORP shaft, but as a sculpted strut in some reconstructions (Type A and B)
• Principal role: cartilage cap over any prosthesis head to prevent extrusion

II. Polymers

1. Polyethylene — Plastipore / Polycel (High-Density Polyethylene Sponge, HDPE)

2. PTFE — Teflon (Polytetrafluoroethylene)

3. Silicone Rubber

4. Proplast

• A composite porous polymer (PTFE + carbon) introduced alongside Plastipore
• Concept: porosity allows fibrous ingrowth
• Largely abandoned due to fragmentation and foreign body reactions over time

III. Ceramics

1. Hydroxyapatite (HA) — Calcium Phosphate Ceramic

2. Combination: HA Platform + Plastipore (or Polyethylene) Shaft

• IAPEX (KJ Lee): hydroxyapatite with polyethylene composite
• Rationale: exploits the bone-bonding capacity of HA at the platform (lateral end, near TM) while allowing easy length adjustment by cutting the Plastipore shaft
• HA platform → less extrusion, tissue bonding
• Plastipore shaft → easily trimmed to exact length needed

3. Bioglass (Bioactive Glass) — Ceravital

IV. Historical Evolution Summary

V. Comparative Summary Table

VI. Key Exam Point

• Zhang et al. meta-analysis (12 studies, n=1,388): no significant difference in stability or hearing outcomes between titanium and non-titanium prostheses
• The severity of middle ear pathology influences outcome more than material choice
• Cummings: "The numerous types of prostheses available attest to the fact that no one implant is perfect."

The Defining Rule

Why This Matters Clinically

• PORP = the stapes superstructure (head + crura) is intact and used as the medial support → "partial" replacement because the lower part of the ossicular chain (stapes superstructure) is preserved
• TORP = the crura are gone, nothing remains above the footplate → prosthesis must span the full height from footplate to TM → "total" replacement

Confirming from Cummings

"A partial ossicular replacement prosthesis (PORP) is used when the stapes superstructure is present, and a total ossicular replacement prosthesis (TORP) is used when the superstructure is absent. Many variations [of material] exist..." — Cummings, Ch. 142