3Lessons from Abandoned Materials: Plastipore and Ceravital

FA graveyard of good intentions

Every prosthesis on a modern ossiculoplasty tray is the survivor of a long process of elimination. Behind the titanium and hydroxyapatite that dominate today lies a quieter history of materials that were once enthusiastically adopted and then abandoned — not because surgeons were careless, but because each promised to solve a real problem and only later revealed a fatal flaw. Studying these failures is far more instructive than memorising the current favourites, because the reasons they failed are exactly the criteria a good prosthesis must satisfy. An ideal ossicular replacement must be biocompatible, must resist extrusion, must be non-resorbable and stable, must transmit sound efficiently, and must be easy to handle in a deep, narrow field. Every abandoned material in this module fell at one or more of these hurdles.

Three materials tell almost the whole story. Solid polyethylene, an early polymer, extruded through the drum. Plastipore (and its sibling Polycel), a porous version of the same polymer, was meant to fix that by letting tissue grow into its pores — and instead provoked a chronic foreign-body reaction that slowly degraded the implant. Ceravital, a bioactive glass-ceramic, bonded beautifully to tissue and rarely extruded — but then quietly dissolved years later. Each failure mode is different, and each teaches a distinct lesson about how the hostile, moist, mobile environment of the middle ear tests an implanted material over a working lifetime that must be measured in decades, not months.

FSolid polyethylene: the extrusion problem

The modern era of synthetic ossiculoplasty began in the early 1950s, when Wullstein placed polymer prostheses to bridge the ossicular chain. The appeal of a synthetic material was obvious: unlike a sculpted autograft it was uniform, available off the shelf, and quick to deploy. Early solid polyethylene prostheses were rigid, inert in bulk, and easy to trim. The trouble was not the chemistry of the polymer but the mechanics of the interface. A hard, non-porous head placed directly against the undersurface of the tympanic membrane concentrates its load on a tiny patch of keratinising epithelium. Over weeks that focal pressure produces low-grade pressure necrosis: the membrane thins, the squamous layer migrates around the foreign body, and the prosthesis is gradually walled off and pushed laterally until it erupts into the external canal. The reconstruction fails, and the patient is often left with a re-perforation.

This extrusionwas the defining early problem of every rigid alloplast placed bare against the drum, and it is worth being precise about why it happens. The drum is a thin, living, three-layered membrane that evolved to vibrate, not to bear a point load. A poorly aerated middle ear compounds the problem: as the drum retracts it is drawn down onto the unforgiving plate, accelerating the whole sequence. Two solutions eventually emerged. The first was to interpose a disc of the patient’s own cartilagebetween the prosthesis head and the drum, spreading the load and keeping the rigid material off the epithelium. The second was to abandon solid polymers altogether. Both lessons — that a bare rigid head extrudes, and that cartilage interposition rescues it — carried directly into the next generation of materials.

TPlastipore and Polycel: when porosity backfires

The cleverest response to extrusion was to make the polymer porous. In the mid-1970s Shea introduced Plastipore, a high-density porous polyethylene whose interconnected pores were designed to invite fibrous tissue ingrowth, anchoring the prosthesis and, it was hoped, taming extrusion [1976]. Polycel, a polyethylene sponge, worked on the same principle. The materials were soft, trimmable, cheap and available, and they were taken up widely: Brackmann, Sheehy and Luxford reviewed more than a thousand Plastipore TORP and PORP operations, reporting a 7% extrusion rate that fell further once cartilage was routinely interposed between the porous head and the drum [1984]. With a cartilage cap and good technique, large series even reported known extrusion of roughly 4% [2001]. On the early evidence, the porous polymer looked like a success.

The flaw was slower and more insidious than extrusion, and it took years to surface. The very porosity that encouraged ingrowth also created an enormous internal surface area for the body to react against. Temporal-bone histopathology of retrieved porous-plastic implants showed a consistent and unwelcome picture: a foreign-body giant-cell reaction visible as early as two months, with particulate plastic engulfed inside the giant cells and progressive microdegradation of the material that increased with time[2007]. In other words, the implant was being slowly eaten. The clinical correlate is striking: a Plastipore prosthesis can give excellent hearing for over a decade and then fail as the polymer disintegrates. Kerr and Riley described exactly this — a prosthesis that functioned for fourteen years before hearing deteriorated, with revision revealing disintegration of the porous polyethylene, multinucleated foreign-body giant cells, and a defect in the stapes footplate where fragments had eroded inward[1999]. That last detail — fragments threatening the inner ear — turned a hearing problem into a safety problem, and the histologic findings led explicitly to a recommendation to caution against the continued otologic use of porous plastic [2007].

TCeravital: the prosthesis that quietly dissolves

Ceramics seemed to offer an escape from the inflammatory liability of polymers. Ceravital is a bioactive glass-ceramic— a material engineered not merely to be tolerated but to chemically bond with surrounding bone and soft tissue. That bioactivity was genuinely attractive: because the surface integrated with tissue rather than sitting inertly against it, Ceravital could often be placed directly against the drum with comparatively little tendency to extrude. Early reports were encouraging. Niparko and colleagues described favourable preliminary results in thirty-seven ears, and Reck and Helms reported five years of histologic and clinical experience suggesting the material was suitable for ossicular reconstruction[1988, 1985]. For a time it looked as though bioactivity had solved the biocompatibility problem that had sunk the polymers.

The catch was the mirror image of the polymer story. Where porous polyethylene degraded by inflammation, Ceravital failed by being too solublein the very environment it was designed to bond with. The material is brittle — difficult to contour without fragmenting — and, more importantly, it is slowly resorbed. A randomized prospective trial comparing Ceravital with Plastipore found similar extrusion rates between the two, but two of thirty-eight Ceravital patients developed late hearing failure attributable to resorption of the prosthesis itself [1990]. The full extent of the problem only became clear with longer follow-up. Brewis, Orrell and Yung revisited Ceravital and showed that absorption of the prosthesis became apparent on average around six yearsafter implantation — far later than extrusion, slippage or atelectasis — and that the rate of absorption rose over time [2003]. The lesson is sharp: a material can pass every short-term test, behave impeccably for years, and still be quietly dissolving. A prosthesis is a lifetime implant, and bioactivity that shades into biodegradability is a liability, not a feature.

CScoring the failures against the ideal

Laying the three materials against the standard criteria for an ideal prosthesis makes the pattern explicit. Each material passedsome requirements convincingly — all three were easy or moderately easy to handle, and each looked acceptable on early hearing — while failing the one criterion that, in the moist, cellular, decades-long reality of the middle ear, mattered most for that material. Solid polyethylene failed non-extrusion. Plastipore failed biocompatibility and long-term stability, degrading under a giant-cell assault. Ceravital failed non-resorbability, dissolving on a timescale that outran most follow-up. The scorecard below lets you toggle between the materials and see each criterion marked, with titanium included as the passing benchmark against which they were all eventually judged.

Two cross-cutting principles fall out of the comparison. First, the failure mode dictates the timescale of detection. Extrusion declares itself in months, so polyethylene’s flaw was obvious quickly. Inflammatory microdegradation and resorption take years, which is precisely why Plastipore and Ceravital enjoyed long honeymoons before their problems became undeniable — and why short or even medium-term series can be dangerously reassuring. Second, the same property can be an asset or a liability depending on context. Porosity was meant to anchor the implant but multiplied the surface for inflammation; bioactivity was meant to integrate the implant but became dissolution. A material is never “good” or “bad” in the abstract — it is good or bad against the full set of demands the middle ear makes over a lifetime.

CWhat survived, and the lesson for selection

The materials that displaced these failures did so by being, above all, biostable and inert. Titanium is light, rigid, non-ferromagnetic and shapeable; it provokes no foreign-body giant-cell degradation, does not resorb, and gives low single-digit extrusion when capped with cartilage at the drum. Hydroxyapatite, a calcium-phosphate ceramic structurally akin to bone, is biocompatible and non-resorbing; its main weakness is brittleness on instrumentation, not dissolution. Where the abandoned materials each failed a core criterion, these pass the whole set — which is exactly why they survived. It is worth noting that Plastipore did not vanish entirely overnight: capped with cartilage and used carefully it gave reliable hearing in experienced hands for years [2001], and the slow accumulation of histologic and long-term clinical evidence, rather than a single catastrophic result, is what finally retired it[2007].

For the clinician, the practical lessons are durable even though the specific materials are obsolete. First, demand long-term, histologically grounded evidence before trusting a new material; early hearing results and short series flatter materials that fail slowly, as both Plastipore and Ceravital did[2003, 1999]. Second, protect the interface: a rigid head against the bare drum extrudes regardless of the polymer, and cartilage interposition is the single most reliable mitigation[1984]. Third, prize biostability over cleverness: an inert material that simply sits still for decades will usually outperform an ingenious one engineered to interact with tissue, because every interaction is also a route to failure [1990]. The graveyard of abandoned materials is, in the end, the clearest possible statement of what we now ask a prosthesis to be.