Acute otitis media. An animal experimental study

Factors affecting sound energy absorbance in acute otitis media model of chinchilla

Acute otitis media (AOM) is a rapid-onset infection of the middle ear which results in middle ear pressure (MEP), middle ear effusion (MEE), and structural changes in middle ear tissues. Previous studies from our laboratory have identified that MEP, MEE, and middle ear structural changes are three factors affecting tympanic membrane (TM) mobility and hearing levels (Guan et al., 2014, 2013). Sound energy reflectance or absorbance (EA) is a diagnostic tool increasingly used in clinical settings for the identification of middle ear diseases. However, it is unclear whether EA can differentiate these three factors in an AOM ear. Here we report wideband EA measurements in the AOM model of chinchilla at three experimental stages: unopened, pressure released, and effusion removed. These correspond to the combined and individual effects of the three factors on sound energy transmission. AOM was produced by transbullar injection of Haemophilus influenzae in two treatment groups: 4 days (4D) and 8 days (8D) post inoculation. These time points represent the relatively early and later phase of AOM. In each group of chinchillas, EA at 250-8000 Hz was measured using a wideband tympanometer at three experimental stages. Results show that the effects of MEP, MEE, and tissue structural changes over the frequency range varied with the disease time course. MEP was the primary contributor to reduction of EA in 4D AOM ears and had a smaller effect in 8D ears. MEE reduced the EA at 6-8 kHz in 4D ears and 2-8 kHz in 8D ears and was responsible for the EA peak in both 4D and 8D ears. The residual EA loss due to structural changes was observed over the frequency range in 8D ears and only at high frequencies in 4D ears. The EA measurements were also compared with the published TM mobility loss in chinchilla AOM ears.

Motion of tympanic membrane in guinea pig otitis media model measured by scanning laser Doppler vibrometry

Otitis media (OM) is an inflammatory or infectious disease of the middle ear. Acute otitis media (AOM) and otitis media with effusion (OME) are the two major types of OM. However, the tympanic membrane (TM) motion differences induced by AOM and OME have not been quantified in animal models in the literature. In this study, the guinea pig AOM and OME models were created by transbullar injection of Streptococcus pneumoniae type 3 and lipopolysaccharide, respectively. To explore the effects of OM on the entire TM vibration, the measurements of full-field TM motions were performed in the AOM, OME and untreated control ears by using scanning laser Doppler vibrometry (SLDV). The results showed that both AOM and OME generally reduced the displacement peak and produced the traveling-wave-like motions at relatively low frequencies. Compared with the normal ear, OME resulted in a significant change of the TM displacement mainly in the inferior portion of the TM, and AOM significantly affected the surface motion across four quadrants. The SLDV measurements provide more insight into sound-induced TM vibration in diseased ears.

Morphological changes in the tympanic membrane associated with Haemophilus influenzae-induced acute otitis media in the chinchilla

OBJECTIVE

The tympanic membrane (TM) couples sound waves entering the outer ear canal to mechanical vibrations of the ossicular chain in the middle ear. During acute otitis media (AOM), dynamic structural changes in the TM can occur, which potentially affect sound transmission. It has remained unclear whether TM changes contribute significantly to the conductive hearing loss associated with human AOM. Studies that systematically and quantitatively assess the impact of morphological and mechanical characteristics of the TM on hearing in animal models of AOM have been few in number and lack detail. Our current study focused on the identification of quantitative morphological changes in the TM of the adult chinchilla.

METHOD

AOM was produced by transbullar injection of the nontypeable (acapsular) Haemophilus influenzae strain 86-028NP into two treatment groups of chinchillas: one 4 days (4D) post bacterial challenge, and a second treatment group after 8 days (8D) post challenge. Structure and thickness were examined histologically at nine locations over the TM in untreated controls and in animals from both AOM treatment groups.

RESULTS

TM thickness was found to have increased significantly (110-150%) at all measured locations of H. influenzae-infected ears when compared with uninfected (normal) TMs at 4D post bacterial challenge. Cellular proliferation and infiltration in the outer epithelial layer were primary contributors to this thickening. In ears infected for 8D, the TM was substantially thicker, a 200-300% increase from uninfected control values, due to edema and cell proliferation in both the outer and inner epithelial layers. In both 4D and 8D ears, thickening of the TM was more prominent in the superior-anterior quadrant.

CONCLUSION

This study provides unequivocal structural evidence that significant TM thickness increases are associated with AOM induced by a well characterized H. influenzae human clinical isolate of low passage number. These and additional thickness data from early and later stages in middle ear infection will be used to derive the mechanical properties of the TM in a future study from our laboratory.

Tissular changes induced by Pseudomonas aeruginosa in an otitis media rat model with tubal obstruction

CONCLUSIONS

This is a suitable model for the study of different features of middle ear inflammation. This model allows manipulations inside the middle ear while preserving relevant structures such as the tympanic membrane, and provides a useful model for the study of interactions between bacterial infection and eustachian tube dysfunction.

OBJECTIVES

Analysis of early and late histological features in an experimental model of Pseudomonas aeruginosa middle ear inoculation in the rat designed for the study of middle ear procedures.

MATERIALS AND METHODS

Thirty Wistar rats were inoculated with Pseudomonas aeruginosa in the tympanic bulla followed by the cauterization of the eustachian tube. Culturing of middle ear effusion was carried out at 7 days follow-up and at sacrifice. Processing of the temporal bones for light microscopy was performed at 7, 14, 30 and 60 days.

RESULTS

Early cultures were positive in most cases, thus proving that middle ear inflammation was due to the presence of inoculated Pseudomona aeruginosa. Mucoperiosteal inflammatory changes similar to those observed in human middle ear infection were seen. Acute inflammatory cell infiltration was seen at 7 and 14 days, gradually decreasing to chronic inflammatory changes with fibroplasia at 60 days. Bone resorption was observed at 7 and 14 days, changing to a bony deposition at 30 and 60 days.

Spontaneous otitis media in Wistar rats: an overlooked pathology in otological research

The rat is commonly employed in otological research, but spontaneous ear infections can confound the results of experimental procedures--wasting time, money, and animals. The authors focus on the incidence of spontaneous otitis media in Wistar rats. They compare disease incidence in animals housed in standard cages with those housed in barrier units, showing that 20% of their conventionally housed animals developed spontaneous otitis media, whereas only 5% of their animals housed in isolated units were infected. These results underscore the importance of strict control of the shipping, housing conditions, and manipulation of animals to be used in otological research.

Histopathologic differences due to bacterial species in acute otitis media

OBJECTIVE

To compare selected features of histopathology in acute otitis media caused by various bacteria and examine potential differences due to bacterial species, as well as possible correlation to experimental and human clinical findings.

METHODS

Rat models of acute otitis media caused by Streptococcus pneumoniae (MC), non-typeable or type b Haemophilus influenzae (NTHI/HIB) or Moraxella catarrhalis (MC) were studied longitudinally up to 6 months after bacterial challenge. Findings related to dynamics of goblet cell density, modeling and remodeling of bone tissue structures and polyp, as well as fibrous adhesion formation and persistence are presented.

RESULTS

Middle ear goblet cell density progressed to peak 2 weeks after bacterial inoculation, thereafter gradually normalizing. However, density and accordingly middle ear secretory capacity was still significantly increased after 6 months in all bacteria, except MC. The HI species induced the highest increase. Initial osteoresorption was followed by massive osteoneogenesis, progressing to a peak after 2-3 months, followed by some degree of normalization, concurrently classic remodeling. Primarily SP, but also the HI species induced more new bone formation than MC. Mucosal polyp and fibrous adhesion formation occurred regardless of bacterial species. Most polyps appeared in the early phases and the HI species induced formation of more polyps and adhesions than the other bacteria.

CONCLUSION

Acute middle ear infection with the Haemophilus species induce the highest increase of mucosal secretory capacity, lasting for at least 6 months after the acute incident. Thus, a subsequent development of secretory otitis media seems more likely following infection with these bacteria. Equivalently, mucosal scarring observed as polyp and fibrous adhesion formation was more severe following Haemophilus infection. S. pneumoniae induced the most marked changes of bone tissue structures, seen as initial osteoresorption and subsequent osteoneogenesis. Overall, infection with M. catarrhalis induced the mildest changes.

Bone modeling dynamics in acute otitis media

OBJECTIVE

A number of middle ear diseases are associated with pathologic bone modeling, either formative or resorptive. As such, the pathogenesis of a sclerotic mastoid has been controversial for decades. Experimental studies on acute middle ear infection have shown varying degrees of both osteoresorption and osteoneogenesis. This study presents data on the dynamics of bone modeling in a rat model of acute pneumococcal otitis media, studied longitudinally from day 1 through 6 months after inoculation.

RESULTS

Qualitative, as well as quantitative histopathology revealed initial osteoresorption, followed by increasing apposition of new bone in the middle ear cavity, initiated at the outer periosteum. Measured bone thickness in four anatomically distinct locations peaked 3 months after inoculation, followed by some degree of normalization. However, bone thickness was still massively increased 6 months after the acute incident. Except in perilymphatic spaces of the otic capsule, resorptive and formative activity were found in all bone tissue structures surrounding the middle ear cavity, including the bony external auditory canal and the ossicles.

CONCLUSION

These findings may support the existence of a perilymphatic barrier of specialized bone and suggest that even a single episode of acute infection may alter properties of ossicular chain conduction. The authors conclude that acute otitis media is accompanied by massive and progressing net osteoneogenesis, already evident at 3 days and peaking 3 months after inoculation, followed by some degree of normalization. This is conceivably in support of the environmental theory of mastoid pneumatization, claiming inflammatory disease as the cause of a sclerotic mastoid.

The mucosa of the middle ear and Eustachian tube in the young rat: number of granulocytes, macrophages, dendritic cells, NK cells and T and B lymphocytes in healthy animals and during otitis media

To gain a better understanding of immune reactions during otitis media, the middle ear and Eustachian tube mucosa were studied as a unit in young rats with respect to the composition of immunocompetent cells before and after middle ear infection via the tube. Using immunohistology, the distribution of NK cells, important for the defence against viral antigens, and of dendritic cells, known to be most capable of antigen uptake, processing and presentation, was determined. Furthermore, the composition of cells of the unspecific immune system (i.e. granulocytes and macrophages) and the specific immune system (i.e. T and B lymphocytes) was studied. Macrophages and dendritic cells were spread over the whole middle ear mucosa, whereas only few NK cells and T and B lymphocytes and almost no granulocytes were detected. In the Eustachian tube mucosa, immunocompetent cells, with the exception of dendritic cells and macrophages, were only rarely seen. After induction of otitis media by severing the soft palate, immunocompetent cells increased in both the middle ear and Eustachian tube mucosa, but surprisingly they were almost absent from the area of the tubal orifice to the middle ear. The results indicate that immune reactions take place similarly in the Eustachian tube and in the middle ear mucosa.

Mucosal changes induced by experimental pneumococcal otitis media are prevented by penicillin V

Penicillin V (pcV) was administered to 50 rats, either before bacterial challenge (prevention group), or after bacterial challenge but before fulminant purulent acute otitis media (AOM) was established (early treatment group). Five animals from each group were killed on days 4, 8, and 12, and 2 and 6 months after challenge. Middle ear mucosa was sampled at six different sites and studied in the light microscope. Untreated pneumococcal AOM in the rat has been shown to cause persistent structural changes of the middle ear mucosa. Both in the early treatment group and in the prevention group, the structural changes were diminished, as compared with those of untreated infected controls. The persistent structural changes seen after 6 months in untreated controls were not seen in animals that had received pcV in conjunction with the AOM episode. Though the beneficial effect on the mucosal changes during the first 2 weeks was more pronounced when pcV was given prophylactically, its use as early treatment would seem to be almost as effective in preventing the persistence of mucosal changes.

The behavior of alloplastic tympanic membranes in Staphylococcus aureus-induced middle ear infection. II. Morphological study of epithelial reactions

Epithelial reactions to Silastic, Estane polyether urethane, polypropylene oxide, and a poly(ethylene oxide hydantoin) and poly(tetramethylene terephthalate) segmented polyether polyester copolymer were investigated after implantation in tympanic membranes and submucosa of noninfected and Staphylococcus aureus-infected rat middle ears. Porous implants made of Estane and polypropylene oxide were completely covered by tympanic-membrane connective tissue, epidermis, and epithelium in 2 weeks and those made of copolymer in between 2 and 4 weeks postoperatively. Silastic implants, which were dense, were not enveloped by tympanic-membrane tissue but rejected. Starting in the 6th postoperative month the proliferative activity and structure of both the tympanic membrane epithelium and epidermis became normal except for the presence of iron-containing secretory epithelium near polypropylene oxide. After initial swelling caused by the surgical trauma, neither the proliferative activity nor the composition of the epithelium covering submucosal implants was affected by the presence of any of the biomaterials. Infection of middle ears bearing implants induced epithelial reactions similar to those associated with infected middle ears without an implant.

The behavior of alloplastic tympanic membranes in Staphylococcus aureus-induced middle ear infection. I. Quantitative biocompatibility evaluation

The biocompatibility of dense Silastic implants and porous implants made of Estane 5714 F1 polyether urethane, polypropylene oxide, and an HPOE/PBT segmented polyether polyester copolymer was evaluated during an induced Staphylococcus aureus middle ear infection. The middle ear response to infection seemed not to be affected by the presence of implants made of either of the polymers. Light microscopical morphometry and transmission electron microscopy showed degradation of the porous implants under study, but not of Silastic implants, which were invariably surrounded by a fibrous capsule. This finding, combined with the degree of porous implant degradation, the composition of the tissues surrounding the implants, and the tissue/biomaterial interface reactions are consistent with the results obtained in the noninfected middle ear. Round-cell infiltrates however, were predominantly associated with implants made of polypropylene oxide and HPOE/PBT copolymer; while the presence of (phagocytosed) microbial debris was associated with copolymer. The present findings indicate that with respect to implant behavior in infected surroundings Estane is the best porous material, whereas the behavior of Silastic implants did not deviate from that in non-infected ears.

Persistent structural changes in the middle ear mucosa of the rat, after an experimentally induced episode of pneumococcal otitis media

To examine the effect of a transient episode of purulent AOM on the middle ear mucosa, an animal model was used. Histological examination was performed after inoculation of pneumococci into the rat middle ear. At 4, 8 and 12 days, and at 2 months after the inoculation, rats were sacrificed on each occasion and samples taken from specific areas of the middle ear mucosa. Structural alterations were noted at all mucosal sites. The normally flat epithelium had become more cuboidal or cylindrical, and numerous ciliated cells occurred in areas originally devoid of these cells. Epithelial cells penetrated the subepithelium forming gland-like structures. In the early phase, day 4 and day 8, inflammatory cells invaded the subepithelial layer except in the tympanic membrane. At 2 months, with the tympanic membrane otimicroscopically and histologically normalized, the structural changes of the mucosa still persisted indicating that a transient episode of pneumococcal otitis media can cause persisting mucosal changes.

The biocompatibility of hydroxyapatite ceramic: a study of retrieved human middle ear implants

The biocompatibility of 11 hydroxyapatite auditory canal-wall prostheses and 4 hydroxyapatite incus prostheses implanted for 4 to 40 months was evaluated by light microscopy, scanning electron microscopy, transmission electron microscopy, and Röntgen microanalysis. These 15 prostheses representing 4% of 375 prostheses, has been removed because of unresolved chronic middle ear infection, residual cholesteatoma, or poor fit. The findings confirmed earlier reports on the biocompatibility of hydroxyapatite in vitro, in animals, and in man. An electron-dense layer was found at the interface with bone and fibrous tissue, and a firm bond between the ceramic and bone at the hydroxyapatite ceramic/bone interface developed. Macropores became filled with bone and fibrous tissue, and the tissue in the individual pores was interconnected. Furthermore the incus prostheses were covered with an epithelium similar to that found in the human middle ear. Findings diverging from those made in other studies were the relatively large amount of exudate in the pores, an apparent increase of degradation during infection, and the accumulation of trace elements in one of the canal-wall prostheses. In all likelihood these three phenomena may be attributed to the unfavorable conditions to which these prostheses were exposed during implantation.

The effect of external stimuli on cultured rat middle ear epithelium. I. Extracellular calcium concentration

The effect of the extracellular calcium concentration on serially cultured rat middle ear epithelium was investigated with phase contrast microscopy, scanning electron microscopy, and transmission electron microscopy, as well as by a method to induce cornified envelope formation with a calcium ionophore. The results show that calcium concentration affects cell morphology and terminal differentiation. Furthermore, a role in the proliferation rate, secretory activity and migration seems likely. Since the extracellular calcium concentration may fluctuate locally during osteoresorption or osteodeposition, both of which occur during otitis media, this concentration might be an important factor in the pathogenesis of both acute and chronic otitis media.

Cytokeratin patterns of tissues related to cholesteatoma pathogenesis

Specimens of cholesteatoma matrix, meatal epidermis, and middle ear epithelium were removed during surgery, and immunohistochemical techniques were used to investigate cytokeratin expression. The use of five chain-specific anticytokeratin monoclonal antibodies and one broad specific anticytokeratin monoclonal antibody showed the divergent behavior of middle ear epithelium compared with the cytokeratin expression of the other two types of epithelium. Middle ear epithelium was characterized by the presence of cytokeratins 4, 8, 18, and 19, whereas in both cholesteatoma and meatal epidermis cytokeratin 10 predominated. Furthermore, cholesteatoma showed an infrequent focal presence of cytokeratins 4, 18, and 19. The similarity between cholesteatoma and meatal epidermis with respect to morphology, and the presence of cytokeratin 10 support an epidermal origin of cholesteatoma. However, a metaplastic origin cannot be excluded, because of the infrequent occurrence of a small amount of cytokeratins 4, 18, and 19 in cholesteatoma matrix that was not found in meatal epidermis but was a component of the cytokeratin pattern of middle ear epithelium.

Tympanic membrane structure during a Staphylococcus aureus-induced middle ear infection. A study in the rat middle ear

In response to a Staphylococcus aureus-induced middle ear infection the tympanic membrane showed infiltration of polymorphonuclear granulocytes, lymphocytes, and macrophages and increased areas covered by ciliary and secretory epithelium. These reactions, which were comparable to the cellular and mucociliary responses seen in the middle ear mucosa during infection, were restricted to the pars flaccida and to predominantly the annular and manubrial regions of the pars tensa. This showed that the greater part of the tympanic membrane, where the lamina propria is composed of collagenous bundles and only very thin layers of loose connective tissue, is hardly affected by or barely responds to the inflammatory stimulus.

The biological performance of calcium phosphate ceramics in an infected implantation site. III: Biological performance of beta-whitlockite in the noninfected and infected rat middle ear

The biological performance of macroporous beta-whitlockite implanted in the rat middle ear was evaluated. The material was studied in the non-infected middle ear and in middle ears infected by Staphylococcus aureus. beta-whitlockite was quickly covered by a normal mucosa. One week post-operatively the macropores were filled with exudate, fibrous tissue, and a small quantity of bone. Six months after the operation the greater part of the macropore area was filled with bone (74%); fibrous tissue accounted for 20%, and exudate for 5%. In histological sections, the macropore area of beta-whitlockite had increased by 68% after six months, indicating biodegradation. Macrophages and multinucleated cells were present in the vicinity of the implant and played a role in this biodegradation. Besides cytoplasmic vacuoles containing calcium phosphate, the cells showed smaller granules containing trace elements originally present in the implant material, such as silicon, titanium, aluminum, iron, and magnesium.

The biological performance of calcium phosphate ceramics in an infected implantation site: I. Biological performance of hydroxyapatite during Staphylococcus aureus infection

In the present study the biological performance of macroporous and dense hydroxyapatite after implantation in the rat middle ear was evaluated during an induced Staphylococcus aureus middle ear infection. The course of the infection was similar to that in the absence of an implant. Hydroxyapatite was frequently integrated with fibrous ingrowths in the middle ear lumen, originating solely from the infection. Good epithelial covering of the implant with all types of epithelial cells of importance for middle ear defence, was found. Increase of the exudate in the pores due to the infection was relatively small, and most of the exudate was restricted to pores on the implant surface. The bony tissue in the pores was not influenced significantly by the induced infection. Degradation of hydroxyapatite was consistent with earlier results obtained in the non-infected middle ear. The results obtained so far suggest that hydroxyapatite is highly suitable for middle ear implantation.

The biological performance of calcium phosphate ceramics in an infected implantation site: II. Biological evaluation of hydroxyapatite during short-term infection

Macroporous hydroxyapatite was implanted submucosally in the rat middle ear and studied after intratympanic injection of a Staphylococcus aureus suspension. The middle ear infection was induced 1 week after the implantation, and the effects of infection on the middle ear and the implant material were evaluated after 1, 3, 7, and 14 days by light and electron microscopy. The findings in the infected middle ear with an implant corresponded well with those described for the infected middle ear cavity without an implant. The reactions of the tissue over the implant were similar to those of the original mucosa of the middle ear. Bone was deposited on the implant and in its pores in relatively large quantities. Biodegradation, due at least partially to phagocytic activity of macrophages and multinucleated cells, was more prominent than previously found. This higher degree of biodegradation may be attributed to the use of the mucosal implantation technique, because this was the only point of divergence with respect to material or methods from earlier work reported by our group. The present results, together with those published earlier, suggest that this material has promising features for use as a bone substitute in reconstructive middle ear surgery. Definitive conclusions on biological performance and biofunctionality will, however, have to await long term clinical trials.

Culture and characterization of rat middle-ear epithelium

This study was performed to design a method for the culture of rat middle-ear epithelium and to apply the method to investigate the characteristics of this epithelium. Culture of explants of middle-ear epithelium in the presence of the epidermal growth factor was successful, whereas serial cultivation required 3T3 feeder cells in addition to the epidermal growth factor. Cultured middle-ear epithelium was studied by phase-contrast microscopy, transmission and scanning electron microscopy, and combined light and scanning electron microscopy (LM/SEM). These techniques showed similarity between the cultured and the natural middle-ear epithelium. Explants and outgrowths showed both flat polygonal and ciliated epithelial cells. In serial cultivation, however, only the first of these cell types was observed. Frequently, a single primary cilium was found on the cell surface. Transmission electron microscopy showed cross-linked envelopes whose formation was promoted by ionophore X537A. Cytokeratin was demonstrated by immunoblotting, immunofluorescence, and immunoperoxidase methods, using an anti-cytokeratin monoclonal antibody. The model described here permits study of the differentiation of middle-ear epithelium in vitro and may be of future value for the study of chronic middle-ear diseases.

Macropore tissue ingrowth: a quantitative and qualitative study on hydroxyapatite ceramic

The aim of this study was to obtain more information about macropore tissue ingrowth into the pores of sintered hydroxyapatite implanted in the rat middle ear, for the assessment of the usefulness of this material in reconstructive middle-ear surgery. The exudate filing the pores during the early post-operative period was gradually replaced by equal amounts of fibrous tissue and bone. The percentage of the macropore area occupied by bone was directly correlated with the macropore size. Bone was deposited not only from the pore wall towards the pore centre, but also in the opposite direction. Bonding osteogenesis was demonstrated. At sites of mechanical irritation, the presence of multinucleated cells and proliferatively active mononuclear phagocytes persisted for as long as a year. Under appropriate conditions hydroxyapatite seems to be a promising material for bone substitution in reconstructive middle-ear surgery.

Epithelial reactions to hydroxyapatite. An in vivo and in vitro study

The intention of this study was to investigate the epithelial reactions to hydroxyapatite ceramic in vivo and in vitro. Shortly after implantation in the rat middle ear, hydroxyapatite was found covered by a mucosal layer. In the early postoperative period the implant was almost completely covered by epithelial cells, which were found to proliferate and also showed migratory activity. After longer intervals the implant was completely covered by epithelium, which was composed predominantly of flat polygonal cells and a relatively small number of ciliated epithelium and goblet cells. All cells showed normal morphology. In vitro experiments showed preservation of the morphology of rat middle-ear mucosa explants with good outgrowth of epithelial cells. In these outgrows, the majority of the cells were flat polygonal, but ciliated epithelium was also seen. No difference was found between the absence and presence of hydroxyapatite. Serially cultured cells displayed normal polygonal morphology, but no ciliated cells were found. Ciliated cells were also absent in control experiments without hydroxyapatite. Growth curves obtained in the absence and presence of hydroxyapatite did not differ significantly from each other.

Hydroxyapatite ceramic as middle ear implant material: animal experimental results

Hydroxyapatite is the main constituent of the mineral matrix of bone. The behavior of porous and dense hydroxyapatite ceramic implants was studied in normal rat middle ears, after induced infection, and in an in vitro assay by light and electron microscopic techniques. All implants were integrated into the middle ears without signs of extrusion, and their mucosal coverings did not appear to differ fundamentally from those of normal ears. The porous hydroxyapatite became filled with fibrous tissue and bone that showed normal morphology, and there was direct bonding of the bone to the implants. Minor biodegradation was established for the porous implants. Hydroxyapatite did not affect cultured middle ear mucosa significantly in vitro. Induced infection failed to show any adverse effect on the behavior of the implants. These observations suggest that hydroxyapatite is very useful for reconstructive ear surgery.