17 Ossicular Reconstruction
Ossicular reconstruction techniques have their historical origin in techniques developed by Wullstein and Zollner in the 1950s. Since this time, reconstruction of the middle ear sound transformer mechanism has continued to evolve. Improvements in material and refinements in technique have occurred with time, and yet consistent complete closure of the airbone gap remains elusive. This chapter describes the historical development of prosthetic material and prosthesis selection, patient selection and evaluation, surgical considerations, and a brief overview of surgical technique. While published surgical results give one an idea of what is possible, each surgeon should rely on their own results to counsel their patients on expected outcomes. Thus, this chapter focuses on recommendations that will optimize hearing outcomes in ossicular reconstruction.
Historical Perspective with a Focus on Prosthetic Materials and Prosthesis Selection
Materials used for the reconstruction of the ossicular chain can be autografts, homografts, or allografts. Autografts are either bone or cartilage. Autograft ossicles are removed from the patient and shaped to be used as interposition grafts. The incus interposition graft is the most common. Homograft ossicles and en block tympanic membranes with attached ossicles are primarily of historical interest. The advantages of using autografts include immediate availability, obvious biocompatibility, low cost, and low extrusion rate. The primary disadvantage is the time and skill required to shape autografts appropriately. Other disadvantages include concerns about possible disease recurrence when used in patients with cholesteatoma, the potential for fixation to adjacent bone of the promontory or canal wall. Historically, homografts have been used to reconstruct the ossicular chain.1 Rejection is rare with the use of homograft ossicles. The use of homograft ossicles has declined because of the fear of potential of transmitting various diseases such as HIV, hepatitis, or Creutzfeldt-Jakob disease.
The concept of using alloplastic material for ossicular reconstruction is not new. In 1952, Wullstein used an oval strut of vinyl acrylic “palavit” as an acoustic transmitter between the mobile footplate and the tympanic membrane graft.2 However, Wullstein abandoned the use of this material because of poor results. Since this time, the use of allografts has become increasingly popular. After the success of polyethylene struts in early stapedectomy surgery, Austin and Shea used polyethylene tubing to reconstruct the ossicular chain in tympanoplasties.3,4 Other contemporaries noted both initial success and failures because of inflammatory reactions and extrusion.5–7 In 1962, Austin reported on the use of polytetrafluoroethylene (PTFE) tubing as a hollow columella in ossiculoplasty.3 Greater compatibility with PTFE over polyethylene was noted. Subsequently in 1969, Palva reported on the use of metallic implants in chronic otitis media.8 While both materials were associated with favorable outcomes in stapes surgery, the outcomes with ossicular chain reconstruction in chronic ear surgery was less successful. In the mid-1960s, the use of solid plastic and metallic materials for ossicular reconstruction waned. Shea reignited the interest in alloplastic materials with the introduction of proplast (a composite of PTFE and vitreous carbon) and plastipore (semi-soft sponge of high-density polyethylene) in 1974 and 1976.9,10 Both materials contain pores that make up 70 to 90% of their volumes. Shea abandoned proplast in favor of plastipore (Fig. 17.1). Since that time, several authors have reviewed their experience with plastipore prostheses. It was initially felt that those prosthesis were well tolerated and would not extrude through a tympanic membrane graft. Sheehy emphasized the need for a piece of the cartilage between the graft and the top of the prosthesis to prevent extrusion (John House, Personal Communication, 1976). This experience is adequately reviewed by Yung and is not discussed here.11
The use of hydroxyapatite in ossicular reconstruction was first reported in 1981 by Grote et al.12 He felt that the advantages of hydroxyapatite included its low weight and rigid nature, the potential for integration with bone, its biocompatibility allowing for placement in direct contact with the tympanic membrane, and low extrusion rates. House and Teufert noted that when the cartilage was not used, the extrusion rate doubled from 3.7 to 7.9%.13 The disadvantages include its brittle nature, difficulty in sculpting or modifying, and its large mass creating high-input impedance. Since its introduction, more user-friendly hydroxyapatite composite prostheses have been introduced by using a hydroxyapatite head plate and a malleable shaft composed of a variety of materials, including Plastipore, Polycel (thermal-fused Plastipore), PTFE, FLEX HA (a mixture of hydroxyapatite and silastic), and HAPEX (hydroxyapatite-reinforced polyethylene composites).
Finally, titanium for ossicular reconstruction was first reported in 1993 and later studied by Dalchow et al.14 The advantages include low weight, high rigidity, adjustable length, corrosion resistance, low sound damping and impedance, and biocompatibility. Despite their biocompatibility, titanium prostheses in general do require the placement of the cartilage between the prosthesis and the tympanic membrane. The use of titanium prostheses has increased in recent years. A variety of titanium prostheses are currently available (Fig. 17.2A to C). Finally, bone cements composed of hydroxyapatite and phosphate have been used to reconstruct limited distal incus defects and to fix prostheses, such as a loose stapes prosthesis wire to the incus.
Figure 17.1 Plastipore ossicular prosthesis.
Other materials that have been used for brief periods of time include gold, bioglass, and en block homograft tympanic membrane with attached malleus and incus.
Patient Selection and Evaluation
Ossicular chain reconstruction maybe necessary when there is disruption or malformation of the ossicular chain owing to infection, trauma, or congenital abnormality. There are many factors to consider in determining the best option for ossicular reconstruction.
Otoscopy
In the presence of a significant conductive hearing loss, one can assume that there is ossicular involvement. The use of the office microscope improves the ability to evaluate the ear. In cases of chronic ear disease, ossicular discontinuity may be diagnosed through a perforation or be visualized through severe atelectasis of the tympanic membrane while incus erosion is commonly the cause of conductive hearing loss. Extensive tympanosclerosis may cause ossicular fixation and many times can be observed on otoscopy. Cholesteatoma involvement of the ossicles can usually be noted on examination. However, the exact extent of involvement may require a high-resolution, thin-section computed tomography (CT) scan or an intraoperative evaluation. Severe eustachian tube dysfunction may require concomitant placement of a tympanostomy tube (Fig. 17.3) or preclude ossicular reconstruction in some cases. A dry ear is preferable before ossicular reconstruction; however, a draining ear does not preclude repair of the tympanic membrane and ossicular reconstruction. Conductive hearing loss in a patient with an intact, normal appearing tympanic membrane would suggest possible ossicular dislocation from head trauma, erosion of the distal incus, or otosclerosis. These conditions maybe elicited on the patient’s history. Careful questioning as to onset, progression, and a family history is important. If the patient complains of hypersensitivity to sound, dizziness with some sounds, fullness in the ear in the presence of some sounds, and has a mild low-frequency conductive hearing loss, one would suspect a dehiscence of the superior semicircular canal. Tuning forks are an important component of the physical examination. They are used to confirm the conductive nature of the hearing loss.
The audiologic examination includes pure tone air and bone conduction with masking, speech reception thresholds, speech discrimination, and possibly tympanometry. An airbone gap greater than 25 dB suggests ossicular involvement. Audiometry should always be confirmed with tuning fork tests. The Weber will lateralize to the ear with the greater conductive hearing loss; the Rinne will reverse with the 512-Hz fork when the airbone gap is greater than 15 dB, and the 1024 will reverse when the gap is greater than 25 dB. Consideration of contralateral ear status is essential to identify the situation of an only hearing or better hearing ear. Imaging studies are rarely necessary to evaluate the middle ear and ossicles; however, thin-section CT may provide useful information in the case of extensive cholesteatoma, malleus fixation (Fig. 17.4), incus dislocation or erosion, otosclerosis, suspected lateral canal fistula, superior canal dehiscence, or suspected congenital ossicular abnormalities.
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