Homograft microlathed femur prosthesis in stapedectomy.

Abstract

The use of homografts in ossiculoplasty has been well documented in the literature. In the early 1980s, nonossicular homograft otic capsule bone was used as a prosthetic material in stapedectomy. We began using homograft femur as a prosthetic material in the early 1990s. In this article, we report the results of a retrospective study of the use of homograft femur prostheses. A series of 300 stapedectomies was performed between Aug. 24, 1992, and Jan. 20, 2000. Total footplate removal with preservation of the posterior crus was our procedure of choice. However, in 116 of these cases, the posterior crus could not be used, and a homograft femur prosthesis was substituted. For these prostheses, all homograft femurs were obtained from the American Red Cross. All prostheses were prepared in the bone laboratory and stored in the bone bank until needed. After an adequate period of follow-up, we tabulated our results. We found that in 89 of 113 cases (78.8%) available for follow-up, the air-bone gap was completely clo sed. In addition, the air-bone gap was closed to within 5 dB in 11 patients (9.7%) and closed to within 10 dB in five patients (4.4%). In all, 105 of the 113 homograftfemurprostheticprocedures (92.9%) resulted in a successful outcome.

Introduction

Historically, homograft stapes and the other two ossicles have been tried in the course of performing stapedectomy. (1-12) Hall and Rytzner first reported using an autograft ossicle as a replacement in 1957. (1) Until the 1990s, homografts were not used for stapes replacement for several reasons, and plastic, (13) titanium wire, (14,15) ethylene tubing, (16) and stainless steel (17-19) were in vogue. But unlike the incus replacement prosthesis, which was fitted to an ossicle on both ends, the stapes prosthesis did not have another ossicle to secure it in the oval window.

In 1990, one of the authors (M.M.) first reported using small blocks of homograft temporal bone (the otic capsule) as a prosthetic material. (20) This was the first series of homograft prostheses to be used in primary stapedectomy. The otic capsule was chosen because, like the ossicles, it is made up of histologically endochondrial bone. Therefore, the otic capsule is more like ossicular bone than any other bone in the body. Ossicles and the otic capsule are not remodeled and replaced by periosteal haversian bone as occurs elsewhere in the skeleton.

In 1992, because of the ease of procurement, we began using periosteal bone (femur) as a replacement source in all ossiculoplasties, including tympanoplasties, tympanomastoidectomies, and stapedectomies. At about the same time, we began using the microlathing technique, which has drastically reduced the amount of time spent in the bone laboratory manufacturing ossicles and which has decreased the cost of ossiculoplasty. (21) In this article, we report the results of our use of homograft femur prostheses in stapedectomy.

Materials and methods

We retrospectively reviewed the outcomes of a series of 300 primary stapedectomies (table 1). Most were performed with local anesthesia and intravenous sedation. In all cases, the preservation of the posterior crus was attempted. (22) Preservation was successful in 161 cases (53.7%), a stainless-steel piston was used in 13 cases (4.3%), and a House wire prosthesis was used in 10 (3.3%).

In the remaining 116 cases (38.7%), a sculpted homograft femur prosthesis was used. In these ears, the remainder of the stapes was removed and a total or near-total footplate removal was performed. A perichondrial graft was obtained from the tragus and placed over the oval window. A femur prosthesis was then placed directly on top of the perichondrial graft in the oval window and then fitted underneath the lenticular process of the incus. Our protocol was to obtain audiologic data at 6 weeks, 3 months, 6 months, and 1 year postoperatively.

The entire process of "manufacturing" the stapes prosthesis takes place in the bone laboratory. The femur arrives from the American Red Cross bone bank packed in dry ice. The bone is removed and stored in formaldehyde (10%). It is then broken down into smaller blocks that are stored in alcohol until the sculpting process is undertaken. From these small blocks, the microlathing technique is used to sculpt the ossicles. (21) The ossicles are then carefully measured, labeled, and transferred to the bone bank. This reception of the donor bone--including the manufacturing of the bone and the storage and fixing material--is described elsewhere in the literature. (21)

Results

The first femur transplant was performed on Aug. 24, 1992, and the 300th was done on Jan. 20, 2000. (We did not include in this study those homograft femur transplants that were placed in revision cases.) We attempted to check each patient audiologically at 6 weeks, 3 months, 6 months, and 1 year postoperatively. The results presented in this article represent our audiometric findings at the 1-year follow-up unless they were not available, in which case the 6-month audiogram was used. In a few cases, results were assessed 15 or 18 months postoperatively.

Data were available on 113 of the 116 patients who received a femur implant (table 2). The other three patients were lost to follow-up after their 1-week postoperative check-up; two of these three patients had previously undergone successful stapedectomy surgery in the opposite ear, and the third lived out of state.

Among the 113 cases, the air-bone gap had completely closed in 89 (78.8%). The gap had closed to within 5 dB in another 11 patients (9.7%) and to within 10 dB in five (4.4%). In all, 105 patients (92.9%) who received a homograft prosthesis had their air-bone gaps closed to within 10 dB, and their outcomes were thus judged to be successful. In one other patient, the air-bone gap closed to within 15 dB.

Conductive loss remained in four patients (3.5%), three of whom subsequently underwent revision surgery and received another homograft femur prosthesis. All three of these patients were found to have had a misaligned prosthesis attached to the edge of the oval window. In two of these patients, revision surgery resulted in a complete closure of the air-bone gap. In the third patient, the air-bone gap had closed at 6 weeks, but at 6 months the conductive loss had returned. This patient did not return for possible surgical correction. We believe that adhesions again pulled the prosthesis off the center of the oval window in this patient.

There was one significant cochlear loss, which represented less than 1% of the 113 patients. This patient's pure tones had improved postoperatively by approximately 10 dB, but the discrimination score fell from 88 to 12%. Fortunately, this patient had earlier undergone a successful stapedectomy in the opposite ear.

Two other patients experienced minor cochlear losses, as detected by bone conduction tests. One patient exhibited an average drop of 15 dB in the three speech frequencies (500, 1,000, and 2,000 Hz), and the other had an average decline of 22 dB. Both experienced minimal improvement in their air-bone gaps but retained a mild to moderate conductive loss. Both maintained good discrimination scores (>88%) in the operated ear, and both considered themselves improved. No postoperative infections occurred in this series, and no facial nerve problems were encountered.

Discussion

Ossiculoplasty techniques, like other forms of middle ear surgery, vary with the otologist. Add to this the wide range of materials used, the variations in instrumentation, and the skills and abilities of individual surgeons, and it is easy to see why there is a lack of uniformity in most procedures. This is certainly true with stapedectomy.

Surgical approaches in stapedectomy can be classified into two broad groups: the small-window fenestra technique and the total or near-total removal of the footplate technique. We have consistently used the total footplate removal technique except in cases of obliterative footplate otosclerosis. The choice of materials is another issue on which surgeons differ widely, not only in stapedectomy but in other types of ossicular replacements, as well. In our practice, homograft bone has been used since the 1960s for most ossiculoplasties. For years we have been proponents of the use of bone in stapedectomy, using the preservation of the posterior crus technique.

The desire to avoid artificial materials in favor of a more physiologic substance such as bone stimulated the development of the femur prosthesis for use as a stapes prosthesis when the posterior crus could not be preserved. First came the development of homograft temporal bone prostheses fashioned from homograft otic capsular bone. (20) Success with this technique led to the development of the femur graft, which simplified the technical aspects of prosthesis production.

The microlathing method of producing homograft ossicles further advanced the use of femur grafts. (21) One cadaver femur can be broken down into multiple ossicles, thus significantly saving on expense. All bone work is performed in the laboratory, saving surgical time. A technician can easily be trained to manufacture the ossicles, further saving the surgeon's time. The technician at our institute spends an average of 15 minutes per ossicle in the manufacturing process.

It appears that femur prostheses, like other bone grafts in ossiculoplasty, will last for the life of the patient. This has proved to be the case in homografts manufactured from otic capsule bone, as many of these prostheses were implanted in the early 1980s. In the series described here, 81 of the femur prostheses have been in place for more than 5 years without showing any evidence of resorption. All four surgical failures (conductive losses) reported here occurred within 6 months of implantation and were thus not related to ossicular resorption. At revision surgery, three of the four grafts were found to be seated on the side of the oval window.

Homograft stapes have been used to bypass stapedial defects in chronic ear disease and when the stapes was inadvertently fractured during a stapes procedure. This article is the first report of a series of patients who received homograft periosteal bone (femur) in primary stapedectomy. Femur bone as a stapes replacement appears to behave in a manner similar to that of other homograft bone in that there does not appear to be a loss of function or resorption, and in our series there have been no extrusions. Our use of this prosthesis has produced good audiologic results that have thus far remained stable in the short and intermediate periods.

Acknowledgments

The authors are indebted to electronics technician John Rains, AA, for his invaluable assistance in the development of the microlathing technique and to Anita Montgomery, BA, for her assistance in the preparation of this manuscript.

Table 1.

Type of repair used in 300 primary stapedectomy patients

Type of repair                n (%)

Preservation of the         161 (53.7)
 posterior crus
Homograft femur prosthesis  116 (38.7)
Stainless-steel piston       13 (4.3)
House wire prosthesis        10 (3.3)
Table 2.

Results with femur prostheses in 113 patients (*)

Result                                 n (%)

Air-bone gap closed or overclosed    89 (78.8)
                                                100 (88.5)
Air-bone gap closed to within 5 dB   11 (9.7)               105 (92.9)
Air-bone gap closed to within 10 dB   5 (4.4)
Air-bone gap closed to within 15 dB   1 (0.9)
Minor cochlear loss                   2 (1.8)
Major cochlear loss                   1 (0.9)
Conductive failure                    4 (3.5)

(*)Three of the 116 patients were lost to follow-up and excluded from
the study.

References

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From the Hough Ear Institute and Otologic Medical Clinic, Oklahoma City.

Reprint requests: Michael McGee. MD, Hough Ear Institute, 3400 N.W. 56th St., Oklahoma City, OK 73112. Phone: [phone]; fax: [phone]; e-mail: [e-mail]

Originally presented at the Middle Section meeting of the Triological Society; Chicago; Jan. 20, 2001.