Inclusion Criteria and Follow-Up Duration Are Important When Evaluating the Outcomes of Inlay Butterfly Cartilage Tympanoplasty

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To the Editor: We would like to address the article entitled “Functional and Practical Outcomes of Inlay Butterfly Cartilage Tympanoplasty” by Kim et al. (1). This is a clinical case-control study on a large group of patients who underwent inlay butterfly cartilage tympanoplasty (IBCT) and underlying fascia graft tympanoplasty. The study is excellent. The authors compare the anatomical and functional success rates of IBCT and fascia graft tympanoplasty. They conclude that IBCT is comparable to the conventional underlay technique in terms of both anatomical and functional success rates. The simplicity of IBCT, the shorter operation time, and the rapid recovery, render IBCT an attractive surgical option. However, the study design and the inclusion criteria weaken the conclusions.
The descriptions of the study design are contradictory. The authors state in the Methods: “We reviewed outcomes of all patients who underwent tympanoplasty in our hospital between January 2011 and August 2012” and “Patients were divided into 2 groups: 1) the inlay butterfly cartilage tympanoplasty group (inlay group, n = 56) and 2) the conventional underlay tympanoplasty using temporalis muscle fascia group (underlay group, n = 56). The randomization was dependent on the period. Patient groups were determined according to the timing of surgery (1).” This is, thus, a retrospective study. Selection bias may be present because patients were not selected randomly. In addition, the decision to take a surgical approach was based on the timing of surgery and the agreement of the surgeon. Therefore, between-group patient distribution was not random. This inevitably means that the groups differ; such differences compromise the conclusions. The anatomical features of the tympanic membrane (size, shape, and location of the perforation) will have differed significantly between the groups despite the stated inclusion criteria.
The inclusion criteria, and factors influencing these criteria, are vague. The authors write, in the Methods: “the inclusion criteria of this study, which were as follows: 1) nonmarginal tympanic membrane perforations that could be seen entirely through a transcanal view, 2) no active ear infection with dried up status, and 3) demonstrated clear pneumatization of the mastoid bone on temporal bone computed tomographic (CT) scan. The exclusion criteria were as follows: 1) active otorrhea or severe myringitis, 2) need for exploration due to severe conductive hearing loss, 3) possible ossicular chain problem, and 4) possible cholesteatoma (1).” The authors do not describe the status of the eustachian tube or whether myringosclerotic plaques were evident. It is well known that eustachian tube dysfunction may result in eardrum atrophy and reperforation in patients undergoing underlay fascia graft tympanoplasty (2,3). However, if an adequately stiff cartilage resists deformation caused by pressure variations, thus preventing eardrum atrophy and reperforation after IBCT, any influence of the eustachian tube is minimal (4–6). In addition, myringosclerotic plaques may significantly affect tympanoplasty success rates. A previous study found that such plaques in the fibrous layer of the eardrum affected the blood supply and reduced the success rate of tympanoplasty if they were large. Migirov and Volkov (7) thought that appropriate freshening of perforation edges, with removal of sclerotic plaques, improved the success rate of tympanoplasty in patients with concomitant myringosclerosis. However, during IBCT, it is not necessary to remove contiguous myringosclerotic plaques. Indeed, stiff plaques are of benefit in that they afford a rigid interlocking surface for the graft (8,9). Nevertheless, we think that myringosclerotic plaques at the perforation edges render the graft weight excessive, causing tympanic membrane fibers to tear during IBCT (10,11). Recently, it has been suggested that the remnant tympanic membrane may not provide adequate graft support during IBCT if tympanosclerotic plaques are present at the perforation edges (10).

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