Optimal graft thickness for different sizes of tympanic membrane perforation in cartilage myringoplasty: a finite element analysis.
OBJECTIVE
The purpose of this study was to determine, using finite element analysis, the optimal graft thickness for cartilage myringoplasty in patients with different sizes of tympanic membrane (TM) perforations.


METHODS
We developed a cartilage plate-TM-coupled model using high-resolution computed tomography and finite element analysis. The geometric models of the perforated TM were generated using Patran and ANSYS software.


METHODS
Three different sizes of TM perforations (15%, 55%, and 85%, representing small, medium, and large perforations, respectively) were created in the pars tensa. A cartilage plate was used to repair the eardrum perforation, and the new TM-cartilage coupled complex was loaded into our three-dimensional biomechanical model for analysis. The frequency-amplitude responses for different cartilage thicknesses were compared with those for natural TM.


RESULTS
Our results show that, first, in cases with 85% perforation, the frequency-amplitude responses that were most similar to natural TM at lower frequencies were for graft thicknesses of 0.2 mm and for 0.1 mm at higher frequencies. Second, in cases with 55% posterior perforation of the TM, assessment of the predicted vibration amplitude of different thicknesses of the cartilage plate showed that a cartilage plate of less than 0.2 mm had a frequency response function similar to that of a natural TM in umbo and stapes footplate displacement. Finally, for a central perforation involving 15% of the TM, a cartilage plate of less than 1.0 mm showed a frequency response function similar to that of TM in umbo and stapes-footplate displacement.


CONCLUSIONS
On the basis of our biomechanical analysis, the optimal thickness of a cartilage graft for myringoplasty appears to be 0.1 to 0.2 mm for medium and large TM perforations. For small perforations, a cartilage of less than 1.0 mm is a good compromise between mechanical stability and low acoustic transfer loss.
Lee
Chia-Fone
CF
Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
Chen
Jyh-Horng
JH
Chou
Yuan-Fang
YF
Hsu
Lee-Ping
LP
Chen
Peir-Rong
PR
Liu
Tien-Chen
TC
D001696:Biomechanical Phenomena; D002356:Cartilage / Q000637:transplantation*; D003198:Computer Simulation; D006801:Humans; D008962:Models, Theoretical; D009225:Myringoplasty / Q000379:methods*; D010036:Otolaryngology / Q000706:statistics & numerical data; D014182:Transplantation, Autologous; D018058:Tympanic Membrane Perforation / Q000601:surgery*