|Year : 2022 | Volume
| Issue : 2 | Page : 88-92
Morphological and Anthropometrical Features of Human Ear Ossicles: A 1-Year Cadaveric Observational Study
RS Mudhol, Sindhu Narahari, Rajesh Radhakrishna Havaldar
|Date of Submission||05-Apr-2021|
|Date of Decision||08-Feb-2022|
|Date of Acceptance||25-Mar-2022|
|Date of Web Publication||30-Jun-2022|
Source of Support: None, Conflict of Interest: None
Introduction: The ossicular chain formed by malleus, incus, and stapes, is considered an essential content of the middle ear and is responsible for the transmission of sound vibrations from the tympanic membrane to the oval window. This study aims to evaluate the morphology and anthropometry of ossicles from human cadavers. Material and Methods: This is a cross-sectional study conducted in the Department of Otorhinolaryngology and Head-and-Neck Surgery of KAHER's JN Medical College, Belagavi, for 1 year. Twenty fresh cadavers (40 sets of ossicles) were dissected using zero-degree endoscope. With gentle manipulation, ossicles were removed to study anthropometry and morphology of each middle ear bone using osseous sizer. Results: Among the three bones, based on mean measurements, the heaviest bone was incus (19.08 mg), followed by malleus (16.65 mg) and the lightest bone was stapes (2.28 mg). The longest bone among the three bones was malleus (7.18 mm), followed by incus (5.71 mm) and stapes (2.70 mm). Malleus showed variations in the distal ends, incus showed variation in the lenticular process and the obturator foramen of stapes had different shapes. Discussion and Conclusion: With a rapid rise in the demand for ossiculoplasty in India, knowledge of morphology and possible anthropometric variation existing in Indian subjects is needed to add up to a better understanding of middle ear dynamics.
Keywords: Incus, malleus, morphology, ossicles, ossiculoplasty, stapes
|How to cite this article:|
Mudhol R S, Narahari S, Havaldar RR. Morphological and Anthropometrical Features of Human Ear Ossicles: A 1-Year Cadaveric Observational Study. J Anat Soc India 2022;71:88-92
|How to cite this URL:|
Mudhol R S, Narahari S, Havaldar RR. Morphological and Anthropometrical Features of Human Ear Ossicles: A 1-Year Cadaveric Observational Study. J Anat Soc India [serial online] 2022 [cited 2022 Aug 11];71:88-92. Available from: https://www.jasi.org.in/text.asp?2022/71/2/88/349464
| Introduction|| |
The special function of hearing is carried out by a small organ like ear and it only makes it more interesting that inside this miniature ear structure, there are three minor bones- malleus(hammer), incus(anvil) and stapes(stirrup) tactically positioned to form a semi rigid structure acting like a bony cable for transmitting sound in the middle ear. The malleus is the first bone and is attached to the eardrum and the stirrup or the stapes is attached to the oval window. The incus is bridged between them, and articulates with both the bones on its either side. This arrangement, along with the ventilation, is the driving force of middle ear mechanics. Discontinuity or fixity of the ossicular chain leads to conductive hearing loss. An eroded incudo-stapedial joint, an absent incus or an absent incus and stapes superstructure together leads to ossicular discontinuity in increasing order of frequency of hearing loss. To restore appropriate sound transmission, ossicular chain reconstruction has to be performed. Several factors have to be considered when selecting a material to use for ossicular reconstruction. This includes ease of availability, stiffness, stability, biocompatibility, and cost-effectiveness. According to Mudhol et al., autografts were preferred for ossicular reconstruction because they had a very low extrusion rate. However, with the development of newer bioactive synthetic prosthesis and moldable materials, the extrusion rate has become low. Hence, we can expect biosynthetic materials to be more popular. To study the morphology and anthropometry of middle ear ossicles during surgery is difficult. Studying them on cadavers gives a better understanding about its variations and dimensions. The knowledge of these ossicle dimensions, their variations, and their morphometric data will help the otologists during reconstructive surgery and also aid in designing better prosthesis.
This study aims to evaluate the morphology and anthropometry of ossicles from human cadavers.
| Material and Methods|| |
This is a cross-sectional study carried out over a period of 1 year (January 2019 to December 2019) from available cadavers for dissection during the study period in J. N. Medical College, Belagavi. All cadavers subjected to dissection were included except temporal bones with any evidence of previous surgeries and those bones with history or evidence of trauma. Each cadaver was numbered categorically and postauricular (Wilde's) incision was taken. Using the instruments shown in [Figure 1], dissection was carried out. Skin and subcutaneous tissue till the periosteal layer was dissected and the external auditory canal was entered. The tympanic membrane was meticulously dissected from the malleus. All three ossicles were visualized using a zero-degree endoscope and their muscle attachments were separated. With gentle manipulation, ossicles were removed. All three ossicles were washed with the hydrogen peroxide solution and each set of ossicles was stored in a clean box after labeling it. Each ossicle was weighed using an Mettler Toledo™ digital analytical balance with 0.1 mg readability electronic weighing machine and its measurements were taken using an osseous sizer. Photographs were taken from a fixed distance using the NIKONTM D3500 DSLR camera. This study was approved by the Institutional Ethics Committee on human subjects research of Jawaharlal Nehru Medical College, Belagavi (MDC/DOME/51) on 24/11/18.
All measurements were noted and their mean, median, and standard deviation were calculated. Statistical analysis was done by Chi-square test, Paired t-test, Independent t-test and Karl Pearson's correlation coefficient method using Statistical Package for Social Sciences version 24 (SPSSTM 24). Developed on 2016 March, IBM Developer by Norman H Nie, Dale H Bent, C. Hadlai Hull Chicago.
| Results|| |
A total of 20 cadavers (40 sets of ossicles) were evaluated, as shown in [Figure 2]. About 70% were male and 30% were female cadavers.
The weight ranged from 12 mg to 21 mg with an average of 16.65 mg. The total length of the malleus ranged from 6 mm to 9 mm with an average of 7.19 mm. The length of the manubrium ranged from 2.5 mm to 5 mm with an average of 4.21 mm. The maximum width of the head ranged from 1.5 mm to 4.5 mm and an average of 2.44 mm. There is no statistical difference between the right and left sides. Out of 40 sets of ossicles, morphologically malleus showed very less variations except that the distal end of 13 bones was straight (30%) and 27 bones were curved (70%) as shown in [Figure 3]. There was no statistical difference noted between the right and left sides [Table 1].
|Figure 3: (a) Straight and curved distal end of manubrium. (b) Fully developed lenticular process and underdeveloped/necrosed lenticular process. (c) Triangular shaped and oval shaped obturator foramen|
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The weight of the incus ranged from 12 mg to 28 mg with an average of 19.8 mg. The total length of the incus ranged from 4.40 mm to 7 mm with an average of 6.74 mm. The total width of the body ranged from 3 mm to 5.50 mm with an average of 3.80 mm. The length of the long process ranged from 2.50 mm to 4.50 mm with an average of 3.80 mm. Out of 40 sets of ossicles, the morphology of the incus showed variation which could be developmental or maybe necrosis of the lenticular process. In 28 (70%) bones, a fully developed lenticular process was seen and in 12 (30%) bones an underdeveloped or necrosis lenticular process was observed [Figure 3]. There was no statistical difference noted between the right and left sides [Table 2].
The weight ranged from 1.50 mg to 3 mg with an average of 2.29 mg [Table 3]. The total height of the stapes ranged from 2 mm to 3.5 mm with an average of 2.7 mm. The length of the footplate ranged from 2 mm to 3 mm with an average of 2.42 mm. The width of the footplate ranged from 1 mm to 2 mm with an average of 1.26 mm. The length of the anterior crus ranged from 1 mm to 2.5 mm with an average of 1.66 mm. The length of the posterior crus ranged from 1.5 mm to 2.5 mm with an average of 2.08 mm. The width of the head ranged from 0.5 mm to 1.5 mm and an average of 1 mm. Out of 40 sets of ossicles, we found 18 (45%) bones having a triangular shaped and around 22 (55%) bones having an oval-shaped obturator foramen, as shown in [Figure 3].
Among all three bones, the heaviest bone was incus (19.08 mg), followed by malleus (16.65 mg) and the lightest bone was stapes (2.28 mg). The longest bone among the three was malleus (7.18 mm), followed by incus (5.71 mm) and last being stapes (2.70 mm).
| Discussion|| |
The human auditory system is a remarkable engineering design that is made up of complex geometries. Although the knowledge of the ossicular chain has been there for around 500 years, there are only a small number of morphometrical studies done on ear ossicles. Quam and Rak provided the foremost set of well-defined measurements by determining the X- and Y-axis of the bone following which all the distances and angles were calculated. However, Hallgrimsson et al. gave one of the most efficient and accurate methods by using computed tomography which provided the measurements of ossicles.
A comparison of morphometry of malleus in our study with other studies is shown in [Table 4]. The weight in our study ranged from 12 to 21 mg with an average of 16.65 mg which was slightly low compared to other studies. The length of malleus in our study ranged from 6 to 9 mm with an average of 7.19 mm which is almost similar to other studies. A comparison of morphometry of incus with other studies is shown in [Table 5]. The length of incus in the present study is almost similar to other studies. The width of the incus is lesser compared to other studies. The mean weight of incus in our study was found to be 19.8 mg which was lesser than that reported by Jyoti and Shama. in India (23.8 mg). This suggests that considerable variations in anthropometry and morphology exist in the same country and hence, designing appropriate prosthesis is a challenge as there are no generalized fixed measurements. A comparison of morphometry of stapes is shown in [Table 6]. According to David Victor et al, the mean total height of stapes is 3.44 mm. The height of the stapes in our study is lesser compared to other studies; the length and width of the footplate are similar in measurements as compared to other studies. In the present study, out of the 40 stapes specimens, the length of the anterior and posterior crus was equal in five specimens and in all other specimens, the posterior crus was longer than the anterior crus. Differences in the shape of foramen obturatum ranging from circular, oval, triangular to even tunnel shaped are mentioned in different studies., Sarrat et al., distinguished numerous shapes of obturator foramen of stapes as round, oval, or angled. In our study, we observed triangular-shaped foramen in 45% of the bones and oval shaped in 55%. Ossiculoplasty is performed by a large number of surgeons using a wide variety of prosthesis materials. According to a study done by Mudhol et al., there was significant betterment in hearing in people with ossiculoplasty done using autologous incus as compared to titanium prosthesis. Surgeons operating in the middle ear should be aware of the dimensions and the possible variations that can be present in the region to perform the needed and anticipated corrections without causing any instability to the structural integrity in middle ear dynamics. Reckoning this, ossicles are of significant importance in reconstructive efforts and a careful assessment of this region should be carried out during ossiculoplasty.
Since it is not practical to assess all the finer details of these structures in live patients, it becomes essential to assess, interpret and analyze with an alternative, the only feasible possibility being cadaveric studies. Till date, very few Indian studies have been done on ossicles. Most of them were done using various digital software, graph sheets, or Vernier calipers for measuring ossicles. These measurements may be associated with errors. In this study, an attempt has been made for the first time to use an osseous sizer, a more accurate tool for the assessment of ossicular morphometry.
| Conclusion|| |
With a rapid rise in demand for ossiculoplasty in our country, this study assesses the possible morphology and anthropometric variation that can exist in Indian cadavers with an intention to add up to the present understanding of middle ear dynamics. With considerable inter- and intra-regional variations in the morphology and anthropometry, we also expect that the effort of this study will motivate several others to carry out temporal bone dissections with an intention to supplement the present understanding with additional information on ossicles and also be conserved in ossicular banks by practicing appropriate safeguarding and sterilization approaches for forthcoming use as homograft in ossiculoplasty. These collected ossicles may be used to substitute eroded middle ear ossicles as an alternative to the commercially available prosthesis.
Approval was obtained from the Ethics Committee of KLE Academy of Higher Education and Research. The procedures used in this study adhere to the tenets of the Declaration of Helsinki.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]