The Goat Model for Exclusive Two Handed Endoscopic Middle Ear Surgery Training: A Novel Technique

Abstract

With the popularity of exclusive transcanal endoscopic ear surgery, the need for a suitable and affordable surgical training model has grown. To develop an ex vivo animal model for exclusive endoscopic ear surgery. In an experimental study, we studied goat middle ear anatomy in 8 specimens to assess the similarity with the human middle ear as a model for two handed endoscopic ear surgery with endoscope holders. After confirming its suitability, we have developed a surgical training program for grommet insertion, canaloplasty, myringoplasty, butterfly tympanoplasty, ossiculoplasty, atticotomy. The goat model is suitable for two handed endoscopic ear surgery using endoscope holder. We describe a novel, exclusively two handed endoscopic approach in an ex vivo animal model for middle ear surgery. The proposed surgical program will guide the trainee endoscopic ear surgeon for a step by step through the main otologic procedures to enhance his or her surgical skills.

Introduction

‘’To innovate does not necessarily mean to expand, very often it means to only simplify’’

- M. Russell Ballard

Minimally Invasive Surgical (MIS) procedure is less invasive than open surgery used for the same indication. It usually involves the use of endoscope allowing manipulation of instruments with indirect observation of the surgical field carried out through small opening onto the skin for approach into the concerned part. MIS is more difficult, precise and challenging from the surgeon’s perspective requiring technical as well as cognitive skill. MIS training requires training methods which include cadaveric studies, animal models or mannequins. Temporal bone has a very complex anatomy and middle ear surgery forms one of the most intricate and challenging surgeries. Till now all the well-established techniques in ear surgery have evolved using the microscope. However since the last decade, endoscopes have been introduced into ear surgery. Endoscopic ear surgery is an evolving science in the field of otology and provides minimally invasive transcanal approach to the middle ear. Though endoscopic techniques are similar to the standard well known microscopic ear surgery techniques, it differs in its approach to the middle ear and adds a new perspectives and dimensions to the understanding of middle ear anatomy and pathology. The only disadvantage of endoscopic ear surgeries is that it is single handed surgical technique in which the non-dominant left hand of the surgeon is utilized for holding and manipulating the endoscope. We have developed endoscope holders (EndoHold¹-Patent Application No. 2313-Mum-2013 and Patent Application No. 3300-Mum-2013) [1–4] to solve the single handed difficulties.

Cadaveric temporal bone dissection courses are conducted all over the world to train aspiring ear surgeons. These enable the trainees to experience, enhance and improve their surgical skills to perform delicate procedures. It provides perception of handling live tissue due to superior tactile feel, helps with instrumentation dexterity, builds up the confidence to perform and most importantly develops the hand-eye-monitor coordination.

Surgical simulation has become a valuable and financially attractive part of surgical education providing the clinician with competency and patient’s safety [5]. Fresh human cadaveric specimens are the standard of good surgical training, but the availability of such specimens is not only limited owing to high costs and strict ethical regulations but may also lead to many illegal activities for procurement of the same [6]. Formalin preserved temporal bone specimens are routinely used for dissection purposes but not only is the tissue quality poor, the strong fumes make the surgical exercise cumbersome. Digital trainers and virtual reality simulators are available but lack the live tissue feel and are expensive. These disadvantages do not exist in animal specimens.

The exclusive transcanal endoscopic approach to surgery of the middle ear was introduced and has developed rapidly in the past several decades [7].

The animal model represents a suitable, inexpensive, and reliable alternative to human cadaveric specimens [8]. The safety of the sheep model has been described for many procedures in head and neck surgery [9]. The sheep model has been validated for training of stapes surgery [10, 11], for implantable devices [12], and for the round window insertion of cochlear implants [13]. Comparative anatomic studies identified similarities and differences between the sheep and the human middle ear [14]. The suitability of the sheep model was confirmed by comparison of radiologic studies [15]. The lamb model was found to be suitable for training and developing surgical skills in an education program for otologic surgeons.

In the past, the use of goat model for surgical training in two handed endoscopic middle ear surgery has never been described in the literature, as per our knowledge. This study is the first of its kind and would stand out to be an efficient, cost effective and simple way of training future endoscopic ear surgeons so that the steep learning curve and long period of learning can be effectively dealt with.

This study compares the human and the goat endoscopic ear anatomy and aims to propose this training model to practice various surgical exercises like harvestation of tragal and conchal cartilage graft, myringotomy and grommet insertion, cartilage butterfly tympanoplasty, ossiculoplasty, stapes surgery and facial nerve decompression.

Materials and methods

The cadaveric Dissection setup for two handed endoscopic middle ear surgery consisted of:

1. Fresh goat heads fixed on the temporal bone holder.

   Specimens were obtained at the local butcher from animals intended for the sale of their meat. All skulls from the slaughterhouse were ‘’by-products’’ and no animal was killed for research purposes.

2. Endoscope (Karl Storz) zero degree, 4 mm length.

3. Three-charge-coupled device camera system (stryker).

4. A high-resolution monitor (Karl Storz).

5. ENDOSCOPE HOLDER- JUSTTACH [16] (details with patent number).

6. Micro ear instruments with otologic drill and a suction machine.

7. SLICE !t CARTILAGE SLICER [17].

The endoscope- camera assembly was fixed on to the endoholder making it a TWO HANDED TECHNIQUE (Fig. 1). The advantage of the two handed technique is that both the hands are free for surgical manipulation as the endoscope is mounted on the endoscope holder. The suction is held in the left hand and the micro ear instruments are held in the right hand similar to the microscopic ear surgery. The endoscope allows the panoramic view of the goat middle ear anatomy and the endoscope holder allows the two handed benefit. The continuous suction and irrigation allows cleaning as well as cooling of the structures.

Fig. 1.

Endoscope holder setup

The Goat Model for exclusive two handed endoscopic middle ear dissection

After thorough anatomic evaluation, we created a step-by-step guide to the exclusive two handed endoscopic middle ear dissection of the goat ear by performing different surgical exercises in otologic surgery.

(1) POSITION AND PREPARATION: (Figs. 1, 2).

Fig. 2.

Goat head mounted on temporal bone holder

The Goat head was fixed on to a temporal bone holder and placed over a tray. The endoscope was attached to the camera and fixed with an endo holder.

(2) HARVESTING AND PREPARATION OF CARTILAGE GRAFT.

The floppy pinna of the goat is overturned and clamped on the adjacent facial soft tissue using artery forceps .The skin on this side of the pinna resembles the human pinna skin and the natural fold hence developed resembles the tragus.

Due to the striking similarity of goat ear cartilage to human pinna cartilage, the following surgical exercises can be practiced on this model.

1. Harvesting and preparation of cartilage graft.

2. Slicing of cartilage for sliced shield cartilage tympanoplasty.

3. Preparing different types of cartilage grafts - mosaics, palisades, struts for ossiculoplasty.

(3) CANALAPLASTY

The bony EAC of the goat is narrow and needs widening using a drill with appropriate sized burr for endoscopic access and proper visualisation of the canal.

(4) MYRINGOTOMY AND GROMMET INSERTION (Fig. 3)

Fig. 3.

a and b Tympanic membrane and myringotomy

This can be practiced by using a myringotome to create a perforation followed by inserting and the grommet.

(5) BUTTERFLY CARTILAGE TYMPANOPLASTY (Figs. 4, 5a, b).

Fig. 4.

Cartilage preparation on slice it

Fig. 5.

a and b Cartilage butterfly

The harvested cartilage is trimmed to the appropriate size using the SLICE IT cartilage slicer keeping the perichondrium intact on both the sides for faster graft vascularization and uptake. Now, using a 15 no. surgical blade/regular slicing blade a groove is created all along the rim of the cartilage so that it resembles the wings of the butterfly. Next, the graft is inserted into the perforation such that the groove rests over the margin of the perforation while the flanges rest on either side.

(6) CREATION AND ELEVATION OF THE TYMPANO-MEATAL FLAP (Fig. 6).

Fig. 6.

Tympanomeatal flap elevation

The most lateral and inferior part of the canal also may be enlarged to allow better maneuvering of the instruments. The more experienced the trainee becomes, the less enlargement of the external auditory canal is necessary. During this part of the dissection, the handling of the endoscope concomitant with the instrument in the external auditory canal may be difficult for a novice endoscopic ear surgeon but will improve with growing expertise.

One principal quality of the otologic surgeon can be trained during this phase is patience. The entire canal wall skin (TMF elevated and removed). After proper dissection of the pars flaccida, the ossicles are identified and dissected. During the dissection into the middle ear, two bony bridges were identified .The first bridge connecting the anterior wall of the canal with the malleus anterior process and second bridge connecting the short process of incus to the posterior canal wall such that both malleus and incus appeared to be present as a sturdy ossicular unit.

(7) ENDOSCOPIC CARTILAGE INTERPOSITION OSSICULOPLASTY.

First, the incudostapedial joint is identified and disarticulated by a hook, the posterior ligaments of the incus are detached from the epitympanic wall, and the incudomalleolar articulation is mobilized with gentle movements. The incus is then removed from the tympanic cavity. The harvested cartilage was used to create a rectangular block with a small Hole to fit into the head of the stapes. Another cartilage vertical strut 6 mm × 2 mm was fashioned and placed between them.

(8) ATTICOTOMY AND ATTIC RECONSTRUCTION (Fig. 7a–c)

Fig. 7.

a–c Trancanal atticotomy

Reconstruction techniques can be practiced by placing the cartilage pieces.

(9) FACIAL NERVE DECOMPRESSION (Fig. 8).

Fig. 8.

Facial nerve

The facial nerve was found to be covered by a thin paper like bone. Facial nerve decompression technique can be practiced on this model.

(10) STAPEDECTOMY TRAINING (Fig. 9).

Fig. 9.

a and b Footplate of stapes and ossicles

Goat models can be used to train surgeons for stapes surgery.

(11) COCHLEAR IMPLANT TRAINING (Fig. 10a–c).

Fig. 10.

a–c Figure showing the facial nerve, turns of cochlea and the internal auditory meatus. The relation of facial nerve with cochlea

Studies have been conducted before where lamb model was used to train cochlear implant surgeons in electrode insertion.

Discussion

Minimal invasive surgery has influenced the techniques in every surgical specialty. This has led to the replacement of conventional procedures with minimally invasive ones, stimulated surgeons to re-evaluate conventional approaches. However, two major drawbacks of the minimal invasive surgery include the prolonged learning curve and increased costs due to investment in the equipment required as well as longer operating times. Residency training requires both time and resources to allow the trainee to improve his or her skills under the supervision of an experienced surgeon. Studies have shown that the amount of time needed by residents to complete a tympanoplasty type I is 1½ times that needed by attending physicians [18]. Every manual task is improved by experience, which may be acquired in the operating room. It should be borne in mind that the number of surgical procedures performed by residents is limited owing to work-hour regulations, economic considerations, and the safety of the patient [19]. Therefore, ex vivo training models are widely used and have become a requirement in otologic surgical procedures, for example, by means of a temporal bone dissection laboratory [20]. However, the access to human cadaveric specimens may be limited owing to financial or regulatory issues. In this situation, the animal model is a valid alternative.

One main issue in developing an animal model for exclusive endoscopic ear surgery is the incongruence of that model to the human anatomy, particularly the external auditory canal. Raising the tympano-meatal flap and maneuvering the micro ear instruments in a possibly bent and narrow external auditory canal is a challenge. An animal model should meet these difficulties and provide adequate training.

The lamb model is a readily available, relatively cheap, and reliable model for otologic surgery. The lifelike feeling of fresh specimens provides excellent tissue properties and dissection. Another advantage is the similar size and presentation of the gross anatomic structures of the ovine ear compared with the human ear [9–11]. The learning curve in endoscopic ear surgery is different from the learning curve for the microscopic technique for ear surgery [21]; therefore, a proper model for exclusive endoscopic ear surgery is required. The use of an endoscope and, therefore, visualization of the performed dissection on a screen improves the supervision and feedback of the supervising faculty member. Both trainee and tutor have the same field of view; therefore, teaching is straightforward, and the suggestions or corrections can be addressed directly.

Anatomic Studies and Procedure

Four fresh goat heads (8 ears) were used for anatomic dissection of the external auditory canal and the middle ear. The external ear covers the external meatus and must be partially amputated to access the canal. The cartilaginous part of the canal is bent in a posterior direction. A bony prominence in the EAC hinders direct access to the tympanic membrane (TM); this obstacle was drilled out and the canal was widened to assess the TM. Compared with human anatomy, the very thin tympanic membrane presents a large pars flaccida posterior and superior to the malleus, covering the epitympanic space. The position and the angle of the external ear canal are the same in goat and in humans, but the bony portion is very small compared to human one. With approximately 3 mm it is too narrow to use common microsurgical instruments [7, 8].

The tympanic membrane appeared elongated and floppy when compared with the human tympanic membrane. The epitympanum showed, a long extension and the glistening ligaments and folds could be appreciated clearly.

While raising the tympano-meatal flap (TMF), the lack of an annulus was observed in all specimens. In humans, parts of the posterior ear canal wall have to be removed to see major parts of the ossicular chain. Lavinsky and Goycoolea were first to describe sheep ear as appropriate model for otologic surgical training for middle ear procedures due to similarities in sheep and human external and middle ear anatomy.

The goat middle ear is similar to the human middle ear. However, we identified some important differences:

1. The malleus of the goat ear lies more anteriorly and has a longer and curved handle, which is attached to the inferior-anterior floor of the tympanic cavity.

2. The body of the malleus is thin hollowed out and fragile.

3. A very large and bulky tensor tympani muscle present medially.

4. The goat incus is of similar shape to the human incus, with a short and a long process articulating with the stapes.

5. The stapes was complete with head, neck, crus and foot plate with a stapedial tendon. The orientation of the stapes foot plate differed from the human stapes foot plate as it was placed at an angle.

6. The facial nerve was in a similar position as in humans but was protected by a bony projection that was drilled out to expose the nerve.

7. The retrotympanum and hypotympanum containing the round window were hidden behind a bony prominence of the EAC.

8. The promontory was projected outward and lower in position as compared to human promontory.

Cordero et al. [11] recently described a model for training endoscopic stapedectomy. In that study, the complete amputation of the cartilaginous part of the EAC and drilling of the bony canal under microscopic view was suggested. In comparison, our model has the advantage of managing the goat ear canal and the creation of a tympanomeatal flap in a purely endoscopic way. Specialized training is needed for the delicate maneuvering of the instruments in the narrow canal, whose limited space is further compromised by the presence of the endoscope.

Limitations—the following limitations were experienced during our study:

1. The anatomic differences between the goat and human middle ear.

2. Absence of the main landmark in tympanomeatal flap elevation—the annulus.

3. Stapes foot plate was present in an angle which would make practicing stapedectomy difficult in a goat ear.

Inspite of these limitations the dissectors observed a remarkable difference in dissecting the human temporal bone after performing the dissection on the goat model. They not only experienced improved dexterity and stability but also got accustomed to working with the drill and delicate instruments in the ear canal with the endoscope in situ.

Conclusions

The goat model for exclusive two handed endoscopic middle ear dissection is a novel approach to learn and practice delicate surgical exercises of endoscopic middle ear surgery .It allows surgical tasks to be replicated giving an opportunity to the trainee to try new skills, make mistakes and allow competency to evolve. This model not only provides excellent tissue quality but also overall satisfaction and a good learning experience.

Funding

This study was not financially supported from external sources.

Compliance with Ethical Standards

Conflict of interest

None.

Ethical Approval

Institutional Ethics Committee has approved the study.