Fig. 5.1
Set of surgical instruments. a scalpel, b needle driver, c surgical and anatomical forceps, d small curved mosquito forceps, e Kocher’s forceps, f scissors, g suture threads, h Killian’s speculum, i small retractors, j suction cannula, k medical gauzes
Set up the diaper on the bench and then the dissection tray on the diaper. Obtain dissection instruments and finally put the head into the dissection tray or on the diaper with the neck extended in the dorsal recumbent position (Fig. 5.2). The anterior part of the sheep’s neck has to be previously shaved.
Fig. 5.2
Set-up of the surgical field
5.3 Slide Tracheoplasty
5.3.1 Skin Landmark Identification
Recognizing the main landmarks on the skin is probably the most simple and fundamental step in all surgical head and neck procedures. Identification by palpation of laryngeal framework in sheep animal model is quite similar to human.
In order to start the procedure, it is useful to identify (Fig. 5.3):
Hyoid bone, partial cover by the muscles
Thyroid cartilage
Cricoid cartilage
Trachea
Fig. 5.3
Superficial landmark identification. HB hyoid bone, ThC thyroid cartilage, Cr cricoid cartilage, Tr trachea
5.3.2 Superficial Layer Dissection
Make a vertical incision about 13 cm in order to show the superficial fascia that covers the muscles of the neck (Fig. 5.4). Incision could be performed with 10 or 15 blade.
Fig. 5.4
Skin incision
In this step the main goal is to elevate only a cutaneous and subcutaneous flap.
When all superficial fascia is exposed, the surgeon has to dissect it on the midline with surgical scissor or blade. After this, to allow a good exposition of the main structures below, it is useful to suture subcutaneous tissue at the lateral skin in its upper and downer part (Fig. 5.5).
Fig. 5.5
Superficial cervical fascia dissected and sutured with subcutaneous tissue. Below, laryngeal’s structures covered by its fascia
5.3.3 Laryngeal Framework Identification
When the dissection of the superficial layers is completed, it is important to identify the main structures of laryngeal framework and muscles that surround it (Fig. 5.6).
Fig. 5.6
Laryngeal framework identification. MyH mylohyoid muscle; HB hyoid bone, partial cover by the muscles; StH sternohyoid muscle; ThC thyroid cartilage; Cr cricoid cartilage; Tr trachea
5.3.4 Infrahyoid Muscle Dissection
Infrahyoid muscles are retracted laterally, resulting in optimal exposure of the lower edge of the thyroid cartilage over its entire width.
It is useful to suture the bigger muscles to subcutaneous layer in order to maintain a wide surgical field. This step simulates the strap muscle dissection on the midline performed in the human procedure in order to expose the hyoid bone and trachea. Sheep thyroid does not have an isthmus so it is not necessary to split thyroid gland on the midline (Fig. 5.7).
Fig. 5.7
Thyroid gland dissected. ThC thyroid cartilage, Thy thyroid gland
Now it is possible to identify all the landmarks (Fig. 5.8).
Fig. 5.8
Strap muscles dissected and mylohyoid muscle. MyH mylohyoid muscle, StH sternohyoid muscle, ThH thyrohyoid muscle, StT sternothyroid muscle, ThC thyroid cartilage, Cr cricoid cartilage, CrM cricothyroid muscle
5.3.5 Dissection of the Trachea
The dissection of the trachea (Fig. 5.9) is done only anteriorly and slightly laterally without identifying the recurrent laryngeal nerves (RNLs). Surgical pearls to avoid RNL injury are:
Stay close contact with the outer perichondrium of the tracheal rings.
RLN identification on sheep animal model is not the goal of the procedure. In human procedure to minimize RLN injury, dissection must be carried out against the trachea without recurrent laryngeal nerve visualization.
Avoid dissection above the posterolateral border of the cricoid plate in order to avoid injury to the RLNs.
Fig. 5.9
Exposure of tracheal laryngeal axis. ThC thyroid cartilage, Cr cricoid cartilage, Tr trachea, Thy thyroid gland
The vascular supply of the trachea is into the tracheoesophageal groove, and it must be preserved.
In patient with LSTS, the dissection is carried on laterally over the whole distance of the stenotic segment, staying in close contact with the tracheal rings to preserve the posterolateral vascular supply to the trachea and avoid damage to recurrent laryngeal nerves.
Remarks
In infants and small children, it has been possible to expose the trachea sufficiently through a collar incision alone. If additional exposure is required, the upper sternum or even the entire sternum may be divided.
5.3.6 Slide Tracheoplasty: Tracheal Transection
The most important steps of slide tracheoplasty are showed in Fig. 5.10.
