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Submandibular Approach to the Mandible (Cadaver)

Transcription

CHAPTER 1

The procedure we will be performing today is a submandibular approach to the mandible. There are many indications for this operation, which include management of fractures, pathology of both the mandible and of the submandibular gland, and also, osteomyelitis. The relevant anatomical features that will be seen today are the platysma, the- the superficial layer of the deep cervical fascia, the submandibular gland, the submandibular node, the facial artery and vein, and finally the inferior border of the mandible, which is covered by the pterygomaxillary sling made by the masseter muscle and the medial pterygoid muscle. The key points of this surgery are a skin incision down to the platysma, dissection through the platysma, dissection through the superficial layer of the deep cervical fascia, at which time we will look for the marginal mandibular branch of the facial nerve. We will also attempt to identify the facial artery and vein, and, dissect and tie off those structures. We will look for the submandibular gland and node and then we will dissect up, through the pterygomaxillary sling to the inferior border of the mandible, at which time we'll expose the mandible.

CHAPTER 2

So as we begin the operation, we first identify anatomical landmarks, which in this case include the inferior border of the mandible, the angle of the mandible, and the posterior border of the ascending ramus. Our incision then is made 1 to 2 cm below the inferior border of the mandible. This can either be done parallel to the mandible, or it can be done in a crease, which we note here. Commonly, the crease- is not at an appropriate angle, so, it's better to make the incision parallel to the inferior border. The incision will be 5 to 6 cm- in length. The head should also be positioned- so that- the surgeon has appropriate visualization of the inferior border and of the planned incision.

CHAPTER 3

Normally, 2% Lidocaine- sorry, can be incised, as long as it is supraplatysmal. Or just plain Epinephrine can also be injected. The skin incision is made- through the dermis, into the fat, down to platysma. At this time, Bovie electrocautery might be used- to manage bleeding vessels.

In a live patient, a- hemostat would be placed through a nick in the anterior most portion of the platysma, passed underneath the platysma, coming out the posterior aspect of the- of the platysma, and an incision made through the platysma. In our cadaver, this is slightly different. At this time one might also undermine the skin margins by 1 to 2 cm to allow for greater exposure. Supraplatysmal extension of the skin flap will- greatly enhance the ability to- visualize the inferior border of the mandible. And will also assist in skin closure. Great, and then let's- see the platysma right there? Let's come underneath that.

Anteriorly though, there is still a segment of the platysma that is not cut. So with careful subplatysmal dissection, and tenting of the platysma, the hemostat is placed underneath, and the platysma is incised. Again, posteriorly. A hemostat is passed under the platysma. And incised.

Care must be taken at this time to make sure that the incision stays, at the level of the skin incision, which is 1 to 2 cm below the inferior border of the mandible. At this time, the superficial layer of the deep cervical fascia may be noted. And the shadow of the submandibular gland and submandibular node might be- seen at this time. I think we got the marg right there. Yep. At this time, care is taken to identify the marginal mandibular branch of the facial nerve. If this nerve is damaged, then- weakness of the commissure, in this patient of the right commissure- would be noted. A nerve stimulator might be used- to identify this branch. In this cadaver- it is fairly clear. Perfect. At this time, careful dissection is made to isolate and retract the nerve. This is usually done with blunt dissection, so as to not transect the nerve. I'll use the scis there. Huh? You can use the scis there, underneath, if you want it. Any bleeding vessels at this point can be managed with Bovie electrocautery, bipolar cautery- clips, or ties. It's always a good idea to feel for the inferior board of the mandible to make sure that- the path and plane of the dissection is in the proper vector.

I'm just trying to better show the submandibular gland here. Right. Here we are trying- Here we're trying to clearly identify the submandibular gland. We're also looking at this time for the submandibular node, or the node of Stahr. So at this point, we see the submandibular gland covered by the marginal mandibular branch. We have the submandibular duct. This is probably posterior belly of the digastric. And here also we see the posterior belly of the digastric muscle.

So now we can- return kind of our dissection to the inferior border. Okay. So, our inferior border is in the superior aspect of the wound, so now we will try to identify the facial artery and vein. Starting to get down to periosteum there. Great. At this point, often the facial artery can be palpated, and its pulsatile nature noted. In a cadaver, it's not as readily noted. So, here we have- excellent visualization of that marginal mandibular branch of the facial nerve. There's a good view of periosteum there. Yes. So, the periosteum is readily noted, at the inferior border of the mandible. This- this periosteum is part of the pterygomandibular sling, which is made up laterally by the masseter muscle and medially by the medial pterygoid muscle. Pterygomasseteric. Pterygomasseteric sling. I'm just wondering if this- So if this is marg… I don't see our vessels at all. So there's- there's masseter there. There's masster muscle here laterally. And again, and in the cadaver- with no blood flow, it's more difficult to identify the vessels. Whereas in a live patient, they are much more readily identifiable. Yeah. At this stage… It's there? I think so. Yeah, that's it. There's venous, so this is nervous here, and that is- that's arterial. The marginal mandibular branch often runs just deep to the superficial layer of the deep cervical fascia. So at this time, we're trying to identify the facial artery and vein, again, a little bit more difficult in a cadaver. At this point, the vessel would be tied in transected, to allow for a full exposure of the inferior border of the mandible. Otherwise, I mean we're totally dissected here. Okay. So then let's tie that off and transect that, okay?

At this point, ligatures are being placed around what appears to be the facial artery. After ligatures are placed, the vessel can then be transected. Now with the vessels transected, and the marginal mandibular branch of the facial nerve- out of the field, we can now clearly identify the inferior border of the mandible- laterally we see the mandible- or laterally we see the masseter, excuse me.

CHAPTER 4

At this stage, a broad malleable retractor could be placed- below the inferior border of the mandible, and the periosteum of the pterygomaxillary sling is then sharply incised, with care taken to- avoid making the incision too lateral, into the- masseter muscle, which can significantly bleed. And this incision can extend- from the angle as far anterior as is allowable through your incision.

And then careful subperiosteal dissection is performed. To release the masseter muscle laterally and expose the lateral border of the mandible. And again, at this time they're going to be persistent bleeding vessels, which are usually managed with a Bovie electrocautery, at this stage. Dissection at this stage can be with a number 9 periosteal elevator, or with varying sizes of... elevators. As subperiosteal dissection continues, and the mandible is exposed, at this time, a fracture might be identified, or- the pathology… If a plate is going to be a place, then as much soft tissue as possible should be removed down to clean bone. That's pretty good. Yeah. If dissection is made superiorly in the area of the mandible, one must be careful to avoid perforation into the oral cavity, through the gingiva At this point, either the pathology can be managed, or the fracture reduced and rigidly fixed, and then closure of the wound would- be carried out at this point.

CHAPTER 5

So in the cadaver, closure might be difficult, but normally the pterygomaxillary sling would be approximated, and this would be done with a 2-0 or a 3-0 chromic suture. Here we're using 4-0 Vicryl suture. And usually this suture would be run to close the sling, but can also be done with interrupted sutures. So the next layer of the layered closure would be the platysma muscle, which can be approximated with 3-0 or 4-0 resorbable sutures. Here we're using a- a 3-0 Vicryl suture. These can be interrupted or running sutures often done as a running suture. Why don't you tie that. Yeah. And at this point, this would rerun anteriorly through the full extent of the platysma. The next layer of sutures would then be subdermal sutures. For brevity, we will show just a few of the- we'll do just a few interrupted sutures to close the- subdermal tissues, and then- skin closure can be formed with a- 6-0 non-resorbable suture. So skin closure can either be done with a non-resorbable suture, or through a subcuticular resorbable or non-resorbable suture. And at this time, care is taken to evert the skin margins, and to take consistent bites, approximately- 2 to 3 mm from the edge of the wound. I'm advancing approximately 3 mm as well. If a non-resorbable suture is used- this would normally be removed in approximately 5 days. And at this point, the wound would be covered with Bacitracin, a small-cut piece of Telfa, and then a Tegaderm, and that dressing would be removed at 24 hours, and the sutures would be removed at 5 days, and at that point, Steri-Strips and Mastisol would be placed.