The Anatomy of Safe Injections: A Guide Through the High-Risk Zones
When we talk about facial injections, the most dangerous areas are those involving the brain and the eye. Consider the supratrochlear artery — it emerges from the back of the eye, connected to the artery and therefore to the brain. Blocking this artery is catastrophic. Deep injections placed directly on the bone in this region are what most commonly lead to such an event. Just alongside it, the supraorbital artery emerges from the same location, carrying the same risks but on a smaller scale. Again, deep injections on the bone here are the most dangerous.
The Lateral Corrugator and the Threat of Ptosis
Another critical area of depth is when treating the lateral corrugator. This muscle runs from the periosteum medially to the dermis laterally. To avoid ptosis — one of the worst side effects of botulinum toxin — you must inject at the right level. If you go underneath the muscle, the eye becomes endangered. Beneath the orbicularis oculi, we are very close to the orbital rim, tiny foramina, and the eye itself. A needle too deep can cause eyelid ptosis and a superior rectus palsy.
Probably the most common area where new injectors make mistakes is around the orbicularis oculi, particularly the inferior lateral part of the eye. You only need to pop the bevel of the needle in 1 to 2 millimeters to be right on top of the muscle. If you keep going, you pass through the fat and strike the origin of the zygomaticus major. This can lead to a droopy smile, especially if the injection is too inferior. Injecting deeply here is particularly risky for an asymmetrical smile — a terrible side effect.
The Nose: A Fear of Blindness
Many clinicians are trained but terrified to treat noses, and for good reason: the risk of blindness. The nose tip is a much lower risk area compared with injecting the nasion. It is in the upper third of the nose where the dorsal nasal arteries and the supratrochlear artery may meet, allowing filler to make its way into the eye in extremely rare cases. In my mind, the choice between needle and cannula is largely about safety. I believe that in this area, a cannula is the safer option.
Nasolabial Fold and Lip Anatomy
You can treat a nasolabial fold with an injection in the pyriform fossa at the nasal base, projecting it forward to reduce shadow. But you cannot use that same injection if the fold runs all the way down to the oral commissure. That is where a cannula becomes much more useful, because I would not want to stick a needle into the intermediate fatty layer of the fold — that is where the artery tends to dip. The facial artery is usually slightly lateral, but it can sometimes snake into the fold, so a cannula is safer here.
Now, consider where the superior labial artery is likely positioned. The artery usually runs above or within the vermilion border. The papers I have reviewed describe it routinely in the vermilion border or slightly above. It is also usually beneath the orbicularis oris — about 60% of the time — within the muscle 35% of the time, and occasionally on top (5%). It can even wiggle around within the same patient. And of course, there are anomalous versions. In fact, when discussing with Julie Horn, she shared an amazing video of an artery pulsating near the wet-dry border. This is a known anomaly called a caliber persistent artery, occurring in around 2 to 3% of people. Sometimes you can feel it or see it pulsating underneath.
Consider this histological cross-section of a lip — the most important bit of anatomy you will see. The muscle runs down the middle of the lip. Anterior to it is a little hypodermic fat and then the dermis. On the other side, beneath the muscle, is where the artery usually lies. As we have said, it is not always at that exact point, but it is usually just inferior to the orbicularis oris. Picture your injection: it should be on the anterior surface of the lip, whether horizontal or vertical. Lips should look like they are falling out of the mouth — that is evolutionarily what they are: the oral mucosa coming out. That is what you aim to achieve.
The Chin: Vessels and Pressure Dangers
In the chin, there are really only two vessels you are likely to hit directly: the mental artery and the submental artery. The inferior labial artery is nearby, but for chin augmentation it is more the submental artery. This artery curves around underneath the mandible and supplies the anterior part of the chin. As we will see, it is much more complex than the simple diagram in textbooks. The submental artery also supplies important structures in the neck: the digastric, geniohyoid, mylohyoid, and stylohyoid muscles that stabilize the floor of the mouth during swallowing. In some people there is an anastomosis between the sublingual artery and the submental artery. This is very important because if you inject high volumes, as we do in the chin, you could affect the tongue's blood supply — a necrotic tongue is extremely debilitating.
There is another type of danger that comes down to injection technique. The easiest way to avoid this problem is to check how much space there is before you inject. In most patients, the tissue feels soft and expands away from the bone, leaving a better shaped chin. But in some patients, the tissue is tightly adhered and will not move. If you ignore this and inject a large volume, the pressure in the chin can become so high that you get superficial blanching. One weird side effect from this is loss of hair in some men — you can lose part of your beard if you over-project a chin. So it is worth thinking about the complex anatomy possible here, not just the simplified versions from textbooks.
The Lower Face: Muscles and Ligaments
The muscles of the lower face are arranged in a specific layout. The anterior facial muscles — those that control the mouth, elevate the lip, and move the chin — are all skin-to-bone or bone-to-skin connections. The muscles of mastication, however, are classic bone-to-bone connections. That is the first general layout. When you add the fat pads, it becomes like tiles on a roof, stacked together, with the deep fat pads on top of other muscles.
Next, think about how the structures are supported. Much of the midface is essentially hanging off the zygoma and the maxilla. All the bony attachments are on those bones, and they are hanging the mouth, the nose, and the chin. There are elevators and depressors, but it is important not to get too focused on individual ligaments first. Picture the distribution of the ligaments — that helps your understanding much more. Most of them fall on an angle between the lateral and anterior face. This line forms a boundary where the function of the face shifts from communication to mastication. The line of ligaments starts with the superior temple septum, then the orbicularis oculi retaining ligament (especially the lateral orbital thickening), the zygomatic cutaneous ligament (the strongest aspect is right on the angle of the zygoma), and the levator labii superioris alaeque nasi — the longest named muscle in the body, which elevates the lip and nostril. This muscle is most commonly treated to stop its elevation so that gums do not show during a smile; the injection is just lateral to the nostril.
Nearby is the infraorbital artery, which runs through the maxilla to become the maxillary artery. The maxillary artery supplies the midface. A blockage would cause a nasopharynx or soft palate necrotic injury, as well as superficial cheek injury. Never inject deeply with a needle near this foramen. Following on along the masseter, you have the upper masseteric cutaneous ligaments, then the mandibular septum, and finally the mandibular cutaneous ligament. This is the line that holds the anterior face in place.
On the other side of the fat pad, above the buccinator muscle, is the risorius muscle. Its origin is on the surface of the masseter, and it contributes to smiling. We come across it in medical aesthetics mainly as a side effect of treating the masseter: accidentally relaxing the risorius affects the patient's smile. That is not a nice side effect at all, and it comes from hitting the origin of the risorius where it attaches to the masseter.
Platysmal Bands and the Nefertiti Lift
The platysma is a very superficial muscle, like a sheet, but it collects into bands. You can relax it, and it is connected into the SMAS. Sometimes relaxing it improves the jawline — that is why the technique is called the Nefertiti lift. However, side effects can occur, similar to treating the lower face. Occasionally, I have seen a few people get asymmetry in their lower mouth because the muscle is not as neat as in the textbook; it is often woven into the depressors. You can sometimes see the depressor anguli oris and the platysmal band woven together. The asymmetry usually appears when smiling, and it seems to happen when you inject very high up. It is worth knowing about.