Determining safe entry sites for filler injections on the lateral canthal vertical line: anatomical study of the midface arterial perforators in soft embalmed cadavers

This study was exempted from full review by the Institutional Review Board (IRB) ethics committee at the Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand (certificate of exemption No. 023/2015; IRB No. 607/58). Written informed consent for publication of photographs was obtained from the nearest living relatives and the living model. We dissected 28 hemiface specimens (14 men, 14 women) of soft embalmed Thai cadavers in the Chula Soft Cadaver Surgical Training Center of the Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital. The average age of these cadavers at death was 78 years ranging from 47 to 92 years. Red latex was injected into the entire specimen before dissection to display contrast within anatomical structures.

We dissected 28 facial arteries after vascular injection to study the middle midface perforators and their distance from the standard axis, diameter, depth, length, and pattern. The middle midface was considered as the area between the midpupillary line and the vertical line at the anterior end of the zygomatic arch.

First, a descending vertical incision was made at the center of the face (from the forehead to the mentum) and 2 incisions perpendicular to this initial incision were also made: one extending from the palpebral fissure towards the auricle, and the second from the oral commissure to the lateral side of the face (Figure 1). Subsequently, the skin was reflected in as thin a layer as possible, to retain terminal perforators, which were visible at the subcutaneous layer. The perforators were identified and cleaned to their termini. Care was taken to avoid damage to these arteries. We classified 3 types of perforators according to their main arterial origin: the buccal artery perforator originating from the buccal branch of the facial artery before it supplies the buccinator, the parotid artery perforator originating from the parotid artery in the parotid gland that branches from the external carotid artery, and the facial artery perforator originating directly from the facial artery.

Figure 1

At the midface, the pattern in which the perforator was located was compared relative to the lateral canthal vertical line and perpendicularly to Frankfort’s horizontal line. The diameter and depth of the middle midface perforator from the skin to its origin and length from the main branch to its terminal were also measured. The distance between the perforator to the standard axes was also measured. The X axis has been established as the Frankfort’s horizontal line, whilst the Y axis as the lateral canthal line (Figure 2).

Figure 2

The origin and distance of the perforator from the X and Y axes using 4 (X, Y) coordinates were measured. The first marked at the perforator’s origin (X₀, Y₀), the second at the oral commissure (X₁ Y₁), the third at the lower alar crease (X₂, Y₂), and the fourth at the upper crease (X₃, Y₃) respectively (Figure 2).

We found that the main arteries providing the long perforators ran within the subcutaneous fatty tissues and were also superficial, ascending parallel to the lateral canthal vertical line and terminating near the lower eye lid to supply the muscles and skin in firmly attached areas of the face, so that gliding was either prevented or reduced.

The perforators can be divided into 3 categories depending on the main arteries from which the perforators originate (Table 1) (Figure 3). The buccal artery perforator (Type I) could be found in most hemiface specimens, and the perforators originated from the buccal branch of the facial artery. The parotid artery perforator (Type II) originated from the parotid artery, and was found in about a quarter of the hemiface specimens. The facial artery perforator (Type III) arises directly from the facial artery, and was found in less than 20% of 28 hemiface specimens. The diameter of the arteries is shown in Table 2.

Table 1

Origin patterns of the perforators at the middle midface region

Table 2

Anatomical measurements of the middle midface perforators

Figure 3

The buccal artery perforator was located in the cheek region and crosses 3 levels from its origin to the oral commissure, lower alar crease, and level of the upper alar crease. The distance from its origin in relation to the lateral canthal line and Frankfort’s horizontal line is shown in Table 2 (Figure 4 A). The distance at the level of the oral commissure, lower alar crease, upper alar crease, and various diameters and depths are shown in Table 2.

Figure 4

The parotid artery perforator, has its origin located above the oral commissure level; consequently, this perforator crossed 2 levels from its origin to the lower alar crease and upper alar crease level. The distance from its origin in relation to the lateral canthal vertical line and in relation to Frankfort’s horizontal line (axis Y₀) are shown in Table 2 (Figure 4 B). The distance at the level of the lower alar crease (axis X₂) and axis Y₂, the upper alar crease level (axis X₃) and axis Y₃, diameter, length, and depth of this perforator are shown in Table 2.

The facial artery perforator crossed 3 levels from its origin to the oral commissure, lower alar crease, and upper alar crease. The distance from its origin in relation to the lateral canthal line (axis X₀) and Frankfort’s horizontal line (axis Y₀) are shown in Table 2 (Figure 4 C). The distance at the level of the oral commissure, the lower alar crease level (axis X₂), and the upper alar crease level (axis X₃), diameter, length, and depth of this perforator are shown in Table 2.

We found that the buccal branch always runs close to the lateral canthal line vertically to supply the lower eye lid in approximately 75% of the specimens. The parotid artery perforator has only one branch in the left hemiface, which runs to supply the lower eye lid. This perforator does not run parallel to the lateral canthal vertical line. The parotid artery perforator deviates because there were 4 branches running across the lateral canthal line at the lower alar level in 4 of 7 specimens. There were 2 facial artery perforators crossing the lateral canthal line between the lower eye lid and tip of the nose level. The diameter of the buccal branch shows a significant sex difference (P = 0.018), the buccal branch diameter in men was larger than in women. However, the buccal artery perforator diameter in men was significantly larger than it was in women (P = 0.019). Table 2 shows the standard deviation of distance X is greater than the mean of distance X because it was defined by vectors when compared with the lateral canthal vertical line (LCVL). If the perforator is medial to LCVL, it was defined as negative. If it was lateral to LCVL, it was defined as positive. There were both negative and positive perforators present. Accordingly, distance X has a wide distribution. Moreover, the mean distance X is not great because the data was calculated using vectors.

Previous studies have failed to investigate perforators along the lateral canthal line, although studies that have investigated perforators in other areas exist. These previous studies have been associated with reconstructive flaps in the near regions, such as the perforal and the nasolabial regions. They studied the number, diameter, and length only. Ng et al. [11] studied facial artery perforators in the nasolabial region and found that the average number of these perforators was 4 (SD 2), the average length was 14.1 (SD 3.5) mm and the average diameter was 0.9 (SD 0.2) mm. Hofer et al. [7] studied the perforators in the perioral region, and showed that facial artery perforators were distributed in a large range of from 3 to 9 per facial artery. The average perforator length was 25.2 mm (range, 13to51 mm). The average perforator diameter was 1.2 mm (range, 0.6 to 1.8 mm). Qassemyar et al. [9] studied the nasolabial sulcus perforator that branched from the facial artery and above to the mandible. In their study the average length of the nasolabial perforator was 12.06 cm. The average number of perforators greater than 0.5 mm per facial artery was 5.05. The mean diameter of the perforators was 0.96 mm.

The present study investigated the course and anatomical features of the perforator arteries along the lateral canthal vertical line. By contrast with previous studies, we found the number of middle midface perforators was less than the perforators in the nasolabial and perioral regions. We found only one perforator in the middle midface along the lateral canthal vertical line. The mean length of the middle midface perforator was longer than the perforators in the nasolabial or perioral region. Our study revealed the mean diameter of middle midface perforator was smaller than that previously reported from studies of European cadavers. This suggests that ethnicity may be associated with the size of these perforators.

Considering the cannula entry site at 2 cm inferolateral to the lateral canthus recommended by Beut, this entry site approximates at the upper alar level in our study, and is 2 cm distant to the lateral canthal vertical line. We conclude that this recommended injection site can reduce the risk of injury to the middle midface perforator because our results show that the buccal artery and parotid artery perforators constitute the majority of the perforators in the middle midface region. They were located proximal to the lateral canthal vertical line. In addition, we found only one facial artery perforator from a total of 28 middle midface perforators that were located laterally to lateral canthal line by about 2.1 cm (Figure 4 C). Therefore, we consider that this cannula entry site is safe and its use poses a low risk of injury to the middle midface perforators.

We performed dissections on the cadavers focusing only on the middle of the midface along the lateral canthal line. We consider that this line is important for filler injections in the midface because clinicians can have access to a wider area of the midface compared with other injection points. A limitation of this study was that we focused our locations primarily at 4 levels (origin, oral commissure, lower alar crease, and upper crease). Future studies should expand the area to cover the entire midface.

The middle midface perforator is a single long perforator artery along the lateral canthal vertical line, which stems most abundantly from the buccal branch of the facial artery. It has the largest diameter and is the longest compared to the other 2 types. The cannula entry point recommended by Beut at 2 cm inferolateral to lateral canthus is a safe injection by which to avoid injury to the middle midface perforator.