Analysis of Dermal Thickness Across 10 Areas and Injection Depth After Polynucleotide Injection Using Rejumate Automatic 0.8-mm 9-pin Injector on the Face Using 33-MHz Sonography

Abstract

Background: Automated injection devices are becoming essential tools in aesthetic medicine, offering precision and consistency in treatments such as polynucleotide (PN) injections for skin rejuvenation. This study aimed to analyze the dermal thickness across facial regions and evaluate the consistency of injection depth achieved with the Rejumate automatic injector.

Methods: A total of 31 patients (average age 48.2 y; 4 men and 27 women) underwent dermal thickness measurements using high-resolution 33-MHz ultrasound in 11 facial regions, including the forehead, temple, orbital rim, lower eyelid, malar, anterior cheek, lateral cheek, posterior cheek, jawline, and chin. Each patient then received a standardized 2-mL PN injection using the Rejumate injector with a 0.8-mm needle across 317 individual points. Injection depth, distribution, and consistency were measured and analyzed.

Results: The average dermal thickness across regions ranged from 0.53 (lower eyelid) to 1.18 mm (temple and posterior cheek). The Rejumate injector demonstrated a high degree of consistency, achieving an average injection depth of 0.55 mm (SD = 0.13 mm), with a median depth of 0.54 mm. The depth range (0.29-0.99 mm) and interquartile range (0.17 mm) indicated controlled depth with minimal variability.

Conclusions: The Rejumate automatic injector reliably delivers PN at a controlled depth, showing minimal variability across injections. This precision supports improved safety and efficacy in PN delivery, providing a valuable reference for clinical application in aesthetic treatments. Given the anatomical differences in dermal thickness across facial regions, this standardized approach may optimize outcomes and increase patient satisfaction.

Fig. 1.

Ultrasound measurement of forehead dermal thickness showing planar DSJ. The DSJ appears relatively planar in this region, which is characteristic of the forehead anatomy.

Fig. 2.

Ultrasound measurement of lateral orbital rim dermal thickness showing planar DSJ. The DSJ appears exceptionally flat in this area, indicating a favorable anatomical structure for sliding and gliding techniques. This planar DSJ facilitates ease of movement during dynamic facial expressions, such as smiling, making it an ideal location for facial treatments requiring precision and flexibility.

Fig. 3.

Ultrasound measurement of anterior cheek dermal thickness showing planar DSJ. The DSJ appears uneven in this region, providing a more fixed structural support that limits sliding movement. This anatomical configuration helps reduce wrinkling and provides firmness during facial expressions, offering protective support to the skin in dynamic conditions, such as smiling.

Fig. 4.

Ultrasound measurement of posterior cheek dermal thickness showing planar DSJ. The DSJ in this area is notably irregular, with the dermis firmly attached to the underlying structures. This indicates a nonmovable anatomical configuration, suggesting limited sliding and a stable, fixed structure in the posterior facial region, which typically remains less dynamic and expressionless compared with other areas of the face.

Fig. 5.

Ultrasound measurement of jawline dermal thickness showing planar DSJ. The DSJ in this area appears very flat, providing an ideal anatomical structure for sliding and gliding. This configuration supports smooth movement during facial expressions, such as smiling, enhancing facial dynamics.

Fig. 6.

Uniform embossing appearance 5 minutes after PN injection with an automatic injector. Five minutes after PN injection using an automatic injector, embossing began to appear gradually, with consistent spacing and uniform size across the injection points. This uniform embossing pattern indicates that a constant depth and precise amount of PN were delivered to each site, demonstrating the injector’s capability for controlled and even distribution.

Fig. 7.

Consistent injection depth and spacing of PN immediately after injection with an automatic injector. High-resolution 33-MHz ultrasound shows uniform injection depth and spacing immediately after automatic PN delivery, before embossing. This demonstrates precise and consistent injection control by the automatic injector.

Fig. 8.

Embossing and diffusion of PN at 10 minutes after injection. High-resolution 33-MHz ultrasound shows visible embossing and diffusion of PN 10 minutes after injection. The material attracts moisture, producing localized swelling indicative of its hydrophilic properties.

Fig. 9.

Dermal thickness distribution across 10 facial regions based on statistical analysis of 31 subjects. This image illustrates the average dermal thickness across 10 distinct facial regions, based on a statistical analysis of 31 subjects. The measured regions include the forehead (0.79 mm), temple (1.18 mm), orbital rim (0.72 mm), lower eyelid (0.53 mm), malar (0.84 mm), anterior cheek (0.89 mm), lateral cheek (1.19 mm), posterior cheek (0.79 mm), jawline (0.75 mm), and chin (0.98 mm).

Fig. 10.

Distribution of injection depths across facial regions for consistent PN administration. This histogram presents the distribution of injection depths for PN administration across multiple facial regions showing a mean depth of 0.55 mm, with a median depth of 0.54 mm, indicating a centered distribution around these values. These data suggest a controlled and consistent injection depth, demonstrating the precision and reliability of the automatic injector used in this study.