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Effect of Needle Sizes 30 G and 32 G on Skin Penetration Force in Cadavers: Implications for Pain Perception and Needle Change during Botulinum Toxin Injections

Tansatit, Tanvaa M.D., M.Sc.; Uruwan, Sukanya M.Sc.; Wilkes, Mikaela M.Biol.Sci.; Rungsawang, Chalermquan Ph.D.

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Plastic and Reconstructive Surgery: December 2021 - Volume 148 - Issue 6 - p 1071e-1073e
doi: 10.1097/PRS.0000000000008558
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Cosmetic botulinum toxin injections usually cause discomfort to the patient. Using a small needle causes less pain compared to using a large needle,1 but a drawback is the price. A 30-G needle costs 2 THB while a 32-G needle costs 15 THB. The physician must decide when a needle is to be discarded. In one study, a 30-G needle was changed after approximately four to six punctures because of increased skin resistance.2 A 32-G needle is less painful than a 30-G needle because of the 25 percent smaller diameter of the 32-G needle.3 Instead of relying on individual tactile sense, we compared the penetration forces of two needle sizes to decide when to change the needle during botulinum toxin treatment.

Forty 30-G and 32-G needles (n = 20 each) were connected to a digital force gauge (DFG5 Bravo; Tech Quality Co., Ltd., Bangkok, Thailand) to compare the peak penetration forces. The 1200 penetrations at a 45-degree angle were conducted on the whole forehead and crow’s feet regions of a fresh cadaver. The distance between each penetration point was 1 mm. Repeated measurement analysis of variance and the independent sample t test were used to determine significant differences between the forces when appropriated.

The skin penetration forces are summarized in Table 1 and Figure 1. At the first insertion, 32-G needles significantly required 75 percent of the force required by 30-G needles (0.15 ± 0.03 N versus 0.20 ± 0.06 N, p = 0.001). Similarly, the 32-G needle required a skin penetration force of 72 percent compared with the 30-G needle at the thirtieth penetration. In addition, there was a rise in the skin penetration forces of both needles at each use. The skin penetration forces of 30-G needles showed a significant increase of 30 percent at the fifth penetration (p = 0.007), whereas the skin penetration force of 32-G needles was significant increased by 33 percent at the eleventh penetration (p = 0.001) compared with first penetration. Repeated injections decrease sharpness of the needle, resulting in a sensation that is more painful. However, there was no statistically significant difference between the forehead and crow’s feet regions (Fig. 2).

Table 1. - Comparison of Skin Penetration Force of 30-G and 32-G Needles during Insertion through the Skin 30 Times
No. of Uses Comparison of Force in Each Use of 30-G Needle (n = 20) Comparison of Force in Each Use of 32-G Needle (n = 20) Comparison of Force between 30-G and 32-G Needles
Mean (SD) Force (N) % Increase (compared with first time) p Mean (SD) Force (n= 20) (N) % Increase (compared with first time) p t Test p
1 0.20 (0.06) 0.15 (0.03) 3.589 0.001*
2 0.22 (0.07) 10.00% 1.000 0.16 (0.03) 6.67% 1.000 3.329 0.003*
3 0.24 (0.08) 20.00% 1.000 0.16 (0.03) 6.67% 1.000 3.770 0.001*
4 0.24 (0.05) 20.00% 1.000 0.17 (0.03) 13.33% 0.189 5.251 <0.001*
5 0.26 (0.07) 30.00% 0.007 0.18 (0.03) 20.00% 0.432 4.877 <0.001*
6 0.26 (0.10) 30.00% 0.170 0.18 (0.05) 20.00% 0.372 3.261 0.002*
7 0.28 (0.08) 40.00% 0.005 0.18 (0.03) 20.00% 0.094 5.097 <0.001*
8 0.28 (0.07) 40.00% 0.074 0.18 (0.03) 20.00% 0.162 5.245 <0.001*
9 0.28 (0.05) 40.00% <0.001 0.19 (0.04) 26.67% 0.333 6.151 <0.001*
10 0.29 (0.05) 45.00% <0.001 0.19 (0.03) 26.67% 0.093 8.559 <0.001*
11 0.29 (0.07) 45.00% 0.002 0.21 (0.05) 40.00% 0.001 4.322 <0.001*
12 0.30 (0.05) 50.00% <0.001 0.20 (0.04) 33.33% 0.001 6.650 <0.001*
13 0.30 (0.06) 50.00% <0.001 0.22 (0.05) 46.67% <0.001 4.427 <0.001*
14 0.33 (0.05) 65.00% <0.001 0.22 (0.04) 46.67% <0.001 8.107 <0.001*
15 0.32 (0.05) 60.00% <0.001 0.22 (0.03) 46.67% <0.001 7.757 <0.001*
16 0.33 (0.06) 65.00% 0.001 0.22 (0.04) 46.67% 0.001 6.707 <0.001*
17 0.34 (0.06) 70.00% <0.001 0.22 (0.04) 46.67% 0.002 7.134 <0.001*
18 0.34 (0.06) 70.00% <0.001 0.23 (0.05) 53.33% 0.001 6.222 <0.001*
19 0.35 (0.07) 75.00% <0.001 0.23 (0.04) 53.33% <0.001 6.786 <0.001*
20 0.34 (0.04) 70.00% <0.001 0.24 (0.04) 60.00% <0.001 7.612 <0.001*
21 0.35 (0.06) 75.00% <0.001 0.23 (0.04) 53.33% <0.001 7.555 <0.001*
22 0.36 (0.06) 80.00% <0.001 0.24 (0.05) 60.00% <0.001 7.447 <0.001*
23 0.35 (0.07) 75.00% <0.001 0.22 (0.03) 46.67% <0.001 7.193 <0.001*
24 0.36 (0.06) 80.00% <0.001 0.25 (0.05) 66.67% <0.001 6.691 <0.001*
25 0.34 (0.06) 70.00% <0.001 0.25 (0.05) 66.67% <0.001 5.205 <0.001*
26 0.37 (0.07) 85.00% <0.001 0.25 (0.04) 66.67% <0.001 6.553 <0.001*
27 0.38 (0.07) 90.00% <0.001 0.25 (0.03) 66.67% <0.001 7.688 <0.001*
28 0.38 (0.05) 90.00% <0.001 0.25 (0.03) 66.67% <0.001 9.193 <0.001*
29 0.37 (0.05) 85.00% <0.001 0.25 (0.04) 66.67% <0.001 7.929 <0.001*
30 0.36 (0.05) 80.00% <0.001 0.26 (0.05) 73.33% <0.001 6.865 <0.001*
*There was a statistically significant difference in force between of 30-G needle and 32-G needle (p <0.05).
There was a statistically significant difference in force of the needle between the first time and the other times (p <0.05).

Fig. 1.
Fig. 1.:
Line graph of the force required to penetrate the skin by 30-G and 32-G needles 30 times. *There was a significant difference between the skin penetration force of 30-G and 32-G needles at each penetration (p < 0.05).
Fig. 2.
Fig. 2.:
Line graph of the force required to penetrate the skin by 30-G and 32-G needles in the forehead and crow’s feet regions 30 times. There was no statically significant difference between the forehead and crow’s feet regions.

The 32-G needle is expensive, but it is suitable for multiple injections. A high production technology makes the 32-G needle strong and long-lasting in utilization.4 Considering the force increment in multiple injections, the 32-G needle can be used for 11 injections while the 30-G needle should be used for only five injections. Furthermore, the skin penetration force of the 30-G needle at the fifth penetration was 0.26 N, while the 32-G needle could be used up to the thirtieth penetration. In addition, the 30-G needle was discarded after the fourth penetration, but the 32-G needle could be used until the twentieth penetration at the skin penetration force of 0.24 N (Table 1). A standard reconstitution of 2.5 ml of normal saline was used for 50 botulinum toxin units and 0.1 ml of 2 units was planned for most injection points. Apparently, the physician can change the 30-G needle after half of the insulin in the syringe is injected, whereas the 32-G needle with insulin syringe is discarded when the syringe is empty.

DISCLOSURE

The authors have no financial interests to declare in relation to the content of this article.

REFERENCES

1. Alam M, Geisler A, Sadhwani D, et al. Effect of needle size on pain perception in patients treated with botulinum toxin type A injections: A randomized clinical trial. JAMA Dermatol. 2015;151:1194–1199.
2. Flynn TC, Carruthers A, Carruthers J. Surgical pearl: The use of the Ultra-Fine II short needle 0.3-cc insulin syringe for botulinum toxin injections. J Am Acad Dermatol. 2002;46:931–933.
3. Barolet D, Benohanian A. Current trends in needle-free jet injection: An update. Clin Cosmet Investig Dermatol. 2018;11:231–238.
4. Nagai Y, Ohshige T, Arai K, et al. Comparison between shorter straight and thinner microtapered insulin injection needles. Diabetes Technol Ther. 2013;15:550–555.

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