Gluteal muscle and subcutaneous tissue thicknesses in adults: a systematic review and meta-analysis

Abstract

Background:

Nurses often administer intramuscular injections at the gluteal site. This study aimed to determine gluteal muscle and subcutaneous tissue thicknesses in adults.

Methods:

Systematic review and meta-analysis. The databases Turkish Medline, Ulakbim, National Thesis Center, Cochrane, Web of Science, Science Direct, PubMed, CINAHL Plus with Full text (EBSCO host), OVID and SCOPUS were screened using the keywords ‘intramuscular injection’, ‘subcutaneous tissue thickness’, ‘muscle tissue thickness’ and ‘needle length’ between April and May 2021. The studies were evaluated with ultrasound. This study was reported according to the PRISMA recommendations.

Results:

Six studies met the eligibility criteria. The total sample size was 734 (women: 432, men: 302). The V method revealed that the ventrogluteal site had a muscle and subcutaneous tissue thickness of 38.071 ± 2.119 and 19.927 ± 2.493 mm, respectively. The geometric method revealed that the ventrogluteal site had a muscle and subcutaneous tissue thickness of 35.989 ± 4.190 and 19.661 ± 3.992 mm, respectively. The geometric method also revealed that the dorsogluteal site had a thickness of 42.560 ± 8.840 mm. According to the V method, females had thicker subcutaneous tissue at the ventrogluteal site than males (Q = 5.37, df = 1, p = 0.0204). Body mass index did not affect the subcutaneous tissue thicknesses at the ventrogluteal site.

Conclusion:

The results show that gluteal muscle, subcutaneous and total tissue thicknesses vary across injection sites.

Introduction

Clinical nurses often administer intramuscular injections, which play a key role in parenteral drug practice (Berman et al., 2016; Nicoll and Hesby, 2002; Potter et al., 2017). More than 12 billion intramuscular (IM) injections for therapeutic purposes are administered every year worldwide (Craven et al., Nicoll and Hesby, 2002). Intramuscular injection sites are deltoid, laterofemoral, rectus femoris, dorsogluteal and ventrogluteal sites (Craven et al., 2013; Dayananda et al., 2014). Healthcare professionals generally prefer to administer large amounts of drugs to the dorsogluteal and ventrogluteal muscles at the gluteal site. Two methods are used (‘V’ and ‘G’ methods) to determine the intramuscular injection site at the ventrogluteal site (Kaya et al., 2015). In the V method, the base of the hand is placed on the greater trochanter. The index finger opens towards the anterior superior iliac spine, while the middle finger opens towards the iliac spine. The middle of the triangle is the IM injection site. In the G method, a triangle is formed with imaginary lines drawn from the greater trochanter to the iliac crest, from the iliac crest to the anterior superior iliac spine and from there to the greater trochanter. Then, median lines are drawn for each vertex of the triangle. The intersection of the three median lines is the IM injection site (Craven et al., 2013). Three methods are used to determine the injection site at the dorsogluteal site. These methods are the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur; the site between the anterior spine iliac spina and the coccyx is divided into three equal parts (three-way split); and it is imaginarily divided into four quadrants (four-way split) (Cocoman and Murray, 2008; Hunter, 2008; Karabacak, 2010). The distance from the sciatic nerve, the thickness of the subcutaneous tissue above the muscle and the thickness of the muscle are taken into account in comparisons between both regions (Cocoman and Murray 2008; Kara et al., 2015). Recent research has shown that IM injections at the dorsogluteal and ventrogluteal sites are unsuccessful in most people with thick subcutaneous tissue (Chan et al., 2006; Larkin et al., 2017). Therefore, there is an ongoing debate about the safety of IM injections administered to the ventrogluteal and dorsogluteal sites.

In addition, nurses should sufficiently understand about physiology and pharmacology to determine the anatomical location of the injection site and choose the right needle (Berman et al., 2017; Nicoll and Hesby, 2002; Potter et al., 2017). The success of intramuscular injections depends on the needle length and the subcutaneous tissue and muscle and total tissue thickness (Cook et al., 2006). Research shows that women and those with high body mass index (BMI) are more likely to have subcutaneous intramuscular injections at the gluteal site (Burbridge, 2007; Chan et al., 2006; Dayananda et al., 2014; Elgellaie et al., 2018; Larkin et al., 2017; Nisbet, 2006; Zaybak et al., 2007). Therefore, we need to know the physical characteristics of patients such as height, weight and BMI (Doğu Kökcü et al., 2021; Elgellaie et al., 2018; Gunes et al., 2008; Larkin et al., 2017). For a successful IM injection, at least 25 mm should enter the muscle with an injection depth of approximately 30 mm (Cook et al., 2006; Ozen et al., 2019).

The success of intramuscular injections at the gluteal site in adults depends on selecting and using a needle of appropriate length for the thickness of the muscle and subcutaneous tissue. There is limited research on this topic (Larkin et al., 2018; Ozen et al., 2019; Takahashi et al., 2014; White et al., 2018, Zaybak et al., 2007). Based on earlier research, this study aimed to determine adults’ gluteal muscle, subcutaneous tissue, and total tissue thicknesses. We think that our results will help healthcare professionals determine the appropriate needle length for intramuscular injections administered to the gluteal site in adults.

Aims and research questions

This systematic review and meta-analysis aimed to determine the gluteal muscle and subcutaneous tissue thickness in adults. The research questions were (1) How thick are the gluteal muscle, subcutaneous tissue and total tissue in adults? and (2) Do gluteal muscle and subcutaneous tissue thicknesses in adults differ by sex and BMI?

Methods

Design

This study adhered to the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA) (Moher et al., 2009). The study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) under protocol code. The research protocol was registered in PROSPERO (CRD42021241793).

Eligibility criteria

Studies eligible for this systematic review met the following criteria (PEOS): Patient (P): adults. Exposure (E): gluteal muscle and subcutaneous tissue thickness measurement. Outcomes (O): gluteal muscle and subcutaneous tissue thickness (muscle and subcutaneous tissue thickness measurements at the ventrogluteal site (V and G methods) and the dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur and four-way split methods). Study design (S): The sample consisted of English and Turkish articles published between January 2010 and May 2021, cross-sectional studies. The exclusion criteria were as follows: (1) unspecified method, (2) lack of access to the full article (articles where full text cannot be accessed because not all results can be accessed), (3) letters to editors and (4) systematic and traditional review studies.

Search strategy

The study was conducted between April and May 2021. The Turkish Medline, Ulakbim and National Thesis Center databases were screened using the keywords, The Cochrane, Web of Science, Science Direct, PubMed (MEDLINE included), CINAHL Plus with Full text (EBSCO host), OVID and SCOPUS databases were screened using the keywords ‘intramuscular injection’, ‘subcutaneous tissue thickness’, ‘muscle tissue thickness’ and ‘needle length’. Pubmed (MEDLINE included) database was screened using keywords as follows: (intramuscular[All Fields] AND injection*OR[All Fields]) AND (subcutaneous tissue thickness*[All Fields] OR subcutaneous tissue thicknesses*[All Fields])) OR (muscle tissue thickness*[All Fields] OR muscle tissue thicknesses*[All Fields]) OR (needle length*[All Fields] OR needle lengths*[All Fields]) AND (‘2000/01/01’[PubDate]: ‘2021/12/31’[PubDate]). The reference lists of the included studies were also checked for additional searching.

Study selection

Two independent researchers checked the titles, abstracts and full-text manuscripts to choose articles for this study. In case of conflicts among these two researchers, a third researcher stepped in to alleviate the disagreements and to reach a consensus. In addition, some studies were excluded during data extraction and meta-analysis due to missing data. Studies with missing data and data that were not appropriate for the purpose of this study were excluded.

Data extraction

Data were extracted using a data extraction tool developed by the researchers. The process revealed data on research setting and time, ventrogluteal and dorsogluteal muscle thickness, subcutaneous tissue thickness and total tissue thickness results, sample size, sex and BMI averages. Two researchers extracted the data independently under the supervision of the senior author. They resolved the differences in their results by rechecking the studies and discussing until they reached a consensus.

Quality appraisal

The methodological quality assessment of the articles included in this systematic review was made with the JBI Critical Appraisal Checklist for Analytical Cross Sectional Studies published by The Joanna Briggs Institute (Moola et al., 2017). The second and the third researchers made the assessment independently and converted the results into one text, which the first researcher then checked. The checklist consisted of eight items scored as ‘yes’, ‘no’, ‘unclear’ and ‘not applicable’.

Data synthesis

The mean thicknesses of muscle and subcutaneous tissue at different sites were continuous variables. The standardised mean difference was calculated at the 95% confidence interval (CI) for each outcome variable. The data were combined using meta-analysis (Comprehensive Meta-Analysis Version 3-Free Trial (https://www.meta-analysis.com/pages/demo.php). Heterogeneity was assessed using the Cochrane Q and Higgins I² tests. All meta-analysis sets had an I² of more than 50%, indicating high heterogeneity. Therefore, meta-analyses were performed using the random effect model. For sensitivity analysis, a meta-regression was conducted to determine the effect of sex and BMI on estimated averages of muscle and subcutaneous tissue thickness. All tests were calculated as two-tailed and p ⩽ 0.05 was accepted for statistical significance.

Results

Screening results

The literature review revealed 7.289 articles. Duplicates were removed. Relevance was evaluated based on titles and abstracts. The screening yielded 27 relevant full-text articles. There is a large body of research on the topic, but there are very few studies evaluating subcutaneous (SC) tissue thickness and muscle thickness with ultrasound. The sample consisted of six articles that reported measurements of muscle and subcutaneous tissue thicknesses at the gluteal site according to the ultrasound method (Table 1). Figure 1 presents the steps of article selection.

Table 1.

Characteristics and main findings of the studies included in the systematic review and meta-analyses.

Publication/country	Data collection year	Study design	Measurement method	BMI (kg/m2) MD ± SS	Sample size Male/female	Main findings	Quality score
Çaliskan et al. (2021), Turkey	2019– 2020	Cross-sectional	Ultrasound	22.09 ± 3.83	91 17/74	V method; -Muscle thickness: 35.10 ± 7.47 -Subcutaneous tissue thickness: 31.65 ± 14.26 -Total tissue thickness: 66.76 ± 15.71 G method; -Muscle thickness: 31.82 ± 8.23 -Subcutaneous tissue thickness: 28.32 ± 12.75 -Total tissue thickness: 60.15±13.49 Dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur); -Muscle thickness: 40.64 ± 6.51 -Subcutaneous tissue thickness: 39.95 ± 12.20	Yes: 6/8
Gunes et al. (2008), Turkey	2007–2008	Descriptive and methodological	Ultrasound	26.2 ± 5.1	114 40/74	V method; -Muscle thickness: 33.4 ± 7.7 -Subcutaneous tissue thickness: 25.4 ± 13.4 Dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur); -Muscle thickness: 36.7 ± 8.2 -Subcutaneous tissue thickness: 26.3 ± 11.7	Yes: 6/8
Kaya et al. (2015), Turkey	2011–2012	A cross-sectional study	Ultrasound	25.31 ± 5.00	120 41/79	V method; -Subcutaneous tissue thickness: 21.26 ± 10.93 -Total tissue thickness: 61.99 ± 14.33 G method; -Subcutaneous tissue thickness: 17.43 ± 9.72 -Total tissue thickness: 57.41 ± 13.22	Yes: 6/8
L arkin et al. (2017), Australia	Not specified	Cross-sectional design	Ultrasound	25.5 ± 3.7	145 83/62	V method; -Muscle thickness: 38.2 ± 9.5 -Subcutaneous tissue thickness: 13.14 ± 8.4 -Total tissue thickness: 51.6 ± 13.11 Dorsogluteal site four-way split method; -Muscle thickness: 51.6 ± 11 -Subcutaneous tissue thickness: 18.2 ± 8.8 -Total tissue thickness: 69.8 ± 14.6	Yes: 6/8
Larkin et al. (2018), Australia	Not specified	Cross-sectional design	Ultrasound	25 ± 4	60 28/32	V method; -Muscle thickness: 36.9 ± 11.2 -Subcutaneous tissue thickness: 12.9 ± 10.2 -Total tissue thickness: 49.8 ± 17.2 G method; -Muscle thickness: 40.2 ± 8.1 -Subcutaneous tissue thickness: 13.3 ± 9.9 -Total tissue thickness: 57.41 ± 13.22	Yes: 5/8
Tugrul et al. (2020), Turkey	2015–2016	Cross-sectional design	Ultrasound	26.45 ± 4.84	150 75/75	V method; -Muscle thickness: 46.98 ± 14.08 -Subcutaneous tissue thickness: 15.44 ± 8.01	Yes: 6/8

BMI: body mass index; MD: Mean, SS: Standard deviation.

Figure 1.

Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols flow diagram of the research process.

Characteristics of studies and participants

One article was in Turkish, while the remaining were in English. Five studies were cross-sectional (Caliskan et al., 2021; Kaya et al., 2015; Larkin et al., 2017, 2018; Tuğrul et al., 2020), and one was a descriptive study (Gunes et al., 2008). The studies collected data through ultrasound using the V and G methods at the gluteal site and PSIS-T and four-way split methods at the dorsogluteal site. They collected data between 2007 and 2020. They were published between 2008 and 2021. The studies were conducted in Turkey (n = 4) or Australia (n = 2). The sample size ranged from 60 to 150 and the total sample size was 680 (396 women and 284 men). Participants had a mean BMI of 22.09 ± 3.83 to 26.45 ± 4.84 (Table 1).

Quality assessment results

Five studies had a quality assessment score of 6/8, while one study had a quality assessment score of 5/8 (Table 1).

Meta-analysis results

Five studies employed the V method to measure mean muscle thicknesses at designated sites (Caliskan et al., 2021; Gunes et al., 2008, Larkin et al., 2017, 2018; Tugrul et al., 2020). The meta-analysis revealed that the V site had an estimated mean muscle thickness of 38.071 ± 2.119 (min–max: 33.918–42.225) (Figure 2).

Figure 2.

Meta-analysis of muscle thickness and forest plots (V method, G method and dorsogluteal site, respectively).

Two studies employed the G method to measure mean muscle thicknesses at designated sites (Caliskan et al., 2021; Larkin et al., 2018). The meta-analysis revealed that the G site had an estimated mean muscle thickness of 35.989 ± 4.190 (min–max: 27.777–44.201) (Figure 2).

Two studies reported mean muscle thicknesses at the dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur) (Caliskan et al., 2021; Gunes et al., 2008). The meta-analysis revealed that the dorsogluteal site had an estimated mean muscle thickness of 38.686 ± 1.970 (min–max: 34.825–42.547) (Figure 2). In these datasets, publication bias among the studies was statistically insignificant (the cut-off point for the site determined by the V method (B0): 11.40101, 95% CI: −17.87398, 40.67600; t = 1.23939, df = 3; p = 0.30332; the cut-off point for the site determined by the G method (B0): 11.40101, 95% CI: −4,58102, 31,53307; t = 2,07207; df = 4; p = 0.106, respectively) (Table 2).

Table 2.

Meta-analysis results of ventrogluteal and dorsogluteal site categorical variables.

	Mean	Standard error	Lower	Upper	Z/p	Q	df	p	I2%	95% Cl (I2)
Muscle thickness
V method (5)	38.071	2.119	33.918	42.225	17.966/0.00	108.431	3	0.30332	96	−17.87, 40.67
G method (2)	35.989	4.190	27.777	44.201	8.58/0.00	38.211	1	0.75738	97	−4,58, 31,53
Dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur) (2)	38.686	1.970	34.825	42.547	19.638/0.00	14.707
Subcutaneous tissue thickness
V method (6)	19.927	2.493	15.041	24.813	7.99/0.00	200.01	4	0.106	97	−4.58, 31.53
G method (3)	19.661	3.992	11.836	27.486	4.925/0.00	71.616	1	0.757	97	−294.33, 313.50
Dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur) (3)	42.560	8.840	25.235	59.886	4.815/0.00	232.040	1	0.196	99	101.70, 168.44
Total tissue thickness
V method (4)	57.585	3.924	49.894	65.277	14.67/0.00	84.705	2	0.810	96	−52.08, 59.13
G method (3)	57.192	1.721	53.818	60.565	57.56/0.00	8.275	1	0.597	75	−109.23, 97.33

Six studies employed the V method to measure subcutaneous tissue thicknesses (Caliskan et al., 2021; Gunes et al., 2008; Kaya et al., 2015; Larkin et al., 2017, 2018; Tugrul et al., 2020). Three studies employed the G method to measure subcutaneous tissue thicknesses (Caliskan et al., 2021; Kaya et al., 2015; Larkin et al., 2018). Three studies employed the dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur) to measure subcutaneous tissue thicknesses (Caliskan et al., 2021; Gunes et al., 2008; Zaybak et al., 2015). The meta-analysis showed that the V method site had an estimated subcutaneous tissue thickness of 19.927 ± 2.493 (range 15.04–24.81). The G method site had an estimated subcutaneous tissue thickness of 19.661 ± 3.992 (range 11.836–27.486). The PSIS-T method site had an estimated subcutaneous tissue thickness of 42.560 ± 8.840 (range 25.23–59.88) (Figure 3). Publication bias was not statistically significant (B0: 13.47602, 95% CI: −4.58102, 31.53307; t = 2.07207, df = 5; p = 0.107 for the V and G method sites; B0: 9.58434; 95% CI: −294.33148, 313.50015; t = 0.40070; df = 2; p = 0.757 for the G method site; B0: 33.36804; 95% CI: 101.70424, 168.44033; t = 3.13892; df = 2; p = 0.196 for the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur method site) (Table 2).

Figure 3.

Meta-analysis of subcutaneous tissue thickness and forest plots (V method, G method and dorsogluteal site, respectively).

Four studies reported mean total tissue thicknesses at the V method site (Caliskan et al., 2021; Larkin et al., 2017; Kaya et al., 2015; Larkin et al., 2018). Three studies reported mean total tissue thicknesses at the G method (Caliskan et al., 2021; Kaya et al., 2015; Larkin et al., 2018). One study reported mean total tissue thicknesses at the dorsogluteal site determined using the four-way split method (Larkin et al., 2017). The meta-analysis showed that the V method site had an estimated total tissue thickness of 57.585 ± 3.924 (range 49.894–65,277). The G method site had an estimated total tissue thickness of 57.192 ± 1.721 (range 53.818–60.565). The dorsogluteal site (four-way split method) had an estimated total tissue thickness of 69.800 ± 1.212 (range 67.424–72.176). Publication bias was not statistically significant (B0: 3.52266; 95% CI: −52.08873, 59.13405; t = 0.27255; df = 3; p = 0.811 for the V method site; B0: −5.94791; 95% CI: 109.23165, 97.33582; t = 0.73173; df = 2; p = 0.598 for the G method site).

Meta-regression results

A meta-regression analysis was performed to determine the effect of sex on the V method muscle and subcutaneous tissue thicknesses. The result showed that muscle thickness was not statistically significant but that subcutaneous tissue thickness was statistically significant (Q = 1.45, df = 1, p = 0.2291; explanatory rate: 0.01% and Q = 5.37, df = 1, p = 0.0204; explanatory rate: 0.31%, respectively). A meta-regression analysis was performed to determine the effect of sex on the G method muscle and subcutaneous tissue thicknesses. The result showed no statistical significance (Q = 3.34, df = 1, p = 0.0677). The model had an explanatory rate of 0.47%.

A meta-regression analysis was performed to determine the effect of sex on the total tissue thicknesses determined using the V and G methods. The result showed no statistical significance (Q = 1.35, df = 1, p = 0.244 and Q = 0.35, df = 1, p = 0.55, respectively). The models had an explanatory rate of 0.12% and 0.13%, respectively (Table 3).

Table 3.

Meta-analysis results on the effect of sex and BMI on muscle, subcutaneous and total tissue thickness at ventrogluteal and dorsogluteal sites.

	Gender					BMI
	Q	df	p	I2 (%)	r 2	Q	df	p	I2 (%)	r 2
Muscle thickness
V method	1.45	1	0.2291	81	0.01	0.67	1	0.4132	97	0.00
Dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur)	0.70	1	0.4042	88	0.00	–	–	–	–	–
Subcutaneous tissue thickness
V method	5.37	1	0.0204	95	0.31	3.52	1	0.0607	97	0.18
G method	3.34	1	0.0677	93	0.47	–	–	—	–	–
Dorsogluteal site four-way split method;	5.26	1	0.0218	72	0.70	–	–	—	–	–
Dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur)	0.92	1	0.3373	98	0.00	–	—	—	–	–
Total tissue thickness
V method	1.35	1	0.2448	93	0.12	2.25	1	0.1333	95	0.27
G method	0.35	1	0.5525	80	0.13	–	–	–	–	–

BMI: body mass index.

Bold value refers to Tissue thicknesses by region.

A meta-regression analysis was performed to determine the effect of sex on subcutaneous tissue thicknesses determined using the dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur) and the dorsogluteal site (four-way split methods). The result showed no statistical significance (Q = 0.92, df = 1, p = 0.3373 and Q = 0.526, df = 1, p = 0.0218, respectively). The models had an explanatory rate of 0.00% and 0.70%, respectively (Table 3).

A meta-regression analysis was performed to determine the effect of BMI on the V method muscle, subcutaneous and total tissue thicknesses. The result showed no statistical significance (Q = 0.67, df = 1, p = 0.41; Q = 3.52, df = 1, p = 0.06 and Q = 2.25, df = 1, p = 0.13, respectively). These models had an explanatory rate of 0.00%, 0.18%, and 0.27%, respectively (Table 3).

Discussion

This systematic review and meta-analysis combined the results of six studies to determine gluteal muscle, subcutaneous, and total tissue thicknesses in adults. The V site had an estimated muscle thickness of 38.071 ± 2.119. The G site had an estimated muscle thickness of 35.989 ± 4.190. The dorsogluteal site had an estimated muscle thickness of 38.686 ± 1.970. The dorsogluteal site had the highest muscle thickness, followed by the V and G sites. The V site had an estimated subcutaneous tissue thickness of 19.927 ± 2.493. The G site had an estimated subcutaneous tissue thickness of 19.661 ± 3.992. The dorsogluteal site had an estimated subcutaneous tissue thickness of 42.560 ± 8.840. The dorsogluteal site had the highest subcutaneous tissue thickness, followed by the V and G sites. The V site had an estimated total tissue thickness of 57.585 ± 3.924. The G site had an estimated total tissue thickness of 57.192 ± 1.721. The dorsogluteal site (four-way split) had an estimated total tissue thickness of 69.800 ± 1.212. The dorsogluteal site (four-way split) had the highest total tissue thickness, followed by the V and G sites. Research shows that the dorsogluteal site has thicker muscle, higher subcutaneous, and total tissue thicknesses than the ventrogluteal site (Coskun et al., 2016; Greenway, 2004; Masuda et al., 2016). Our results indicate that healthcare professionals should administer intramuscular injections at the ventrogluteal site rather than the dorsogluteal site because the former provides a safe injection in terms of subcutaneous tissue thickness. Thick subcutaneous tissue may prevent the needle from reaching the muscle in injections at the gluteal site (Larkin et al., 2018). Researchers assert that the dorsogluteal site should not be the first site of choice for injections due to the risk of sciatic nerve injury and vascular injury (Akbıyık, 2021; Berman et al., 2016; Dinc, 2014; Potter et al., 2017). The subcutaneous tissue at the dorsogluteal site was thicker than that at the V and G sites. Healthcare professionals using standard length needles at the dorsogluteal site are more likely to administer injections into the subcutaneous tissue. Therefore, the ventrogluteal site should be their first site of choice if possible. In addition, the needle length is critical for a successful intramuscular injection because subcutaneous tissue thickness determines whether or not the needle reaches the muscle. The needle should be 2.75–3.5 cm (1–1.5 inches) long for a successful IM injection (Akbıyık, 2021; Berman et al., 2016). For a successful intramuscular injection, the needle should have an injection depth of about 30 mm and be inserted about 25 mm into the muscle (Chan et al., 2006; Ozen et al., 2019). Our results indicate that the needle should be 24 mm (19 + 5), 24 mm (19 + 5) and 47 mm (42 + 5) long for the V, G and dorsogluteal sites (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur), respectively. For a successful IM injection, subcutaneous tissue should be thinner than 25 mm, and the total tissue should be 35 mm thick (Cook et al., 2006; Ozen et al., 2019). The effectiveness of medication and the success of an intramuscular injection depends on whether or not the medication is administered into the muscle (Tanioka et al., 2018). Healthcare professionals should take the subcutaneous tissue thickness into account and choose the right needle for the injection site. Healthcare professionals in some countries e.g. the United States need long needles to administer intramuscular injections to people with obesity, but such needles are not available (Strohfus et al., 2017). According to our observations, healthcare professionals in clinics in Turkey use standard needles (32–38 mm long) to administer intramuscular injections. Therefore, we recommend an intramuscular injection guide for nurses. In addition, hospitals should procure needles in different sizes.

There was a significant difference in V site subcutaneous tissue thicknesses between males and females. Sex had an explanatory rate of 31%. However, BMI had no effect on V site subcutaneous tissue thicknesses. Research shows that women have thicker subcutaneous tissue than men (Boyd et al., 2013; Burbridge, 2007; Chan et al., 2006; Dayananda et al., 2014; Doğu Kökcü et al., 2021; Kaya et al., 2015; Nisbet, 2006; Zaybak et al., 2007). Zaybak et al. (2007) conducted a study on obese individuals and reported that women had thicker subcutaneous tissue at the ventrogluteal and dorsogluteal sites than men. Therefore, they concluded that the success rate of intramuscular injections was higher in men than in women. Burbridge (2007) determined that women were mostly administered subcutaneous injections. These results indicate that healthcare professionals should take the sex of the patient into account and choose the right needle to administer intramuscular injections at the V site. Sample selection may be the reason why sex does not affect other sites. BMI is another factor affecting the site and needle selection for safe intramuscular injections (Strohfus et al., 2017). However, our results showed no effect of BMI on subcutaneous, muscle, and total tissue. This may be because our sample mainly consisted of normal-weight individuals. Therefore, future studies should focus on subcutaneous, muscle, and total tissue thicknesses in individuals with different BMI. Healthcare professionals should choose the right-size needles to reach the muscle during intramuscular injections (Chan et al., 2006; Nisbet, 2006). Zaybak et al. (2007) reported that 1.5 inches needles were not long enough to reach the muscle in ventrogluteal or dorsogluteal intramuscular injections in adults with a BMI greater than 24.9 kg/m². In addition, nurses fail to administer intramuscular injections properly for four reasons. First, they tend to use shorter needles in skinny-looking people (Greenway, 2014). Second, they do not usually base needle size selection on comprehensive patient evaluation (Cocoman and Murray, 2008; Wynaden et al., 2015). Third, they believe that shorter needles cause less pain (Greenway, 2014; Wynaden et al., 2015). Fourth, they do not know much about what length of needles to use for intramuscular injections (McWilliam et al., 2014). Nurses who choose the right-size needle and the right insertion depth based on individual differences are more likely to administer intramuscular injections properly and ensure patient comfort and medication effectiveness (Yasuhara et al., 2012). To that end, they need to focus on three variables: body size, subcutaneous tissue thickness, and injection site. These results indicate that nurses have no standards by which to abide when choosing the right-size needle for intramuscular injections.

Limitations

This study had four limitations. First, the number of studies and the total sample size were limited. Second, the sample consisted mainly of young and healthy individuals. Therefore, the results are sample-specific. Third, the subcutaneous tissue and muscle thicknesses may have been affected by sex and BMI. However, we performed meta-regression analyses to keep this effect under control. Fourth, heterogeneity between studies was high in all meta-analyses, which may have weakened the power of the findings. We used the Random Effect model in analyses with high heterogeneity to keep the fifth limitation under control.

Conclusion

The ventrogluteal site determined using the V method had a muscle thickness of 38.071 ± 2.119 mm. The ventrogluteal site determined using the G method had a muscle thickness of 35.989 ± 4.190 mm. The ventrogluteal site determined using the V method had a subcutaneous tissue thickness of 19.927 ± 2.493 mm. The ventrogluteal site determined using the G method had a subcutaneous tissue thickness of 19.661 ± 3.992 mm. The ventrogluteal site determined using the dorsogluteal site (the region above the imaginary diagonal line connecting the posterior iliac spine and the greater trochanter of the femur) had a subcutaneous tissue thickness of 42.560 ± 8.840 mm. Women had thicker subcutaneous tissue at the V site than men. Sex and BMI had no effect on subcutaneous, muscle, and total tissue thicknesses at the other sites. Healthcare professionals should take these results into account when choosing the right size needles for successful intramuscular injections.

Implications for clinical practice and research

Nurses should choose the ventrogluteal site (V and G methods) to administer intramuscular injections because it has the thinnest subcutaneous tissue at the gluteal site. If they are to administer intramuscular injections at the dorsogluteal site, they should choose longer needles to reach the muscle because the dorsogluteal site has a thick subcutaneous adipose tissue. Educators should teach students and healthcare professionals to take the subcutaneous tissue thickness into account when choosing the right-size needle to administer intramuscular injections at the gluteal site. Hospitals should consider our results and their patients’ characteristics when purchasing the right-size needles for intramuscular injections. Researchers should conduct similar studies with different age groups and BMI subgroups.

Key points for policy, practice and/or research.

• The dorsogluteal site has thicker muscle than the ventrogluteal site.

• The dorsogluteal site has thicker subcutaneous tissue than the ventrogluteal site.

• According to the V method, women have thicker subcutaneous tissue at the ventrogluteal site than men. BMI does not affect subcutaneous tissue thicknesses. Sex and BMI do not affect subcutaneous, muscle and total tissue thicknesses determined using the geometric (G) method at the gluteal site and the injection site determined at the dorsogluteal site.

• Healthcare professionals should take these results into account when choosing the right-size needles for successful IM injections.

Biography

Emel Gulnar is an associate professor of nursing at Kırıkkale University, Turkey. Her research interests are nursing education, intramuscular injection, urinary incontinence and nursing care.

Yadigar Ordu is a lecturer in the Cankiri Karatekin University, Home Patient Care Program. Her research interests are nursing education, intramuscular injection, game-based learning and the nursing process.

Sule Biyik Bayram is an assistant professor of nursing at Karadeniz Technical University, Turkey. Her research interests are nursing education, virtual reality, fundamentals of nursing and nursing care.

Nurcan Çalışkan is a professor of nursing at Gazi University, Turkey. Her research interests are psychomotor skills teaching, nursing care, concept and theory.