Association between deltoid muscle attenuation and sedation requirement in anterior shoulder dislocation

Abstract

Background

Objective radiological predictors of sedation requirement during closed reduction of anterior shoulder dislocation have not been clearly established. This study aimed to evaluate the association between humeral head displacement parameters and computed tomography (CT)-based deltoid muscle morphology and attenuation with sedation requirement.

Methods

A total of 467 patients presenting with anterior shoulder dislocation between May 2020 and February 2026 were retrospectively screened, and 213 patients were included after applying exclusion criteria. Closed reduction was performed without sedation in 182 patients and under procedural sedation in 31 patients. Humeral head displacement length, humeral head area, and the displacement length-to-head area index (HNADI) were measured on anteroposterior radiographs. CT measurements included anterior, lateral, and posterior deltoid muscle thicknesses, total cross-sectional area, and deltoid muscle attenuation (Hounsfield Units, HU). Independent predictors of sedation requirement were analyzed using multivariate logistic regression.

Results

Patients requiring sedation were significantly older (p=0.022), and age remained an independent predictor in multivariate analysis (OR=1.052, p=0.003). Deltoid HU was significantly higher in the sedation group (p<0.001) and independently associated with sedation requirement (OR=1.133, p<0.001). Humeral head displacement length, humeral head area, HNADI, and deltoid muscle morphometric parameters were not independently associated with sedation requirement.

Conclusion

Sedation requirement during closed reduction of anterior shoulder dislocation is associated with advanced age and increased deltoid HU rather than bony displacement parameters. CT-based assessment of deltoid HU may have potential as an adjunctive parameter for pre-procedural sedation planning.

Introduction

Anterior shoulder dislocation is one of the most common large joint dislocations encountered in emergency departments and typically requires closed reduction to relieve pain, restore function, and prevent complications. A key determinant of successful reduction is the ability to overcome periarticular muscle spasm. For this purpose, procedural sedation and analgesia (PSA) is frequently used. However, PSA is associated with potential drawbacks, including cardiopulmonary complications such as hypoxia and hypotension, the need for close monitoring, and prolonged emergency department stay [1]. Therefore, identifying patients who truly require sedation and optimizing patient selection remain clinically important [2].

In recent years, alternative approaches such as non-sedated reduction techniques, intra-articular local anesthetics, and regional nerve blocks have been shown to achieve comparable success rates in selected patients [3, 4]. Randomized studies have demonstrated that intra-articular lidocaine may provide similar efficacy to procedural sedation while reducing the need for intensive monitoring and shortening emergency department stay [5, 6]. Nevertheless, objective criteria that can reliably predict which patients can tolerate reduction without sedation and which will require it have not been clearly established. In current clinical practice, the decision to use sedation is largely based on subjective factors, including pain tolerance, anxiety level, and clinician experience.

Previous studies investigating predictors of reduction difficulty are limited and have primarily focused on clinical parameters [7]. However, the mechanical resistance encountered during reduction may not depend solely on pain perception but also on structural factors, including the degree of bony displacement [8]. In addition, periarticular soft tissue characteristics have been relatively underexplored. While radiographic assessment of humeral head displacement may reflect the mechanical difficulty of reduction, computed tomography (CT)-based evaluation of deltoid muscle morphology and quality may provide additional insight into muscle resistance and relaxation capacity.

The deltoid muscle, consisting of anterior, lateral, and posterior segments, plays a crucial role in shoulder stability and dynamic control. CT-derived parameters such as muscle thickness, cross-sectional area, and attenuation (Hounsfield Units, HU) allow quantitative assessment of muscle composition, including fatty infiltration. Recent studies have demonstrated that muscle HU is associated with muscle quality and functional outcomes in various orthopedic conditions [9, 10]. However, the relationship between these parameters and sedation requirement during shoulder dislocation reduction has not yet been investigated.

The aim of this study was to evaluate the association between radiographic humeral head displacement parameters and CT-based deltoid muscle morphology and attenuation with the need for sedation during closed reduction in patients with anterior shoulder dislocation without associated fractures. We hypothesized that greater humeral head displacement and higher deltoid HU would be associated with an increased likelihood of requiring sedation.

Materials and methods

Study design and ethical approval

This retrospective study was approved by the Institutional Review Board of Basaksehir Cam and Sakura City Hospital (Approval No: 2026-90; March 16, 2026) and conducted in accordance with the Declaration of Helsinki.

Patient selection

A total of 467 patients who presented to the emergency department with anterior shoulder dislocation between May 2020 and February 2026 were retrospectively reviewed.

Patients were excluded if they had: (1) associated surgical neck or humeral head fractures (n = 112), (2) absence of shoulder computed tomography (CT) imaging (n = 96), (3) posterior or inferior shoulder dislocation (n = 18), (4) prior surgery on the affected shoulder (n = 12), (5) multiple trauma or hemodynamic instability (n = 9), or (6) incomplete or inadequate imaging data (n = 7).

After applying the exclusion criteria, 213 patients were included in the final analysis.

Sample size calculation

A priori sample size calculation was performed using G*Power software (version 3.1.9.7). Assuming a medium effect size (0.66), α = 0.05, power (1 − β) = 0.90, and an allocation ratio of 6.33, a minimum of 210 patients (at least 30 in the sedation group and 180 in the non-sedation group) was required. In the absence of prior studies directly evaluating this outcome, a medium effect size was assumed.The final sample size (n = 213) met this requirement.

Inclusion criteria and clinical management

Inclusion criteria were acute (< 24 h) anterior glenohumeral dislocation without associated proximal humeral fracture. Closed reduction was performed without sedation in 182 patients and under procedural sedation in 31 patients. The decision to administer sedation was made based on clinical assessment, patient pain tolerance, and physician preference. Closed reduction was initially attempted without sedation in all patients. Sedation was considered after unsuccessful initial attempt or inadequate patient tolerance. The decision was made by experienced emergency physicians based on clinical evaluation, including patient condition, comorbidities, cooperation, and anticipated difficulty of reduction [11]. Procedural sedation aimed to achieve a depressed level of consciousness while preserving the patient’s ability to maintain airway control and oxygenation [12].

Radiographic measurements

Standard anteroposterior shoulder radiographs obtained prior to reduction were evaluated. Humeral head displacement length was defined as the linear distance between the anterior glenoid rim and the most medial point of the humeral head (mm) [8]. Humeral head area was measured by manually outlining the cortical margins of the humeral head (mm²). The displacement length-to-head area index (HNADI) was calculated by dividing displacement length by humeral head area (Fig. 1). All measurements were performed using a digital PACS system.

Fig. 1.

Measurement of humeral head displacement length and humeral head area on anteroposterior shoulder radiograph

CT measurements and standardization

CT images were obtained using a multi-detector CT scanner with a tube voltage of 120 kV. CT imaging was performed across multiple scanners within the institution as part of routine clinical workflow. Axial images were reconstructed with a slice thickness of 1–1.5 mm using a standard soft tissue kernel.

CT scans were obtained immediately after reduction as part of routine clinical evaluation, minimizing potential variability in timing. All measurements were obtained from a standardized axial slice at the level of the glenoid fossa where the mediolateral diameter was maximal and the humeral head center was visible. Anterior, lateral, and posterior deltoid muscle thicknesses were measured at the point of maximal thickness of each respective segment, defined as the maximum anteroposterior thickness anterior and posterior to the humeral head and the maximum mediolateral thickness lateral to the humeral head. Measurements were based on the widest cross-sectional dimension of each muscle segment rather than bony landmarks. The entire deltoid muscle was manually segmented on the same slice to calculate total cross-sectional area (mm²), and mean deltoid muscle attenuation (Hounsfield Units, HU) was obtained from the segmented region [9, 13] (Fig. 2). To assess intraobserver reliability, radiographic and CT measurements were repeated by the same observer in a randomly selected 30% subset of the study population after a 48-hour interval to minimize recall bias. Intraclass correlation coefficients (ICC) were calculated to evaluate measurement consistency [14].

Fig. 2.

Deltoid muscle thickness, cross-sectional area, and muscle attenuation (HU) measurements on axial CT

Reduction techniques

Closed reduction procedures were performed in the emergency department by experienced physicians using one of the following techniques based on clinical preference: traction–countertraction, Stimson, or Milch method.

Statistical analysis

Statistical analyses were performed using IBM SPSS Statistics for Windows, version 27.0 (IBM Corp., Armonk, NY, USA). A p-value < 0.05 was considered statistically significant. Categorical variables were expressed as frequencies and percentages, while continuous variables were presented as mean ± standard deviation or median (minimum–maximum), depending on distribution. Normality was assessed using the Kolmogorov–Smirnov test. For comparisons between sedation and non-sedation groups, independent samples t-test was used for normally distributed variables and Mann–Whitney U test for non-normally distributed variables. The chi-square test was used for categorical variables. Multivariate logistic regression analysis was performed to identify independent predictors of sedation requirement. Variables considered clinically and radiologically relevant, including demographic variables (age, sex) and radiological measurements, were included in the model. Results were reported as odds ratios (OR) with 95% confidence intervals.

Results

A total of 467 patients presenting with anterior shoulder dislocation were retrospectively evaluated. Due to the exclusion criteria, 254 patients were excluded, and 213 patients were deemed eligible for analysis. Intraobserver reliability analysis demonstrated excellent agreement for all measurements (ICC > 0.90).

Among the included patients, 141 of 182 patients (77.5%) in the non-sedation group were male and 41 (22.5%) were female, whereas in the sedation group, 24 of 31 patients (77.4%) were male and 7 (22.6%) were female. There was no statistically significant difference between the groups in terms of sex distribution (p = 0.995). Logistic regression (LR) analysis also confirmed that sex had no independent effect on sedation (p = 0.640; OR = 1.480). Sex did not play a determining or confounding role in the decision for sedation, and the sex profile of the patients was not considered a factor influencing sedation requirement (Table 1).

Table 1.

Comparison of demographic and clinical characteristics of patients according to sedation status

	Sedation status		P
	No (n = 182)	Yes (n = 31)
Gender			0,995*
Male	141 (77,5)	24 (77,4)
Female	41 (22,5)	7 (22,6)
Total	182 (100,0)	31 (100,0)
Side			0,436*
Right	116 (63,7)	22 (71)
Left	66 (36,3)	9 (29)
Total	182 (100,0)	31 (100,0)
Age	29,5 (18–93)	43 (18–79)	0,022†

Bold values indicate statistically significant differences (p < 0.05)

*Chi-square test; n(%)

†Mann-Whitney U test; median (minimum-maximum)

n=Number of patients

When age was evaluated, the median age of patients in the non-sedation group was 29.5 years (range: 18–93), whereas the median age in the sedation group was 43 years (range: 18–79). This difference between the groups was statistically significant (p = 0.022). In the multivariate LR model, age remained strongly significant (p = 0.003; OR = 1.052). Age was identified as a persistent independent risk factor, increasing the likelihood of requiring sedation by 5.2% per year, independent of other clinical and radiological variables (Table 1).

No statistically significant difference was observed between the groups in terms of anterior and posterior deltoid thickness. The median anterior deltoid thickness was 18 mm (5–36) in the non-sedation group and 20 mm (10–30) in the sedation group (p = 0.280). The median posterior deltoid thickness was 23 mm (12–42) in the non-sedation group and 24 mm (12–38) in the sedation group, with no significant difference (p = 0.650) (Table 2).

Table 2.

Comparison of radiological measurements of patients according to sedation status

Radiological measurements	Sedation status		P*
	No (n = 182)	Yes (n = 31)
Anterior deltoid length (mm)	18 (5–36)	20 (10–30)	0,280*
Lateral deltoid length (mm)	15 (5–34)	17 (10–40)	0,022*
Posterior deltoid length (mm)	23 (12–42)	24 (12–38)	0,650*
Deltoid area (mm2)	4000 (1800–7300)	4500 (2200–7500)	0,109*
Deltoid attenuation (HU)	45 (15–70)	50 (35–86)	< 0,001*
Humeral head displacement (mm)	38,58 ± 8,64	39,38 ± 9,03	0,738†
Humeral head area (mm2)	2300 (1400–3700)	2300 (1584–2824)	0,488*
HNADI	0,017 (0,007 − 0,032)	0,017 (0,008 − 0,029)	0,650*

Bold values indicate statistically significant differences (p < 0.05)

*Mann-Whitney U test; median (minimum-maximum)

†Independent samples t-test; (mean ± standard deviation)

n=Number of patients

Lateral deltoid thickness was higher in the sedation group; the median value was 15 mm (5–34) in the non-sedation group and 17 mm (10–40) in the sedation group, and this difference was statistically significant in univariate analysis (p = 0.022). However, when included in the multivariate logistic regression model, lateral deltoid thickness lost its significance as an independent predictor (p = 0.722; OR = 1.019) (Table 2).

Deltoid HU values were measured as a median of 45 (15–70) in the non-sedation group and 50 (35–86) in the sedation group. This difference was highly statistically significant (p < 0.001). This significance remained strong in the multivariate LR model (p < 0.001; OR = 1.133). Deltoid HU was identified as an independent predictor of sedation requirement, increasing the probability of requiring sedation by approximately 13.3% for each unit increase (Table 2).

Mean humeral head displacement values (mm) were 38.58 ± 8.64 in the non-sedation group and 39.38 ± 9.03 in the sedation group. There was no statistically significant difference between the groups (p = 0.738). The degree of humeral head displacement was not a discriminative factor for sedation preference (Table 2).

For humeral head area (mm²), the median value was 2300 in both groups (ranges: 1400–3700 and 1584–2824, respectively), with no statistically significant difference (p = 0.488). The size of the humeral head did not influence sedation requirement (Table 2).

When HNADI values were evaluated, the median was 0.017 (0.007–0.032) in the non-sedation group and 0.017 (0.008–0.029) in the sedation group. No statistically significant difference was observed between the groups (p = 0.650). This parameter was not useful in predicting sedation requirement (Table 2).

According to the results of the multivariate logistic regression analysis, when all variables were evaluated together, deltoid HU remained a statistically significant risk factor (p < 0.001; Exp(B) = 1.133). Each unit increase in deltoid HU increased the likelihood of requiring sedation by approximately 13.3%.

Age was another variable that remained statistically significant in the multivariate model (p = 0.003; Exp(B) = 1.052). Each one-year increase in age was associated with a 5.2% increase in the probability of requiring sedation. All other radiological measurements and sex were not independently associated with sedation when other factors were controlled for.

Discussion

The most important finding of this study is the identification of an independent association between advanced age, increased deltoid HU, and the requirement for sedation during the reduction of anterior shoulder dislocation. Although reduction techniques and analgesia methods have been extensively investigated in the literature, radiological parameters predicting sedation requirement have been evaluated in a limited number of studies.

Furuhata et al. demonstrated a statistically significant positive correlation between increasing age and the need for sedation in a retrospective series of 156 patients with anterior shoulder dislocation [15]. In our study, age was also found to be independently significant in the multivariate model, and each one-year increase was shown to increase the likelihood of requiring sedation. This finding may be related to differences in pain perception in older patients, increased joint stiffness, and clinicians’ preference for more controlled procedures. Additionally, age-related changes in periarticular soft tissue characteristics may necessitate greater analgesic support during reduction.

In a recent study investigating the relationship between the position of the humeral head relative to the glenoid and complications that may occur during reduction, Gunsoy et al. reported that the position of the humeral head relative to the glenoid is a significant risk factor for the development of iatrogenic fractures during reduction [8]. This finding suggests that bony displacement characteristics may be mechanically important during the reduction process. However, in our study, humeral head displacement length, humeral head area, and their ratio (HNADI) were not found to be associated with sedation requirement. This result suggests that while bone position may be a determinant of complications during reduction, the need for sedation may not be explained to the same extent by bony displacement parameters.

In imaging studies evaluating shoulder function, thickness and cross-sectional measurements of the anterior, lateral, and posterior segments of the deltoid muscle have been assessed. Meyer et al. analyzed the shape and thickness of deltoid muscle segments using magnetic resonance imaging in patients with chronic rotator cuff tears; however, these measurements were not found to be significantly associated with functional shoulder parameters [16]. This finding suggests that the relationship between deltoid muscle morphology and clinical outcomes may not always be direct. Indeed, recent studies focusing on muscle composition have demonstrated that muscle quality cannot be fully reflected by morphological measurements alone. In a recent study published in 2025, intermuscular adipose tissue was shown to be more determinant than intramuscular fat content in defining muscle attenuation, and it was emphasized that muscle attenuation may be a more sensitive parameter for evaluating muscle function [17]. However, no study in the literature has evaluated the relationship between these parameters and sedation requirement. In our study, anterior, lateral, and posterior deltoid segment lengths and total muscle area were objectively measured using CT; however, these morphometric parameters were not found to be independently associated with sedation requirement.

In recent years, CT-based muscle analyses have emerged as reliable and quantitative methods for evaluating muscle quality. Hounsfield Unit (HU) values are indirect indicators of muscle attenuation and fatty infiltration and provide important information regarding the biomechanical properties of muscle [18]. In our study, the independent association between deltoid muscle attenuation and sedation requirement suggests that muscle quality may be associated with the mechanical resistance encountered during reduction. Increased HU values reflect reduced fatty infiltration but may also be associated with increased passive muscle stiffness, which may limit spontaneous muscle relaxation during reduction. Higher HU values, reflecting a more compact muscle structure, may be associated with increased resistance to muscle relaxation and which may be associated with an increased likelihood of requiring sedation. In the literature, muscle attenuation has also been shown to be associated with clinical outcomes. Liang et al. reported a significant relationship between proximal humerus fractures and lower deltoid muscle attenuation [9]. These findings support the notion that muscle attenuation, rather than muscle area, may better reflect functional capacity and biomechanical resistance.

These findings indicate that, in patients presenting with anterior shoulder dislocation in the emergency department, radiographic bony displacement parameters alone are may be insufficient for sedation planning and that periarticular muscle quality may also be taken into consideration. In particular, sedation requirement may be more likely in patients with advanced age and increased deltoid HU. Additionally factors such as patient anxiety, pain tolerance, and physician preference may also influence sedation decisions and should be considered when interpreting these findings.

This study has several limitations. First, due to its retrospective design, not all clinical variables that may influence the decision for sedation could be controlled. The decision to administer sedation was not based on a rigid standardized protocol but was made by experienced emergency physicians according to clinical evaluation. As sedation may have been more frequently preferred in patients anticipated to have difficult reductions, a degree of selection bias cannot be excluded. In addition, the use of different reduction techniques (traction–countertraction, Stimson, and Milch methods) may have resulted in variability affecting the difficulty of reduction and consequently influenced the results. Although CT imaging was performed immediately after reduction, the potential influence of early post-reduction soft tissue changes, including edema, on muscle attenuation values cannot be completely excluded. As this is a retrospective exploratory analysis, the imaging parameters were evaluated to investigate their association with sedation requirement and were not used to guide clinical decision-making. These findings should therefore be interpreted as hypothesis-generating and require prospective external validation before clinical implementation. Future studies should be designed as prospective and multicenter investigations evaluating clinical and radiological parameters affecting sedation requirement within a standardized protocol. In particular, studies in which sedation decisions are based on predefined objective criteria, reduction techniques are standardized, and clinical variables such as pain scores, time to presentation, and first-time versus recurrent dislocation are included in the analysis would contribute to the validation of these findings. Furthermore, studies evaluating the integration of HU-based muscle quality measurements into clinical decision-making algorithms may better clarify the potential role of this parameter in sedation planning.

Conclusion

Sedation requirement during closed reduction of anterior shoulder dislocation is associated with advanced age and increased deltoid muscle HU, independent of bony displacement parameters. While increasing age was found to increase the likelihood of sedation, deltoid HU measured on CT was also identified as an independent predictor. In contrast, humeral head displacement length, humeral head area, and HNADI were not found to be significant in predicting sedation requirement. These findings indicate that, in reduction planning, not only bony position but also periarticular muscle quality may be taken into consideration.

Authors’ contributions

Mehmet Önüt: Conceptualization, study design, data collection, data analysis, manuscript writingAziz Furkan Günay: Methodology, data analysis, softwareMete Özer: Data collection, investigation, visualizationMehmet Ali Talmaç: Methodology, validationYiğit Önaloğlu: Data collection, investigation, validationAll authors read and approved the final manuscript.

Funding

The authors received no financial support for this study.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Institutional Review Board of Basaksehir Cam and Sakura City Hospital (Approval number: 2026-90, Date: March 16, 2026). Written informed consent was obtained from all participants prior to enrollment.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.