Identification of factors related to pain from musculoskeletal injections

Abstract

Background

Musculoskeletal injections are a common clinical procedure, often intended to reduce joint or muscular pain in patients. Further identification is warranted to identify additional clinical variables that may lead to increased or decreased pain perception with musculoskeletal injections.

Objective

To examine clinical, demographic, and injection‐related factors with patient‐perceived pain during musculoskeletal injections, which expands upon prior studies.

Design

Cross‐sectional study.

Setting

Retrospective study involving outpatient orthopedic clinics. Consecutive adult patients (age ≥ 18 years) undergoing musculoskeletal injections were reviewed.

Patients

A total of 1371 injections from 935 patients were eligible for the analysis. Exclusion criteria included cognitive disability, non‐English‐speaking patients, and aphasia.

Interventions

N/A.

Main Outcome Measures

Patients reported their pre‐, intra‐, and postprocedural pain on a numerical scale from 0 to 10. Pain scores, demographics, and injection specifics were analyzed after retrospective chart review for their effect on intraprocedural pain.

Results

A total of 1371 injections (62.4% female, mean age 58.6 ± 16.1 years, body mass index 29.6 ± 7.3 kg/m²) were included for analysis. The median intraprocedure pain score was 2. According to the multivariate linear regression model, female gender (B = 0.42; 95% confidence interval [CI] = 0.15–0.69; p < .01), ultrasound image guidance (B = 0.66; 95% CI = 0.22–1.10; p < .01), presence of a trainee (B = 0.44; 95% CI = 0.15–0.73 p < .01), and body mass index (B = 0.04; 95% CI = 0.01–0.06; p < .01) were significantly associated with greater intraprocedure pain score, whereas use of sodium bicarbonate (B = −0.68; 95% CI = −1.01 to −0.35; p < .01), age (B = −0.01; 95% CI = −0.02 to −0.01; p = .04), and injectate volume (B = −0.06; 95% CI = −0.13 to −0.01; p = .04) had significant, inverse associations with intraprocedure pain score. The logistic regression model showed the significant association of presence of trainee (odds ratio = 1.86; 95% CI = 1.23–2.83; p < .01) to intraprocedure pain score of ≥1 (vs. 0).

Conclusions

This study identified clinical and demographic variables associated with worsened injection pain that may improve the counseling and expectations of patients and ideally lead to reduction in experienced procedural pain. Lower pain scores were associated with use of sodium bicarbonate, absence of a trainee, palpation guidance, and male gender of the patient.

INTRODUCTION

Interventional pain control in the form of injections has grown exponentially over the past few decades in the practice of musculoskeletal medicine. ¹ Joints and bursae are frequently injected for diagnostic and therapeutic purposes. Typically, therapeutic injections consist of an anesthetic agent coupled with a corticosteroid. ² Past literature has revealed that lidocaine is the most commonly used anesthetic with triamcinolone or methylprednisolone as the steroid of choice. ³

Several studies have delved into factors that may influence patients' perceived pain with injections. Some have examined the effect of injection‐related pain due to certain medications, such as propofol ⁴ and potassium chloride. ⁵ Needle diameter, ⁶ speed of injection, ⁷ acidity of the solution, ⁸ injection site, ⁹ and type of procedure ¹⁰ all appear to play a role in the amount of pain a patient feels with the procedure; though much of the literature revolves around subcutaneous administration as opposed to deeper musculoskeletal structures and intra‐articular injections. ¹¹ Additionally, pharmacologic and nonpharmacologic techniques to reduce injection‐related pain in children, generally related to vaccine administration, have been studied. ¹² Limited studies have examined the role of anxiety, ¹³ physician prediction, ¹⁴ preprocedural pain level, ¹³ music, ¹⁵ and ethyl chloride pretreatment. ¹⁶ However, further study is warranted to identify additional clinical variables that may lead to increased or decreased pain perception with musculoskeletal injections.

Having an improved understanding of factors that might be associated with injection‐related pain could help practitioners better counsel patients in expectations and diminish perceived pain. Fear and pain avoidance behaviors can cause patients to avoid doctor visits, which may, in turn lead to delayed diagnosis and recovery. This study aimed to explore what patient‐ and injection‐related factors contribute to a patient's perception of pain. We hypothesized that gender, age, body mass index (BMI), use of sodium bicarbonate, and the presence of a trainee would affect painfulness of injections.

MATERIALS AND METHODS

Study design

This was a retrospective study involving outpatient orthopedic clinics, collecting data on which factors may contribute to patient‐reported pain during injections using immediate patient recall. During the data collection period, clinicians had decided as a group to record the pain related to a procedure for quality improvement to identify factors that they could adjust in their practice. The patients were asked about their preprocedural, intraprocedural, and postprocedural pain, with subsequent chart review performed to gather data. Patients who underwent musculoskeletal injections were included in the study, and data were collected between August 2021 and January 2022. This retrospective study was approved by the institutional review board of the primary author's institution and did not require written consent from all participants, as it was deemed minimal risk.

Patients

Consecutive adult patients (age ≥ 18 years) undergoing ultrasound‐ or palpation‐guided nonspinal musculoskeletal injections were reviewed. Exclusion criteria included cognitive disability, non‐English‐speaking patients, and aphasia.

Physicians/injections

For each injection, one of five fellowship‐trained sports medicine physicians either performed or closely supervised a trainee at their discretion in their typical form of practice; all physicians had at least 5 years of experience with ultrasound‐guided injections. Intra‐articular, peritendinous, perineural, and ganglion cyst injections were included using an ultrasound‐guided or palpation‐guided approach. Injectates included only corticosteroids, hyaluronic acid, and/or local anesthetics. Some physicians buffered their local anesthetic at a 10:1 ratio of lidocaine to sodium bicarbonate. No epinephrine was used in any injection. Physicians were allowed to administer injections as they would in a standard setting. Two chose to inject anesthetic first with a smaller‐gauge (25 gauge or smaller) needle, then follow it approximately 30 seconds later with a larger‐gauge (22 gauge or larger) needle to inject the injectate. Two used a single needle, where they injected anesthetic, then unscrewed the syringe to inject the injectate when in the proper location. The final physician used each technique approximately half the time. Some physicians used ethyl chloride spray when they deemed necessary; none used it on every patient.

Data collection

Patients were asked for preprocedural body part‐specific pain when brought into a clinic room. Following the procedure, the physician remained in the room to address patient concerns, discuss next steps in treatment with the patient, and briefly monitored for adverse events, in line with standard of care protocol for musculoskeletal injections. The postinjection discussion lasted around 2–4 minutes for most physicians. After the physician left the room, the medical assistant proceeded to ask the patient to rate their intraprocedural pain (described later) and body part‐specific postprocedural pain. The intensity was reported by patients verbally using a numerical, continuous scale of 0–10, with 0 being no pain whatsoever and 10 being the worst pain imaginable. The intraprocedure pain score was recorded by staff members (without physician present) as to how painful the procedure was for them, from clinic room arrival to procedure completion. For example, if a patient came in for a left knee injection, they may report a preprocedural pain of 6 in their knee and then a postprocedural knee pain of 0 following the injection due to the anesthetic. They may then describe the pain during the procedure (intraprocedural pain) as a 4. Patients were not given information beforehand to monitor the pain of the procedure. During documentation, physicians ensured that their progress note template included intraprocedural pain as an element of their note, allowing for the medical assistant to clearly document the pain score and for a complete capture of all encounters.

The following data were recorded for each patient: preprocedural pain, intraprocedural pain, postprocedural pain, which physician was performing the injection, age, gender, BMI, injection location, guidance (ultrasound or palpation guidance), a local anesthetic (medication[s] and needle gauge, if any), injectate (needle gauge, type of medication[s], dosage, and volume), presence or absence of a trainee for the procedure, use of sodium bicarbonate mixed in with local anesthetic, and use of ethyl chloride spray (topical anesthetic, where ethyl chloride is sprayed onto the skin, cooling the skin surface). This information was directly extracted from the physician's note. Any missing data points were excluded pairwise in univariate analysis and listwise in multivariate analysis. After completion of the study, it was identified that postprocedure pain had 46.5% of missing data. The missing data were identified to be due to inadequate medical assistant data collection, where staff for some physicians recorded all postprocedure scores, whereas others recorded none. Thus, this variable was not used in the analysis.

Statistical analysis

Demographics and clinical characteristics of patients were summarized using descriptive statistics. A multiple linear regression model was built to examine the associations of select covariates on intraprocedure pain. Before building the model, important covariates were identified via the variable selection process. First, gender, image guidance, age, and BMI were chosen as essential covariates in the final model based on the investigators' expertise (a priori selection). Then, a series of simple linear regression models (univariate models) were run to identify additional covariates potentially associated with intraprocedure pain. Any variable with p < .20 was subsequently chosen as important covariates, ¹⁷ including attending physician, presence of trainee, local needle gauge, use of sodium bicarbonate, and injectate volume. The initial model including all the select covariates above revealed substantial multicollinearity, as indicated by variance inflation factors >10 for attending physician and sodium bicarbonate. ¹⁸ Based on further inspection, of the five physicians, three did not use sodium bicarbonate at all and one used it once, whereas another used it 99.5% of the time. To eliminate multicollinearity, attending physician was removed from the list of covariates, which was justified because it was not one of the covariates of interest, rather was chosen to adjust the final model. As a result, the final set of covariates were gender (categorical), image guidance (categorical), presence of trainee (categorical), local needle gauge (categorical), use of sodium bicarbonate (categorical), age (continuous), BMI (continuous), and injectate volume (continuous). Because some patients had multiple visits and received more than one injection (ie, correlated observations), and because the distribution of intraprocedure pain was positively skewed with both integer and noninteger values included, the model was built using the bootstrapped, cluster‐robust variance estimator with 10,000 replications (resampling with replacement over patients), adjusting for visit number. ¹⁹ , ²⁰ , ²¹ , ²² , ²³ A regression coefficient (B) and its 95% confidence interval (CI) were computed for each covariate in the model. Predicted means of intraprocedure pain score for statistically significant variables were then calculated from the final model to aid in interpretations. In terms of categorical variables, a predicted mean was calculated for each category, whereas values of 25th and 75th percentiles in the raw data were used to calculate predicted means for continuous variables. As the secondary analysis, a multiple logistic regression model with the cluster‐robust variance estimator ²⁰ , ²⁴ was fit to the data on the dichotomous outcome variable of intraprocedure pain (0 vs. ≥1), using the same set of covariates, with the calculations of an odds ratio (OR) and its 95% CI for each covariate. Predicted probabilities of intraprocedure pain score ≥1 for statistically significant variables in the logistic regression model were calculated, following the same approach used for the linear model. All the analyses were performed using Stata/MP 18.0 (StataCorp LLC, College Station, TX), with an α level .05 for statistical significance.

RESULTS

A total of 1371 injections from 935 patients were eligible for the analysis. Demographics and clinical characteristics of the patients are summarized in Tables 1 and 2. Close to two thirds of the patients (n = 855; 62.4%) were female, with a mean age of 58.6 ± 16.1 years, and with a mean BMI of 29.6 ± 7.3 kg/m². Of all the injections, 51.6% (n = 708) were joint injections (Table S1 lists all specific injections). The majority of patients reported intraprocedure pain of 2 or less (median = 2 [interquartile range, 1–3]); Figure 1].

TABLE 1.

Demographics and clinical characteristics of patients (categorical variables; N = 1371 injections).

Variable	Frequency (%)
Gender
Male	516 (37.6)
Female	855 (62.4)
Image guidance
Ultrasound	1260 (91.9)
None	107 (7.8)
Missing	4 (0.3)
Local anesthetic type
Lidocaine (Xylocaine)	1325 (96.6)
Multiple	4 (0.3)
None	36 (2.6)
Missing	6 (0.4)
Local anesthetic needle gauge
22	26 (1.9)
25	981 (71.6)
27	263 (19.2)
Missing	101 (7.4)
Injectate type
Dexamethasone	61 (4.4)
Methylprednisolone (Depo‐Medrol)	767 (55.9)
Triamcinolone (Kenalog)	348 (25.4)
Betamethasone (Celestone)	7 (0.5)
Zilretta (extended‐release)	71 (5.2)
Hyaluronic acid (Synvisc, Euflexxa)	58 (4.2)
Anesthetic only	30 (2.2)
None	29 (2.1)
Injectate anesthetic type
Bupivacaine (Marcaine)	101 (7.4)
Lidocaine (Xylocaine)	271 (19.8)
Ropivacaine	680 (49.6)
Multiple	24 (1.8)
None	273 (19.9)
Missing	22 (1.6)
Injectate needle gauge
18–22	516 (37.6)
25–27	813 (59.3)
Missing	42 (3.1)
Trainee involvement
Trainee performed	347 (25.3)
Trainee observed	168 (12.3)
Trainee present	5 (0.4)
No trainee present	837 (61.1)
Missing	14 (1.0)
Sodium bicarbonate used
Yes	756 (55.1)
No	615 (44.9)
Ethyl chloride used
Yes	25 (1.8)
No	1341 (97.8)
Missing	5 (0.4)
Structure injected
Joint	708 (51.6)
Peritendinous	460 (33.6)
Ganglion	25 (1.8)
Perineural	68 (5.0)
Other	76 (5.5)
Missing	34 (2.5)
Size of joint injected (if structure injected is joint; out of 708)
Small joint	92 (13.0)
Intermediate joint	111 (15.7)
Large joint	505 (71.3)
Injection body location
Lower extremity	817 (59.6)
Upper extremity	485 (35.4)
Nerve	54 (3.9)
Missing	15 (1.1)

Note: Some patients received more than one injection, as there were 935 unique patients.

TABLE 2.

Demographics and clinical characteristics of patients (continuous variables; N = 1371 injections in 935 patients).

Variable	N	Mean (SD)	Median (IQR)	Min, Max
Age (years)	1371	58.6 (16.1)	61 (48–70)	18, 96
Body mass index (kg/m2)	1366	29.6 (7.3)	28.1 (24.4–32.8)	15.8, 65.5
Injectate dose (mg)	1301	31.0 (12.8)	40 (20–40)	0, 80
Injectate volume (mL)	1342	4.0 (2.7)	4.5 (2–6)	0, 50
Preprocedure pain	1236	4.6 (2.5)	5 (3–6.5)	0, 10
Postprocedure pain	734	3.1 (2.7)	3 (0–5)	0, 10
Fluid aspirated (mL)	148	14.0 (21.3)	3 (0.5–20)	0, 145

Abbreviations: IQR, interquartile range; Max = maximum value; Min, minimum value.

FIGURE 1.

Distribution of intraprocedure pain (N = 1371). Note that some patient described their pain score as between two whole numbers. For example, though the highest number patients reported a pain score of 1, a small group (around 20) described it between 1 and 1.5.

The final multiple linear regression model is shown in Table 3. Female gender, ultrasound image guidance, presence of trainee, and BMI were significantly associated with greater intraprocedure pain (p < .05), after adjusting for the other covariates. Specifically, females were expected to have greater intraprocedure pain by about a half point (B = 0.42, p < .01). On the other hand, use of sodium bicarbonate, older age, and higher injectate volume were significantly associated with lower intraprocedure pain (p < .05), with 0.68 points lower pain score by use of sodium bicarbonate (B = −0.68, p < .01), controlling for the other covariates. It should be noted, however, that although age, BMI, and injectate volume were statistically significant in the model, their beta coefficients and 95% CIs were fairly close to 0.00, indicating that their associations to intraprocedure pain were likely minimal/trivial, if any. These associations are further illustrated by the predicted means of intraprocedure pain score calculated using the final multiple linear regression model (Table 4). The multiple logistic regression model revealed presence of trainee (p < .01) as the significant covariate (Table 5), with an increased odds of reporting ≥1 of intraprocedure pain by about 30% (odds ratio = 1.29). The predicted probabilities of intraprocedure pain score ≥1 for presence and absence of trainee were 0.88 (95% CI = 0.84–0.92) and 0.80 (95% CI = 0.76–0.83), respectively.

TABLE 3.

Multiple linear regression model on intraprocedure pain by select covariates.

Independent variable	B	95% CI	p value
Gender (vs. male)
Female	0.42	0.15 to 0.69	<.01
Image guidance (vs. none)
Ultrasound	0.66	0.22 to 1.10	<.01
Trainee present (vs. no)
Yes	0.44	0.15 to 0.73	<.01
Local needle gauge (vs. 27)
22	−0.73	−1.72 to 0.26	.15
25	0.23	−0.17 to 0.63	.26
Sodium bicarbonate used (vs. no)
Yes	−0.68	−1.01 to −0.35	<.01
Age	−0.01	−0.02 to −0.01	.04
Body mass index	0.04	0.01 to 0.06	<.01
Injectate volume	−0.06	−0.13 to −0.01	.04

Note: N = 1246; Wald χ ² (9) = 57.13; Model p < .001. Bold p value: p < .05.

Abbreviations: B, unstandardized regression coefficient; CI, confidence interval.

TABLE 4.

Predicted means of intraprocedure pain for statistically significant variables in multiple linear regression model.

Independent variable	Predicted mean of intraprocedure pain score	95% CI
Gender
Male	2.06	1.86–2.26
Female	2.48	2.30–2.66
Image guidance
Ultrasound	2.37	2.22–2.51
None	1.71	1.29–2.12
Trainee present
Yes	2.59	2.37–2.81
No	2.15	1.97–2.33
Local anesthetic needle gauge
22	1.43	0.52–2.33
25	2.39	2.22–2.55
27	2.16	1.81–2.50
Sodium bicarbonate used
Yes	2.01	1.81–2.21
No	2.69	2.47–2.92
Age (years)
48 (p25)	2.42	2.26–2.58
70 (p75)	2.21	2.04–2.39
Body mass index (kg/m2)
24.4 (p25)	2.14	1.98–2.30
32.8 (p75)	2.44	2.27–2.60
Injectate volume (mL)
2 (p25)	2.45	2.26–2.64
6 (p75)	2.19	2.02–2.37

Abbreviations: CI, confidence interval; p25, 25th percentile; p75, 75th percentile.

TABLE 5.

Multiple logistic regression model on intraprocedure pain (0 vs. ≥1) by select covariates.

Independent variable	OR	95% CI	p value
Gender (vs. male)
Female	1.14	0.79–1.64	.49
Image guidance (vs. none)
Ultrasound	1.29	0.73–2.29	.38
Trainee present (vs. no)
Yes	1.86	1.23–2.83	<.01
Local needle gauge (vs. 27)
22	0.40	0.11–1.40	.15
25	1.49	0.83–2.69	.18
Sodium bicarbonate used (vs. no)
Yes	1.19	0.77–1.85	.43
Age	0.99	0.98–1.00	.05
Body mass index	1.02	1.00–1.05	.10
Injectate volume	0.98	0.93–1.03	.43

Note: N = 1246; Wald χ ² (9) = 27.51; Model p = .001. Bold p value: p < .05.

Abbreviations: CI, confidence interval; OR, odds ratio.

DISCUSSION

This study aimed to investigate the clinically relevant factors that may contribute to patient‐reported pain during injections of joints and other musculoskeletal structures, including peritendinous, ganglion, and perineural injections. Our analysis revealed that several of these factors, namely gender, image guidance, presence of trainee, use of sodium bicarbonate, age, BMI, and injectate volume were related to patient‐reported pain. A fair number of studies have examined pain related to intramuscular and subcutaneous injections. One literature review identified that manual pressure or rhythmic tapping lowers pain, as can injection site, needle gauge, injection speed, formulation of injectate, and injection volume. ¹¹ However, to the authors' knowledge, only one large study ¹³ has examined the effects of clinical variables on procedure‐related pain for musculoskeletal injections, which identified that preprocedure pain level, anxiety toward the procedure, higher baseline physical activity, and less information provided before the procedure were associated with greater procedure‐related pain. ¹⁰ Our study demonstrated that several factors were independently related to pain.

Gender

Female gender was associated with greater reported pain levels in both joint‐specific injections and all injections. This is consistent with previous work, which found that female gender is associated with higher reports of pain intensity in general. ²⁵ However, findings from a systematic review by Racine et al. argued against the concept of greater generalized pain sensitivity in females and instead provided examples of types of pain that were consistently more painful based on gender. ²⁶ Alternately, a review by Fillingim et al. concludes that although women consistently report higher levels of experimentally induced pain, evidence is inconsistent when examining clinically induced pain. ²⁷ Psychological differences and societal norms may also explain this difference in pain perception. It is generally more culturally acceptable for women to express emotion and discuss experiences, both positive and negative, particularly in more conservative cultures, ²⁸ of which our study site may be representative. Therefore, our study may reflect a gender‐related response bias with men underreporting their pain. ²⁹

Body mass index

Higher BMI was related to significantly higher self‐reported intraprocedural pain, although the strength of the association was minimal/trivial. These findings are supported in part by prior work ³⁰ that examined the relationship between increased pain severity and obesity. Increased adipose tissue may obscure clarity in ultrasound images, thus affecting needle guidance and increasing the technical difficulty of the injection. Technically difficult injections inherently take more time, which may affect pain perception. More tissue must be locally anesthetized for complete relief. Additionally, the longer needles often required by greater injection depth may cause increased anxiety surrounding a procedure.

Image guidance

Patient‐reported pain scores while using ultrasound were significantly greater than those of blind injections. Although literature supports image guidance for improved pain outcomes, ³¹ no studies have compared the painfulness of the two procedures, making this study unique. Ultrasound guidance may extend the procedure time, though, affecting a patient's perception of pain. Or, the increased medicalization of the procedure requiring additional bulky equipment, such as an ultrasound machine, may increase anxiety and fear surrounding the procedure. The retrospective nature of this study likely carries significant bias, however; physicians clinically decided whether to use guidance, and technically challenging injections are typically performed with ultrasound (perineural/peritendinous injections, injections on those with increased body habitus, or those with alterations in bony anatomy such as severe bone spurring). Thus, the simpler injections were likely performed by palpation and could be less painful. Only a prospective, randomized future study would best answer this question.

Local anesthetic composition

The present study demonstrated significantly lower pain scores when sodium bicarbonate was added to buffer lidocaine for local anesthesia. In other words, when lidocaine was used as a local anesthetic, buffering with sodium bicarbonate reduced pain compared to lidocaine alone. Evidence shows buffering the injectate with sodium bicarbonate at a 1:10 ratio ³² will reduce pain ⁸ because lidocaine is significantly more acidic than physiologic pH. Alternatively, no difference has been demonstrated in reported pain when comparing buffered and nonbuffered injectates. ³³ This study adds to the substantial body of evidence that buffering lidocaine with sodium bicarbonate reduces patient‐reported pain. It should be noted that the addition of sodium bicarbonate to local anesthetic had the most considerable effect of any factor, reducing pain by about 0.68 points. This absolute value is low, but when the majority of pain scores were <3, it is a considerable proportion of reported pain scores. There was no significant effect of the use of local anesthetic on patient‐reported pain. However, as previously noted, this was likely subject to significant selection bias, as providers were more likely to eschew local anesthetic for more straightforward injections.

Age

Participant age was statistically significant in the reduction of patient‐reported pain, but the association was minimal/trivial. A review on the influence of age on pain by Yezierski ³⁴ concluded that nociceptive sensitivity increases with age under naive, inflammatory, and neuropathic conditions but that general sensory perception is decreased secondary to the loss of receptors. However, Ostrom et al. ³⁵ identified that increasing age is typically associated with a reduction in pain. It is possible that with increasing age, participants are more likely to have a prior history of painful procedures and tests and are therefore more accustomed to the pain. Additionally, for similar reasons, older patients may have reduced procedure‐related anxiety due to repeated exposures to injections and blood draws, ³⁶ thereby decreasing perceived pain.

Injectate volume

The volume of injectate (not including local anesthetic volume) was significantly associated with patient‐reported procedural pain, but similar to BMI and age, the effect was minimal/trivial. Increased pain with higher volumes could be surmised to occur with joint capsule distension or tissue stretch, thus activating nociceptors. Other studies found that increasing injectate volumes ⁷ , ⁹ led to increased reports of pain, but these involved only subcutaneous injections, which differs from the musculoskeletal injections in this study. Of note, the mean injectate volume in this study was 4 mL. This study did not use standardized volumes for specific joints, leaving it up to physician discretion to determine the appropriate volume for an injection location. Generally, smaller volumes were used for smaller joints and vice versa. Despite more volume being used on larger joints, the capsule of said joints may be more capable of tolerating the increased volume without distension; therefore, pain scores may not correlate with volume but rather may correlate instead with a volume‐to‐joint size ratio, which was not recorded.

Needle gauge

Decreasing needle diameter (increasing needle gauge) did not have a significant impact on patient‐reported pain. Smaller diameter needles are known to be less painful. ³² However, there was no difference in pain when comparing needles in a narrow‐gauge range in a review by Usach et al. ¹¹ Our study contained a gauge range between 18 and 27, and practitioners likely used smaller needle size when appropriate; thus, again, a randomized prospective study would be required to better evaluate this research question to avoid selection bias.

Trainee involvement

Our multiple linear and logistic regression models showed a statistically significant association of presence of trainee to increased patient‐reported procedural pain. Although the authors were unable to find other studies that directly examined trainee impact on procedure‐related pain, other studies have explored if trainee involvement affects outcomes of the procedure itself. Prior work has identified that trainee involvement in fluoroscopically guided injections does not increase fluoroscopic time or dose for most injections. ³⁷ Similarly, trainee involvement does not affect immediate patient complications or reported improvement in pain following the injection. ³⁸ Again, the retrospective nature of this study confounds the picture, as supervising physicians would be less likely to let more junior trainees perform complicated injections. The role of the trainee was not recorded as well (eg, simply observing or actually performing); further study needs to evaluate pain‐related factors if a trainee performs the injection or merely observes.

Limitations

The main limitation to this study is the retrospective, nonrandomized nature. Because providers were able to perform the injection in their typical and adopted manner, selection bias likely played a large role. Additionally, a staff member recorded verbally reported pain rather than patients recording their own pain level. It is possible that actual pain may be greater than that which was reported, due to self‐perceived pressure to minimize discomfort. Inclusion criteria were quite broad, thus allowing for a significant amount of variability in the diagnoses, as well as types and locations and volumes of injections performed, which likely influenced injection pain but were not fully captured. Finally, there is no universal manner to perform each of the injections as the pathway of the needle differs based on the patient, pathology, habitus, and anatomical variations in neurovascularity. This lack of standardization in approach may create bias, but it also increases the generalizability of the study. Because numerous physicians from multiple institutions took part, we do not identify specific procedure‐related factors (eg, technique, mannerisms, discussions with patient, etc.) that may be related to pain.

CONCLUSIONS

Injections are commonly performed as diagnostic and/or therapeutic interventions in sports medicine. This study found that the following factors were significantly associated with greater patient‐reported pain levels during musculoskeletal injections: female gender, ultrasound image guidance, and the presence of a trainee. The use of sodium bicarbonate was associated with significantly lower patient‐reported pain during the musculoskeletal injections. There was also a trend that age, BMI, and injectate volume were important variables to consider for intraprocedure pain. Randomized, prospective studies could clarify factors that reduce intraprocedural pain and reduce selection and response bias. Clinicians should consider the use of sodium bicarbonate during injections. Future work should consider how the factors associated with increased pain can be mitigated.

DISCLOSURE

We have no conflicts of interest to report.

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Supporting information

Table S1. Information on all injections (N = 1371).

Faust CD, Teramoto M, Pietruszka ST, et al. Identification of factors related to pain from musculoskeletal injections. PM&R. 2026;18(1):6‐14. doi: 10.1002/pmrj.13437

DATA AVAILABILITY STATEMENT

The dataset used in this manuscript is not publicly available but is available from the authors under reasonable request.