Pre-injection local anesthesia does not affect experienced pain in intra-articular hip injections

Abstract

BACKGROUND

Intra-articular hip injections (IAHIs) are commonly used for diagnostic and therapeutic purposes but are often associated with patient anxiety and fear. The disparity between anticipated and experienced pain during IAHIs and the role of pre-injection local anesthesia in pain modulation remains unclear.

AIM

To investigate the difference between anticipated and experienced pain during IAHIs and the impact of pre-injection local anesthesia.

METHODS

This prospective study enrolled 60 patients undergoing IAHI, 30 receiving pre-injection superficial local anesthesia and 30 serving as a control group without pre-injection local anesthesia. Pain levels were assessed using numeric rating scales.

RESULTS

Patients significantly overestimated anticipated pain compared to experienced pain (6.43 ± 2.48 vs 3.68 ± 2.37, P < 0.001). Pre-injection local anesthesia did not significantly reduce experienced pain (3.19 ± 2.38 vs 4.20 ± 2.29, P = 0.130).

CONCLUSION

Patients overestimate anticipated pain during IAHIs. Pre-injection local anesthesia does not reduce experienced pain.

Key Words: Hip; Injection; Patient experience; Pain; Practice management

Core Tip: This study evaluated anticipated vs experienced pain during intra-articular hip injections (IAHIs) in 60 prospectively recruited patients, with or without pre-injection local anesthesia. Anticipated pain was significantly overestimated compared to experienced pain, and pre-injection local anesthesia did not affect the experienced pain. These results suggest that the hip joint capsule may significantly contribute to nociception during IAHI, more so than the superficial soft tissues along the needle trajectory. Ultimately, these findings provide valuable insight into the pain experienced during IAHI and may help improve patient experiences.

INTRODUCTION

Intra-articular hip injections (IAHIs) are routinely performed for diagnostic and therapeutic purposes. While IAHI-specific injection-related pain is poorly characterized in existing literature, the deep nature of the hip joint and need for longer needles can cause substantial concerns regarding IAHI-related pain, apprehension, and anxiety among patients. While injection-related pain is largely recognized, the disparity between the expected and experienced pain during injection procedures is a known and well-studied phenomenon in many medical fields including dentistry[1], obstetrics[2], and urology[3], yet it remains poorly elucidated in the orthopedic practice of IAHI injections. Unlike other medical injections, IAHIs involve the navigation of deep extraarticular anatomy to reach the hip joint and needle penetration of the hip capsule, which is densely innervated with nociceptive fibers[4]. Additionally, the implications of hip injections for a chronic painful joint associated with conditions such as osteoarthritis may further influence procedural pain perception and warrant an investigation of procedural pain specific to IAHI[5].

A meta-analysis conducted by McLenon and Rogers[6] demonstrates treatment avoidance due to patients’ fear of needles, and factors such as needle size, injection speed, and patient anxiety have been shown to contribute to injection-related pain perception[7,8]. Therefore, there is value in understanding how to minimize injection-related pain and how to optimize pain management strategies and reduce experienced pain and anxiety associated with IAHI. Multiple techniques exist to decrease IAHI-related pain, including the use of adjunctive agents such as ice, ethyl chloride spray, transdermal analgesia, and local injected analgesia[9]. However, the use of pre-injection and post-injection analgesia is rare and typically physician-initiated rather than patient-requested[10]. While the pre-injection of local analgesia into superficial tissues in the projected trajectory of the spinal needle is a well-described technique to decrease experienced pain on needle insertion, the true efficacy of this practice remains unclear[11]. This study aimed to describe the difference between anticipated and experienced pain during IAHI, with the secondary aim of evaluating the impact of pre-injection local anesthesia on pain experience in IAHI. We hypothesize that there is a significant difference between anticipated and experienced pain during IAHI. Additionally, we hypothesize that experienced pain during IAHI is not affected by local anesthesia administration prior to hip injection.

MATERIALS AND METHODS

Study groups

A total of 60 patients were prospectively enrolled into one of two injection groups: Group A, which received superficial local anesthesia administered prior to intra-articular injection (study group), and group B, which underwent IAHI without local pre-injection anesthesia (control group).

Study design

Institutional Review Board approval was granted before study enrollment. Data were prospectively collected from patients undergoing IAHI between January 2021 to January 2022. Inclusion criteria selected for patients undergoing first-time IAHI as indicated by an orthopedic surgeon either for diagnostic (e.g. lidocaine test, arthrography) and/or therapeutic (steroid injection for osteoarthritis) purposes. Participants were 18 years of age or older, had no previous hip joint injections, and could fill in the survey questionnaire. Exclusion criteria excluded patients under 18 years of age, patients with a known history of hypersensitivity or allergy to the injectant material (e.g. local anesthetics, steroids), and patients lacking the ability to sign informed consent or to complete a survey questionnaire. Patients with previous hip joint injections were also excluded, due to the possibility that these patients could recall the prior pain experienced.

Injection technique

With the patient positioned supine, antiseptic solution was administered in a circular manner over the hip. A linear 13-6 MHz transducer (SonoSite^™ M turbo; SonoSite Inc., Bothell, WA 98021, United States) was placed in an oblique longitudinal plane over the femoral neck (Figure 1A). Once the anatomic landmarks were identified, patients in group A underwent local anesthesia infiltration with 5 mL 1% lidocaine injected along the planned trajectory of the intra-articular injection using a 38 mm 21-gauge needle. The 38 mm 21-gauge needle was then replaced with a 90 mm 21-gauge spinal needle, maintaining the needle in an in-plane manner to ensure constant needle visualization. The needle was then advanced under direct visualization through the joint capsule (Figure 1B) at the anterior joint recess at the femoral head and neck junction (Figure 1C). Subsequently, 1 mL of 1% lidocaine was injected to confirm intra-articular position under sonographic visualization and unresisted flow of the local anesthesia prior to the administration of the diagnostic or therapeutic injection. The same technique was used for injection among patients in group B without the pre-injection infiltration of local anesthesia in the needle trajectory.

Figure 1 Injection into the hip joint under ultrasound guidance. A: The transducer was placed in an oblique longitudinal plane along the femoral neck’s long axis; B: The needle advanced under direct visualization through the joint capsule (orange arrow); C: The needle advanced under direct visualization through the joint capsule into the anterior joint recess at the junction of the femoral neck and head (orange arrow).

Outcome measures

Prior to IAHI, a questionnaire about pain and anxiety related to the procedure was administered. The questionnaire was comprised of three sections, including: (1) Two numeric rating scales (NRS) scores scaled from numbers 0 to 10, where 0 represented no pain and 10 represented the worst pain imaginable[12], with the first score measuring anticipated pain before the injection and the second score measuring experienced pain during the procedure; (2) The Beck Anxiety Inventory (BAI) scale, which is used to assess anxiety level[13], consists of 21 items, each scored from 0-3 points totaling 0-63 cumulatively. Final scores ranging from 0-7 reflect a minimal level of anxiety, while scores 8-15 reflect mild anxiety, 16-25 moderate anxiety, and 26-63 severe anxiety. After answering the BAI scale, a history of any anxiety disorders was documented, as well as any consumption of prescribed anxiety medications; and (3) A numeric evaluation of five factors that may influence the patient’s fear of injections as suggested by Nir et al[14], including pain, appearance of the needle and syringe, needle size, seeing others receiving the injection, and negative previous injection experiences outside of IAHI, with each factor graded between 0 (no influence) and 5 (maximal influence). The data from the aforementioned questionnaires were collected and pooled for analysis.

Statistical analysis

As projected from existing research, a sample size of 25 subjects per treatment group was estimated to provide a statistical power of 80%[15]. Hypothesis testing was conducted using both parametric and non-parametric methods, depending on the distribution of the data. For continuous outcomes, analyses of variance were used to evaluate between-group differences with treatment group established as a fixed effect. Paired t-tests were used for within-group comparisons of continuous variables, such as anticipated vs experienced pain. For correlations, Pearson’s coefficient was calculated when data displayed normality; otherwise, Spearman’s rank correlation was used. The interpretation of correlation coefficients followed conventional stratification: Negligible (0.00-0.30), low (0.30-0.50), moderate (0.50-0.70), high (0.70-0.90), and very high (0.90-1.00)[16]. Significance thresholds were set at P < 0.05 for all tests, with two-tailed analyses to minimize type I error risk. All statistical analyses were conducted using SPSS version 24 software (IBM Corp, Armonk, NY, United States).

RESULTS

Patient demographics

Sixty patients were ultimately deemed eligible for inclusion. The mean age was 38.4 (SD = 14.09, range: 18-75) years. Ultimately, 29 of the patients were male with a mean age of 34.9 (SD = 10.98, range: 18-61) years while 31 were female with a mean age of 41.9 (SD = 16.19 range: 18-75) years. The mean age was not significantly different between male and female patients (P = 0.08). There was also no significant difference in age between the local anesthesia and control groups (P = 0.161).

Anticipated and experienced pain

There was no significant difference between local anesthesia and control groups regarding the patient-estimated NRS score (local anesthesia: 6.19 vs control: 6.68, P = 0.489) and experienced NRS score (local anesthesia: 3.19 vs control: 4.20, P = 0.130). However, there was a significant difference among the entire cohort regarding anticipated vs experienced pain, with anticipated pain estimated at an NRS score of 6.43 (SD = 2.48) vs experienced pain reported at 3.68 (SD = 2.37) (P < 0.001).

Local anesthesia

When stratified by study group, significant differences were similarly observed among anticipated and experienced pain, with participants receiving local anesthetic reporting anticipated and experienced pain scores of 6.19 (SD = 2.48) and 3.19 (SD = 2.38), respectively (P < 0.001) and participants in the control group reporting scores of 6.68 (SD = 2.51) and 4.2 (SD = 2.29), respectively (P < 0.001) (Table 1). The net difference in anticipated and experienced pain did not differ between injection methods (local anesthesia: Δ = 3.0 vs control: Δ = 2.48; P = 0.498).

Table 1 Anticipated vs experienced pain.

Parameter	n	Anticipated pain, mean ± SD	Experienced pain, mean ± SD	Net difference (Δ)
Study population	60	6.43 ± 2.48a	3.68 ± 2.37	2.75
Use of local anesthesia
Study (local anesthesia)	30	6.19 ± 2.48a	3.19 ± 2.38	3.00
Control (no local anesthesia)	30	6.68 ± 2.51a	4.20 ± 2.29	2.48

^aP < 0.001 vs experienced pain in the same row is significantly different.

Patient sex

Discrepancies among anticipated and experienced pain remained statistically significant when participants were stratified by sex, with female patients reporting anticipated and experienced NRS scores of 6.88 (SD = 1.96) and 4.12 (SD = 2.60), respectively, (P < 0.001) and male patients reporting scores of 6.0 (SD = 2.87) and 3.26 (SD = 2.09), respectively (P < 0.001). However, when comparing scores by sex (Table 2), there were no significant differences between male and female patients’ anticipated [6.00 (SD = 2.87) vs 6.88 (SD = 1.96), respectively; P = 0.209] and experienced [3.26 (SD = 2.09) vs 4.12 (SD = 2.60), respectively; P = 0.203] pain. Additionally, the net difference between anticipated and experienced pain was not significantly different between male and female patients (male: ∆ = 2.74 vs female: ∆ = 2.76, P = 0.970).

Table 2 Factors influencing fear of injection.

Parameter	n	Factors influencing anxiety
		Fear of pain	Appearance of the needle and syringe	Needle size	Seeing others receiving injection	Negative previous experience	BAI
Study population	60	2.84	2.54	2.51	1.23	1.23	4.26
Use of local anesthesia
Study (local anesthesia)	30	2.68	2.2	2.23	1.25	1.06	4.33
Control (no local anesthesia)	30	3	2.88	2.77	1.23	1.42	4.15

BAI: Beck Anxiety Inventory.

BAI and fear of injections

The results of the BAI questionnaire are presented in Table 3. Stratifying both study groups by the local anesthetic and control populations as well as by sex (Table 2) did not yield significant differences in BAI measures or associated anxiety-inducing factors. However, a low to moderate correlation was found between anticipated mean NRS score and BAI, fear of pain, needle visualization, needle size, seeing others receiving an injection, and previous injection experience (0.288, 0.587, 0.511, 0.394, 0.202, and 0.420, respectively).

Table 3 Anticipated and experienced pain scores, net differences, Beck Anxiety Inventory scores, and other factors influencing needle-related pain (e.g., fear of pain, needle size) stratified by sex.

Anticipated pain vs experienced pain					Factors influencing anxiety
Sex	n	Anticipated pain, mean ± SD	Experienced pain, mean ± SD	Net difference (Δ)	Fear of pain	Appearance of the needle and syringe	Needle size	Seeing others receiving injection	Negative previous experience	BAI
Males	29	6.0 ± 2.87a	3.26 ± 2.09	2.74	2.78	2.54	2.4	0.92	1.36	3.44
Females	31	6.88 ± 1.96a	4.12 ± 2.60	2.76	2.9	2.58	2.59	1.5	1.05	5.15

^aP < 0.001 vs experienced pain in the same row is significantly different.

BAI: Beck Anxiety Inventory.

DISCUSSION

The findings of this study offer several key insights into IAHI-related pain. Firstly, there are significant differences between anticipated and experienced pain in IAHI, with patients overestimating anticipated procedural pain. Secondly, the administration of pre-injection local anesthesia did not significantly affect the ultimate experienced pain of IAHI. Finally, anticipated pain only weakly correlates with BAI scores and other injection-related factors including fear of pain, needle visualization, needle size, and prior injection experiences. There were no significant differences among anticipated and experienced pain when stratified by patient sex. These findings confirmed our hypothesis and demonstrated a high overestimation of anticipated pain, which may have important implications for patient education and managing expectations.

The hip joint capsule is considered an important trigger of nociception that may modulate experienced pain during IAHI. Saxler et al[17] showed a significantly higher density of afferent nerve fibers in the hip capsules of patients with painful osteoarthritis than those without antecedent hip pain. The abundant distribution of nociceptors in the painful hip capsule may explain how both patients in both study groups, one with pre-injection local anesthesia and one control, experienced similar levels of pain. The results of the present study and lack of significant pain modulation with pre-injection local anesthesia may support a substantial capsular contribution to experienced pain in IAHI.

Additionally, anticipated IAHI pain was consistently and significantly higher than experienced pain. This finding reinforces existing research demonstrating a significant discrepancy between anticipated and experienced pain during injection procedures in a variety of medical specialties[1-3]. These results further validate the phenomenon of overestimating pain perception prior to medical interventions and subsequently emphasize the importance of realistically managing patient expectations regarding procedural pain in IAHI. Educating patients regarding the tendency to overestimate anticipated pain in IAHI may offer value in managing procedure-related anxiety and closing the gap in anticipated and experienced pain. Psychological interventions, such as cognitive-behavioral therapy (CBT), offer a promising approach to managing injection-related anxiety and enhancing patient experiences. Previous studies have shown that even a single session of CBT can be both effective and practical in significantly reducing symptoms of needle phobia[18,19]. Given the high propensity for study participants to overestimate anticipated pain, applying psychological principles targeted towards fear reduction pre-IAHI may prove beneficial in improving patient experiences.

Understanding the factors that contribute to injection-related anxiety may increase our understanding of anticipated IAHI pain. Patients with a fear of needles report avoidance of medical care involving needles[20]. For example, vaccine-related pain contributes to vaccine non-adherence[21], dental injections contribute to dental anxiety and avoidance of dental care[22], and injection anxiety and needle phobia contribute to avoidance of recommended treatments among patients with insulin-dependent diabetes[23]. Along these lines, Nir et al[14] described how factors such as fear of pain, needle size, a history of fainting, and the act of watching others undergo injections are highly and independently associated with a fear of injections. In the present study, however, the correlation between anticipated pain and BAI, fear of pain, needle visualization, needle size, and previous injection experiences only reached low to moderate significance. This discrepancy may be explained by the differences in outcome measures, as Nir et al[14] defined fear of injections according to subjectively recorded perceptions of fear rather than pain scores, like in the present study. Regardless, extrapolating the specific sources of injection-related fear may offer value in understanding anticipated pain.

In the present study, there were no appreciable differences between male and female participants in either anticipated or experienced pain, with only slight variations in mean anticipated and experienced pain scores observed (6.88 vs 6.00, 4.12 vs 3.26, respectively). In general, women may have higher levels of anticipated and experienced pain in healthcare settings than men[24]. Additionally, prior research suggests that biological factors such as hormonal modulation, nociceptive fiber density, and pain receptor distribution may contribute to variability between these demographics[25,26]. Furthermore, cultural differences and gender norms or expectations may affect willingness to disclose pain[27]. Regardless, both male and female participants in the present study experienced similar levels of anticipated and experienced pain in contrast to many findings in existing literature, suggesting that these factors do not contribute to IAHI as they may to other medical disciplines.

This study has limitations. Firstly, the use of self-reported pain scores introduces subjectivity, as individual pain perception and reporting can be influenced by psychological, cultural, and contextual factors. Future studies employing objective observed measures of pain such as inflammatory cytokines or similar biomarkers and functional neuroimaging may provide further non-subjective insight into injection-associated pain. Additionally, this study's sample size, while sufficient for detecting significant differences in primary outcomes, may limit nuanced subgroup analyses and study generalizability to a diverse population. Variability in social and technical factors between providers with unstandardized pre-procedural counseling as well as variations between patient psychological factors such as resilience, coping mechanisms, and cultural influences may further nuance or confound results. Despite these limitations, the present study provides valuable insights into the disparity between anticipated and experienced pain during IAHIs and the lack of a significant benefit with the use of pre-injection local anesthesia for IAHI.

CONCLUSION

The findings of the present study demonstrate significantly overestimated anticipated vs experienced pain during IAHI. Additionally, pre-injection local anesthesia does not offer benefits in decreasing IAHI-related pain, suggesting that the hip joint capsule may significantly contribute to nociception during IAHI more than superficial soft tissues in the needle trajectory. Ultimately, these findings offer value in understanding experienced pain during IAHI and can be applied to improve patient experiences with IAHI.