Prospective Evaluation of a Single Corticosteroid Injection in Radial Tunnel Syndrome

Abstract

Background: The role of corticosteroid injections in the treatment of radial tunnel syndrome (RTS) has not been evaluated in depth. The purpose of this study was to evaluate the utility of a single corticosteroid injection as a therapeutic modality for RTS. Methods: We enrolled 40 patients with a clinical diagnosis of RTS. Our primary outcome was the quick Disabilities of the Arm, Shoulder and Hand (qDASH) score at 1 year. Each patient was then treated with a single corticosteroid injection in the proximal forearm at the posterior interosseous nerve (PIN). Patient follow-up occurred at 2 weeks, 3 months, and 1 year. Results: The cohort had a mean age of 49 years, and 35 patients completed 1 year of follow-up. Outcomes based on qDASH and visual analog scale (VAS) showed significant improvement from baseline, with mean qDASH decreasing from 49.4 ± 7.0 points to 35.8 ± 7.5 points (P = .03) and 28.5 ± 7.3 points (P = .01) at 12 and 52 weeks, respectively, and VAS decreasing from 6.0 ± 0.8 points to 3.4 ± 0.9 points (P = .005) and 2.9 ± 0.8 points (P = .003) at 12 and 52 weeks, respectively. During the study period, 8 of 35 patients (23%) failed nonoperative treatment and went on to surgical decompression of the PIN. A minimal clinically important difference in qDASH was achieved in 57% of subjects at 1-year follow-up. Conclusions: Nonoperative management with corticosteroid injection can be used as a therapeutic measure with potential long-term benefits in the treatment of RTS.

Introduction

Radial tunnel syndrome (RTS) is a poorly understood condition involving compression of the posterior interosseous nerve (PIN) in the forearm. RTS presents with lateral elbow and forearm pain without weakness and is distinguished from PIN palsy by the absence of motor loss. Diagnosis is based primarily on the patient’s history and physical examination, as nerve conduction testing and radiologic studies are typically negative.^4,10

Nonoperative treatments including splinting, ergonomic training, nerve gliding exercises, ultrasound, massage, and strength and stretching exercises have been described and found to have minimal efficacy in relieving symptoms.² Meanwhile, operative intervention to decompress the radial nerve has been reported with variable success in limited case series.^{1,8-9,12-15,17} Roles and Maudsley described 38 patients diagnosed clinically with RTS, or what they termed “resistant tennis elbow,” who were treated with radial tunnel decompression and noted that 35 of 38 (92%) had excellent or good surgical results.¹⁵ Moss and Switzer reported similar findings in a retrospective analysis of 15 patients, with 14 of 15 achieving good to excellent pain relief and function.¹³

The role of corticosteroid injections in the treatment of RTS has not been evaluated in depth. Ritts et al noted the positive prognostic effect of radial nerve block on later surgical outcomes.¹⁴ Another study reported on the use of steroid injections and therapy.¹⁶

In this study, we aimed to prospectively investigate the effect of a corticosteroid injection on pain relief and functional improvement using standardized outcome measures, as well as progression to surgery, in a cohort of patients clinically diagnosed with RTS. We hypothesized that a single injection of corticosteroid would serve a therapeutic role in patients with RTS.

Materials and Methods

We designed a prospective study to evaluate the impact of a single corticosteroid injection in patients diagnosed with RTS. Following institutional review board approval, 40 patients (13 men and 27 women) were prospectively enrolled from the practice of a single orthopedic hand surgeon after the diagnosis of RTS. Inclusion criteria included a clinical diagnosis of RTS, age > 17 years, and willingness to undergo a corticosteroid injection. A positive clinical diagnosis was defined as tenderness to palpation 3 to 4 cm distal to the lateral epicondyle in the area of the mobile wad over the distribution of the radial nerve and reproduction of this pain with resisted forearm supination or middle finger extension. Patients with multiple sclerosis, PIN syndrome, history of stroke, rheumatoid arthritis, allergy to corticosteroid, and those concurrently taking oral steroids were excluded from study participation.

After written informed consent was obtained, each patient completed a demographic questionnaire; a quick Disabilities of the Arm, Shoulder and Hand (qDASH) instrument; and a visual analog scale (VAS) for pain. Collected demographic data included age, body mass index (BMI), hand dominance, side of complaint, concurrence of lateral epicondylitis, carpal tunnel syndrome, cubital tunnel syndrome, cigarette and nicotine use, medical comorbidities, and employment status. The primary outcome measure was qDASH score at 1 year.

Each patient was then treated with a single corticosteroid injection (0.25 mL of lidocaine 1% and 0.75 mL of Celestone 6 mg/mL) administered using a 27-gauge × 1 ¼ inch needle placed at the PIN, in the area of maximal tenderness, typically within the mobile wad. No specific attempt was made to block the PIN. However, the aforementioned clinical criteria of tenderness to palpation and pain with resisted forearm supination or middle finger extension in the proximal forearm were noted to subside in all patients immediately after injection. Each patient followed up at 2 weeks in the office; at 3 months, patients either came to clinic or were contacted by telephone; and all patients were contacted by telephone at 1 year for qDASH and VAS results. Recurrence of pain and progression to radial tunnel surgery were also noted. Patients who were unable to be reached by telephone and those who opted out from participating in this study were not included in the final analysis.

Statistical Methods

A sample size calculation was performed to determine the number of patients needed to observe a minimal clinically important difference (MCID) in the qDASH score. A change in score between 15 and 20 points is considered the threshold for MCID using this instrument.⁵ Considering a change of 15 points and assuming a standard deviation of 20 points, it was determined that a sample of 28 patients would provide 80% power to detect a 15-point difference in the qDASH score. The sample was inflated to 40 to compensate for loss to follow-up and to allow, if possible, the ability to explore the effect of covariance on outcome following an injection. Descriptive summary statistics such as means and standard deviations for continuous data as well as frequency and proportions for categorical data were calculated to characterize the study group. Mixed-effects linear regression was used to examine change in qDASH and current pain score from pre-injection to 52 weeks post injection. Separate analyses were conducted to determine change in score over time for the entire group as well as differences in score between those with concurrent lateral epicondylitis and those with a concurrent neuropathy (carpal tunnel syndrome and/or cubital tunnel syndrome). The results of these analyses are presented as mean differences in score with 95% confidence intervals. The alpha level for all statistical tests was set at P = .05.

Results

During the period of study enrollment from September 2014 to February 2016, a total of 40 patients were assessed for eligibility and enrolled. Five patients were lost to follow-up during the follow-up period, including 1 patient who withdrew from participation at the 3-month mark and 4 patients who could not be reached by telephone at 2 weeks or later. Thus, 35 patients were available for analysis.

The mean patient age within this cohort was 49 years (range, 31 to 70 years) and average BMI was 29 kg/m² (range, 21-51 kg/m²) (Table 1). The dominant arm was affected in 31 of 40 patients (78%). Ipsilateral carpal tunnel syndrome was diagnosed in 14 of 40 patients (35%), while ipsilateral cubital tunnel syndrome was present in 16 of 40 patients (40%). Thirty-one of 40 patients (78%) also had lateral epicondylitis within the affected arm. Seven (18%) had a diagnosis of diabetes, and 4 of 40 (10%) had been diagnosed as having fibromyalgia. Twenty-eight were employed with an even distribution between light, moderate, and severe-intensity work, and 12 of 40 self-reported as unemployed at the time of enrollment.

Table 1.

Demographic Data.

Average age (y)	49 (31-70)
Sex
Male	13	32.5%
Female	27	67.5%
Body mass index (kg/m2)
Normal	7	17.5%
Overweight	18	45.0%
Obese	15	37.5%
Dominant arm affected
Yes	31	77.5%
No	9	22.5%
Lateral epicondylitis
Yes	31	77.5%
No	9	22.5%
Cubital tunnel syndrome
Yes	16	40.0%
No	24	60.0%
Carpal tunnel syndrome
Yes	14	35.0%
No	26	65.0%
Fibromyalgia
Yes	4	10.0%
No	36	90.0%
Diabetes
Yes	7	17.5%
No	33	82.5%
Occupational intensity
Unemployed	12	30.0%
Mild	11	27.5%
Moderate	8	20.0%
Severe	9	22.5%

Note. Shown here are baseline demographic characteristics of the study population.

Prior to injection, the mean qDASH was 49.4 ± 7.0 points and mean VAS for pain was 6.0 ± 0.8 points. The mean qDASH improved over time with significant decreases to 35.8 points (95% confidence interval [CI] = 28.3-43.3, P = .03) and 28.5 points (95% CI = 21.2-35.8, P = .01) at 12 and 52 weeks, respectively (Figure 1). Similarly, the mean VAS improved over time with significant decreases to 3.4 points (95% CI = 2.5-4.3, P = .005) and 2.9 points (95% CI = 2.1-3.7, P = .003) at 12 and 52 weeks, respectively (Figure 2). In patients with an ipsilateral compressive neuropathy (carpal tunnel syndrome and/or cubital tunnel syndrome), the mean reduction in qDASH was significant at 2 weeks (−17.1 points, P = .01), 12 weeks (−20.0 points, P = .01), and 1 year (−17.0 points, P = .01) compared with baseline. For those patients with concomitant lateral epicondylitis, the mean reduction in qDASH was significant only at 1 year (−19.0 points, P = .03). Regarding MCID in qDASH, defined as a change of 15 points in this study, a discernable effect was observed in 10 (29%), 13 (37%), and 20 (57%) patients at 2, 12, and 52 weeks, respectively.

Figure 1.

Quick DASH over time. There were significant reductions in quick DASH noted at 12 and 52 weeks compared to baseline after a single cortisone injection into the radial tunnel. DASH = Disabilities of the Arm, Shoulder and Hand.

Figure 2.

Visual analog scale (VAS) for pain over time. There were significant reductions in visual analog scale for pain noted at 12 and 52 weeks compared with baseline after a single cortisone injection into the radial tunnel.

There were no complications from injection. During the study time period, 8 of 35 patients (23%) failed to improve following cortisone injection and went on to radial tunnel decompressive surgery.

Discussion

There are minimal data to guide clinicians in the diagnosis and treatment of RTS. The role of nonoperative management has been minimally studied, except as mentioned in reports of surgical treatment.^14,15 This study was created to evaluate a single nonoperative intervention for RTS. We demonstrated that most patients with RTS experienced significant improvements in function and pain at 12 weeks and 1 year compared with baseline after a single corticosteroid injection to the proximal forearm. In addition, 57% of patients achieved a MCID in qDASH at 1 year compared with baseline, while 23% of patients underwent surgical decompression of the PIN after initial positive response to corticosteroid injection with recurrence of pain.

While Edgell et al. and others have noted the therapeutic and positive prognostic value of corticosteroid injection in the carpal tunnel, the use of corticosteroid injection in patients with RTS has been not been reported in depth.^3,6 Sarhadi et al presented their series of 25 patients with RTS who received a single injection of 2 mL of 1% lidocaine and 40 mg of triamcinolone in 1 mL of carrier and found that 18 patients (72%) had resolution of their symptoms at 6 weeks follow-up based on clinical examination findings.¹⁶ Sixteen patients (64%) continued to have long-term pain relief at 2 years or more. Surgical decompression was performed in 9 patients (36%) due to failed nonoperative treatment. Although our study utilized different outcomes based on qDASH and VAS, we report similar rates of long-term improvement in pain and procession to surgical decompression.

Whereas Sarhadi et al relied on clinical examination alone to evaluate patient response to corticosteroid injection at subsequent follow-up, we utilized a validated, standardized outcome instrument in the qDASH to measure changes in function over time compared with baseline in response to a single corticosteroid injection. Gummesson et al reported that the qDASH had excellent reliability for upper extremity disorders, thus minimizing information bias or measurement errors over a given period.⁷ In addition, although patient response to qDASH remains subject to confounding with concomitant upper extremity musculoskeletal conditions, we noted that patients with concomitant compressive neuropathy or lateral epicondylitis still had significant mean reduction in qDASH at 1 year, demonstrating the efficacy of this intervention. This finding contrasts with other studies which demonstrated that concomitant diagnoses blunted the improvement seen with outcomes measures.¹¹

This study has many limitations. Without a control or comparative cohort, it remains unknown what proportion of improvement in function or pain might have been due to the placebo effect of injection or observation. However, given the paucity of patients presenting with RTS, the enrollment of a control group of adequate size would be difficult. In addition, the accuracy of needle placement within the radial tunnel was not confirmed; ultrasound guidance would be a possible addition to this technique. However, the immediate subsidence of pain at this site in all patients with injection suggests that our injections were performed with high accuracy and reliability. Finally, we observed significant mean reductions in qDASH for patients with RTS and concomitant lateral epicondylitis or compressive neuropathy. These coexisting pathologies have potential to confound patient-reported pain and functional outcomes in the affected arm. To mitigate this effect, patients were reminded to focus their responses toward their distinct radial tunnel symptoms and nonetheless demonstrated improvement in both function and pain outcomes over time.

There are several published series reporting a high cure rate with surgical decompression of the PIN in the radial tunnel, but the natural history of this condition is unknown.^12,14,15 Most patients in our study responded successfully to treatment with steroid injection, and surgical decompression of the radial tunnel was performed when nonoperative treatment had failed. Based on our findings, a single corticosteroid injection can have long-lasting benefit in the treatment of RTS. Further study of corticosteroid injection for the treatment of RTS in a randomized, double-blinded, placebo-controlled trial is warranted.