Local steroid injections have proven to be an effective treatment option for patients with CTS. The injection is usually performed blindly by palpating anatomical landmarks [12]. More recently, the use of ultrasound to guide injections has emerged and gained popularity.
In this study, 30 affected hands with mild or moderate CTS were treated with local corticosteroid injection, either blindly or guided by ultrasound. Significant improvements in clinical and ultrasonographic parameters were observed in both groups at 4 weeks after procedure, with significantly improved results under ultrasound guidance.
Controversial results were shown in previous series examining the performance of steroid injections when administered blindly or with ultrasound guidance. Two large meta-analyses of 448 and 469 patients showed the effectiveness of applying ultrasound with better outcomes and improved severity and functional status [13, 14]. Conversely, in a series of 60 hands in 47 patients, the benefit of ultrasound was not significant, despite satisfactory results in both groups [15]. This disparity could be attributed to the different designs, the type and dose of injectates, the etiology of the CTS between groups, and the experience of operators administering drugs using both techniques.
Introduction of ultrasound provided additional benefits in a study of 46 affected median nerves, with shorter time to achieve symptom relief (4 days post-injection) and sustained efficacy up to 12 weeks [16].
Evers et al. [17] evaluated the long-term outcome of local steroid injections (mean 7.2 years) in 689 hands. They observed a significant treatment-free survival rate in the ultrasound-guided treatment group. Re-treatment was required in 72% of patients compared with 55% of blindly and with ultrasound guidance, respectively. Using ultrasound reduced the risk of failure by 55%.
Cartwright et al. [18] examined 29 affected median nerves after steroid injection. They reported improved clinical and electrophysiological changes and a significant reduction in CSA 1 week after injection and suggested that reversible neuro-edema and congestion, rather than neuro-demyelination, may underlie the symptoms of CTS.
As in another series, normalization of FR was also observed in our study, 2 weeks after surgical release, even before improvement in nerve conduction studies [19].
Of note, improvement in other ultrasonographic signs indicative of successful injection has been reported, including decreased vascularity and increased median nerve mobility [18] with diminished palmar bowing of the flexor retinaculum and increased transverse sliding distance of the median nerve [20]
With ultrasound guidance, the needle can be placed in-plane or out-of-plane. In our study, we chose the in-plane ulnar approach because it matches well with our experience with other ultrasound-guided procedures. Lee et al. [21] analyzed the results obtained after steroid injections in 75 hands with ultrasound guidance (in-plane and out-of-plane ulnar approaches) and blindly. They reported significantly better clinical and ultrasonographic results in the ultrasound-guided in-plane group at 4 and 12 weeks after injection. This approach allows for good recognition of the various structures of the carpal tunnel, visualization of the entire needle, proper placement of the needle tip, and delivery of steroids into the perineural space without nerve injury [8].
Local steroid injections within 1 cm of the median nerve have been shown to pose a risk of injury [22]. Our needle was placed as close to the nerve as possible, and there were no side effects in the ultrasound-guided group. The virtue of ultrasound use in reducing the risk of nerve injury had been demonstrated previously in various reports [23, 24]. On the contrary, in our study, 33.3% of the blind group experienced transient nerve irritation. In a study of 102 patients, median nerve irritation (expressed as numbness in the fingers) was more pronounced with blind injections (observed in 14% of patients with blind injections versus 2% with ultrasound-guided injection) [25].
To our knowledge, secondary cases of CTS were not included in previous serious. In our study, we enrolled five secondary cases to be injected blindly and under ultrasound guidance and showed significant clinical and sonographic improvement at both groups. Ultrasonography adds diagnostic value in identifying the underlying etiology of secondary CTS. Validating these data requires another larger series.
The current study has some limitations. First, the relatively small sample size compromised our results. Second, we did not integrate our results with post-injection electrophysiological changes, as we relied primarily on ultrasonography. Third, data were lacking for long-term follow-up. Finally, two different operators with different specialties performed the injections.
