Introduction
Trigger finger, which is also known as stenosing tenosynovitis, is caused by the thickening of the first annular (A1) pulley surrounding the flexor tendon of the finger. It is the most common hand disease that causes pain and dysfunction of the hand [
1]. Trigger finger can be nonsurgically treated using splints, nonsteroidal anti-inflammatory drugs, or conservative treatment by injecting steroids into the aponeurosis. Surgical methods such as percutaneous incision or invasive A1 pulley incision are performed when conservative methods are ineffective [
1-
3].
Local steroid injection in the trigger finger, which was first reported in 1953 by Howard et al. [
4], is a convenient technique and produces excellent results (therapeutic efficiency of 60%-93%) [
5-
7]. It is important to accurately inject the steroid into the flexor tendon sheath to increase the therapeutic effect of steroids and reduce side effects such as tendon rupture, skin atrophy, and discoloration, which can occur because of local injection [
8,
9]. However, there is only a 36% to 49% probability that the drug will be accurately injected into the flexor tendon sheath during actual steroid injection [
10,
11], and only a few studies have reported the steroid injection technique and its clinical results in trigger finger.
This study aimed to introduce our steroid injection technique for trigger finger, which uses tendon excursion of the flexor tendon, and to evaluate the clinical outcomes in patients who received this technique as the primary treatment. Our hypothesis was that the technique simultaneously provided satisfactory finger function restoration and low complication rates.
Discussion
Trigger finger, which was first described by Notta [
13] in 1850, is a stenosing tenosynovitis of the flexor tendon that causes pain and dysfunction of the hand [
1]. Ever since Howard et al. [
4] first used hydrocortisone injection as a treatment for trigger finger, therapeutic results of 60%-93% have been reported, and local steroid injection is known as the primary treatment method for trigger finger [
5-
7]. In the present study, the efficacy of our steroid injection technique was investigated. Our injection technique uses tendon excursion during injec-tion to accurately deliver steroids into the flexor tendon sheath. It showed excellent results and low complication rates.
To increase the therapeutic effect of topical steroid injection, it is important to accurately inject the steroid into the flexor tendon sheath [
8]. However, there is a low probability that the steroid will be accurately injected into the flexor tendon sheath during blind steroid injection. In a study by Kamhin et al. [
10], the distribution of methylene blue was visually confirmed during surgical treatment after injecting methylene blue solution into the flexor tendon sheath of 77 patients scheduled for surgical treatment of trigger finger. Only 38 patients (49.4%) reported that methylene blue was injected into the flexor tendon sheath. In a study by Fowler et al. [
11], the distribution of iopamidol contrast dye was examined by live fluoroscopy in 25 patients; only nine patients (36.0%) reported that the dye was injected into the flexor tendon sheath. To accurately inject steroids into the tendon sheath during blind injections, Freiberg et al. [
14] inserted the needle deep into the flexion tendon from the proximal part of the A1 pulley, extended and flexed the finger to observe that the needle moved together, and then withdrew the needle gradually until the needle did not move with the finger. It was suggested that the drug should be injected at the position where the needle did not move while it was being pulled out. This is similar to our injection technique, which uses tendon excursion, but it is different in that the needle is pulled out of the flexor tendon by repeatedly performing extension and flexion movements of the finger instead of withdrawing the needle.
During injection, if the finger is well flexed and extended, the needle can come out of the flexor tendon well. In other words, with proper tendon excursion during injection, the tip of the needle can be positioned into the flexor tendon sheath (
Fig. 5). In the present study, the efficacy of steroid injection in the other fingers (except the thumb) was 88.2%, which was higher than that seen in the thumb at 75.4% (p=0.048). We thought that the reason why the treatment results of the thumb were not as good as those of other fingers could be the difference in the accuracy of the injection location between the thumb and other fingers. The distance of tendon excursion is generally 3.0 to 3.4 cm for the flexor digitorum profundus (FDP) and 2.8 cm for the flexor pollicis longus (FPL) in the neutral state of the wrist [
15]. Because the distance of tendon excursion of FDP is longer than that of FPL, there may be differences in the accuracy of the injection location. We believe that these differences could affect the difference in treatment outcomes between the thumb and other fingers.
In the trigger finger, as the A1 pulley surrounding the flexor tendon thickens, the tunnel for tendon excursion narrows, and the tendon excursion of the flexor tendon becomes limited [
1]. Quinnell [
12] classified the stages of the trigger finger by its symptoms. In fingers of Quinnell grade IV, there were limitations in our injection technique due to fixed tendon excursion because such fingers are fixed in a bent or nonflexed state. In this study, 16 patients (9.4%) had grade IV disease, and the treatment rate was 43.8% (7 of 16), which was significantly lower than those of Quinell grade II (88.9%, 88 of 99) and grade III (87.5%, 49 of 56). This difference in the treatment rate may be caused not only by the difference in the degree of initial symptoms but also by the possibility that inaccurate injection occurred because of the limitation in the tendon excursion distance due to the restriction of the extension movement during injection.
Although local steroid injections are effective for treating various musculoskeletal disorders, complications may arise. The potential complications of local steroid injection include infection, skin depigmentation, tendon rupture, and fat atrophy [
8]. The injection site is crucial when administering a steroid injection (
Fig. 6). If the steroid injection is intratendinous, it is highly likely to damage the tendon tissue and lead to necrosis of the collagen bundle of the tendon, which results in tendon rupture [
16,
17]. There have been a few reports of rupture of the flexor digitorum tendon after steroid injection for trigger finger [
18]. Several studies have been reported that extrasheath injection is as effective as intrasheath injection [
19,
20]. However, extrasheath injection has the potential to cause skin depigmentation and/or fat atrophy because the steroid spreads into subcutaneous tissue. It has been reported that fat atrophy can cause 1% depigmentation in 5% of patients after local steroid injection [
21]. In the present study, the results showed a low incidence of complications; only one digit (0.6%) had subcutaneous tissue atrophy, and only two digits (1.2%) had skin depigmentation. We believe that the reason for the relatively low incidence of complications is that our technique induces intrasheath injection as much as possible. In addition, the fact that the injection per digit was not performed more than twice and that the second injection was performed at an interval of more than 6 weeks may have reduced complications.
Ultrasound-guided injection is a widely used technique for intrasheath injection and has been reported to have excellent treatment rates of 91.4% to 93.4% [
22,
23]. However, it requires a lot of time and is expensive compared with blind injection techniques. On the other hand, our injection technique is simple, quick, inexpensive, and easy to follow even by unskilled operators.
This study had several limitations. First, this was a retrospective study, and there was no control group that did not use our technique. Therefore, it was difficult to analyze the therapeutic effect of injections using our technique. Randomized controlled trials may be needed to provide a higher level of evidence. Second, our technique is to inject into the tendon sheath, which first requires intratendon needling. Although steroids are not injected directly into the tendon, it has the potential to cause microtrauma to the tendon. Finally, the confirmation of whether steroids were accurately delivered into the flexor tendon sheath was limited. Intrasheath injection was judged via the naked eye and by palpation of thrills. It may be necessary to accurately check whether the steroid is injected into the intrasheath by using ultrasound. Despite these limitations, our findings are meaningful because they provide evidence of the clinical effects of our technique and are valuable as a report that introduces our injection technique for trigger finger.