Lumbar disc herniation (LDH) is one of the most common causes of nerve root pain and results from the displacement of the nucleus pulposus inside the vertebral canal. It may also manifest as lumbosacral radiculopathy due to pressure on the spinal nerve roots [1]. This condition presents with dermatomal pain due to compression of the nerve root and weakness and paresis of the muscle groups and can be diagnosed with a positive straight leg raise (Lasègue) test [2]. Several studies have shown that trigger points (TPs) are common in patients with radiculopathy. The presence of TP-related pain in radiculopathy, in addition to peripheral neuropathy, is a major factor of symptom aggravation [3]. TPs are irritable spots in the skeletal muscle and may manifest as palpable nodules [4]. They are common sources of regional neuromusculoskeletal pain that are widely accepted by clinicians and researchers [5]. Simons et al. [6] defined TPs as painful foci in a taut band in the skeletal muscle. These foci can be active or latent; active TPs cause spontaneous pain and motor symptoms with nerve stimulation, whereas latent TPs do not cause painful symptoms. In addition, active TPs have shown the presence of chemical mediators, such as bradykinin and serotonin [7]. Pharmacological agents, manual and physical therapy, dry needling, TP injection, and botulinum toxin injections have been widely used for the treatment of TP; however, the most important step is treating the main cause of its pathogenesis [8]. TP injections are primarily performed using lidocaine or prilocaine, and while several studies have used lidocaine, few have used prilocaine.

Therefore, we investigated the efficacy of gluteal TP injections using prilocaine in patients with lumbosacral radiculopathy and pain in the gluteal region.

No significant differences were observed in age, sex, or baseline VAS score between the case and control groups (p>0.005) (Table 1). The VAS scores at 1 and 3 months were significantly (p<0.05) lower in the case versus the control group and significantly (p<0.05) lower than baseline values in both groups (Table 1, Fig. 1). There were no significant differences (p>0.005) in baseline ODI scores between groups, and the ODI scores at 1 and 3 months were significantly (p<0.05) lower in the case than control groups and significantly (p<0.05) lower than the baseline values in both groups (Table 1, Fig. 2).

Low back pain (LBP) is a common problem that is treated by both primary care and specialty physicians. While its etiology includes several factors, LBP is usually associated with muscular components. Identifying the cause of LBP in clinical practice is challenging because there are usually several causes. Intervertebral disc herniation, one of the most common causes of LBP, affects the nerve roots, leading to lumbosacral radiculopathy [12], which is often accompanied by lumbar and gluteal local TPs. Patients with TPs experience additional pain and discomfort, which can complicate radiculopathy treatment [13].

In a study of 207 patients with gluteal TPs, Adelmanesh et al. [12] found that 74.6% had TPs ipsilateral to the radiculopathy. Active TPs located in the gluteus minimus muscle can mimic sciatica during the chronic phase of radiculopathy [12]. The location of the TPs is often not anatomically clear. Nevertheless, Akamatsu et al. [14] identified TPs as entry points of the spinal accessory nerve into the trapezius muscle and tendon in a cadaver study. TPs may result from trauma to or overload of specific muscle groups. Repetitive strain injuries can cause the formation of chronic TPs. Instead of the generic term “muscle pain,” terms such as local soft tissue pain, local fibromyalgia, and idiopathic myalgia may be used. TPs can be palpated as taut bands in specific locations [15]; the palpation of these tender spots causes a local twitch response, which activates alpha motor neurons. In our study, a local twitch response was obtained at the active TP foci. A detailed history and physical examination are essential for the diagnosis of a TP due to limited diagnostic laboratory tests [16].

Iglesias-González et al. [17] evaluated 42 patients with nonspecific LBP and revealed that TPs in the lumbar area and hip muscles are particularly important sources of nonspecific LBP. They also demonstrated that patients with nonspecific LBP have a greater disability and worse sleep quality than individuals without a TP [17]. TP injection is preferred when conservative methods fail [9]. Various conservative approaches can be used in the management of TP, the most common of which are dry needling and local anesthetic administration. The gauge of the needle used for TP injection can also affect treatment success. While previous studies used 21-, 25-, and 27-gauge needles [18], we preferred to use a green 21-gauge needle in the present study.

The injection site should be cleaned with an antiseptic agent and sterilized prior to performing the injection [19]. We used Betadine to clean the site, with the patient in a prone position, using the technique of Simons et al. [6] for the injection, which we believed to be more effective [20]. In vitro studies have revealed that local anesthetics reduce the release of free oxygen radicals from polymorphonuclear leukocytes (PMNLs) [21]. In vivo studies have shown that local anesthetic administration inhibits adhesion and leukocyte migration [2223]. Local anesthetics have also been found to decrease the release of histamine from mast cells and leukotriene B4 from PMNLs as well as the release of interleukin-1 (IL-1) [24]. Due to their short half-lives and lower local irritant effects, lidocaine and prilocaine are the most commonly used local anesthetics for injection [9]. Hameroff et al. [25] administered bupivacaine 0.5%, etidocaine 1%, or physiologic saline to the neck and lumbar muscles and observed a greater pain decrease with the use of local anesthetics compared with saline, although no difference was noted between the two anesthetics. Frost [26] treated patients with acute lumbar pain with either mepivacaine or saline and observed no difference after 2 weeks.

In the present study, patients undergoing medical therapy and an exercise program comprised the control group. The group receiving TP injections had significantly reduced pain and improved functional status compared with the controls. The different results obtained by various studies may be due to the differences in the gauge of the needle or active ingredient used as well as the method of application. Any failure to precisely localize the TP and injection of a spot adjacent to the TP may also yield unsatisfactory results. We believe that the mechanism of action and features of the anesthetic are also important determinants of TP injection success. Yuan et al. [27] showed that lidocaine inhibits lipopolysaccharide-related inflammatory mediator release from microglia and reported that the mechanism of action involves the blockage of the p38 mitogen- activated protein kinase and nuclear factor-kappa B signaling pathways. Lidocaine has anti-inflammatory effects on monocytes, macrophages, and neutrophils as well as on LPS, thereby inhibiting nitric oxide, prostaglandin E2, tumor necrosis factor-α, IL-1β, and monocyte chemotactic protein-1 [28]. Given that molecules such as IL-1 are often present in the vicinity of TPs, lidocaine reduces the secondary pain due to the TP via both neurological and biochemical mechanisms. The effectiveness of various procedures, such as injections in the epidural space, facet joints, and locally sensitive TPs as well as nerve blocks, has been discussed in large database collection trials that question the efficacy of injection therapy in patients with posterior back pain [29]. Statements on the efficacy of multiple injections and various nerve blocks in the literature compared with such nonspecific studies have shown high heterogeneity [1925].

Although few studies have used prilocaine, we prefer its use for TP injection. We found that it was effective for the treatment of TPs, and its mechanism of action may be similar to the biochemical processes involving lidocaine. Further molecular studies on the exact biochemical mechanisms of prilocaine are warranted.

Our study showed that patients with radiculopathy, which was possibly due to secondary TPs in the gluteal region, have favorable results with TP injection. We suggest that TP injection be part of the treatment of lumbosacral radiculopathy in selected patients.