To the best of our knowledge, this is the first case where successful low back pain relief was obtained with the use of ESP block in a patient with FBSS who experienced recurrent low back pain after undergoing two back surgeries.
ESP block is a novel, ultrasound-guided, peripheral nerve block that was first described for the treatment of chronic thoracic neuropathic pain . The present report shows that ESP block at the lumbar vertebral level is as effective as that at the thoracic vertebral level, which is described in previous reports [5, 6]. ESP block is considered an extensive cutaneous sensory block because it affects either the dorsal rami or both the dorsal and ventral rami of the spinal nerves [5, 6]. In this case, a cold test determined that ESP block administered at the transverse process of L2 affected the dorsal rami of the lumbar spinal nerves from T12 to L5, but not the ventral rami. Although several studies have reported that ESP block affects both the dorsal and ventral rami of the spinal nerves [5, 8], a cadaver study showed that the ventral rami are not always blocked . In addition, there may be differences between lumbar and thoracic ESP blocks . Although FBSS is caused by multiple factors, low back pain in FBSS may be precipitated by the dorsal rami of the spinal cord . Thus, ESP block is expected to alleviate low back pain in patients with FBSS. Indeed, as observed in the present case of FBSS, ESP block was highly effective in the treatment of low back pain. We used 20 ml of 0.1875% ropivacaine on the basis of previous studies [5, 6, 10]. Although there is no study on the appropriate dose of the local anesthetic, our dose was probably sufficient because adequate pain relief was obtained without adverse events. Several other blocks can affect the dorsal rami of the spinal nerves, such as the retroraminal block and thoracolumbar interfascial plane block [11, 12]. The injection site for both these blocks is close to that for ESP block. However, ESP block for FBSS, particularly that in the lumbar region, has not been adequately compared with these blocks. ESP block has several advantages. First, it is an easy and a safe procedure. The target is located on the transverse process, which gives a strong echo on ultrasound images and can be easily identified. Therefore, concerns regarding excessive advancement of the needle and inadvertent injection into the epidural or intrathecal space are limited. Second, the analgesic effect of ESP block is observed over a wider area. In this case, a cold test confirmed the effects between T12 and L5. This is an advantage over other regional analgesic techniques such as the trigger block and the medial branch block, which have effects limited to the injected area. Finally, surgical scar formation, which is a natural stage of tissue healing after surgery  and may limit drug spread to the target site, does not affect ESP block. The point at which drugs are injected for ESP block lies between the erector spinae muscle and the transverse process and is outside the surgical area, particularly that for the PLIF maneuver. Thus, there is likely to be minimal scar formation at the drug-injection site.
In general, the first choice for the treatment of FBSS is medication therapy . However, this patient was already undergoing treatment with 27 different medications; therefore, she was not treated with additional medication because of polypharmacy concerns. Epidural block is a good choice for interventional therapy in pain clinics , but caudal epidural block was not effective in this case, probably because fibrotic adhesions formed by previous surgeries may have created separations within the epidural space , which interfered with the spread of the analgesic solution. As a more invasive treatment that can be used when conservative treatment is ineffective in cases of FBSS, SCS can play an important role in pain management . A limitation of SCS is that some patients have reported complications, such as lead migration, local wound infection, pocket pain, loss of therapeutic effects, and cerebrospinal fluid leak with headache; these do not occur with ESP block . Epiduroscopy is another option that may allow the physician to directly visualize the adhesions in the epidural space; this has also been reported to be effective . However, this procedure is more invasive than ESP block and can only be performed at specialized institutions, particularly in Japan. For the above reasons, ESP block may be a valuable primary treatment option before the implementation of more invasive treatments for FBSS-associated low back pain.
There were three limitations to this case study. First, this report is just a case report, so it remains unclear whether ESP block is always an effective treatment for low back pain associated with FBSS, which can cause pain of various origins. For example, if low back pain originates inside the spinal canal, ESP block may not be effective. Further large-scale clinical studies are necessary for the generalization of our results. Second, this case involved a small woman, which makes it difficult to generalize our results. However, there is no relationship between low back pain in FBSS and physique. Thus, ESP could serve as a valuable treatment option for low back pain in patients with FBSS. Third, this report only showed the clinical effects of ESP block for FBSS, not the underlying mechanism. Further studies involving volunteers and cadavers subjected to lumbar surgery are necessary to clarify the mechanism.
In conclusion, the findings from this case suggest that ESP block is an easy and safe procedure and can serve as an effective treatment option for FBSS-associated low back pain.