Posterior Sacrococcygeal Plexus: Application to Spine Surgery and Better Understanding Low-Back Pain.

OBJECTIVE: The sacral dorsal rami form the posterior sacrococcygeal plexus (PSCP), which has been scantly studied. This study's goal was to clarify the PSCP s detailed anatomy and discuss its clinical relevance. METHODS: Ten sides of 5 fresh-frozen cadavers were dissected for this research. After the muscles covering the sacrum were removed, the PSCP was identified and traced under the operating microscope until the entire plexus was exposed. The contributions to this plexus and its relations to surrounding anatomic structures were recorded. RESULTS: The PSCP was found on all sides and was composed of a medial trunk (MT), communicating branches, and a lateral trunk. Each sacral dorsal ramus's MT formed a series of loops created by adjacent sacral dorsal rami placed between the transverse tubercles and the posterior sacral foramina. The MT, communicating branches, and lateral trunk demonstrated potential entrapment sites. CONCLUSIONS: To our knowledge, this is the first anatomic study that provides detailed images that indicate 3 potential sites where surrounding structures could entrap the PSCP. Knowledge of its detailed anatomy might help in better understanding low-back pain, targeting pain sources and guide spine surgeons for avoiding injury to these nerves.

Pelvic Electric Potential as a Marker of Autonomic Dysfunctions and Risk Factor of Neurogenic Arrhythmias in Humans.

Differential high-resolution ECG (V1-V2) and pelvic electric potential measured between the coccyx and perineum were recorded simultaneously in resting supine position in men with autonomic nervous system disorders (N=37). In healthy volunteers (N=23), the effective (rms) value of PEP presented by median and interdecile range was 30 (20-80) µV within the frequency band of 0.03-80 Hz. In patients, the corresponding value was significantly higher: 140 (80-280) µV. In both groups, the amplitude harmonic spectrum of pelvic electric potential decreased monotonically with frequency according to 1/f1.6 law. In some patients (N=16), rare single or grouped high-amplitude impulses (up to 1 mV) of pelvic electric potential with total duration of about 1 sec were observed; of them, some persons (N=7) demonstrated practically one-to-one synchronous relations between these impulses and arrhythmia episodes indicating abnormal activity of the autonomic nervous system as their most probable common cause. The high-amplitude pelvic electric potential impulses were also observed in ECG records as interference signals with an amplitude attaining 50 µV. Thus, high-resolution ECG and pelvic electric potential can reveal the risk of abnormal neurogenic influences on the heart. The data obtained are discussed in relation to diagnostics of the autonomic nervous system disorders, neurogenic arrhythmias, and risk of sudden cardiac death.

The anatomy of the sacrococcygeal cornual region and its clinical relevance.

There has been no systematic study of the anatomy of the region between the sacral and coccygeal cornua. Reference texts describe an intercornual ligament connecting these structures. The aim of this study was to investigate the anatomy of this region, which may be relevant to unexplained cases of coccygeal pain (coccydynia) and local nerve blocks. The bony anatomy of the sacrococcygeal (SC) cornual region was analyzed in 33 CT scans obtained from supine adults of mostly European origin with no known SC pathology, 7 µCT scans of cadaver SC specimens, and 105 Asian Indian adult skeletons. A further five cadaver SC specimens were examined histologically. SC cornual fusion was seen in 45% of CT/µCT scans (mean age 67 years, 20 males) and in 20% of adult skeletons (78 males); there was no association with age or sex. In the absence of SC fusion, the mean intersacrococcygeal cornual gap was 7.1 ± 2.4 mm; this was bridged by an intercornual ligament composed of parallel vertical collagen fibers reinforced by elastin fibers on its anterior surface. Small nerve branches were observed adjacent to the ventral aspect of the intercornual ligament and, in one case, traversing the ligament. Ipsilateral sacral and coccygeal cornua are therefore normally bridged by an intercornual ligament that is probably innervated. The cornua are fused on one or both sides in 20-45% of adults. These findings may have implications for some cases of coccydynia and for anesthetists performing local nerve blocks.

Redefining the coccygeal plexus.

The coccygeal plexus is variably described in anatomy texts and has rarely been studied despite the idiopathic nature of coccydynia in up to one-third of affected patients. The plexus was therefore investigated using a combination of microdissection and histology. The distal sacrum and coccyx in continuity with ischiococcygeus were removed en bloc from 16 embalmed cadavers (mean age 78 ± 10 years, 7 females) with no local disease. Ten specimens underwent microdissection of the coccygeal plexus and the remaining six were examined histologically after staining with hematoxylin and eosin and S100 immunohistochemistry to demonstrate nerve fibers. The coccygeal plexus is formed within ischiococcygeus from the ventral rami of S4, S5, and Co1 with a contribution (gray rami communicantes) from the sacral sympathetic trunk. It gives rise to anococcygeal nerves which pierce ischiococcygeus and the sacrospinous ligament to supply the subcutaneous tissue on the dorsal aspect of the coccyx. Some branches from the plexus pass medially anterior to the coccyx. The coccycgeal plexus is formed within ischiococcygeus rather than on its pelvic surface and appears to supply skin in the anococcygeal region. It probably also contributes to the innervation of ischiococcygeus, the sacrospinous ligament, coccygeal ligaments, and periosteum. It deserves to be considered as a potential pain generator that may be implicated in some patients with coccydynia.

Paracoccygeal corkscrew approach to ganglion impar injections for tailbone pain.

A new technique for performing nerve blocks of the ganglion impar (ganglion Walther) is presented. These injections have been reported to relieve coccydynia (tailbone pain), as well as other malignant and nonmalignant pelvic pain syndromes. A variety of techniques have been previously described for blocking this sympathetic nerve ganglion, which is located in the retrorectal space just anterior to the upper coccygeal segments. Prior techniques have included approaches through the anococcygeal ligament, through the sacrococcygeal joint, and through intracoccygeal joint spaces. This article presents a new, paracoccygeal approach whereby the needle is inserted alongside the coccyx and the needle is guided through three discrete steps with a rotating or corkscrew trajectory. Compared with some of the previously published techniques, this paracoccygeal corkscrew approach has multiple potential benefits, including ease of fluoroscopic guidance using the lateral view, ability to easily use a stylet for the spinal needle, and use of a shorter, thinner needle. While no single technique works best for all patients and each technique has potential advantages and disadvantages, this new technique adds to the available options.