Comparison of Diagnostic and Therapeutic Efficacy of Periarticular And/or Intraarticular Lidocaine Injections Under Ultrasound Guidance in Sacroiliac Joint Dysfunction Diagnosis and Treatment

The sacroiliac joint is a true diarthrodial joint, surrounded by an articular space containing synovial fluid and encased in a fibrous capsule, but it has unique features not typically found in other diarthrodial joints. The sacroiliac joint contains both hyaline cartilage and fibrocartilage and is characterized by a discontinuous posterior capsule with protrusions and depressions that minimize movement and enhance stability. As a result, the sacroiliac joint is only described as a true synovial joint in its anterior portion. In contrast, the posterior connection, formed by the sacroiliac ligaments, the gluteus medius and minimus muscles, and the piriformis muscle, is a syndesmosis-type joint. The sacroiliac joint is richly equipped with neuro-sensors and proprioceptors. Information regarding its innervation pattern has been a subject of considerable debate. Solonen et al. revealed, based on previous studies, that the innervation of the joint is provided by branches from the lumbosacral plexus, the superior gluteal nerve, the dorsal rami of S1 and S2, and the obturator nerve. However, despite several studies, the exact innervation remains unclear. It has been suggested that the anterior portion is innervated by the sacral plexus, while the posterior portion is innervated by the spinal nerves. It has been proposed that the dominant innervation occurs via the L4-S1 nerve roots, with some contributions from the superior gluteal nerve. Several authors argue that the joint is solely innervated by the sacral dorsal rami. Bernard et al. proposed that the posterior innervation originates from the lateral branches of the posterior rami of L4 to S3, and the anterior innervation is from the region between L2 and S2 segments.

Nakagawa et al. reported that nerve fibers traveling to the sacroiliac joint originate from the ventral rami of L4 and L5, the superior gluteal nerve, and the dorsal rami of L5, S1, and S2. In contrast, Grob and colleagues found that sacroiliac joint innervation is almost entirely derived from the sacral dorsal rami.

Fetal pelvic dissections confirmed that the innervation of the sacroiliac joint originates from the dorsal rami due to the neural fibers being located exclusively in the dorsal mesenchyme.

Murata et al. assessed sensory innervation of the sacroiliac joint in rats and concluded that sensory neurons from the dorsal root ganglia of L1 to S2 on the same side innervate the joint. They also noted that sensory fibers from the L1 and L2 dorsal root ganglia pass through the paravertebral sympathetic chain.

Histological analyses of chronic painful sacroiliac joints have confirmed the presence of nerve fibers within the joint capsule and adjacent ligaments. A recent cadaver study by McGrath and Zhang found that the long posterior sacroiliac ligament received afferent input from S2 in 96% of samples, S3 in 100%, S4 in 59%, and rarely from S1 (4%). Nerve fascicles contained both myelinated and unmyelinated nerve fibers, as well as two morphotypes of paciniform mechanoreceptors and a single non-paciniform mechanoreceptor, suggesting that pain and proprioception may be transmitted through the sacroiliac joint. Szadek et al. concluded that the presence of calcitonin gene-related peptide and substance P immunoreactive fibers in the anterior capsule and interosseous ligaments provides a morphological and physiological basis for pain signals originating from these structures. They also suggested that infiltration techniques used to diagnose sacroiliac joint pain should consider both extra-articular and intra-articular approaches. Sakamoto et al. showed that most mechanoreceptor units in the sacroiliac joint are high-threshold group 3 units, which may have a neuropathic function. However, they argued that proprioceptive function in the sacroiliac joint is limited.