The long posterior sacroiliac ligament: A histological study of morphological relations in the posterior sacroiliac region

Sacroiliac innervation

PURPOSE

To investigate the innervation pattern of the sacroiliac region, especially with regard to the sacroiliac joint (SIJ). Dorsal SIJ innervation was analyzed and described. Our main hypothesis was that nerves reach the SIJ dorsally, passing ligamental compartments, as this would explain dorsal SIJ pain.

METHODS

To examine sacroiliac innervation, we followed the nerves in over 50 specimens over several years. Plastinated slices were evaluated, nerves in the region were stained histologically, and the data were summarized as 3D models.

RESULTS

The Rami communicans and posterior branches of the spinal nerves and their branches that form a dorsal sacral plexus and communicating branches, together with corresponding vessels, were observed to form neurovascular bundles embedded by tiny fatty connectives in gaps and tunnels. Branches of L5-S1 pass the inner sacroiliac ligaments (the interosseous sacroiliac ligament and axial interosseous ligament). The outer sacroiliac ligaments (posterior sacroiliac ligaments, long posterior sacroiliac ligament, sacrotuberal ligament, thoracolumbar fascia) are passed by the S1-S4 branches. However, although the paths of these nerves are in the direction of the SIJ, they do not reach it. It is possible that impingement of the neurovascular bundles may result in pain. Moreover, the gaps and tunnels connect to the open dorsal SIJ.

CONCLUSION

Our findings suggest that Bogduk's term "sacroiliac pain" correlates to "sacroiliac innervation", which consists of "inner-" and "outer sacroiliac ligament innervation", and to ventral "SIJ pain". The watery gaps and tunnels observed could play a significant role in innervation and thus in the origins of SIJ pain.

LEVEL OF EVIDENCE

Individual cross-sectional studies with consistently applied reference standard and blinding.

Analysis of Complications in Sacroiliac Joint Fusions Using FDA 510(k) Cleared Devices

STUDY DESIGN

This was a level III-retrospective cohort study.

OBJECTIVE

The objective of this study was to present an unbiased report of the current rate of severe complications for Federal Drug Administration (FDA) 510(k) cleared sacroiliac joint (SIJ) fusions and investigate the underlying cause of these complications.

SUMMARY OF BACKGROUND DATA

The number of yearly SIJ fusions is on an upward trend. Currently, the most utilized implants to fuse the SIJ have been FDA 510(k) cleared devices. Studies reporting on complications following SIJ fusions are mostly industry-sponsored.

MATERIALS AND METHODS

The Manufacturer and User Facility Device Experience (MAUDE) database was searched for all reported FDA 510(k) cleared SIJ fusion device complications. Several data points were obtained from each report and recorded. The Hospital Inpatient National Statistics and the Center for Medicare and Medicaid Services (CMS) was also searched for the number of SIJ fusions performed each year.

RESULTS

A search of the MAUDE database returned 1115 reports, with the first report on June 30, 2011, and the last report on July 28, 2020. Patient injury was the most common type of event reported at 97.5% (1080/1107). Death was reported in 3 patients (0.3%). Malposition was the most common device problem at 49.5% (548/1107). The root cause of these events was primarily user error at 58.2% (644/1107). Revision surgery or reoperation occurred in 92.8% (1028/1107) of reports. Data for SIJ fusions through CMS showed an overall trend of increasing yearly SIJ fusions.

CONCLUSIONS

The majority of complications reported to MAUDE for FDA 510(k) cleared SIJ fusion devices are user error due to improper placement of implants. These complications are likely underreported, and there is currently no formal tracking system of total SIJ fusions performed to calculate accurate complication and revision rates. Patient injury and health care costs can potentially be reduced with improved education, training, and oversight, which is currently lacking.

Sacroiliac Joint Anatomy

The sacroiliac joint can be a source of low back pain. This review article summarizes current anatomic evidence of the innervation of the intraarticular and extraarticular parts of the sacroiliac joint relative to bony landmarks identifiable with fluoroscopy and ultrasound. This article aims to provide clinicians with an anatomic basis for clinical application to diagnostic blocks and radiofrequency ablation for sacroiliac pain to optimize clinical outcomes.

Ligaments stabilizing the sacrum and sacroiliac joint: a comprehensive review

The sacroiliac joint is a diarthrodial synovial joint in the pelvis. Anatomically, it is described as a symphysis, its synovial joint characteristics being limited to the distal cartilaginous portion on the iliac side. It is a continuous ligamentous stocking comprising interconnecting ligamentous structures and surrounding fascia. Its ligaments, the primary source of its stability, include the anterior, interosseous and dorsal sacroiliac, the iliolumbar, sacrotuberous, and sacrospinous. Structural reinforcement is also provided by neighboring fascia and muscles. Lower back pain is a common presentation of sacroiliac joint disease, the best-established treatments being corticosteroid injections, bipolar radiofrequency ablation, and sacroiliac joint fusion.

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.

Quantification of fat in the posterior sacroiliac joint region: fat volume is sex and age dependant

Fat is appreciated as a structural component of synovial joints. It may serve a shock-absorbing function for the incongruent surfaces, vessels and ligaments, but has not been investigated in the posterior sacroiliac joint (PSIJ). Sixty-six cadaveric hemipelves were serially-sectioned and photographed. The amount of visible fat in the PSIJ was quantified using a modified version of Cavalieri’s method. Total volume, fat volume and fat percentage of the PSIJ were calculated in predefined sub-regions. Fat is consistently present in the PSIJ (1.9 ± 1.3 cm³). Fat volume correlates with the PSIJ total volume (p < 0.0001; r = 0.73) and age (p = 0.024; r = 0.24), and is smaller in males (1.4 ± 0.8 cm³) than females (2.4 ± 1.5 cm³). Fat volumes in the middle and inferior sub-regions of the PSIJ show side- (p < 0.0001) and sex-differences (p = 0.013 females, middle sub-region). Age and PSIJ total volume correlate between sexes in various sub-regions (p = 0.05 females superior sub-region; males inferior sub-region). Fat percentage differs between sexes and sub-regions (p = 0.018 females, superior sub-region) but is independent of age and sides. The presence of fat within the PSIJ is a normal finding and shows sex-dependant and age-related differences. It is unclear whether fat is linked to age-related degeneration or has a shock-absorbing role in stress- and load-dissipation in the PSIJ.

A systematic review of the morphology and function of the sacrotuberous ligament

The sacrotuberous ligament (STL) has been linked to conditions such as pelvic girdle pain and pudendal nerve entrapment, yet its contribution to pelvic stability is debated. The purpose of this review was to explore the current understanding of the STL and highlight any gaps in knowledge regarding its anatomy and function. A systematic search of the literature was conducted, focussing on the morphology and attachments of the STL, the relationship of the STL with surrounding structures, and its neurovascular supply and function. A total of 67 papers and four textbooks were obtained. The attachment sites of the STL are largely consistent; however, the extent of its connections with the long head of biceps femoris, gluteus maximus, piriformis, the posterior layer of the thoracolumbar fascia, and sacrospinous ligament are unclear. Morphometric parameters, such as mean STL length (6.4-9.4 cm), depth (0.3-0.4 cm), and width (1.8-3.5 cm, at its mid-point) are variable within and between studies, and little is known about potential side-, age-, or sex-related differences. The STL is pierced in several sites by the inferior and superior gluteal arteries, but information on its innervation pattern is sparse. Functionally, the STL may limit sacral nutation but it appears to have a limited contribution to pelvic stability. Some morphological aspects of the STL warrant further investigation, particularly its connections with surrounding structures, innervation pattern and function. Knowledge of the detailed anatomy and function of this ligament is important to better understanding its role in clinical conditions. Clin. Anat. 32:396-407, 2019. © 2018 Wiley Periodicals, Inc.

A comprehensive review of the sub-axial ligaments of the vertebral column: part I anatomy and function

BACKGROUND

As important as the vertebral ligaments are in maintaining the integrity of the spinal column and protecting the contents of the spinal canal, a single detailed review of their anatomy and function is missing in the literature.

METHODS

A literature search using online search engines was conducted.

RESULTS

Single comprehensive reviews of the spinal ligaments are not found in the extant medical literature.

CONCLUSIONS

This review will be useful to those who treat patients with pathology of the spine or who interpret imaging or investigate the anatomy of the ligaments of the vertebral column.

A comprehensive review of the sub-axial ligaments of the vertebral column: part II histology and embryology

BACKGROUND

As important as the vertebral ligaments are in maintaining the integrity of the spinal column and protecting the contents of the spinal canal, a single detailed review of their histology and embryology is missing in the literature.

METHODS

A literature search using online search engines was conducted.

RESULTS

Single comprehensive reviews of the histology and embryology of the spinal ligaments are not found in the extant medical literature.

CONCLUSIONS

This review will be useful to those who study or treat patients with pathology of the spine.

Sacroiliac joint pain as an important element of psoriatic arthritis diagnosis

Psoriatic arthritis (PsA) is a chronic inflammatory disease characterized by the coexistence of arthritis with psoriasis of the skin and nails. The sacroiliac joints were observed in 34-78% of patients with psoriatic arthritis. Due to such a high prevalence of SIJ dysfunction, understanding pathophysiology of pain and the associated pain pattern becomes a very important aspect of PsA diagnosis. As far as the etiology of SI joint dysfunction is concerned, it has not been disambiguated yet. Among the main causative factors, injuries and strains of the structures surrounding the joint are noted. Joint pathology usually manifests itself by pain occurring within the area of the joint. The causes of pain may be divided into two categories: intra-articular and extra-articular. Pain caused by the SI joint may be nociceptive or neural in nature, whereas the pain pattern characteristic of the joint correlates with its innervation and is consistent with S2 dorsal rami.

Experimental pelvic pain facilitates pain provocation tests and causes regional hyperalgesia

The extra-articular sacroiliac joint (SIJ) structure is a potential source for low back and pelvic pain. This study hypothesised that experimental pain induced in a superficial pelvic ligament causes (1) hyperalgesia to pressure, (2) distinct pain referral, and (3) an increased frequency of positive pain provocation tests of the SIJ complex. Thirty healthy subjects (15 females) participated in this study designed as a randomised crossover trial. Pain was induced in the long posterior sacroiliac ligament by injection of hypertonic saline, with the contralateral ligament injected with isotonic saline as control. Pain intensity was assessed on an electronic visual analogue scale (VAS). Pressure pain thresholds (PPTs) and pain provocation tests were assessed on 3 occasions: at baseline, after injection, and when pain had subsided. PPT sites were located bilaterally at the injection site, lateral to spinous processes of S2 and L5, and at the gluteus medius and gastrocnemius muscles. Hypertonic saline caused significantly higher VAS scores and more extended pain referral than isotonic saline (P<0.001). PPTs at the injection site and lateral to S2 were significantly reduced after hypertonic saline compared with baseline and isotonic saline (P<0.002). Significantly more subjects had positive pain provocation tests after hypertonic (67% of subjects) compared with isotonic saline (20%; P<0.001). These data demonstrate that the extra-articular SIJ structure accommodates nociceptors that are capable of inducing pain referral and regional hyperalgesia sensitive to manual pain provocation tests similar to what previously have been found in pelvic girdle pain patients.

Functional morphology of the thoracolumbar transversospinal muscles

STUDY DESIGN. A qualitative and semiquantitative study of the morphology of the human thoracolumbar transversospinal (TSP) muscles. OBJECTIVE. To further define the functional morphology of the thoracolumbar TSP muscles. SUMMARY OF BACKGROUND DATA. The TSP muscle group plays an important role in vertebral function but few studies have rigorously investigated their morphology throughout the thoracolumbar region and details on the location of motor endplates (MEPs) and fiber types are sparse. METHODS. Thoracolumbar TSP muscles were examined by microdissection in five cadavers (seven sides). MEPs were identified using acetylcholinesterase histochemistry in muscles between T5 and S4 unilaterally in two cadavers. The relative proportions of type I and type II skeletal muscle fibers were determined using immunohistochemistry on whole cross sections of every TSP muscle from one side of one cadaver (T5-S4). RESULTS.TSP morphology was homogeneous and consistent throughout the thoracolumbar region. Notable differences to standard descriptions included: (1) consistent attachments between muscles; (2) no discrete cleavage planes between muscles; and (3) attachment sites over the sacrum and to lumbar zygapophysial joints. Previously undescribed small muscles were found attaching to the medial sacrum. All TSP muscles were multipennate, with fibers arranged in parallel having one MEP per muscle fiber. Muscles were highly aerobic (mean proportion of type I fibers 89%), with the proportion of type I fibers decreasing caudally. A significantly greater proportion of type I fibers were found in the midthoracic compared to the low lumbar regions. CONCLUSION. The complex morphology of the TSP muscles indicates that they would be better classified as spinotransverse muscles. They are multipennate, highly aerobic, with fibers organized in parallel, an arrangement lending itself to "fine-tuning" of vertebral movements. Understanding their morphology has implications for investigation, treatment, motor control, and biomechanics.

An anatomical ultrasound study of the long posterior sacro-iliac ligament

The long posterior sacro-iliac ligament (LPSL) is directly posterior to the sacro-iliac joint and a potential source of lower back and pelvic pain. Its sonographic anatomy has not been described in detail. The aim of this study was to define and measure the ligament in healthy young women using ultrasound (US). The LPSL was scanned in 30 healthy women (median age, 22 years; range, 20-34) using a high-resolution linear transducer (7.5-10 MHz). The ligament was consistently visualized as a hyperechoic laminated linear structure between the posterior superior iliac spine and the lateral aspect of the third transverse sacral tubercle. Its length, thickness, and the angle between it and the posterior superior iliac spine were measured by an experienced sonographer bilaterally in both semiflexed standing and lateral decubitus positions. Four female cadaver pelves (age range, 57-93 years) were also scanned and dissected to validate US observations. In the semiflexed standing position, mean LPSL length was 37.9 ± 2.4 mm, mean thickness 1.57 ± 0.38mm, and median angle 18.5°. There was no statistically significant difference with equivalent values in the lateral decubitus position. Intrarater repeatability was fair to substantial in both positions (intraclass correlation coefficient, 0.39-0.66), improving to moderate to substantial (intraclass correlation coefficient, 0.57-0.80) using the mean of two measurements. There was good overall agreement between LPSL length and thickness in cadavers measured by US and dissection. These findings document the sonographic appearance, length, and thickness of the LPSL and provide useful normative data for understanding potential LPSL pathology, particularly in relation to pregnancy-related pelvic girdle pain.

Bony landmarks in the sacral region: the posterior superior iliac spine and the second dorsal sacral foramina: a potential guide for sonography

PURPOSE

Identification of the second dorsal sacral foramen (S2F) by sonographic imaging is a possible first step in localising the branches of the dorsal sacral rami. The aim of this investigation is to develop an imaging approach to assist the rapid identification of S2F using a well-known regional landmark, the posterior superior iliac spine (PSIS).

METHODS

Twenty-seven skeletal specimens were digitally imaged. Repeated measurements were undertaken of the angle and distance (D(1)) between PSIS and S2F, maximum width of S2F (D(2)), interforaminal distance between contralateral S2F (D(3)), distance between S1F and S2F (D(4)), and distance between S2F and S3F (D(5)). Sonographically guided needle placement was further undertaken to validate these osseous measurements in five intact cadavers.

RESULTS

In skeletal material, repeated measurements indicated high intraclass correlation coefficients. No statistically significant difference existed in any measure between sides. Combined measurements indicated that S2F was located 46.4 ± 14.9° from the PSIS in both sexes, with a statistical trend toward a greater angle in females. D(1) had a mean value 2.2 ± 0.62 cm but was significantly shorter in females. The mean values of D(2) and D(3) were 0.75 ± 0.18 cm and 2.98 ± 0.27 cm, respectively, with no significant difference between sexes. The mean value of D(4) was 1.42 ± 0.27 cm with a statistical trend toward a slightly smaller value in females. The mean value for D(5) was 1.28 ± 0.15 cm. Sonographically guided needle placement in cadavers tended to validate these osseous measurements.

CONCLUSIONS

S2F has a mean maximum width of 0.76 cm and lies approximately 2-3 cm from the PSIS, 45° inferior to the horizontal. The medial left and right borders of S2F are approximately 3 cm apart. The upper three ipsilateral dorsal sacral foramina are 1-1.5 cm apart. These measurements may be useful for sonographers imaging the dorsal sacral region and eventually, for the potential identification of neurovascular branches of the dorsal sacral rami.