Sacral Anatomy Research Articles

Neuraxial blockade in children

Epidural blockade in children has become more popular for postoperative analgesia in recent years owing to increased experience, greater confidence and the development of appropriate equipment. In the UK, about 2000 lumbar epidural and continuous caudal blocks are performed each year. Spinal anaesthesia remains popular for babies at risk of postoperative apnoea, but is increasingly being superseded by light general anaesthesia with desflurane or sevoflurane combined with caudal blockade, which produces more rapid recovery from anaesthesia. Contraindications to neuraxial blockade are the same as for adults (patient or parental refusal, coagulation abnormalities, septicaemia, raised intracranial pressure, meningitis, infection at the entry site, allergy to local anaesthetics) but also include myelomeningocele (spina bifida) and, for a caudal epidural, abnormal sacral anatomy.

Radiographic markers in spondyloptosis: implications for spondylolisthesis progression.

Radiographic analysis of spinopelvic morphology and posterior element dysplasia in spondyloptosis. Spondylolisthesis treatment protocols are based on age, symptomatology, and slippage degree. Spinopelvic morphology and dysplasia can determine progression. Frequency of two denominators of high-grade spondylolisthesis-degree of dysplasia and spinopelvic morphology-is unknown. To determine common radiographic denominators of spondyloptosis-degree of posterior bony hook dysplasia and spinopelvic morphology-as prognostic factors for spondylolisthesis progression. Patients with spondyloptosis were reviewed. Bony dysplasia at lumbosacral junction was graded. Pelvic incidence and sacral kyphosis were measured. A total of 53 patients had a mean sacral kyphosis of 56 degrees and pelvic incidence of 76 degrees; 62% of patients had posterior element dysplasia. Prognostic factors for spondylolisthesis progression, such as percent of slippage, do not identify lower-grade slips at risk for progression. Progression is linked to increased shear stress across the lumbosacral junction and inability to resist it. Increased stress is related to increased verticality of the lumbosacral joint, which is individually predetermined by pelvic incidence and sacral anatomy. Pelvic incidence is fundamental in determining sagittal spine curvature required for economic spinopelvic balance. Pelvic incidence is independent of adaptive changes in higher-grade spondylolisthesis. Pelvic incidence in our spondyloptosis series (76 degrees) is higher than in normal (48.2-53.2 degrees ) and low-grade spondylolisthesis (64.5 degrees). Posterior element dysplasia decreases mechanical resistance to lumbosacral shear stress. Incidence of dysplasia in our series (62%) is higher than that reported in low-grade spondylolisthesis. Analysis of pelvic incidence and posterior element dysplasia may aid in estimation of risk for progression of spondylolisthesis.

The impact of sacral root anatomy on selective electrical stimulation for bladder evacuation.

Although different structures have been studied with electrostimulation to elicit bladder evacuation, only the sacral root remains feasible for clinical application at present. However, the resultant concomitant contractions of the bladder and sphincteric muscles have been the principal problem over the last few decades. Attempts to identify fibers within the sacral ventral root that innervate the detrusor predominantly have been made by microsurgery alone or in combination with advanced electrical blocking techniques. This article evaluates our past and present efforts to achieve voiding in light of the mixed nature of sacral root anatomy.

Iliosacral screw fixation: early complications of the percutaneous technique.

To report on the early complications related to the percutaneous placement of iliosacral screws for the operative treatment of displaced posterior pelvic ring disruptions. Prospective, consecutive. Level-one trauma center. One hundred seventy-seven consecutive patients with unstable pelvic ring fractures. One hundred two male and seventy-five female patients ranging in age from eleven to seventy-eight years (mean, thirty-two years). Operative procedures were performed urgently according to the patient's clinical condition. Anterior pelvic reductions and fixations were performed by using internal and external fixation techniques. Accurate closed or open reductions of the posterior pelvic ring disruptions were accomplished by using a variety of surgical techniques dependent on the specific pattern of pelvic ring disruption. Closed manipulative reductions of the posterior pelvic ring were attempted for all patients. Open reductions were necessary in those patients with unacceptable closed manipulative reductions as assessed fluoroscopically at the time of operation (more than one centimeter in any field of fluoroscopic imaging). Plain inlet and outlet radiographs were obtained postoperatively at six weeks, three months, and twelve months. A pelvic computed tomography scan was performed postoperatively to assess fracture or dislocation reduction and the implant safety. Annual follow-up pelvic radiographs were obtained. Residual pelvic deformities were quantified based on these imaging modalities. There were no posterior pelvic infections. Minimal blood loss was associated with this technique. Complications occurred due to inadequate imaging, surgeon error, and fixation failure. Fluoroscopic imaging was inadequate due to obesity or abdominal contrast in eighteen patients. Five screws were misplaced due to surgeon error. One misplaced screw produced a transient L5 neuropraxia. Fixation failures related to either crandiocerebral trauma, delayed union, noncomplicance, and a deep anterior pelvic polymicrobial infection secondary to a urethral tear occurred in seven patients. There were two sacral nonunions that required debridement, bone grafting, and repeat fixation prior to healing. Iliosacral screw fixation of the posterior pelvis is difficult. The surgeon must understand the variability of sacral anatomy. Quality triplanar fluoroscopic imaging of the accurately reduced posterior pelvic ring should allow for safe iliosacral screw insertions. Anticipated noncompliant patients or those with craniocerebral trauma may need supplementary posterior pelvic fixation. Low rates of infection, blood loss, and nonunion can be expected.

Radiographic recognition of the sacral alar slope for optimal placement of iliosacral screws: a cadaveric and clinical study.

Malpositioning of iliosacral screws happens more often when common variations in the morphology of the upper sacral segments are unrecognized. Radiological-anatomic correlations of sacral anatomy were studied in 10 fresh-frozen cadaveric pelvises without evidence of skeletal disease, obtained from six male and four female donors. Eighty consecutive patients with complicated pelvic fractures treated operatively by the same surgeon using percutaneously placed iliosacral screws were evaluated. Variations in the sacral alar anatomy and slope found in upper sacral segmentation anomalies are common. Surgically important and predictable abnormal morphological patterns can be easily identified using pelvic outlet and lateral sacral plain radiographs along with computed tomographic scans. On the true lateral projections, the iliac cortical density adjacent to the sacroiliac joint parallels the sacral alar slope and is almost always caudal and posterior to it; it delineates the anterior extent of the "safe zone" for iliosacral screw insertion. Thus, the lateral sacral image provides the surgeon with a better understanding of the sacral alar slope and can help prevent iliosacral screw placement errors. The lateral sacral image should always be used intraoperatively with the inlet and outlet images to guide iliosacral screw placement.

The Iliac Buttress

Fifty randomly selected computed tomographic (CT) scans of the lumbosacral spine (25 males and 25 females) were studied to determine: 1) if the lateral sacral masses could safely accept a 7 mm diameter rod (i.e., intrasacral rod insertion) and 2) what percentage of patients, both males and females, demonstrated coverage of the posterolateral sacrum by the ilia (i.e., iliac buttressing). In all patients the lateral masses (i.e., the lateral intrasacral mass measurements) appeared wide enough on CT to allow for safe insertion of a 7 mm diameter rod, or other similar size implant, down to at least the level of S2. The smallest distance measured for the width between the posteromedial margin of the sacroiliac joint and the lateral cortex of the S1 neuroforamen (i.e., the lateral intrasacral mass measurement) at its location approximately midway (anteroposterior) through the sacrum on CT cuts was 17 mm (mean 28 mm). This would appear to give adequate room for a 7 mm diameter rod to be inserted at this level in the lateral sacrum (i.e., intrasacral rod insertion). Forty-six patients (24 males, 96%; and 22 females, 88%) appeared to have sufficient CT coverage of the sacrum to conceptually provide for so called "sacroiliac buttressing" of rods, if rods or other implants were to be inserted distally into the lateral masses. After a review of the sacral anatomy by CT it appears that: 1) insertion of rods into the lateral sacral masses (i.e. intrasacral rod insertions), or intrasacral fixation with other similar size implants, would be possible and apparently safe; and 2) the ilia along with the sacroiliac interosseous ligaments sufficiently surround the back and sides of the posterolateral sacrum in most patients (92%), at least by CT assessment, to conceptually offer an indirect "buttress" for implants so inserted. Theoretically, this could biomechanically help resist the flexural loads across the lumbosacral level and possibly provide a method for improved sacral fixation with spinal instrumentation in certain patients.

Surgical Anatomy of the Sacrum

Anterior sacral anatomy was studied to allow safe sacral screw placement. The study included 27 bony sacra. Intrapelvic dissections were performed. Cadaveric specimens were dissected and photographed. The position and angulation of the first sacral foramen was extremely variable. After the position of the L5 root, sacral roots, and iliac vessels, was considered, safe posterior sacral screw implantation could be assured through placement above the level of the first sacral foramen directed medially toward the promontory, parallel to the superior sacral end-plate. Complications of indiscriminate screw placement included L5-root damage, iliac vein penetration, and intractable perineal pain due to sacral root injury. Preoperative computed tomography with the scanner gantry tilted to parallel the superior sacral end-plate defined the great vessels, neural foramens, inclination of the superior sacral end-plate, and prominence of the posterior ileum. Surgical accuracy was evaluated after surgery with computed tomography.