S3 Foramen Research Articles

Proximity of iliosacral screws to neurovascular structures after internal fixation.

The placement of iliosacral screws for the stabilization of pelvic ring lesions is technically demanding. The postoperative computed tomography scans of 31 patients who had 57 iliosacral screws placed for various indications were studied to determine the proximity of these screws to neurovascular structures. The closest distance of the screws from the S1 foramen averaged 3 mm. (range, 0-10.5 mm); the average closest distance to the anterior cortex of the sacral ala was 4.8 mm (range, 0-15.3 mm). The corridor for the insertion of the screws between the S1 foramen and the anterior cortex of the sacrum averaged 21.7 mm (range, 16.2-28.9 mm). Trigonometric analysis of these dimensions suggests that deviations of the surgeon's hand by as little as 4 degrees may direct iliosacral screws either into the S1 foramina or through the anterior cortex of the sacrum.

Radiologic evaluation of iliosacral screw placement.

This study analyzed anteroposterior, lateral, inlet, and outlet radiographic representations of different iliosacral screw orientations and evaluated anatomic features of the superior aspects of the sacral alae. The purpose of this anatomical and radiologic study was to assess the value of anteroposterior, inlet, outlet, and lateral views with regard to the planning of iliosacral screw placement, to determine if screws penetrating the sacral surfaces and foramina can be detected during or after operation, and to evaluate the anatomy of the superior aspects of the sacral ala quantitatively. Direct iliosacral screw fixation has recently become popular because it provides stable fixation using reasonably small implants and is biomechanically equal or superior to other techniques of internal fixation. However, misinterpretation of the relationship of pelvic radiographs and the position of a screw may result in incorrect screw placement during surgery or misdiagnosis of postoperative neurologic complications. The morphology of the sacrum is complex. No previous data relative to the superior aspect of the sacral alae are available. Four bony pelves were used to model the different iliosacral screw orientations possible during iliosacral reconstruction. A drill bit was inserted laterally from the posterior ilium through the sacroiliac joint and into the S1 vertebra. Radiographs were taken from anteroposterior, lateral, inlet, and outlet views for evaluation of placement. Twenty-two dry sacra were obtained for anatomic evaluation of the superior aspects of the sacral alae. All symmetrical structures were measured bilaterally. Measurements included three angular and two linear parameters. The results showed that a misdirected drill bit penetrating the anterior aspect of the ala is best appreciated by the inlet view. A misdirected drill bit penetrating the superior aspect of the ala or the S1 foramen is best represented in the outlet view. The average angle between the coronal plane of the S1 vertebra and the anterior aspect of the ala was 27.1 degrees; between the superior aspect of the S1 vertebral body and superior edge of the ala, 36.9 degrees; and between the superior aspect of the S1 vertebral body and posterosuperior edge of the ala, 24.5 degrees. The inlet view shows the orientation of screws relative to the coronal plane and extraosseus screws extending anterior to the ala, whereas the outlet view elucidates the placement of screws relative to the transverse plane and extraosseus screw tips extending into the sacral foramina or superior to the ala. Evaluation of preoperative pelvic computed tomography scans may be helpful in understanding the unique morphology of each individual patient and enhancing the safety of iliosacral screw placement.

Sacral (S3) segmental nerve stimulation as a treatment for urge incontinence in patients with detrusor Instability: Results of chronic electrical stimulation using an implantable neural prosthesis

AbstractPurpose: We studied the effects of sacral (S3) nerve stimulation in patients with urge incontinence due to detrusor instability.Materials and Methods: A permanent S3 foramen electrode was implanted in 18 patients (average age 46 years) who had shown a good response during temporary stimulation via a percutaneously placed wire electrode. Average followup was 29 months.Results: The average voiding frequency and pad use per 24 hours decreased significantly. Improvement in several urodynamic parameters was noted. The correlation between symptomatic and urodynamic improvement was incomplete.Conclusions: Neuromodulation appears to be a valuable treatment option in these patients.

Sacral (S3) Segmental Nerve Stimulation as a Treatment for Urge Incontinence in Patients with Detrusor Instability: Results of Chronic Electrical Stimulation using an Implantable Neural Prosthesis

Purpose We studied the effects of sacral (S3) nerve stimulation in patients with urge incontinence due to detrusor instability. Materials and Methods A permanent S3 foramen electrode was implanted in 18 patients (average age 46 years) who had shown a good response during temporary stimulation via a percutaneously placed wire electrode. Average followup was 29 months. Results The average voiding frequency and pad use per 24 hours decreased significantly. Improvement in several urodynamic parameters was noted. The correlation between symptomatic and urodynamic improvement was incomplete. Conclusions Neuromodulation appears to be a valuable treatment option in these patients.

Neural Stimulation for Chronic Voiding Dysfunctions

Neural stimulation of the sacral nerve roots could become an acceptable and promising modality in controlling variable forms of difficult voiding dysfunctions. A total of 50 patients who presented with various forms of voiding dysfunction underwent initial screening by percutaneous nerve evaluation of the S3 nerve root guided by movements of the levator ani and toes. Only 17 patients demonstrated a satisfactory response to percutaneous nerve evaluation and subsequent subchronic wire testing for 4 to 5 days, and they were eligible to enter the study. The studied patients (13 women and 4 men) were classified into 2 groups according to presentation. Group 1 included 8 patients who presented mainly with nonobstructive chronic urinary retention. All 8 patients were on intermittent self-catheterization except 1 with a suprapubic tube. The 9 patients in group 2 mainly presented with other forms of voiding dysfunctions, including pain (suprapubic and perineal), frequency and/or urgency. All patients were neurologically free, and had failed pharmacological and surgical attempts to correct the problems. In both groups radiological and ultrasound evaluations of the urinary tract as well as cystourethroscopy were within normal limits. Urodynamic studies were performed preoperatively and postoperatively. Unilateral S3 foramen implantation was performed on the selected side in all patients. Followup ranged from 3 to 52 months.All patients were followed preoperatively and postoperatively by voiding and itemized symptom score diary as well as a quality of life questionnaire. Each symptom and question were given certain grades that reflect the severity or importance to the patient. The symptom scores and the quality of life questionnaires were analyzed preoperatively and postoperatively.In group 1 voided volume (expressed as a percentage of total bladder capacity) was significantly increased at 6 months (23 ± 7.5% preoperatively versus 81.9 ± 7.7% postoperatively, p <0.05) and, accordingly, residual volume (also expressed as a percentage of total bladder capacity) was significantly decreased. The maximum flow rate increased to 18.0 ± 2.6ml. per second postoperatively compared to 7.8 ± 3.1ml. per second preoperatively. The number of intermittent self-catheterizations per day decreased to 1.3 ± 0.8 compared to 4.2 ± 0.6 preoperatively (p <0.05). Uninhibited bladder contractions with vesicosphincteric dyssynergia disappeared in 1 patient, while they persisted in 1 for up to 6 months.In group 2 the average improvement in pain and difficulty to start voiding was 85%, frequency improved by 37%, urgency by 42%, and leaking episodes and number of diapers per day decreased by 50%. Uninhibited bladder contractions disappeared in 1 patient within 6 months. No significant difference was observed in any of the other urodynamic parameters. The impact of voiding problem on patient activities and quality of life was considerably improved. The appliance was well tolerated with no serious complication. The prosthesis was removed in 1 patient due to local pain at the site of the pulse generator. We believe that neural stimulation is a valid option in treating select cases of voiding dysfunction.

Treatment of unstable bladder

We present our experience with 2 spinal-injury patients tested for urinary incontinence via implanted sacral nerve electrodes. In each patient, spinal injury occurred at the T-12 level, with presentation of spontaneous detrusor activity. Associated weakness of the voluntary sphincter mechanism was evident urodynamically. Neurostimulation via wire electrode in the S3 foramen produced good sphincter closure. Voiding secondary to spontaneous detrusor triggering could thereby be suppressed, eliminating embarrassing incontinence without interfering with the patient's ability to empty the bladder at regular intervals. The therapeutic principles of neurostimulation applicable to patients with spastic bladders are underscored by these 2 cases.