Sacral neuromodulation is an effective treatment method for lower urinary tract dysfunction. It is most often performed by placing a tined lead electrode in the third sacral (S3) foramen. To identify the third sacral foramen, many authors use bony landmarks that are not always visible on fluoroscopy. A detailed analysis of the topological properties of the S3 foramen with surrounding bone landmarks can improve the technique of implantation and tined lead electrode positioning. Three-dimensional (3D) technology enables fast and accurate implantation of the electrode and eliminates exposure of the patient and healthcare staff to radiation. The aim of the study was to examine the 3D sacral morphometry of the third sacral foramen and to develop a method of 3D implantation of the tined lead electrode for sacral neuromodulation.

Patients who had undergone abdominal CT scanning were randomly assigned to the prospective study group. The Image Archiving and Communications System and Digital Imaging and Communications in Medicine (DICOM) were used for image processing. Randomization was performed by the random selection of every 10th woman from the computer tomography (CT) examination database at the radiology clinic over a period of 6 months. Women were enrolled according to the following inclusion criteria: age greater than 18 years, scanning of the minor pelvis by computer tomography and display of the sacral bone in three planes. The exclusion criteria were the following: traumatic, osteoporotic deformities of the sacral bone or distal sacral bone disorder. To determine the sacral morphometry, three measurement planes of the sacral bone were used in coronary, axial and sagittal projections. The medial, lateral, cranial and caudal diameter of the S3 foramen were measured. The most important measurement was that of the lumbosacral distance between the lumbosacral junction and the cranial point of the foramen S3. Next in importance was the distance between the midsagittal sacral plane and medial point of the foramen S3. According to the morphometric analysis, a 3D model of sacral bone was created pre-operatively and subsequently formed the planimetric basis for the creation of a sacral bone model by using a 3D printer (Figure 1). The tined lead electrode was implanted using the 3D model of sacral bone. This cross-sectional study was carried out between March and November 2016. All women included gave their informed
consent as a part of standard diagnostic and therapeutic procedures. Institutional review board (IRB) approval for the study was obtained through the ethics committee at the University Hospital in Martin, Slovakia on 10 March 2016, No. 18/2016. Statistical analysis was performed using IBM SPSS 24.0 (Armonk, NY). Descriptive and analytical statistics were used. A significance level of P < 0.05 was used.

The study included 149 patients, of whom 132 (88.6%) were evaluated, and their mean age was 54.4 ± 14.3 years (range 19–77). The morphometric analysis determined the mean distance between the lumbosacral junction and the cranial part of the foramen S3 (72.1 ± 6.3 mm) and between the midsagittal sacral plane and medial point of the foramen S3 (11.8 ± 3.3 mm) (Figure 2). The differences between the right and left sites were not statistically significant. The width and height of the dorsal foramen S3 was greater than 10 mm in 54/132 cases (40.9%), 5–10 mm in 71/132 cases (53.8%) and less than 5 mm in 7/132 cases (5.3%). After creating a 3D model of sacral bone, 3D navigation was launched during electrode implantation. Of 17 tined lead electrode implants, navigation was used in 8 cases and without navigation in 9 cases. Implantation time significantly decreased from 48.1 min ± 12.2 min (non-navigation group) to 15.1 min ± 10.3 min (navigation group). Significant exposure to radiation was also reduced from 15.4 min ± 5.4 (non-navigation group) to 5.6 min ± 2.3 min (navigation group).

An important clinical goal is to shorten the implantation time, increase the neuromodulation efficiency by correct positioning of the electrode and reduce the amount of radiation exposure associated with this 3D procedure.

Sacral morphometry confirmed the different sizes of the foramen S3 and created a new 3D model for 3D printing. The 3D sacral bone model allows for better navigation of tined lead electrode implantation in the sacral neuromodulation of lower urinary tract dysfunction.

Female Pelvic Med Reconstr Surg 2013;19: 23-30