Sacral Nerve Stimulation Technique

Once it has been established that the patient is an appropriate candidate for Interstim therapy, the implantation follows 2 steps. The first step is a test phase, followed by implantation of the device if the patient has a satisfactory response during the test phase.

Prior to the test phase, the patient is asked to complete a voiding diary, which will serve as a baseline. The initial test phase may be performed in the office or the operating room.

The patient is placed in a prone position, and his or her lower back and gluteal region are prepared and draped. The patient’s socks are removed so that the physician can visualize the feet.

A portable c-arm and fluoroscopy are used to identify the midline of the spine and level of the S3 foramen. The skin is marked and the area infiltrated with local anesthetic. A 20-gauge, 3.5-inch insulated foramen needle is then inserted into the S3 foramen on each side at a 60° angle relative to the skin under fluoroscopic guidance. A lateral image can be used to confirm the location and depth in the foramen.

The needles are then stimulated to confirm appropriate positioning. If the needles are in the correct position, there will be bellows contraction of the pelvic floor due to contraction of the levator muscles and plantar flexion of the great toe. The patient, if awake, will be able to confirm correct positioning with contraction or tingling of the pelvic floor muscles. If the needles are in the S2 foramen, plantar flexion of the whole foot with lateral rotation will occur with stimulation. If the needles are in the S4 foramen, there will be no lower extremity movement despite bellows response.

Once correct positioning of the needles has been confirmed, temporary lead wires are passed through the foramen needles, and the needles are removed carefully to prevent dislodgement of the leads. The temporary leads with unipolar electrodes are steri-stripped to the patient’s back and a dressing placed.

The patient then goes home with an external stimulator after instruction regarding its use. Prophylactic antibiotics are often given while the temporary leads are in place. The temporary leads are typically left in place for 5-7 days while the patient completes treatment voiding diaries.

When the patient returns to the office, the baseline and treatment voiding diaries are compared. Patients are deemed to have a positive test response if a 50% or greater improvement is noted compared to baseline. Patients who demonstrate a positive test response are candidates for full implantation.

The second phase involves implantation of the permanent device.

This is performed in the operating room under anesthesia. The patient is placed in a prone position and prepared and draped in a sterile fashion. Perioperative antibiotics are administered.

The next step depends on whether a permanent quadripolar lead was placed during the first phase (see image below) (often the case if the first phase is performed in the operating room) or temporary leads were placed (office based first phase).

If the permanent quadripolar was placed during the first phase, the second phase is quick and does not require fluoroscopy. The incision where the temporary connector was placed in the buttock is opened and the permanent implantable pulse generator (IPG) is connected to the lead and buried in a deep subcutaneous pocket in the right buttock (see images below). It is important to ensure the IPG is functioning properly prior to closure of the incision.

If the first phase was performed in the office and temporary leads are in place, fluoroscopy will be needed, and the quadripolar lead is placed on the side on which the patient had the best in-office test response. The lead is tunneled deeply through the subcutaneous fat to an incision in the buttock region, where the IPG will be placed. The lead is connected to the IPG and buried in the deep subcutaneous pocket. ^[11]