Technique

The method for implantation of the lead and the wires is similar. The patient is placed in the prone position with a 30-degree flexion at the hips. This position places S3, S4, and S5 into the vertical plane. The patient is given local anesthesia and, under fluoroscopic guidance, the S3 sacral foramen is located using a crossed-hair technique developed by Chai and Mamo.4

The horizontal axis is defined at the inferior borders of the sacroiliac joints, and the vertical axis is the midline (Figure 7-2.1). Once these are marked on the skin, points that are 2 cm lateral and cephalad on both sides are marked. This is the skin location of S3. We identify a point 2 to 3 cm above this mark and infiltrate with 2% lidocaine. The needle is introduced at an angle of 60 degrees (Figure 7-2.2).

Once the foramen is located, on both anterior/posterior and lateral views, the needle is stimulated. Both the motor and sensory responses are monitored. The lead is

Figure 7-2.1. Crossed-hair technique.

Table 7-2.1. Motor and sensory responses observed with stimulation of the S2,

S3,and S4

S2

S3

S4

Motor

• Lateral rotation of

• Bellows (contraction

• Bellows activation

the leg

of the levator ani

of the posterior

• Contraction of the

muscles causing a

levator ani muscles

toe and foot

deepening and

• No motor response

• Contraction of the

fattening of the

of the leg or foot

calf

buttocks groove)

• Contraction of the

• Plantar flexion of

superficial pelvic

the hallux caused

fbor

by sciatic nerve

stimulation

Sensory

• Pulling sensation

• Paresthesia of the

• Pulling sensation

of the vagina or

perineal skin,

in the rectum

base of the penis

external genitalia

• Pulling sensation of

the vagina, rectum,

or bladder base

Figure 7-2.1. Crossed-hair technique.

quadripolar, and each one is stimulated separately to determine the lead that has the most optimal placement. Table 7-2.1 is a guide for motor and sensory responses observed with stimulation of the S2, S3, and S4 nerves.

Once the placement is confirmed,either the wire or tined lead is placed. The wire is fed through the foramen needle. The needle is removed, and the wires are then taped carefully to the back. In the case of the staged implant, the lead is placed through a sheath, and its placement is verified by fluoroscopy. A small incision is created at the future neu-

rostimulator pocket site in the upper buttock. A trocar is used to tunnel the lead to the neurostimulator pocket, the percutaneous lead extension is connected, and the connection is buried at the site. The wires are brought out at a separate site, usually the contralateral side, and the connection site is closed in two layers.

During the second stage, the patient is brought back to the operating room and given local anesthesia with sedation. The pocket is opened, and the lead is disconnected from the extension wire. The wires are pulled out from the externalized side to prevent the exposed wires from being brought through the subcutaneous tissues. The

Figure 7-2.2. Appropriate needle orientation within S3 foramen. The needle entry is 60 degrees to the horizontal.

(Reprinted with the permission of The Cleveland Clinic Foundation.)

Figure 7-2.2. Appropriate needle orientation within S3 foramen. The needle entry is 60 degrees to the horizontal.

(Reprinted with the permission of The Cleveland Clinic Foundation.)

Figure 7-2.3. Lateral view of radiograph showing the implanted lead.

pocket is developed for the neurostimulator. The lead is connected to the neurostimulator. Connections are sealed with silicone glue and the boot is placed over the connection and tied with prolene suture. Care is taken not to create a trigger point by placing the wires around the neu-rostimulator. The wound is closed in two layers (Figure 72.3).

Because a foreign body is being introduced into the patient, prevention of wound infections is imperative. We administer preoperative antibiotics to cover coliforms and skin flora. For the first stage and complete implantation,the patient is placed in an operating room equipped with laminar airflow. The pocket developed for the neurostimu-lator is irrigated copiously with neomycin irrigation. It is important not to immerse the neurostimulator in a liquid medium because this may cause it to malfunction. A two-layer closure is desirable should the skin open, so that there is a closed layer beneath.

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