more than halved may receive the permanent implant,

consisting of a foramen electrode fixed to the sacrum.

an extension cable and a subcutaneously placed pulse

generator (Fig. 3b).

EI/itlence. The results in patients wíth an unstable

bladder were recently summarized by Bosch [37];

60-70% of patients respond to a test stimulation.

Most studies in implanted patients showed a mean

decrease in the grade of instability during cystometry.

Symptomatically, about half of patients wíth urge

incontinence and no neurogenic causes had > 90%

improvement in their incontinence. wíth 25% having a

50-90% improvement and another 25% < 50% improve-

ment. The latter patients should be considered failures.

because the results of the permanent implant are

apparently worse than those of the test stimulation. As

in other types of neuromodulation. the correlation

between the urodynamic and the symptomatic improve-

ment is only partial. In two comparative muIticentre

studies invoIving patients wíth refractory urge incon-

tinence and urgency-frequency. respectively (not

necessarily wíth urodynamicalIy confirmed detrusor

instability) half of the patients in whom the PNE test

was successful were implanted [38.39]. Implantation

was delayed for 6 months in the reinaining patients. who

received standard medical treatment and comprised the

control group. The stimulation groups had significantly

better symptomatic results than the control groups at

6 months of folIow-up.

Suitable patients. At present. the only way to determine

whether a patient is a candidate for implantation is a PNE

testo Attempts to identify factors predicting the success of

SNS failed [39.40]. On average. men do less well than

women. probably because men have more severe grades

of bladder overactivity than women before they become

incontinent [37]. Psychological factors seem to play an

important role [37.41]. A neurogenic cause of the

. bladder overactivity is no reason to exclude a patient

fram treatment; good r~sults have been reported in

patients with a variety of neurogenic lesions [42.43].

Long-term effectiveness. In 45 patients wíth a mean

follow-up of 47 months the cure rate decreased to "" 80%

and 65% after 1 and 1.5 years. respectiveIy. but sub-

sequently remained constant through the fifth year [44].

The symptomatic results obtained at 6 months remained

stable during a mean follow-up of 44 months in seven

of nine women wíth neurogenic urge incontinence

[43]. The symptoms retum to the baseline leveI wíthin

a few days' aftei discontinuing SNS [38.39].

Side-effects antl complications. The need to reposition the

electrode after migration is the most frequently reported

complication. occurring in "" 20% of patients [39.44].

Fracture of the electrode or the extension cable and

technical problems wíth the pulse generator occasionally

occur. A few patients complained 01' pain at the site of the

pulse generator. which resolved after repositioning. Pain

in the leg can be resolved by reducing the stimulation

amplitude. Other complications are rare; nerve damage

caused by continuous stimulation has not been reported

[39.44].

Current clevelopments

Two-stage implant. Displacement of the electrode during

the PNE test may give a falsely negative resulto Janknegt

et aI. [45] therefore repeated the test by placing a

permanent electrode and an extension cable in patients

in whom displacement was suspected. and connecting

those to an external pulse generator. The permanent

pulse generator was placed at a later stage if the patient

had a good response (which was the case in eight of the

10 patients). The current search for better test electrodes

will hopefully reduce the need to perform extra surgical

procedures [46].

Bilateral stimulation antl sacraI Iaminectomy. Bilateral

stimuIation combined wíth a small sacraI laminectomy

to alIow optimum eIectrode placement and fixation

was first described by Hohenfelh1er et aI. [47]. The

value of the increased invasiveness of SNS remains to

be determined.

Buttock placement of the pulse generator. The pulse

generator is traditionally placed in a lower abdominal

pocket. Buttock placement has the advantage that the

patient needs no repositioning during the operation and

saves "" 1 h of operative time [48].

ConditionaI neuromodulation. Oliver et aI. [49] found

that neuromodulation applied only at moments of an

increased leveI of urge suppressed this sensation. The

usefulness of conditional neuromodulation in patients

has still to be determined; it will extend the longevity of

the pulse generator. which at present is 5-7 years.

Percutaneous posterior tibial nerve stimulation

Intuitively. the pelvic region is the most logical place to

seek a site for neuromodulation. but physiological

mechanisms permit suppression of bladder overactivity

from a more distant location.

Technique. A 34 G stainless steel or other thin needle is

inserted 5 cm cephalad from the medial malleolus and

just posterior to the margin ofthe tibia (Fig. 4). This point

is known as the Sp-6 point in acupuncture. The needle is

advanced to the medial edge ofthe fibula. A ground pad is

usually attached to the medial surface of the calcaneous.

Flexion of the great toe upon electrical stimuIation

indicates' the correct positioning of the needle; a tingling

sensation is often felt. Treatment usually takes place

weekly for 10-12 weeks over 20-30 mino