As a primary procedure for GSI, colposuspension is generally considered to be the most effective, giving a cure of up to 85%. (1) An alternative to colposuspension is the TVT (Gynecare, Edinburgh) with reported cure rates of over 80%.(2) A proportion of women develop new symptoms following surgery for stress incontinence. These include symptoms of urgency and urge incontinence. The incidence of detrusor instability (DI) following colposuspension has been reported to be up to 16%, (3) although the incidence of urgency symptoms is not well reported. A significant proportion of women experience delayed voiding following colposuspension, others will have difficulty voiding long-term.(4) Studies of urethral profile pressures before and after incontinence surgery show no consistent changes in resting profiles, but enhancement of pressure transmission following successful procedures.(5)

Aims of study
To evaluate changes in urodynamic variables within the context of a randomised trial comparing TVT to colposuspension as a primary procedure for genuine stress incontinence.

Methods
The trial was conducted at 14 centres in the UK and Ireland and included urologists and gynaecologists, university and district general hospitals. Women with urodynamically proven GSI were randomised to TVT or colposuspension. None had DI, major voiding problems, prolapse requiring treatment or previous surgery for incontinence or prolapse. TVT was performed under local anaesthesia and sedation as described by Ulmsten.(2) Colposuspension was performed under general or regional anaesthesia. Assessment performed prior to treatment and at six months post operatively included symptom and quality of life questionnaires in addition to 1 hour pad test, filling and voiding cystometry and resting and stress urethral pressure profilometry by microtransducer (in some centres).

Results
344 patients were recruited to the study and randomised. There were 28 withdrawals prior to surgery, 23 in the colposuspension group and 5 in the TVT group. 170 underwent TVT and 146 colposuspension, as per protocol. The two groups were comparable in terms of age, BMI, parity, menopausal status. There was no significant change in volume at first sensation of filling, cystometric capacity, detrusor pressure rise on filling or provocation for either procedure. Twelve patients (7%) in the TVT group and 13 (9%) in the colposuspension group were recorded as having DI at 6 months post-operatively which was not present pre-operatively. Overall there was a small reduction in both free flow and catheterised flow, and a small increase in voiding pressure; this was not significantly different between procedures. Voiding difficulty was defined as 2 out of 3 of the following: peak flow <15ml/s; maximum voiding pressure >50cmH₂O; residual volume >100ml. On this basis 6 patients (7%) in each group had voiding difficulty at 6 months post-operatively (complete data on all these variables was available for only 91 patients in each group). Genuine stress incontinence was recorded during cystometry in 17 (10%) patients following TVT and 20 (15%) following colposuspension. Urethral pressure measurements were available on 48 patients (25 TVT and 23 colposuspension). There no significant changes in resting maximum urethral closure pressure (MUCP) or functional urethral length (FUL) for either procedure. MUCP (stress) and FUL (stress) increased for both procedures; this reflects an increase in pressure transmission ratio (PTR) seen maximally in the second and third quartiles of the functional urethral length following both operations.

Conclusions
There is a small incidence of both detrusor instability and voiding difficulty at 6 months following both procedures; this is somewhat lower than previously reported in respect of colposuspension. Although patients experience less delay in voiding in the post-operative period following TVT, this is not reflected in subsequent urodynamic variables. The mechanism of cure following these procedures appears to be similar; neither is consistently associated with outflow obstruction. Although the surgical approach in the one case is to the bladder neck, and in the other to the mid-urethra, the enhancement in PTR is in both cases seen across the 2nd and 3rd quartiles of the functional urethral length. KW was supported by a grant from Johnson and Johnson, who also provided materials and additional support to collaborating centres.

1. BJOG 1994;101(5):371-374.
2. IUGJ & PFD1996;7(2):81-85.
3. BJU 1979;51(3):204-207.
4. O & G 1987;69(1):33-38.
5. BJOG 1983;90(10):934-939.