Results from the use of polyacrylamide hydrogel
The last Cochrane report on periurethral injection from 2017 (11) concludes that there is no unequivocal difference in effect between the various injection methods that were assessed, and that the results for injection therapy are better than for conservative treatment, but poorer than for colposuspension. Polyacrylamide hydrogel is not included in this report, but this substance is likely to be at least as effective as other agents used for periurethral injection, and probably safer (12, 13). An American study from 2014 that compared polyacrylamide hydrogel with collagen injection in 345 women found these methods to be of equal value (12), and a recent review article that compared polyacrylamide hydrogel (Bulkamid) with polydimethyloxane (Macroplastique) came to the same conclusion (13). As long as the results for polyacrylamide hydrogel are approximately on a par with those of other injection techniques, we may assume that this substance also fails to measure up to tension-free vaginal tape or colposuspension. It should be noted, however, that injection therapy is used most often as a reserve method when tension-free vaginal tape is deemed undesirable, and results from studies of polyacrylamide hydrogel are therefore not directly comparable to other methods because of their different patient selection. To date, only two studies that directly compare injection therapy with other surgical methods have been published (14, 15). No studies that compare polyacrylamide hydrogel with tension-free vaginal tape or colposuspension have been published.
It is nevertheless generally accepted that injection therapy is a more gentle method with a lower risk of complications than tension-free vaginal tape (8, 11, 14). In contrast to tension-free vaginal tape, injection therapy does not result in any notable obstruction, meaning that there is less risk of postoperative bladder voiding problems (11). The procedure is quicker and simpler to perform, and the recovery period is short. In practice, more than one or two days of sick leave is rarely necessary.
All published studies on injection with polyacrylamide hydrogel have found statistically significant improvement in the degree of leakage and/or quality of life: 45–86 % of the patients are defined as 'responders' (defined as continent or with more than 50 % improvement, alternatively 'satisfied') and 24–43 % became fully continent with follow-up of up to three years (8, 13, 16).
Only a single study with more than three years' follow-up has been published to date (17). This study had eight years of follow-up and showed that 25 % of the patients were continent at that time, while another 17 % had improved their condition. The King's Health Questionnaire's QoL (Quality of Life) score had fallen from 11 to 2 (i.e. improved quality of life), and 38 % had undergone repeat surgery over the period, either with a further injection or tension-free vaginal tape. Vaginal ultrasound examination showed that the injection deposits were present in all patients (17).
All operations for stress incontinence in women in in Norway must be reported to the Norwegian National Female Incontinence Registry, a national registry with reporting obligation (1). For the years 2014–2016, a total of 6 570 tension-free vaginal tape procedures and 217 polyacrylamide hydrogel injections were reported to the registry (S. Kulseng-Hanssen, personal communication).
An American economics study concluded that polyacrylamide hydrogel is less costly than tension-free vaginal tape in a one-year perspective (18), and the Cochrane report from 2017 concludes that injection therapy with up to two injections is cheaper than tension-free vaginal tape (11).