Contigen is a GAX collagen, a highly purified suspension of bovine collagen in approximately 60% vol/vol phosphate-buffered saline containing approximately 95% type I collagen and approximately 1% to 5% type III collagen. The GAX makes collagen less susceptible to fibroblast-secreted collagenase that may result in resorption of the implant and loss of long-term efficacy. Although the resorption of GAX collagen is reduced, this implant is clinically characterized as having resorptive properties resulting in the need for repeated injections (top-off injections once or twice a year) to maintain its long-term efficacy. Persistence of the implant itself has been demonstrated with magnetic resonance imaging of the urethra at intervals of up to 22 months after injection, but the measured volume was less than that injected. Because 2% to 5% of patients are sensitized to collagen through dietary exposure, all patients must undergo a skin test 30 days before treatment; the implant itself at the submucosal location elicits a minimal inflammatory response without foreign body reaction. The properties of this bulking agent allow versatility in its technical application (periurethral, submucosal, or transurethral approach) depending on physician preferences.

As with most anti-incontinence procedures, it is difficult to analyze the outcome of Contigen injection therapy for urinary incontinence because of varying definitions of reported "cure." Early results have reported subjective cure rates of 85% to 95%. In a multicenter trial reported by O'Connell et al.1 in 1995 on periurethral Contigen injection for 160 females with ISD, 93.8% had significant improvement and 78.1% were completely dry after the injection. That same year, Monga et al.2 reported on 60 women with genuine stress incontinence using periurethral collagen injections. Subjective success rates were 86% at 3 months, 77% at 12 months, and 68% at 24 months. The long-term (>2 years) success rates are not as favorable (26%-65%), but some long-term cures are noted in this and other trials.

Despite the widespread and long-term application of this implant for the treatment of SUI, treatment-related morbidity has been minimal. Reports of transient urinary retention ranges from 1% to 21% and is managed with intermittent catheterization or short-term catheter use. Urinary tract infection occurs in 1% to 25% of cases, and self-limited hematuria may occur in 2% of cases. Other reported but rare complications include periurethral abscess formation, de novo instability, and a reaction at the previously negative skin test site after a Contigen implant treatment.

When initially introduced for the treatment of ISD in patients with nonmobile urethras, the use of the Contigen implant as well as other bulking agents for patients with hypermobility was somewhat controversial. There have been numerous and well-characterized reports by several centers showing no significant difference in outcome in SUI patients with or without urethral hypermobility. This finding has continued to serve as a strong argument for the use of injectable bulking agents as a first line, minimally invasive therapy for the treatment of SUI, even before the use of oral medications with their requirement and cost of daily administration and attendant side-effect profiles. Continued outcome studies with defined case selection criteria and improved implant material with outpatient technical applications under local anesthesia will continue to define the proper place for this form of SUI treatment, especially in choosing more invasive treatments. In 1997, Berman and Kreder3 analyzed the cost effectiveness of collagen compared with a sling procedure for type III incontinence, and concluded that surgery was more cost effective than collagen.

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