The proportion of patients with PPI at 1, 3, 6 and 12 months after RALP was 85.2%, 72.2%, 55.8% and 38.8%.
Patients with PPI at one month had shorter membranous urethral length, with average 11.77 mm, Standard deviation (SD) 2.87 while patients without PPI had average length of 13.98 mm, SD 2.42;p=0.04. Patients with PPI also had shorter prostatic urethral length (average 44.04 mm, SD 6.28 vs 49.21, SD 5.91;p=0.04). In the multivariate logistic regression no statistically significant association was found.
Incontinent patients at three months after RALP had shorter levator ani muscle (average 5.19, SD 0.64 vs 5.67, SD 0.86,p=0.03), shorter prostatic urethral length (average 43.63, SD 5.83 vs 47.90, SD 7.12,p=0.03), lower prostate volume [median 37.89 cc, interquartilic range (IQR) 33.18-49.7 vs 53.18 cc, IQR 39.64-61.47, p=0.03) and larger obturator internus muscle thickness (median 20.89 mm ,IQR 33.18-49.7 vs 18.74 mm, IQR 16.75-20.33,p=0.02). In the multivariate analysis, higher levator ani muscle thickness was associated with lower risk of incontinence (p=0.015,OR 0.255) and thicker OIT was associated with higher risk of PPI at three months (p=0.023, OR 1.65).
At 6 months patients with PPI had shorter membranous urethral length (median 10.62 mm,IQR 10.1-12.7 vs 12.24 mm,IQR 11.21-14.20),p=0.05. In the multivariate logistic regression an association was also found (OR=3.58, 95%CI 1.01-12.72).
Finally, at 12 months patients with urinary incontinence had thinner levator ani muscle (average 5.04 mm (SD 0.60), vs 5.50 mm (SD 0.80), p=0.039 and higher proportion of history of LUTS (63.2% vs 26.7%, p=0.01). In the multivariant logistic regression, both levator ani muscle thickness and the history of LUTS were associated with the risk of incontinence (OR=0.22, 95%CI 0.05-0.88),(OR=4.54, 95%CI 1.21-17.02).
Intravesical prostatic protrusion, the ratio levator ani/prostate volume, the puborectalis muscle thickness and the angle between membranous urethra and prostate axis were not associated with the risk of PPI (p>0.05).
We found no statistically significant differences in age,BMI,history of LUTS, diabetes, ASA risk, preoperative ISUP, prostate cancer risk group, preoperative PSA,surgeon experience ,clinical and pathological stage,nerve preservation status and proportion of affected margins(p>0.05).
In the final multivariate logistic regression analysis with repeated measures, every additional millimetre in levator ani muscle thickness was associated with a 64% reduction in the risk of incontinence (OR=0.36). Finally, each millimetre increase in prostatic urethral length resulted in a 0.5% reduction in the risk of incontinence (OR=0.94).
Longer membranous urethral length and thicker levator ani muscle were associated with faster continence recovery [HR 2.08(1.027-4.22) and 2.04(1.005-4.15)]. The remaining variables did not exhibit an association with the time to continence recovery (p>0.05) (figure 2).
Membranous urethral length exhibited a negative correlation with the severity of incontinence in pad-test scores throughout the follow-up period (Pearson coefficients at 1,3,6 and 12 months: -0.46, -0.36, -0.38, -0.30). Likewise, the prostatic urethral length showed a negative correlation with PPI severity at 3 months (Pearson coefficient with pad-test at 3 months -0.30).