Membranous urethral length helped predict near-continence after prostatectomy, not full dryness

Design

External validation in a prospective cohort

Population

500 men with pre-prostatectomy MRI, open or robotic surgery, 2015–2023

Primary outcome

Continence at 1 year (0 pads/day and 0–1 pad/day)

Effect

0–1 pad: C-statistic 0.69 (0.61–0.76), net benefit; 0 pads: 0.64 (0.59–0.69), poor calibration, no net benefit

A short membranous urethra on pre-operative MRI is associated with worse continence after radical prostatectomy, but models built on it had not been externally validated. This Canadian study applied an existing model — age, nerve-sparing plan, prostate volume, surgical approach and membranous urethral length — to 500 men with pre-prostatectomy MRI and prospectively recorded continence (2015 to 2023). It was published in May.

Median membranous urethral length was 11 mm. At one year, 62% used no pads and 90% used 0 to 1 pad a day. For pad-free continence the model discriminated poorly (C-statistic 0.64, 95% CI 0.59 to 0.69), calibrated poorly and offered no net benefit. For 0 to 1 pad it did better (0.69, 0.61 to 0.76), with moderate calibration and net benefit across relevant thresholds.

Measuring the membranous urethra on the staging MRI costs nothing and gives a patient a more personal estimate of his chance of being nearly dry. It should not be used to promise complete dryness.

• Ask the radiologist to report membranous urethral length on every pre-prostatectomy MRI.
• Use it with age, prostate volume and nerve-sparing plan to counsel about near-continence (0–1 pad) at one year.
• Do not use the model to predict complete pad-free continence; it performed poorly for that.
• Consider pre-operative pelvic floor muscle training for men with a short membranous urethra, though this study did not test it.
• Record pad use at one year in your own patients to calibrate what you tell the next man.

Why it matters

Continence is what men fear most after prostatectomy, and a free measurement on an existing scan sharpens the estimate.

Don't overread it

Discrimination was modest even for 0–1 pad, and length was measured retrospectively; this refines counselling rather than selecting patients.

The statistics, in plain English

A C-statistic of 0.69 means the model ranks a continent man above an incontinent one about 69% of the time — better than chance but far from perfect. Decision-curve 'net benefit' means using the model would lead to better decisions than treating everyone the same, across a range of risk thresholds.

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