Displacement sequence and elastic properties of anterior prostate/urethral interface during micturition of spinal cord injured men

Abstract

The management of complex micturition problems frequently encountered in patients with spinal cord injury (SCI) may be facilitated by characterization of the elastic properties of the prostate. To this end, we have developed a method of evaluating changes in prostate biomechanics using ultrasound (US) images obtained during routine diagnostic urodynamic evaluations. Ultrasound video sequences of the prostate and urethra during voiding were digitized simultaneously with bladder pressure measurement on 76 patients with spinal cord injury, having a mean age of 47 +/- 16 years. Computer enhancement of the bladder/prostate/urethral interface from sequences of 2-D US images facilitated measurement of midprostatic urethral displacement during micturition. Of 76 patients, 21 were able to initiate voiding. Maximum urethral diameter was 12.0 +/- 1.3 mm, with corresponding maximum voiding pressure of 61.6 +/- 1.9 cmH(2)O. Urethral/prostatic pressure strain elastic modulus (Ep) was 960 +/- 624 N/m(2) and stiffness (beta) calculated as the inverse of compliance was 2.8 +/- 0.1. The diameter of the urethra at P(det50+), during the opening phase, was 0.4 +/- 0.1 mm and, during the closing phase, was 0.7 +/- 0.1 mm. During voiding, the anterior prostate was displaced to a greater extent than the posterior prostate. These observations suggest that distension of the prostate/urethra during micturition is hysteretic and nonuniform and indicates regional differences in compliance within the prostate/urethra interface. These regional differences lend support to the concept that the posterior prostate is implicated in the active process of micturition involving the fibromuscular stroma. Clinical application of this method could include quantification of the biomechanics of micturition consequent to spinal injury, prostatic enlargement, and the impact of targeted evaluation of pharmacological interventions.