Developments in the understanding of the pathophysiology of urethral sphincter mechanism in competence in the bitch.

Developments in understanding the pathophysiology of urinary incontinence caused by urethral sphincter mechanism incompetence (SMI) are reviewed. SMI is a multifactorial condition; affected bitches have shorter urethras, reduced urethral tone and more caudally positioned bladder necks than continent bitches. Other factors thought to be important in the aetiology of SMI include neutering, breed, body size, docking and obesity. Most of the recent developments in the understanding of SMI have resulted from radiographic and urodynamic investigations of normal and affected bitches. The urodynamic technique of urethral pressure profilometry is discussed and its contribution as an investigative tool reviewed.