Anatomy and Pathogenesis of the Urethral Injury

Pelvic fractures are the major source and etiology of posterior urethral distraction injuries, occurring at a rate of 20 per 100,000 population. Motor vehicle and motorcycle injuries are associated with the highest incidence of pelvic fractures (15.5%) followed by pedestrian injuries (13.8%), falls from heights greater than 15 ft (13%), car occupants (10.2%), and occupational crush trauma (6%). The majority of injuries occur in the first four decades, with a mean age of 33 years including an 8% pediatric occurrence (<12 years).

Pelvic fractures are a marker of severe posttraumatic injury and are associated with intra-abdominal and urogenital injuries in 15%-20% of patients. The most commonly injured organ in pelvic fractures is the posterior urethra (5.8%-14.6%), followed closely by the liver (6.1%-10.2%) and the spleen (5.2%-5.8%) [4]. The bladder and bladder neck are frequently involved, and injury to these structures needs to be identified and included in the equation of the surgical strategy. Associated perfora tion injury of the rectum is critical to identify but rarely seen with pelvic fracture trauma [17]. The life-threatening injuries take precedence in diagnosis and management over the urethral injury, but in those patients who survive, the urethral injury will be the source of chronic complex disability and morbidity. Urinary incontinence in the male depends on the bladder neck proximally and the external sphincter distally. The distal external sphincter mechanism may be destroyed by this posterior urethral injury or during subsequent reconstruction and continence will, therefore, be dependent on bladder neck function alone. Most men, however, are continent following repair of this injury and will reveal a closed bladder neck on preope-rative cystography and cystoscopy. A few patients will be noted to have a persistently open, funneled bladder neck or a bladder neck quadrant scar seen on transvesical cystoscopy, which support the potential of a concomitant bladder neck injury.

The type of fracture correlates as a risk factor for urethral injury based on the observations of broken pelvic rami, sacroiliac diastases or posterior and anterior arch disruptions. Pelvic fractures are classified by stability and by the forces that are responsible for the fracture. These forces are noted to be 1) lateral compression injury (side-to-side force), 2) anterior-posterior compression injury (front-to-back force), and 3) vertical shear (down-to-up force). Lateral compression fractures are the most common types of pelvic injuries and are most often associated with urethral disruption. The most serious pelvic fracture is the Malgaigne with the highest morbidity and morality. This fracture is produced by a vertical shear force and usually consists of breaking of the anterior ipsilate-ral pubic rami as well as posterior disruption through the sacrum, sacroiliac joint, or ileum. This is usually an unstable fracture with marked bony deformity and upward displacement of the hemi-pelvis and has the highest incidence of urethral separation [11, 12].

The risk for urethral injury increases with the number of broken pubic rami and the coexistence of posterior pelvic bone disruption. However, the contributing pathogenesis of pelvic fractures and the specific urethral anatomy that is disrupted has not yet been completely and accurately defined. The traditional concept that the prostatomembranous junction is the weak point and that the shearing force of the injury produces separation at that point has been revised. Following rupture of the prostatic and bladder attachments, the compressed pelvis and its hematoma forces the prostate upward, resulting in membranous urethral cephalad retraction and displacement with rupture at the bulbomembranous junction. The fibrous gap between the prostate and the bulbous urethra involves primarily the membranous component and the proximal edge of the bulb. The proximal and distal urethral lumens may be thus mal-aligned in both an anteroposterior and a lateral displacement. Consequently,

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