Urethral Muscles

There are two sets of muscles in connection with the urethra; one set might be said to aid in expelling the urine and the other in retaining it. The expulsors are the longitudinal and circular fibres surrounding the urethra just outside the mucous membrane and the accelerator urinae or bulbocaverytosus muscle. The sphincters are the compressor urethra or external sphincter muscle, and the internal sphincter at the neck of the bladder, composed of fibres continued from the bladder and prostate. The portion of these fibres surrounding the internal meatus just beneath the mucous membrane is called the annulus urethralis.

It has been supposed that if the bladder becomes distended the internal sphincter involuntarily relaxes and allows the urine to enter the prostatic urethra, and it is then stopped by the voluntary contraction of the external sphincter, which is the true sphincter. Leedham Green {Brit. Med. four., August, 1906) claims that the internal sphincter holds tight in the living subject even when the bladder is over-distended. Sections made of formalin-hardened bodies seem to support this view.

Practical Applications

A knowledge of both the length and calibre of the urethra is essential in the use of both catheters and bougies or sounds. If urine begins to flow when a catheter is introduced 20 cm. we know the urethra is of normal length. Urine may flow when the bladder is distended as soon as the catheter passes the membranous portion, about 17 cm. (6 3/4 in.) from the meatus. In hypertrophy of the prostate the prostatic urethra is much increased in length and it may be impossible to reach the bladder by an ordinary catheter. It may require one 25 or 30 cm. (10 to 12 in.) long. The position of a stricture is located by its distance from the meatus. If a sound is stopped by a stricture inside of 15 cm. (6 in.) from the meatus we know it is anterior to the triangular ligament. Strictures are most frequent where the subpubic curve is lowest, viz., at the bulbomembranous region. They are then called deep strictures. They are next most frequent toward the anterior portion, while strictures of the prostatic portion are almost unknown.

Passage Of Sounds And Catheters

In passing a catheter or sound its beak should be kept applied to the roof of the urethra, otherwise its point will catch in the dilated bulbous portion and strike on the triangular ligament below the opening for the urethra. To aid the beak to follow the subpubic curve the handle is depressed. In difficult cases the index finger of the opposite hand is introduced in the rectum and the beak is felt at the membranous portion a short distance in front of the apex of the prostate and guided upward into the bladder (Fig. 474). If the penis is grasped near the glans and drawn up the instrument, the urethra may so stretch that the sound will not reach to the bladder. To avoid this it should be grasped lower down toward the scrotum. The urethra is so flexible and loose that straight instruments, such as cystoscopes, can readily be passed by skilful hands. In hypertrophy of the prostate, long instruments, with big curves if of metal, are essential. Many rubber catheters are too short for this purpose. In passing small, filiform bougies they are to be directed at first toward the floor of the urethra to avoid the lacunae on the roof. If they do catch they are allowed to remain and so prevent the ones subsequently introduced catching in the same place. The vascular net-work in the submucous tissue bleeds readily and the skill evinced by the surgeon in passing urethral instruments is in inverse ratio to the amount of bleeding produced.

Fig. 474.   Method of passing the sound. The index finger in the rectum is guiding the sound through the membranous urethra.

Fig. 474. - Method of passing the sound. The index finger in the rectum is guiding the sound through the membranous urethra.

Otis claimed that a penis 3 in. in circumference had a normal urethra admitting a No. 30, French scale, sound; 3 1/4 in. No. 32; 3 1/2 in. No. 34; 3 3/4 in. No. 36, and 4 in. No. 38. White and Martin state that a 3 in. circumference admits a No. 26 to No. 28; 3 1/4 in. Nos. 28 to 30; 3 1/2 in. Nos. 30 to 32; 3 3/4 in. Nos. 32 to 34; and a 4 in. Nos. 34 to 36. We agree with the latter, and often the meatus though normal in appearance must be incised to admit the above sizes. The distensibility of the urethra is such, especially in its deeper portions, that after incision of the meatus very large sounds can be introduced. For this reason urethrotomes should not cut to the full size. Teevan's urethrotome only cuts up to 22 French and the additional size is obtained by stretching with sounds. This instrument in one case was made to cut to 26 French but death followed from hemorrhage and a return was made to No. 22. It cuts on the roof, and the dorsal artery of the penis or the artery to the bulb was probably divided. To avoid hemorrhage, deep strictures are treated by dilatation or external urethrotomy and penile strictures only are cut internally. Keegan has shown that the calibre of the urethra in small children is sufficient to allow the use of the lithotrite and so avoid a cutting operation.

Spasmodic stricture results from contraction of the urethral muscles due to some irritation. This irritation may be from the urine, from organic stricure, fissure of the anus, hemorrhoids, etc. It causes retention of urine, which can be relieved by passing a full-sized catheter, or by hot baths, etc. Notice the firmness with which the urethra grasps a sound as it is withdrawn.

Traumatic Stricture

This is usually located in the bulbous portion, just in front of the triangular ligament. The urethra is compressed between the pubic bone and the vulnerating body. It is treated by passing in a full-sized catheter either with or without the aid of a perineal incision.