Role of male pelvic floor muscles and anterior fibromuscular stroma in males on α1‐blocker treatment: A magnetic resonance imaging study

Dynamic motion of the pelvic floor muscles during voiding was analyzed using real‐time magnetic resonance imaging. To evaluate the contraction of the pelvic floor muscles, striated urethral sphincter distance, levator ani muscle thickness and anterior fibromuscular stroma distance were measured. The percent contraction of the striated urethral sphincter from before voiding to just before initiation of voiding was 14% in the normal group and 5% in the voiding dysfunction group. The percent contraction of the anterior fibromuscular stroma from before voiding to just before initiation of voiding was 11% in the normal group and 1% in the voiding dysfunction group; the percent contraction of the muscles was significantly greater in the normal group (P < 0.05). Striated urethral sphincter and anterior fibromuscular stroma contraction at initiation of voiding open the bladder neck and urethra. This plays an important role in the smooth initiation of voiding.     

An anatomical description of the male and female urethral sphincter complex

PURPOSE: We performed a detailed study of the lower urinary tract of the male and female human fetus to elucidate the anatomy of the urethral sphincter complex in both sexes and its relationship to the surrounding organs and tissues. MATERIALS AND METHODS: A total of 12 male and 14 female normal human pelvic specimens ranging from 17.5 to 38 weeks of gestation were studied by serial sections and immunohistochemical analysis. Three-dimensional reconstructions were created from serial sections to demonstrate the anatomy of the lower urogenital tract and urethral sphincter in both sexes. Specific attention was directed to the sphincteric muscle of the urethra. RESULTS: The urinary continence mechanism is formed by a combination of detrusor, trigone and urethral sphincter muscles with distinctive histological characteristics in both sexes. In males the external urethral sphincter covers the ventral surface of the prostate as a crescent shape above the verumontanum, horseshoe shape below the verumontanum and crescent shape along the proximal bulbar urethra. The levator ani muscles form an open circle around the external sphincter with a hiatus at the ventral aspect. In females the external urethral sphincter covers the ventral surface of the urethra in a horseshoe shape. Caudally the same horseshoe-shaped external sphincter increases in size to envelop the distal vagina. The levator ani muscles do not support the proximal urethra. The smooth and striated muscle components of the urethral sphincter complex are inseparable in both sexes. CONCLUSIONS: The developmental anatomy of the urethral sphincter complex is analogous in both sexes. The male and female urinary sphincter mechanism is composed of detrusor, trigone and urethral muscles, each of different muscular origins. The levator ani does not surround the ventral aspect of the urethra and may not have an active role in continence in both sexes. This new concept in the anatomy of male and female sphincter morphology may help to refine our reconstructive and ablative surgical techniques.     

Continence and some properties of the urethral striated muscle of male greyhounds

OBJECTIVE: To determine the properties of the striated muscle of the greyhound (dog) urethra and to consider its role in maintaining continence. Materials and methods The thickness of the muscle layers and the muscle types were determined by examining sections stained with haematoxylin and eosin or Masson's trichrome. These factors were correlated with the mechanical and electrical responses of muscle strips to nerve stimulation, and compared with muscle from other breeds of dog and other parts of the animal. RESULTS: The striated muscle formed approximately 70% of the membranous urethra and was predominantly (68%) type IIa muscle (i.e. fast but fatigue-resistant). The mean resting membrane potential was -74 mV; nerve stimulation produced an action potential with a mean amplitude of 97 mV and contraction lasting about 200 ms. All responses were abolished by D-tubocurarine. The contractions were well maintained with continuous or intermittent stimulation. The properties were intermediate between those of the anconeus (slow) and the extensor carpi radialis (fast) muscles. CONCLUSIONS: The distribution, fibre type and contractile characteristics would enable the striated urethral muscle to maintain tension for continence at rest and provide additional continence during sprints.     

The role of the pelvic floor in female urinary incontinence

This paper presents a review of the various factors believed to be involved in female urinary continence. Components within the wall of the urethra include smooth muscle, the striated muscle of the rhabdosphincter, elastic connective tissue, a subepithelial vascular component, and the urethral epithelium. Extramural factors comprise the fascial support of the bladder neck and proximal urethra, the transmission of intra-abdominal pressure to the urethra, and the periurethral muscles of the pelvic floor. Special emphasis is placed on the periurethral muscles, and the anatomy, innervation, and histochemistry of the levator ani are discussed. This account is followed by consideration of evidence that partial denervation of the levator ani may be an etiological factor in female genuine stress incontinence of urine. Finally, various non-invasive methods for the relief of genuine stress incontinence are discussed, including pelvic floor exercises and the use of intravaginal cones and electrostimulation.     

Striated muscle fiber compositions of human male urethral rhabdosphincter and levator ani

PURPOSE: We clarified the contractile properties of human male periurethral striated muscle fibers to better understand how the rhabdosphincter and the levator ani maintain urinary continence. MATERIALS AND METHODS: Muscle specimens were obtained from 52 male patients who underwent radical prostatectomy or radical cystectomy. The specimens were frozen in liquid nitrogen. Frozen sections (10 microm thick) were stained with myofibrillar ATPase at different pH values (pH 4.2, 4.6 and 10.6), and evaluated for quantitative parameters and fiber type distribution. Myosin heavy chain analysis was performed using SDS-PAGE. RESULTS: Of all 52 cases 37 provided specimens that could be divided into the 2 major fiber types, type 1 (slow twitch) and type 2 (fast twitch). Although type 1 muscle fibers were predominant in RS and LA muscle groups (RS 69.6 +/- 2.7%, LA 67.0 +/- 2.0%), mean muscle fiber size was significantly smaller in RS (mean area 906 +/- 86 microm(2)) than in LA (mean area 2,967 +/- 170 microm(2)) (p <0.0001). In 11 specimens type 2 muscle fibers could be subdivided into types 2A (fast fatigue resistant) and 2B (fast fatigable). Type 2A fibers were significantly more prevalent than type 2B fibers (p <0.05). Likewise, MHC analysis of these 11 specimens found a significantly higher percentage of fiber type 2A expression products (MHC 2A) than of fiber type 2B expression products (MHC 2X) (p <0.05). CONCLUSIONS: RS and LA contribute to urinary continence mechanism by slow contraction. Moreover, the smaller mean size of muscle fibers in RS suggests more fatigue resistance compared with muscle fibers in LA because small fibers have a shorter diffusion distance for metabolic substrates. These results should help contribute to a more detailed understanding of the function of periurethral striated muscles in the human male.     

Contractile properties of the proximal urethra and bladder in female pig: morphology and function

AIMS: To compare the contractile properties of proximal urethral and bladder muscle of the female pig. MATERIALS AND METHODS: In two proximal segments (I and II) of the urethra, small muscle bundles were excised to measure the force-length (maximum force) and the force-velocity (unloaded shortening velocity) relation using the stop-test. The rate of force development was calculated using phase plots. Contractile properties of urethral and bladder segments were statistically compared using the Mann-Whitney U-test. Immunohistochemical staining of whole circumference urethral cross sections was used to identify the location of smooth and striated muscle fibres. RESULTS: On isometric force development, the urethral muscle bundles revealed a fast ( approximately 0.5 sec) and a slow ( approximately 2.1 sec) time constant, whereas in bladder only a slow ( approximately 2.3 sec) component was measured. On average, isometric force was highest in bladder. The length range over which force was produced was smallest in urethral segment II, followed by urethral segment I and finally bladder. The unloaded shortening velocity was 0.15, 0.25 and 0.35 1/sec, respectively. Histological preparations showed that smooth as well as striated muscle was present in proximal urethra. In urethral muscle bundles, spontaneous contractions were measured with a frequency of 0.4 Hz. CONCLUSIONS: Differences in contractility found between urethra and bladder may be ascribed to the presence of striated muscle in the proximal urethra. The regulation of tone and spontaneous contractions may be part of the continence mechanism in the female pig urinary tract.     

Contractile properties of urethral smooth muscles of young and aged female dogs: Morphological and pharmacological aspects

BACKGROUND: Alpha1-adrenoceptors are highly concentrated in the urethral smooth muscles and may play an important role in the contraction of this area. However, detailed examinations of age-related changes of the properties of urethral smooth muscle have rarely been undertaken. METHODS: The contractile properties of urethras from young non-parous and old parous female beagles were determined with a urethral function study, macroscopic autoradiography for urethras using [3H]-labeled tamsulosin and morphometry of the urethral muscles. RESULTS: The antagonistic effect (pA2) of prazosin for norepinephrine was 7.76+/-0.13 in young dogs and 7.62+/-0.06 in aged dogs. The specific binding of [3H]-tamsulosin (a relatively selective alpha1A-adrenoceptor antagonist) was recognized diffusely in proximal urethras with in vitro autoradiography. The density of binding in smooth muscles was approximately 60 and 40% in circular longitudinal layers, respectively, for both dogs. CONCLUSIONS: The female canine urethra had alpha1A, and alpha1L-adrenoceptors. No age-related changes were seen in the function of the proximal urethra, distribution of alpha1-adrenoceptor binding sites and smooth muscle densities.     

Needle emg registration of striated urethral wall and pelvic floor muscle activity patterns during cough,valsalva, abdominal,hip adductor,and gluteal muscle contractions in nulliparous healthy females

The aim of the present study was to describe co-activity patterns of the striated urethral wall muscle and the pelvic floor muscles (PFM) during contraction of outer pelvic muscles. Six healthy nulliparous physical education students, mean age 19.5 years (19–21) participated in the study. Concentric needle EMG and a Dantec amplifier were used for registrations. EMG activity was continuously recorded with the participants lying in a supine position. EMG was recorded during relaxation, contraction of the PFM. valsalva maneuver, coughing, hip adductor contraction, gluteal muscle contraction, backward tilting of the pelvis, and sit-ups. The procedure was performed with the needle in the striated muscle of the anterior wall of the urethra and then repeated with the needle set lateral to the urethra in the PFM. The results showed that the striated urethral wall muscle was contracted synergistically during PFM, hip adductor, and gluteal muscle contraction, but not during abdominal contraction. Both hip adduction, gluteal muscle, and abdominal muscle contraction gave synergistic contraction of the PFM. Thus the urethral wall striated muscle and the PFM react differently during abdominal contraction. © 1994 Wiley-Liss, Inc.     

Levator ani muscle in women with genitourinary prolapse: Indirect assessment by muscle histopathology

The objective of this study was to assess the state of innervation in levator ani muscle sites using muscle histopathology. Asymptomatic women and patients with genitourinary prolapse were included. Histopathologic analysis allows indirect assessment of a muscle's innervation. Therefore, levator ani muscle was collected in a standardized fashion during abdominal surgery and frozen in the operating room using isopentane slush cooled by liquid nitrogen. Serial sections of levator ani muscle in cross-section were studied with standard histochemical and immunohistochemical techniques. The staining patterns from these histochemical techniques allowed quantitative determination of the ratios of fiber types I, IIA, and IIB and their fiber diameters. Objective assessment of fiber type grouping was performed. The distribution of both fiber type percentage and diameter were non-parametric. Therefore, the Mann-Whitney U-test was used to analyze the data for statistical differences between the means for these variables. There was no statistical difference in levator ani muscle fiber type percentage and diameter in patients with prolapse and/or urinary incontinence when compared to asymptomatic women. Levator ani muscles have a higher proportion of slow fibers (66%) than found in other human female muscle (48%). There was no evidence for denervation/reinnervation in any of the biopsy specimens. In this study, levator ani muscle biopsies from incontinent and/or prolapse patients were neither denervated nor reinnervated. © 1996 Wiley-Liss, Inc.     

Morphometry of the aging female rat urethra

Muscles in the limbs change with age, but the aging process of urethral muscles is unknown. Therefore, we compared smooth and striated muscle content in the female rat urethra in young (12 month) and old (32 month) animals, using immunochemical techniques. All the striated skeletal fibers at both ages contain slow myosin. Urethral diameter does not change with age (young, 1.44±0.08 mm; old, 1.46±0.10 mm,n=5), nor does the external sphincter width (young, 0.088±0.016 mm; old, 0.080±0.017 mm,n=5). Neither smooth nor skeletal muscle volume in the urethra is changed with age (skeletal: young, 20.72±2.94%; old, 19.95±2.35%. Smooth: young, 22.26±2.98%; old, 26.75±2.35%,n=5). The external striated sphincter is separate and distinct from the pubococcygeal region of the levator ani muscle, but is closely apposed to another layer of longitudinally oriented fibers into the vaginal musculature. The morphometric analysis shows no difference in urethral architecture in aging female rats.EDITORIAL COMMENT: This paper presents a well planned experimental animal model looking specifically at the morphologic characteristics of the aging female rat urethra. Although this information cannot be directly transferred and applied to our knowledge of the aging human female urethra, such research is extremely important. Hopefully, understanding the structure and function of the urethra in other animals will clarify the same in humans. This type of research is critical in finding an appropriate animal model for basic science research in female urology.     

Direct effect of amezinium on rabbit urethra: Effect of estrogen and progesterone treatment

The effect of amezinium, a new antihypotensive agent, and hormonal treatment on the female rabbit urethra was investigated. Cumulative dose responses were obtained for amezinium and norepinephrine on strips of muscle from the urethras of ovariectomized female rabbits by means of the tissuebath system. Amezinium enhanced the response to electrical field stimulation and showed a direct contractile response on the urethra. These responses were only about 20% of the maximum norepinephrine response. The contractile response to amezinium was completely blocked by prazosin. When rabbits were pretreated with estrogen, with or without progesterone, for 4 weeks, the response to amezinium increased to 40% of the maximum norepinephrine response. Although amezinium enhances muscle contractile responses to electrical stimulation, this effect is strong when amezinium is used alone; concurrent estrogen treatment improves the effects of amezinium.EDITORIAL COMMENT The authors present their initial investigation on the effect of amezinium on the tone of female rabbit urethral muscle. The study is well designed, using classical experimental methodology. The investigators show that amezinium has a moderate contractile effect on female rabbit urethral muscle strips. This effect is blocked by the addition of prazosin, a direct adrenergic antagonist, resulting in urethral muscular relaxation. The effect of amezinium is enhanced by pretreatment with estrogen, either alone or in combination with progesterone. Pretreatment with progesterone has no significant impact on the urethral muscular contraction caused by amezinium. Amezinium has been used in human studies for the treatment of hypotension, and appears to be well tolerated. Only further extensive investigation will show whether this interesting compound has clinical use in the treatment of female genuine stress urinary incontinence.     

INNERVATION OF THE STRIATED MUSCLE OF THE MEMBRANOUS URETHRA OF THE MALE DOG

Purpose

To identify the functional innervation of the striated muscle layer of the post-prostatic urethra of male dogs.

Materials and Methods

Detailed anatomic dissection of the pelvic and pudendal nerves was carried out. The pressure and contractile responses to stimulation of these nerves were recorded in vivo and in vitro.

Results

Small branches of the pelvic nerve entered the membranous urethra but passed through the striated muscle to the inner smooth muscle layer. Stimulation of the nerve with 1 msec pulses at 10 Hz produced a slow contraction of the urethra which was unaffected by d-tubocurarine. Pudendal nerve branches entered the striated layer from the caudal end. Stimulation produced a rapid, visible contraction that was abolished by d-tubocurarine. Field stimulation of isolated strips of striated muscle resulted only in rapid, d-tubocurarine sensitive contractions.

Conclusions

The striated muscle of the membranous urethra is innervated exclusively by the pudendal nerve.     

Urethral function after cystectomy: a canine in vivo experiment

Summary To study the function of the pelvic floor and the isolated urethra after removal of the bladder, 5 male and 5 female mongrel dogs were used in an acute in vivo experiment. Urethral pressure changes secondary to unilateral stimulation of the pelvic and pudendal nerves were recorded. After baseline data of the intact system were documented, the following procedures were carried out: separation of the urethra from the bladder neck (prostate), nerve-sparing cystectomy (cystoprostatectomy), and cold-knife incision through the entire length of the proximal urethra. Pressure recordings were repeated after each step of surgery. Pudendal nerve stimulation resulted in rapid and large pressure rises in the distal urethra (reaction typical of striated muscle). This response remained unchanged after all three surgical steps. Pelvic nerve stimulation provoked pressure rises within the urethra of a pattern typical of smooth muscle. The findings persisted after separation of the urethra from the bladder neck (prostate) and after cystectomy, but were not observed after urethrotomy. Contractions secondary to pudendal nerve stimulation were inhibited by curare, which did not affect the reaction to pelvic nerve stimulation. Our experiments demonstrate that in the dog the continuity of bladder and urethra is not required for the function of urethral closure mechanisms. The contractile potency of the urethral smooth muscles remains intact after nerve-sparing cystectomy. We believe that problems with the baseline continence of surrogate bladders should mainly be ascribed to a lack of surgical caution in preserving the autonomic nerves of cystectomy. A poor response to stress conditions cannot be explained by damage to the neural pathway of the striated sphincter, as the pudendal nerve is not at risk during nerve-sparing cystectomy. In our opinion mechanical malfunction of the striated muscle components secondary to scarring at the site of the anastomosis is the main reason for stress incontinence after orthotopic bladder replacement.     

女性盆底肌磁共振弥散张量成像价值分析

目的探讨磁共振弥散张量成像(DTI)在女性盆底肌成像应用中的可行性。方法筛选35名无孕育史、无盆底疾病的年轻志愿者(对照组)和35名初产妇(研究组),分别行盆底肌常规磁共振成像(MRI)扫描和DTI扫描,测量肛提肌和肛门括约肌复合体的部分各向异性分数(FA)值,计算其平均值。并使用计算机软件描绘肛提肌和肛门括约肌复合体的三维纤维示踪图。结果对照组35名志愿者肛提肌平均FA值是(0.41±0.02),研究组35名初产妇肛提肌平均FA值是(0.34±0.03),差异有统计学意义(P0.05);对照组肛门括约肌复合体平均FA值为(0.70±0.03),研究组为(0.65±0.03),差异有统计学意义(P0.05)。DTI三维失踪成像可清晰显示初产妇肛提肌、肛门括约肌的肌肉形态改变。结论 DTI可以对女性盆底肌进行量化分析和三维形态学观察,有利于女性盆底肌肉损伤的早期诊断,值得临床推广。     

Topographical relationship between urethral rhabdosphincter and rectourethralis muscle: A better understanding of the apical dissection and the posterior stitches in radical prostatectomy

Objectives:   To clarify the topographical relationship between the urethral rhabdosphincter and the rectourethralis muscle as these structures lying dorsally to membranous urethra are important factors to post-prostatectomy urinary continence.
Methods:   Pelvic floor specimens including prostate, bulbus penis, and anorectum, obtained from 15 male cadavers (ages at death 66 to 80 years), were examined with standard histologic and immunohistochemical techniques using semiserial sagittal and transverse sections.
Results:   The rectourethralis muscle was defined. It was found to be located at the interface between the levator ani muscle and rectum. It was not possible to histologically identify the fibromuscular node known as the perineal body. The urethral rhabdosphincter was found to be inserted into the rectourethralis muscle, which is composed of the smooth muscle fibers. Abundant nerves passed between the rectourethralis muscle and the levator ani, or through the rectourethralis muscle. The urethral rhabdosphincter was closely attached to the apical or ventral portion of the rectourethralis muscle. Morphologically, the membranous urethra was fixed to the rectourethralis muscle through the urethral rhabdosphincter.
Conclusions:   The rectourethralis muscle influences the stabilization of membranous urethra. The posterior stitches for the reconstruction of the dorsal musculofascial plate might injure the nerve fibers running along and through the rectourethralis muscle.     

A comparative study of the human external sphincter and periurethral levator ani muscles

Specimens from the human male and female external urethral sphincter and the periurethral levator ani muscle have been examined using histochemical and electron microscopic techniques. In both sexes the external sphincter consists of a single population of type I (slow twitch) fibres with a mean diameter of 17.47 +/- 0.7 micrometers in the absence of muscle spindles. In contrast, the periurethral levator ani possesses muscle spindles and the constituent fibres form a heterogeneous population of type I and type II (fast twitch) fibres, with mean diameters of 45.5 +/- 0.8 micrometer and 59.5 +/- 3.4 micrometers respectively. These findings indicate that the external urethral sphincter is functionally adapted to maintain tone over prolonged periods and may be of considerable importance in producing active urethral closure during continence. The anatomical location and fibre characteristics of the levator ani muscle suggest that these fibres actively assist in urethral closure, particularly during events which cause elevation of intra-abdominal pressure. In view of the differences in fibre characteristics between the external urethral sphincter and the levator ani, EMG activity recorded from a single site in the levator ani may not be representative of the functional status either of other levator ani muscle fibres or of the external urethral sphincter.     

Topographic anatomy of the male perineal structures with special reference to perineal approaches for radical prostatectomy

AIM: Although perineal approaches for radical prostatectomy have recently gained renewed attention as excellent methods for minimally invasive surgery, the most commonly used techniques, Belt's and Young's approaches, have inadequacies regarding the topographical relationship between the rectourethral and levator ani muscles. METHODS: Using macroscopic observations of sagittal slices of 27 male pelvises and smooth muscle immunohistochemical staining of semiserial sections of another eight pelvises, we investigated the topographical anatomy of the perineal structures and their interindividual variations in elderly Japanese men. RESULTS: The inferomedial edge of the levator ani was located 5-15 mm lateral to the midsagittal plane in an area between the urethra and the rectum. The rectourethral smooth muscle had a superoinferior thickness of 5-10 mm and occupied a space between the right and left levator slings. The levator was adjacent to, or continuous with, the striated anal sphincters. A thick connective tissue septum, composed of smooth muscle, was evident between the rectal smooth muscle and the anal sphincter-levator ani complex. CONCLUSION: Because the connective tissue septum guides the surgeon's finger upwards towards the rectoprostatic space, Belt's approach appears relatively easy; however, rectal injury can sometimes occur if the surgeon loses this guidance. In contrast, if the levator edge is identified as the first step in Young's approach, the rectourethral muscle can be precisely divided, leaving a 3-5-mm margin from the rectum and sphincter-levator complex. Clinical investigations are now required to modify Young's approach based on the present results.     

The pathophysiology of stress urinary incontinence in women and its implications for surgical treatment

Stress urinary incontinence is a symptom that arises from damage to the muscles, nerves, and connective tissue of the pelvic floor. Urethral support, vesical neck function, and function of the urethral muscles are important determinants of continence. The urethra is supported by the action of the levator ani muscles through their connection to the endopelvic fascia of the anterior vaginal wall. Damage to the connection between this fascia and muscle, loss of nerve supply to the muscle, or direct muscle damage can influence continence. In addition, loss of normal vesical neck closure can result in incontinence despite normal urethral support. Although the traditional attitude has been to ignore the urethra as a factor contributing to continence, it does play a role in determining stress continence since in 50% of continent women, urine enters the urethra during increases in abdominal pressure, where it is stopped before it can escape from the external meatus. Perhaps one of the most interesting yet least acknowledged aspects of continence control concerns the coordination of this system. The muscles of the urethra and levator ani contract during a cough to assist continence, and little is known about the control of this phenomenon. That operations cure stress incontinence without altering nerve or muscle function should not be misinterpreted as indicating that these factors are unimportant.     

Levator ani muscle: new physioanatomical aspects and role in the micturition mechanism

The anatomy of the levator ani muscle was studied in relation to the urinary bladder. The study was performed on 23 cadavers by dissection and microscopic examination. The levator ani is funnel-shaped and consists of a transverse portion called the levator plate and a vertical portion called the suspensory sling. The levator plate is a cone and consists of two “lateral masses” and two “crura,” with the levator hiatus occupying its anterior part. Three crural patterns could be identified: classic, crural overlap, and crural scissors. The levator crura are connected to the intrahiatal organs by the hiatal ligament; the pubovesical ligament constitutes the anterior part of this ligament. The suspensory sling forms a vertical cuff around the intrahiatal organs, from which it is separated by a “tunnel septum.” Its urethral portion ends in multiple fibrous septa, which penetrate the striated urethral sphincter. The levator ani plays an important role in bladder-neck fixation provided by the suspensory sling and hiatal ligament. Levator ani and hiatal ligament subluxation leads to ptosis of the urinary bladder. Furthermore, the present study demonstrates that the urethra is located in the infralevator compartment and is thus protected from the effect of intraabdominal pressure. A chronic increase in intraabdominal pressure leads to levator subluxation and sagging and to urethral exposure to intraabdominal pressure, which seems to interfere with the micturition mechanism. The infralevator location of the urethra might have a bearing on the pathogenesis and treatment of stress urinary incontinence.     

Anatomy and physiology of the male urethral sphincter and its preservation in prostatic surgery

Radical prostatectomy is commonly used in the management of localized prostate cancer. Urinary incontinence after prostatectomy is of great concern to many patients. Improved understanding of the anatomy of the external urethral sphincter complex has resulted in a statistically significant decrease in the incidence of postprostatectomy incontinence. Most recent anatomic studies have described the external urethral sphincter complex as consisting of an intrinsic rhabdosphincter surrounding the smooth musculature of the urethra and an extrinsic sphincter incorporating the levator ani muscle and the pelvic floor. Both form a condensed striated muscle ring around the membranous urethra. Preservation of as much as possible of the normal anatomy of the sphincter mechanism and its nerve supply results in an excellent return to continence after radical prostatectomy. Received: 26 February 1999 / Accepted: 20 May 1999