INVESTIGATIVE UROLOGY

Digital Three-Dimensional Modeling of the Male Pelvis and Bicycle Seats: Impact of Rider Position and Seat Design on Potential Penile Hypoxia and Erectile Dysfunction
Gemery JM, Nangia AK, Mamourian AC, Reid SK
Department of Radiology, Dartmouth-Hitchcock Medical Center, Lebanon, NH, USA
BJU Int. 2007; 99: 135-40

• Objective: To digitally model (three-dimensional, 3D) the course of the pudendal arteries relative to the bony pelvis in the adult male, and to identify sites of compression with different bicycle riding positions as a potential cause of penile hypoxia and erectile dysfunction.
• Subjects and Methods: 3D models were made from computed tomography scans of one adult male pelvis (a healthy volunteer) and three bicycle seats. Models were correlated with lateral radiographs of a seated rider to determine potential vascular compression between the bony pelvis and seats at different angles of rider positioning.
• Results: Pelvis/seat models suggest that the most likely site of compression of the internal pudendal artery is immediately below the pubic symphysis, especially with the rider leaning forward. For an upright rider, the internal pudendal arteries do not appear to be compressed between the seat and the bony pelvis. Leaning partly forward with arms extended, the seat/symphysis areas were reduced to 73 mm(2) with standard seat and 259 mm(2) with a grooved seat. Leaning fully forward, the seat/symphysis areas decreased (no space with standard seat; 51 mm(2) with a grooved seat) and both the ischial tuberosities and the pubic symphysis might be in contact with the seat.
• Conclusion: A grooved seat allows better preservation of the seat/symphysis space than a standard seat, but the rider’s position is more important for preserving the seat-symphysis space (and reducing compression) than is seat design alone. Any factors which influence the seat-symphysis space (including an individual’s anatomy, seat design and rider position) can increase the potential for penile hypoxia and erectile dysfunction/perineal numbness.
  
  
• Editorial Comment
  The first published article associating bicycling with erectile dysfunction appeared 20 years ago and referred to a man riding a stationary bicycle that experienced transient tight sensations around the glans penis during the exercise and progressive impairment of sexual potency over a period of more than one year. After lowering the bicycle seat the attacks of impaired penile sensation disappeared, and one month after the patient discontinued the bicycle exercises, sexual potency returned (1). The authors proposed a vascular compression for explain the abnormal penile sensation and a neural compression for impotence (1). Ten years later, a study included 260 participants in a Norwegian annual bicycle touring race of 540 km. Thirty-five of 160 responding males (22%) reported symptoms from the innervation area of the pudendal or cavernous nerves. Thirty-three had penile numbness or hypoesthesia after the tour. In 10, the numbness lasted for more than one week. Impotence was reported by 21 (13%) of the males. It lasted for more than one week in 11, and for more than one month in three. The symptoms afflict both experienced cyclists and novices. In some, the complaints may last up to eight months. The authors concluded that changing the hand and body position on the bike, restricting the training intensity, and taking ample pauses might also be necessary in prolonged and vigorous bicycle riding to prevent damage to peripheral nerves (2). Since then, many studies showed the association of bicycling with erectile dysfunction and genital numbness as well as associated the symptoms with the body position and bicycle characteristics (3,4).
  The present study by Gemery et al. created digital 3-dimensional models of pelvis, pudendal arteries and bicycle seats to evaluate potential sites of compression of the vessels. The authors hypothesized that the type of seat in conjunction with the rider’s position differentially affects the orientation and compression of the pudendal arteries. This precise morphological study supports the hypothesis that the compression occurs between the top of the forward portion of the bicycle seats and the undersurface of the pubic symphysis, and is associated with the rider’s position. Based on their results, the authors suggested that the rider’s position has a greater role than seat design in potential compression.

References

1. Solomon S, Cappa KG: Impotence and bicycling. A seldom-reported connection. Postgrad Med. 1987; 81: 99-100.
2. Andersen KV, Bovim G: Impotence and nerve entrapment in long distance amateur cyclists. Acta Neurol Scand. 1997; 95: 233-40.
3. Sommer F, König D, Graft C, Schwarzer U, Bertram C, Klotz T, et a.: Impotence and genital numbness in cyclists. Int J Sports Med. 2001; 22: 410-3.
4. Dettori JR, Koepsell TD, Cummings P, Corman JM: Erectile dysfunction after a long-distance cycling event: associations with bicycle characteristics. J Urol. 2004; 172: 637-41.

Dr. Francisco J.B. Sampaio
Full-Professor and Chair, Urogenital Research Unit
State University of Rio de Janeiro
Rio de Janeiro, RJ, Brazil
E-mail: sampaio@urogenitalresearch.org