Bicycle seat neuropathy is recurrent perineal numbness in a cyclist after prolonged cycling and carries the risk of impotence in the long run if unchecked.
It is also known as pudendal neuralgia or pudendal nerve entrapment syndrome [In stricter sense, Pudendal nerve entrapment could be due to other causes as well.]
The injuries and symptoms are due to either vascular or neurologic injury to the pudendal nerve to caused when body weight is supported on a narrow seat.
The symptoms are typically relieved when the person gets off the cycle.
It has been reported to occur in females too though males are more affected.
The pudendal nerve arises from the S2-4 nerve roots of the anterior division of the sacral plexus. It is the nerve of the perineum and pelvic floor, supplying lower buttocks, perineum, rectum and external genitalia.
The pudendal nerve arises from the anterior division of ventral rami of 2nd, 3rd and 4th sacral nerves of the sacral plexus.
The nerve emerges from the pelvis through the greater sciatic foramen, below the piriformis muscle, course around the sacrospinous ligament and leaves the gluteal region through the lesser sciatic foramen to enter into the pudendal canal.
The pudendal canal is formed by the fascia of the obturator internus muscle or obturator fascia.
The pudendal canal is also called Alcock canal. The Alcock canal is enclosed laterally by the ischial bone and medially by the fascial layer of the obturator internus muscle. The pudendal nerve exits the canal ventrally, below the symphysis pubis, and innervates the genital and perineal regions.
It encloses Internal pudendal artery, Internal pudendal veins and pudendal nerve.
Within the pudendal canal the nerve divides into branches for rectum penis and perineum.
Ischemia of the pudendal nerve is thought to be the event that causes this neuropathy.
It has been hypothesized that compression of the pudendal nerve occurs as it passes through the Alcock canal and leads to the symptoms. It is also called therefore Alcock canal neuropathy.
Long-distance cycling results in the indirect transmission of pressure onto the perineal nerve within the Alcock canal.
Another hypothesis is that bicycle seat neuropathy is due to temporary and transient ischemic injury to the dorsal branch of the pudendal nerve secondary to compression of the nerve between the bicycle seat and the symphysis pubis.
Bicycle seat design or shape may be the major factor in the development of bicycle seat neuropathy.
The seats which support the ischial tuberosities decrease pressure on the perineal area and thus chances of nerve compression. The lower position of the handlebar also leads to the weight transfer to pubis and perineum and thus increased chances of bicycle seat neuropathy.
Recent studies have also demonstrated that bicycle seat also affects penile blood flow and penile oxygen pressure and design changes can improve this.
Typical presentation, both in recreational or professional cyclist, is a complaint of numbness or impotence after cycling.
Different persons feel the symptoms after different periods. The symptoms have also been reported with stationary bikes.
The severity of the symptoms varies from person to person. Some cyclists report mild numbness only.
In others, more severe symptoms such as impotence or urinary incontinence may be reported.
Amount of time on the cycle, multi-day rides and position on the seat should be enquired.
Any recent increase in training volume or any changes in bicycles, bicycle setup, or bicycle position should be noted.
To rule out other causes of neuropathy, the patient should be enquired about a history of
- Metabolic disorders
- Endocrine or vascular disease
- Perineal trauma
- Intra-abdominal malignancies
The examination involves urogenital [the penis, testicles (in males), and perineal area.] and neurologic examination [motor and sensory function of the region]
Laboratory studies are not indicated in the diagnosis making but could be indicated for workup of paresthesias or impotence.
These tests may include
- Vitamin B-12 levels
- Folate levels
- Thyrotropin levels
- Tests for diabetes
- Lipid profile
Doppler ultrasound of the vascular structures may be indicated.
X-rays and CT are considered in abdominal diseases and trauma to the pelvis.
The treatment mainly involves evaluation and improvement of bicycle seat and riding position.
The cyclist should be advised to change his or her position on the bike (eg, ride with hands on the top of the handlebars vs having hands down in the drops or riding with aero bars [tri-bars]).
The patient is encouraged to stand up intermittently to relieve pressure or to stop cycling temporarily until the symptoms resolve.
Change in type and shape of the seat is crucial. Elevation of the nose of the bicycle seat may worsen the condition, as more pressure is placed upon the Alcock canal and the pudendal nerve.
Changing the seat height and tilt position may help
There is no need for any medication.
The patient should be reevaluated after making the changes to ensure that improvement in symptoms is occurring. Continued symptoms despite changes in the bicycle seat position and training volume may indicate a different source of the symptoms and should be reevaluated.
Continued symptoms can lead to complications like impotence and incontinence. Therefore the patient should be kept in strict follow-up.
Transient impotence is known. It resolves over time once the pressure is relieved from the perineal region. It can take more than 1 month to resolve.
Prevention of Bicycle Seat Neuropathy
The injury may be prevented by
- Proper fit seats. Newer seats are better designed
- Frequent change of position
Newer designs in bicycle seats allow for the reduction of perineal pressure by providing a bicycle seat with the middle portion cut away.
The prognosis and recovery from bicycle seat neuropathy is very good. However, the rate of recovery is variable and may be influenced by the amount of time the athlete previously spent cycling.
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