The S3 dermatome covers the inner buttock and the skin around the ischial tuberosity and the gluteal fold, forming part of the saddle area. It lies between S2 on the posterior thigh and S4-S5 around the anus. Some genital skin is also included.
| Nerve root | S3 |
|---|---|
| Area | Inner buttock, skin over the ischial tuberosity and the infragluteal fold |
| How to test | Light touch and pinprick are compared side to side at the ISNCSCI key sensory point: over the ischial tuberosity or in the infragluteal fold. |
| Nerve Supply | Posterior cutaneous nerve of thigh (perineal branches); Pudendal nerve; Medial cluneal nerves |
Carries touch, pain and temperature sensation from this strip of skin to the spinal cord through the S3 dorsal root.
Saddle numbness involving S3 to S5 is a red flag for cauda equina syndrome or a conus medullaris lesion. These sacral dermatomes are easy to overlook in a quick exam and should be tested directly whenever back pain comes with bladder, bowel or sexual symptoms. Dermatome maps differ between sources (Foerster, Keegan and Garrett, and modern evidence-based maps disagree), and neighbouring dermatomes overlap, so borders are approximate.
Compression of the sacral roots causing saddle anaesthesia, urinary retention and bowel dysfunction; urgent imaging and decompression are needed.
A lesion of the lower end of the spinal cord causing symmetric saddle numbness and early bladder and bowel dysfunction.
This website uses cookies to enhance your experience. Some are essential for site functionality, while others help us analyze and improve your usage experience. Please review your options and make your choice.
If you are under 16 years old, please ensure that you have received consent from your parent or guardian for any non-essential cookies.
Your privacy is important to us. You can adjust your cookie settings at any time. For more information about how we use data, please read our privacy policy. You may change your preferences at any time by clicking on the settings button below.
Note that if you choose to disable some types of cookies, it may impact your experience of the site and the services we are able to offer.
Some required resources have been blocked, which can affect third-party services and may cause the site to not function properly.
This website uses cookies to enhance your browsing experience and ensure the site functions properly. By continuing to use this site, you acknowledge and accept our use of cookies.
