From the Guidelines
The S1 (first sacral) nerve is primarily distributed to the gluteal region, posterior thigh, and lower leg, specifically innervating the muscles of these areas, including the gluteal (motor only), peroneal, and tibial nerve territories.
Key Points
- The S1 nerve is part of the lumbosacral plexus, which is formed from the L1 to L5 ventral rami with contributions from T12 and S1 to S4 1.
- The sacral plexus terminal branches, including the S1 nerve, supply motor and sensory innervation to the gluteal region, lateral, and posterior thigh and lower leg 1.
- The S1 nerve is involved in the formation of the sciatic nerve, which exits the pelvis through the greater sciatic foramen and is a common site of entrapment neuropathies 1.
- Clinical manifestations of S1 nerve dysfunction can include pain, dysesthesia, and/or burning or electric sensation in the distribution of the nerve, as well as weakness and sensory loss in the affected areas 1.
Clinical Relevance
- The diagnosis of S1 nerve dysfunction can be challenging and may require electrodiagnostic studies and imaging, such as MRI, to confirm the diagnosis and localize the site of nerve compression 1.
- Treatment of S1 nerve dysfunction depends on the underlying cause and may include surgical, interventional, or noninvasive therapies 1.
From the Research
Distribution of the S1 Nerve
The S1 nerve root is known to innervate several muscles in the lower extremities. According to 2, the S1 nerve root typically supplies the medial head of gastrocnemius, soleus, and abductor hallucis. However, the study also found that most muscles have a dual innervation, with one nerve root being dominant.
Muscles Innervated by the S1 Nerve
Some of the muscles innervated by the S1 nerve include:
- Medial head of gastrocnemius
- Soleus
- Abductor hallucis
- Extensor digitorum brevis (in some cases) 2
- Lateral head of gastrocnemius (in some cases) 2
Anatomical Location of the S1 Nerve
The S1 nerve root is located in the dorsal sacral foramen, and its position can be predicted using the lumbar facet joint 3. The horizontal distance from the spinous process to the dorsal S1 foramen is approximately 25.9-26.2 mm for men and 26.2-26.8 mm for women 3.
Innervation Patterns
The S1 vertebral body is densely innervated, with the highest nerve density seen at the centrum (anatomic center) 4. Nerve fibers penetrate the S1 vertebral body via the lateral aspects, consistent with being branches of the anterior sacral nerve 4. The nerves within the S1 vertebral body are likely composed of a mixed population of nociceptive and autonomic fibers 4.