From the Guidelines
The L5 nerve root is primarily responsible for numbness and tingling in the lateral side of the foot, as it supplies sensation to this area. When considering the anatomy of the lumbar spine and the distribution of nerve roots, it becomes clear that the L5 nerve root plays a crucial role in innervating the lateral aspect of the foot. This is because the L5 nerve root exits the spinal canal at the L4-L5 level and travels down to supply sensation to the top of the foot and the first web space, as well as the lateral side of the foot 1.
Key Points to Consider
- The L5 nerve root is responsible for sensation in the lateral side of the foot
- Compression or irritation of the L5 nerve root, often due to a herniated disc at the L4-L5 level, can cause numbness and tingling in this area
- Understanding the anatomical relationship between the lumbar spine and the nerve roots is essential for diagnosing and treating lower back conditions that cause radiating symptoms into the lower extremities
- A focused examination, including straight-leg-raise testing and a neurologic examination, can help assess the presence and severity of nerve root dysfunction 1
Clinical Implications
- Clinicians should be aware of the typical lumbar nerve root distribution and how it relates to symptoms such as numbness and tingling in the lateral side of the foot
- A thorough history and physical examination, including evaluation of knee strength and reflexes, great toe and foot dorsiflexion strength, and distribution of sensory symptoms, can help identify the underlying cause of these symptoms 1
From the Research
Lumbar Vertebrae and Numbness in the Lateral Side of the Foot
- The lumbar vertebrae area responsible for numbness and tingling in the lateral side of the foot is associated with the L5 nerve root 2, 3.
- The L5 nerve root is typically affected by compression or irritation at the L4-L5 or L5-S1 levels 2, 4.
- Studies have shown that lumbosacral transitional vertebrae can alter the function of lumbar nerve roots, including the L5 nerve root 5, 3, 6.
- In patients with lumbosacral transitional vertebrae, the S1 nerve root may serve the usual function of the L5 nerve root, leading to altered symptoms 3.
- Extraforaminal L5 nerve root compression can occur between lumbosacral transitional vertebrae and sacral ala, or due to intervertebral osteophytes 5, 6.
- Symptoms of L5 nerve root compression can include numbness and tingling in the lateral side of the foot, as well as weakness of ankle inversion and plantar flexion 2, 6.