Why Do My Legs Suddenly Give Out?

A feeling of sudden leg weakness, causing your legs to give out or buckle can be alarming. Weakness in your leg(s) may occur from problems in the nerves and/or muscles in your lower body and is usually treatable. Rarely, the underlying cause may be a serious medical condition requiring immediate medical attention.

Here are a few potential causes for leg weakness resulting in sudden buckling and possible falls.

Radiculopathy

When a nerve root (part of a spinal nerve as it exits the spine) between L1 to S3 in your lower back is compressed, you may experience radiculopathy symptoms in your leg. The most common type of radiculopathy involves the sciatic nerve (formed by the L4-S1 nerve roots) and is called sciatica.¹Giuffre BA, Jeanmonod R. Anatomy, Sciatic Nerve. [Updated 2018 Dec 16]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482431/. Sciatica is typically felt as shooting pain that starts in the back and radiates through the back of the leg into the foot.

See What You Need to Know About Sciatica

Other radiculopathy symptoms can include leg weakness, heaviness, and/or loss of function. Radiculopathy typically affects one leg at a time. You may also feel pain, numbness, and/or tingling in the affected leg.²Davis D, Vasudevan A. Sciatica. [Updated 2019 Feb 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507908/ Higher nerve root compression (L1-L3) can affect the front of the thigh and groin region.

Radiculopathy usually occurs as a result of nerve root compression from a herniated disc, spinal stenosis (narrowing of the bony openings for nerve roots), spondylolisthesis (a vertebral body slipping forward on another), or other degeneration in the lumbar spine. The sciatic nerve controls the movement of the muscles in the thigh, calf, leg, and foot and is the most common source of radiculopathy.²Davis D, Vasudevan A. Sciatica. [Updated 2019 Feb 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507908/

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Depending on the severity of radiculopathy, your leg weakness may range from:

• Difficulty in lifting the foot
• Difficulty in lifting the entire leg
• Loss of balance while walking or an unstable gait

Radiculopathy usually resolves with nonsurgical treatments, including physical therapy, regular exercise, heat and cold therapy, and/or medication. Rarely, surgery may be required if a nerve root is severely compressed and/or the leg weakness persists and/or progresses.²Davis D, Vasudevan A. Sciatica. [Updated 2019 Feb 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507908/

Central canal stenosis

Narrowing of the spinal canal is called central canal stenosis. Your spinal canal houses the spinal cord. Central canal stenosis can cause compression of the spinal cord and reduction in its blood supply. Narrowing of this canal can occur in the neck, upper back, and/or lower back.³Raja A, Hanna A, Hoang S, et al. Spinal Stenosis. [Updated 2019 Jul 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441989/ The spinal cord ends at L1 in adults. Stenosis below this level is not from cord compression but compression of nerve roots.

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Central canal stenosis may occur due to severe disc herniation, abnormally overgrown bone (bone spurs), or thickening of the spinal ligaments.³Raja A, Hanna A, Hoang S, et al. Spinal Stenosis. [Updated 2019 Jul 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441989/ Other causes include trauma (bleeds) and tumors which grow into the spine.

Read more: Central Canal Stenosis Causes and Risk Factors

You may experience³Raja A, Hanna A, Hoang S, et al. Spinal Stenosis. [Updated 2019 Jul 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441989/:

• Weakness in both legs
• Difficulty in walking
• Loss of balance
• Pain after walking variable distances (neurogenic claudication)

Central canal stenosis may be treated nonsurgically or surgically depending on its severity. If the spinal cord compression is severe (more than 30%) with marked leg weakness, surgery may be indicated.³Raja A, Hanna A, Hoang S, et al. Spinal Stenosis. [Updated 2019 Jul 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441989/

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Diabetic neuropathy

Diabetes mellitus can cause damage to the nerves and muscles in your legs and feet. These nerves typically receive lesser blood supply in diabetes, damaging their structure. The strength and thickness of the muscles are also significantly reduced in diabetic neuropathy, leading to leg weakness.⁴Alam U, Riley DR, Jugdey RS, et al. Diabetic Neuropathy and Gait: A Review. Diabetes Ther. 2017;8(6):1253–1264. doi:10.1007/s13300-017-0295-y

A few common symptoms include⁴Alam U, Riley DR, Jugdey RS, et al. Diabetic Neuropathy and Gait: A Review. Diabetes Ther. 2017;8(6):1253–1264. doi:10.1007/s13300-017-0295-y:

• Weakness in the leg and ankle
• Loss of balance and unsteady gait
• Aching, burning, or sharp pain in the leg
• Numbness or complete loss of sensation in the leg and feet, typically affecting the areas covered by a stocking (in the hands, the areas covered by a glove may be affected)

Foot symptoms in diabetic neuropathy are usually managed with medications, special shoe inserts, and/or special type of footwear.

Cauda equina syndrome

Cauda equina syndrome is a rare, but serious medical condition. This syndrome occurs when the lower part of the spinal cord (cauda equina) is compressed due to tumors, collection of fluid (abscess), or severe disc herniation.

Cauda equina syndrome may cause:

• Sudden, severe weakness in both legs⁵Kim K-H, Kim DH. Diagnosis and Treatment of Spinal Pain. In: Minimally Invasive Percutaneous Spinal Techniques. Elsevier; 2010:1-28. doi:10.1016/b978-0-7020-2913-4.00001-x
• Numbness in the groin, buttocks, genitals and/or inner thighs (saddle numbness)⁵Kim K-H, Kim DH. Diagnosis and Treatment of Spinal Pain. In: Minimally Invasive Percutaneous Spinal Techniques. Elsevier; 2010:1-28. doi:10.1016/b978-0-7020-2913-4.00001-x
• The inability to control your bowel and/or bladder movements⁵Kim K-H, Kim DH. Diagnosis and Treatment of Spinal Pain. In: Minimally Invasive Percutaneous Spinal Techniques. Elsevier; 2010:1-28. doi:10.1016/b978-0-7020-2913-4.00001-x
• An inability to pass urine, reduced urinary sensation, loss of desire to pass urine, or a poor stream⁶Fairbank J, Mallen C. Cauda equina syndrome: implications for primary care. Br J Gen Pract. 2014;64(619):67–68. doi:10.3399/bjgp14X676988

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If you experience any of these symptoms, consult your doctor immediately. Doctors advise treating this condition within 24 to 48 hours of symptom occurrence in order to preserve lower limb function.⁵Kim K-H, Kim DH. Diagnosis and Treatment of Spinal Pain. In: Minimally Invasive Percutaneous Spinal Techniques. Elsevier; 2010:1-28. doi:10.1016/b978-0-7020-2913-4.00001-x^,6Fairbank J, Mallen C. Cauda equina syndrome: implications for primary care. Br J Gen Pract. 2014;64(619):67–68. doi:10.3399/bjgp14X676988^,7Petr O, Glodny B, Brawanski K, et al. Immediate Versus Delayed Surgical Treatment of Lumbar Disc Herniation for Acute Motor Deficits. SPINE. 2019;44(7):454-463. doi:10.1097/brs.0000000000002295

If you experience leg weakness and are unsure about the cause, consult your doctor. A doctor can conduct specific clinical and diagnostic tests to identify the underlying cause for your leg weakness and formulate an effective treatment plan.

Learn more:

When Sciatica Pain Is a Medical Emergency

Understanding Neuropathy Symptoms