Lumbosacral Plexus Injury (Lumbosacral Plexopathy)

Anatomy of the lumbosacral plexus

The lumbosacral plexus is formed by nerve roots from the lower spine (L1 to S4), which join and branch in the back of the abdomen and pelvis before forming the main nerves of the leg:

• Lumbar plexus (L1 to L4): forms the femoral nerve (thigh muscles that straighten the knee, sensation of the front of the thigh) and obturator nerve (inner thigh)
• Sacral plexus (L4 to S4): forms the sciatic nerve (back of the thigh, lower leg and foot), gluteal nerves (buttock muscles) and pudendal nerve (perineum)

Because many nerves pass through the plexus, damage produces weakness and numbness that do not match a single nerve or a single spinal root.

Causes

• Trauma: pelvic fractures, sacral fractures and hip dislocations, often from car crashes or falls from height. See pelvic fracture.
• Bleeding: retroperitoneal hematoma, often in people on anticoagulants or with bleeding disorders, compressing the plexus.
• Diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy): inflammation of small blood vessels in the nerves, usually in older adults with type 2 diabetes, often after weight loss. It starts with severe thigh pain, followed by weakness and wasting.
• Tumors: cancers of the cervix, uterus, prostate, rectum or colon, lymphoma or sarcoma spreading to or pressing on the plexus. Pain is often the first symptom.
• Radiation plexopathy: months to years after pelvic radiation, typically painless weakness.
• Surgery and childbirth: hip replacement, pelvic surgery, positioning during surgery, and difficult deliveries can stretch or compress nerves.
• Infection or abscess, such as a psoas abscess.
• Aneurysms of the aorta or iliac arteries.

Symptoms

• Weakness of hip flexion, knee straightening, hip movement or ankle and foot movements, depending on the part involved
• Foot drop if the sciatic portion is affected
• Numbness or tingling in the thigh, leg or foot
• Pain in the low back, buttock, hip or leg, sometimes burning or severe
• Muscle wasting of the thigh or calf over weeks
• Reduced or absent reflexes at the knee or ankle
• Difficulty walking, climbing stairs or standing from a chair
• Usually one-sided, but diabetic amyotrophy can spread to the other leg

Diagnosis

• Neurological examination: mapping which muscles are weak and where sensation is lost, and checking reflexes.
• Nerve conduction studies and electromyography (EMG): confirm a plexus problem and distinguish it from nerve root compression (lumbar radiculopathy) or single-nerve injury. Best performed about 3 weeks or more after onset.
• MRI of the lumbar spine and pelvis: looks for disc herniation, tumors, inflammation and nerve swelling.
• CT: for fractures, bleeding and tumors, especially after trauma.
• Blood tests: glucose and HbA1c, clotting tests, inflammatory markers.

Treatment

• Treat the cause: stabilization of pelvic fractures, reversing anticoagulation and draining large hematomas, cancer treatment, controlling diabetes.
• Pain management: nerve pain medicines such as gabapentin, pregabalin, duloxetine or amitriptyline. Opioids may be needed short term for severe pain.
• Immunotherapy: steroids or IV immunoglobulin are sometimes used for diabetic amyotrophy, though evidence is limited.
• Physical therapy: strengthening, maintaining range of motion and gait training.
• Orthotics: an ankle-foot orthosis for foot drop, knee braces for knee buckling.
• Assistive devices: canes or walkers.
• Surgery: nerve repair, grafting or nerve transfers for some traumatic injuries.

Outlook

Recovery depends on the cause and severity. Nerve stretch and compression injuries can improve substantially over 6 to 24 months as nerves regenerate slowly, roughly 1 mm per day. Diabetic amyotrophy usually improves partially over months to years, though some weakness may remain. Plexopathies from tumors or radiation tend to be progressive. Ongoing rehabilitation helps maximize function.

Frequently asked questions

What is a lumbosacral plexus injury?

It is damage to the network of nerves in the lower back and pelvis that supply the hips, buttocks and legs. It causes weakness, numbness and pain in a pattern involving more than one nerve. Causes include pelvic trauma, bleeding, tumors, radiation and diabetes.

What are the symptoms of lumbosacral plexopathy?

Typical symptoms are leg weakness, numbness or tingling, pain in the back, buttock or leg, foot drop, muscle wasting of the thigh or calf, and difficulty walking. Symptoms are usually on one side and depend on which part of the plexus is affected.

What is diabetic amyotrophy?

Diabetic amyotrophy, also called diabetic lumbosacral radiculoplexus neuropathy, is a type of lumbosacral plexopathy in people with diabetes. It typically starts with severe thigh pain, followed by weakness and wasting of the thigh muscles, often after weight loss. It usually improves slowly over months to years.

Can a lumbosacral plexus injury heal?

Many injuries improve over time, especially stretch and compression injuries and diabetic amyotrophy, though recovery can take 6 months to 2 years and may be incomplete. Physical therapy, braces and pain management support recovery. Injuries from tumors or radiation are less likely to improve.