What nerve deficits and symptoms develop from a herniated disc in L3-L4?

Nerve Deficits and Symptoms from L3-L4 Disc Herniation

A herniated disc at the L3-L4 level primarily affects the L4 nerve root, causing pain in the medial knee area, weakness in the quadriceps muscle, and diminished patellar reflex. 1

Clinical Presentation

Pain and Sensory Symptoms

• Pain and/or numbness in the medial aspect of the knee joint is present in approximately 80% of patients with L3-L4 disc herniation 1
• Patients may experience radicular pain that radiates down the anterior and medial thigh to the knee 2, 1
• Sensory disturbances typically follow the L4 dermatome distribution (medial leg and foot) 1

Motor Deficits

• Quadriceps muscle weakness is a hallmark finding, present in 27-70% of patients with L3-L4 disc herniation 1
• Iliopsoas muscle weakness may be observed in 60-95% of cases 1
• Anterior tibial muscle weakness can occur in up to 43% of patients 1

Reflex Changes

• Depression or absence of the patellar tendon reflex is common, occurring in 27-100% of patients 1
• This is a key diagnostic finding that helps differentiate L3-L4 from other levels of disc herniation 2

Special Tests

• Femoral Nerve Stretch Test (FNST) is positive in 91-95% of cases, making it highly sensitive for L3-L4 disc herniation 1
• Straight Leg Raise Test (SLRT) is less reliable for L3-L4 herniations, positive in only 13-87% of cases 1

Diagnostic Considerations

Clinical Diagnosis

• The distribution of pain and numbness is more useful for accurate level diagnosis than objective neurological findings alone 1
• Pain localized to the medial knee joint strongly suggests L4 nerve root involvement 1
• Lateral disc herniations at L3-L4 are more easily diagnosed clinically than central herniations 3

Imaging

• MRI without contrast is the preferred imaging modality for confirming L3-L4 disc herniation 2
• CT is highly accurate for diagnosing lateral L3-L4 disc herniations 3

Clinical Course and Management

• Most patients with L3-L4 disc herniation can experience relief with conservative management 4
• Conservative treatment typically includes physical therapy, pain management, and activity modification for 6 weeks 2
• Lateral L3-L4 herniations may respond more poorly to conservative management than central herniations, with a shorter duration from symptom onset to surgical intervention (34.8 days vs. 154.4 days) 3

Potential Complications

• If left untreated, progressive neurological deficits may develop 5
• Although rare, cauda equina syndrome can occur with large central disc herniations, presenting with urinary retention (90% sensitivity), saddle anesthesia, and bilateral lower extremity weakness 2
• Persistent pain and functional limitations may lead to decreased quality of life and disability 6

Differential Diagnosis

• L2-L3 disc herniation typically presents with pain and numbness proximal to the knee joint 1
• L4-L5 disc herniation typically affects the L5 nerve root, causing weakness in foot dorsiflexion and great toe extension 2
• Lumbar spinal stenosis may present with similar symptoms but typically includes neurogenic claudication (leg pain with walking relieved by sitting) 2