When One Vertebra Slips Forward Over Another

What is Spondylolisthesis?
Spondylolisthesis is a spinal condition in which one vertebra slips forward over the vertebra below it, most commonly in the lower (lumbar) spine. This slippage can lead to back pain, leg pain, nerve compression, and spinal instability, affecting daily activities and quality of life.
The condition may develop gradually or appear after injury, and its severity can range from mild and asymptomatic to severe with neurological symptoms.

What Happens in Spondylolisthesis?

In a healthy spine, vertebrae are stacked and aligned. In spondylolisthesis, this alignment is disturbed due to:

• Defects in the vertebra
• Degenerative changes
• Stress fractures
• Trauma or congenital weakness

This forward slip can narrow the spinal canal or nerve exit pathways, leading to pain, numbness, or weakness in the legs.

Types of Spondylolisthesis

• Isthmic – Due to a defect or stress fracture in the pars interarticularis (common in younger patients)
• Degenerative – Due to age-related disc and joint degeneration (common in older adults)
• Congenital – Present from birth due to abnormal spinal development
• Traumatic – Caused by acute injury
• Pathological – Due to bone disease, infection, or tumors

Stages (Grades) of Spondylolisthesis

Spondylolisthesis is graded based on the percentage of vertebral slippage:

🔹 Grade I (Mild)

• < 25% slip
• Often asymptomatic or mild back pain
• Usually managed conservatively

🔹 Grade II (Moderate)

• 25–50% slip
• Back pain with possible leg pain
• May require injections or advanced physiotherapy

🔹 Grade III (Severe)

• 50–75% slip
• Significant pain, posture changes, nerve symptoms
• Surgical evaluation often required

🔹 Grade IV (Very Severe)

• 75–100% slip
• Marked instability and neurological compromise
• Surgery is usually necessary

🔹 Grade V (Spondyloptosis)

• Complete vertebral displacement
• Rare and severe condition
• Requires complex surgical correction