Spondylolysis and spondylolisthesis are conditions affecting the facet joints that align the vertebrae one on top of the other. Spondylolysis is a weakness or stress fracture in the facet joint area. This weakness can cause the bones to slip forward out of normal position, called spondylolisthesis, and kink the spinal nerves. Treatment options include physical therapy to strengthen the muscles. A back brace may be used to support the spine. In some cases, surgery can realign and fuse the bones.

Anatomy of the facet joints

Your spine is made of 24 moveable bones called vertebrae that provide the main support for your body, allowing you to bend and twist. Each of the vertebrae are separated and cushioned by a gel-like disc, keeping them from rubbing together. The vertebrae are connected and held to each other by ligaments and joints, called facet joints (see Anatomy of the Spine).
The upper facet joint and the lower facet joint are connected by a narrow bridge of bone called the pars interarticularis (Fig. 1). The inferior facet of one vertebra fits perfectly into the superior facet of the one below it – overlapping like shingles – beginning with the vertebra at the base of your skull and ending at your tailbone.
Figure 1. The superior and inferior facets articulate together to form a facet joint. Each vertebra has two facet joints, one pair that connects to the vertebra above (superior facets) and one pair that connects to the vertebra below (inferior facets). The thin bridge of bone between the superior and inferior facets is called the pars interarticularis.

What are spondylolysis and spondylolisthesis?

Spondylolysis (spon-dee-low-lye-sis) and spondylolisthesis (spon-dee-low-lis-thee-sis) are separate, yet related conditions. Spondylolysis usually comes first, though not always. The term comes from "spondylo," which means spine, and "lysis," which means to divide. Spondylolysis is a breakdown or fracture of the narrow bridge between the upper and lower facets, called the pars interarticularis. It can occur on one side (unilateral) or both sides (bilateral) and at any level of the spine, but most often at the fourth or fifth lumbar vertebra (Fig. 2). If spondylolysis is present, then you have the potential to develop spondylolisthesis.The more common type of spondylolisthesis is due to a degenerative process. This occurs at the fourth and fifth lumbar vertebra, most commonly. This is usually associated with narrowing of the spinal canal and compression of the nerves.
Figure 2. Spondylolysis is a breakdown or fracture of the pars interarticularis.
Spondylolisthesis is the slipping forward of the vertebral bone. The term "listhesis" means to slip forward (Fig. 3). It occurs when the weakened pars interarticularis separates and allows the vertebra to move forward out of position causing pinched nerves and pain. Spondylolisthesis usually occurs between the fourth and fifth lumber vertebra or at the last lumbar vertebra and the sacrum. This is where your spine curves into its most pronounced "S" shape and where the stress is heaviest.

Slippage is measured on a scale from grade 1 slippage (25%) to grade 4 (100%). The more the lower back curves in (swayback or lordosis), the steeper the grade.

What are the symptoms?

Mild cases of spondylolysis and spondylolisthesis usually cause minimal pain. In fact, the conditions are often found by accident when a person has an X-ray of the back for an unrelated reason.
When spondylolysis and spondylolisthesis do cause pain, you may experience low back pain, stiffness, and muscle spasms. You may also have sciatica (pain radiating down one or both legs), or numbness, though this is not common. Leg pain will usually be worse when you stand or walk.
You may have very subtle symptoms,like tightness in your hamstrings or find that you can no longer touch your toes, but not feel any nerve pain.

The degenerative slip usually manifests as difficulty in walking, which progressively increases with time. You may find that walking a certain distance brings about heaviness, tingling or pain in one/both buttocks/lower limbs. When you sit down, the symptoms get relieved, but are brought on by walking again. this type of pain is termed as "neurogenic claudication”.

How is a diagnosis made?

When you first have pain, consult your doctor. He will take a complete medical history to understand your symptoms, any prior injuries or conditions, and determine if any lifestyle habits are causing the pain. Next a physical exam is performed to determine the source of the pain and test for muscle weakness or numbness.
X-rays view the bony vertebrae in your spine and can tell your doctor if any of them are too close together or whether you have arthritic changes, bone spurs, fractures, or any slippage of the vertebrae.

An MRI is ordered to confirm the clinical findings and also to scan for any anomalies.

What is the treatment?

Usually lytic slips are treated with pain killers, activity modifications, wearing braces and ergonomic changes. If leg pain is the main issue, nerve root injections may be given for pain relief. if all non-operative measure fail, surgery in the form of spinalfusion may be recommended. In cases of degenerative slips, limited rest, pain-killers and exercise usually help. but in cases where this does not work, surgery is offered the surgery entails decompressing the nerves with/without spinal fusion.