Spondylolysis (Pars Defect)

How spondylolysis develops

Spondylolysis is a type of stress fracture. Each vertebra has a pair of pars interarticularis, thin sections of bone linking the joints above and below. Repeated backward bending (extension) and twisting concentrate stress on the pars. In a growing spine, this repeated load can cause a stress reaction and then a crack. It may be on one side (unilateral) or both sides (bilateral).

Risk factors

• age 10 to 18, during growth spurts
• sports with repeated hyperextension and rotation: gymnastics, dance, figure skating, diving, football linemen, wrestling, weightlifting, cricket fast bowling, volleyball, tennis serving
• rapid increases in training intensity
• family history and some inherited bone features
• more common in boys, but frequent in female gymnasts

Spondylolysis vs spondylolisthesis

Symptoms

• aching low back pain, often on one side, sometimes spreading into the buttocks
• pain worse with arching the back, twisting, running and jumping
• pain relieved by rest
• tight hamstrings and stiffness
• in some, no symptoms at all; many adults with an old pars defect never had pain

Leg pain, numbness or weakness are uncommon in spondylolysis alone and suggest nerve root compression (sciatica) or significant slippage.

Diagnosis

• Examination: pain on standing on one leg and leaning backward (single-leg hyperextension test), tight hamstrings, and a neurological exam
• MRI: detects early stress reactions before a visible crack, without radiation; increasingly preferred in young people
• CT scan: best for showing the bony defect and healing
• X-rays: may show the defect ("Scottie dog collar" on oblique views) and any slippage, but miss early stress injuries
• SPECT bone scan: sometimes used to show active stress injury

Treatment

Rest from aggravating activity

Stopping sports and activities that cause pain, usually for 6 to 12 weeks, allows healing. Early stress reactions caught before a full crack have the best chance of bony healing.

Physical therapy

• core stabilization exercises (deep abdominal and back muscles)
• hamstring and hip flexor stretching
• pain-free flexion-based exercises initially
• gradual, sport-specific return over weeks

Bracing

A rigid or soft lumbar brace is used in some cases to limit extension and reduce pain, typically for 6 to 12 weeks, though evidence that bracing improves healing is mixed.

Pain relief

Acetaminophen or NSAIDs, following the label.

Surgery

Rarely needed. Considered for persistent pain after 6 to 12 months of non-surgical treatment, progressive slippage, or neurological symptoms. Options include direct repair of the pars defect in young people or spinal fusion for significant spondylolisthesis.

Return to sport

Most athletes return to their sport within 3 to 6 months once they are pain-free, have full movement and strength, and can perform sport-specific movements without pain. A fibrous (non-bony) union is common and is often pain-free.

Outlook

Most young people with spondylolysis do well with non-surgical treatment. Some with bilateral defects develop slippage over time, so follow-up X-rays may be done during growth.

Frequently asked questions

What is spondylolysis?

Spondylolysis is a stress fracture in a small part of the back of a vertebra called the pars interarticularis, usually in the lowest lumbar vertebra. It is common in teenagers who play sports involving repeated backward bending and twisting.

What are the symptoms of spondylolysis?

The main symptom is low back pain that is worse with arching the back, twisting or playing sport, and improves with rest. Tight hamstrings are common. Some people have no symptoms at all.

Can spondylolysis heal?

Yes, especially when caught early as a stress reaction. With rest from sport and physical therapy, many fractures heal with bone. Others heal with fibrous tissue but become pain-free and stable, allowing a full return to activity.

How long does it take to recover from spondylolysis?

Most young athletes return to sport within 3 to 6 months. The timeline depends on how early it was diagnosed, whether the fracture heals, and how quickly pain-free movement, strength and core control return.