Subacute Annular Tear at S1: Anatomy, Symptoms, and Management

A subacute annular tear at the L5–S1 disc involves disruption of the outer annulus fibrosus (3–12 weeks post-injury). The S1 vertebra forms the lumbosacral junction.

Mechanism

Axial loading + flexion/rotation (lifting, twisting) → annular fiber failure. Nucleus pulposus may irritate sinuvertebral nerve or compress S1 root.

Clinical Features

• Low back pain ± radiation to buttock/posterior thigh (S1 dermatome).
• Aggravated by sitting, bending, Valsalva.
• Possible S1 radiculopathy: lateral foot numbness, weak plantar flexion, absent ankle jerk.

Diagnosis

MRI (high-intensity zone on T2, contrast enhancement). CT/discography if surgical planning.

Treatment

• Conservative (first-line): Activity modification (avoid flexion/load), NSAIDs, physical therapy (McKenzie, core stabilization), epidural steroid injection if radicular.
• Surgical: Discectomy/annuloplasty if refractory >6–12 weeks with concordant imaging and disabling symptoms.

Prevention

Core strengthening, hip-hinge lifting, ergonomic posture, smoking cessation (nicotine impairs disc nutrition).