Surgical Management for a Case of Baastrup's Disease With Concomitant Multiple Lumbar Spondylolysis and Epidural Cyst.

Baastrup's disease is a degenerative condition characterized by the close approximation of adjacent spinous processes. Interspinous bursal cysts may extend into the epidural space, resulting in symptomatic central canal stenosis. Lumbar multiple spondylolysis, characterized by defects in more than one lumbar lamina, is a rare condition often associated with trauma or repetitive stress. This case report presents a 56-year-old male plumber who presented with low back pain and bilateral leg numbness. He had intermittent claudication at 500 m. Imaging revealed L4 spondylolytic spondylolisthesis, L5 spondylolysis, and Baastrup's disease at L3-L4 with an extradural cyst. He underwent L4-L5 posterior lumbar interbody fusion with cyst resection and direct repair of the L5 pars defect using a lamina hook system. Histopathology confirmed a synovial cyst. Symptoms resolved postoperatively, and he regained full mobility. At two years, imaging showed solid L4-L5 fusion with preserved L5-S1 motion. This case highlights the importance of limited fusion to avoid excessive segmental immobilization, with a combined fixation approach providing symptom relief and spinal stability.