A 52-year-old man presents with progressive lower back pain and bilateral leg claudication that worsens with walking and improves with sitting. Imaging shows degenerative disc disease at L4–L5 with facet joint hypertrophy and ligamentum flavum thickening. Neurological examination reveals diminished ankle reflexes bilaterally and mild weakness in foot dorsiflexion. Which of the following best explains the mechanism of neurological deficit in this patient?