The intervertebral disc is a fibrocartilaginous structure between adjacent vertebral bodies consisting of a gelatinous nucleus pulposus centrally surrounded by concentric lamellae of collagen fibres in the annulus fibrosus. It allows limited movement between adjacent vertebrae while absorbing compressive loads on the spine. With age and loading the nucleus pulposus dehydrates and the annulus develops fissures, predisposing to herniation and contributing to the spectrum of degenerative disc disease.
Intervertebral disc herniation occurs when nucleus pulposus material escapes through a defect in the annulus fibrosus and compresses adjacent nerve roots, producing radiculopathy with dermatomal pain, paraesthesia, and neurological deficit. The L4 to L5 and L5 to S1 discs are most commonly herniated. The straight leg raise test stretches the L5 and S1 nerve roots and is positive when leg pain is reproduced below the knee at less than 60 degrees of hip flexion. Conservative management resolves most disc herniations, with surgical discectomy reserved for significant neurological deficit or failure of conservative care.
Nucleus pulposus extrusion through an annular defect compressing nerve roots and producing radiculopathy with dermatomal leg pain, reproduced by the straight leg raise test and managed with physiotherapy and selective nerve root blocks before surgery.
Age-related disc dehydration and annular degeneration producing axial back pain, reduced spinal segment height, and predisposition to herniation, managed with exercise, manual therapy, and pain management.
