Degenerative Disc Disease

Degenerative disc disease is a spectrum of age related and load related structural change within the intervertebral disc, ranging from asymptomatic desiccation to herniation, endplate disease and secondary stenosis. It is the most frequent structural finding in patients with neck and low back pain.

Pathophysiology

• Loss of proteoglycan and water in the nucleus pulposus leads to desiccation and reduced disc height.
• Annular fissures develop, allowing nuclear material to herniate and nociceptive nerve fibres to grow into the inner annulus.
• Inflammatory cytokines (TNF alpha, IL-1 beta, IL-6) and phospholipase A2 sensitise nerve roots.
• Loss of height increases facet joint loading, producing facet arthropathy, osteophytes, ligamentum flavum buckling and eventually canal or foraminal stenosis.
• Vascular insufficiency of the cartilage endplate impairs nutrient diffusion.

Risk factors include age, genetic predisposition (heritability above 50% in twin studies), smoking, obesity, repetitive heavy lifting, whole body vibration and previous injury.

Epidemiology and imaging

• Degeneration on MRI is present in about 40% of asymptomatic adults at age 40 and in most people by age 60.
• The most affected levels are L4 to L5 and L5 to S1 in the lumbar spine, and C5 to C6 and C6 to C7 in the cervical spine.
• Pfirrmann grading (I to V) describes signal intensity and height loss on T2 sequences.
• Modic changes describe endplate marrow signal: type 1 is oedema (T1 low, T2 high) and associated with pain, type 2 is fatty replacement, and type 3 is sclerosis.

The natural history of acute radiculopathy is favourable. About 70 to 90% of lumbar radicular pain resolves within 6 to 12 weeks, and herniated fragments frequently regress.

Discogenic axial pain

• Deep, central, poorly localised low back or neck pain, aggravated by sitting, flexion, Valsalva, lifting and prolonged static posture.
• Referred pain into the buttock, thigh or shoulder girdle, without neurological deficit.
• Morning stiffness lasting under 30 minutes. Episodes recur and fluctuate.

Lumbar radiculopathy

• L4: anterior thigh and medial leg pain, weak quadriceps, reduced knee jerk.
• L5: lateral leg and dorsum of foot pain, weak ankle dorsiflexion and great toe extension, foot drop. Reflexes preserved.
• S1: posterior leg and lateral foot pain, weak plantarflexion and eversion, reduced ankle jerk.
• Straight leg raise reproducing leg pain between 30 and 70 degrees is sensitive but not specific. A crossed straight leg raise is highly specific.

Cervical radiculopathy

• C6 and C7 roots are most often involved. Neck, scapular and arm pain with dermatomal paraesthesias, weakness of elbow flexion or extension, and reduced biceps or triceps reflexes.
• Spurling test reproduces radicular pain with ipsilateral extension and rotation with axial load.

Cervical myelopathy

• Hand clumsiness, gait imbalance, Hoffmann sign, hyperreflexia and clonus.

Red flags requiring urgent evaluation

• Cauda equina syndrome: saddle numbness, urinary retention or incontinence, bowel dysfunction, bilateral leg weakness.
• Progressive motor deficit.
• Fever, weight loss, cancer history, intravenous drug use, immunosuppression, night pain, or major trauma suggesting infection, tumour or fracture.

Diagnosis is clinical. Most patients with non-specific symptoms and no red flags need no imaging in the first 6 weeks, because findings are common in asymptomatic people and rarely change management.

Indications for imaging

• Red flags.
• Persistent radicular symptoms beyond 6 weeks when intervention is considered.
• Progressive or severe neurological deficit.
• Suspected myelopathy.

Investigations

• MRI (T1, T2 sagittal and axial, STIR if infection or fracture is a concern) is the preferred study. Findings must be correlated with the clinical root distribution.
• Plain radiographs, including standing flexion and extension views, for instability, spondylolisthesis, deformity and facet disease.
• CT when MRI is contraindicated or bony detail is required.
• EMG and nerve conduction studies at 3 weeks or more after onset when the clinical picture is unclear or to exclude peripheral neuropathy and plexopathy.
• Blood tests (CBC, ESR, CRP, calcium, alkaline phosphatase, protein electrophoresis) when infection, myeloma or metastatic disease is suspected.
• Discography is not recommended because of poor specificity and accelerated degeneration of punctured discs.

First line, all patients

• Reassurance, education on the favourable natural history, and encouragement to stay active. Bed rest beyond 1 to 2 days is harmful.
• Supervised physiotherapy and graded exercise, with core stabilisation, extension or flexion directional preference exercises, and aerobic activity.
• Heat. Spinal manipulation or acupuncture can give modest short term relief.
• Weight loss and smoking cessation.

Drug therapy

• Paracetamol has little efficacy for axial pain but can be used at 1 g up to four times daily.
• NSAIDs: naproxen 500 mg twice daily, ibuprofen 400 to 600 mg three times daily, or celecoxib 200 mg daily, for the shortest effective course with gastric protection.
• Muscle relaxant for acute spasm: cyclobenzaprine 5 to 10 mg three times daily, or tizanidine 2 to 4 mg three times daily, for no more than 1 to 2 weeks.
• Chronic axial pain: duloxetine 30 mg daily increased to 60 mg after a week.
• Radicular pain: short oral prednisolone course (for example 30 to 50 mg daily for 5 to 7 days) may give brief improvement. Gabapentin 300 mg at night titrated to 1800 mg/day or pregabalin 75 to 150 mg twice daily can be tried, with limited benefit shown in sciatica.
• Opioids only for short term severe pain (tramadol 50 mg every 6 hours as an example). Avoid long term use.

Interventional treatment

• Epidural steroid injection for radicular pain persisting beyond 4 to 6 weeks: transforaminal, interlaminar or caudal, using dexamethasone 10 mg (non-particulate steroid preferred for cervical and transforaminal routes to reduce embolic infarction risk) or triamcinolone 40 mg or methylprednisolone 40 to 80 mg for lumbar interlaminar injections. Benefit is short term (2 to 6 weeks), and a maximum of three to four injections per year is typical.
• Medial branch blocks followed by radiofrequency ablation for facet mediated pain.
• Intradiscal procedures and basivertebral nerve ablation (for Modic type 1 and 2 change with chronic axial pain) are selective options with limited evidence.

Surgery

• Cauda equina syndrome: decompression within 24 hours.
• Radiculopathy with severe or progressive motor deficit, or disabling pain persisting 6 to 12 weeks despite conservative care: microdiscectomy (lumbar), or anterior cervical discectomy and fusion or cervical disc arthroplasty (cervical). Early surgery speeds recovery, but long term outcomes equal those of conservative care.
• Cervical myelopathy: decompression, through anterior or posterior approaches depending on levels and alignment.
• Axial discogenic back pain: lumbar fusion or disc replacement offers modest benefit over structured rehabilitation and is considered only after failure of a full non-operative programme and with concordant single level disease.
• Perioperative cefazolin 2 g IV before incision.

Chronic pain and follow-up

• Cognitive behavioural therapy and graded activity for persistent pain, with early psychosocial assessment. Recurrence is common, so a long term exercise plan matters.