Osteoarthritis

 

• Pathophysiology

  • Can be primary (aka idiopathic), which is localised or generalised, or secondary, which is usually localised. Nodal OA is a primary OA involving the hands.
  • Traditionally considered a mechanical problem, although likely that there is some inflammatory component, especially in primary OA.
  • Initially involves thinning of the hyaline cartilage, until the underlying bone is exposed and becomes damaged due to direct stress.

• Signs and symptoms

  Primary nodal OA:

  • Tender, swollen joints with reduced movement.
  • Typically affects the DIPs, thumb carpometacarpal (CMC) joint, and knees.
  • Muscle wasting.
  • Squaring of hand due to thumb adduction and bony swelling at CMC.
  • Heberden's nodes at the DIP, and Bouchard's nodes at the PIP.

  Secondary OA:

  • Typically affects the knee, hip, or spine.
  • Painful joint, exacerbated by movement and worse in the evening.
  • Joint gelling – stiffness after resting – and instability.
  • Hip OA typically radiates to the groin and buttocks. Spinal OA may compress a nerve and radiate down the leg.

• Risk factors

  Age >50 years.

  Nodal OA:

  • Post-menopausal women.
  • Family history.

  Secondary:

  • Mechanical strain from obesity, trauma, or employment.
  • Joint disease: inflammatory arthritides, CPPD.
  • Haemochromatosis
  • Osteoporosis reduces the risk.

• Investigations

  Diagnosis can be clinical – especially if patient >45 years old – and doesn't require radiological evidence.

  However, X-rays can help rule out other conditions and are needed in younger patients or atypical histories. In osteoarthritis, may see LOSS:

  • Loss of joint space (asymmetrical), reflecting thinning of the cartilage.
  • Osteophytes, reflecting proliferation and ossification of cartilage in unstressed areas.
  • Subchondral sclerosis.
  • Subchondral cysts, reflecting fluid-filled microfractures.

  Bloods:

  • CRP/ESR to rule out inflammatory cause.

• Management

  Lifestyle and physical therapy:

  • Exercise to improve strength and joint stability.
  • Reduce weight.
  • Walking aids.
  • Physio

  Pharmacological:

  • Regular paracetamol ± topical NSAID gel (knee or hands only), then move up the pain ladder if needed. Paracetamol is traditionally preferred for long-term use over NSAIDs as it's safer, but recent research question its efficacy.
  • If adding/switching to NSAID PO (standard or coxib), stop topical NSAID and give PPI. Unlike paracetamol, there is good evidence of efficacy.
  • Further options: intra-articular steroid injections, topical capsaicin for hand or knee OA.
  • Glucosamine and chondroitin are not recommended.

  Non-pharmacological:

  • TENS, joint support.

  Surgical:

  • Joint replacement.

• Total joint replacement

  Background

  • Usually hip (THR) or knee (TKR), but other joints possible.
  • Commonly used in OA, but can also be used for inflammatory arthritides.

  Indications

  • Severe functional impairment
  • Severe sleep impairment.
  • Severe radiological changes.
  • Resistant to medical treatment.

  Contraindications

  • Severe, widespread disease i.e. is it worth fixing just this 1 joint?
  • Severe CV disease.
  • Systemic or skin infection.
  • TKR-specific: PVD.
  • THR-specific: neuropathic hip, non-ambulator.

  Prosthesis material

  Hip:

  • Metal acetabulum – which may have a metal, polyethylene, or ceramic coating – articulating with a metal or ceramic head.
  • May be fixed in place with an antibiotic-containing bone cement.

  Knee:

  • Two metal parts, with polyethylene articular surface.

  Post-op management

  • Movement and weight-bearing as soon as possible, usually starting the next day.
  • Discharge usually within 3 days, with DVT prophylaxis for 2 weeks for knee and 4 weeks for hip.

  Outcomes

  • Hip: 95% last 10 years, 70% last 20 years.
  • Knee: similar, if not better.
  • High rates of patient satisfaction, but takes 6 weeks until improvement felt, with continued improvement over 1 year.

  Complications

  General:

  • Infection, so give prophylactic antibiotics. Deep infection will usually require revision.
  • Ongoing pain or stiffness.
  • DVT is relatively common, but usually asymptomatic and risk substantially reduced by anticoagulation. PE risk is <1%.
  • Periprosthetic fracture.
  • Other medical complications: MI, pneumonia, death (1/500).

  Hip:

  • Dislocation
  • Leg-length discrepancy: minimized with correct operative procedure. Shoe raise can be used to compensate.
  • Nerve injury: sciatic nerve, causing foot drop, or superior gluteal nerve, causing weak abductors and Trendelenburg gait.

  Knee:

  • Peroneal nerve injury.

  Surgical alternatives

  • Arthroscopy, which is rarely effective.
  • Osteotomy to re-align joint surfaces if deformed e.g. valgus deformity.
  • Joint fusion (arthrodesis): considered if there is high infection risk and/or joint mobility is not required.
  • Partial joint replacement.