Osteoarthritis

Overview

Osteoarthritis (OA) is the most common form of arthritis. It is not simple "wear and tear". It is a disease of the whole joint: cartilage, the bone under it, ligaments, menisci, synovium and capsule all change.

Cartilage thins and cracks. The bone underneath reacts by becoming dense and growing bony spurs (osteophytes) at the joint edges. The result is a painful, stiff joint that works less well. In older people, OA of the knee and hip is a leading cause of disability.

Definition and types

• Primary OA: no underlying cause found. Often familial, especially the nodal hand form in women.
• Secondary OA: follows a known joint insult (see table below).

Risk factors

• Age and female sex (more common in women after about 55 years and around the menopause).
• Obesity: the strongest modifiable risk, mainly for knee and hand OA.
• Heredity: nodal and generalised OA run in families.
• Trauma: fractures into a joint, meniscal and cruciate tears (knee).
• Joint shape problems: hip dysplasia, hypermobility.
• Occupation and sport: farmers (hip), miners (hip, knee), repetitive sport.
• Osteoporosis is linked with a lower risk of OA.

Pathology (brief)

• Normal cartilage is mostly water with type II collagen and aggrecan (a proteoglycan).
• In OA, enzymes (matrix metalloproteinases) and cytokines (IL-1, TNF-alpha) break the matrix down faster than it is rebuilt.
• Cartilage surface fibrillates and ulcerates; exposed bone develops microfractures, cysts and sclerosis.
• New bone forms at the margins as osteophytes.
• Mild synovial inflammation is common, so flares can be warm and swollen.

Clinical features

Symptoms

• Pain on movement and weight-bearing, eased by rest (mechanical pain). Late disease may hurt at night.
• Morning stiffness lasting only minutes (usually under 30 minutes), and stiffness after inactivity ("gelling").
• Loss of function: walking, stairs, gripping.
• Usually slow onset and gradual worsening.

Signs

• Crepitus on movement.
• Bony (hard) enlargement of the joint.
• Reduced range of movement; deformity.
• Small effusion and mild warmth in flares.
• Muscle wasting (e.g. quadriceps) and instability.

Clinical patterns

Nodal hand OA

• Typical in women around the menopause, familial.
• Affects the DIP joints more than the PIP joints.
• Early phase: painful, red, swollen finger joints. This settles over months to years.
• Leaves hard bony lumps: Heberden nodes (DIP) and Bouchard nodes (PIP).
• Thumb base (first carpometacarpal) OA often coexists, giving the "squared hand" with an adducted thumb.
• Function is usually fairly well kept.

Knee OA

• Common, often bilateral, strongly linked with obesity.
• The medial compartment is affected most, giving a varus (bow-legged) deformity.
• The patellofemoral joint is often involved (pain on stairs and rising from a chair).
• A Baker (popliteal) cyst may form behind the knee; if it ruptures, calf pain and swelling mimic DVT.

Hip OA

• Pain in the groin, sometimes felt in the thigh or knee.
• Internal rotation is lost first.
• Superior-pole disease is commoner in men and often one-sided; medial disease is commoner in women with hand OA.

Other patterns

• Spine: facet joint OA and disc degeneration (spondylosis); may narrow the canal or root foramina.
• Erosive OA: rare, inflamed DIP and PIP joints with central erosions ("gull-wing" X-ray look).
• Crystal-associated OA: calcium pyrophosphate deposition, typical in the knee and wrist of elderly women.
• Generalised OA: hands plus knees, hips, first MTP and spine.

Investigations

Differential diagnosis

Also consider gout or pseudogout (acute hot joint), psoriatic arthritis (DIP joints with nail changes) and referred pain (hip pain felt in the knee).

Management

The aim is to relieve pain and keep function. Treat the patient's symptoms, not the X-ray.

1. Education and lifestyle (for everyone)

• Explain the condition; reassure that it is not always progressive.
• Weight loss if overweight: even a small loss reduces knee load and pain.
• Exercise: quadriceps and hip strengthening, land-based programmes, hydrotherapy.
• Walking stick held in the hand opposite the painful hip or knee; good footwear and insoles.

2. Drugs

• Topical NSAIDs (good for knee and hand) or oral NSAIDs/coxibs, used intermittently at the lowest effective dose.
• With an oral NSAID in older patients or those with dyspepsia, add a proton pump inhibitor.
• Paracetamol has only a small effect but is still used as a simple add-on.
• Topical capsaicin as an extra.
• Intra-articular corticosteroid for a painful flare with effusion; short-term benefit; avoid frequent repeats in one joint.
• Opioids: last resort, with care in the elderly.
• Glucosamine and chondroitin: no meaningful benefit. Hyaluronic acid injections: limited benefit.

3. Surgery

• Total hip or knee replacement (arthroplasty) for severe pain or disability despite other measures. It greatly improves pain and function.
• Main serious risks: venous thromboembolism and infection.
• Others: unicompartmental knee replacement, realignment osteotomy, joint fusion (e.g. first MTP), excision arthroplasty of the thumb base.
• Arthroscopic washout of an OA knee rarely helps.

Complications and prognosis

• Progressive pain, deformity and loss of independence.
• Falls and reduced mobility; depression.
• Drug side effects (NSAID gastric and renal damage).
• Many patients stay stable for years; X-ray changes do not always worsen.

Quick revision

• OA = whole-joint disease; cartilage loss plus bony overgrowth.
• Pain worse with use; stiffness lasts minutes.
• DIP = Heberden; PIP = Bouchard; thumb base gives the squared hand.
• X-ray: LOSS (narrowing, osteophytes, sclerosis, cysts).
• ESR, CRP, RF, ANA normal; aspirate viscous with few cells.
• Knee: medial compartment, varus deformity, Baker cyst.
• Weight loss and exercise first; topical/oral NSAIDs; steroid injection for effusion.
• Severe disease: joint replacement.

Written by The House Job from standard references (Kumar and Clark's Clinical Medicine; Apley's System of Orthopaedics and Fractures).

FAQ