Osteoarthritis of the knee

Osteoarthritis of the knee is very common and is a major cause of morbidity, especially in the older population. 

Radiographic features

The hallmarks of knee osteoarthritis are the same for most other joints:

• joint space narrowing: usually asymmetric, typically of the medial tibiofemoral compartment and/or patellofemoral compartment ³
• subchondral sclerosis
• osteophyte formation: patellofemoral osteophytes are more associated with pain ³

Radiograph

Plain radiographs are the workhorse of imaging including follow-up, although there is a poor correlation between radiographic findings and clinical symptoms ^1,2. 

Grading

• Ahlbäck classification system
• Kellgren and Lawrence system

MRI

The following features are seen additionally on MRI ¹:

• synovial thickening
• bone marrow oedema
• cartilaginous defects (partial or complete)
• bursitis
• iliotibial band syndrome

Treatment and prognosis

Often the patient will proceed to total knee joint replacement (arthroplasty). In younger patients with unicompartmental symptoms, a high tibial osteotomy may be performed. 

Differential diagnosis

Other causes of degenerative joint disease, for example:

• CPPD
• haemophilic arthropathy
• osteochondritis dissecans