26th January 2024

Background

Epidemiology

Osteoarthritis (OA) is the most common form of joint disease, and is thought to be a leading cause for pain and disability worldwide. It has an estimated overall prevalence of 24% and 11% for knee and hip OA respectively, in the general adult population.

Pathophysiology 

OA is a clinical syndrome characterised by joint pain, which causes varying degrees of functional limitation and a reduced quality of life. It is a disorder of synovial joints, which occurs when joint damage caused by repeated excessive loading or injury triggers a repair process, culminating in structural changes to the joint. These structural changes can lead to characteristic features of OA, including localised loss of cartilage, remodelling of adjacent bone and formation of osteophytes, and inflammation of the synovial membranes. Periarticular damage can also lead to capsular stretching, muscle weakness and ligament laxity. Any synovial joint can be affected, but the most commonly affected peripheral joints are the knees, followed by hips and small joints of the hands.

Causes and risk factors 

The exact cause of OA is unknown, but it is thought to result from an interaction between genetic, biological and biomechanical factors. Heritability of hand, hip and knee OA is estimated at around 40-60%. Increasing age is the strongest risk factor for developing OA, particularly after the age of 50 years, and is more common in females than in men. Other risk factors include obesity, high bone mineral density and low oestrogen levels. Biomechanical factors such as joint injury, occupational and recreational joint stresses, articular congenital deformities, history of inflammatory arthropathy, joint laxity and reduced muscle strength can all contribute to an increased risk in the development of OA.

Definitions 

OA can be classified as either primary or secondary:

• Primary (idiopathic): no history of preceding joint injury
  • Localised: affecting hands, knee, hip or foot
  • Generalised: affecting hands and another joint
• Secondary: occurs following a pre-existing insult to the joint, e.g. congenital abnormality, trauma, inflammatory arthropathies, repetitive physical or occupational strain.

References 

• Pereira D, Peleteiro B, Araujo J, et al. The effect of osteoarthritis definition on prevalence and incidence estimates: a systematic review. Osteoarthritis Cartilage 2011;19:1270–85.
• Conaghan PG, Dickson J, Grant RL. Care and management of osteoarthritis in adults: summary of NICE guidance. Bmj. 2008 Feb 28;336(7642):502-3.
• National Institute for Health and Care Excellence (Great Britain).Osteoarthritis: care and management. National Institute for Health and Care Excellence (NICE); 2014