What causes joint space narrowing in arthritis?

From the Guidelines

Joint space narrowing in arthritis is primarily caused by the progressive breakdown of articular cartilage that normally cushions the joints, as described in the 2020 American College of Rheumatology guideline for the management of osteoarthritis of the hand, hip, and knee 1. This process occurs through mechanical wear and tear, enzymatic degradation of cartilage matrix, and inadequate repair mechanisms in osteoarthritis. In inflammatory arthritis like rheumatoid arthritis, the synovial membrane becomes inflamed, releasing destructive enzymes and inflammatory mediators that actively erode the cartilage. Key factors contributing to joint space narrowing include:

• Mechanical wear and tear
• Enzymatic degradation of cartilage matrix
• Inadequate repair mechanisms
• Inflammation of the synovial membrane As cartilage thins, the space between bones visible on X-rays decreases, which doctors refer to as joint space narrowing. This process is often accompanied by subchondral bone changes, including sclerosis and cyst formation. Osteophytes (bone spurs) may develop at joint margins as the body attempts to stabilize the damaged joint. The loss of cartilage leads to bone-on-bone contact, causing pain, stiffness, and reduced range of motion. Joint space narrowing represents irreversible damage, which is why early intervention with appropriate medications and lifestyle modifications is crucial to slow disease progression and preserve joint function, as emphasized in the EULAR recommendations for the management of early arthritis 1. Regular monitoring of disease activity, adverse events, and comorbidities should guide decisions on choice and changes in treatment strategies to reach the target of clinical remission, as recommended in the 2017 EULAR update for the management of early arthritis 1. Non-pharmacological interventions, such as dynamic exercises and occupational therapy, should be considered as adjuncts to drug treatment in patients with early arthritis, as suggested in the 2017 EULAR update for the management of early arthritis 1. Overall, the management of arthritis should focus on slowing disease progression, preserving joint function, and improving quality of life, as outlined in the 2020 American College of Rheumatology guideline for the management of osteoarthritis of the hand, hip, and knee 1.

From the Research

Joint Space Narrowing in Arthritis

Joint space narrowing in arthritis is a complex process that involves the degradation of cartilage and the subsequent reduction of the space between joints. The main causes of joint space narrowing are:

• Inflammation, which leads to the production of enzymes that break down cartilage 2, 3
• Cartilage breakdown, which is mediated by metalloproteinases (MMPs) and other enzymes 3, 4
• Loss of cartilage thickness, which can be measured using magnetic resonance imaging (MRI) 5

Factors Contributing to Joint Space Narrowing

Several factors contribute to joint space narrowing, including:

• Grades of joint space narrowing, which are associated with specific amounts of cartilage loss 5
• Regional distribution of cartilage loss, which can vary depending on the location and severity of the disease 5
• Subchondral bone area, which can increase in advanced osteoarthritis 5
• Risk factors, such as Kellgren/Lawrence radiographic grade and diagnosis of primary osteoarthritis, which can predict a more rapid decline in joint space width 6

Mechanisms of Cartilage Breakdown

The mechanisms of cartilage breakdown in arthritis involve a complex interplay of enzymes, cytokines, and other molecules, including:

• Metalloproteinases (MMPs), which are activated by cytokines such as IL-1beta and TNFalpha 3
• Tissue inhibitors of MMPs (TIMPs), which can inhibit MMPs 3
• Signaling pathways, such as the NF-kappaB and MAP kinase pathways, which regulate the production and activation of MMPs 3