Osteoarthritis: causes, symptoms and solutions for pain relief

Osteoarthritis is the most common joint disease. It primarily affects the knees, hips, hands, and spine and can progressively limit daily movements and activities. However, contrary to a still widespread belief, osteoarthritis is not simply a joint that "wears out" with age.

Osteoarthritis is a disease of the entire joint, combining changes in the cartilage, the underlying bone, the synovial membrane, and the tissues surrounding the joint. Its causes are multiple, and its progression varies greatly from one person to another.

Understanding how it works makes it easier to distinguish what favors its onset, what causes the pain, and the solutions that can actually help relieve it.

What exactly is osteoarthritis?

Osteoarthritis is a chronic disease that progressively affects all the structures of a joint. It is characterized in particular by:

• Changes and degradation of the articular cartilage;

• Changes in the bone located under the cartilage (subchondral bone);

• An inflammatory reaction of the synovial membrane;

• The possible appearance of osteophytes (bone spurs);

• Changes in the surrounding ligaments, tendons, and muscles.

Osteoarthritis can affect virtually any joint, but the knees, hips, hands, and spine are the most frequently affected.

According to the World Health Organization (WHO), approximately 528 million people were living with osteoarthritis worldwide in 2019, an increase of 113% compared to 1990. About 73% of those affected were over 55 years old, and 60% were women.

Osteoarthritis is not, however, an inevitable consequence of aging. It can appear in younger people, particularly after a joint injury or in the presence of certain risk factors.

Why is cartilage important?

To understand osteoarthritis, one must first understand the role of cartilage.

Articular cartilage covers the ends of the bones. Its particularly smooth surface and mechanical properties allow it to support and distribute the stresses exerted during movement. It works in tandem with the synovial fluid, produced by the synovial membrane, which lubricates the joint.

Cartilage contains, in particular:

• Water;

• Collagen (mainly type II);

• Proteoglycans;

• Chondrocytes (the specialized cells that maintain its matrix).

Articular cartilage is a tissue with very little vascularization, possessing a limited capacity for spontaneous repair. When degradation mechanisms exceed maintenance and repair capacities, its structure and mechanical properties progressively deteriorate.

A global disease of the joint

The expression "cartilage wear" is convenient for explaining the disease simply, but it does not completely describe the biological reality. Research published in Nature considers osteoarthritis as an impairment of the entire osteochondral unit.

The cartilage, subchondral bone, synovial membrane, ligaments, tendons, and muscles constantly interact with one another. Changes in one tissue directly influence the others:

• Cartilage: progressive loss of its structure and shock-absorbing properties.

• Subchondral bone: remodeling, bone condensation, and changes in its structure.

• Synovial membrane: possible local inflammation (synovitis).

• Joint edges: formation of osteophytes.

• Muscles and tendons: loss of strength, stiffness, and alteration of joint function.

Osteoarthritis results from a complex imbalance between mechanical stresses, biological processes, and the adaptation capacities of the tissues.

What happens in an osteoarthritic joint?

1. The cartilage degrades

Chondrocytes normally attempt to maintain the balance of the cartilage matrix. In osteoarthritis, this balance is broken: enzymes degrade the matrix faster than the cells can repair it. This progression varies considerably from one person to another, as noted by the work of Inserm.

2. The subchondral bone transforms

The bone located under the cartilage actively participates in transmitting loads. In osteoarthritis, its abnormal remodeling plays a key role in the progression of the disease and in the genesis of pain.

3. The synovial membrane becomes inflamed

Lining the inside of the joint, the synovial membrane can present with an inflammation called synovitis. It is accompanied by swelling, increased pain, and worsening symptoms. Osteoarthritis is therefore not a strictly "non-inflammatory" disease.

4. Osteophytes appear

The joint sometimes produces bone growths on its edges. Visible on X-rays, these osteophytes do not systematically trigger pain.

Why does osteoarthritis hurt?

Cartilage itself does not contain nerve fibers: it is therefore incapable of directly transmitting a painful sensation. The pain actually comes from the surrounding structures:

• The subchondral bone;

• The inflamed synovial membrane;

• The ligaments and the joint capsule;

• Muscles and tendons subjected to abnormal tensions.

This is why the pain felt does not necessarily correspond to the intensity of the abnormalities visible on an X-ray. A person can have severe radiological osteoarthritis without major pain, while another will suffer intensely with minimal lesions on imaging.

Common misconceptions vs. Scientific reality

What are the main causes and risk factors?

Osteoarthritis is multifactorial:

1. Age: The risk increases over time, but osteoarthritis is not a fatality of aging.

2. Joint trauma: Fractures, severe sprains, meniscal lesions, or sports injuries (post-traumatic osteoarthritis).

3. Overweight and obesity: Increases mechanical stress on weight-bearing joints and generates metabolic inflammatory factors (WHO).

4. Repeated mechanical stress: Carrying heavy loads or repeated movements in a professional or sports setting.

5. Genetics: Particularly influential in osteoarthritis of the hands.

6. Metabolic factors: Diabetes and metabolic syndrome increase the risk of joint impairment.

Symptoms and manifestations by joint

The main symptoms combine exertional pain, short morning stiffness (often less than 30 minutes), loss of mobility, and sometimes cracking or swelling.

• Knee (gonarthrosis): Pain when walking, using stairs, or moving from a seated to a standing position.

• Hip (coxarthrosis): Pain in the groin crease or buttock, hindering walking and putting on shoes.

• Hands: Impairment of the fingers or the base of the thumb (rhizarthrosis), leading to deformities and stiffness.

• Spine: Frequent but very often asymptomatic; imaging alone is not enough to diagnose the cause of back pain.

How to establish a diagnosis?

According to the clinical guidelines from NICE, the diagnosis of osteoarthritis is primarily clinical in people aged 45 and over presenting with activity-related pain and morning stiffness absent or lasting less than 30 minutes.

X-rays are useful in case of doubt or to exclude other pathologies. They can show narrowing of the joint space, osteophytes, or condensation of the subchondral bone.

How to effectively relieve osteoarthritis?

While there is no treatment to cure osteoarthritis or regrow cartilage, management can significantly improve symptoms and quality of life.

       ┌────────────────────────────────────────────────────────┐
       │   1. Adapted physical activity & Strengthening         │
       │   2. Weight management & Lifestyle                     │
       │   3. Physical therapy & Patient education              │
       └──────────────────────────┬─────────────────────────────┘
                                  │
                   (If relief is insufficient)
                                  ▼
       ┌────────────────────────────────────────────────────────┐
       │   4. Targeted analgesic treatments (topical NSAIDs)    │
       │   5. Local injections (corticosteroids)                │
       │   6. Assistive devices & Orthoses                      │
       └──────────────────────────┬─────────────────────────────┘
                                  │
                    (As a last resort / Severe stage)
                                  ▼
       ┌────────────────────────────────────────────────────────┐
       │   7. Surgery (Joint replacement)                       │
       └────────────────────────────────────────────────────────┘

1. Adapted physical activity (APA)

Proposed as a first-line treatment by the French National Authority for Health (HAS), physical activity combines muscle strengthening, stretching, proprioception, and endurance (walking, cycling, swimming). Movement nourishes cartilage and strengthens protective muscles.

2. Weight management

For individuals who are overweight, a 5 to 10% loss in body weight significantly reduces pain and pressure on the knees and hips (NICE).

3. Physical therapy (Physiotherapy)

Helps maintain joint mobility, strengthen muscle groups, and relearn how to move without apprehension. Sara, a physical therapist, has integrated Niuk into her tools for treating her patients.

4. Heat and cold therapy

Heat relaxes muscle tension and decreases stiffness. Cold relieves painful flare-ups accompanied by inflammation or swelling. The Niuk Santé cold therapy roll-on has demonstrated its effectiveness through an observational study conducted with 170 patients in physical therapy clinics.

5. Medications

Non-steroidal anti-inflammatory drugs (NSAIDs) in topical gel form are preferred as a first-line treatment. Oral NSAIDs or analgesics should be used at the lowest effective dose for the shortest duration possible.

6. Injections and surgery

A corticosteroid injection can provide temporary relief during an acute flare-up. In cases of severe damage resistant to other treatments, joint replacement surgery (hip, knee) offers excellent functional results.

When should you seek urgent medical attention?

See a doctor promptly if the pain:

• Occurs suddenly or follows a significant injury;

• Is accompanied by major swelling, or a red or hot joint;

• Is associated with fever;

• Results in a total inability to bear weight on the limb;

• Becomes intensely painful at night or at rest in an unusual way.

Frequently asked questions

Scientific sources and references

• World Health Organization (WHO): Osteoarthritis fact sheet, WHO.

• French National Authority for Health (HAS): Physical activity prescription guide – Peripheral osteoarthritis, HAS.

• Inserm: Information file and research status on osteoarthritis, Inserm.

• NICE (National Institute for Health and Care Excellence): Osteoarthritis in over 16s: diagnosis and management (NG226), NICE.

• Nature Reviews Rheumatology: Goldring MB, Goldring SR. Changes in the osteochondral unit during osteoarthritis, Nature, 2016.

• French Health Insurance (Ameli): Understanding and treating knee osteoarthritis, Ameli.fr.