Osteoarthritis in Dogs Isn't Just "Wear and Tear"—Here's What We Now Know

By Steve Mehler, DVM, DACVS

For years, veterinarians described osteoarthritis (OA) as a simple consequence of aging: joints wore out like the tread on an old tire. The cartilage gradually disappeared, bones rubbed together, and pain followed.

It was a convenient explanation.

It also turns out to be incomplete.

Today, we know osteoarthritis is not simply a disease of mechanical wear and tear. It is a complex, active disease involving inflammation, changes in joint biology, and failure of the joint's normal repair mechanisms. This shift in understanding has completely changed how we think about preventing and treating arthritis in dogs.

The Old Theory: Like Worn-Out Tires

The traditional explanation made intuitive sense.

Imagine driving the same car for 200,000 miles. Eventually the tires wear down. Similarly, if a dog runs, jumps, and walks for years, the cartilage eventually "wears out."

But if that were true, every active dog would develop severe arthritis.

They don't.

Some working Border Collies remain remarkably mobile into old age, while a young Labrador with a cranial cruciate ligament tear may develop arthritis within months.

Something more is happening.

Osteoarthritis Is an Active Disease

Healthy joints are surprisingly dynamic.

Cartilage isn't an inert cushion—it is living tissue that is constantly being remodeled.

Specialized cells called chondrocytes continuously balance:

• Building new cartilage

• Breaking down old cartilage

• Repairing microscopic damage

In a healthy joint, these processes remain in balance.

In osteoarthritis, that balance is lost.

Instead of simply wearing away, the joint begins producing inflammatory chemicals that accelerate cartilage destruction faster than it can be repaired.

The Whole Joint Becomes Diseased

One of the biggest advances in arthritis research is the realization that OA is a whole-joint disease.

It's not just cartilage.

The disease affects:

• Cartilage

• Bone beneath the cartilage (subchondral bone)

• Joint capsule

• Synovial membrane

• Ligaments

• Menisci

• Muscles surrounding the joint

Every tissue begins influencing the others.

That is why osteoarthritis often continues progressing even after the original injury has healed.

Inflammation Drives the Disease

Many owners think inflammation only occurs immediately after an injury.

In reality, chronic low-grade inflammation can persist for years inside an arthritic joint.

Cells release inflammatory mediators such as:

• Interleukin-1 (IL-1)

• Tumor necrosis factor alpha (TNF-α)

• Interleukin-6 (IL-6)

• Prostaglandins

• Matrix metalloproteinases (MMPs)

These molecules:

• Damage cartilage

• Increase pain sensitivity

• Stimulate further inflammation

• Prevent normal cartilage repair

It's a vicious cycle.

Cartilage Doesn't Have Nerves…

One surprising fact:

Cartilage itself has no nerves.

So why does arthritis hurt?

Pain comes from other tissues, including:

• Inflamed synovium

• Thickened joint capsule

• Stretched ligaments

• Bone marrow lesions

• Subchondral bone remodeling

• Surrounding muscles

This explains why two dogs with identical X-rays can have completely different levels of pain.

Radiographs tell only part of the story.

Injury Can Start the Process

Many cases of canine osteoarthritis begin with an orthopedic problem rather than simple aging.

Common triggers include:

• Cranial cruciate ligament tears

• Hip dysplasia

• Elbow dysplasia

• Patellar luxation

• Osteochondritis dissecans (OCD)

• Previous fractures involving joints

Even after successful surgery, inflammatory pathways may remain activated, allowing arthritis to continue progressing over time.

Why Weight Matters More Than You Think

Many people assume excess weight simply puts more force on joints.

That's true—but it's only part of the story.

Fat tissue is biologically active.

It produces inflammatory hormones known as adipokines, including:

• Leptin

• Adiponectin

• Resistin

These substances can increase joint inflammation throughout the body.

This helps explain why weight loss often improves arthritis more than expected from reduced mechanical stress alone.

Arthritis Changes the Nervous System Too

Chronic pain doesn't remain confined to the joint.

Over time, the nervous system itself becomes more sensitive—a process called central sensitization.

The spinal cord and brain amplify pain signals.

As a result:

• Dogs may react to smaller amounts of pain.

• Pain can persist even after inflammation improves.

• Early treatment becomes increasingly important.

This is one reason veterinarians now emphasize controlling pain sooner rather than waiting until dogs are severely lame.

Modern Arthritis Treatment Targets Multiple Pathways

Because osteoarthritis is much more than cartilage wearing out, treatment has become much more comprehensive.

Modern management often includes:

• Weight management

• Controlled exercise

• Physical rehabilitation

• Omega-3 fatty acids (EPA and DHA)

• Non-steroidal anti-inflammatory drugs (NSAIDs)

• Anti-nerve growth factor (NGF) therapies, such as Librela when appropriate

• Joint-supportive nutrition

• Environmental modifications at home

The goal isn't simply masking pain.

It's reducing inflammation, improving function, slowing progression, and maintaining quality of life.

The Bottom Line

Osteoarthritis isn't simply the inevitable consequence of a joint "wearing out."

It is an active, biologically complex disease involving inflammation, altered joint metabolism, bone remodeling, and changes in the nervous system.

The encouraging news is that because arthritis is an active disease—not just passive deterioration—we have many opportunities to intervene.

The earlier arthritis is recognized and managed, the better chance we have of keeping dogs comfortable, active, and enjoying life for years to come.

Key Takeaways

• Osteoarthritis is not simply "wear and tear."

• Inflammation plays a central role in joint damage.

• The entire joint—not just cartilage—is affected.

• Fat tissue contributes to arthritis through inflammatory hormones.

• Pain comes from many tissues besides cartilage.

• Early, multimodal treatment offers the best chance of preserving mobility and quality of life.