Cartilage

What it is and where it lives

Cartilage is a smooth, rubbery tissue that covers the ends of bones inside a joint. The medical term is hyaline cartilage, and it’s made of specialized cells (chondrocytes) surrounded by a protein matrix (mostly collagen and proteoglycans). Its two jobs are simple: minimize friction so joints glide smoothly, and absorb shock so bone-on-bone impact is cushioned.

Cartilage isn’t the hard, visible cartilage of an ear or nose. It’s slippery, almost gelatinous, and sits directly on the bone surface inside your knee, hip, shoulder, and every other joint. It’s what makes movement pain-free and fluid.

The meniscus is not cartilage (sort of)

Patients often confuse cartilage with the meniscus of the knee. The meniscus is also made of cartilage, but it’s fibrocartilage — a different type. The meniscus is the C-shaped cushion floating inside the knee. Hyaline cartilage is the slippery coating on the tibia and femur that surrounds the meniscus. Both are cartilage by chemistry, but they look and behave differently. The meniscus can sometimes be repaired surgically; hyaline cartilage cannot.

Why cartilage heals poorly

Hyaline cartilage has virtually no blood supply. This is a trade-off: the avascular structure makes it smooth and slippery, perfect for bearing weight and gliding, but terrible for self-repair. When you break a bone, blood rushes to the fracture site, and repair cells arrive within days. Cartilage damage gets no such response.

Once cartilage is damaged — from a direct blow, repetitive wear, or injury — it doesn’t regenerate. The damaged area stays damaged. This is why cartilage defects are one of orthopedic surgery’s hardest problems to solve. Small defects may fill with scar tissue (fibrocartilage) that isn’t as smooth as the original. Large defects progress to osteoarthritis.

Osteoarthritis is cartilage wear

Osteoarthritis is the progressive loss of cartilage in a joint. It develops gradually. Years of normal use, or accelerated wear from injury or malalignment, thins the cartilage layer. As it wears, the underlying bone is exposed. The joint becomes stiff, achy, and inflamed. This is why osteoarthritis is called “wear-and-tear arthritis” — it’s literally the wearing away of the cartilage surface.

Once osteoarthritis begins, we can’t regrow the lost cartilage. We can manage inflammation, improve joint mechanics, and in some cases use injections like hyaluronic acid or PRP to slow progression, but we can’t restore lost cartilage. This is why early intervention — treating injuries quickly, controlling weight, and optimizing movement patterns — is so important.

Protecting cartilage

Because cartilage can’t repair itself, the strategy in orthopedics is prevention and slowing decline:

• Avoid high-impact repetition. Running is fine, but distance runners are at higher risk of knee osteoarthritis. Swimming and cycling are easier on joints.
• Maintain a healthy weight. Every pound of body weight increases the load on knees, hips, and spine by 3–4 times during walking. Weight loss is cartilage protection.
• Keep muscles strong. Strong quadriceps and hip muscles protect the knee and hip. Weak muscles allow poor joint mechanics and accelerated cartilage wear.
• Treat injuries promptly. A meniscus tear or ligament injury changes how the joint moves. Early repair or rehabilitation prevents secondary cartilage damage.
• Fix malalignment. Knock-knees or bowlegs shift load unevenly across the joint, concentrating wear on one side. Sometimes bracing or inserts help.

Current treatment options

We can’t regrow lost cartilage, but we can slow decline and manage symptoms. Hyaluronic acid injections improve lubrication and may reduce inflammation. Platelet-rich plasma (PRP) may slow cartilage degeneration in early osteoarthritis. Bracing and physical therapy optimize how the joint moves and distribute load more evenly. For advanced arthritis with severe cartilage loss, joint replacement becomes necessary.

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