What joint cartilage is
It is a smooth, springy tissue a few millimetres thick that covers the ends of the bones. It has no blood vessels and no nerves. That means two things: a small defect may not hurt at first, and when cartilage is lost, the body cannot rebuild it as it was.
A focal defect or osteoarthritis?
They are two different situations, and the difference decides the treatment. A focal defect is a pothole in otherwise healthy cartilage, usually after an injury in a younger person. In osteoarthritis the wear is spread across the whole surface.
Cartilage repair operations have a place in focal defects. They do not help widespread wear.
How the damage happens
- A sudden injury, often together with an ACL tear or a kneecap dislocation.
- Repeated strain in sports with jumping and twisting.
- Osteochondritis dissecans, mostly in teenagers and young adults.
- An unstable knee or a missing meniscus, which leave the cartilage unprotected.
- A leg out of line, which overloads one spot.
Symptoms and diagnosis
Pain on loading, swelling after activity and, if a piece of cartilage breaks off, catching or locking of the knee. With the cartilage behind the kneecap, pain appears on stairs and after sitting for long.
An MRI scan shows the position, size and depth of the defect. Grading has four stages, from softening of the cartilage to full loss with bare bone. Standing X-rays show the alignment of the leg.
Is surgery always needed?
No. Small, shallow defects and sore cartilage behind the kneecap are usually treated without an operation:
- Targeted physiotherapy, with a focus on the quadriceps and the hip muscles.
- Adjusting training and loads for a while.
- Weight control.
- In selected cases, injections of hyaluronic acid or PRP.
Surgery is discussed when the defect is deep, causes symptoms despite treatment, or a loose piece sits inside the joint.
Cartilage repair operations
- Chondroplasty. Keyhole smoothing of the unstable edges of the defect.
- Microfracture. Small holes in the bone under the defect bring blood and cells, which form a fibrous cartilage. It suits small defects.
- Mosaicplasty (OATS). Small plugs of bone and cartilage are moved from a part of the knee that bears little load to the defect. The gap is filled with true hyaline cartilage.
- Cell-based techniques and scaffolds. For larger defects, in selected patients.
- Osteotomy. When the leg is out of line it is corrected, so the repaired spot can rest.
If there is instability or a meniscus problem, it is treated together. Otherwise the cartilage repair does not last.
Who is a good candidate
Results are best in younger, active people with a single focal defect, a stable knee, an intact meniscus and a well-aligned leg. Smoking and extra weight lower the chances of success.
When the wear is widespread, these techniques have no place. Treatment then follows the path of osteoarthritis.
Recovery
Cartilage matures slowly, and recovery asks for patience. The leg usually takes partial weight, on crutches, for about six weeks, while knee movement starts early because it feeds the cartilage.
Cycling and swimming return within the first months. Sports with impact and twisting usually return after six to twelve months, depending on the technique and the size of the defect.
Common questions
Can cartilage grow back?
Not by itself. Operations fill the gap either with fibrous cartilage or by moving healthy cartilage. PRP and hyaluronic acid reduce symptoms; they do not regrow cartilage.
What is chondromalacia of the kneecap?
It is softening or wear of the cartilage behind the kneecap. It causes pain at the front of the knee, on stairs and when sitting. In most cases it improves with physiotherapy.
Will a cartilage defect turn into arthritis?
Not always. Small defects can stay stable for years. Large, deep ones in a load-bearing spot raise the risk, which is why they are worth following up.
Medically reviewed by Manos Skotidis, MD, MSc. This information is educational and does not replace a medical examination.