Knee cartilage injury

Articular cartilage is the smooth surface that covers the ends of the bones in the knee joint. It can be damaged in a single injury, such as a twist or a kneecap dislocation, or worn away gradually in one area. Unlike bone, cartilage has no blood supply and does not repair itself, so a defect that causes symptoms tends to persist — which is why assessment concentrates on the size and depth of the damage and on what else in the knee is loading it.

Symptoms

  • Pain in one part of the knee, brought on by activity and settling with rest.
  • Swelling that recurs after use rather than being constantly present.
  • Catching, clicking or a sense of something giving way, where a fragment of the surface has come loose.
  • Aching after prolonged standing, stairs or squatting.
How knee cartilage is damaged

Cartilage is damaged in two broad ways. A single impact or twisting injury can shear a piece of the surface away, sometimes with a fragment of the bone beneath it — a kneecap dislocation is a common cause of damage at the back of the kneecap and at the outer edge of the femoral groove. More often the surface wears in one area over time, under a knee that is poorly aligned, unstable, or has lost meniscal tissue, so that load is concentrated where it would normally be spread. Cartilage has no nerve supply of its own: the pain comes from the surrounding tissue and from the bone underneath, which is one reason symptoms and the size of a defect correspond so imperfectly.

How it is assessed

Assessment begins with how the problem started and what the knee has done since, followed by an examination of both knees so the affected side can be compared with the other. Imaging is used where it would change what is done, rather than as a matter of routine.

In clinic

The examination locates where the pain is, looks for an effusion after activity, and tests the alignment and the stability of the knee — a defect caused by instability, or by a limb that carries load through one compartment, will not be settled by treating the surface alone. Tenderness over a femoral condyle with the knee bent, and pain reproduced on loaded bending, help localise the area involved.

Imaging

Standing X-rays show alignment and joint space, and are how a focal defect is distinguished from generalised osteoarthritis — a distinction that matters, because the treatments differ. MRI with cartilage-sensitive sequences shows the size and depth of the defect and the state of the bone beneath it; it detects deeper defects reliably and superficial ones less so. Arthroscopy remains the most accurate assessment, and is not undertaken for that reason alone.

Stage and severity

Cartilage damage is described by its extent and depth, and by whether other structures in the knee are affected.

Extent of the damage
The surface area of the defect, usually given in square centimetres. Size is one of the main factors in which treatment is appropriate, with smaller and larger defects handled differently.
Depth of the damage
Graded from softening of the surface, through partial-thickness fissuring, to a defect reaching the bone beneath. The two grading systems in common use, ICRS and Outerbridge, both describe this progression.
With other injuries
Meniscal loss, ligament instability or malalignment alongside the defect. These change what the damaged area is asked to carry, and are usually addressed alongside it rather than afterwards.
Associated injuries

Cartilage damage is often not an isolated finding. Loss of meniscal tissue increases the load carried by the surface beneath it; a knee that gives way from an anterior cruciate ligament injury subjects the cartilage to repeated shear; and a limb whose alignment carries load through one compartment concentrates it there. Where the surface at the back of the kneecap is involved, how the kneecap tracks is usually part of the picture. Treating the defect without addressing what is loading it is a common reason for a poor result.

Treatment options

The two options below are set out side by side. Which applies depends on the findings, the structures involved and what you need to return to.

Non-surgical care

What it involves
Activity modification to reduce impact and deep loading, strengthening of the quadriceps and hip, weight management where it applies, and pain relief or an injection where symptoms warrant it.
Typical course
A structured programme over several months, with symptoms and function rather than the scan as the measure of progress.
Considerations
Reasonable first-line management for many defects, including some that look substantial on imaging, because the size of a defect predicts symptoms poorly. It does not repair the surface; it changes what is asked of it.
Follow-up
Reviewed after a course of rehabilitation, with surgery considered if symptoms persist and localise to the defect.

Surgical treatment

What it involves
The options are chosen by the size and depth of the defect and by where it sits: stimulating repair tissue from the bone beneath, transferring plugs of cartilage and bone, transplanting donor tissue, or implanting cultured cartilage cells. Malalignment, meniscal deficiency or instability is corrected at the same time where it is present.
Typical course
Most cartilage procedures involve a period of protected weight-bearing and controlled movement while the repair tissue matures, followed by a graded return to loading over several months.
Considerations
Suited to a symptomatic, well-localised defect in a knee that is otherwise stable and well aligned — not to generalised osteoarthritis, where the approach is different. Smaller defects are commonly treated with simpler techniques and larger ones with cell-based or osteochondral grafting; results after marrow stimulation are known to decline over the longer term.
Follow-up
Reviewed through the protected phase and as loading is reintroduced.

What recovery involves

Recovery depends on which treatment is used. The stages below apply to a cartilage repair procedure, and the timings are typical rather than fixed — progress is judged on what the knee can do at each stage.

  1. Protection

    The first six weeks

    Protected weight-bearing as directed, with controlled movement to nourish the repair tissue and prevent stiffness.

  2. Loading

    Weeks 6 to 12

    Progress to full weight-bearing, restore full movement, and rebuild quadriceps strength.

  3. Strength

    Months 3 to 6

    Progressive strengthening and a return to low-impact activity such as cycling and swimming.

  4. Return to impact

    From around six to twelve months

    Graded return to running and, where appropriate, to sport — later than after most other knee procedures, because repair tissue matures slowly.

Page information

Reviewed by
Dr Lai Kah Weng
Version
1.0
Review date
September 2026
Next review
September 2027

References

  1. Brittberg M, Winalski CS. Evaluation of cartilage injuries and repair. J Bone Joint Surg Am. 2003;85-A(Suppl 2):58–69.
  2. Outerbridge RE. The etiology of chondromalacia patellae. J Bone Joint Surg Br. 1961;43-B(4):752–757.
  3. Hinckel BB, Thomas D, Vellios EE, et al. Algorithm for treatment of focal cartilage defects of the knee: classic and new procedures. Cartilage. 2021. doi:10.1177/1947603521993219

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