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Articular Cartilage

Knee Cartilage Injuries

Cartilage does not regenerate spontaneously — but current treatment options can repair, protect and, in many cases, delay knee replacement by years.

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60%Arthroscopic knees with a chondral lesion
<2 cm²Microfracture threshold
Grade IVExposed bone — no cartilage
80%ACI/MACI success at 5 years
Articular Cartilage

Why Are Cartilage Injuries So Difficult?

Articular (hyaline) cartilage is the smooth lining of the bony surfaces of the knee. It has no blood vessels and no nerves — which makes it unique in its function, but also extremely limited in its capacity for self-repair.

A cartilage injury may be focal (a "pothole" in a specific area) or diffuse (global degeneration — osteoarthritis). Focal lesions in young patients are the most treatable, and the ones where cartilage restoration techniques achieve the best results.

Symptoms include mechanical pain (worse on weight-bearing), recurrent swelling, crepitus and occasional locking. MRI is the most sensitive examination, but definitive assessment is arthroscopic.

⚠ Hyaluronic acid and PRP injections are described by some as "regenerative" — but none has robust evidence of cartilage regeneration. They may offer temporary symptomatic relief, but they do not repair the structural damage.

Layers of Articular Cartilage

Superficial Zone (tangential) Transitional Zone Radial Zone (deep) Calcified Zone (tidemark) Subchondral Bone Gr.I Gr.II Gr.III Gr.IV Focal lesion Total thickness: 2–4 mm No blood vessels Limited self-regeneration
Classification

ICRS Classification of Chondral Lesions

The ICRS classification (International Cartilage Repair Society) is the reference system. The grade guides the treatment decision.

GradeDesignationHistological DescriptionTypical Treatment
Grade I Superficial Softening and superficial fissures — cartilage intact at depth. Surface fibrillation. Conservative treatment, activity modification, symptomatic injections
Grade II Partial Lesion <50% of cartilage thickness. Fissures that do not reach the subchondral bone. Conservative; in symptomatic lesions with conservative failure: arthroscopic debridement or biological techniques
Grade III Deep Lesion >50% of thickness, without exposing bone. Deep fissures. Cartilage structurally compromised. Microfracture (<2cm²), OATS, ACI/MACI — depending on size, location and age
Grade IV Full Thickness Cartilage completely destroyed with exposed subchondral bone. Osteochondral. Osteochondral restoration techniques (OATS, OCA, ACI/MACI with bone support), knee replacement in selected cases
Treatment Options

Available Treatments

The choice of treatment depends on the grade, size and location of the lesion, the patient's age and their activity level.

Activity Modification

Reducing high-impact activities. Replacing them with swimming, cycling and pool-based exercises. Essential as the foundation of any treatment.

All grades — first line
Good evidence

Anti-inflammatories and Analgesics

Symptomatic control of pain and inflammation. Paracetamol is preferable for chronic use. NSAIDs for acute flares, with renal and GI caution.

Grades I–II, osteoarthritis flares
Good evidence (symptomatic)

Physiotherapy and Strengthening

Strengthening the quadriceps, hamstrings and knee stabilisers. Reduces joint loading and improves function. Proven effective in moderate osteoarthritis.

All grades
Solid evidence

Weight Control

Every extra kg of body weight generates 4–6 kg of additional load on the knee. Weight loss is one of the interventions with the greatest impact on the progression of osteoarthritis.

Overweight with osteoarthritis
Robust evidence

Microfracture

Perforations in the subchondral bone to release stem cells and form repair fibrocartilage. Most effective in lesions <2 cm². The result is inferior to the original hyaline cartilage.

Focal lesions <2 cm², Grade III–IV
Moderate evidence

OATS / Mosaicplasty

Transplant of osteochondral cylinders from a non-weight-bearing area to the lesion. True hyaline cartilage. Limited to lesions up to ~4 cm² by donor availability.

Lesions 1–4 cm², Grade III–IV
Good evidence

ACI / MACI

Implantation of autologous chondrocytes (cells from the patient's own cartilage, cultured in the laboratory) on a collagen membrane. Durable results in large lesions. Success rate ~80% at 5 years.

Lesions >2–3 cm², Grade III–IV, young patients
Solid evidence

Osteochondral Allograft (OCA)

Transplant of cartilage and subchondral bone from a tissue bank (cadaver). For extensive lesions or those with bone involvement where autologous OATS is insufficient.

Extensive lesions (>4 cm²), Grade IV
Moderate evidence

Unicompartmental Knee Replacement

Replacement of only one compartment of the knee. For osteoarthritis confined to one compartment with poor alignment. Preserves knee structures relative to total replacement.

Unicompartmental osteoarthritis, >50–55 years
Excellent results

Total Knee Replacement

Complete replacement of the articular surfaces. Last line — for advanced symptomatic osteoarthritis that has failed all other options. >90% of knees function for 15–20 years.

Advanced osteoarthritis, no alternative
Excellent evidence

Intra-articular Corticosteroids

Rapid relief of pain and inflammation in acute flares. Temporary effect (weeks to months). Repeated use may accelerate chondral degeneration — limit to 3–4/year.

Acute flares, symptomatic osteoarthritis
Symptomatic effect

Hyaluronic Acid ("Viscosupplementation")

Improves joint lubrication. Moderate symptomatic relief in mild to moderate osteoarthritis. It does not regenerate cartilage — it should not be presented as a "regenerative" treatment.

Grade I–II osteoarthritis, symptomatic relief
Modest effect

PRP (Platelet-Rich Plasma)

A concentrate of growth factors from the patient's own blood. Emerging evidence for mild osteoarthritis and tendon injuries. It does not consistently regenerate cartilage — the term "regenerative" is imprecise.

Mild osteoarthritis, tendinopathies
Moderate evidence

⚠ A Note on "Regenerative" Injections

PRP and hyaluronic acid are frequently marketed as "regenerative" treatments for cartilage. Current scientific evidence does not support this claim. These injections may offer symptomatic relief — but they do not repair the structural damage to the cartilage. The decision to perform them should be based on realistic expectations and precise clinical indications.

Decision Algorithm

Lesion Size Guides the Technique

In general terms, the size and depth of the focal chondral lesion determine the most appropriate surgical repair technique.

<2 cm²

Microfracture

The simplest technique, with good short-term results. It forms fibrocartilage — functionally inferior to hyaline cartilage in the long term.

1–4 cm²

OATS / Mosaicplasty

Transplant of true hyaline cartilage from the non-weight-bearing area. Limited by the availability of an autologous donor.

>2–3 cm²

ACI / MACI

Ideal for large lesions in young patients. Cultured cells form hyaline-type cartilage. Durable results at 5–10 years.

Frequently Asked Questions

Questions About Cartilage

Articular hyaline cartilage has a very limited capacity for self-regeneration — it has no blood vessels. Cartilage restoration techniques (microfracture, MACI, OATS) induce the formation of new tissue, but the cartilage formed is fibrocartilage or "hyaline-like" cartilage — never exactly the same as the original.
There is no robust scientific evidence that any type of injection regenerates articular cartilage. Hyaluronic acid and PRP may offer temporary symptomatic relief in the early stages of osteoarthritis, but they do not repair the structural damage. They should be considered as a symptomatic treatment, not a regenerative one.
Knee replacement is the last line of treatment, when all other options have failed. Many patients with moderate osteoarthritis control their symptoms with physiotherapy, weight loss, activity modification and medication for years. Knee replacement is reserved for advanced osteoarthritis with significant functional limitation that does not respond to conservative treatment.
In young patients with focal lesions, cartilage restoration techniques (OATS, ACI/MACI) achieve the best results. The goal is to preserve the native knee as much as possible and delay the eventual need for a knee replacement. Assessment by a specialist is essential to determine the most appropriate technique for the size and location of the lesion.
NC

Dr. Nuno Camelo Barbosa

Orthopaedic Surgeon · Knee Subspecialist
Hospital Lusíadas Porto · Hospital Misericórdia Vila do Conde · Paços de Ferreira

CartilageCartilage restorationArthroscopy

Do you have questions about your knee cartilage?

Chondral lesions require specialist assessment. The treatment window in young patients is limited — do not delay your appointment.

Book an Appointment 926 850 194

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