Articular cartilage has no nerve supply and no blood supply. This is why damage to the cartilage lining of the knee can be silent for a long time and why, by the time it becomes symptomatic, the damage is often more advanced than the symptoms suggest.
This guide explains what articular cartilage is, what happens when it is damaged, and when surgery is the right option. It covers the main surgical procedures for cartilage damage in the knee and what a realistic recovery looks like.
What Is Articular Cartilage?
Articular cartilage is the smooth, white tissue that covers the ends of the bones inside the knee joint. Its role is to absorb load and allow the joint surfaces to glide smoothly past each other during movement. A healthy layer of articular cartilage is approximately two to four millimetres thick and has a very low coefficient of friction, allowing the knee to move efficiently under significant load.
Because cartilage has no direct blood supply, it cannot heal itself in the way that bone or muscle can. Damage to cartilage does not trigger the normal inflammatory repair response that leads to healing. This is the central challenge in treating cartilage injuries: the body's usual repair mechanisms do not apply, and cartilage that is lost is not replaced spontaneously without intervention.
What Causes Cartilage Damage?
Cartilage damage in the knee has several distinct causes, and the treatment approach depends on understanding which type of damage is present.
Osteochondritis Dissecans
Osteochondritis dissecans (OCD) occurs when a segment of bone and its overlying cartilage loses its blood supply and begins to separate from the surrounding tissue. It most commonly affects the medial femoral condyle - the inner surface of the lower end of the thigh bone. OCD is seen particularly in adolescents and young adults and is associated with repetitive loading during skeletal growth.
In skeletally immature patients (adolescents with open growth plates) the healing potential is considerably greater than in adults. With activity modification and protected loading, stable lesions in this age group can sometimes heal without surgery. When surgery is required in younger patients, fixation of the fragment is usually the first approach, given the better biological environment for healing.
In adult patients, stable lesions may still be managed conservatively in the first instance. If the fragment becomes unstable or detaches, it may form a loose body within the joint - causing mechanical symptoms such as locking or catching - and surgical intervention is usually required.
Acute Chondral Injury
A direct blow to the knee, or a twisting injury such as an ACL tear or patellar dislocation, can cause an acute chondral injury - a focal area of cartilage damage that occurs at the moment of injury. These injuries are often identified on MRI or at the time of arthroscopic surgery for an associated injury such as a meniscus tear.
Acute chondral injuries range from superficial surface changes to full-thickness defects reaching the underlying bone. Management depends on the size and depth of the defect and the age and activity level of the patient.
Degenerative Chondral Damage
Cartilage can also deteriorate gradually over time, particularly in patients with prior knee injury, malalignment, or a history of significant loading. This type of damage is distinct from osteoarthritis, though the two can coexist.
The distinction matters for treatment. A focal cartilage defect in a younger patient with otherwise healthy surrounding cartilage is a different problem from diffuse cartilage loss in the context of established arthritis, and the appropriate surgical options differ considerably.
Symptoms
The symptoms of cartilage damage depend on the size, location, and depth of the defect. Pain is the most common symptom, typically felt within the knee joint during activity - particularly loading and impact - rather than at rest. Swelling after activity is also common.
Because cartilage has no nerve supply, damage can be present and progressive for a significant amount of time before producing noticeable symptoms. By the time pain is consistent, the defect may be larger than early symptoms would have indicated.
Mechanical symptoms (clicking, catching, or locking) suggest either a loose body within the joint or a destabilised cartilage fragment. These symptoms warrant prompt assessment.
How Is Cartilage Damage Diagnosed?
If cartilage damage is suspected, your GP or physiotherapist can arrange x-rays of the knee. X-rays do not show cartilage directly, but they provide important information about joint space, bone alignment, and any bony changes associated with the lesion. In osteochondritis dissecans, changes to the subchondral bone may be visible on x-ray.
An MRI scan provides detailed images of the cartilage surfaces and can identify the size, depth, and location of a defect. In New Zealand, an MRI is arranged through the specialist after referral; it is not typically requested in primary care. Where the clinical picture suggests significant or unusual cartilage pathology, an MRI arthrogram may provide additional detail about the cartilage surface.
Diagnostic arthroscopy (direct visualisation of the joint through keyhole surgery) remains the most precise way to assess cartilage and is often performed at the time of definitive treatment.
Non-Surgical Management
Not all cartilage defects require surgery. The initial approach for most patients involves a period of supervised physiotherapy, activity modification, and analgesia.
Physiotherapy focuses on reducing load on the affected area, strengthening the muscles around the knee to redistribute joint forces, and maintaining range of motion. Anti-inflammatory medication can help manage symptoms in the short term. Intra-articular corticosteroid injection may provide temporary relief in patients with associated synovitis.
Non-surgical management is most appropriate for small, superficial defects, for patients with significant medical comorbidities, or for those unable to commit to the rehabilitation required after cartilage surgery. The decision to proceed to surgery takes into account the size of the defect, the patient's age and activity level, and whether symptoms are responding to conservative measures.
Surgical Treatment
When surgery is indicated, the appropriate procedure depends on the viability of any fragment, the size and depth of the defect, the patient's age, and the overall condition of the knee.
Osteochondral Fragment Fixation
When an osteochondral fragment, most commonly from trauma or OCD, remains viable and in reasonable position, fixation aims to preserve the native cartilage rather than remove or replace it. Using arthroscopic or minimally open techniques, the fragment is reduced and secured to the underlying bone with bioabsorbable pins or screws. These implants are resorbed by the body over time and do not require a second procedure for removal.
Fragment fixation is the preferred surgical approach in younger patients with traumatic cartilage lesions or OCD, where the native cartilage has the best biological environment for healing back to the subchondral bone. Dr Boyle has published on the long-term outcomes of this approach in the Journal of Bone and Joint Surgery: when fixation is technically successful, results are durable. Preserving the native cartilage, rather than replacing it with repair tissue, remains the priority wherever the fragment is suitable for fixation.
Arthroscopic Loose Body Removal and Debridement
Where a cartilage fragment has detached and is not suitable for fixation, arthroscopic removal of the loose body relieves catching and locking. Debridement (smoothing unstable cartilage edges) may be performed at the same time. These are relatively minor arthroscopic procedures with a short recovery.
Microfracture / Microdrilling
Microfracture and microdrilling are marrow stimulation techniques used for small, full-thickness cartilage defects with healthy bone beneath. Small holes are made in the exposed bone surface to allow bone marrow cells to reach the defect and form a fibrocartilage repair tissue. Microfracture and microdrilling are best suited to defects smaller than approximately two to three square centimetres and are performed arthroscopically.
Osteochondral Autograft Transfer (OATS)
OATS involves transplanting one or more cylindrical plugs of healthy cartilage and bone from a low-load area of the knee to fill the defect. Because the transplanted tissue is the patient's own, it integrates reliably. OATS is suitable for focal defects of moderate size and produces durable results in appropriately selected patients.
Recovery
Recovery from cartilage surgery varies significantly depending on the procedure performed and the size of the defect treated.
After arthroscopic loose body removal, most patients are weight-bearing quickly and recover within two to six weeks. After microfracture, a period of protected weight-bearing (typically six weeks) is required to allow the repair tissue to mature, with a graduated return to activity over three to six months. After OATS, recovery follows a broadly similar timeline, though this varies with defect size and location.
Throughout all cartilage procedures, physiotherapy plays a central role. The quality and consistency of rehabilitation significantly influences the outcome, and close engagement with a physiotherapist throughout the recovery period is essential.
Getting a Referral
If you have persistent knee pain during activity, mechanical symptoms such as locking or catching, or if you have been told there is cartilage damage on a previous MRI or at the time of knee surgery, a specialist assessment is the appropriate next step.
Your GP or physiotherapist can arrange x-rays of the knee and provide a referral for orthopaedic assessment. If the cartilage damage occurred as a result of an injury, the assessment and any subsequent treatment may be eligible for ACC cover.
Key Points
Articular cartilage cannot repair itself
Cartilage has no blood supply, which means it cannot mount the normal healing response that occurs after injury to bone or muscle. Damage is permanent without intervention, and cartilage that is lost is not replaced spontaneously.
Cartilage damage is often more advanced than symptoms suggest
Because cartilage has no nerve supply, significant damage can develop silently over time. By the time pain becomes consistent, the defect is frequently larger than the early symptoms would have indicated. This is why timely assessment matters.
The right procedure depends on the fragment, defect size, and patient age
When a viable fragment is present, particularly in younger patients with traumatic lesions or OCD, fixation with bioabsorbable pins or screws is the preferred first approach, preserving the native cartilage. Where fixation is not possible, small full-thickness defects may be treated with microfracture and larger focal defects with OATS. The choice is made on an individual basis after full assessment.
Cartilage damage and osteoarthritis are not the same thing
A focal cartilage defect in a younger patient with otherwise healthy surrounding cartilage is a different problem from the diffuse cartilage loss of established osteoarthritis. The surgical options for focal defects aim to restore a normal cartilage surface - this is not appropriate for, and is distinct from, treatment of arthritis.
Cartilage surgery requires careful patient selection
The best outcomes are seen in younger, active patients with focal defects, healthy surrounding cartilage, no significant malalignment, and no established arthritis. The procedure offered will depend on your individual clinical circumstances.
Physiotherapy is central to recovery, not optional
The quality of rehabilitation after cartilage surgery significantly affects outcomes. Working closely with a physiotherapist through the full recovery period, whether three months or twelve, is as important as the surgery itself.
This article is for general educational purposes only and does not constitute medical advice. Please consult your GP, physiotherapist or a specialist for advice about your individual circumstances.
