Knee Cartilage Restoration
What Is Knee Cartilage Restoration?
Articular cartilage is the smooth, white, slightly elastic tissue that caps the ends of the bones forming the knee joint. It spreads load over a wide area and lets the joint surfaces glide over each other with very little friction. Knee cartilage restoration is the collective name for the surgical methods used to fill a defect in that surface, reduce pain and swelling and improve how the knee tolerates load. For a wider picture of how this fits alongside other knee problems, the knee overview is a useful starting point.
Two distinctions matter from the outset. First, these methods were not designed for widespread wear across the joint surface; they are meaningful for focal defects bounded by healthy cartilage. Second, the repair tissue produced by most techniques is not identical to native hyaline cartilage — it often behaves more like fibrocartilage, with different mechanical durability and long-term behaviour. How such defects arise and how symptoms are assessed is covered on the knee cartilage injury page.
Why Cartilage Does Not Heal on Its Own
Articular cartilage has no blood vessels, no lymphatics and no nerve supply; it is nourished mainly by diffusion from the joint fluid. Without a blood supply, the cells and growth factors that normally start a healing response cannot reach the injured area, so the natural repair capacity is very limited. Superficial defects confined to the cartilage layer usually do not fill in on their own and may widen at their edges over time.
The picture changes somewhat when a defect reaches through to the subchondral bone beneath: cells from the marrow can then form a repair tissue that fills the gap. That tissue, however, is predominantly fibrocartilage — less resilient under load than hyaline cartilage and prone to thinning. Because cartilage itself carries no nerve endings, a defect can stay silent early on; the pain usually arises from the subchondral bone, the joint lining and the capsule. This is why the severity of symptoms and the size of a defect are not always proportional.
Who Is a Candidate, and Who Is Not?
Candidacy rests on several factors weighed together rather than on any single measurement: the size and depth of the defect, its location (a weight-bearing femoral condyle, the trochlea or the back of the kneecap), the patient's age and activity demands, whether the symptoms genuinely match the defect, whether the leg is aligned or drifts into varus or valgus, whether meniscal tissue has been preserved, and whether the ligaments are competent. The best candidate is usually an active younger or middle-aged adult with a single contained defect, acceptable alignment, functioning menisci and ligaments, and the ability to see a long rehabilitation through.
Conversely, widespread wear involving much of the joint surface, opposing lesions on both sides of the joint, older age with low activity demand, uncontrolled systemic illness, active joint infection, significant excess weight, smoking and situations where a lengthy rehabilitation cannot be followed all reduce the expected benefit or point towards a different plan. Where wear is generalised, the emphasis shifts from filling a defect to managing symptoms; those steps are set out on the knee osteoarthritis treatment page.
Assessment and Imaging Before Surgery
Assessment begins with the history: where the pain sits, episodes of swelling, catching or locking, and difficulty with loaded movements such as stairs and squatting. Examination looks at tender points, fluid within the joint, range of motion, muscle strength, alignment and ligament stability.
Weight-bearing X-rays show the joint space, the bony anatomy and any signs of established wear; when needed, a full-length leg film is used to measure the mechanical axis and quantify any deviation. MRI outlines the borders and depth of the defect, shows changes in the subchondral bone such as oedema or cysts, and assesses the menisci and ligaments. Even so, the true size of a lesion and the quality of the surrounding cartilage sometimes become clear only once the joint is inspected, so the plan may deliberately be staged around a diagnostic knee arthroscopy.
Cartilage Restoration Techniques
No single technique is superior for every patient. The choice weighs the size and depth of the defect, its location, whether the underlying bone is involved, the patient's age and expectations, and any previous procedures. The main options are:
- Bone marrow stimulation (microfracture and its variants): small holes or channels are made in the subchondral bone at the base of the defect so that marrow cells form a clot and, within it, a repair tissue. It is relatively straightforward and done in a single stage, but the tissue formed is largely fibrocartilage, and the technique is generally reserved for small, contained defects.
- Osteochondral autograft transfer (OATS, mosaicplasty): cylinders of bone and cartilage are harvested from a non-weight-bearing part of the patient's own knee and transferred into the defect. The advantage is that the transplanted surface is genuine hyaline cartilage; the limits are the finite amount of donor tissue and the possibility of symptoms at the harvest site, which is why it suits small to medium defects.
- Osteochondral allograft transplantation: a donor bone-and-cartilage block obtained from a tissue bank is shaped to match the defect and implanted. Because there is no harvest site to sacrifice, it is an option for larger lesions and for defects where the bone beneath the cartilage has also been lost; graft availability, storage conditions and integration of the graft with the host bone are the decisive issues.
- Cell-based methods (ACI and MACI): a two-stage process. A small sample of healthy cartilage is taken at arthroscopy and the cells are expanded in the laboratory; at the second stage they are delivered into the defect, either directly or seeded onto a membrane. These methods are considered for larger defects and require two operations, a waiting interval and specialised laboratory support.
- Biological adjuncts: platelet-rich plasma or bone marrow-derived cellular products are sometimes discussed as an addition to surgical treatment in selected cases. They do not fill a cartilage defect on their own, the evidence behind them is mixed, and they are not presented as a routine requirement.
Correcting Associated Problems
A cartilage defect is rarely an isolated finding, and even the best technique underperforms if the mechanical environment around it is left uncorrected. Deviation in leg alignment concentrates load on the damaged compartment and keeps stressing the repaired area; in carefully selected patients a knee osteotomy that shifts load towards the healthier compartment is planned in the same sitting or as a separate stage. Loss of meniscal tissue likewise concentrates load onto a small area, so a meniscus tear is assessed and, wherever possible, a tissue-preserving solution is chosen.
Ligament competence is the third determinant. If the knee gives way repeatedly, the repair tissue is subjected to shearing loads long before it has matured, so an associated problem such as an ACL tear is addressed together with, or ahead of, the cartilage procedure.
Anaesthesia and Duration
The procedure may be carried out under general or spinal anaesthesia, often with a regional block to help control pain afterwards. An arthroscopic procedure for a small defect is comparatively short, whereas an open graft transfer, an allograft implantation, the second stage of a cell-based method or a simultaneous osteotomy lengthens the operation considerably. Some patients go home the same day, while those who have had additional work may prefer a short hospital stay. No fixed timing is promised; the plan is explained in advance according to the scope of the operation.
The First Period After Surgery
The governing principle in the early phase is to protect repair tissue that has not yet matured. Weight-bearing permission depends on the technique and the location of the defect: for lesions on a weight-bearing femoral surface, crutches and restricted loading are used for a period, whereas lesions behind the kneecap or in the trochlea often allow weight-bearing while a brace limits how far the knee is bent. Pain and swelling are managed with ice, elevation and appropriate medication, and the wound is kept dry.
Avoiding complete immobility matters as much as protection. Ankle movements, thigh muscle contractions and passive or assisted knee motion within the permitted range are started early. A continuous passive motion (CPM) machine is used in some protocols to support early controlled movement, but the evidence for its benefit is debated and it is not a requirement for every patient.
Rehabilitation
Rehabilitation advances in stages and is guided by goals reached rather than by the calendar. The first stage aims at controlling swelling, restoring range of motion and reactivating the quadriceps. Loading is then increased step by step, with closed-chain strengthening, balance and proprioception work supported by the hip and trunk muscles. Later, as walking quality normalises, endurance and controlled dynamic loading are introduced.
Repair tissue takes months to mature, so the early disappearance of pain is not on its own a reason to increase load. The pace of the programme is individualised to the size of the defect, the technique used, any procedures done at the same time and the patient's response.
Return to Sport
Return to sport is decided on measurable criteria rather than a date. The main ones are lasting resolution of swelling and effusion, pain-free range of motion close to the other side, thigh muscle strength approaching that of the uninvolved leg, and acceptable symmetry on single-leg hop and landing tests.
Progression towards those criteria follows a sequence: straight-line running, then change of direction, then sport-specific drills, and finally contact or high-impact activity. How long this takes varies considerably with the technique, the size and site of the defect and any accompanying osteotomy, meniscal or ligament work, which is why a fixed return date is not given.
Risks and Complications
Cartilage surgery carries its own set of risks: prolonged swelling and effusion, stiffness from restricted motion or adhesions, infection, deep vein thrombosis, wound healing problems and pain that does not settle as much as hoped. There are also technique-specific issues — cyst formation or bony overgrowth in the subchondral bone after marrow stimulation, donor-site symptoms after autograft transfer, incomplete integration of an allograft, and delamination or overgrowth of the graft after cell-based methods.
In some patients symptoms do not improve enough and a further procedure becomes necessary. The risks vary with the technique chosen, the size and site of the defect, tissue quality, alignment and patient-related factors, so expectations are discussed openly before surgery.
Alternatives and Factors Affecting the Outcome
Not every cartilage defect needs surgery. Activity modification, weight management, targeted strengthening and physiotherapy, walking aids where needed and pain management form the first step for many patients. When involvement becomes widespread and much of the joint surface is affected, the assessment widens to include partial or total knee replacement. Cartilage restoration is an option for selected patients between those two extremes; it cannot be claimed to replace joint replacement or to make it unnecessary in every case.
The outcome is shaped by the size, depth and location of the defect, how long symptoms have been present, the patient's age and activity level, body weight, smoking, leg alignment, the state of the menisci and ligaments, the degree of any accompanying wear in the joint, and adherence to rehabilitation.
When Should You See a Doctor?
After surgery, increasing redness, drainage from the wound, fever, steadily worsening pain, rapid swelling of the knee, one-sided calf pain and swelling or sudden shortness of breath should be assessed without delay. Before surgery, knee pain that does not settle with rest, recurrent episodes of swelling, catching or locking and difficulty on stairs all warrant a proper assessment. To have a knee cartilage problem evaluated, you can contact Assoc. Prof. Serkan Sürücü.