Articular cartilage repair / replacement
- The articular cartilage is the thin layer of smooth, shiny, white, glistening tissue that covers the surfaces of the ends of the bones in the knee joint, making the joint surfaces very low friction, to allow smooth movements.
- Articular cartilage has no blood supply, so when the tissue is damaged or becomes worn, it does not grow back or repair itself.
- If articular cartilage damage in a knee joint is causing significant symptoms then it can be treated effectively via knee arthroscopy.
- Partial thickness articular cartilage damage can be smoothed off and stabilised by radiofrequency chondroplasty.
- Small (<2cm2) areas of full thickness articular cartilage damage with bare bone exposed can be treated with microfracture.
- Larger areas of full thickness articular cartilage damage (with bare bone exposed) may require bigger, more complex techniques, such as articular cartilage grafting with a Chondrotissue graft.
The articular cartilage layer covering the surfaces of the bones inside the knee joint is a highly specialized layer of tissue that is extremely smooth and low friction, which allows the joint to move smoothly. Articular cartilage can be damaged either from direct impact, it can be damaged from disorders such as osteochondritis dissecans, or it can be damaged from simple wear and tear with time (degeneration). Degeneration of the articular cartilage can occur secondary to increases pressures/forces in the knee as a result of meniscal damage or ligament injuries. Alternatively, articular cartilage degeneration can occur spontaneously, from simply osteoarthritis (which is partly genetically determined).
Either way, regardless of the cause of any damage to the articular cartilage, unfortunately the articular cartilage has no blood supply, and it does not therefore heal or repair itself, or regenerate.
CLICK HERE for more information about articular cartilage damage and the symptoms that it can cause
If a patient has articular cartilage damage in the joint and if it is causing significant enough symptoms then the knee is quite likely to end up needing surgery of some kind. The actual type of procedure potentially required will depend on the depth of any damage (partial vs full thickness), the size of the surface area involved, the extent of any associated damage in the joint and the age and functional aspirations/demands of the patient.
The following surgical treatment options refer more to focal areas of articular cartilage damage in younger, higher demand patients. More widespread generalized articular cartilage damage / wear and tear in older patients tends more to represent ‘arthritis’ in the joint.
If there is partial thickness articular cartilage damage, with rough unstable cracks or flaps of cartilage, then this can be smoothed off and stabilized surgically with a tiny probe called a radiofrequency probe. This is like a tiny microwave on the end of a stick. The probe is passed into the knee with a knee arthroscopy and the energy waves emitted from the end of the probe superheat just the very surface layers of the articular cartilage without causing any heating or damage to the deeper layers of cartilage tissue underneath. This smoothes off the surface of the tissue, stablising the joint surface, which:-
- decreases pain,
- improves function,
- helps prevent further amounts of cartilage flaking off, and
- helps keep the knee going for longer, delaying the time when bigger more invasive surgical procedures might potentially become necessary.
The rehab after radiofrequency chondroplasty tends to be fairly quick and easy (depending on what other potential surgical procedures may have been undertaken in the knee at the same time), with early fully weight bearing and a rapid return to full function, with the help of physiotherapy rehab treatments.
CLICK HERE to read more about radiofrequency chondroplasty
If there are any loose unstable chunks of cartilage inside the knee joint then these can cause pain, swelling and mechanical symptoms such as catching, giving and/or locking. In addition, smaller pieces of loose cartilage in the joint tend to end up being ground down by the joint surfaces, which produces debris in the joint. This can irritate the lining of the knee (the synovial membrane), which can become inflamed (synovitis). The lining of the knee is very rich in nerve fibres, and hence synovial inflammation causes knee pain as well as the synovium also producing increased quantities of synovial joint fluid, which causes swelling. In addition to this, debris in the knee can act like sand in a care engine cylinder, and cause ‘third body particle wear’ in the joint, exacerbating any joint degeneration.
Knee arthroscopy, washout and removal of loose bodies is an easy, straight forward, low risk operation that is very effective in dealing with loose pieces of articular cartilage in the joint (and which also allows the rest of the knee to be checked carefully so that any other potential issues can also be addressed).
If there is more severe articular cartilage damage in the joint, and specifically if there is an area of full thickness cartilage loss with bare bone exposed, and if the size of the surface area of any defect is not too large, then arthroscopic microfracture can be an effective option.
The surfaces of the knee joint can be thought of as being a bit like a Crunchie bar — the deeper bone is like a honeycomb that has a very rich blood supply and which is full of bone marrow and stem cells. However, this is covered by a hard egg-shell like cortex of bone, called the subchondral bone plate, which acts as a barrier. The articular cartilage is like the chocolate layer on the surface of the Crunchie bar, but the hard layer of bone underneath acts as a barrier, and unfortunately the articular cartilage itself has no blood supply.
With microfracture, the edges of any defect are smoothed off and stabilized, getting rid of any irregular, loose or unstable flaps of tissue. The base of the defect is then cleared to expose the fresh surface of the subchondral bone plate. The subchondral bone plate is then punctured with a tiny metal pick, and perforated with multiple small holes. These holes allow the underlying bone to bleed into the defect. The blood forms a clot, and this clot is rich in bone marrow cells, including stem cells, which have great healing potential (it is sometimes referred to as the ‘superclot’). If this clot is protected sufficiently then it tends to mature into tissue called fibrocartilage, which is half way between normal articular cartilage (which is sometimes called ‘hyaline cartilage’) and scar tissue. Its mechanical properties are not as good as normal healthy articular cartilage, but the fibrocartilage is far better than just exposed bare bone.
There is, however, a limit to what can be achieved with microfracture. It tends to work best on smaller sized defects, particularly if they are 1cm2 or less. In defects larger than about 2cm2 (i.e. just 1.5cm x 1.5cm or so) it is harder for the ‘superclot’ to stay in place and to take and mature successfully, and so the results tend to be worse. Also, microfracture tends to work best on the femoral condyles (the end of the thigh bone), but not quite so well on the tibial plateau (the top of the shin bone) or in the patellofemoral joint (behind the kneecap).
Overall, approximately 80% of patients end up happy with the results of microfracture when viewed at 5-year follow-up. However, studies show that the results do tend to drop off and deteriorate with time, after this.
If the damage to the articular cartilage on one of the joint surfaces in the knee exceeds about 2cm2 then microfracture tends not to be the best treatment of choice. Instead, it might be necessary to potentially consider articular cartilage grafting / transplantation in the knee.
In the past, surgeons in Sweden developed a technique whereby normal cartilage cells could be harvested from one of the non-weight-bearing surfaces of the joint and cultured in a lab to make them multiply. Six weeks later the cells would then be ready to inject back into the knee underneath a layer of periosteum (tissue taken from the surface of the bone at the front of the shin). This helped new ‘hyaline-like’ cartilage tissue to grow back into a defect, and success rates in the region of about 80% were reported. This technique is called ‘Autologous Chondrocyte Implantation’, or ACI.
The ACI technique was developed further, and surgeons then began to use flaps of collagen to cover defects (with the cultured cells injected underneath), rather than periosteum, which made the operation a bit better.
The next development was that some companies/surgeons then started to impregnate the collagen membrane with the cultured cells, to give a membrane with living cartilage cells already in it, rather than injecting the cells under the membrane as a paste at the time of the operation. This was referred to as ‘Matrix-induced Autologous Chondrocyte Implantation’ (MACI), and again, good results (in the region of about 80%) have been reported.
However, the most up-to-date and (in my opinion) the best technique currently available for replacing larger areas of full thickness articular cartilage loss is the use of the Chondrotissue articular cartilage graft. This involves preparation of the base of the defect as for ACI or MACI, followed by widespread microfracture of the subchondral bone plate. The defect is then covered over with a Chondrotissue graft that is cut to size and glued in place using bioaborbable fibrin glue. The Chondrotissue graft is a porous bioabsorbable foam-like membrane. The stem cell rich blood from the microfractured bone surface seeps into the graft, which acts as a matrix and scaffold that new cartilage tissue grows into, and the scaffold is then gradually absorbed, leaving fresh new hyaline-like articular cartilage.
CLICK HERE to read more about Chondrotissue grafting.
There are pros and cons with each of the potential different surgical options for articular cartilage replacement:-
- Ideal for small defects (<2cm2)
- Can be performed fully arthroscopically at the same time as any arthroscopy
- Poor results for bigger defects (>2cm2)
- Creates fibrocartilage, not normal hyaline articular cartilage
- Better for larger cartilage defects
- Creates more normal looking new articular cartilage
- Very expensive
- Complicated procedure and complicated processes/logistics
- Requires 2 separate operations (1 to harvest the cartilage cells, 1 to implant the cultured cells)
- Has been associated with problems of cartilage overgrowth, which can necessitate further surgery in up to 40% of patients.
- Ideal for larger (or even very large) cartilage defects
- No cell harvesting/culture required, therefore can be done as a single-stage procedure (rather than 2 separate operations)
- Considerably less complicated procedure and logistics than ACI/MACI
- Considerably cheaper than ACI/MACI
- Histological studies demonstrate regeneration of excellent new hyaline-like articular cartilage.
- Still can be somewhat expensive, though considerably less so than ACI or MACI
My firm preference for the treatment of articular cartilage defects that are greater than 2cm2 or for smaller defects that have failed attempts at previous microfracture is to use the Chondrotissue graft, which in his hands has given the best results.