Articular Cartilage Repair of the Knee



Mention knee cartilage to most people and they will tend to think about the wedge shaped shockabsorbers of the knee - the menisci. However, there is another form of cartilage in the knee that causes knee problems – the articular cartilage - the white gristle covering the adjacent surfaces of 'articulations' or 'joints'.


by Karen Hambly BSc(Hons) MCSP



Articular cartilage has been known to be a potential problem for quite a while! In Roman times after gladiators had ‘dissected’ each other fighting, their physician, Galen, witnessed human tendons, cartilage and ligaments and made the observation that “athletes … get arthritis”. 250 years ago a famous anatomist noted that “ulcerated cartilage is a troublesome thing and once destroyed, is not repaired” (Hunter 1743). Thousands of people each year experience symptoms related to chondral (joint cartilage) and osteochondral (joint cartilage and bone) defects.



We are in the 21st century now so why does articular cartilage damage continue to be such a ‘troublesome thing’? Well to give you a better insight into why that is the case it is useful for you to know a bit more about the structure of articular cartilage, the role that it performs and how it gets damaged.


What is articular cartilage?


Articular cartilage is found in all moving joints in the body (synovial joints) and its role is to protect the bones by keeping the surfaces of the bones apart from each other, to absorb shock and to help make movement smooth. Articular cartilage does this by providing a protective, wear resistant surface to the end of the moving bones. In the knee articular cartilage covers the ends of the femur (medial femoral condyle, lateral femoral condyle and the trochlea), the top of the tibia (tibial plateau) and the back of the patella.


These images of the rounded end of the femur bone show ....   knee-condyle.jpg meniscus01.jpg

Articular cartilage is a particular type of cartilage called hyaline cartilage (derived from the Greek word hyalos, meaning glass). Hyaline cartilage is a hard, white shiny material with a unique structure that creates a surface that allows the bones to glide easily past each other as the knee joint moves. It varies between individuals but it is generally between 2 and 4mm in depth in the knee and it has an amazingly low coefficient of friction – just 1/15th that of ice – now that’s very slippery. The special nature of this material, however, also makes it particularly vulnerable once it becomes damaged.



How can you damage articular cartilage?


Articular cartilage injuries are common. The normal structure and function of articular cartilage can be upset relatively easily and damage to the articular cartilage often results.There are several ways in which your articular cartilage can become damaged.


  1. * Sudden direct blow to the cartilage (traumatic) e.g. a high-energy injury such as a bad fall on directly onto your knee or during sporting activities.
  2. * Slow damage to the cartilage following a knee injury (post-traumatic).
  3. * Wear and tear over time (degenerative joint disease or DJD) – especially when there is malalignment or instability in the joint and/or if you are overweight.
  4. * Immobilisation for long periods of time as articular cartilage is nourished by joint movement so immobilisation can result in damage.
  5. * Osteochondritis dissecans is a condition that is thought to occur due to poor blood supply to the underlying bone resulting in a piece of cartilage and subchondral bone separating from the articular surface.

It is possible to just damage the articular cartilage on its own but you often find articular cartilage damage in conjunction with injury to other tissues in the knee particularly ligaments and menisci. If you have had a previous injury to your ligaments and/or menisci then you are at greater risk of articular cartilage damage due to the altered mechanics of the joint even if the original injury has been successfully repaired eg anterior cruciate ligament reconstruction.




A general misconception is that articular cartilage damage and osteoarthritis only affect people in their 50’s or older. Although there is a greater incidence of articular cartilage problems in this age group young people damage their articular cartilage too, especially in sports or via osteochondritis dissecans.


If the knee joint is out of position (malaligned), unstable or if the knee cap is being pulled to one side too much stress could be placed on particular parts of the joint surface and this is known to accelerate degenerative changes in the articular cartilage. This has important implications for cartilage repair surgery that will be discussed later.



How do I know if I've damaged my articular cartilage?


Articular cartilage is difficult to diagnose. There isn’t a particular test at present that can be carried out as part of a physical examination that is able to reliably diagnose an articular cartilage injury in the same way as you can, for instance, for a ligament injury. The history of your problem can provide many clues. Was there a specific incident when the injury occurred or has it developed over time? When and where are you getting your pain, what makes your pain worse and what eases it, is the problem getting better or worse – this type of information is useful guidance. There are a variety of symptoms that you may experience but they vary considerably between individuals and can often mimic other common knee injuries. You may or may not have pain and you could have no, or limited, swelling. Yes you may experience locking if a piece of articular cartilage has broken off and is a loose body in the joint or you may experience catching or giving way. You are likely to have some muscle wasting and difficulty in activities such as going up and down stairs, walking or running but then people with any moderate knee injury are likely to as well. This is why articular cartilage damage is the ‘cinderella’ of knee problems. It tends to be diagnosed only after other structures have been ruled out – “well if it isn’t your meniscus or ligaments, what else could it be, perhaps we should look at the articular cartilage?”


Plain X-rays aren’t very helpful in diagnosing articular cartilage defects, especially early stage ones, as they only show bony injury. Articular cartilage injuries are often not seen on x-ray unless there is some bony malalignment and/or bony damage.


MRI scans are increasingly being used to help to diagnose articular cartilage and new cartilage specific protocols are emerging that are becoming very valuable in the evaluation of articular cartilage. However, MRIs are expensive tools and articular cartilage scans need longer imaging time which has cost implications. In addition waiting times for MRI scans can also be lengthy in some countries.


At present the ‘gold standard’ for diagnosing articular cartilage problems is to take a look directly inside your knee with a small camera in a ‘keyhole’ procedure called an arthroscopy. Often articular cartilage damage is only identified after an MRI scan or when your surgeon takes a look inside your knee joint with an arthroscope. This can be a real problem due to the length of time it takes to identify that the articular cartilage has been damaged and the implications of this delay.

How do I know how much articular cartilage damage I


have done?


If you have an MRI scan or an arthroscopy and it shows articular cartilage damage your surgeon will often refer to a grade of damage. The grading system that is commonly used is a scale between 0 and 4 where:






cartilage is normal and intact

1 cartilage has some softening and blistering
2 partial thickness (less than 50%) defect or minor tears in the surface of the cartilage
3 deeper defect (more than 50%)
4 full thickness cartilage loss with exposure of the subchondral bone grade-4.jpg

In addition to the grade of the damage doctors will also measure the size of each defect in square centimetres. Small defects are generally considered to be less than 2cm2. The amount of articular cartilage damage can therefore be calculated from the number of defects, their depth and their size. However, it is important to remember that although the amount of damage is an important factor the location of the defect(s) can also influence the symptoms you are getting in terms of pain and function and the repair options available to you. In particular ‘kissing lesions’ (articular cartilage damage on both the articulating joint surfaces) can pose a real problem as it is bone on bone with movement.


You may be surprised to hear that pain isn’t a particularly good indicator of the extent of the articular cartilage damage. One person can have severe pain with a single small defect and then another person can have very little pain with several large full thickness defects. An important piece of the jigsaw is being missed out if we focus too closely on just the articular cartilage. It is important to look at what’s happening at the underlying bone and consider the overall health of the knee joint as well in order to build the complete picture. Over the last five years researchers have been looking more closely at the whole osteochondral (articular cartilage and the underlying ‘subchondral’ bone) unit and there is increasing evidence to indicate that changes in one of the components of the osteochondral unit affects the other.


What happens when you damage articular cartilage?


In most tissues it is blood that delivers the essential nutrients for tissue regeneration. Articular cartilage doesn’t have a blood supply (it is avascular) and therefore it has an extremely limited capacity for self-repair. In general, partial thickness defects do not heal by themselves and can often get worse over time. In addition to not having a blood supply articular cartilage also has no nerve supply (it is aneural). This is in contrast to the bone immediately below the cartilage which is abundantly supplied with both nerves and blood. If the articular cartilage damage is shallow (grades 1 or 2) you may not experience any pain from the defect at this stage as the sensitive nerve endings in the subchondral bone are still covered with some articular cartilage. Some people have articular cartilage defects and don’t even know about them initially. A recent study found a large number of patients who underwent ligament reconstruction surgery had articular cartilage defects but had very few symptoms (Shelbourne et al 2003). On the other hand, when a chondral defect does go all the way down to the bone (grade 4) the nerve endings in the subchondral bone become exposed and you are more likely to feel pain especially when pressure is put on the nerves.


When a chondral defect goes all the way down to the bone the blood supply in the subchondral bone can start a healing process in the defect. This results in the formation of scar tissue made up of a type of cartilage called fibrocartilage. Although fibrocartilage is able to fill in articular cartilage defects its structure is significantly different to that of hyaline cartilage. Fibrocartilage is much denser and it isn’t able to withstand the demands of everyday activities as well as hyaline cartilage and is therefore at a higher risk of breaking down.


If an area is unstable fragments of articular cartilage may break off from the subchondral bone and surrounding articular cartilage and become mobile in the knee joint. These fragments can not only cause mechanical problems, such as catching and locking, but can also induce chemical changes in the knee joint as the fragments breakdown and result lead to inflammation of the lining of the joint (synovitis).




Does EVERY articular cartilage defect end up as




This is the million dollar question that anyone with an articular cartilage defect wants answered. Is my articular cartilage defect going to get worse and progress to osteoarthritis?

A recent study has found that small articular cartilage defects do progress to osteoarthritis over time (Wang et al 2006). However, other studies have found that some defects repair with fibrocartilage and can last for many years.


Which defects do progress to osteoarthritis? It is not clear as yet exactly which factors are associated with any progression but there is an emerging concept of a process of articular cartilage loss over time (chondropenia). The important point is that it is a process. An articular cartilage defect that initially may be relatively small still has the potential to have a physical and chemical ‘domino effect’ on the surrounding ‘normal’ articular cartilage. Excessive stress on an articulating surface of a joint that already has articular cartilage damage may accelerate further degenerative changes. Correction of any malalignment or instability that is present can help to ‘normalise’ stress. There is also some evidence to indicate that articular cartilage defects that don’t have clearly defined margins and are poorly shouldered have an increased risk of progression as well.


So is repairing articular cartilage just delaying the inevitable in terms of progression to osteoarthritis in the knee? The answer at the moment is that no one can really be sure. Currently there is no concrete evidence to show that articular cartilage repair can prevent the progression of a defect to osteoarthritis. Ongoing studies are showing promising results but most have only short follow up times at present so the longer term outlook for patients is still unclear. However, it does look increasingly likely that repairing articular cartilage defects can slow down the degeneration of the joint compared to if the defect was left untreated. Therefore, at present, articular cartilage repair procedures are treatments aimed at providing relief of your symptoms and improvement in your function. Articular cartilage repair procedures MAY slow down the progression of a defect to osteoarthritis later in life but the jury is still out on this one.


Can articular cartilage be restored once damaged?


The ultimate goal of any treatment is to restore the surface of the joint to ‘normal’ hyaline articular cartilage. This has been the quest of surgeons for the last two decades and it has lead to the development of a range of surgical procedures that will be summarised later. Many of these procedures have been able to ‘fill in the pot holes’ caused by articular cartilage damage but even in the most promising procedures the new tissue isn’t exactly the same as natural articular cartilage. The repair tissue may look like hyaline but it is not the same mechanically - it is hyaline-like. So at present we can’t ‘restore’ the structure of normal articular cartilage but we can ‘repair’ a defect with a similar tissue.


If articular cartilage can’t be restored to it’s normal structure why then would you considerhaving surgery to repair a defect with a tissue that probably isn’t as good? After all articular cartilage repair carries the risks of any surgical procedure and you should always have a good reason for consenting to any surgery. Is this hyaline-like repair tissue good enough to make it worth putting yourself through the surgery?


Well, articular cartilage damage isn’t life threatening but it can, and often does, threaten quality of life as it can lead to not only pain but also swelling, reduced mobility and restrictions on your activity. By recovering the subchondral bone in an articular cartilage repair procedure the pain can be signficantly reduced and at the same time the articulating surface is reestablished.


The questions as to how long the repair tissue lasts for and how durable it is compared to normal articular cartilage are still being answered. Articular cartilage repair is a relatively new technology and there are still a lot of ‘ifs’ or ‘possiblys’ to be addressed. There are an increasing number of clinical trials that are following articular cartilage repair patients over time to see how well, and how long, the articular cartilage repairs last.


Which articular cartilage repair procedure?


There are a number of articular cartilage repair procedures in general use at present and a lot more in development. The selection of a procedure can be quite confusing especially if you are given several options by your surgeon. One of the reasons for this is that selecting an articular cartilage procedure isn’t black and white and the different procedures often overlap with each so that there may be more than one option available to you.


Articular cartilage repair procedures may differ in the technologies and surgical techniques that they use but they all share a common philosophy of repairing articular cartilage whilst keeping options available in case you need them in the future. In this way you don’t ‘burn your bridges’ by opting for an articular cartilage repair procedure.


From a patient’s perspective the main reasons for opting for articular cartilage repair are to -


  • * Provide pain relief
  • * Improve function
  • * Hopefully slow the progression of the damage
  • * Hopefully delay joint replacement surgery

The articular cartilage repair procedure has to match your particular needs otherwise it won’t be successful for you as an individual. Things that need to be taken into account are your age, activity level (including work, lifestyle and sports), size and location of your defect(s), how long you’ve had your symptoms and any previous surgery you may have had.


There are some contraindications to articular cartilage repair procedures with the three main ones being advanced osteoarthritis, rheumatoid arthritis and total menisectomy. In addition, articular cartilage repair should only take place if any mechanical malalignment and ligament laxity is either corrected prior to or at the same time as the articular cartilage repair procedure.


For all articular cartilage repair procedures your surgeon will need to gain your informed consent to the procedure and you must be willing and able to commit to and complete the rehabilitation programme.


Articular cartilage repair procedures can be broadly categorised into four groups as follows:


Group 1   Arthroscopic lavage and debridement
Group 2   Marrow stimulating techniques
Group 3   Osteochondral autografts and allografts
Group 4   Cell-based repairs including autologous chondrocyte implantation

An overview of each of these categories will now be presented but for more detailed information of the surgical techniques we suggest referring to the published literature and additional information sections at the end of this article.


Arthroscopic Lavage and Debridement


These are procedures that are carried out via ‘keyhole’ (arthroscopic) surgery. Lavage is basically washing out the knee joint and debridement is removing any unstable or degenerative articular cartilage flaps. These can be useful palliative treatments to reduce pain, mechanical irritation and inflammatory mediators but any benefits tend to be short-term only. Although these procedures are invariably classed as treatment options for articular cartilage damage they should not be viewed as articular cartilage repair procedures. They can’t be articular cartilage repair procedures as they don’t repair the articular cartilage – they give the knee joint a bit of a clean-up. The main group of patients that often receive some benefit from this procedure are those patients with very small defects (less than 1cm2) and localised mechanical symptoms due to small flaps or loose pieces of articular cartilage.


Marrow Stimulation Techniques


These surgical techniques have been around for almost half a century. All the techniques that fall under marrow stimulation are based on two key steps.


  1. 1. The removal of damaged cartilage to expose the underlying bone.
  2. 2. Penetration of the subchondral bone to expose the blood vessels and generate a blood clot within the defect.

The older marrow stimulation techniques used abrasion and/or drilling using fine wires to penetrate the subchondral bone. There are disadvantages with these techniques though as the heat produced by the abrasion/drilling can cause cells to die (necrosis). Twenty years or so ago the newer technique of microfracture was introduced where, instead of motorised, heat producing tools, a fine bone pick (awl) is used to punch into the subchondral bone at 2-3-mm intervals to a depth of 2-4mm.


Microfracture is frequently used as a first line treatment for articular cartilage defects in younger patients (< 30-40 years) with a small (<2cm2) isolated chondral defect. The reason for this is that microfracture is generally an arthroscopic procedure and if the microfracture doesn’t work it is possible to move onto another, but usually more invasive, cartilage repair technique.


Studies have shown that microfracture techniques often don’t fill in the chondral defect fully and the repair material is fibrocartilage which is not as good mechanically as hyaline cartilage. The blood clot is very delicate after surgery and needs to be protected. In terms of time, the clot takes about 8 weeks to convert to fibrous tissue and is usually fibrocartilage by about 4 months post surgery. This all has implications for rehabilitation that will be discussed in a later section.


Defects as a result of a sudden injury seem to do better than defects from wear and tear damage. Patients can often do well for 1 or 2 years after microfracture but then symptoms often start to return as the fibrocartilage wears away. However, for some patients the repair tissue doesn’t wear away so quickly and this is why the technique is often used as an intermediate step. If it works- fantastic, if it doesn’t then you can move onto another articular cartilage repair procedure. However it is always worth bearing in mind that there is an increased risk of problems with multiple surgeries.


Osteochondral Autografts and Allografts


Osteochondral = bone and articular cartilage

Auto = your own

Allo = someone else’s


Sometimes you will see this type of procedure also referred to as ‘OATS‘, ‘osteoarticular transfer system’ or ‘mosaicplasty’.



Osteochondral Autograft Transfer


Cylindrical plugs of articular cartilage attached to subchondral bone are taken from a non-weighting bearing area of the knee such as the edges of the femoral condyle with an instrument similar to a small apple corer. These plugs are then inserted into matching holes that have been drilled in the chondral defect. This is all completed during a single surgery arthropscopically where possible or if this isn’t possible then via a small arthrotomy (open incision). The plugs are comprised of hyaline cartilage but the spaces around the plugs fill in with fibrocartilage as does the donor site.


One of the problems with this technique is something called donor site morbidity – that is what happens to the area that the healthy tissue plug was taken from after the surgery. In effect OATS is a bit like ‘robbing peter to pay paul’ and consequently it is often limited to chondral defects less than 4cm2 in size. The patella also presents an additional challenge due to the unique stress and loads that the patella has to accommodate.



Osteochondral Allografts


This is basically the same procedure as osteochondral autograft but instead of getting the plugs from your own body they are taken from a deceased donor. One of the advantages of using allografts over autografts is that more osteochondral tissue can be taken so larger areas of defects can be repaired. However, allografts are often not available or are very difficult to come by in some countries.


A recent progression to osteochondral allografts is the development of a procedure called ‘Mega-OATS‘.

Mega-OATS is version of osteochondral allograft where a single large plug is used to fill larger chondral defects. Mega-OATS is not widely used at present but where it is it is reserved for younger patients with large chondral defects.


For all of the variations of osteochondral grafting the surgical technique is important as with all articular cartilage repair procedures. The plugs should be flush with the surrounding articular cartilage and ideally should be positioned so that they follow the contours of the articular surface.

Autologous Chondrocyte Implantation


Autologous = from yourself


Chondrocyte = cartilage cells

Autlogous Chondrocyte Implantation = Autologous Chondrocyte Transplantation


In the past articular cartilage repair procedures have tended to generate fibrocartilage repair tissue or, at best, a combination of hyaline and fibrocartilage repair tissue. In the 1980’s the first orthopaedic tissue-engineered cartilage repair procedure was introduced – autologous chondrocyte implantation or ACI – with the aim of providing a hyaline repair tissue. Over the last 20 years the procedure has become more widespread and it is currently probably the most researched articular cartilage repair technique. At present most ACI procedures are in two stages:


  • Stage 1: The first stage involves an arthroscopic assessment of the chondral defect. If the defect is suitable for ACI then a small sample of cartilage is taken from a non-weight bearing area of the femur. This sample is sent to a specialist laboratory where the cartilage cells (chondrocytes) are nurtured and encouraged to multiply until there are a sufficient number to fill the defect (many millions). This usually takes between 3 and 6 weeks.
  • Stage 2: The second stage is when the chondral defect is trimmed back to a point where all the surrounding edges are healthy cartilage and the underlying bone is exposed. Then the cells are reintroduced back into the defect. Unlike the first stage, in most countries at present, this stage is not arthroscopic – it is via an open arthrotomy.

ACI is an umbrella term for cell-based cartilage repair procedures and there are a number of variations with slightly different materials and/or surgical procedures. The first ACI procedure retained the cells in place using a cover of periosteum (a fibrous covering over the bone) from the tibia (shin bone) which is sutured (stitched) to the adjacent healthy cartilage to provide a watertight chamber into which the newly grown cartilage cells are injected. Periosteal ACI procedures have produced good results, sometimes too good, as the cartilage cells tend to overgrow in some patients and cause problems. In addition there is an extra incision needed to surgically remove the periosteum. Therefore scientists have developed membranes made of collagen that perform the same role as periosteum in order to reduce these problems. Variations of ACI that you may come across include CACI (collagen autologous chondrocyte implantation) where a collagen membrane is used to replace the periosteal tissue and the cells are injected into the chamber or MACI (matrix-induced autologous chondrocyte implantation) where the cartilage cells are seeded directly onto a membrane which is then glued into the defect. This is a fast moving area in medicine with new variations of the ACI technique emerging all the time.


There are a lot of differences in the ACI procedures that are available for patients across different countries. For instance in the USA at present the Food and Drugs Administration haven’t approved the use of the artificial membranes that have been in use in Europe for several years now and some countries, Italy for example, are using arthroscopic techniques for ACI when most counties are still performing open surgery. In addition, ACI is expensive compared to other articular cartilage repair procedures due to the two stages and the cost of growing the cartilage cells and there are quite a few countries where it is difficult to get insurance companies to agree to ACI procedures.


For more information on ACI take a look at the published literature and additional information on this topic.




First of all osteotomy isn’t an articular cartilage repair technique. So why is it in this section I hear you ask? Well because osteotomies are surgical procedures that can help to protect areas of articular cartilage damage and they are therefore commonly performed in conjunction with articular cartilage repair procedures. So what is an osteotomy?


Osteo is bone and otomy is to take away so an osteotomy is a procedure where the surgeon removes a wedge of bone from either your thigh bone (femur) or more commonly the shin bone (tibia). Osteotomies are techniques that are used to correct the mechanical alignment of the knee by surgically repositioning the joint. This is useful when you have articular cartilage damage in one area (compartment) as the osteotomy will help to shift some of the forces from the damaged part of the joint to the other side of the joint so giving some protection to the damaged side of the knee.


There are several different surgical techniques and you may come across the terms ‘opening wedge’ and ‘closing wedge’. An opening wedge osteotomy means that a wedge is opened up where as a closing wedge osteotomy is where a wedge of of bone is taken out as shown in the diagram to the right. The choice of osteotomy will depend on what aspect of mechanical alignment needs to be corrected. The most common osteotomy that is used for patients with tibiofemoral malalignment is a high tibial osteotomy (HTO). For patients with patellofemoral (knee cap) malalignment the osteotomy procedure that is used is called either a tibial tuberosity osteotomy (TTO) or tibial tuberosity transfer (TTT).


It must be noted that an osteotomy isn’t a solution to the problem of the articular cartilage damage but by off loading the damaged area it can help to delay its progression. If articular cartilage damage is present in both sides of the knee joint then an osteotomy isn’t suitable. The rehabilitation is also lengthy. Therefore osteotomy is generally reserved for young, active patients.


Why is rehabilitation after articular cartilage repair so




Rehabilitation following ANY articular cartilage repair procedure is long and demanding. There are many variations in rehabilitation protocols so it is not possible to discuss specific guidelines in this article. If you are planning to have, or have had, an articular cartilage repair you should be given a rehabilitation programme based on the surgical procedure and your individual needs. This section will provide you with an insight into why rehabilitation is so important and give you an understanding of the general principles of rehabilitation after articular cartilage repair.


First of all let’s address the question “why is rehabilitation so long after articular cartilage repair?” Well, the main reason is due to the time that it takes for the cartilage cells to adapt and mature into repair tissue – basically cartilage is extremely slow to adapt. To give you some idea full adaptation of muscle takes approximately 35 weeks whereas cartilage only undergoes 75% adaptation in 2 YEARS! This can be seen visually in the graph below. Rehabilitation needs to mirror the adaptation of the cartilage repair and therefore it tends to be slower than rehabilitation programmes for the repair of other tissues, for instance the anterior cruciate ligament. The progression of rehabilitation is always limited by the speed of adaptation of the slowest tissue so if that is the articular cartilage then you can see why rehabilitation after articular cartilage repair takes a while. If the rehabilitation progresses too quickly the new cartilage repair is put under too much stress and as the weakest link it can fail


Source: Cas Rekers



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General principles of articular cartilage rehabilitation


There are many factors that need to be taken into account when considering rehabilitation following articular cartilage repair but the main ones are:


  • * The location of your defect.
  • * The size of your defect.
  • * What articular cartilage repair procedure you have had.
  • * If you have had any other surgical procedures such as an osteotomy or an anterior cruciate ligament reconstruction.

The overall aim of the rehabilitation process is to restore your function whilst protecting and facilitating the adaptation of the repair tissue.


Whichever articular cartilage repair procedure is carried out there is always the issue of the delicacy of the repair tissue after the surgery. In an ACI the repair tissue can be just cells in a fluid under a thin membrane and for microfracture the repair tissue is initially just a blood clot. On one hand there is a need to protect the repair tissue but on the other hand controlled movement is essential for the health of the new repair tissue and for restoring function. So this is very much a double-edged sword and this is one of the reasons why you need to be on the same wavelength as your surgeon and therapist with regards to rehabilitation and make sure you stick to the guidelines you are given. Even if you think you are doing well and don’t have symptoms it doesn’t mean that your repair is ready to move on. Communication is the key.


Early controlled movement is important for articular cartilage repair but any excessive loading will increase the risk of damage to the delicate repair tissue. In order to minimise this risk you need to know a bit more about the two main ways in which you can stress your cartilage repair.


  1. Cyclical compressive stress is when one articular surface squeezes the articular cartilage on the opposite articular surface for a short time and then the pressure is released allowing the compressed articular cartilage to go back to its original volume. This is good for the articular cartilage as this is the mechanism by which it is naturally nourished in the joint and compressive stress helps the cartilage to adapt and increase in thickness.
  2. Shear stress is when one articulating surface slides across the other. Shear stress should be avoided as much as possible as it disrupts the articular cartilage fibres resulting in wear.

There are a number of ways in which your rehabilitation programme will be designed so that your repair receives a good level of compressive stress but not the excessive shear stress that could cause damage to the repair.


In the early stages after surgery, especially, in the USA you will probably need to use a continuous passive motion (CPM) machine which takes your leg passively through a controlled range of movement. If you aren’t given a CPM machine don’t worry, access to these is limited in some countries and where this is the case you will be given some gentle exercises to do such as a facilitated heel slide.


For the first few weeks after your surgery you may have restrictions on the amount of weight you can put through your leg and everyone who has had cartilage repair surgery will be on crutches initially. Some people will also be in a brace for a number of weeks that limits the amount you are able to bend your knee. These restrictions will be dependent on, in particular, where your articular cartilage damage was as the joint mechanics are different between the tibiofemoral joint and the patellofemoral joint. So just because someone has had the same articular cartilage repair procedure to you they may have a very different rehabilitation program due to the difference in location of their defect.


Throughout your rehabilitation program your surgeon and therapist will advise you on which exercises are more likely to produce shear stress on your articular cartilage repair site and which exercises will help to provide an optimal amount of compressive stress to facilitate cartilage.


The surgery for articular cartilage repair procedures are one day – rehabilitation can last up to 2 years or longer. The length of time for rehabilitation has implications for your normal every day life. You should be aware of these BEFORE you decide to go ahead with articular cartilage repair surgery. Many of the articular cartilage repair procedures will need you to be non weight bearing or only partially weight bearing for a period of time. This means that you will be on crutches and have reduced mobility. You will need to consider child care, transportation, time off work, getting around the house, shopping, cooking and other activities of daily life. Going through an articular cartilage repair procedure doesn’t just affect you the patient, it affects everyone around you too – family, friends and work colleagues. Therefore, it is always a good idea to take someone close to you along to the appointments with the surgeon before the surgery so they can appreciate the postoperative implications



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Published Literature


Alford, J. W. and Cole, B. J. (2005) Cartilage restoration, Part 1: Basic science, historical perspective, patient evaluation, and treatment options. Am J Sports Med, 33(2): 295-306.


Alford, J. W. and Cole, B. J. (2005) Cartilage Restoration, Part 2: Techniques, Outcomes, and Future Directions. Am J Sports Med, 33(3): 443-460.


Dunn, W. R., Lyman, S., Lincoln, A. E., Amoroso, P. J., Wickiewicz, T. and Marx, R. G. (2004) The effect of anterior cruciate ligament reconstruction on the risk of knee reinjury. Am J Sports Med, 32(8): 1906-14.


Brittberg, M., Peterson, L., Sjogren-Jansson, E., Tallheden, T. and Lindahl, A. (2003) Articular cartilage engineering with autologous chondrocyte transplantation. A review of recent developments. J Bone Joint Surg Am, 85-A Suppl 3109-15.


Hambly, K., Bobic, V., Wondrasch, B., Van Assche, D. and Marlovits, S. (2006) Autologous chondrocyte implantation postoperative care and rehabilitation: Science and practice. Am J Sports Med


Jakobsen, R. B., Engebretsen, L. and Slauterbeck, J. R. (2005) An analysis of the quality of cartilage repair studies. J Bone Joint Surg Am, 87(10): 2232-2239.


Knutsen, G., Engebretsen, L., Ludvigsen, T. C., Drogset, J. O., Grontvedt, T., Solheim, E., Strand, T., Roberts, S., Isaksen, V. and Johansen, O. (2004) Autologous Chondrocyte Implantation Compared with Microfracture in the Knee. A Randomized Trial. J Bone Joint Surg Am, 86(3): 455-464.


Mithofer, K., Peterson, L., Mandelbaum, B. R. and Minas, T. (2005) Articular cartilage repair in soccer players with autologous chondrocyte transplantation: functional outcome and return to competition. Am J Sports Med, 33(11): 1639-1646.


Peterson, L., Brittberg, M., Kiviranta, I., Akerlund, E. L. and Lindahl, A. (2002) Autologous chondrocyte transplantation. Biomechanics and long-term durability. Am J Sports Med, 30(1): 2-12.


Mandelbaum, B. R., Browne, J. E., Fu, F., Micheli, L., Mosely, J. B., Jr., Erggelet, C., Minas, T. and Peterson, L. (1998) Articular cartilage lesions of the knee. Am J Sports Med, 26(6): 853-61.


Shelbourne, K. D., Jari, S. and Gray, T. (2003) Outcome of Untreated Traumatic Articular Cartilage Defects of the Knee: A Natural History Study. J Bone Joint Surg Am, 85(90002): 8-16.


Steadman, J. R., Briggs, K. K., Rodrigo, J. J., Kocher, M. S., Gill, T. J. and Rodkey, W. G. (2003) Outcomes of microfracture for traumatic chondral defects of the knee: average 11-year follow-up. Arthroscopy, 19(5): 477-84.


Wang, Y., Ding, C., Wluka, A. E., Davis, S., Ebeling, P. R., Jones, G. and Cicuttini, F. M. (2006) Factors affecting progression of knee cartilage defects in normal subjects over 2 years. Rheumatology, 45(1): 79-84.


Wroble, R. R. (2000) Articular Cartilage Injury and Autologous Chondrocyte Implantation: Which Patients Might Benefit? Physican and Sportsmedicine, 28(11).


Additional Information


Web articles


Bobic, V. ISAKOS Current Concepts. The utilisation of osteochondral autografts in the treatment of articular cartilage lesions.


Diduch, D.R. & Cohen, S.B. Joint repair: Treatment options for articular cartilage injury.


Johnson, D. Articular cartilage update


Luscombe, K. & Oliva, F. A Short Basic Sciences Review of Articular Cartilage.


Niall, D.M.& Bobic, V. ISAKOS Current Concepts. Bone Bruising and Bone Marrow Edema Syndromes: Incidental Radiological Findings or Harbingers of Future Joint Degeneration?


Minas, T. Autologous chondrocyte implantation for chondral defects of the knee.


Wroble, R.R. Articular Cartilage Injury and Autologous Chondrocyte Implantation Which Patients Might Benefit?


Tissue Engineering Companies


Ars Arthro - Patient Information


Fidia Advanced Biopolymers


Geistlich Biomaterials - Patient information


Genzyme Biosurgery - Carticel Patient Information


OBI OsteoBiologics - Patient Information


Tigenix - Patient Website


Other Useful Sites


The Cartilage Research Foundation


Webcast of Carticel Articular Cartilage Repair
NB This webcast is not for the faint hearted as it shows video of the actual surgical procedure.


Cartilage Restoration Symposium Videos
NB These videos are not for the faint hearted as they show images of actual surgical procedures.



ACKNOWLEDGEMENT: This is article was originally written by Karen Hambly for the


KNEEguru website as a KNEEguru Keynote