More than a simple hinge

Orthopaedic surgeon Dr Thirukumaran provides Fit For LIfe information about knee pain and a solution to such pain for certain patients – autologous chondrocyte implantation. 

THE knee joint’s main function is to bend and straighten. However, it can also twist and rotate to some degree. To do this, the knee joint relies on different structures –bones, ligaments, tendons and cartilage.  

The knee joint involves three bones – the thighbone or femur, the tibia (one of the bones in the lower leg; the other bone in the calf, the fibula, is not involved in the joint) and the kneecap or patella (along the front of the femur).  

Ligaments are fibrous bands that connect bones to each other. The knee has four important ligaments that connect the femur to the tibia: the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). These provide front and back and rotational stability to the knee.  

Comparing healthy and damaged cartilage in a knee joint.

The medial collateral ligament (MCL) and lateral collateral ligament (LCL) provide medial and lateral stability to the knee.  

These ligaments are often affected when the knee is subjected to movements beyond its normal range. Hence, sports professionals often injure these ligaments, and serious injuries can often threaten the career of such athletes. 

Tendons are also fibrous bands, but unlike ligaments, these connect bones to muscles. The important tendons in the knee are the quadriceps tendon (connects the quadriceps muscle on the front of the thigh to the patella) and the patellar tendon (connects the patella to the tibia – technically this is a ligament because it connects bones).  

Cartilaginous structures called menisci lie within the end of the bones that form a joint. These structures are crucial as they provide both space and cushion for the knee joint.  

When problems arise in the knee, the primary symptom is pain. Take note that the nerves that provide sensation to the knee come from the lower back and also provide hip, leg, and ankle sensation.  

Hence, pain from a deeper injury (called referred pain) can be passed along the nerve to be felt on the surface. Knee pain, therefore, can arise from the knee itself or be referred from conditions of the hip, ankle, or lower back.  

In general, knee pain is either immediate (acute) or long-term (chronic). Acute knee pains can be caused by an acute injury or infection. Chronic knee pains are often from injuries or inflammation (such as arthritis) but can also be caused by infection. 

Elderly knees 

In the elderly, the most common cause of knee pain is osteoarthritis. Osteoarthritis is caused by degeneration of cartilage in the knee. In its extreme form, the cartilage will be completely eroded, and the femur will rub on the tibia (bone on bone). When this occurs, it results in a chronically painful knee that is often more painful with activity.  

Simply put, cartilage is the shiny, smooth white tissue found at the end of bones that form joints. It consists of a matrix of connective tissue called chondrocytes, which are held in a matrix of connective tissue.  

This cartilage, along with joint fluid, is responsible for the smooth and pain-free movement of the knee joint.  

Arthritis can be caused by wear and tear (osteoarthritis), infection( septic arthritis) and autoimmune inflammation (rheumatoid arthritis) among others. 

In total knee reconstruction, all damaged cartilage from the knee joint is removed and the articulating surfaces of the knee are resurfaced with artificial surfaces such as metal or plastics.

Osteoarthritis or wear and tear arthritis is the most common cause of arthritis and joint pain in the elderly. This wear of articular cartilage especially occurs in the weight bearing joints and the knee joint is the most common joint involved.  

As this disease progresses the joint may also become deformed as cartilage wear occurs and this can commonly result in bow legs as seen in many people above 60. 

Unfortunately articular cartilage is one of the body tissues with a limited ability of regeneration. Thus once damaged or degenerated, the area of damaged cartilage is usually permanent.  

Young knees 

In the young, knee pain is generally caused by damage to the ligaments, menisci or cartilage, chiefly as a result of trauma from sports or road traffic accidents. Ligament injury, especially the anterior cruciate ligament, is extremely common among athletes. 

Twenty years ago, this injury would have ended careers. Now, surgery is now so successful that the ligament can be reconstructed in less than two hours with minimal pain or scars. Patients can return to the same level of competitive sport and the list of athletes who have successfully undergone such procedures are long and include Alan Shearer, Ruud Van Nistelrooy, Roy Keane, Fredie Lundjberg among others. Menicus injuries also can be successful repaired. 

Articular cartilage injury in a young person, until recently, posed a more difficult problem. As mentioned earlier, cartilage does not regenerate and replacement with artificial surfaces are not an option in the young and active. Knee pain from cartilage injury thus used to be permanent.  

Treatment options 

Current available medication does not stimulate any repair or regeneration of cartilage. No scientific evidence consistently show that the popular joint supplements or joint foods sold over the counter have any beneficial effect, contrary to popular belief. 

Fortunately, surgical options are available. In the elderly, a total knee replacement is an excellent option. In this surgery, all damaged cartilage from the knee joint is removed and the articulating surfaces of the knee are resurfaced with artificial surfaces such as metal or plastics. Total knee replacement is an excellent treatment option as it renders the patient pain free and can also correct stiffness and deformity.  

However it is not ideal in the young and active as these artificial materials have a limited accumulated load tolerance and will eventually fail. 

When the knee is injured, pain and swelling ensues due to substances released by the body that cause inflammation.

As with other areas in medicine a more biological or natural solution looks to be the ideal solution ? 

Replacing cartilage 

ACI or autologous chondrocyte implantation is one of the few treatment options for this problem. Developed in Sweden in the late 1980s, it now beginning to gain acceptance worldwide. 

In this procedure, healthy articular cartilage is “harvested” from an uninjured area of the patient’s joint. Chondrocytes or cartilage cells derived from this are then cultured and multiplied in a laboratory. These are then re-implanted in the joint to replace damaged areas of cartilage. These cells grow and replace the damaged cartilage and clinical results have shown that the patient experiences excellent relief of symptoms. 

Used widely now in Europe and the US, the only drawback of this technique is that an expensive, well-equipped laboratory with highly specialised scientists are necessary for the culturing of the chondrocytes. Surgeons also need to be well trained in the operative technique. 

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