Cartilage (joint surface) damage is serious as cartilage heals poorly, and damage may be the beginning of a process leading to arthritis.

 

What is the articular cartilage of the patella?

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The shiny white cartilage surface of the patella is at the back of the patella, where it makes contact with the cartilage of the femur as the knee is bent and straightened.

Damage to the patellar cartilage is often mirrored by damage to the femoral cartilage as well, and then this is referred to as 'patello-femoral' damage.

Management tends to be a combination of management of any underlying faulty mechanics and management of the joint cartilage itself.

 

What is chondromalacia?

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Chondromalacia is a word used to describe the condition of joint cartilage when it becomes softened.

Chondro=cartilage

Malacia=softened.

That is all that chondromalacia means! Unfortunately, this term was used in many publications, both on the web and in professional medical publications as if it was a discrete diagnosis, involving pain in front of the knee, difficulty with stairs, crackly noises on bending the knee and other symptoms now accepted as general symptoms of any patellar disorder.

This has caused tremendous distress for patients. They are often told that they have 'chondromalacia' and they accept this as a diagnosis and seek a specific management. But in fact their symptoms may be due to any one of the patellar disorders, and what they really need is a proper assessment of the patella, the gait, the trunk and the feet, and a proper diagnosis.

chondromalacia

In the medical literature, authors are mostly now taking care to put this term into its proper context, using it to describe the cartilage changes a surgeon may note when he examines the cartilage surfaces during arthroscopy, for example, as you see in this photograph. Such softening is also known as Grade I on the Outerbridge scale of cartilage damage, when the surgeon can 'dimple' the softened cartilage with a blunt probe. But on the internet there is still widespread misuse of the term.

 

Grades of cartilage damage

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Surgeons will grade the cartilage degeneration for the record, so that they can compare any changes over time. Although there is more than one classification, the gradations are based on -

  • The first stage is early joint damage with softening which the surgeon can feel while probing. This is chondromalacia. There is no break in the integrity of the cartilage, but it is clearly unhappy. It may be associated with pain and crunchy noises in the knee.
  • The next step is when the surface begins to break up, but the bone itself still has a covering of cartilage. There may be fissures (cracks) or fronds (crabmeat).
  • Then the bits start to break off and float into the joint. At this stage the process may accelerate due to the damaged surfaces giving off enzymes which themselves are destructive. The lining of the joint (synovium) sometimes becomes inflamed.
  • Eventually the underlying bone becomes exposed, and the cartilage is unable to heal across the gap without assistance.
  • The irritated bone tries to heal by itself, but in a deranged way, pushing up edges of bone at the joint surfaces and in the notch where the cruciate ligaments lie. These are called 'osteophytes' ('bone mushrooms') and they can restrict the joint's movement and damage the ligaments.
  • The degeneration then often progresses to the menisci and they too start to degenerate.

 

Patellofemoral resurfacing

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Patellofemoral resurfacing is a form of partial knee replacement where only the undersurface of the patella and the groove of the femur are replaced with artificial components.

The patellar component is usually a high density plastic (eg polyurethane) and the femoral groove is replaced with metal (eg titanium). The components may be replaced on their own. 

trochlear implant patella to show cut for resurfacing patellar resurfacing
Trochlear groove resurfacing on the femur. The patella showing how the undersurface is cut and discarded. The undersurface is replaced with plastic.

 

Controversy about patellar resurfacing with TKR

Although femoral resurfacing is now well accepted the patellar component of patellofemoral resurfacing remains a controversial topic, particularly in relation to patellar resurfacing as part of a total knee replacement (TKR). Not resurfacing the patella during a total knee replacement may lead to pain and the procedure may be opted for as a secondary step for this reason. However, although pain is not a big feature of resurfacing of the patella, the procedure can be associated with complications such as fracture of the patella, fracture, loosening or dissolution of the components.

Reports from surgeons who are familiar with resurfacing of the patella and trochlear, however, suggest the results are improving as the procedure becomes more refined.


The controversy of patellar resurfacing in total knee arthroplasty: Ibisne in medio tutissimus?. Schindler OS. Knee Surg Sports Traumatol Arthrosc. 2012 Jul; 20(7): 1227–1244.

 

Consequences of a patellectomy

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Patellectomy is the procedure of surgical removal of the patella.

Complete removal is called 'complete patellectomy', as compared to 'partial patellectomy' where only a part of the patella bone is removed.

If you have read the section on patellar mechanics you will know that the patella lies right within the tendon of the quads muscle. To remove it, a cut is made in the tendon and the patella is freed and removed like a nut from its shell, leaving the tendon itself still functional, although inefficiently so.

 

Problems after patellectomy

Patellectomy is never (or should never) be undertaken lightly. Although it may be unavoidable in certain cases, the change in anatomy has significant consequences -

  • Extension lag - the 'lever' mechanism of the quads muscle becomes less efficient without the patella, and it may be impossible to actively achieve the last few degrees of extension
  • Increased laxity - the loss of the 'spacer' effect of the patella leaves the quads tendon lax, and prone to dislocation
  • Vulnerable femoral joint surface - without the protection of the bony patella, the important cartilage covering the end of the femur is easily damaged by knocks and falls (which themselves may be more frequent because of the laxity)
  • Knee replacement limitations - knee replacement is problematic after patellectomy. The relatively recent development of 'resurfacing' procedures offers some hope for relief of instability (replacement of the trochlea with an artificial metal surface).

 

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