PatelloFemoral Replacement : A resurfacing of the worn back of knee cap section of the knee, preserving the "main tibio-femoral " joint.

Pain

Where is it felt?

Back of the knee cap (knee cap = patella) wear typically causes pain at the front of the knee, sometimes below or underneath the knee cap. Commonly, it is also felt to the outer side of the knee cap. Patients often find it difficult to precisely locate the pain and will point with their index finger  or using both hands at the front of the knee, feeling it is "inside".

Occasionally it is felt behind the knee, in the midline, a few inches above and below the crease at the back of the knee. This is referred pain feedback via the Middle Geniculate Nerve. This particular nerve supplies the back of the knee relaying feeling or pain from the end of the thigh bone, upon which the knee cap slides over.

Pain is typically worse on:

• Stair or slope ascent or descent.  Reasonably good whilst walking on the flat. 
• Arising from a low seat such as a toilet seat or car seat,
• Semi squatting positions for example lunges
• Squatting is particulary difficult for those with back of knee cap wear.

Giving Way:

The knee can threaten to give way or give way on activities such as stair descent, or going up or down a step or kerb. This is because there is, or potentially could be, so much pain that an automatic protective reflex prevents the thigh muscle working causing the knee to drop 4 inches or so to avoiding  pain or further damage. The partial giving way is a protective mechanism.  It is a bit like the petrol cutting out on an engine, it is not possible to overide it.

Treatment:

In the early stages the following are often helpful:

• Weight reduction - for each pound lost there is 4 lbs less going through the knee cap when going up and down on stairs.
• Vastus medialis strengthening programme ( Specialist knee exercises)
• Taping - a physiotherapy technique to offload the outer side of the knee cap
• Specialist Knee Brace - a method for offloading the out side of the knee cap.
• Injection of cortisone.

The next level of treatment is appropriate for some:

Key hole surgery

This minor procedure can be helpful in assessing  the tracking of the knee cap. It may also involve a  Lateral Release, which if required, can help correct patella mal-tracking, easing discomfort. Trimming or smoothing-off irregular surfaces behind the knee cap is also very beneficial. The procedure includes thorough lavage ( removing inflammaory chemicals using a saline wash) and an injection of hydrocorticone, which works very well in reducing pain levels.

The evidence for lateral release in wear and tear behind the knee cap, indicates patients pain is reduced by 50%.

The next level depends on the degree of wear and the degree of maltracking.

Either formal realignment surgery (Tibial Tubercle Anteromedialisation) - this makes use of a persons own surfaces in a different way and offloads the worn areas, or patellofemoral prosthetic resurfacing. The choice depends on the amount and location of the arthritis.  Investigations such as CT and MRI are helpful in the decision making.