Kneecap pain is often enigmatic, that is it comes and goes or may be experienced in different places at different times.
Although Patellofemoral Syndrome is commonly flagged as the cause of a patient's pain experienced around the kneecap, patellofemoral syndrome itself is not a discrete condition, but rather a group of symptoms related to the alignment or tracking of the kneecap but which may have a variety of contributing causes. These causes may be related, for example a flat foot may also contribute to stress on the lower back, and both of these may lead to pain around the kneecap via different routes. Symptoms may vary depending on muscle fitness, muscle balance (eg quadriceps/hamstrings balance), footware, insoles, cycle saddle height, alterations in gait, unusual levels of exercise, or combinations of such factors.
Plicae are normal folds of joint lining, and they vary from person to person. Some people have no plicae at all and other may have plical folds stretching right across the joint space. The problem with surgeons being vague about plicae is that the medical literature has in the past stressed that plicae are normal and do not cause pain, while many other authors have convincingly demonstrated certain thickened plica as causing joint surface damage. Plicae may go unreported on MRI scan, even though they may be visible, as the radiologist may be one of those clinicians who consider them to be unimportant.
Referred pain is pain experienced in one place but which is actually being triggered in another.It is important that the investigating clinician keeps in mind that pain experienced in the knee may in fact be arising elsewhere.
Trigger point pain
Trigger points are 'knots' in the muscles that may cause tenderness at discrete points around the knee, but they also may trigger pain which appears to come from the knee itself. To add to the difficulty knee problems may cause trigger points to flare up.
Pain referred from the hip
Children may be born with hip problems, for example Perthes Disease, and complain only of knee pain. Adolescents with Slipped Capital Epiphysis of the hip may experience pain in the knee. Adults with hip arthritis may experience severe knee pain.
A hip examination should be a normal part of any investigation of knee pain. It is a curious fact that a hip problem may present with only the symptom of pain experienced in the knee. In this case the knee may be blamed although it may be completely normal.
Pain referred from the lower spine
A low back problem, such as a herniated disc, may lead to pain in the knee, and also pain in other parts of the lower leg. Usually the pain is experienced in a specific distribution depending on the which vertebral disc is damaged.
Complex regional pain syndrome
Previously called RSD (reflex sympathetic dystrophy) is another form of referred pain. This is a condition where the knee has suffered an insult - injury or surgery - and the pain, instead of getting better, becomes unremitting and out of proportion to the apparent situation. The patient may also feel funny feelings in the region, and the skin may become discoloured and blotchy and exquisitely sensitive to even the slightest touch.
This diagnosis is often missed in the early stages - but it is important to be aware of it as it may respond to early treatment, but if allowed to progress the limb may become permanently wasted.
Different clinicians may use different words when describing the same problem. There is no clear standardisation of patellar terminology. So this makes the interpretation of medical publications frequently confusing as authors and readers may have different ideas of what is being described.