Patellofemoral pain

The examination of the patient begins with the 'history', whereby the doctor spends time listening to his patient.

• how the problem began, how it progressed and the situation at the moment
• what treatment has been given to date
• what makes the problem worse and what makes it better

A 'history' is not merely letting the patient talk. It is a subtle process, whereby the doctor guides the patient's recollection of events, so that the important diagnostic pointers are not missed. The doctor helps the patient recall the time sequence of events,and what management might have been undertaken in the past. This can be very time consuming when a patient is not well informed - that is why a course like this is so invaluable.

The nature of the injury

Many of the problems causing pain around the knee cap are not accompanied by a specific injury. Onset of pain is frequently insidious - it 'creeps up' on the patient, often becoming aggravated by unusual exercise.

But if there has been a specific injury, it may shorten the differential diagnosis.

If the pain began with a direct blow (or fall) the doctor will be (should be) thinking of local damage and inflammation. This may include a fracture, a neuroma, an inflamed plica, synovitis, bursitis or joint cartilage damage.

The mechanism of injury will give important clues to the diagnosis. So the doctor should ask -

• How did the injury occur? - A fall onto the knee cap or a direct blow can split or shatter the patella. A medial plica can become bruised. A chunk may be chipped out of the joint surface. A direct blow above the knee may bruise or tear the muscle or tendon, and cause a bursa to be inflamed. A direct blow to a previously unsymptomatic suprapatellar plica may cause it to become symptomatic, and it may later become scarred and continue to cause problems. A strain (eg weightlifter) may rip some muscle fibres, tear the tendons or avulse the patellar tendon from the bone. An awkward twist in a knee vulnerable to patellar instability may result in -
  • patellar subluxation - A sudden 'catching' as the patella rides up the side of the trochlea, traumatising the joint surface.
  • patellar dislocation - As the patella rides right over the edge of the trochlear wall, the medial restraints (eg medial patello-femoral ligament) may rip, leaving the knee even more vulnerable than before.

An injury may be further aggravated by quads and hamstrings wasting or shortening, which as we know, can themselves lead to pain around the knee cap -

• How long ago was the injury and how has it been managed?
  • quads wasting or inhibition - The quads muscle becomes 'inhibited' very easily where the knee has suffered an insult - there may be neither damage to the muscle nor wasting, but the quads simply won't 'fire'. Without appropriate physiotherapy inhibition may progress to actual wasting, with diminution of the muscle bulk. This may result in maltracking and pain around the patella.
  • hamstrings shortening when limping or using crutches - Holding the knee for days or weeks in a bent position, for example when using crutches, may result in shortening of the hamstrings, again affecting the mechanics of the knee and making it even more vulnerable to injury.

The nature of the pain

The exact nature of the pain will often point the doctor in the right direction. The doctor therefore inquires about many aspects of the pain, for example -

• Was the pain brought on by an injury?
• Where is the pain specifically located?
• What aggravates and quiets the pain?
• Is the skin particularly sensitive in this or that area? Is there numbness, tingling, or burning?
• What is the nature of the pain? - Is the pain dull and unremitting? Is it intermittent and fleeting? Does it only hurt after something is felt to 'catch'? Arthritic pain is described as 'gnawing' because it seems to be constantly there but gets worse in little bursts.
• where is the pain specifically located? - Though we are discussing pain around the knee cap, it is important to keep in mind that disorders of the extensor mechanism may manifest with pain on either side of the knee or even in the back of the knee! Very often it is vague, and the patient simply rubs the front of the knee with the flat of the hand when asked about the distribution of the pain. However, when a patient uses their index finger to locate a specific locus of pain, it is diagnostically very helpful -
  • over the front of the patella - stress fracture, traumatic fracture, bipartite patella, pre-patellar bursitis
  • immediately under the patella, along its edge - patellar tendinopathy, fat pad syndrome, Sinding-Larsen & Johansson syndrome
  • on the bump a thumbsbreadth below the patella - Osgood Schlatter's condition
  • immediately above the knee cap, along its edge - quadriceps tendinopathy
  • on the inner aspect of the patella - medial patellar plica
  • on the outer aspect of the patella - patellar tilt
• Is the pain present day and night? - If the pain is present day and night, patellar malalignment is not likely the problem. Continuous pain points to deeper issues, like osteochondritis dissecans.
• What aggravates and quiets the pain? - It may be useful diagnostically if the pain is consistently brought on by a specific activity. Some classic examples include -
  • running - repetitive flexion and extension during running may inflame the ilio-tibial band on the outer aspect of the knee as it slips back and forth over the little bony bump known as the femoral epicondyle
  • jumping - jumping activities like ballet may bring on pain just below the patella as a result of patellar tendinopathy
  • breaststroke - inflammation of the bursa under the pes anserine tendons on the inner aspect of the knee, just below the joint line
  • kneeling - prolonged kneeling, such as in carpetlaying may lead to an inflamed pre-patellar bursa

History of swelling

Does the knee become visibly swollen? - In most of the long list of conditions interfering with the mechanics of the knee, swelling is absent. Swelling in association with pain around the knee cap gives you a clue that there is an abnormal process going on inside the knee cavity itself -

• generalised swelling - this implies that there is either blood or excessive joint fluid inside the knee. Blood would usually be indicative of traumatic damage - a tear or a fracture. Excessive joint fluid indicates an irritated inner joint lining. This may be as a consequence of chemicals released from damaged bone or meniscus, locally damaged joint lining, or a general disorder of the joint lining (synovitis). So, for example, a painful plica without swelling may indicate a simple mechanical problem, but the presence of swelling may indicate that the tissues are very irritated or there has been damage to the joint surface.
• localised swelling - a localised swelling implies that the problem lies outside of the joint cavity. The swelling may be due to fluid filling a bursa, for example. A tense bursa (eg pre-patellar bursa) may look fairly dramatic and be acutely painful.
• Do other joints also swell? - There are several well recognised forms of arthritis in which the knee becomes involved as simply one aspect of a more generalised inflammatory disorder. Examples include rheumatoid arthritis and gout.

Noises in the knee

Noises inside the knee often cause patients considerable anxiety. To be honest, we simply do not know what causes many of the noises described by our patients, but some do appear to be 'benign' - ie not significant.

• Crepitus - Crepitus is a fine crackling sensation, palpable with the flat of the palm, and with a sound like 'rice krispies' being scrunched in the hand. This symptom is very often associated with stress to the patella itself, for example from malalignment or a plica. Its presence implies damage to the joint cartilage.
• Other noises - Patients may report a variety of noises, or 'popping' or 'snapping' sensations.
• Snapping on the lateral aspect of the knee is a classical symptom of a tight ilio-tibial band. Snapping on the medial side of the patella is classically a tight medial plica.

Pseudolocking, instability, catching

Let's start by defining 'locking'. In locking the knee excursion gets blocked at a particular angle, and the patient is unable to achieve a full excursion.

'Pseudo-locking' is similar, except that the patient, after a very short time, can overcome the block and get the knee moving again. Pseudolocking may be due to a plica, amongst other things not related to our current topic.

'Catching' is a sensation during normal movement, when a sudden pain is experienced and the knee does not go through its full excursion, being halted reflexly. It may be due to something catching in the joint (eg synovium), or to ''- the knee cap momentarily leaving the groove of the trochlea and riding up its wall.

'Subluxation' is another common symptom where are is some confusion - this time with semantics. The word means different things to different people. To a patient, it is a symptom. To a radiologist it is an x-ray sign, which may or may not be associated with symptoms. To the examining doctor it may mean just that HE is able to 'sublux' the patella. Like 'chondromalacia', we need to be sure of what we are talking about when we use this term.