#condition - Knee

Anterior Knee Pain

‘Anterior Knee Pain’ is NOT a diagnosis ! It is simply a symptom – meaning that a patient is complaining of pain at the front of the knee.

Symptoms at the front of the knee may be due to a variety of possible causes. The exact site of the pain and the nature of the actual symptoms will give a strong guide as to the potential likely causes.

Site of the pain

Pain directly behind the kneecap – this implies that there might be some damage (cartilage damage or arthritis) in the joint where the back of the kneecap contacts the front of the knee – the patellofemoral joint. Problems with the patellofemoral joint can be caused by trauma (eg falling directly onto the front of the knee), by wear and tear (degeneration/arthritis) or problems can arise due to biomechanical problems, such as maltracking (where the kneecap sits too far over to one side rather than sitting normally in the middle of the front of the knee).

Pain in front of the kneecap with swelling – can be due to an inflamed sack of fluid called prepatellar bursitis.

Pain just below the kneecap – this can be due to either inflammation of the patellar tendon (patellar tendonitis) or scarring/inflammation of the tissue behind the patellar tendon (known as the fat pad).

Pain around the inner side of the front of the knee – this can be due to a shelf of scar tissue inside the knee rubbing, called a medial plica.

Why is anterior knee pain worse with certain activities?

When the knee is relatively straight and the quadriceps muscles contract, the kneecap is pulled upwards and the forces between the back of the kneecap and the front of the knee are not that great. However, when the knee is bent (flexed), the large forces of the contracting quads, pulling the kneecap one way, are counterbalanced by large tension in the patellar tendon, attaching the kneecap to the front of the shin. The resultant force is a massive force pushing the kneecap hard onto the front of the knee.

This is why anterior knee pain is so often worse with certain specific activities, such as:-

  • going up / down stairs (particularly down)
  • sitting for long periods (eg in a cinema)
  • driving long distances

The knee feels like it 'pops out'

People who suffer from ‘dislocations of the knee’, with feelings of the knee popping out are often suffering from patellar instability.

The back surface of the kneecap is V-shaped and it sits, like a keel, in a groove than runs in the front of the knee (the trochlear groove).

In some patients, the groove in the front of the knee is too shallow (trochlear dysplasia) and the back of the kneecap is flatter than it should be. The kneecap tends to slip out too far to the outer (lateral) side, and can dislocate sideways out of the groove in the front of the knee as the knee is bent.

Other patients with normal knee anatomy may suffer a traumatic patellar dislocation after trauma, and this can cause ongoing patellar instability.

Patellar instability is a serious condition. Apart from the fact that when the knee gives way, the individual may fall over and badly hurt themselves, each time the patella dislocates the structures inside the knee such as the articular cartilage can suffer increasing levels of damage, increasing the risk of arthritis in the knee in the future. Also, with every dislocation the soft tissues at the front of the knee get stretched further, potentially making the patella even more unstable and increasing the likelihood of further additional dislocations in the future.

Patients suffering from patellar instability should be investigated thoroughly as soon as possible – often with X-rays and MRI scans and sometimes with keyhole surgery (arthroscopy), to indentify the exact contributory causes of the instability so that a treatment plan can be tailored to each particular patient’s problems. This often requires surgical stabilisation procedures.

Patellar maltracking

This is a very common problem. Maltracking pretty much always means lateral maltracking of the patella. The patella normally runs smoothly up and down the trochlear groove in the middle on the front of the knee. However, if the patella sits too far over to one side, then it will rub against the edge of the trochlear groove and cause pain from pressure overload and, eventually, increased wear and tear.

There are many reasons for lateral patellar maltracking, with patients often having more than one of the possible contributory factors at the same time. Some of the things that may cause maltracking include:-

  • weakness in the vastus medialis (VMO) muscle on the inner side of the knee
  • tight tissues on the lateral (outer) side of the knee
    inwardly rotated hips
  • an outwardly angled shin bone (valgus knee)
    flat and outwardly rotated feet (pronated planovalgus feet)
  • trochlear dysplasia (too shallow a groove in the front of the knee)
  • patellar dysplasia (back surface of the patella flat instead of ‘V’-shaped)
  • patella alta (where the kneecap sits too high up at the front of the knee)

As you can see, with this many different things potentially contributing to patellar maltracking, it is essential that the whole leg is assessed fully, both by thorough clinical examination and also with X-rays and/or MRI scans. Only when a very clear picture of the causes has been identified can one formulate a proper treatment plan.

Chondromalacia patella

 

Artroscopic view of the patellofemoral joint

Artroscopic view of the patellofemoral joint

Chondromalacia patella is softening of the cartilage at the back of the kneecap. It causes pain around the front of the knee. It can arise secondary to excess stress on the kneecap from pressure overload secondary to problems like maltracking. However, in young females (teenage / twenties) if often comes on for no apparent cause.

It is important to make sure that the knee is investigated fully, to rule out underlying pathology. If there is nothing at all wrong with the knee apart from just soft cartilage on the back of the patella, then this is best treated by rest (avoiding things that bring on the pain) plus possibly physiotherapy.

Medial plica syndrome and scarring/inflammation of the fat pad

When the knee joint forms in the developing embryo, it starts as two separate compartments; one for the developing femur and one for the developing tibia. The two compartments gradually fuse together, forming the one single cavity of the knee joint. In many people (about 15% of the population) the shelf of tissue in the knee from where the compartments fused together fails to shrink away completely and they are therefore left with shelves or bands of soft tissue inside the knee. These shelves/bands of tissue are called plicae.

The most common plica is a medial plica, which sits at the front inner side of the knee. At the very front of the knee, behind the kneecap and patellar tendon, there is another band of tissue that is sometime present, called the ligamentum mucosum.

In those people who have these shelves/bands of tissue but the tissue is thin and the person is not very physically active, the plicae may cause no symptoms at all. However, if the plicae are thick and if the patient does a lot of exercise, then the plicae can rub inside the knee and become inflamed.

Inflamed plicae cause pain in the knee, normally around the front/inner side or directly behind the patellar tendon. Patients tend to be able to start running but the pain then comes on gradually and gets worse the further they run.

If a plica is causing bad enough symptoms to stop someone from exercising or playing sport, then it is worth having it treated. Treatment of plicae is straight forward. You can try a steroid/cortisone injection, but these often fail to help with plicae. However, the definitive treatment is to have a knee arthroscopy (keyhole surgery), where the plica or ligamentum mucosum is simply removed. The plicae have no actual function in the knee and most patients make a fairly rapid and complete recovery and are able to get back to full activities/sport.

Patellar tendonitis

Patellar tendonitis is also knows as ‘Jumper’s Knee’. The forces across the knee with running and other forms of exercise are huge. The massive forces generated by the quadriceps muscles are transmitted through the kneecap and then down to the tibia (shin bone) by the patellar tendon, which attaches to the tibia at the lump of bone called the tibial tuberosity.

MRI demonstrating patellar tendinosis and ossicle (Osgood-Schlatters disease)

MRI demonstrating patellar tendinosis and ossicle (Osgood-Schlatters disease)

Any tendon in the body can get inflamed, particularly tendons that receive a lot of use. Inflammation in the tendon causes pain that tends to come on with exercise. Pain from patellar tendonitis is felt at the front of the knee, just below the kneecap, and is made worse by activities such as running, squatting or going up/down stairs a lot.

If patellar tendonitis is present for too long then the tendon can become degenerate and full of scar tissue. The scar tissue acts as a block, preventing new blood vessels from growing into the area to heal up the tendon.

In some patients, a small beak of bone can develop at the bottom tip (inferior pole) of the patella, which presses and rubs against the back of the top part of the patellar tendon when the knee bends. This is called patellar impingement, and can be an underlying cause of patellar tendonitis.

The two best investigations for diagnosing patellar tendonitis are MRI or Ultrasound scans.

Mild symptoms from patellar tendonitis or tendinosis can be managed with:

  • anti-inflammatories
  • rest
  • physiotherapy

For more serious or persistent symptoms one option available is to perform Dry Needling of the tendon. This involves puncturing the patellar tendon in multiple spots with a small needle through the skin with some local anaesthetic. This causes small amounts of bleeding into the tendon which seems to initiate a healing response, helping the tendonitis to settle down. The results of Dry Needling are best when the technique is combined with physiotherapy treatments, particularly focusing on what are termed ‘eccentric loading’ exercises.

In cases where non-surgical treatments have failed, surgery can normally give a very good chance of curing patellar tendonitis or tendinosis.

Surgery involves having an arthroscopy (keyhole surgery) of the knee to check everything from the inside, combined with a mini-open tendon decompression. This is where the inflamed or degenerate portion of the tendon is trimmed away. The surgery encourages new blood vessels to grow into the area, which helps the tendon to heal up. At the same time, underlying causes like bone spurs on the patellar, can easily be trimmed away to prevent tendon impingement.

Surgery for patellar tendonitis/tendinosis is not large and is usually very successful. However, it does require an extensive period of rehab, with 6 weeks rest (often with crutches) followed by 6 weeks of intensive physiotherapy, with return to running or impact delayed until 3 months post-op at the earliest.