What is the patellar tendon?
The patellar tendon is at the front of the knee and sits in between the patella (kneecap) and the front of the top of the tibia (shin bone). The patellar tendon attaches to the tibia the tibial tuberosity, which is the prominent lump of bone just below the front of the knee (some people’s tibial tuberosity is particularly prominent, and this is most often due to Osgood Schlatter’s Disease).
Massive forces pass through the patellar tendon when the quads muscles contract. In a normal tendon there is a constant cyclic process whereby the microfibers of collagen in the tendon fatigue and break, but the living cells in the tendon repair these fibres on an ongoing basis. This is what happens in all tendons and ligaments, which are all living structures.
What causes patellar tendinopathy?
The balance of this damage-heal cycle can be disrupted for a variety of reasons. This can be due to overload on the tendon, or too much repetitive strain (as can happen in runners) or it may be due to the blood supply to the tendon not quite being good enough (in which case the cells might not be able to be sufficiently active to heal the collagen fibres fast enough). This can lead to inflammation within the tendon, as part of the attempted healing process, and the inflammation can cause pain.
Inflammation in a tendon is called ‘tendonitis’.
If the inflammatory process continues for too long then scar tissue can build up within the tendon, and the tendon can begin to become degenerate.
Degeneration in a tendon is called ‘tendinosis’.
Tendinosis can cause pain within a tendon, just like tendonitis. With tendonitis, there tends to be an increased blood supply to the tendon (the tendon is trying to heal itself). However, with tendinosis there tends to be a decreased blood supply to the damaged part of the tendon, possibly because scar tissue starts to act as a kind of barrier.
Investigation of patellar tendinopathy
Proper full investigation of anterior knee pain should include all of the following:-
- X-rays (specifically including a patellar skyline view)
- MRI (to look for cartilage/ligament damage inside the joint)
- Ultrasound scanning
Treatment of patellar tendinopathy
There are various treatments available for patellar tendinopathy, depending on the severity of the condition, depending on what other potential treatments might also have been tried, and depending on whether the underlying pathology is inflammatory tendonitis or degenerative tendinosis. The potential treatments include:-
- rest, ice and anti-inflammatories
- injection therapies
- ESWT (Shock Wave Therapy)
- Surgical Decompression
Surgical intervention for patellar tendinopathies is, nowadays, a fairly rare occurrence – and the reason for this is simply that the various non-surgical treatments tend to have a very good success rate. Generally, one should always tend to start with the smaller, less invasive and lower risk treatments, working one’s way up the list of options only as necessary.
There are two smalls group of patients in whom the non-surgical treatments often fail, and who are considerably more likely to need surgery on their knee:-
1) Some people have a beak of bone at the bottom end of the patella, which bumps into the back of the top part of the patellar tendon when the knee is bent deeply. This is called patellar tendon impingement. In these patients, unless the underlying cause of the impingment is addressed, the patellar tendinopathy is unlikely to settle. With these patients, a small operation to trim away the prominent beak of bone tends to cure the problem.
2) In some adolescents, there can be stress overload at the bottom end of the patellar tendon, where it attaches to the tibial tuberosity. This causes inflammation at the tendon-bone junction, which results in increased bone formation in this area, leading to a prominent tibial tuberosity at the front of the top of the shin, which can be tender and which can hurt with exercise. This is called Osgood Schlatter’s disease. Osgood Schlatter’s is not dangerous in any way, but it can affect children’s ability to participate in sport, as the only real treatment that is effective is rest. Osgood Schlatter’s nearly always settles with time, when the growth plate at the front of the tibia matures and closes, which happens around the age of about 15 or so. There is a small group of people, however, in whom small bits of loose bone (ossicles) end up forming at the front of the top of the tibial tuberosity, just behind (deep to) the bottom end of the patellar tendon. Sometimes, this can irritate the patellar tendon and cause inflammation (distal patellar tendinopathy). Again, in this group of patients the standard non-surgical treatments for patellar tendinopathy often don’t work, in which case a small operation to remove the loose ossicles normally cures the problem.