The patellar tendon is the structure lying below the kneecap (patella) attaching the quadriceps muscle to the tibia. Through the patellar tendon the quadriceps contraction allows the knee to extend or straighten. It is thought that the patella is a bone thickening (sesamoid bone) in the quadriceps tendon. Occasionally the patella itself can be two, three or even four discrete sesamoids, which can be associated with problems behind the patella.
Patellar tendon pain can occur in a number of different sports, most commonly in those that load the area (eg, weightlifting) but also in jumping sports and those that produce significant deceleration forces through the tendon, eg, basketball, squash, fencing, jumpers and field sports with high traction forces (such as hockey played on Astroturf). All patellar tendon pain was once referred to as ‘jumper’s knee’.
In the early stages of patellar tendinitis the most common symptom is tenderness over the bottom (the ‘lower pole’) of the patella. This tenderness is more usually felt after exercise and the athlete often finds it uncomfortable to squat or kneel. In my experience it is more common in the dominant leg and generally more common in men. As the problem evolves the athlete develops pain during exercise. The pain can become continuous both at rest and during training; unfortunately it is only at this later stage that athletes tend to seek medical advice.
It is thought that the first symptoms of patellar pain correlate with fluid or oedema in the patellar tendon, often close to the lower pole of the patella. Very little inflammation if any occurs and studies show degenerative changes in the tendon rather than any clear inflammatory process. This syndrome of degenerative change in the patellar tendon is called ‘patellar tendinosis’. Problems in the mid-third of the tendon are rarer but they can occur at the tendon insertion.
There are separate problems in adolescents both at the top (Sinding- Larsen-Johansson syndrome) and bottom (Osgood-Schlatter syndrome) of the tendon which reflect an overload of the tendon-bone interface. Technically this is an ‘enthesitis’ and has a more inflammatory basis. The management of these conditions needs special consideration and is outside the scope of this article.
There are various elegant theories about how patellar tendinosis arises. I suspect the cause is multi-factorial but it is important to stress that no one knows with certainty what actually happens to cause the problem.
The theory I like the most is that of a mechanical impingement of the back of the tendon. As the knee bends the angle of patella to patellar tendon changes at the lower pole of the patella. The effect of this is to create direct pressure on the back surface of the patellar tendon – and probably more so if there is an accentuated bony bulge at the lower pole of the patella. This effect is more likely to occur if the quadriceps muscle group is too tight, causing the patella to ride higher on the femoral condyles.
Several other predisposing factors have been hypothesised. Weak quadriceps muscles in comparison with hamstring strength and control would increase the shear forces on the patellar tendon and potentially increase mechanical impingement. Hypomobility of the lumbar spine at the L3-L4 level could also affect neural firing to the extensor apparatus of the knee and might increase shear forces through the tendon. A loss of eccentric control of the patellar tendon may lead to increased strain through the tendon and damage.
The diagnosis of patellar tendinosis isn’t difficult. Very often the proximal patellar tendon is tender and there may even be some thickening in chronic cases. Very often the findings are mixed with a degree of retropatellar (behind the patella tendon) swelling (Hoffa’s fat pad) and perhaps even some quadriceps wasting. The discomfort can be quite global around the front of the knee and difficult for the athlete to localise. However in almost all cases a sensitive spot on the patellar tendon can be found.
Confirmation of the diagnosis relies on ultrasound by an experienced doctor or radiologist who is used to looking at patellar tendon injuries. While there are technical difficulties in interpreting ultrasound scans, the main advantage lies in their ability to pick up areas of oedema (which are hypoechoic) and for the knee to be examined while flexed and extended, with and without load.
X-ray may only show calcification in the tendon at a late stage in the condition and as a first investigation is not usually helpful. MRI scanning is not good at picking up early, subtle cases of patellar tendinosis, unless there is a high degree of suspicion of the problem and the radiologist is asked specifically to comment on the tendon area. Overall, the sensitivity of MRI scans for this problem is low and the technique’s value is further compromised by being a static investigation.
It is said that in 40% of presenting cases of patellar tendinosis the symptoms are on both sides. I think this figure is a little high and may reflect that 40% of people with patellar tendinosis will at some stage have symptoms on both sides. Almost all athletes, however, are able to recall on which leg the symptoms started.
There is nothing to be gained by doing exercise that produces increasing levels of discomfort to the patellar tendon. I find it quite useful to ask the athlete to quantify their perception of discomfort in the patellar tendon on a scale of 0-10, where 0 is no pain at all and 10 is the most severe pain that they have had in the tendon. Any activity that produces a rise in discomfort, say, from 3 to 6 during exercise should be stopped.
As this injury has no inflammatory component, it is illogical to use non-steroidal anti-inflammatory medication. Likewise, there is no proven benefit from anti-inflammatory electrical modalities in physiotherapy (such as ultrasound therapy).
It is crucial to assess hip extension and quadriceps stretch, as these will influence retropatellar tendon impingement. Controlled lunging and step-down tests may give an indication of the eccentric control on the tendon. If this is difficult to do because of pain on the affected side, check the unaffected knee to help you get a better picture of the likely pre-injury proprioception of the area.
It is also important to assess proximal stability and hip control. An isokinetic machine cannot often replicate function but it may give the examiner help in assessing the relative strength of the hamstring and quadriceps muscles at different arcs of movement. It is difficult to find normalised data for elite sportsmen and women, so you may, for instance, need to obtain data from the rest of a squad (who are hopefully pain free!) for comparative purposes.
There has been a lot of published work on the benefit of eccentric exercises and in my practice I have seen significant benefits to the athletes I treat.
The key to the rationale behind eccentric drills is that they are the best way of promoting tendon remodelling: the regrowth and reordering of collagen tissue in place of the oedematous (fluid filled) degenerative tissue typical of tendinosis.
The athlete needs to be taught eccentric exercises (See table 1). A 45-degree slope is required and (at a later stage) a weights bar. Initially the athlete stands straight on the slope, then flexes his/her knees to 90 degrees, returning to a straight position again (see illustration below left).
|Stage||Exercise||No of legs|
|1||Two legs, 90 degree squat, no slope||2|
|2||Two legs, 90 degree squat on 45 degree slope||2|
|3||Single leg for squat phase (eccentric); two legs
return phase (concentric), on slope
|4||10kg bar; single leg for squat phase, two legs
return, on slope
|5||Single leg only throughout, on slope||1|
The movement down must be done slowly (to a count of three) and the return can be done quickly (to a count of one). When away from home the slope can be replaced by the edge of a curb or step so that opportunities can be taken whenever possible to do the drills.
The number of repetitions is determined by the amount of discomfort felt in the patellar tendon. I advise athletes to stop a sequence of repetitions when they perceive an ache in the patellar tendon of 3/10, using the scale described above. The rationale for this is to stimulate the patellar tendon eccentrically to a fixed (symptomatic) level each day, but without such a high score as to produce pain and further damage. I suggest to athletes that they can do these repetitions as often as possible every day and many achieve the repetitions two to four times a day.
The exercise sequence can be progressed as shown in table 1. For some athletes stage 1 is too easy and they cannot bring on any discomfort in the patellar tendon. For others, the ratelimiting factor is quadriceps fatigue and for this reason they can use two legs in returning to the standing position (see stages 2 to 4).
As the stages progress the athlete will be able to increase the number of repetitions they can perform before the symptoms come on at a discomfort level of 3/10. There will be some days when the athlete can manage more repetitions than others, but normally they will be able to move on to the next stage after two to four weeks – so improvement in this condition is usually measured in months, not weeks.
The rate of progression will vary from athlete to athlete, dependent in large part on how often they perform the exercises. If more pain occurs in the tendon, the athlete should be advised to rest for two to three days and then drop back one stage in the rehab exercise progression.
Alongside the eccentric exercises, it is important to address other possible contributory factors, such as:
Also ask the athlete’s coach for his or her comments on poor technique, particularly in the lunging sports. Consider what footwear is being worn on various surfaces; clearly, high traction shoes on high traction surfaces will prejudice recovery and encourage relapse.
It is very difficult to give evidencebased advice on prevention, as there is little conclusive research on predisposing factors to patellar tendinosis. Introduce plyometric drills and lunging routines with care, and check regularly for knee symptoms. Drills involving a group of athletes should not be progressed at the speed of the best in the group.
Regular hip and quadriceps stretching routines may be helpful. When athletes change training venue, particularly to new indoor courts where traction forces may be higher, be cautious about maintaining routine lunging drills. It will be very interesting to see if controlled eccentric drills in routine training influence the incidence of patellar tendinosis in athletes without symptoms.