Article at a glance:
- Malcolm Davies and Fares Haddad report on recent research work to tackle the incidence of patellar tendinitis;
- This article looks at the causes of jumpers knee;
- And why it is causing some athletes to retire
Classically patellar tendinitis has been explained as chronic inflammation of the tendon connecting the kneecap (patella) to the main shin bone (tibia), at the point of connection to the kneecap (see figure 1). Recent research has, however, effectively revised our understanding of the condition – and with it a change in terminology: it is more correct these days to refer to the condition as tendinosis.
Symptoms start with pain after exercise, which can progress to pain during exercise. In extreme circumstances the tendon may weaken and rupture. The pain can be debilitating and even force you to retire from high level sport.
Figure 1: Patellar tendinosis (jumper’s knee)
Who is at risk and why
Ferretti(3) was the first to describe the causes of patellar tendinosis, dividing them into intrinsic (specific to the individual) and extrinsic (environmental) factors. Intrinsic causes were:- gender
- age
- knee alignment
- Q-angle (longitudinal angle of the front of thigh muscle)
- position of the kneecap
- rotation of main leg bones (tibia and femur)
- the overall shape and stability of the knee.
- the nature of the activity (jumping and continuous stress being the major culprits); and
- the consistency of the playing surface (hard surfaces such as concrete being most risky).
In the 1990s a British research team came up with an alternative explanation, suggesting that the tendon was being crushed by the kneecap when it was forced into the sharp angle created by extreme bending at the knee (flexion)(4), in effect producing an impingement syndrome. A more recent study on the motion of the knee in flexion has shown that the tendon is not being kinked and crushed(5).
More recent research has shifted the focus of blame away from environmental factors and towards more individual causations. In an American study of healthy competitive athletes, Witvrouw et al(1) used a series of body measurements to try to detect a link between intrinsic risk factors and the development of tendinosis. All 138 trial participants performed the same amount of high-intensity, highly competitive activities, across a variety of disciplines, and 19 of them developed tendinosis. The only identifiable common risk factors were poor flexibility of the hamstrings and quadriceps (rear and front of thigh) muscle groups. Contrary to Ferretti’s belief, there was no apparent gender difference. This research suggests that you may be able to reduce your tendinosis risk with a good stretching programme.
Another recent US study supports these findings, and underlines the importance of intrinsic risk factors. This study shows a higher incidence of tendinosis among subjects whose kneecaps naturally had a higher tilt when they did knee bends(6). It would seem logical that if the patellar tilt is greater (producing more tension on the top of the patella from the quadriceps tendon), then a front of thigh stretch regime ought to be able to reduce the strain on the tendon.
Likewise, the greater your ‘Q’ angle, the more strain is likely on the knee, increasing the risk of knee pain and tendinosis. The Q angle is an estimate of the alignment of the knee in relation to the angle of the thigh and lower leg. Variations in the angle are usually related either to rotation at the hip joint or the shape of the foot on standing. Thus someone with ‘knock knees’ would typically have a large Q angle. People with flat feet tend to force the outsides of their feet out and push their knees inwards. Studies have shown that some athletes with patellar tendon problems have an increased Q angle(7).
Management
Physiotherapy can stabilise the condition, avoiding the need for surgery(8). Eccentric (anti-gravity) loading of the tendon, as happens when performing a decline squat, seems to give good results, although it is unclear exactly why this should be. Recent research has recommended a protocol for this rehab regime(8).Single-leg decline squat (see figure 2):
- Stand on a decline board (optimum recommended angle is 25 degrees).
- With feet face forwards, lift one foot off the ground
- Lower slowly from standing upright on one leg to as deep a flexion position as pain allows, performing three sets of 15 reps, twice daily.
- For best results exercise through pain, gradually increasing the load by holding weights in both hands(8).
Figure 2: Single-leg decline squat
Recent developments
The most exciting development has been the introduction of prolotherapy, claimed to be as successful as surgery in treating symptoms(9). This claim is based on studies which show an increased formation of blood vessels in the affected tendons, along with nerve growth and unusually high levels of pain receptors and stimulators(10). When these blood vessels are destroyed with a sclerosant (injectable irritant) using ultrasound guidance, pain is relieved. The reduction in symptoms appears to be related to how much of the abnormal blood vessel growth is eradicated(11).The researchers are still unsure what exactly triggers the pain of patellar tendinosis, but what is clear is that the pain and collagen damage are not a result of inflammation(9,12). None of the usual chemicals or cells associated with inflammation are present in patellar tendinosis. This would cast doubt on the value of treatments using steroids or non-steroidal anti-inflammatories (NSAIDS).
In another development, animal studies of blood injections have shown some promising results for tendon strengthening(13). Tendons are notoriously slow to heal and have high rates of re-rupture because of their poor blood supply. This study only assessed short-term strengthening, but if it gets past the hypothetical stage it could have broad implications for the treatment of damaged or ruptured tendons.
Surgery
Where surgery is necessary, the inflamed fat pad surrounding the tendon is removed; the visibly abnormal areas of tendon are cut out and any abnormal blood vessels are cauterised. Any abnormal tissues on the kneecap at the site of tendon attachment will also be removed. This can be done either as open surgery or a keyhole procedure (under local or more usually general anaesthetic). Overall outcomes are comparable, but on average the arthroscopy patient will enjoy a four-month advantage in recovery time and return to full sporting activities, because of the less invasive approach.Conclusion
Patellar tendinosis can be a disastrous condition for the sports enthusiast if not dealt with promptly. Yet potential sufferers could probably be identified with simple screening and given prophylactic stretching and physiotherapy exercises. Further research is needed to decide how useful other rehab aids such as orthotics and knee braces might be in treatment or prevention of patellar tendinosis. It may be impossible to eradicate the condition from sports that carry the highest risk, but prolotherapy and autologous blood injection could one day substantially reduce the need for surgery.Malcolm Davies is specialist registrar in trauma and orthopaedics at University College Hospital, London
Fares Haddad BSc MCh (Orth) FRCS (Orth) is a consultant orthopaedic surgeon at University College London Hospital and editorial consultant to Sports Injury Bulletin
References
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- Long Term Prognosis for Jumper’s Knee in Male Athletes. A Prospective Follow-up, Am J Sports Med 2002; 30:689-692
- Epidemiology of Jumper’s Knee, Sports Med 1986; 3(4):289-295.
- Magnetic Resonance Imaging of Patellar Tendinitis, J Bone Joint Surg Br 1996; 78:452-457
- Is Impingement the Cause of Jumper’s Knee?, Am J Sports Med 2002; 30:388-395
- Evidence of Abnormal AP Patellar Tilt in Patients with Patellar Tendinitis with Use of a New Radiographic Measurement, Am J
- Kinematics of Cycling in Relation to Anterior Knee Pain and Patellar Tendinitis, J Sports Sci 2003; 21:659-657
- Eccentric Decline Squat Protocol for Patellar Tendinitis in Volleyball Players, Br J Sports Med 2005; 39:102-105
- Neovascularization in Chronic Patellar Tendonosis. Promising Results after Sclerosing Neovessels outside Tendon, Challenges
- Tendon Tissue Demonstrated High Amounts of Free Glutamate and Glutamate NMDAR-1 Receptors But No Signs of Inflammation in
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- Histopathology of Common Tendinopathies. Update and Implications for Clinical Management, Sports Med 1999; 27:393-408
- Response of Rabbit Patella Tendon after Autologous Blood Injection, Med Sci Sports Ex 2002; 34:70-73