PATELLAR TENDINOPATHY
JUMPER'S KNEE
Anatomy
The patellar tendon is a strong band of fibrous connective tissue that attaches the lower (inferior) pole of the kneecap (patella) to the shin bone (tibia). Contraction of the quadriceps muscles creates tension in the patellar tendon (tensile load) and this force is then transmitted to the tibia. The resultant movement occurring at the knee is determined by the type of muscular contraction performed (concentric, isometric, eccentric).
Causes
Sports that involve jumping and landing (e.g. volleyball, basketball and triple jump) or sudden changes of direction (e.g. football and tennis) place large amounts of tensile load on the patellar tendon at a very quick rate (rate of loading).
In these activities, tendons act like trampoline springs, storing energy as they are tensioned then releasing this energy to produce efficient movement. The patellar tendon is also exposed to compressive loads when direct pressure is exerted on the tendon (e.g. kneeling), or during knee flexion (bending) as the tendon wraps around the tip of the patella. Tensile and compressive tendon loading is normal in everyday life but excessive, repetitive loading of the patellar tendon, beyond a level that can be tolerated, is thought to be the main cause of patellar tendinopathy. A tendon’s load tolerance may be exceeded if an individual increases their volume (total workload per session), frequency (number of sessions per week) or intensity of activity (or combinations of these variables) too quickly.
The exact mechanisms of how tendinopathy develops in response to excessive loads is not fully understood, but tendons display characteristic changes at a microscopic level that can be visualised on imaging (ultrasound and MRI).
Presentation
Pain is localised to the patellar tendon, most commonly at the tendon’s insertion to the inferior pole of the patella (image 2), and is load dependent; the individual experiences more pain as greater load is placed on the tendon. Tendon pain can improve during an activity once the tendon has ‘warmed up’ but may be worse over the following days when the tendon is loaded again. This pain can lead to impaired performance or reduced function, and may render the individual unable to participate in patellar tendon loading activities altogether.
Patellar tendinopathy is described as ‘reactive’ when a sudden, unaccustomed amount of tensile or compressive load is applied to the tendon. For example, an athlete returning to sport following a long layoff due to injury may place an unaccustomed amount of tensile load on the patellar tendon by performing large volumes of running. Excessive compression may be the result of a heavy fall onto the front of the knee, where a direct, blunt force has been applied to the patellar tendon. In the reactive phase, the tendon may appear swollen with significant morning pain and stiffness, whereas in long standing (chronic) cases morning stiffness typically improves through the day.
Diagnosis
Pain is usually present when palpating (poking) the inferior pole of the patella but this can also be present in other knee conditions, therefore pain reproduction during patellar tendon loading activities may be more diagnostic in a clinical setting. The single leg decline squat is recommended as a low-load clinical test, while vertical or horizontal landing can be used as a high-load test if symptoms are not reproduced during lower loads. Pain levels during provocative testing should be recorded on a numerical rating scale (0-10) and used to monitor the individual’s response to treatment.
Imaging
MRI and ultrasound imaging are useful modalities to confirm or exclude the clinical suspicion of patellar tendinopathy, with ultrasound considered the preferred method in the hands of a skilled operator. It is important to note that a significant proportion of athletes will have pathological changes on imaging without pain, or tendon pain in the absence of abnormal imaging. In addition, clinically relevant improvements in symptoms do not necessarily correspond with significant structural changes in pathological tendons. However, athletes with abnormalities on imaging are nearly five times more likely to develop tendon pain than those with normal tendons.
Used alone, pain reproduction during a single leg decline squat, history of tendon pain or a VISA-P questionnaire score under 80 may not accurately identify patellar tendon abnormalities on ultrasound; the absence of these clinical findings more accurately identified those without abnormalities. Therefore, imaging results should be used alongside clinical signs/symptoms and the patient’s history in the diagnosis of patellar tendinopathy.
Treatment
The ultimate goal of treatment is to increase the individual’s ability to tolerate load by implementing a physiotherapist-led, graduated loading programme. It is important to note that these programmes target other body parts and psychological aspects of rehabilitation, in addition to the quadriceps muscles and patellar tendon itself. The patient should be educated on the condition to address any fears or misconceptions they may have and to promote compliance with exercise. Realistic timeframes and expectations for recovery should be set at the start of treatment to prepare the individual for what lies ahead.
Patellar tendinopathy should initially be managed with a period of relative rest from activities that place excessive load on the tendon and aggravate symptoms. The volume, intensity and frequency (or combinations of these variables) of energy storage and release exercises should be modified to reduce tensile load and control pain, but complete cessation of exercise should be avoided if symptoms permit. Low impact aerobic exercises (e.g. cycling) or machine weight exercises are usually non-provocative and can be performed to maintain a positive load through the tendon during these periods of relative rest. Activities that place significant compressive load on the patellar tendon (e.g. kneeling) should also be minimised where possible, or modifications should be made if kneeling is unavoidable (e.g. knee pads).
The hip, knee and ankle should be assessed for any deficits in range of motion, endurance and strength. Reduced weight-bearing ankle dorsiflexion (<36.5°) is a risk factor for patellar tendinopathy, while weak gluteal or calf muscles may place greater demand on the quadriceps muscles/patellar tendon. Calf and gluteal strength exercises are generally recommended in rehabilitation, as these muscles play an important role in sharing load through the hip, knee and ankle (kinetic chain) during high-load activities.
Tendon Loading Programmes:
Recent studies have demonstrated that isometric and isotonic loading using a knee extension machine provide similar improvements in pain relief and function over a 4-week period for in-season athletes with patellar tendinopathy. Based on limited evidence, isometrics may provide slightly more pain relief, immediately after performing the exercise, for short periods (approximately 45 minutes) when compared with isotonics. However, isotonic exercises are important to restore strength through functional ranges of knee movement and this is not achievable with isometrics alone. If machine weights are not available, isometric loading can be achieved by performing a Spanish squat.
Eccentric exercises may be ineffective, or even provocative, for some in-season athletes. Eccentric exercises have been shown to be effective in longstanding cases of patellar tendinopathy but there is superior evidence for heavy slow resistance (HSR) exercises. HSR involves lifting heavy weights slowly, then gradually increasing the weight and reducing the number of repetitions per set over a 12-week period. The exercises are performed through a specific range of motion, combining concentric and eccentric muscle activity. Improvements in pain and function have been shown to be similar between eccentric and HSR exercise, but patient satisfaction and positive structural changes in the tendon are greater following HSR.
The magnitude of load (weight and time under tension) placed on the tendon appears to be a key factor for positive tendon adaptation rather than the type of muscle contraction. For a given load the force exerted on a tendon during concentric or eccentric exercise is the same but individuals are capable of lifting heavier loads eccentrically. If performed correctly, eccentric exercises therefore allow greater force to be placed on the tendon but any concentric deficits that are present may not be addressed with eccentrics alone.
Despite high-quality evidence supporting the use of double-legged HSR exercises, expert opinion has suggested that HSR programmes should be performed using one leg at a time to ensure the unaffected limb does not dominate during the exercise. Resisted knee extension is also recommended as this exercise specifically targets the quadriceps muscles and patellar tendon, whereas the exercises described in the literature utilise movements that involve multiple joint and muscles. It is important to note that patients with coexisting patellofemoral pain (pain at the front of the knee) may not tolerate leg extension machine exercises.
In the final stages of rehabilitation, it is important to reintroduce energy storage and release exercises to expose the tendon to higher rates of loading in preparation for a full return to tendon loading activities. These should be progressed gradually, manipulating volume, frequency and intensity (or combinations of these variables) as symptoms allow. For example, jumping activities can be started using both legs or vertical jumps, then eventually transitioning to single leg or horizontal jumps. Longer rest periods are recommended during this phase of rehabilitation, but isometric or isotonic exercises can be performed on ‘rest days’ if the individual responds favourably.
Patellar tendinopathy should therefore be managed on a case-by-case basis, monitoring the tendon’s response to these various forms of loading whilst tailoring rehabilitation to the individual’s requirements. If pain during a provocative test (e.g. single leg decline squat) is no worse within 24 hours of loading, the individual has tolerated the activity but if pain is worse, the load should be adjusted accordingly.
Graduated loading programmes should be performed for at least 12 weeks, even if symptoms improve significantly within this period of time. Over one third of athletes may be unable to return to their sports within 6 months of initiating treatment, while approximately one half of athletes may be forced to retire from sports. Increased duration of symptoms corresponds with poorer outcomes, regardless of the treatment modality used.
Adjunct treatments
Medication:
Various medications (e.g. non-steroidal anti-inflammatory drugs (NSAIDs), doxycycline, EGCG (green tea)) have been recommended in reactive presentations but it is important to note that these interventions have not been validated by research. Anti-inflammatory drugs have been shown to inhibit the formation of collagen (an important protein providing tendon strength) and may negate any positive structural changes induced by tendon loading exercises; therefore, NSAIDs may not be appropriate in non-reactive presentations.
Topical glyceryl trinitrate (GTN) and hyaluronic acid injection, both combined with eccentric exercise and moderate, slow resistance exercise had the highest probability of being the most effective interventions. Administration of a cortisone steroid injection (glucocorticoid) has significant negative effects on tendon cells and is likely to have a long-term detrimental effect on tendon health.
Extracorporeal Shockwave Therapy (ESWT):
Based on high-quality evidence, ESWT does not appear to be superior to sham ESWT for short-term pain or function
Surgery:
If conservative management has failed to relieve symptoms, surgical intervention can be considered but the optimal procedure has not yet been determined.
Written by: Richard Norris
Peer reviewed by:
Jarrod Antflick | Tendon Consultant | @JarrodAntflick
References
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