INTRODUCTION
Anterior knee pain in athletes can be caused by a series of anatomical structures. Tendinopathy of the patellar tendon, a source of anterior knee pain, is more often characterized by locality pain in the lower pole of the patella and pain related to the load that increases with the requirement of knee extensors, especially in activities that store and release energy in the patellar tendon (1).
The symptoms can be so intense that lead to functional impairment in sport. It is believed that this condition results from repeated tension in the knee extensors mechanism, and therefore more prevalence in activities involving jumps, which explains why this condition is also known as “jumper’s knee” (2).
Cook JL et al (3), found that more than a third of athletes who showed up for tendon treatment were unable to return to sport in 6 months, and it was reported that 53% of athletes with patellar tendinopathy were forced to retire from sport (3, 4).
This type of tendinopathy is a condition observed mainly in young athletes (15 – 30 years old), especially men, and football is one of the sports where this type of conditions is observed. (5)
The force required to jump, receive the jump, chance direction and decrease speed in football requires the tendon to store and release energy repeatedly (2). The storage and release of energy (similar to a spring) of the long lower limb tendons are essential characteristics for high performance, while reducing the energy cost of human movements (2, 6).
PHYSICAL ASSESSMENT
As mentioned before, patellar tendinopathy, as one of the many potential diagnoses that produce anterior knee pain, has specific and defining characteristics (7) consisting of:
- Pain located at the lower pole of the patella (7);
- Load-related pain, which increases with the requirement in knee extensors, especially in activities that store and release energy in the patellar tendon (3, 7).
Other signs and symptoms, such as pain when sitting, squatting and climbing stairs for a long time, may be present. Tendon pain occurs instantly with the load and ceases almost immediately when the load is removed. Pain is rarely felt in a state of rest (8).
Evaluating the irritability of pain is a fundamental part of the patellar tendinopathy, and consists of determining the duration of the worsening of symptoms (during the load) after storage and energy release activities as a training session (5).
One of the tests to reproduce the symptoms associated with patellar tendinopathy is the slope squat test, in which a single leg squat should be performed at approximately 25-30 degrees of knee flexion (figure 1) (9).
Studies suggest that up to 24 hours of pain provocation after energy storage activities can be acceptable during rehabilitation (10), defining “irritable” pain when there is a pain provocation greater than 24 hours (5).
Figure 1 - Slope Squat Test
In addition to the local examination of the tendon, it is necessary to perform a complete evaluation of the entire lower extremity, in order to identify potential deficits in the thigh, knee and ankle/foot region. Atrophy or reduction in muscle strength is often observed and can be objectively evaluated with clinical tests (5, 7).
CLASSIFICATION
In 1973, Blazina et al (11) classified the patellar tendinopathy based only on clinical characteristics (table 1). This classification system includes four progressive phases classified according to the severity of the condition.
Table 1 - Classification system according to Blazina et al (11)
There are other classifications systems based on imaging characteristics, however their usefulness is not well established, and the above-mentioned classification system remains the most referenced in clinical studies (12).
CONSERVATIVE MANAGEMENT AND REHABILITATION
The most researched and described type of intervention in the literature for management and rehabilitation in patellar tendinopathy is exercise, especially eccentric exercise (13).
However, eccentric exercise as an intervention in patellar tendinopathy can be quite aggressive for patients with a high level of irritability, particularly during the sports season (14). In addition, eccentric exercise, if used alone, fails to address specific deficits that may exist throughout the kinetic chain, such as weakness in gastrocnemes (5).
Malliaras et al (5), proposed a 4-phase rehabilitation progression protocol. The focus of the program is the development of load tolerance by the tendon, musculoskeletal unit and kinetic chain. We can see key exercises for each phase in figure 2. Progression criteria should be individualized, based on pain, strength and function (table 2) (5).
Figure 2 - Rehabilitation protocol, adapted from Malliaras et al (5)
Table 2 - Rehabilitation protocol and progression criteria, adapted from Malliaras P et al (5)
First, load modification is used in order to reduce pain. This initially envolves reducing high-load energy storage activities that can aggravate pain. The volume and frequency (number of days per week in which they are performed) of higher intensity activities, such as the maximum jump, may need to be reduced (5).
Both the load modification and the possible progression of this are based on careful monitoring of pain. A little pain is acceptable during and after exercise, but symptoms should be resolved reasonably quickly after exercise and should not progressively worsen throughout the charging program, as monitored by the 24-hour response (5).
PHASE I - ISOMETRIC LOAD
5 repetitions of quadricipital isometric exercise from 45 seconds to 70% of the maximum voluntary contraction shows effects on reducing pain in the patellar rendon up to 45 minutes after exercise, a response associated with the reduction in inhibition of the quadriceps motor cortex, which is associated with patellar tendinopathy (5, 15).
Isometric exercises are indicated to reduce and control tendon pain and start the load of the musculoetendinous unit when pain limits the ability to perform isotonic exercises (3).
Isometric exercises, using a leg extension machine, are ideal for patellar tendinopathy since it allows to isolate the quadriceps (5). Experts say that performing isometric exercises with medium knee flexion (around 30-60 degrees of knee flexion) is more comfortable. Load should be increased as quickly as tolerated and the exercise should be performed, if possible, on a single leg (5).
The dosage of the exercises depends on individual factors, but the evidence and clinical experience indicate (3, 5, 15):
At this stage it's extremely important to progress the load based on the athlete's tolerance and, as previously mentioned, regulary reassess the response to pain through load tests (5).
PHASE II - ISOTONIC LOAD
Isotonic exercise is started when it can be performed with minimal pain (3/10 or less). A positive response to regular pain reassessement remains important. Isotonic charge is important to restore muscle volume and strengh through functional amplitudes of motion (5).
Initially, the flexion of the knee during exercises with and without weight support should be limited between 10-60 degrees, depending on the pain then we progress to 90 degrees or more, as the pain allows and based on the requirements of the sport. Experts also point that the total extension of the knee can be provocative in the early stage of performing isotonic exercises (5).
We should give priority to exercises that can be easily progressed to unilateral load, including leg press, split squat and the traditional leg extension (5).
The leg press and leg extension can be started immediately, and the split squat should be added when the technique and capacity under load are adequate (5). Kongsgaard et al (16), recommend:
Phase I exercises must be maintained on off days to control pain within the limits of muscle fatigue and pain associated with isotonic load (5).
PHASE III - ENERGY STORAGE LOAD
The re-introduction of energy storage loads in the myotendinose unit is essential to increase tendon load tolerance and improve power as a progression to RTS (5).
The beginning of this phase is based on the following criteria of strengh and pain (5):
The choise of exercise will depend on the individual requirements of the sport. Thus, the selection and parameters of energy storage programs can vary greatly between athletes participating in different sports, as well as between positions in the same sport (5).
Therefore, planning for this phase requires careful communication with the athlete and the coach, in order to properly determine the frequency of training, volume and intensity, as well as the type of energy storage exercises (5).
Energy storage exercises may include (5):
Jumps and ground reception;
Change of direction and deceleration activities.
The introduction of energy storage exercises is often the most provocative phase, so initially this type of load is performed every 3 days, based on a 72 hour collagen response (5).
Phase I isometric loads can be used in combination to control pain after energy storage exercises. However, the increase in pain after the load test on the day after a phase III training session indicates that the load tolerance has been exceeded (irritable pain) and the load should be adjusted (5).
PHASE IV - RETURN TO SPORT
The progression to sports specific training can and should be started when the athlete completes the progressions os phase III that reproduce the demands of the sport (5).
At this time, the exercises of the third phase are replaced by a gradual return to training and, eventually, to competition. In the initial phases, the training must correspond to the volume and intensity of the final progression of phase III, gradually progressing to volumes and intensities similar to sports training exercises, in order to replicate the participation and demands of sports (5).
RTS is started when complete training is tolerated without the provocation of symptoms and when there are no significant strengh deficits (5).
BIBLIOGRAPHIC REFERENCES
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15. Rio E, Kidgell D, Purdam C, et al. Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. Br J Sports Med 2015;49:1277–83.
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17. Bohm S, Mersmann F, Arampatzis A. Human tendon adaptation in response to mechanical loading: a systematic review and meta-analysis of exercise intervention studies on healthy adults. Sports Med-Open. 2015;1:7.
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