Background Anterior knee tendon problems are seldom reported in badminton players although the game is obviously stressful to the lower extremities.
Hypotheses Painful anterior knee tendons are common among elite badminton players. The anterior knee tendons exhibit colour Doppler activity. This activity increases after a match. Painful tendons have more Doppler activity than tendons without pain.
Study design Cohort study.
Methods 72 elite badminton players were interviewed about training, pain and injuries. The participants were scanned with high-end ultrasound equipment. Colour Doppler was used to examine the tendons of 64 players before a match and 46 players after a match. Intratendinous colour Doppler flow was measured as colour fraction (CF). The tendon complex was divided into three loci: the quadriceps tendon, the proximal patellar tendon and the insertion on the tibial tuberosity.
Results Interview: Of the 72 players, 62 players had problems with 86 tendons in the lower extremity. Of these 86 tendons, 48 were the anterior knee tendons. Ultrasound: At baseline, the majority of players (87%) had colour Doppler flow in at least one scanning position. After a match, the percentage of the knee complexes involved did not change. CF increased significantly in the dominant leg at the tibial tuberosity; single players had a significantly higher CF after a match at the tibial tuberosity and in the patellar tendon both before and after a match. Painful tendons had the highest colour Doppler activity.
Conclusions Most elite badminton players had pain in the anterior knee tendons and intratendinous Doppler activity both before and after match. High levels of Doppler activity were associated with self-reported ongoing pain.
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Badminton is a popular sport, with more than 150 national associations/federations worldwide. Despite this popularity, there is a small number of literature on badminton-related injuries. Epidemiological studies report a high incidence of injuries to the lower extremities, and the most frequent knee injury in racquet sports is the patellofemoral pain syndrome.1,–,3 In contrast, jumper’s knee is seldom reported as a problem in badminton.1 3,–,6
Blazina used the term “jumper’s knee” for the first time in 1973. He described the symptoms and clinical findings from the infrapatellar or suprapatellar regions—that is, patellar and quadriceps tendinitis.7 In 1978, others added the symptoms from the insertion on the tibial tuberosity.8 9 Thus, the term jumper’s knee may be used in all three locations.
In the mid-1980s, greyscale ultrasound (US) became an important method to detect morphological changes in tendon structures.10,–,14 Greyscale US is considered a valid procedure, and the interobserver reliability is good.15 16 However, the morphological changes that form the basis for the US abnormalities are more or less permanent once they have developed.17
The use of Doppler US in the evaluation of musculoskeletal disease is increasing.18,–,22 With power or colour Doppler, areas with increased blood flow may be found, and the amount of colour may be quantified.19 23 24 This is used in disorders where hyperaemia is an integral part of the condition—arthritis, bursitis, epicondylitis and tendonitis. The suffix -itis is controversial when added to a tendinous structure because it is debated whether inflammation is part of the disease. It is, however, unquestionable that hyperaemia is present. The amount of colour Doppler activity in Achilles tendonitis is associated to some extent with disease activity, and intratendinous hyperaemia seems to be a sign of active disease in recreational athletes.17 25 On the other hand, Doppler flow in the Achilles tendon may be induced by stressful activity in healthy controls.26
The aim of this study was to clarify characteristics of the elite badminton player with an interview and investigate the presence of and distribution of possible intratendinous flow in the anterior knee tendons in elite badminton players with the following hypotheses: (1) painful anterior knee tendons are common among elite badminton players; (2) elite badminton players have intratendinous colour Doppler activity in the anterior knee tendons; (3) Doppler activity increases after a match; and (4) players with painful tendons have more Doppler activity than players without.
Materials and Methods
Denmark Open is a six-star, $250 000, international badminton tournament in Denmark. All the 320 players in Denmark Open 2004 were invited to participate in the study. The only inclusion criterion was participation in the tournament, and there were no exclusion criteria. Seventy-two players (23%) accepted an interview and if possible had an US examination of the anterior knee tendons before and after a match.
The study was approved by the local ethical committee (KF01-045/03).
The players were interviewed about basic characteristics, the amount and type of training, and the amount of tournaments. The players were specifically questioned about present and former symptoms or injuries in the anterior tendons of the knee, and if they had had treatment or currently received treatment. Episodes with pain were defined as pain to a degree that had limited the amount of training for more than 1 week. “Dominant” and “non-dominant” were used instead of left and right. We classified according to the racket arm: for right-handed players, the right leg was the dominant, and vice versa.
The interview was done before the US examination, and the interviewer did not take part in the US examination.
A Siemens Acuson Sequoia (Mountain View, California) with a 14-MHz linear transducer, type 15L8W, was used for scanning. The colour Doppler (CD) frequency was 7 MHz, and the Nyquist limit was ±0.014 m/s. The lowest wall filter was applied, and the Doppler gain was set just below the level that produced random noise. With these settings, all colours in the image were generated by flow. Blooming, where the colour bleeds outside the vessels, was accepted as a systematic error.
The players were placed supine with both legs relaxed and with a 10-cm pad behind the knees.
The anterior tendons were scanned in longitudinal and transverse planes in three anatomical locations: the quadriceps tendon, the superior part of the patellar tendon and the patellar tendon insertion. Care was taken to minimise transducer pressure. In each location, CD was applied in the longitudinal plane. A 4-s film clip was stored whenever there was intratendinous Doppler activity.
The US examination was made by STP, an investigator with more than 15 years of experience in musculoskeletal US; he was blinded to the results of the interview and did not speak with the players during the examination.
From each film clip, the image with maximum CD activity was selected and transferred to DataPro (Noesis, Courtaboeuf, France) to calculate the colour fraction (CF). This programme reports the total number of pixels and the number of colour pixels inside a region of interest (ROI). The CF was calculated as colour pixels/total pixels.17 23
Three ROIs were evaluated (fig 1):
The quadriceps tendon 1 cm proximally and distally to the base of the patella.
The patellar tendon 0.5 cm proximally and 1.5 cm distally to the apex of the patella.
The insertion on the tibial tuberosity 1.0 cm proximally and distally to the first bone contact.
All ROIs included a 2 cm tendon and were constructed to include nearly all occurring Doppler activity in the tendons under investigation.
Mean and median values (SDs) and independent-sample t tests were calculated using the computerised SPSS V.12.0 system. The level of significance was 0.05. Positive predictive values were calculated as the portion of players with positive test results who were correctly diagnosed.
Seventy-two players (23%) of the 320 players who registered at the tournament were interviewed; 22 women (31%) and 50 men (69%) from 14 countries.
The players had the following basic characteristics (mean (SD, range)): age (years) 25.0 (3.5, 18 to 34), weight (kg) 73.5 (9.2, 51 to 100), height (cm) 179.1 (14.0, 164 to 207), body mass index 22.5 (1.7, 18.1 to 25.9) and years playing badminton 17.9 (4.3, 10 to 30).
All players but one were healthy; a female player was on medication for Crohn’s disease. Forty-six players (64%) played with orthopaedic inserts in their shoes and had done that for a mean of 5.4 (3.1) years.
The current amount of total training (badminton, endurance and strength; mean (SD, range)) was 18.2 (4.2, 6.5 to 29) hours/week, number of competitions per year was 13.1 (4.1, 2 to 25). There was no change in amount of training and number of competitions in the preceding 3 years. Sixty-two players (86%) had problems with 86 tendons in the lower extremity in the 3 years preceding the tournament. Forty-eight of the 86 tendons (44%) were anterior knee tendons. Nineteen of the anterior knee tendons (40%) were painful at the tournament. Twenty-three players reported pain within the previous 3 years, 14 players had present pain and 35 players had never experienced pain in the anterior knee tendons.
In 27 (73%) of the players with anterior knee tendon problems (present and previous), the onset of pain had begun slowly. Fifty-six per cent reported pain before, during and after activity; the remainder reported pain before (4%), during (15%), after (6%), before and during (2%), before and after (2%), and during and after (15%) activity. The median duration of symptoms for those who had previous pain was 2 months (range 1–24 months), and for the present painful knee tendons, 30 months (range 1–120 months). Of the painful knee tendons, 30 (62.5%) were on the dominant side and 18 (37.5%) on the non-dominant side.
There were no statistically significant differences in age, weight, years playing badminton and self-reported training loads between players with and without anterior knee pain.
Men had significantly more painful anterior knee tendons than women (χ2 test, p = 0.028). No differences were found with respect to single or double players (χ2 test, p = 0.163), or racket side (χ2 test, p = 0.264).
Eighty-six per cent of players accepted pain as part of the game, 50% played with ongoing pain and 21% used painkillers, mainly non-steroidal anti-inflammatory drugs (NSAIDs), to be able to play.
Of the 72 players interviewed, 64 (89%) were scanned before a match and 46 (64%) were re-scanned after a match. The mean follow-up time after a match was 65 min (114), median 38 min (range 7 min to 10 h and 43 min).
There were 10 women and 36 men. Twenty-eight were primarily single players, 18 double players. Forty-one of the 46 players were right-handed and 5 were left-handed.
Of the 46 players (92 anterior knee tendon complexes), 9 players (13 tendon complexes) were painful at the beginning of the tournament, 17 players (19 tendon complexes) had recovered from anterior knee tendon pain. Twenty players reported two pain-free knees (present and previously), 60 tendon complexes without pain were reported all together.
At baseline, the majority of anterior knee tendon complexes, 85 of 92 (92%) had CD flow in at least one scanning position (of three possible). Forty players (8 women and 32 men) had bilateral CD flow. Five players (2 women and 4 men) had unilateral CD flow. Only one female player had no Doppler flow in her knees at all.
After the match, 85 of 92 (92%) anterior knee tendon complexes had CD flow in at least one scanning position. Forty-one players (10 women and 31 men) had bilateral CD flow. Three male players had unilateral CD flow and two male players had no Doppler flow in their anterior knee tendons at all. No other pathology than intratendinous flow was diagnosed.
Most participants had CD flow in all three of the anterior knee tendons (the quadriceps (Q), the patellar (P) and the tibial tuberosity (TT)) both before and after match; this included overall results, dominant and non-dominant side, single and double players.
Quantitatively, before and after a match, the majority of tendons (Q, P, TT) had little or no CD activity; for instance, 59% of the examined locations had CF ≤5%; examples are given in fig 2.
Self-reported pain and CF
The CF values were related to self-reported pain both before and after a match. The anterior knee tendon complexes were divided into three pain categories: present pain, previous pain and never pain. The CF representative for the whole knee tendon complex in an individual was defined as the maximum value found in the three loci (maximum CF). The results are listed in table 1.
A significantly higher mean maximum CF was found in the group with present pain compared with both previous pain and never pain. This was the case both before (p = 0.04 and p = 0.002) and after a match (both p = 0.02). The difference between previous pain and never pain was not significant neither before nor after a match (p = 0.12 and p = 0.88).
When the three loci were related to self-reported knee pain one by one, the patellar tendon showed the same tendency as above. A significantly higher mean CF was found in the group with present pain compared with both previous pain and never pain, both before (p = 0.02 and p = 0.007) and after a match (p = 0.01 and p = 0.02).
In the quadriceps tendon, a significant increase in CF was seen after a match in tendons that had never been painful compared with tendons with present pain (p = 0.007).
We tested the ability of CF to predict knee pain by plotting fraction of players with knee pain as a function of CF threshold. For each CF threshold value—for example, 5, 9, 14, we calculated the number of tendons with a CF equal to or higher than the given value; the fraction of tendons with knee pain were plotted. The graph illustrates the positive predictive value of CF in predicting knee pain (fig 3). For example, only around 50% of elite badminton players with CF=30 had pain in their knee tendons.
The interview revealed that pain in the anterior tendons of the knee is a common problem among elite badminton players, confirming the first hypothesis. Of the 72 interviewed players, 37 (51%) had previous or present pain in the anterior tendons of the knee in the previous 3 years; 14 players (19%) had present pain at the interview. Moreover, the players participated in the tournament in spite of the pain, some using NSAIDs. The present findings in badminton players are similar to those that have been reported in other types of sports: volleyball, basketball and running, but never reported as a problem in badminton players.7 15 27 29 30
Male badminton players had a significantly higher incidence of painful anterior knee tendons, p = 0.028, in contrast to an epidemiological study of volleyball players, where no sex-related differences were reported.29 We did not find a correlation among age, weight, height, years playing badminton, training load, racket arm or type of player (single or double) in the previous or present painful knees versus players who never had experienced pain in the anterior knee tendon complex during the past 3 years. The similar discordance between symptoms and possible risk factors could be explained by the fact that all participants in this tournament were among the elite with a very high amount of training. In other sports, training load and pain have been reported to correlate,29 and future studies in badminton players with a more varied degree of tendon stress might show correlations between US findings and training load.
We had problems recruiting players for interview and US examination. Some players declined and explained that they were focused on their upcoming matches and that they thought an interview and US examination would be a possible distraction. The small percentage of participation, 22.5% (72 of 320), may have biased the study towards the most affected, for volunteering especially for the US examination. Despite this possible bias, it is evident that a substantial number of elite badminton players had anterior knee tendon pain.
As in other studies of elite sports,27 31,–,34 many of our participants accepted pain as part of the game, and this did not keep them from training or participating in competitions, often using painkillers.
The primary aim of this study was to investigate possible intratendinous flow in anterior knee tendon complexes in elite badminton players. We found that nearly all players had intratendinous flow, and the second hypothesis was confirmed.
The general opinion has been that any intratendinous Doppler activity is abnormal.28 35 36 If this were true, 98% of the players in our study had at least one pathological tendon before a match. This general opinion is being challenged in more recent literature where sensitive Doppler equipment is being used. Present high-end US equipment has the ability to detect flow in normal tendons32 37 and in normal joints.38 39
With sensitive equipment, it has been shown that normal tendons develop intratendinous Doppler activity as a response to exercise,26 40 and may be an indication of physiological remodelling after activity. The high incidence of intratendinous CD activity in the present study could be explained by the high training activity by the players. With an average of 18 h of training per week, we expect that these tendons are in a regenerative phase most of the time.
The issue is then to be able to distinguish between physiological CD activity and possible pathological activity. Cut-off values are needed, above which pathology is present. Such cut-off values will have to be individualised depending on equipment, settings and software updates. Also, the flow of the tendon may be influenced by other factors such as physical activity before examination. Therefore, valid scoring systems are difficult to establish. Several authors just refer to the tendons as vascular or non-vascular.27 32 A semiquantitative scoring system has been suggested, but not presented with exact differentiation between “normal” and “pathological”.20 To our knowledge, there are two procedures to measure the amount of intratendinous CD flow. In one system, the colour spots inside the tendon are connected to form lines expressing the length of vessels24; the other measures the area of the tendon covered by colour—the CF.17 23 We chose not to use the first scoring system for two reasons: (1) we have no way of knowing whether closely spaced colour spots belong to the same vessel; and (2) with our CD sensitivity, we see large confluent areas, which cannot be expressed with lines. Both scoring systems report a number and seem well-suited to measure change over time. A threshold or other ways of distinguishing normal from abnormal flow have not been established, however.
In this study, the match did not result in significantly increased intratendinous flow—the third hypothesis was not confirmed. We attribute this to the large training load of elite players, where the tendons more or less always are in a state corresponding to the “after-match” situation. Also, in some cases, we had a very long interval between match and follow-up scan, which may have allowed the tendons to regain their before-match perfusion.
We detected significantly more flow (higher CF) in painful tendons than in non-painful tendons (both previously and never painful). Thus, the fourth hypothesis was confirmed. However, despite the association between CD flow and pain, we were not able to establish a useful cut-off value to distinguish between painful and non-painful tendons (fig 3).
According to the interview, a large proportion of elite badminton players had experienced anterior knee tendon problems and play regularly with knee pain often assisted by medication. Thus, pain in the anterior knee tendons was a prominent problem for elite badminton players. Male players were more affected than female players.
Intratendinous CD flow was found in most elite badminton players both before and after a match. Self-reported anterior knee pain at the tournament was associated with the most CD flow. However, in elite badminton players, no threshold could be established that, with a reasonable accuracy, could distinguish between painful and non-painful knee tendons.
What is already known on this topic
“Jumper’s knee” is a common disease in athletes, but not reported as a problem among badminton players. US is a good and reliable tool to detect intratendinous greyscale changes. Doppler US is able to detect hyperaemia, which is considered to be a sign of disease.
What this study adds
A substantial fraction of elite badminton players had jumper’s knee. Doppler US can detect intratendinous Doppler activity in most players, also in players without symptoms. There is an association between knee tendon pain and Doppler activity.
This study was supported by the OAK Foundation, The Foundation for Research in Eastern Denmark and Siemens Medical Solution.
Competing interests None declared.
Ethics approval The study was approved by the local ethical committee (KF01-045/03).
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