Physiotherapy management of patellar tendinopathy (jumper’s knee)
http://www.journalofphysiotherapy.com/article/S1836-9553(14)00091-5/pdf
Autor: Aliza Rudavsky, Jill Cook
Department of Physiotherapy, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Australia
Introduction
Patellar tendinopathy (jumper’s knee) is a clinical diagnosis of
pain and dysfunction in the patellar tendon. It most commonly
affects jumping athletes from adolescence through to the fourth
decade of life. This condition affects health and quality of life by
limiting sports and activity participation for recreational athletes
and can be career-ending for professional athletes. Once symptoms
are aggravated, activities of daily living are affected, including
stairs, squats, stand to sit, and prolonged sitting.
Patellar tendinopathy clinically presents as localised pain at the
proximal tendon attachment to bone with high-level tendon
loading, such as jumping and changing direction. Tendon pain at
the superior patellar attachment (quadriceps tendinopathy) and at
the tibial attachment occurs less frequently, but the diagnosis and
management are similar to jumper’s knee. It is commonly clinically
diagnosed in conjunction with imaging (ultrasound or magnetic
resonance, often to exclude differential diagnoses such as
patellofemoral pain), where structural disruptions on the scans
represent areas of tendon pathology. Importantly, there is a
disconnection between pathology on imaging and pain; it is
common to have abnormal tendons on imaging in people with
pain-free function.1 The term tendinopathy will be used in this
review to mean painful tendons. The term tendon pathology will
be used to indicate abnormal imaging or histopathology without
reference to pain.
Treatment of patellar tendinopathy may involve prolonged
rehabilitation and can ultimately be ineffective. Management is
limited by a poor understanding of how this condition develops,
limited knowledge of risk factors and a paucity of time-efficient,
effective treatments. Many treatment protocols are derived from
evidence about other tendinopathies in the body and applied to the
patellar tendon; however, the differences in tendons at a structural
and clinical level may invalidate this transfer between tendons.
This review discusses the prevalence of patellar tendinopathy,
associated and risk factors, assessment techniques and treatment
approaches that are based on evidence where possible, supplemented
by expert opinion.
Prevalence
Patellar tendinopathy is an overuse injury that typically has a
gradual onset of pain. Athletes with mild to moderate symptoms
frequently continue to train and compete. Determining the
prevalence of overuse injuries such as patellar tendinopathy is
difficult because overuse injuries are often not recorded when
injuries are defined exclusively by time-loss from competitions
and training.2 The time-loss model only records acute injuries and
the most severe overuse injuries, making it difficult to gather an
accurate estimate of the prevalence of patellar tendinopathy in the
athletic population.
Studies that have specifically examined the prevalence of
patellar tendinopathy showed that the type of sport performed
affected the prevalence of tendinopathy.3 The highest prevalence
in recreational athletes was in volleyball players (14.4%) and the
lowest was in soccer players (2.5%);3 the prevalence was
substantially higher in elite athletes. Tendon pathology on imaging
in asymptomatic elite athletes was reported in 22% of athletes,
male athletes had twice the prevalence as female athletes, and
basketball players had the highest prevalence of pathology (36%)
amongst the sports investigated: basketball, netball, cricket and
Australian football.4 It is not only a condition that affects adults;
the prevalence of patellar tendinopathy in young basketball
players was reported as 7%, but 26% had tendon pathology on
imaging without symptoms.4
Patellar tendon rupture, however, is rare. The most extensive
analysis of tendon rupture reported that only 6% of tendon
ruptures across the body occurred in the patellar tendon.5 The
majority of patellar tendon ruptures that do occur are in the older
population (mean age 65 years).5 All those who had a patellar
tendon rupture had pathology in the tendon.6 Because this is a
relatively rare injury, it will not be discussed in this review.
Aetiology
The pathoaetiology of tendinopathy is unknown and there are
several models that attempt to describe the process.7–9 Of these the continuum model of tendinopathy has the most overt clinical
correlation.7 The continuum model places tendon pathology in
three somewhat interchangeable stages: reactive tendinopathy,
tendon dysrepair and degenerative tendinopathy (Figure 1). Many
patellar tendons have a combination of pathology state (reactive
on degenerative pathology). A degenerative patellar tendon with a
circumscribed degenerative area is thought to have insufficient
structure to bear load resulting in overload in the normal area of
the tendon, leading to a reactive tendinopathy in this area.
The capacity for tendon pathology to move forward and back
along the continuum was demonstrated in the patellar tendons of basketball players.10 Players were imaged with ultrasound each
month during the season and those with reactive tendinopathy
and tendon dysrepair both progressed (to degenerative tendinopathy)
and regressed (to normal tendon) through the season.10
Whilst it is known that pathology on imaging does not necessarily
indicate painful patellar tendinopathy, certain changes (ie, the
presence of large hypoechoic regions on ultrasound) may increase
the risk of developing patellar tendinopathy.11
It is also unknown at what age a patellar tendon is susceptible to
pathology, but it does occur in young athletes.4 Studies have shown
that tendon tissue is inert and does not renew after the age of 17,
suggesting that once tendon is formed in puberty its structure is
relatively stable.12 An early age of onset of patellar tendinopathy is
supported by data that shows only two players developing it after
the age of 16 in a school for talented volleyball players.13
The aetiology of pain appears somewhat independent of
underlying tendon pathology. Pain is frequently associated with
pathological tendons, however tendon pain in apparently normal
tendons has been demonstrated.14 Overload is reported as the key
factor associated with pain onset.15 Overload is defined as activity
above what the tendon has adapted to at that point in time, and can
occur by a sudden and substantial increase in the volume of
jumping or a return from injury/holiday without gradually
ramping back into a regular schedule. The use of energy storage
and release loads in jumping and change of direction is typically
characteristic of overload causing patellar tendinopathy pain. Nonenergy-storage
loading or non-jumping activity (eg, cycling or
swimming) and repetitive low loading (in runners) rarely
aggravate the patellar tendon; other pathologies are generally
suspected in these cases.
Risk and associated factors
Several studies have examined intrinsic and extrinsic risk and
associated factors for both pathology and patellar tendinopathy
(Table 1). Risk factors for pathology and risk factors for pain are
likely to be different and will be distinguished in this section.
Biomechanical studies of painful tendons will not be discussed, as
altered mechanics may be an outcome of having a painful patellar
tendon, however, they would certainly be considered as part of a
management paradigm.
Extrinsic factors
An increase in training volume and frequency has been
associated with the onset of patellar tendinopathy in several
studies.16,17 Clinically, this is the most common factor that triggers
patellar tendinopathy. Other factors, such as change in surface
density and shock absorption, may have an effect as well. Although
harder surfaces can increase patellar tendinopathy symptoms,8
they are less likely to be an issue nowadays as most indoor sport is
now played on standard sprung wooden floors. Surface density and
amount of shock absorption in both the shoes and the surface
should still be considered, as athletes may be vulnerable whentraining on hard floors, athletic tracks, or surfaces with high
horizontal traction.
Intrinsic factors
Several studies have attempted to identify specific anthropometric
characteristics that may increase the risk of patellar
tendinopathy symptoms. These characteristics include: height,
weight, lower limb joint range of motion, leg length, body
composition, lower limb alignment, and the length and strength
of the hamstring and quadriceps. Thigh muscle length (shorter or
less extensible quadriceps and hamstrings) has been associated
with patellar tendinopathy,18–20 whilst greater strength has been
associated with reduced pain and improved function.18 Conversely,
better knee extensor strength and jumping ability has been
reported in athletes with patellar tendinopathy, especially in
jumps involving energy storage.16,21 Young women, but not young
men, with tendon pathology have been found to have a better
vertical jump performance than those without pathology.20
Clinical observation aligns with patellar tendinopathy being more
prevalent among athletes with better jumping ability.
Different lower limb kinematics and muscle recruitment order
in horizontal landing phase have been associated with tendon
pathology.22 Edwards et al demonstrated the horizontal braking
force to place the highest load on the patellar tendon. They
suggested that the compression through the patellofemoral joint
and the patellar tendon and the tensile loading with the knee
flexed all contribute to pathology in those with asymptomatic
tendon pathology.
Lower foot arch height,18 reduced ankle dorsiflexion,23 greater
leg length discrepancy, and patella alta in men24 have each been
associated with patellar tendinopathy. Boys and men are two to four
times more likely to develop patellar tendinopathy than girls.16,25
Increased waist circumference in men is associated with greater
prevalence of pathology on ultrasound. It has been reported that
men with a waist circumference greater than 83 cm are more likely
to have abnormal changes on imaging (74% versus 15% in those
with less than 83 cm).26 One study found that athletes with
patellar tendinopathy were generally younger, taller and weighed
more than those without patellar tendinopathy.3 Infrapatellar fat
pad size was significantly larger in those with tendinopathy than in
controls.27
Assessment
History
There are few papers providing evidence on assessment
procedures, therefore this section is based on expert opinion. As
with all musculoskeletal conditions, a detailed history is very
important and must first identify if the tendon is the likely source
of pain. This is determined initially in the history by asking the
person to indicate where they feel their pain during a patellar
tendon-loading task (such as jumping and changing direction).
They should point with one finger to the tendon attachment to the
patella; more widely distributed pain should raise the possibility of
a different diagnosis. Second, a history should identify the reason
that the tendon has become painful; this is classically due to
tendon overload. Two common overload scenarios are seen: a large
increase in overall load from a stable base (eg, beginning
plyometric training or participation in a high-volume tournament)
or returning to usual training after a significant period of
downtime (eg, return to training after 4 to 6 weeks time off for
an ankle sprain or holidays). Elite athletes can have repeated
loading/unloading periods due to injuries and season breaks over
several years, which gradually reduces the capacity of the tendon
to tolerate load and leaves it vulnerable to overload with small
changes in training. No identifiable change in load or pain induced
from a load that should not induce patellar tendinopathy (such as
cycling) should suggest alternative diagnosis.
Pain behaviour also has a classic presentation: the tendon may
be sore to start activity, respond variably to warm-up (from
completely relieving symptoms to not at all) and will then be
worse the next day, which can persist for several days. The athlete
will rarely complain of night pain and morning stiffness (unless
symptoms are severe), but will complain of pain with prolonged
sitting, especially in a car. Pain with sitting can be a good
reassessment sign as the condition improves. Pain during daily
activity is also common; stairs and squatting are provocative.
Most athletes who present clinically with patellar tendinopathy
are good power athletes; they will describe being good at jumping
and being quick, especially in change of direction.28 They will
complain that their tendon pain affects their performance,
reducing the attributes that allow them to excel at sport.
When taking a history, it is critical to document all previous
treatment that the patient has explored, including all types of
interventions and rehabilitation strategies, descriptions of the
successful and unsuccessful interventions, and details of all
exercises including number of repetitions, sets, weights and
frequency. Many people will consult a variety of physiotherapy,
orthopaedic and sports medicine professionals; inconsistency of
care may prolong the rehabilitation process. The history should
document all the known risk factors for tendinopathy, such as
diabetes, high cholesterol, seronegative arthropathies and the use of
fluoroquinolones. These are known to contribute to other tendinopathies,
but their role in the patellar tendon is unknown. Finally, the
examiner should ask about past injury and medical history,
including previous injuries that have necessitated unloading or
time off from sports activity or that may have altered the manner in
which the athlete absorbs energy in athletic manoeuvres.
Examination
The VISA-P (Victorian Institute of Sports Assessment for the
Patellar tendon) should be completed as a baseline measure to
allow monitoring of pain and function. The VISA-P is a brief
questionnaire that assesses symptoms, simple tests of function and
ability to participate in sports. Six of the eight questions are on a
visual analogue scale (VAS) from 0 to 10, with 10 representing
optimal health. The maximal score for an asymptomatic, fully
functioning athlete is 100 points, the lowest theoretical score is 0
and less than 80 points corresponds with dysfunction.29 It has high
impedance, so it is best repeated monthly and the minimal
clinically significant change is 13 points.30 Tenderness on
palpation is a poor diagnostic technique and should never be
used as an outcome measure;31 however, pain pressure threshold,
as measured by algometry, has been found to be significantly lower
in athletes with patellar tendinopathy (threshold of 36.8 N) when
compared to healthy athletes.
Observation will nearly always reveal wasting of the quadriceps
and calf muscles (especially gastrocnemius) compared to the
contralateral side; the degree of atrophy is dependent on the
length of symptoms. Athletes who continue to train and play, even
at an elite level, are not immune to strength and bulk losses, as they
are forced to unload because of pain.
Clinical tests
A key test is the single-leg decline squat. While standing on the
affected leg on a 25 deg decline board, the patient is asked to
maintain an upright trunk and squat up to 90 deg if possible
(Figure 2).32 The test is also done standing on the unaffected leg.
For each leg, the maximum angle of knee flexion achieved is
recorded, at which point pain is recorded on a visual analogue
scale. Diagnostically the pain should remain isolated to the tendon/
bone junction and not spread during this test.33 This test is an
excellent self-assessment to isolate and monitor the tendon’s
response to load on a daily basis.
Kinetic chain function is always affected;15,18,23,33 the leg
‘spring’ has poor function, and is commonly stiff at the knee and soft at the ankle and hip. The quality of movement can be assessed
with various single-leg hop tests and specific change of direction
tasks. Record pain (VAS) and function at take off and landing,33 and
note if more load induces more pain. If possible, measurement of
angles and individual joint moments through video/biomechanical
analysis can help with more elite athletes. Hop tests for height and
distance can also be used to assess kinetic chain quality, as well as
providing an objective means of monitoring progress.
Muscle strength, assessed through clinical and functional
measures (repeated calf raise and decline squats), is useful to
assess the level of unloading in the essential muscles. Dorsiflexion
range of movement is a critical assessment, as the ankle and calf
absorb much of the landing energy.34 Stiff talocrural joint
dorsiflexion,26 general foot stiffness and/or hallux rigidus all
contribute to increased load on the musculotendinous complexes
of the leg.
Imaging
Imaging with traditional ultrasound and magnetic resonance
can identify the presence of pathology in the tendon. Ultrasound
tissue characterisation, a novel form of ultrasound, can quantify
the degree of disorganisation within a tendon and may enhance
clinical information from imaging (Figures 3 and 4).35 Imaging will
nearly always demonstrate tendon pathology, regardless of the
imaging modality used. The presence of imaging abnormality does
not mean that the pathology is the source of the pain so clinical
confirmation, as described above, is essential. More importantly,
the pathology is commonly degenerative, often circumscribed and
does not change over time, so imaging the tendon as an outcome
measure is unhelpful, as pain can improve without positive
changes in tendon structure on imaging.35 In elite jumping sports, such as volleyball, patellar tendon changes are nearly the norm,
which needs to be considered when interpreting clinical and
imaging findings.
Differential diagnosis
The history and examination are crucial to distinguish patellar
tendinopathy from other diagnoses including: patellofemoral
pain; pathology of the plica or fat pad; patellar subluxation or a
patellar tracking problem; and Osgood-Schlatter disease.36
Physiotherapy management
While pathology in a patellar tendon may not ever completely
resolve, symptoms of patellar tendinopathy can generally be
managed conservatively. This section will draw from the literature
on therapeutic management of patellar tendinopathy, as well as
clinical expertise and emerging areas of research.
Active interventions
Intervention is aimed at initially addressing pain reduction,
followed by a progressive resistive exercise program to target
strength deficits, power exercises to improve the capacity in the
stretch-shorten cycle, and finally functional return-to-sport
training (Table 2). Daily pain monitoring using the single-leg
decline squat provides the best information about tendon response
to load; consistent or improving scores suggest that the tendon is
coping with the loading environment.
Pain reduction
Reducing an athlete’s symptoms requires load management,
although it is important to avoid complete cessation of tendon
loading activities, as that will further reduce the load capacity of
the tendon.33 Removing high-load drills from training, reducing
frequency of training (twice a week is tolerable for many tendons)
and decreasing volume (reducing time of training) are all useful
means of reducing load on the tendon without resorting to
complete rest.
Sustained isometric contractions have been shown to be
analgesic.37 In painful patellar tendinopathy (usually a reactive
or reactive on degenerative pathology), pain relief can be obtained
for 2 to 8 hours with heavy sustained isometric contractions.
Voluntary contractions at 70% of maximum, held for 45 to
60 seconds and repeated four times is one loading strategy that
has been shown to have a large hypoalgesic effect. This loading can
be done before a game or training, and can be done several times a
day.38 If the tendon is highly irritable, bilateral exercise, shorter
holding time and fewer repetitions are recommended.38 Additionally,
medication may help to augment pain reduction and/or
pathological change in a reactive tendon,39 so consultation with a
physician is advised.
Strengthening
Eccentric, heavy slow resistance, isotonic and isometric
exercises have all been investigated in patellar tendinopathy.
Eccentric exercises have generally been shown to have good
short-term and long-term effects on symptoms and VISA-P scores.
There are several different types of eccentric patellar tendon
loading exercises; however, there is no difference in the results of a
12-week eccentric training program between the bilateral
weighted squat (Bromsman device) twice a week and the
unilateral decline squat daily.40
Several interventions have used the 25 deg single-leg decline
squat, which has been shown to have better outcomes than a
single-leg flat squat.41 Two investigations have shown that angles
above 15 deg are equivocal,42,43 and that the decline board is
effective by increasing the moment arm of the knee.44
Two studies have investigated the effect of eccentric exercise in
the competitive season. Visnes et al reported no overall effect and a
short-term worsening with decline squat training on function in
symptomatic athletes continuing a regular training program,
compared to a regular training program only.45 Fredberg et al
showed an increased risk of injury for asymptomatic athletes with
pathology on ultrasound who completed a prophylactic eccentric
decline squat training program.46 This suggests that the addition of
eccentric exercise while an athlete is in a high-load environment is
detrimental to the tendon. When comparing an eccentric decline
squat protocol to a patellar tenotomy, there was no difference in
the outcomes and both showed improvement.47 Surgical intervention
is not recommended over an exercise rehabilitation
program in the first instance.
Heavy slow resistance exercises were investigated by
Kongsgaard and colleagues,48 who compared the effects of a peritendinous corticosteroid injection to the proximal patellar
tendon to a decline squat eccentric exercise protocol and a heavy
slow resistance protocol in people with patellar tendinopathy. All
three groups showed improvements at 12 weeks; however, at 6
months only the groups using the eccentric exercises and the
heavy slow resistance exercises still showed improved VISA-P and
VAS scores. The heavy slow resistance group showed improved
tissue normalisation of the collagen and also demonstrated better
clinical presentations than the eccentric group within the 12-week
follow-up.
Combined exercises with eccentrics, concentrics and plyometric
training for the Achilles tendon were studied by Silbernagel and
colleagues.49 Athletes were allowed to continue training in their
sports during the first 6 weeks of rehabilitation, as long as their
pain did not go over 5/10 on the VAS during activity and returned
to normal by the next morning.49 While this study was
investigating Achilles tendinopathy, this combined approach is
often used clinically with patellar tendinopathy and should be
considered as a treatment option.
Functional strengthening and return to sports
Functional strengthening must address high-load tendon
capacity as well as kinetic chain deficits and movement patterns.
Once these patterns have improved, the athlete should begin
sports-specific training. Faster contractions can progress loads
towards the stretch-shorten cycle that forms the basis for return to
sports. Early drills should include: skipping, jumping and hopping,
progressing to agility tasks, direction changes, sprinting and
bounding movements. It is important to quantify these tasks and
use a high-low-medium-load day approach in early reintroduction
of high-load activities and return to sports. Also, include training
specificity when returning an athlete back to their sport, including
movement assessment for optimal kinetic chain loading.
Passive interventions
Other techniques may be useful in augmenting an exercise
program; however, there is little evidence for effect of passive
treatments for patellar tendinopathy.
Exercise, pulsed ultrasound
and transverse friction massages have been compared, and
exercise had the best effects in the short and long term.50 Manual
therapy techniques, including myofascial manipulation of the knee
extensor muscle group, have had a positive effect on reducing pain
in patellar tendinopathy patients in short-term and long-term
follow-up.51 Other passive therapies, including braces and taping
techniques, are often used clinically to help unload the patellar
tendon, however, no evidence supports their efficacy. Passive
therapies are best used to reduce symptoms in season so the
athlete can continue to participate in rehabilitation and sport.
Other interventions
Extracorporeal shockwave therapy, corticosteroid injections,
platelet-rich plasma and other injections are interventions
frequently used in the clinical setting, yet have limited evidence
supporting their use in patellar tendinopathy. There was no benefit
of extracorporeal shockwave therapy compared to placebo for inseason
athletes with chronic patellar tendinopathy.52 A direct
comparison between platelet-rich plasma and extracorporeal
shockwave therapy showed significantly better outcomes in the
platelet-rich plasma group at 6-month and 12-month follow-up,
compared to the extracorporeal shockwave therapy group;
however, both groups showed similar and significant improvements
at the 2-month follow-up.53 Peritendinous corticosteroid
injection, oral steroidal medication, or iontophoresis may be useful
and effective at quickly reducing cell response and pain in a
reactive tendon,38 however, the long-term outcomes are worse
than those obtained with exercise.48 Corticosteroid injection,
however, is not indicated in degenerative tendinopathy.38
Analgesic injections may alter an athlete’s perception of pain
and ability to moderate activity, this absence of symptoms has
been associated with poorer outcomes and is not advised in
season.38
Studies of the efficacy of platelet-rich plasma injections as a
treatment for tendinopathy show little effect.54 A literature review
in 2011 showed positive outcomes for several injection-based
studies with small sample sizes;55 further research is needed.
Surgical interventions including arthroscopic shaving and sclerosing
injections are improving in their ability to reduce pain and
amount of time out of sports.56 When considering surgery, it is
important to factor in stage of tendinopathy and treat it as part of a
well-rounded rehabilitation program involving kinetic chain
exercises, education in proper landing technique and management
of load and return to sports.38
Education
It is important for the athlete to have realistic expectations of
the rehabilitation process and to understand that management of
their symptoms is required throughout their sports career,
whether recreational or professional. The athlete must know
how to monitor symptoms and adjust participation and loading
appropriately throughout the rehabilitation process and in return
to sport, and should always maintain strength exercises twice
weekly throughout their sporting careers.
Tendons generally have a delayed response to load and will
cause minimal pain during activity, but flare 24 hours later.
Regular pain monitoring will help guide and progress the exercise
program and should be maintained after return to sport. The best
monitoring is the single-leg decline squat, which an athlete can use
to self-assess symptoms in order to determine response to
rehabilitation and participation in their sport. A journal of
symptoms and pain on decline squat will help the athlete to
identify triggers, monitor loading response and learn to manage
symptoms independently.
Factors affecting prognosis
Return to sport can be slow and is often dependent on severity
of the pain and dysfunction, the quality of rehabilitation, and
intrinsic and extrinsic factors. Gemignani et al associated mild
pathology in the tendon to 20 days of rehabilitation before return
to sports, and more severe pathology with approximately 90 days
until return to sport.57 However, these imaging-based guidelines
may underestimate return-to-sport time, considering that other
factors affect prognosis. The athlete who presents with a high level
of kinetic chain dysfunction, regardless of pain level, will take
considerable time (6 to 12 months) to recover both muscle and
tendon capacity. This is complicated if the athlete aspires to return
to a high level of performance, for example an elite high jumper
will require much more rehabilitation than a recreational football
player, as the jumping demands differ greatly.58 Even within elite
sport there are levels of loading for the patellar tendon, a volleyball
player will jump and land much more than a basketball player and
will also require greater rehabilitation time. Regardless, impatience
with rehabilitation creates a poorer prognosis; time, proper
rehabilitation and appropriate graded return to sports are an
effective treatment.
Factors affecting response to therapy
Pain in tendinopathies is poorly understood, however, there is
emerging evidence in support of an element of central sensitisation
or pathophysiological up-regulation of the central nervous
system.59,60 A small study has demonstrated that athletes with
patellar tendinopathy have a lower mechanical pain threshold and
greater sensitivity to vibration disappearance than non-injured
athletes.61 Local pathology, such as neovascularisation, lacks
evidence as the primary pain driver,62 which is yet to be
determined.
Avenues for further research
More research is required to fully understand how a tendon fails
in adaptive capacity and pathology develops, and what causes the
pain in the tendons that is so specific to loading. Intervention
studies to clarify an optimal loading program, as well as the
eventual development of a prevention program would also be
beneficial.
Conclusions
Research has increased our understanding of patellar tendinopathy
and pathology but there is still more to discover. Currently,
the most important factors in managing athletes with patellar
tendinopathy are to educate them about how to modify loading
according to symptoms, to ensure that they understand how to
increase or decrease loading appropriately, and to assess and
modify intrinsic and extrinsic factors that may be contributing to
overload.
Ethics approval: Nil
Competing interests: Nil
Source(s) of support: Professor Cook is supported by the
Australian Centre for Research into Sports Injury and its Prevention,
which is one of the International Research Centres for
Prevention of Injury and Protection of Athlete Health supported by
the International Olympic Committee (IOC). Prof. Cook is
supported by a NHMRC practitioner fellowship (1058493).
Acknowledgements: We thank SI Docking for the supply of the
tendon ultrasound figures.
Correspondence: Aliza Rudavsky, Department of Physiotherapy,
Monash University, Australia. Email: aliza.rudavsky@monash.
edu
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