Evidence-Based Treatment of Hamstring Tears

COMPETITIVE SPORTS AND PAIN MANAGEMENT
Evidence-Based Treatment of Hamstring Tears
Spencer T. Copland, John S. Tipton, and Karl B. Fields
Moses H. Cone Sports Medicine Fellowship and Family Medicine Residency, Moses Cone Health System,
Greensboro, NC
COPLAND, S.T., J.S. TIPTON, and K.B. FIELDS. Evidence-based treatment of hamstring tears. Curr. Sports Med. Rep., Vol. 8,
No. 6, pp. 308Y314, 2009. Hamstring tears are exceedingly common in a variety of athletic populations and contribute to a significant
amount of morbidity and time lost from sport. Many modifiable and nonmodifiable risk factors have been identified with hamstring injury.
There is strong evidence that Nordic hamstring exercises can decrease the risk of hamstring injury, limited evidence that sports specific
anaerobic interval training and isokinetic strengthening can reduce injury rates, and limited evidence that daily static stretching after injury
can increase recovery rate. The majority of medical, surgical, and rehabilitative intervention studies have limitations based on the total
number of hamstring injuries included in a given study, reliance on retrospective cohort studies, and conclusions based on case series that
limit the utility of the information. Most do not provide a level of evidence greater than expert opinion.
INTRODUCTION
Hamstring muscle injuries are common in both recreational
and elite athletes. Depending on the severity of the
injury, the athlete may require considerable time off from
sport (9,11,14,29,31,33,35,41). Hamstring tears traditionally
have been classified as mild (grade I), moderate (grade II),
and severe (grade III). Grade I injuries signify a small tear of
the muscle or tendon, minor swelling, and pain with no or
minimal strength loss. Grade II strains are more complete
partial tears, with definite loss of strength and pain. Grade III
tears are complete ruptures of the musculotendinous unit
with a complete loss of muscle function, and they typically
develop a large hematoma.
EPIDEMIOLOGY
Rates of hamstring muscle injury vary by differing injury
definitions and sporting populations. Prevalence rates range
from 8% to 25%, with return to sport occurring from 2 wk to
never, with large variability based on severity. One study
Address for correspondence: Karl B. Fields, M.D., Director, Moses Cone Sports
Medicine Fellowship, Moses Cone Health System, Family Medicine Residency and
Sports Medicine Fellowship, Professor and Associate Chairman, Department of
Family Medicine, UNC-Chapel Hill, 1125 N. Church Street, Greensboro, NC
27401 (E-mail: bert.fields@mosescone.com).
1537-890X/0806/308Y314
Current Sports Medicine Reports
Copyright * 2009 by the American College of Sports Medicine
308
reports a single-season prevalence rate greater than 50% in
elite soccer players (3). Recurrent hamstring injury rates
generally are higher than initial injuries. Most studies found
rates of reinjury for the ensuing sporting season higher than
30% and some up to 60%Y70% (29,31,35,41).
RISK FACTORS
Several risk factors have been attributed to hamstring injury
and can be divided into modifiable and nonmodifiable
factors and their interplay. Modifiable risk factors include
fatigue, low hamstring strength, lack of warm-up, greater
training volume, poor muscle flexibility, cross-pelvic posture,
poor lumbo-pelvic strength, and biomechanical problems.
Nonmodifiable factors include age, previous hamstring and
lower extremity muscle injuries, and being of black or Aboriginal
ethnic origin (9,11,30,31).
The key identifiable risk factor for hamstring strain is a
previous injury. Most studies involved Australian Rules football
and noted that athletes with a previous history of hamstring
strain were two to six times more likely to suffer
subsequent strains during their lifetime (2,8,18,31,45). Most
subsequent strains occurred within the first 2 months after
return to sport, although the risk continued over time
(2,8,15). In some reports, athletes were three times more
likely to suffer another hamstring injury even after a year
(18). Researchers theorize that regeneration and remodeling
of an injured muscle may continue for up to 9 months after
injury. A debate still exists regarding whether recurrence of
hamstring injury arises from inadequate rehabilitation and
premature return to sport, or whether an intrinsic risk is
Copyright @ 200 9 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.

created by the initial injury (2,33,43,45,46). Recurrence
remains high even with thorough rehabilitation and functional
improvement. Some researchers believe that skeletal
muscles, including hamstrings, are at risk for reinjury because
of scar tissue formation and muscular architectural reorganization
(11,45), although others dispute this contention (46).
Another issue involves size (measured by imaging) and
severity (defined by number of days missed from competition)
of the initial hamstring injury and subsequent association
with recurrent injury within the same season. While
some found no relationship (23), one study noted a high risk
of recurrence within two seasons in athletes with severe
strains (Q18 d missed) (48). Other injuries may predispose
the athlete to hamstring strain, which reinforces the notion
of hamstrings belonging to a larger kinetic chain. History of
previous calf or quadriceps muscle injury, knee injury, or
osteitis pubis increased the risk of subsequent hamstring injury
(31,45). A potential explanation is that the biomechanics
of running after any lower extremity injury is altered
and predisposes athletes to hamstring injury (31).
A recent meta-analysis suggests that hamstring flexibility
has no significant association with injury (35). Confounders
affecting this type of research include questions about how
best to measure hamstring flexibility, since motion occurs
at the hamstring and at the lumbo-pelvic junction. In addition,
because athletes already were relatively flexible because
of a regular stretching routine in training, hamstring inflexibility
was less likely to be an issue in those with hamstring
injuries (7).
The flexibility of other muscles groups in the thigh, particularly
the quadriceps, may be of more significance than
that of the hamstring group. In one study, an inverse relationship
was found between increased quadriceps flexibility
and incidence of hamstring strain. The athletes who were
able to achieve greater than 51- knee flexion in a modified
Thomas test were less inclined to suffer a hamstring strain. In
the same study, tight hip flexors also posed a significant risk
for hamstring injury. However, older-aged athletes in this
subgroup were a potential confounder (14). A possible biomechanical
reason explaining why tight hip flexors may
predispose athletes to hamstring injury is that tight muscles
create higher potential energy during hip extension and knee
flexion in the pre-swing phase of gait. This generates
increased forward propulsion of the leg during swing due to
passive recoil of these muscles, which then increases the
eccentric load on the hamstrings to decelerate the limb (17).
Isolated decreased hamstring strength appeared to be a risk
factor in a prospective study on track and field athletes. In
these runners, the injured extremity had significantly less
hamstring strength compared with the uninjured side (49).
Similar findings were demonstrated in the largest published
hamstring risk factor study with 672 total hamstring injuries
in Australian Rules footballers (32). Not all studies support
this finding. Another study of Australian Rules football
noted that a 10% between-leg strength discrepancy was not
a significant predictor of future hamstring strain in their
sample of 12 injuries (8).
Strength imbalances between quadriceps and hamstrings
may play a larger role than isolated hamstring strength. A
significantly reduced ratio of hamstring strength to quadri-
ceps strength (H:Q) in the injured side was found in several
studies (11,32,49). The hamstrings eccentrically slow the
lower limb during the swing phase of running before extending
the hip to achieve forward motion. This braking function
also is critical in kicking motion (17,33,48). The ability to
exert lower limb swing force possibly is greater in individuals
with increased quadriceps strength relative to hamstring
strength. This potentially places a greater requirement on the
hamstring to decelerate the lower limb. Some researchers
speculate that professional players, particularly in kicking
sports, may be developing too much quadriceps strengthening,
which may predispose them to hamstring injury (35).
One study with low injury rates did not support the role of
strength imbalance as a risk factor for hamstring injuries (8).
Increasing age appears to be the most prominent intrinsic
risk factor for hamstring injury, with several studies of
Australian footballers reporting a significant relationship
(14,15,17,18,31,45). Specifically, athletes older than 23 yr
were 1.3 to 3.9 times (17,31) and athletes older than 25 yr
were 2.8 to 4.4 times (14,15) more likely to suffer a hamstring
injury than younger players. Data suggest that risk of
injury increases by 30% annually (45). Different theories
have been proposed linking hamstring injury and age. One
theory suggests that age promotes a reduction of crosssectional
area of the hamstrings such that the muscles can no
longer produce sufficient tension to resist load before failure
(35). Confounders in this observation include that the pivotal
studies were performed on athletes who were relatively
young. A second novel theory is that hamstring strain may
be caused by age-related lumbar degeneration leading to L5
and S1 nerve impingement and subsequent hamstring muscle
fiber degeneration (31).
Studies also point to race and ethnicity as intrinsic factors,
with athletes of black descent being significantly more likely
to suffer hamstring strain (45,48). In Australian Rules football,
professional Aboriginal footballers were 11.2 times more
likely to suffer hamstring strains than non-Aboriginal footballers
(45). In another study involving the English professional
football leagues, hamstring injury was not specific
to any one nationality or ethnic group. Rather, injury was
related to all players of black racial background (48).
Body mass index (BMI) inconsistently was associated with
risk of either initial or recurrent hamstring strains, with two
positive and two negative studies (2,15,31,45). Weight also
was linked variably with risk of hamstring injury where some
prospective cohort studies did not find a significant association
with incidence of hamstring strain (2,15,32,45),
whereas others studies did (14,31).
SPORT-SPECIFIC RISKS
A higher level of competition was a risk factor of hamstring
injury. One study involving soccer in the English
Premier League (EPL) showed a significantly higher prevalence
of hamstring strain in the Premier division versus
Division 2 (48). Similarly, a study performed on Australian
Rules football demonstrated a significantly higher prevalence
(920%) in the Australian Football League (AFL) versus the
lower division South Australian National Football League
Volume 8 c Number 6 c November/December 2009 Treatment of Hamstring Tears 309
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(SANFL) (45). This may reflect the increased physical burden
in the higher leagues where the tempo of the games may
be faster and training more demanding.
Playing positions that required more running also correlated
with hamstring injury rates. Outfield players exhibited
a higher incidence (22% to 37%) of hamstring strain compared
with goalkeepers in English soccer and Australian
Rules football (32,48). In soccer, Australian Rules football,
and in the rugby union, the players who ran more, kicked
more, and covered more of the field had the highest risk of
hamstring injury (9,48).
Another injury mechanism for hamstring strains is slowspeed
stretching exercises carried out to an extreme joint
position, as in ballet dancers. Hamstring strains in different
sports, with similar injury conditions to dancers, show a
resemblance in symptoms, injury location, and recovery time
to dancers. These particular hamstring injuries occurred
during movements reaching a position with combined
extensive hip flexion and knee extension. The incidence
and prevalence rates during these types of injuries were not
calculated. While not reaching statistical significance, there
was a trend suggesting that the time to return to preinjury
status was longer in athletes with strains of the stretching
type than in athletes with strains during high-speed running
(mean 31 wk vs 16 wk) (4,5).
PHYSICAL EXAMINATION
Hamstring injury evaluation follows a pattern similar to
evaluation of other musculoskeletal injury: inspection,
palpation, range of motion, strength testing, and special
maneuvers. Any swelling, ecchymosis, atrophy, and scars
should be noted during the inspection. Particular attention
also should be placed on gait analysis, including motion at
the hips, knees, and feet.
The length of the hamstring should be palpated for
tenderness or any muscle defects from the popliteal fossa to
the ischial tuberosity, where the semitendinosus, semimembranosis,
and the long head of the biceps femoris originate.
The semitendinosus can be followed to its insertion at the
pes anserinus, where it is felt as the most posterior and
inferior tendon. The biceps femoris tendon is found easily on
the lateral knee where it should be palpated to its insertion
on the fibular head. The semimembranosis inserts deep to
the pes anserinus on the posterior tibia and can be felt
through the semitendinosus and gracilis tendons (25,38,39).
Knee flexion and extension range of motion can be
estimated or easily quantified with a goniometer. To evaluate
hamstring strength, have the patient in the supine position
with his or her knee flexed to 90-. The patient should flex
concentrically his or her knee towards the buttock region
against resistance, while stabilizing the thigh above the knee.
To place more emphasis on the biceps femoris, the knee
should be rotated externally, while internal rotation will activate
the semitendinosus and semimembranosis. Additionally,
eccentric hamstring strength should be assessed with the
patient supine and with knee flexion from 15- to 30-.
Overall strength of hamstrings also can be tested concentrically
at 90- knee flexion and eccentrically at 15- of knee
flexion with the patient prone, which allows the examiner to
observe for defects or fasciculations while testing. Evaluation
of range of motion, strength, and for muscle defects allows
the clinician to grade the severity of injury (grades I, II, or
III), which directly relates to rehabilitation and return to
play. The Lasègue test (straight leg raise) should be
performed if radiculopathy is present. Dynamometer strength
testing frequently was used in published trials, but it is less
relevant for day to day use by clinicians (28,38,39,50).
INJURY LOCATION AND IMAGING
In the majority of studies, the biceps femoris was the most
commonly injured hamstring. Injury to the semimembranosis
was less common, followed by the semitendinosus (4,13,23,45).
However, these numbers differ in other studies and are
complicated by the fact that more than one muscle often is
injured (5,13). Proximal injuries including tendon avulsion
(based on their relationship to the origin of the short head of
the biceps femoris) were more common than distal injuries,
regardless of which muscle was involved. Most occurred in the
musculotendinous junction, which is really a 10- to 12-cm
transition zone in which myofibrils contribute to form the
tendon. Bony avulsion of the ischium was rare in adults and
usually occurred in the skeletally immature (4,5,13,23,47).
In the setting of hamstring injuries, ultrasonography and
magnetic resonance imaging (MRI) are the modalities of
choice. Both provide detailed information about the injury
with respect to localization and characterization. Ultrasound
is attractive because it is less expensive, portable, and can be
implemented in the office setting. Moreover, dynamic assessment
of the hamstring tendon with ultrasonography provides
additional information about its integrity in varying degrees
of resisted contraction. Ultrasound is highly user-dependent
but has excellent sensitivity in the acute phase of injury
when inflammatory fluid is in the soft tissue. As the fluid
resolves (usually within 2 wk), ultrasonography becomes less
accurate in showing myofibrillar abnormalities, while MRI
remains sensitive. MRI is more reliable in depicting hamstring
tendon and osseous avulsion injuries and injuries that
are in the deeper musculotendinous junction. MRI also allows
accurate assessment of the degree of tendon retraction
and of tendon edge morphology (23). This gives the surgeon
important information since tendon avulsion may require
surgical repair (24Y26,38,39,47). When experienced musculoskeletal
ultrasonographers are available, this should be the
initial form of imaging because the cost is much lower and
the sensitivity is good. However, in much of the United
States, MRI remains the imaging modality of choice.
TREATMENT EVIDENCE
There is no consensus regarding treatment for hamstring
tears. Many interventions commonly are done, but limited
randomized controlled trials and quality prospective studies
guide the medical, surgical, and rehabilitation treatments
prescribed by clinicians. Moreover, many of the published
risk factor studies are retrospective or assess only a small
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number of injured athletes. Even when randomized controlled
trials have been conducted, most have low total
numbers of injured athletes, which potentially explains the
variability among study results. A comprehensive analytical
review by Bahr from the Oslo Sports Trauma Research
Center provides invaluable insight into the methodological
deficits of the majority of published hamstring studies (6).
This methodological and statistical approach to evaluating
sports injury evidence and its specific relationship to hamstring
injury seems sound and points out the limitations of
our ability to analyze hamstring injury risks and treatment
interventions. Published cohort risk factor studies all have
low numbers of total injuries, with one exception (32). They
are necessarily powered to detect only a strong relationship,
and a negative result potentially could be untrue from Type 2
error V failing to observe a difference when in truth there is
one. Reproducibility and precision of measurement at baseline
of a modifiable risk factor affect its ability to determine associations.
If a specific measurement is less precise, then greater
numbers of test subjects and injuries are needed to detect an
association. Bahr used statistical modeling to determine the
number of injuries needed in studies to have adequate power
to determine the association of given risk factors. Risk factors
with a small to moderate association to hamstring injury would
only be detected in studies with 200 or more injured patients.
Even risk factors with a strong association to hamstring injury
would require a study with 20 to 50 injured athletes (6). The
following section discusses evidence-based treatment and also
includes the largest human retrospective studies and case series
when no other evidence is available.
REHABILITATION
Many rehabilitation programs exist for hamstring tears,
but only a few are based on randomized controlled trials. A
2007 Cochrane Review included three randomized controlled
or comparative trials dealing with hamstring rehabilitation
(29). A randomized controlled trial by Malliaropoulos
et al. found that static stretching started 48 h from injury in
grade II hamstring tears four times daily compared with once
daily decreased athlete_s time to normal range of motion
(5.6 vs 7.3 d; P G 0.001) and unrestricted activity (13.3 vs
15 d; P G 0.001) (28). Sherry and Best performed a prospective
randomized comparison study of 24 athletes with
acute hamstring strain into two groups: static stretching,
isolated progressive hamstring resistance exercise, and icing
(STST group) or progressive agility and trunk stabilization
exercises and icing (PATS group). Reinjury was less likely in
the PATS group at 2 wk after return to sport (RTS) (0% vs
54.5%; P = 0.003) and at 1 yr (8% vs 70%; P = 0.006), but
there was no statistical difference in injury time to RTS (41).
A randomized controlled trial comparing manipulation of the
sacroiliac joint to control in athletes with hamstring strains
and sacroiliac dysfunction showed increased hamstring muscle
peak torque, but did not evaluate clinical outcomes (10).
Early mobilization including stretching and strengthening
following a brief period of immobility of 2Y6 d depending on
severity of injury has some evidence for decreasing scar
formation and reruptures.
Delaying the onset of rehabilitation and stretching programs
for at least 48 h, including those mentioned previously,
is based on this earlier work (21,22,28,29,41).
Physical therapy treatment modalities such as cryotherapy,
heat, compression, elevation, ultrasound, electrical stimulation,
and massage frequently are used to treat muscle injuries.
There is a lack of randomized controlled trials in their use for
the treatment of hamstring tears (29,33,35). Cryotherapy
appears safe and can be used for pain relief, and it is the only
modality other than mobilization (manipulation) that has
evidence to support its use. However, there is some evidence
suggesting that early heat application to the injury may
prolong rehabilitation (21). Multiple meta-analyses have
found therapeutic ultrasound to be no better than placebo,
and there is conflicting evidence regarding the use of
electrical stimulation and laser therapy in muscle injury
(21,29). A PubMed search and review did not find any
adequately powered human trials to recommend for or
against anti-fibrotic manual therapy, such as ASTYM or
Graston techniques.
MEDICAL THERAPY
The physiological impact of COX-1 and COX-2 inhibition
and impaired prostaglandin function by nonsteroidal
antiinflammatories (NSAID) and subsequent decrease in
inflammatory cells and pain perception is well-established.
There is only one published study examining the role of
NSAID in hamstring strain healing. In a double-blind,
randomized controlled trial (N = 75), patients were given
either one of two NSAID or placebo, and all completed the
same physical therapy course including RICE (rest, ice,
compression, elevation), ultrasound therapy, deep transverse
friction massage, stretching, and strengthening. In this study,
there was no difference in pain, swelling, strength, or
endurance among the three groups. In their severe injury
subgroups, the placebo group had significantly better pain
scores compared with the NSAID groups at day 7 (37).
The use of corticosteroid for muscle or tendon injury is
controversial, and many physicians have a clinical concern
that corticosteroid may increase the likelihood of complete
rupture, which has been reported in hamstring and other
muscle-tendon-bone unit injuries. Theoretically, corticosteroids
could suppress pain and inhibit fibroblast proliferation
and collagen synthesis V scar formation V by inhibiting the
inflammatory cascade and cytokine production (40,42). One
retrospective case series of 58 National Football League
players with palpable grade II and grade III hamstring tears
had 100% of included athletes return to play following
intramuscular corticosteroid injection with no known ruptures
or other complications (27). Injection of an antifibrotic
agent has been beneficial in animal laboratory studies, but no
human data exist.
SURGERY
Due to the relative rarity of hamstring rupture, published
evidence on hamstring surgery outcomes are all based on case
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series and expert opinion, and to our knowledge, there are no
randomized controlled trials or prospective surgical outcome
studies.
The usual mechanism for proximal hamstring avulsion is
forceful eccentric contraction with knee extension and hip
flexion, and it is seen most commonly seen in waterskiing.
Proximal avulsions can be divided into complete, partial, and
bony apophyseal injury, typically seen in the skeletally
immature, where classically, surgery is reserved for retraction
greater than 2 cm (39,47). Many partial avulsions do well
with nonoperative treatment, but in limited case series,
complete ruptures treated nonoperatively did poorly with the
great majority ultimately seeking surgery. When conservative
treatment fails in partial proximal avulsions, surgical treatment
has allowed 87%Y100% of patients return to sport
(24,47). Surgical outcomes from repair of complete proximal
hamstring avulsions have yielded good to excellent results in
71%Y100% of cases in the largest case series, and postoperative
strength returned to 84%Y98% of the contralateral
side. Delayed surgical repair in complete proximal
ruptures has yielded worse postoperative strength and
potential sciatic nerve involvement with surrounding scar
formation (24,38,39,47).
Lempainen et al. report the largest case series (N = 18) on
surgical treatment of distal partial and complete hamstring
tears, including all cases at Mehiläinen Sports Trauma
Research Center from 1992 to 2005. In their series, 14 of
18 patients returned to sport at preinjury levels, and 13 of 18
reported excellent results. However, all (4/4) partial semimembranosus
tears treated with surgery did poorly (25).
There has been recent attention in the medical literature
to persistent radicular pain at the ischial tuberosity and the
gluteal and proximal hamstring region. It is associated with
prior hamstring injury and variably has been termed the
hamstring syndrome (36), proximal hamstring syndrome
(50), and proximal hamstring tendinopathy (26). Different
authors have postulated that this entity is caused by taut
tendinous band or scarring around the sciatic nerve. But a
recent article by Lempainen et al. is the first to evaluate
histopathological findings. All surgical samples from these
tendons showed signs of tendinosis. In their surgical series,
they achieved 89% good to excellent results and return to
sport with semimembranosis tenodesis and reattachment to
the biceps tendon without neurolysis (26). Other authors
achieved similar results (77%Y88% RTS) surgically with
either tendon debridement (50) or partial tenodesis (36). But
in contrast to Lempainen, all other authors contended that
complete dissection of the sciatic nerve from adherent tissue
was a critical component.
PREVENTION
While there is limited evidence-based research on the
prevention of hamstring strains, several studies have recently
been published. Included in the literature are eleven
prospective studies that specifically examine an intervention
that influences injury incidence in a human population. No
studies have evaluated preventative measures that decrease
incidence of complete hamstring avulsion.
Four studies evaluated eccentric strength training as a tool
to prevent hamstring injuries (1,3,9,16). Askling et al.
evaluated 30 elite soccer players, where 15 players underwent
a 10-wk preseason hamstring training program using a device
designed for eccentric hamstring overload for 10 wk. The
incidence of injury in the training group was significantly
lower (3/15) compared with the control group (10/15) during
the 10-month study (3). A randomized controlled trial
of community-level Australian Football players (N = 220)
compared Nordic hamstring eccentric training (Fig.) to basic
stretching (control) and showed no statistically significant
difference in injury rates. In this study, five training sessions
were completed in a 12-wk period, and there was a 47%
dropout rate from session 1 to session 2 (16). A study of
British professional rugby players showed that the group
using stretching, concentric strengthening, and Nordic hamstring
exercises decreased hamstring injury incidence to
0.39 per 1000 player hours (95% CI 0.25Y0.54) compared
with strengthening without Nordic hamstring exercises
1.1 (0.74Y1.1) and strengthening plus stretching 0.59
(0.34Y0.84) (9).
Arnason et al. recently published a much larger scale
prevention study that compared Nordic hamstring eccentric
training (Fig.) or a hamstring flexibility program to teams
that opted not to participate (52%). The study included
players from the Norwegian and Icelandic top soccer leagues
Figure. Nordic hamstring lowers. An eccentric strength training exercise where one person stabilizes an athlete_s lower extremities, and starting at 90the
athlete lowers himself or herself during the eccentric stage of muscle contraction. The forward movement should be resisted by flexing the hamstrings
for as long as possible, and subsequently a push-up motion is used to elevate the body with minimal concentric hamstring contraction to the initial
position for another repetition.
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for the 1999Y2002 seasons, representing over 330,000
exposure hours and 183 injuries. The eccentric strengthening
group underwent warm-up stretching and a gradually
increased eccentric hamstring protocol described by Mjølnes
et al., then three times weekly during the preseason and two
times weekly during the competitive season. This intervention
yielded a significantly lower injury rate compared with
those teams that did not do eccentric training (RR = 0.43,
P = 0.01) and compared with baseline data from previous
years (RR = 0.42, P = 0.009). Flexibility training alone did
not reduce injury risk (1).
One prospective study with military basic training compared
three times daily hamstring stretching, and the injury
rate for all lower extremity injuries decreased from 29% in
the control to 17% in the intervention group (19). A larger
(N = 1538) randomized controlled trial from the Australian
military showed that a daily stretching program was no better
than normal military training without stretching (34).
Multiple studies have evaluated the role of hamstring
flexibility in hamstring injury prevention, but the data are
conflicting (1,19,33Y35,44).
One study of Australian Football players evaluated the
impact of sports-specific training, anaerobic interval training,
and stretching fatigued muscle, and found a significant
difference in hamstring injury rates compared with preintervention
rates (44). Two studies implemented an isokinetic
preseason evaluation assessment and isokinetic training
regimen to correct for quadriceps-hamstring (H/Q) imbal-
TABLE. Strength of recommendation taxonomy (SORT).
SORT: Key Recommendations for Practice
A preventative program of Nordic hamstring
exercises can decrease injury risk.
Isokinetic strength training to correct for
hamstring-quadriceps imbalances could reduce
injury rates.
Sports specific anaerobic interval training could
reduce injury rates.
Daily static stretching started 48 h after injury could
increase recovery rate.
Warm-up exercise and clothing may decrease injury
rates.
Cryotherapy appears safe and may have a role in
pain control.
Progressive agility and trunk stabilization exercises
should be considered during rehabilitation and
may make reinjury less likely.
When conservative treatment fails in partial
proximal hamstring avulsions, surgery has given
most patients good to excellent results.
For complete proximal hamstring avulsions, delayed
surgery has resulted in worse postoperative
strength and possible sciatic nerve involvement.
Evidence
Rating References
A 1
B 12,20
B 44
B 28
C 43
C 21
C 41
C 24,47
C 24,38,39,47
A = consistent and good-quality patient-oriented evidence; B =
inconsistent or limited quality patient-oriented evidence; C = based on
consensus, usual practice, opinion, disease-oriented medicine, or case series
for studies of diagnosis, treatment, prevention, or screening.
ances (12,20). Crosier et al. performed a multi-year, multinational
intervention study of professional soccer players that
found that athletes with H/Q ratio imbalances had a much
higher injury risk (RR = 4.66, CI = 2.01Y10.8). Normalizing
the H/Q ratio with an isokinetic strength training program
made the risk no different from those athletes with a normal
H/Q ratio preseason (Absolute Risk Reduction = 1.6%,
Number Needed to Treat = 63) (12).
Warm-up exercise and clothing designed to keep hamstring
muscles warm frequently have been cited as potentially
modifiable factors for injury prevention, but few human intervention
studies exist. One study in club rugby players with
prior hamstring injury examined 1.5-mm neoprene shorts as
a temperature intervention, and found that players who intermittently
wore them were less likely to injure their hamstrings
when wearing neoprene (3 vs 57, out of 1000 playing
hours). Only five players wore the shorts all season (43).
CONCLUSION
The majority of the medical, surgical, and rehabilitative
interventions commonly used to treat hamstring injuries lack
strong evidence. The most compelling evidence for hamstring
tear treatment lies in recent prevention studies.
Arnason_s prospective intervention study exhibited 183
injuries in 330,000 exposure hours; thus the results carry
statistical power. There is significant evidence that an
eccentric hamstring program of Nordic hamstring exercises
can decrease injury risk (1). There is limited evidence that
daily static stretching can increase recovery rate after injury
(28). Two interventions, sports-specific anaerobic interval
training and isokinetic hamstring strength training, have
limited evidence that they could reduce injury rates (12,44).
For other hamstring research, the limitations based on total
hamstring injuries included in a given study, reliance on
retrospective cohort studies, and conclusions based on case
series limit the utility of any information that can be
concluded from the papers and do not provide a level of
evidence greater than expert opinion (Table).
Hamstring injuries are a major problem in sports, and their
occurrence inherently is influenced by multiple factors. If
we are to establish an evidence-based approach to their
prevention and treatment, future studies should be prospective
cohort studies and randomized controlled trials that
include adequate numbers of participants and injuries to
reach statistical significance even after multivariate analysis
is applied to enhance validity.
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