Acute injuries of the hamstring muscle complex (HMC) are frequently observed in various
sports disciplines both in elite and recreational sport, and are the most common injury in
soccer. Despite intensive research into prevention and management of acute HMC injury during
the last decade epidemiological data show no decline in injury and re-injury rates. In this
regard a recent study prospectively observed 374 Danish elite soccer players during a
12-month period and registered 46 first-time and eight recurrent HMC injuries (incidence
rates: 12.3% [first-time injuries] and 2% [recurrent injuries]). Statistically significantly
more players experienced a first-time acute HMC injury during a match than during training.
Moreover, among 32 players who suffered from acute HMC injury in a period of 12 months before
the study, eight players incurred an injury that fulfilled the criteria for a recurrent
injury (incidence: 25%). Approximately two thirds of the first-time injuries were categorized
as moderate, with time to return to play between 8 to 28 days.
Anatomical and functional aspects of the HMC predispose it to injury, including the fact that
the muscles cross two joints and undergo eccentric contraction during the gait and running
cycle.
Acute HMC injury typically occurs through an eccentric mechanism at the terminal stages of
the swing phase of running. The long head of the biceps femoris (LHBF) muscle is most
commonly affected, and within the LHBF muscle, the proximal myotendinous junction and
proximal locations are most commonly affected.
The diagnosis of acute HMC injury is based on the presence of acute-onset pain in the
posterior thigh, and presence of the triad of pain on contraction, stretching and palpation.
Imaging has a role in confirming the site of injury and characterizing its extent, providing
some prognostic information and helping plan treatment. In this regard both magnetic
resonance imaging (MRI) and ultrasonography (US) have been shown to be effective for
identification of hamstring strains and tendinopathy. Both MRI and US provide detailed
information about the HMC with respect to localization and characterization of injury.
Several clinical, MRI and US determinants were established that are associated with a longer
recovery time in nonoperative management of acute HMC injury. However, it is important to
realize that for an individual HMC injury none of these MRI and US determinants show a direct
correlation with the time to return to play. Accordingly, the prognosis of HMC injuries
should not be guided by imaging findings alone.
Precise classification of acute HMC injury has important implications for treatment and
prognosis (i.e., time to return to play), as outlined in detail below. There are anatomical
differences between a Type 3a injury (minor partial muscle tear ≤ 5 mm;
intrafascicle/bundle-tear) and a Type 3b injury (moderate partial muscle tear > 5 mm;
interfascicle/bundle-tear).
Acute HMC injuries Type 4 (i.e., subtotal or complete muscle tear or tendinous avulsion)
require early surgical repair. However, acute HMC injuries Type IV are rare.
The treatment of choice of acute HMC injuries Type 3a and 3b is a progressive
physiotherapeutic exercise programme. Besides this, there is currently only insufficient
scientific evidence to support other treatment methods, including local infiltrations. In
particular, injections of platelet-rich-plasma (PRP) showed no effect when compared to
control.
It is of note that another study that was published very recently in the The New England
Journal of Medicine demonstrated the negative clinical consequences of protracted
immobilization after an acute muscle injury Type 3b in recreational sports. Starting
rehabilitation two days after injury rather than waiting for nine days shortened the interval
from injury to pain-free recovery and the time to return to play by approximately three weeks
without any significant increase in the risk of reinjury. The authors of this study concluded
that the observed difference supports the importance of early loading of injured
musculotendinous tissue.
Acute muscle injuries Type 3a and 3b have different time frames for recovery and return to
play, with optimal treatment between 10 and 14 days in case of Type 3a and on average
approximately six weeks in case of Type 3b. However, particularly in case of acute HMC injury
Type 3b there is considerable interindividual variability in the time frame for return to
play.
Most importantly, particularly the high reinjury rate of acute HMC injury suggests that
commonly utilized rehabilitation programs may be inadequate at resolving possible muscular
weakness, reduced tissue extensibility, and/or altered movement patterns associated with the
injury. Accordingly, there is need for developing innovative treatment options particularly
for acute HMC injury Type 3b.
Very recently it was demonstrated that extracorporeal shock wave therapy (ESWT) may
accelerate regeneration after acute skeletal muscle injury. The use of extracorporeal shock
waves in medicine was first reported over 30 years ago as a treatment for kidney stones, and
is commonly referred to as 'extracorporeal shock wave lithotripsy', or 'ESWL'. Extracorporeal
shock waves are also used as a treatment for musculoskeletal conditions such as plantar heel
pain and boney non-union, and is commonly referred to as 'extracorporeal shock wave therapy'
(ESWT) to differentiate from ESWL.
There are three different types of extracorporeal shock waves that could be used in ESWT for
acute HMC injury Type 3b, focused, defocused and radial, and several modes of operation of
focused, defocused and radial extracorporeal shock wave generators.
To our knowledge randomized controlled trials (RCTs) testing efficacy and safety of rESWT for
acute HMC injury Type 3b have not yet been published. In contrast, rESWT has become an
established treatment modality for various musculoskeletal conditions such as calcifying
tendonitis of the shoulder, tennis elbow and plantar fasciopathy, to mention only a few.
Among the 44 RCTs on rESWT currently listed in the PEDro database (status of September 09,
2017), 29 (66%) were performed with the rESWT device Swiss DolorClast (Electro Medical
Systems, Nyon, Switzerland).
The investigators of the present study have extensive practical experience with rESWT for
various musculoskeletal conditions using the Swiss DolorClast. Most importantly, all of us
have already gained practical experience with rESWT for acute HMC injury Type 3b in athletes.
One of our most prominent patients was a professional soccer player at a European top club
(regularly playing in the UEFA Champions League) who incurred a HMC injury Type 3b and
returned to play (full 90-min match with his national team) 35 days later. In the
aforementioned studies published in the New England Journal of Medicine the cumulative
probability of resumptions of sports activity on day 35 after acute HMC injury Type 3b in
professional soccer players or recreational athletes was only respectively 20% or 5% after
treatment with a rehabilitation program.
Considering the limited evidence of efficacy and safety of rESWT for acute HMC injury Type
3b, further research is needed to support the use of rESWT for this condition. Taking into
account the proven efficacy and safety of rESWT using the Swiss DolorClast for treating
musculoskeletal conditions, the widespread use of the Swiss DolorClast based on its proven
efficacy and safety, and our own very promising pilot data of rESWT using the Swiss
DolorClast for treating acute HMC injury Type 3b in athletes it is reasonable to hypothesize
that (i) the combination of rESWT and a specific rehabilitation program is effective and safe
in treatment of acute HMC injury Type 3b, (ii) this combination therapy is statistically
significantly more effective than the same specific rehabilitation program alone, and (iii)
this combination therapy will gain widespread acceptance as soon as effectiveness and safety
will be demonstrated in a randomized controlled trial. This is the main purpose of the
proposed study.