Science has been described as the ‘systematic classification of experience’. With that in mind,
David Joyce presents up-to-date knowledge surrounding muscle injuries and their classification. As he explains, by being armed with this information, clinicians can be better equipped to move more rapidly along the road of evidence-based prevention and rehabilitation programming
Performance support teams working with athletes the world over often agonise over injury lists. Of course, people go into sport knowing that the risk of injury is an everpresent, but particularly galling are the so-called ‘preventable’ injuries. In most cases, the injury that springs most readily to mind as ‘preventable’ is that of the soft tissue (musculotendinous unit) variety. Whether fair or not, it’s a fact that the efficacy of many sports medicine departments around the world is measured by the incidence of muscle strains in their athletes. What is undeniable however is the fact that we need to understand our ‘foe’, if we are to reduce the risks of it defeating us.
The extent of the problem
In most team-based running sports, muscle injuries consistently rank among the chief causes for playing and training time missed, accounting for anywhere between a fifth and a half of all time loss injuries in the various football sports around the world. Broadly speaking, a football manager can expect a player to sustain a muscle injury every two years, with around a fortnight missed for every injury
Ekstrand, J., Hagglund, M., and Walden, M. (2011) Injury incidence and injury patters in professional football: The UEFA injury study.BJSM, 45, 553-558..
Of course, not every player on the squad will sustain a muscle injury, so, let’s just ask for a license to extrapolate here. What we can say is that approximately half a squad will sustain a muscle injury in a season. A football squad usually comprises somewhere between 24-30 players, meaning that 12-15 players will sustain a muscle injury, with an average time out of two weeks. A simple calculation shows that this totals 24-30 weeks out which, given the tight fixture scheduling, may mean 30-45 games missed, And when you consider that most successful teams in world sport need to have consistent team selections that are not hampered by injury, muscle injuries are clearly a problem worth understanding!
In sports such as Australian Rules football, the formalised central epidemiology reporting system does not reflect pre-season injuries (an injury is only counted if it results in a missed match). This means muscle injuries are going to be underreported. Any reporting study, therefore needs to clearly define what constitutes an injury.
According to the UEFA Champions League study by Hagglund and his co-workers, an injury is said to have occurred when an incident takes place during a scheduled training session or a match that results in an absence from the next scheduled training session or match
Hagglund, M et al. (2005). Methods for epidemiological study of injuries to professional football players: developing the UEFA model. BJSM, 39, 340-346.. Whilst this may give us an indication of injury prevalence (how often something happens), we are really interested in injury severity (how long someone is out for). This is easily calculable by determining the number of days missed. The same UEFA study defined the following:
- Minimal injury (1-3 days missed)
- Mild injury (4-7 days missed)
- Moderate injury (8-28 days missed)
- Severe injury (>28 days missed).
Box 1: When do muscle injuries occur? |
Injuries to the musculotendinous unit without direct trauma usually occur during high speed, forceful contractions, often when an individual is fatigued. Whether this is more likely to occur during training or in competition depends on a couple of factors. In basketball, there is about a 3:1 match—to-training session ratio, whereas it is the reverse in rugby union. Therefore, the exposures to activities that are implicated in injuries are less during basketball training than they are in a match. The intensity of the competition is usually higher in a match as well, thus accounting for the fact that muscle injuries are six times more likely to occur in a soccer match than they are in training(1). The fatigue issue is one that sports scientists have feverishly endeavour to uncover. Quadriceps and hamstring injuries are most common in the final stages of both the first and second halves of a football match, and we see a spike in calf injury incidence in the final 15 minutes of the second half. |
Box 2: Traditional muscle injury classification | | |
Direct or indirect trauma | Extent of the damage | Functional grading system |
Direct trauma in sport is usually the result of a blunt blow, most commonly from another opponent. The most common example of this is a contusion to the thigh, often referred to as a ‘corked thigh’, or a ‘charlie horse’. Another example is when the sharp edge of a ski cuts across another person resulting in a laceration of the muscle. The risks for both of these mechanisms are often thought to be largely unmodifiable, and so therefore most attention in sport is directed to the indirect trauma mechanism. | Most members of the sporting public understand the grading system cited in sports medicine textbooks the world over. This is based upon a combination of clinical and radiological findings where the grades are: 1. Some stretching but no tearing of muscle fibres 2. Partial tear of the muscle3. Complete rupture of the muscle | This method of classifying injuries does not depend on radiological findings, but rather is a way of communicating the current function of a muscle. For example, imagine a hockey player sustains a calf injury. Initially she is unable to walk without a limp and so is functionally a grade III. After a time, she is able to walk but not run and so is functionally a grade II. With good rehabilitation, she is able to run but still is restricted in full sprinting and so is now thought to have a grade-I calf strain. |
Indirect trauma refers to forces generated within the body that are imparted on the internal muscle architecture. Again, this can be divided into one of two groups — contractionbase and stretch-based. Contractionbased indirect traumas are by far the most common examples of ‘gardenvariety’ muscle strains. They result in pain and dysfunction early and then follow a predictable recovery path. Stretch-based muscle strains are less common, often present well immediately but take a much longer time to fully recover. The most commonly thought of example of this is a water skier who tips their ski, forcing the leg overhead at speed, stretching the hamstrings beyond their tolerance level. | This method has held us in good stead for many decades, but our imaging has advanced to the point where this system is a bit too simplistic, and does not fully or accurately describe the injury, its severity and subsequent prognosis. | The problem with this system is that it provides little in the way of prognostic value, particularly in the acute stages of an injury. |
The MLG-R classification system
Last year, a group of researchers and practitioners from FC Barcelona and Aspetar published the third iteration of their Muscle Injuries Clinical Guide
Pruna et al. (2015). Muscle Injuries Clinical Guide 3.0.. This classification system seeks to provide a lot more information regarding the injury severity, and therefore help guide the appropriate management. Let me take you through this clumsy sounding acronym:
- M = Mechanism. This refers to whether it is a direct (D) or indirect (I) mechanism, as we have discussed previously.
- L = Location. This refers to where the injury is localised. For direct injuries (D), it could be located in the proximal third (Dp), middle third (Dm), or distal third (Dd). Indirect injuries (I) are categorized according to the type of connective tissue that is implicated, whether that is tendon (IT) (more severe) or the more common musculotendinous junction (IJ). These are then subdivided according to whether they are proximal (ITp/IJp) or distal (ITd/ IJd). The final indirect location (IF) refers to those indirect mechanisms that are thought to have injured the myofascia. In my experience, these recover at up to twice the rate of injuries involving the contractile mechanisms.
- G = Grade. This requires MRI verification and refers to the extent of the damage expressed as a percentage of the cross sectional area (CSA) of the affected muscle (see Box 3).
- R = Re-injury. This is the final brick in the nomenclature wall that denotes how often this injury has occurred. So, if this was the first time occurrence, it would be classified as a R0, whereas if it was the 4th time the same injury had occurred to the same muscle, it would be written as R4.
Box 3: Grading according to damage expressed as % of cross-sectional area (CSA) |
0 = athlete presents with all the clinical symptoms of a muscle injury but it is undetectable on MRI. This is often referred to as a functional muscle injury, as opposed to a structural muscle injury. |
1 = 1-10% of CSA |
2 = 11-25% of CSA |
3 = 26-50% of CSA |
4 = 50+% of CSA |
MLG-R examples
Let’s look at some real examples to bring this seemingly complicated system to life:
Example 1
Last weekend, the captain of our football club was running for the ball and felt a sudden grab in the back of his thigh. Despite having endured many injuries over the years, he’d never experienced anything like this before. He had to come off to be assessed and it was determined that he could not come back on to play any further part of the match. The following day, we sent him for an MRI and it revealed a tear of his biceps femoris tendon, 13 cm below the ischial tuberosity with almost a third of the CSA of the muscle torn as well. Accordingly, his injury would be classified as: Left Biceps Femoris ITp3R0.
Example 2
Three weeks ago, one of our forwards was waiting to receive the ball from a teammate. The kick was a bit too high and allowed an opponent to smash into the back of him to spoil his attempt. Despite our best efforts, he was unable to continue playing due to the extreme pain coming from his hamstrings whenever he tried to run. Whilst we do not scan every single injury at our organisation, we decided to in this case because he began to complain of some tingling down in his calf and we were concerned about bleeding and swelling compressing his sciatic nerve. The results of the scan showed that he had extensive bleeding coming from his left biceps femoris and the affected tissue accounted for about 20% of the muscle’s CSA. He felt particularly aggrieved because he had just returned from a similar injury two weeks before. Accordingly, we notated this injury as a Left Biceps Femoris Dm2R1.
Example 3
Last year, when I was working in rugby union, one of our second row players complained of an odd chest pain. He thought it may have occurred following a collapse of a scrum. He was point tender near his sternum, had difficulty with horizontal arm flexion. I suspected that he had sustained a pectoralis major injury. Subsequent imaging revealed almost a complete separation of the lower half of the sternal head of his pectoralis major, an extremely uncommon injury. Under this classification system, his injury would be written down as a Right Pectoralis Major (sternal head) IJd4R0.
Conclusion and practical value of precise classification
As more specialists become involved with the care of these athletes, ranging from sports doctors, to radiologists, to physiotherapists, to strength coaches, it is really important to ensure that we are all on the same page when communicating about the mechanism, location and extent of a soft tissue injury.
Whilst this classification system proposed by the folk from FC Barcelona and Aspertar may seem convoluted, it is actually a very efficient method of concisely and accurately communicating the injury, ensuring consistency in terminology. Sub-categorising in this manner provides us with the first step in ensuring consistency in data collection/ epidemiology, and in communication. This in turn can help clinicians by more accurately guiding the top-quality class management that all athletes deserve.