Muscle Injuries

Original Editors - Els Van Haver

Top Contributors - Els Van Haver, Naomi O'Reilly, Wanda van Niekerk, Kim Jackson, Lucinda hampton, Vidya Acharya, Nina Lefeber, Admin, Evan Thomas, Mande Jooste, Jess Bell, Maxime Tuerlinckx, Uchechukwu Chukwuemeka, Claire Knott, 127.0.0.1 and Rachael Lowe

Introduction

Rectus-femoris-injury-distal MTJ-rupture

Muscle injuries is a broad term encompassing many pathologies and these are common injuries in both elite and amateur athletes as well as in the general population.

Skeletal muscle injuries represent a great part of all traumas in sports medicine, with an incidence from 10% to 55% of all sustained injuries. The muscles and muscle groups more frequently involved are the hamstrings, rectus femoris, and the medial head of the gastrocnemius. They should be treated with the necessary precaution since a failed treatment can postpone an athlete’s return to the field with weeks or even months and increase the risk of re-injury.

Image 1: Complete rupture of the rectus femoris distal myotendinous junction with a craniocaudal defect gap of approximately 3cm.

There are a number of types of muscle injury that can occur: laceration, contusion, degenerative diseases (eg Muscular Dystrophies) and strain.

• A laceration occurs when the muscle is cut by an external object, this usually occurs during traumatic accidents such as road traffic or industrial accidents.
• A contusion occurs when there is a compressive force to the muscle and usually occurs in contact sports eg in football when two players collide, knee to thigh in a tackle.
• Strain injuries occur when muscle fibres cannot withstand excessive tensile forces placed on them and are therefore generally associated with eccentric muscle action. Strains most commonly occur in muscles working across two joints e.g. hamstrings, gastrocnemius during periods of rapid acceleration and deceleration, by placing the muscle in a lengthened state over two joints and contracting forcefully

Types of Skeletal Muscle Injuries

Literature does not reveal great consensus when it comes to classifying muscle injuries, despite their clinical importance. However, the most differentiating factor is the trauma mechanism. Muscle injuries can, therefore, be broadly classified as either traumatic (acute) or overuse (chronic) injuries.

Acute injuries are usually the result of a single traumatic event and cause a macro-trauma to the muscle. There is an obvious link between the cause and noticeable symptoms. They mostly occur in contact sports such as rugby, soccer and basketball because of their dynamic and high collision nature.

Overuse, chronic or exercise-induced injuries are subtler and usually occur over a longer period of time. They result from repetitive micro-trauma to the muscle. Diagnosis is more challenging since there is a less obvious link between the cause of the injury and the symptoms. The below video gives a brief talk on these chronic injuries.

Muscle Injury Classification

Traditional Classification Systems

Muscle injuries are a common injury in sports. Historically a three-tier grading system based on clinical signs had been used to guide the prognosis of a muscle strain. Grading systems are useful in that it provides an indication of the severity or extent of the injury. With imaging advancements such as MRI and Ultrasonography, there is now the benefit of combining clinical and radiological findings and this has led to “new” muscle injury grading and classification system

Modern muscle injury classification systems

• Munich Consensus System
  • International clinical and basic science experts developed a comprehensive muscle injury classification and grading system.
  • Key points from Munich Consensus System:
    • Classification differentiates between direct (contusion and laceration) and indirect muscle injury
    • Indirect muscle injuries further classified as functional or structural injuries
    • Further subclassified into the type of injury and subclassified into either a diagnostic group (e.g. fatigue induced muscle disorder; delayed onset muscle soreness (DOMS); or muscle or spine-related neuromuscular disorder) or severity grade (minor partial, moderate, subtotal, complete or avulsion).
    • Muscle injury is approached in a comprehensive way and includes descriptors such as acute, overuse, direct and indirect injury.

Read the full article here: Terminology and classification of muscle injuries in sport: The Munich consensus statement

• British athletics system
  • Pollock et al designed a classification for non-contact muscle injuries
  • The system grades injury from 0 – 4, based on clinical and MRI features
  • The injury is then sub-classified further to reflect the principle anatomic structures involved:
    • a = myofascial; b = within muscle usually at the musculotendinous junction; c = intra-tendinous tears
  • Grade 0 injuries – MRI negative and described as a “focal neuromuscular injury” or a muscle injury consistent with DOMS
  • If there is suspicion of a neural component involved  - N can be applied as additional differentiator
  • Grades 1 -3 refer to small, moderate or extensive tears respectively to the muscle tissue (determined by the extent of oedema and tissue disruption, as well as by tissue involved)
  • Grade 4 refer to complete tears of either muscle or tendon
  • BAMIC (British Athletics Muscle Injury Classification) provides a framework for clinical reasoning and rehabilitation decision-making
  • Read the full article here: British athletics muscle injury classification: a new grading system

• Chan System
  • Chan et al proposed a 3-layered anatomical classification system - this is mainly an imaging-based classification system
  • The injury’s anatomical location is: proximal musculotendinous junction, muscle or distal musculotendinous junction
  • The injury is then sub-classified as proximal, middle or distal
  • Thereafter the injury is defined by the principle tissue involved (e.g. intramuscular, myofascial, perifascial, myotendinous or a combination)
  • Read this article here: Acute muscle strain injuries: a proposed new classification system

• Barcelona System
  • The medical department of FC Barcelona and international colleagues proposed a muscle injury classification and grading system based on 4 tiers/layers
  • MLG-R System
    • M - Mechanism of injury
    • L - Location of injury
    • G - Grading of severity
    • R - Number of muscle re-injuries
  • From clinical history – mechanism of injury (direct (D) or indirect (I))
  • Indirect injuries are further identified as sprinting or stretch related
  • Second and third identifiers are MRI variables – anatomical location and grade of injury
  • Fourth identifier relates to re-injury status
  • Read this study here: Muscle Injuries in Sports: A New Evidence-Informed and Expert Consensus-Based Classification with Clinical Application

• Grading based on connective tissue injury
  • Prakash et al proposed a MRI grading system to be used to assess the extent of injury and the integrity of connective tissue structures involved
    • Grade 0 -oedema or fluid adjacent to intact connective tissue (tendon/aponeurosis/epimysium) without myofibril detachment
    • Grade 1 - myofibril detachment without connective tissue change
    • Grade 2 - myofibril detachment with adjacent connective tissue increased signal, delamination or defect, but no retraction
    • Grade 3 - myofibril detachment with adjacent connective tissue retraction indicating failure

Muscle Injury Types

Muscle Strains

A strain to the muscle or muscle tendon is the equivalent of a sprain to ligaments. It is a contraction-induced injury in which muscle fibres tear due to extensive mechanical stress. This mostly occurs as a result of a powerful eccentric contraction (see EIMD) or over-stretching of the muscle. Muscles will most likely tear during sudden acceleration or deceleration. Therefore, it is typical for non-contact sports with a dynamic character such as sprinting, jumping.

The Munich Consensus statement on Terminology and classification of muscle injuries in sport categorised Strain severity as::

Grade I (Mild)

• Involves only a small number of fibres in the muscle.
• There is no decrease in strength and there is full active and passive range of motion.
• Localised pain
• Pain and tenderness are often delayed to the next day.

Grade II (Moderate)

• Involves a significant number of muscle fibres torn
• Acute and significant pain is accompanied by swelling
• Pain is reproduced on muscle contraction
• Strength is reduced
• Movement is limited by pain

Grade III (Severe)

• A complete tear/rupture of the muscle. This means either the tendon is separated from the muscle belly or the muscle belly is actually torn in 2 parts.
• Severe swelling and pain and a complete loss of function are characteristic for this type of strain. 
• This is seen most frequently at the musculotendinous junction.

A number of factors predispose an athlete to muscle strains:

• Inadequate Warm-up
• Insufficient Joint Range of Motion
• Excessive Muscle Tightness
• Fatigue / Overuse / Inadequate Recovery
• Muscle Imbalance
• Previous Injury
• Faulty Technique / Biomechanics
• Spinal Dysfunction

Common Strain Injuries

• Hamstring Strain
• Quadriceps Muscle Contusion
• Calf Strain
• Groin Strain 
• Rotator Cuff Tears
• Rupture Long Head Biceps
• Achilles Rupture

Muscle Contusion

A muscle contusion is usually the result of a direct blow from an opposition player or contact with equipment in collision sports, such as football, rugby and hockey. The blow causes local muscle damage with associated bleeding. A bruise, or contusion, is a type of haematoma of tissue in which capillaries and sometimes venules are damaged by trauma, allowing blood to seep, haemorrhage, or extravasate into the surrounding interstitial tissues. Bruises, which do not blanch under pressure, can involve capillaries at the level of the skin, subcutaneous tissue, muscle, or bone. As a type of haematoma, a bruise is caused by internal bleeding into the interstitial tissues which do not break through the skin, usually initiated by blunt trauma, which causes damage through physical compression and deceleration forces. Trauma sufficient to cause bruising can occur across a wide range of sports. Bruises often induce pain, but small bruises are not normally dangerous alone. Sometimes bruises can be serious, leading to other more life-threatening forms of haematoma, such as when associated with serious injuries, including fractures and more severe internal bleeding. The likelihood and severity of bruising depend on many factors, including type and healthiness of affected tissues.

Muscle Cramp

Muscle cramps are sudden, involuntary muscle contractions or over-shortening. While cramps are generally temporary and non-damaging, they can cause mild-to-excruciating pain and paralysis-like immobility of the affected muscle. The onset is usually sudden, and it resolves on its own over a period of several seconds, minutes, or hours. Cramps may occur in a skeletal muscle or smooth muscle.

Muscle cramps during exercise are very common, even in elite athletes. Muscles that cramp the most often are the calves, thighs, and arches of the foot. Such cramping is associated with strenuous physical activity and can be intensely painful; however, they can even occur while inactive/relaxed. Around 40% of people who experience skeletal cramps are likely to endure extreme muscle pain and may be unable to use the entire limb that contains the "locked-up" muscle group. It may take up to seven days for the muscle to return to a pain-free state.

According to Brukner & Kahn disturbances at various levels of the central and peripheral nervous system and skeletal muscle are involved in the mechanism of cramp and may explain the diverse range of conditions in which cramp occurs. Other popular theories as to the cause of cramps include dehydration, low potassium or low sodium levels, inadequate carbohydrate intake or excessively tight muscles but these hypotheses appear to be falling out of favour as the weight of evidence supports the ‘neural excitability’ hypothesis.

Muscle Soreness

Muscle soreness after exercise is commonly referred to as delayed onset muscle soreness (DOMS). DOMS is common in individuals who engage in strenuous and unaccustomed exercise and physical activity. It is classified as a grade 1 muscle strain injury and is characterised by localised tenderness and soreness. It typically peaks between 24 to 72 hours after a bout of exercise but eventually disappears after five to seven days. Soreness is accompanied by a prolonged strength loss, a reduced range of motion, and elevated levels of creatine kinase in the blood. These are taken as indirect indicators of muscle damage, and biopsy analysis has documented damage to the contractile elements. The exact cause of the soreness response is not known but thought to involve an inflammatory reaction to the damage.

Pain perceived during exercise is considered to result from a combination of factors including acids, ions, proteins, and hormones. Although it is commonly believed that lactic acid is responsible for this pain, evidence suggests that it is not the only factor.

Repair Process

The healing process in the injured skeletal muscle consists of overlapping phases of degeneration, inflammation, regeneration, and fibrosis. Efficient regeneration of the injured muscle is thought to compete with fibrotic healing, and excessive fibrosis is thought to impede regeneration. This balance depends mainly on the cells and factors that are present at the degeneration and inflammation stages of healing. Regardless of the underlying cause, the processes occurring in injured muscles tend to follow the same pattern. Functional recovery, however, varies from one type of injury to another. Two phases can be distinguished in the repair process.

Destruction Phase 

Starts with the actual trauma that causes muscle fibres to tear. Immediate necrosis of myofibres takes place due to deterioration of the sarcoplasm, a process that is halted within hours after the trauma by lysosomal vesicles forming a temporary membrane. An inflammatory process takes place as a reaction to the torn blood vessels. Specialised cells start removing necrotised parts of the fibres.

Repair and Remodeling Phase

The actual repair of the injured muscle takes place. Myofibres start regenerating out of satellite cells (= undifferentiated reserve cells) and a connective tissue scar is being formed in the gap between the torn muscle fibres. In the first 10 days after the trauma, this scar tissue is the weakest point of the affected muscle.  After 10 days, however, eventual re-rupture will rather affect adjacent muscle tissue than the scar tissue itself, although full recovery (up to the point of pre-injury strength) can take a relatively long time. Vascularisation of the injured area is a prerequisite for recovering from a muscle injury. New capillaries originate from the remaining injured blood vessels and find their way to the centre of the injured area. Early mobilisation plays a very important role since it stimulates the vascularisation process. Similar wise, intramuscular nerves will regenerate to re-establish the nerve-muscle contact.

Regeneration Strategies

After a trauma, skeletal muscles have the capacity to regenerate and repair in a complex and well-coordinated response. This process required the presence of diverse cell populations, up and down-regulation of various gene expressions and participation of multiples growth factors. Regeneration Strategies based on the combination of stem cells (satellite cells), growth factors and biological scaffolds have already shown promising results in animal models. A better understanding of the cellular and molecular pathways as well as a better definition of the interactions (cell-cell and cell-matrix) that are essential for effective muscle regeneration, should contribute to the development of new therapies in humans.

Image 3: Biological scaffold composed of extracellular matrix.

Diagnostic Procedures

Both for acute and chronic injuries, thorough subjective examination is primary in identifying muscle injuries. Particular attention to the history of occurrence of the trauma is needed. A clinical examination and testing of the muscle function together with the patient's recollection of what happened, are mostly sufficient for making the right diagnosis. In some cases, additional tests (MRI, X-ray, Ultrasound, CT Scan) may be required to determine the extent of the injury or to identify possible additional injuries.

The video below gives a good insight into diagnostic procedures for muscle injuries

Physiotherapy Treatment

Acute Skeletal Muscle Injuries

The past few years the POLICE principle (an updated version of RICE-principle) has generally been considered as being the best method to minimise swelling and relief pain within the first 24 to 48 hours. Although the different components of the RICE-principle have each shown their effectiveness in experimental studies, the use of the all-round concept is yet to be proved in randomised clinical trials. These methods focus on the acute management and do not really provide any information on the sub-acute and chronic stages of soft tissue healing. More recently Dubois and Esculier (2019) proposed two new acronyms to optimise soft tissue recovery: PEACE and LOVE. These two acronyms (PEACE and LOVE) include the full range of soft tissue injury management from immediate care to subsequent management. It also highlights the importance of patient education and addressing the psychosocial factors involved that will aid recovery. It also highlights the potentially harmful effects of using anti-inflammatory medication for recovery. Read more about the Peace and Love principle in the management of soft tissue injuries here.

Evidence for early mobilisation

After first aid, therapy must be tailor-made according to the severity and extent of the injury. A short period of immobilisation after the trauma prevents excessive formation of scar tissue (which will have a deleterious effect on mobility and strength of the healed muscle) and prevents re-rupture by allowing the scar tissue to gain sufficient strength to bear contraction forces. Immobilisation should not be continued after the acute phase (first few days) to avoid the negative effects such as muscle atrophy, retarded strength recovery and excessive formation of connective tissue within the muscle.

Early mobilisation already starts after a few days, if the acute phase has passed without further complications and recovery seems to be progressing. In comparison to immobilisation, mobilisation induces significant histological changes such as increased vascularisation of the injured area, better regeneration of muscle fibres and more parallel orientation. It has the additional advantage that the muscle will sooner gain its original strength.

The active treatment needs to be built up gradually from isometric exercises to isotonic exercises. Only if those exercises can be performed without pain, isokinetic training should be started.

As muscle injuries generally recover well with conservative treating, surgical intervention is only to be considered in cases with very specific indications:

• Large intramuscular haematoma
• Complete muscle tear (a strain of third degree)
• Partial strain (2^nd degree) if more than half of the muscle belly is affected
• Scar adhesions that cause persistent pain and limited extension (>4-6 months)

Chronic Skeletal Muscle Injuries

Overuse sports injuries outnumber acute, instantaneous injuries in almost every athletic activity. Because they do not instantly, disable the person, they attract less medical attention than acute injuries. Their frequency of occurrence is almost always underestimated in surveys of athletic injuries. The treatment of overuse sports injuries is made difficult by various factors e.g. an insidious onset. When athletes actually present for treatment, the injuries are well established and more difficult to manage successfully. Injury occurs when cumulative forces exceed the tissue’s ability to withstand such forces— either due to isolated macro traumatic events or repetitive micro-traumatic events. Often, specific biomechanical or physiological factors predispose an athlete to injury. A physiotherapist should properly identify and assist the athlete in correcting these conditions to treat, prevent, and possibly reverse the detrimental effects. As always, prevention is always the best treatment but, failing that, the next best thing is proper and successful rehabilitation.

Clinical Bottom Line

Treatment of muscle injuries usually has good outcomes. Physiotherapists must ensure the muscle is rehabilitated in all functional aspects before resuming usual activities or high demand sporting activities. The management of soft tissue injuries, whether it is a hamstring strain or an ankle sprain, should not just focus on short-term damage control. Clinicians should also focus on long-term outcomes and focus on treating the person with the injury and not just treating the injury of the person.