Injury Type and Classification in Sport

Original Editor - Wanda van Niekerk based on the course by Ian Gatt

Top Contributors - Wanda van Niekerk, Kim Jackson, Lucinda hampton, Nupur Smit Shah, Ewa Jaraczewska and Jess Bell  

Introduction

Being physically active and / or taking part in sports have many health benefits, but there is also the risk of injury. Sports injuries can occur anytime during training sessions or during competition. Various musculoskeletal connective tissues can be affected by injury. In sports epidemiology, injury surveillance is important as it is key to understanding injuries and it contributes to the development of injury prevention programmes.

Definitions

The International Olympic Committee Injury and Illness Epidemiology Consensus group define injury as:

“Injury is tissue damage or other derangement of normal physical function due to participation in sports, resulting from rapid or repetitive transfer of kinetic energy.”

Classification of an injury refers to "the process of describing or categorising an injury (i.e. by its location, mechanism or underlying pathology)"

The grade of an injury refers to the severity of the injury.

Classification of Injuries

Relationship of Injury to Sports Activity

Injuries may result:

• Directly from participation in sport (can be during competition or training)
  • Examples of this include: collision between players or overuse from repetitive training

• Indirectly from participation in activities related to competition or training
  • Example: athlete slipping and sustaining an injury when in the Olympic village

• Activities not related to participation in sports
  • Example: an athlete is involved in a car crash

Mode of Onset

Traditionally injuries are classified as injuries with a sudden onset (acute injury) or injuries with a gradual onset (overuse), but one also needs to consider an acute injury due to overuse.

• Acute episode = sudden injury because of an exchange of large quantities of kinetic energy (collision between athletes)
  • Mechanism is acute, and the presentation is sudden onset

• Overuse episode = gradual accumulation of low energy transfer over time (development of tendinopathy induced by repetitive movement or stress fracture)
  • Mechanism is repetitive, and the presentation is a gradual onset

• Acute episode due to overuse = combination of both mechanisms ( for example an athlete with a repetitive training regime resulting in tendinopathy or tendon weakness, but sustains an acute tendon tear during a jump)
  • Mechanism is repetitive, and the presentation is a sudden onset

Often a thorough subjective assessment and history taking will provide insight into the mode of onset. Radiological investigations may also be helpful in determining if an injury was an acute episode or whether it was an acute episode due to overuse.

Table 1. Examples: Assessment of Mode of Onset

Mechanism	Presentation	Example
Acute	Sudden onset	Sprinter pulls up suddenly in a race, stops and hobbles a few steps, in pain with a hamstring injury. Footballer falls on an outstretched hand, putting all the weight through the palm of the hand and hyperextending the wrist resulting in a scaphoid fracture
Repetitive	Gradual onset	Swimmer experiences a gradual increase in shoulder pain during the season, MRI indicates rotator cuff tendinopathy Dancer experiences progressive pain with and after activity and tenderness over the second metatarsal. Imaging indicates stress fracture of the second metatarsal
Repetitive	Sudden onset	Gymnast experiences a tibial fracture on landing from a vault; CT imaging reveals pre-existing morphological changes consistent with a bone stress injury

Mechanism of Injury

This can be as a result of direct contact or non-contact mechanisms.

Table 2. Examples: Classification as a Mechanism for Injuries

Injury	Type of Contact	Example
Non-contact	No evidence of disruption of a player's movement patterns	Basketball player landing and twisting ankle with no contact with other players
Contact Indirect	Through another athlete	ACL tear in a football player landing off-balance after being pushed on his shoulder by an opponent while in the air
Contact Indirect	Through an object	Downhill skier suffers concussion from a crash after hitting the gate with his knee
Contact Direct	With another athlete	Rugby player sustains an ACL tear as a result of a direct tackle to the knee
Contact Direct	With an object	Volleyball player being hit in the face by a spiked ball, resulting in a assessment and management of concussion

Body Region Categories

Injuries can be further classified into the specific body region and more specifically the area involved.

Table 3. Categories of Body Regions and Areas for Injuries

Region	Body Area	Region	Body Area
Head and neck	Head Neck
Upper limb	Shoulder Upper arm Elbow Forearm Wrist Hand	Lower Limb	Hip/groin Thigh Knee Lower leg Ankle Foot
Trunk	Chest Thoracic spine Lumbosacral Abdomen	Unspecified	Region unspecified
Lower limb	Hip/groin Thigh Knee Lower leg Ankle Foot	Multiple regions	Single injury crossing ≥ 2 areas

Tissue and Pathology Type Categories

Further classification can be to the specific tissue type and pathology involved. Table 4 indicates the main tissue and pathology types. You can also have a look at Table 5 in this article for more detail and notes on these categories: International Olympic Committee Consensus Statement: Methods for Recording and Reporting of Epidemiological Data on Injury and Illness in Sports 2020 (Including the STROBE Extension for Sports Injury and Illness Surveillance (STROBE-SIIS)). For example, Tendinopathy includes the paratenon, partial tear and tendon subluxation and bone stress injury will include bone marrow oedema, stress fracture and periostitis.

Table 4. Categories of Tissue and Pathology Types for Injuries

Tissue	Pathology Type	Tissue	Pathology Type
Muscle/tendon	Muscle injury Muscle contusion Muscle compartment syndrome Tendinopathy Tendon rupture	Ligament/Joint capsule	Joint sprain (ligament tear or acute instability episode) Chronic instability
Nervous	Brain/spinal cord injury Peripheral nerve injury	Superficial tissue/Skin	Contusion (superficial) Laceration Abrasion
Bone	Fracture Bone stress injury Bone contusion Avascular necrosis Physis injury	Vessels	Vascular trauma
Cartilage/Synovium/Bursa	Cartilage injury Arthritis Synovitis/capsulitis Bursitis	Stump	Stump injury
Internal organs	Organ trauma	Non-specific	Injury without tissue type specified

See also: Sport Injury Classification for more detail on classifying ligament, tendon and bone and articular cartilage injuries.

Muscle 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 systems over the last couple of years.

The table below is from the Munich Consensus statement on Terminology and classification of muscle injuries in sport and provide an overview of previous muscle injury classification systems.

Table 5. Overview of previous muscle injury classification system (from Terminology and classification of muscle injuries in sport: The Munich consensus statement)

	O'Donoghue 1962	Ryan 1969 (initially for quadriceps)	Takebayashi 1995, Peetrons 2002 (Ultrasound-based)	Stoller 2007 (MRI-based)
Grade I	No appreciable tissue tearing, No loss of function or strength, Low-grade inflammatory response	Tear of few muscle fibres, Facia in tact	No abnormalites or diffuse bleeding with/without focal fibre rupture, less than 5% of the muscle involved	MRI-negative = 0% structural damage, Hyperintense oedema with or without haemorrhage
Grade II	Tissue damage, Musculotendinous unit strength reduced, Some residual function	Moderate amount of fibres torn, Facia in tact	Partial rupture: focal fibre rupture more than 5% of the muscle involved with/without fascial injury	MRI-positive with tearing up to 50% of the muscle fibres. Possible hyperintense focal defect and partial retraction of muscle fibres
Grade III	Complete tear of musculotendinous junction, Complete loss of function	Many fibres torn with partial tearing of fascia	Complete muscle rupture with retraction, fascial injury	Muscle rupture = 100% structural damage. Complete tearing with or without muscle retraction
Grade IV	none	Complete tear of the muscle and fascia of the muscle-tendon unit	none	none

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: diagnostic group (e.g. fatigue induced muscle disorder, delayed onset muscle soreness (DOMS)); muscle or spine-related neuromuscular disorder; 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

Grading

• 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

Cohen system

• Developed a hamstring injury classification system
• Specifically for professional American football players
• Novel scoring system based on age and a range of MRI variables
• Read more about this here: Hamstring injuries in professional football players: magnetic resonance imaging correlation with return to play

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

Table 6 provides an overview of some of the newer muscle injury classification systems.

Table 6. Comparison of recent muscle injury classification systems

Chan et al., 2012	Mueller-Wolfahrt et al., 2013	Pollock et al., 2014	Valle et al., 2017	Prakash et al., 2018
Grading based in radiological finding and site of lesion I = Proximal musculotendinous junction II = Muscle A = Proximal B = Middle C = Distal a = Intramuscular b = Myofascial c = Myofascial/perifascial d = Myotendinous e = Combined III = Distal musculotendinous junction	A. Indirect muscle disorder/injury Functional muscle disorder Type 1: Overexertion-related muscle disorder 1A Fatigue induced muscle disorder 1B Delayed onset muscle soreness (DOMS) Type 2: Neuromuscular muscle disorder 2A Spine-related neuromuscular 2B Muscle-related neuromuscular Structural muscle injury Type 3: Partial muscle tear 3A Minor partial muscle tear 3B Moderate partial muscle tear Type 4: (Sub)total tear Subtotal or complete muscle tear Tendinous avulsion B. Direct muscle injury Contusion Laceration	Grade 0: Referred pain 0a - focal muscle soreness with normal MRI 0b - generalised muscle soreness (DOMS) with normal MRI Grade 1 - small injuries to the muscle a = myofascial injury b = muscle or musculotendinous junction c = tendon involvement Grade 2 - Moderate injuries (tears) a = myofascial injury b = muscle or musculotendinous junction c = tendon involvement Grade 3 = Extensive tears a = myofascial injury b = muscle or musculotendinous junction c = tendon involvement Grade 4 = Complete tears a = myofascial injury b = muscle or musculotendinous junction c = tendon involvement	Mechanism of injury (M) D = Direct I = Indirect Location of Injury (L) P - injury located in proximal third of muscle belly M - injury located in the middle third of muscle belly D - injury located in the distal third of the muscle belly Grading of severity (G) 0 -3 based on MRI No of muscle re-injuries (R) 0 - 1st episode 1 - 1st re-injury 2 - 2nd re-injury...	MRI-based grading Grade 0 - oedema or fluid adjacent to intact connective tissue, no 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

Recent reviews investigating muscle injury classification systems

• Time for a paradigm shift in the classification of muscle injuries
• Classification and grading of muscle injuries: a narrative review
• An update on the grading of muscle injuries: a narrative review from clinical to comprehensive systems
• Quality assessment of muscle injury classification in sports: a systematic literature review
• Workshop on Muscle Injuries by Bruce Hamilton - New Zealand:

Structure vs Function

• Structure = Form

• Function = is the product of a structure which plays any specific role

"There is a close relationship between structure and function, however, if we consider that humans are complex, we can appreciate why function is not always directly linked to structure." For example athletes participating at a high level, but if they would undergo imaging there may be indications of existing pathologies. The imaging may show that the form (structure) is compromised, but function is not. Some examples of this are:

• MRI findings were similar in symptomatic and asymptomatic shoulders of young elite swimmers. Asymptomatic shoulders may have many and various abnormalities on MRI, that may be radiologically significant but are not clinically significant.
• Rajeswaran et al. (2014) found a significant amount of underlying pathology in the lumbar spines of asymptomatic elite junior tennis players that were not clinically detectable.
• A high prevalence of asymptomatic osteochondral lesions with subchondral bone marrow oedema in the foot and ankle of elite professional soccer players have been reported.

Considering that form may be affected but not function, this highlights again the biopsychosocial element and an holistic approach towards an athlete. Also, it highlights the consideration of objective and quantifiable information when managing injuries and understanding function. An example of taking this approach is:

Athlete using a handheld dynamometer

The Takei Handheld Dynamometer: An Effective Clinical Outcome Measure Tool for Hand and Wrist Function in Boxing

• longitudinal retrospective injury surveillance of the Great Britain boxing squad from 2010 till 2014
• Findings:
  • a difference of less than 15% between left and right hand/wrist power grip measures is considered normal
  • a difference of 20% between left and right hand/wrist power grip measures is considered indicative of pathology
  • a difference of more than 20% between left and right hand/wrist power grip measures is considered highly indicative of pathology
• In a cohort of elite amateur boxers, the Takei Handheld Dynamometer was shown to be reliable and valid in detecting significant hand and wrist injuries and can be used as an objective marker to assess injury, progression of rehabilitation and training availability.

General Guidelines

• Appreciate the diverse type of injuries and classifications and consider the clinical application of this.
• Consider the difference between sudden (acute) vs gradual (repetitive) vs sudden (repetitive) onset.
• Think about structure vs function and use objectivity to assist in injury management, training availability and rehabilitation.