Risk Factors and Injury Mechanisms in Sports Injuries

This article is currently under review and may not be up to date. Please come back soon to see the finished work! (6/04/2022)

Original Editor - Wanda van Niekerk

Top Contributors - Wanda van Niekerk, Jess Bell, Kim Jackson and Lucinda hampton  

Introduction

Musculoskeletal injuries are common among athletes of all levels. The nature of these injuries vary among different sports, but the majority of these injuries are often as a result of a combination of factors and it is sometimes difficult to establish the specific mechanism that leads to injury. Epidemiological studies in sports show that the rate of injury in athletes varies from 10%-65% and for this reason, one of the main goals of sports physiotherapists and other professionals in sports is to prevent injury.A key step in evidence-based injury prevention is to identify possible risk factors for injury. Intrinsic risk factors such as strength, balance, joint mobility, biomechanics are often of interest as these are modifiable, whereas extrinsic risk factors such as age and previous injury are non-modifiable. Understanding modifiable risk factors is necessary for the design of effective targeted risk mitigation strategies.This may lead to the development of accurate and reliable tests to investigate risk factors, which is a necessary tool for athlete screening, monitoring of athletes over time and determine the efficacy of injury prevention programmes.

Risk Factors

Bahr and Krosshaug (2005) described risk factors for injury and mechanisms of injury. Internal risk factors that may predispose an athlete can include:

• Age
• Biological sex
• Body composition
• Health
• Physical fitness
• Anatomy
• Skill level
• Psychological factors

With the exposure to external risk factors, the athlete then becomes susceptible to injury. External risk factors include:

• Sports factors
• Protective equipment
• Environment

With the occurrence of an inciting event, the athlete is injured. Examples of inciting events are:

• Playing situation
• Player/opponent behaviour
• Gross biomechanical description (whole body)
• Detailed biomechanical description (joint)

Comprehensive model for injury causation designed by Bahr and Krosshaug

Meeuwisse et al., (2007) focused on the intrinsic and extrinsic risk factors for injury and developed a dynamic, recursive model of aetiology in sports injury. This injury prevention model highlights the fact that “adaptations occur within the context of sport (both in the presence and absence of injury) that alter risk and affect aetiology in a dynamic, recursive fashion.” It is suggested that one should look further than the initial risk factors preceding an injury and consider how these risk factors may have changed during various cycles of training or participation.

Dynamic model of aetiology in sport injury

It is evident that there are multiple factors involved in the risk of injury occurrence and the interaction between these factors may increase the risk. Herrington et al. provides a detailed list of these factors:

• Training-related factors
  • Training volume, load, intensity
  • Type of training
  • Training and competition schedule
  • Rest
• Motor control factors
  • Posture
  • Movement patterns
  • Muscle tone
  • Technique
  • Sport specific movements
• Psychological factors
  • Beliefs
  • Fears
  • Coping strategies
  • Self-efficacy
  • Catastrophising
  • Emotional status (stress, depression, anxiety)
• Health-related factors
  • Diet
  • Medication
  • General health
  • Fatigue
  • Sleep patterns
• Non-modifiable factors
  • Gender
  • Age
  • Maturation stage
  • Body type
  • Genetics
  • Previous injuries
• Environmental factors
  • Training/competition surface
  • Equipment
  • Clothing
  • Weather
  • Coaching
• Conditioning factors
  • Strength
  • Endurance
  • Muscle length
  • Joint range of motion
  • Chronic capacity
• Additional demands
  • Home
  • Work
  • Family
  • Social
  • Leadership
  • Media
  • Sponsors
• Other factors
  • Sport specific skill level
  • Ranking and status
  • Goals of athlete

Bolling et al. (2019) illustrates the complexity and multiple levels of these factors involved in injury occurrence.

A multilevel system map with factors, strategies and stakeholders in relation to injury and their prevention. Starting at the centre of the map (ie, the athlete) and moving distally; (A) entails artists-related intrinsic injury factors; (B) presents external injury factors; (C) describes the main preventive strategies (eg, load management, safety and preparation) which are driven by the factors from the inner two circles; (D) represents the stakeholders in the system as well as how they connect to the strategies and factors across the multiple levels.

Injury Mechanisms

Injury mechanism can also be referred to as the “inciting event.” From a biomechanical perspective, considering tissue properties and load characteristics, an injury will be the result of the transfer of energy to tissue and the mechanical load will be in excess of the tissue's load tolerance.

This is different for each type of tissue and is dependent on the type of load, the rate of load, the frequency of load and the magnitude of the load. Key points to remember when considering the biomechanical perspective is that biomechanics must explain how the injury is a result of mechanical load in excess of the tissue's loadbearing tolerance or how the mechanical load has reduced the tissue's tolerance level to a point where normal mechanical loads cannot be tolerated.

When considering an epidemiological model, load and load tolerance is influenced by the main elements of the model - the intrinsic risk factors, the extrinsic risk factors and the inciting event.

It is important to have a precise description of the injury mechanism or "inciting event". This information may be used to develop specific injury prevention measures for specific types of injuries and even for specific sports. The description of the injury mechanism may include information on different levels. These levels may include:

• Sports situation
  • team action
  • skills performed before and at point of injury
  • player position
  • court position
• Athlete behaviour
  • player performance
  • opponent interaction
• Whole body biomechanics
  • description of whole-body kinematics and kinetics
• Joint/tissue biomechanics
  • description of joint/tissue kinematics

An example of how these categories is implemented is:

Categories of injury mechanism descriptions with an example of boxing

Category	Elements	Example of factors describing the injury mechanism: Knock-out in boxing
Playing/Sports Situation	Team action	Uppercut, hook
	Skill performed before, and at, the point of injury	Counterattack
	Court position	Foot work
	Player position	Forced into the corner/to the ropes Ring-side referee decision Inter-boxer distance
Athlete/opponent behaviour	Player performance	Awareness
	Opponent interaction	Aggressiveness
	Player attention	Punching power Punching speed Balance
Whole-body biomechanics	Coarse description, often static of whole body kinematics and kinetics	Centre of mass velocity Punching force Punching direction Weight distribution of the legs
Joint/tissue biomechanics	Detailed description of joint/tissue kinematics and kinetics	Energy transfer Head acceleration Pressure distribution and localisation

There are more examples in Table 1 of this article: Understanding injury mechanisms: a key component of preventing injuries in sport

Sports physiotherapists and sports professionals should know that each injury type has its typical patterns and the same for sports. Staying informed through keeping up with evidence-based literature is important for professionals working with athletes in all specific sports.

Read more on Injury Type and Classification in Sport

Sports Injury Prevention Models

Van Mechelen Injury Prevention Model

Van Mechelen Injury Prevention Model

Van Mechelen (1992) developed the fundamental, conceptual model for the prevention of sports injuries, which has since been developed and further adapted in relation to many sports and specific types of injuries. The four steps of action in this model are:

• Identification of the magnitude of the problem (prevalence and incidence of injuries)
• Identification of the cause and mechanism of injury
• Development and implementation of an injury prevention strategy
• Evaluation of the effectiveness of the intervention

Dynamic Model of Aetiology in Sports Injury

Meeuwisse et al., (2007) focused on the intrinsic and extrinsic risk factors for injury and developed a dynamic, recursive model of aetiology in sports injury. With this model it is suggested to look further than just a snapshot of the initial predisposing factors to an injury and consider that these factors change and adapt within the context of the sport.

Translating Research Into Injury Prevention Practice (TRIPP) Model

The TRIPP model by Finch (2006) considered the context of interventions and behavioural features of athletes and sports professionals. The TRIPP framework is an extension of the Van Mechelen model and includes two additional steps that are necessary for the translation of the effectiveness of injury prevention strategies into real life practice. The two additional steps include the understanding of the real world for which the specific intervention is being developed and the evaluation of this intervention in a real-world setting.

Translating research into injury prevention practice (TRIPP) Framework

Team-Sport Injury Prevention Cycle

Recently a new model has been proposed for injury prevention in team sports: the Team-sport Injury Prevention (TIP) cycle. The three key phases in this model are:

• (Re)evaluate
• Identify
• Intervene

This model incorporates key aspects of previous models but also adds insight into implementation aspects. Read more about this here: A new model for injury prevention in team sports: the Team-sport Injury Prevention (TIP) cycle.

See also: Injury Prevention in Sport

Screening

Musculoskeletal screening is commonly practiced in several sports. For many years the aim of screening was seen to be identifying the athletes at risk of injury and to implement injury prevention programmes for these athletes. Screening cannot predict if an athlete will get injured, but screening can help in finding predisposed athletes. Having a predisposition to a certain injury does not mean that the athlete will get injured. Furthermore, if an athlete does not have a predisposition to an injury this is also not a guarantee that the athlete will not be injured. Athletes become vulnerable to injury when they are exposed to load and inciting events.

Read more about Musculoskeletal Injury Risk Screening here: https://www.physio-pedia.com/Musculoskeletal_Injury_Risk_Screening

n the literature, there is the issue of prediction or association. Most of the available literature looks at retrospective studies where an association between a certain physical factor and an injury is seen, as opposed to using a certain physical factor in a retrospective (should this not be prospective???)check please! manner to investigate if it can actually predict an injury.[9] However, this does not mean that screening should not be performed, as "screening remains essential in our efforts to protect athletes’ health."[11] https://www.physio-pedia.com/Musculoskeletal_Injury_Risk_Screening

Add video on injury risk and screening as well

Examples where a specific condition/finding is seen as a causality that then creates an effect

GIRD in overhead athletes

Wilke et al (2011) reported that a loss of 20 degrees internal rotation and a loss of 5% of TROM increases the risk of injury x2 in professional baseball pitchers Correlation of glenohumeral internal rotation deficit and total rotational motion to shoulder injuries in professional baseball pitchers

Shanley et al (2011) showed that a loss of more than 25 degrees into internal rotation is predictive for arm injury in professional baseball players

More recently Rose and Noonan suggested that GIRD in isolation is not a pathologic process, throwers with GIRD often present to the clinic due to the development of shoulder pathology. Direct quote – check Glenohumeral internal rotation deficit in throwing athletes: current perspectives

So, GIRD in isolation may not be an issue, but just one of the things present when an athlete comes to the clinic with an injury. What came first? The injury and then the loss of internal rotation or the loss of internal rotation and then the injury? (Ian Gatt, 2022)

Hogan et al showed that the presence of scapular dyskinesis may increase the risk of shoulder injury but their findings were not statistically significant. It may very well be that scapular dyskinesis may only be a significant risk for shoulder injury only when other factors associated with sports injury risk are present (ie training load, etc) Hogan C, Corbett JA, Ashton S, Perraton L, Frame R, Dakic J. Scapular dyskinesis is not an isolated risk factor for shoulder injury in athletes: A systematic review and meta-analysis. The American Journal of Sports Medicine. 2021 Aug;49(10):2843-53.

Complex System and Risk Identification

Sport injuries are multifactorial. Bittencourt et al (2016) Bittencourt NF, Meeuwisse WH, Mendonça LD, Nettel-Aguirre A, Ocarino JM, Fonseca ST. Complex systems approach for sports injuries: moving from risk factor identification to injury pattern recognition—narrative review and new concept. British journal of sports medicine. 2016 Nov 1;50(21):1309-14.suggested the complex system approach for sports injuries where the focus is on injury pattern recognition rather than on risk factor identification. The authors argue that a reductionist view is taken in sports injury aetiology investigations where “a phenomenon is simplified into units and analysed as the sum of its basic parts.” With this approach statistics used are correlation and regression analysis, and despite the effort, it is still difficult to identify or isolate predictive factors to injury. A complex systems approach should rather be considered, where athletes are considered as complex(much like the majority of human health conditions) and the injury as a result of the complex interaction among a web of determinants (biomechanical, behavioural, physiological, psychological).

Sports injuries are complex and a result of interactions between different factors and this may create a risk of injury and an emerging injury pattern. To prevent sports injuries risk profiles need to be identified and this entails moving away from only identifying risk factors to a more complex approach of risk pattern recognition. Clinicians should be well informed on the interaction between risk factors to plan an effective preventative intervention. (Bittencourt et al)

Read the full article here:

Link to article

https://www.youtube.com/watch?v=IaC0vNeQ1c0

Screening and Preventative measures

There are different views on screening and it’s use in athletes. Screening can not predict which athlete will sustain an injury, but there many benefits of athlete screening.

You can read more on Musculoskeletal Injury Risk Screening

And Musculoskeletal Injury Prevention  add links to other PP pages

An editorial by Verhagen et al (2017) summarises how screening can be important for an athlete.

Positive Predictive Values

One of the main injury risk factors is previous injury. The authors use the example of ACL injuries and used different mathematical approaches and looked at risk ratio. Applying the traditional predictive diagnostic test on the data to determine if a previous ACL injury is a predictor of a new ACL injury, a positive predictive value of 29% was reported (i.e., 29% of the participants with a new injury had a previous injury). Using the risk ratio approach, it was reported that the risk of sustaining an ACL injury when having had a previous ACL injury is 3.6 times higher when compared to having had no previous ACL injury.

Predicting injury versus Estimating risk of injury

In medicine, screening is a strategy to identify an unrecognised disease in individuals with or without symptoms (add ref from article). When applying this to sport, the idea would be to determine if an athlete is injured. However, the aim of injury prevention is to intervene before an injury occurs and this changes the context of screening in sports and finding the elements (risk factors) that can lead to injury. In injury risk factor screening, one is looking for an athlete with certain traits that may predispose the athlete to injury. However, there are limitations to paradigms commonly used in screening and that professionals involved in sports do not always consider. These are: Complexity and Temporality.

Complexity

Injury occurs when different extrinsic and intrinsic risk factors interact with a timely injury mechanism. (Bittencourt ref) These occurrences are complex, multifactorial, and unpredictable. When screening athletes this complex and unpredictable reality needs to be considered otherwise the screening process may appear meaningless.

Temporality

Risk factors do not stand still and vary over time. Often screenings are performed at a set point in time (i.e., preseason screening, baseline screening) and injury rates would then be investigated over the following season or period. However, if the screening test were performed regularly the results will change over time as training and match demands will have an effect. Furthermore, risk factors identified in athletes at a preseason screening will most likely be addressed and therefor the injury risk will be influenced or reduced. Therefor, screening should be a temporal approach with repeated measures, rather than a snapshot in time.

Watch this video where Nicol van Dyk, the second author of this paper discusses their rationale.

https://www.youtube.com/watch?v=lvP_KtQf3Xc

Workload: Mediators and Moderators

Spikes in training and competition workload is also an injury risk. This workload-injury relationship can be further analysed through mediators and moderators. Mediators can be seen as the steps that explain the association between a variable and an outcome. (“Why changes in workloads might cause injuries?”) For example: Rugby league players with spikes in running workload (as determined by the acute: chronic workload ratio) are at an increased risk for a non-contact injury. The mediator in this scenario can be neuromuscular fatigue as increased workloads cause higher levels of fatigue and this may predispose the athlete to an injury.

The moderators are seen to modify the effect of a variable on an outcome. (‘What characteristics make certain athletes more robust or susceptible to injury at given workloads?”) For example, high aerobic fitness protects against spikes in workload (ref). Thus, aerobic fitness moderates the workload effect by reducing the risk of rapid workload increases.

See Figure 1 in this article:

Again, this may seem a simplified approach, but the complexity of injuries needs to be considered as well as the temporality of risk factors.

General Guidelines on Risk Factors and Injury Mechanisms

The effectiveness of screening has been questioned by clinicians and researchers

Individual risk factors are important; however, it is their summation within a complex individual, over a period, which should be considered (complexity and temporality)

Consider both mediators and moderators

Understand the sport you are working with and recognise injury risk patterns

Risk Factors and Injury Mechanisms

Injury Causation Model

Sports physiotherapists and other sports professionals recognise that the identification of the causes of injury is an important step in injury prevention as this can lead to the development of effective injury prevention programs. A model originally described by Meeuwisse (1994) and adapted and expanded upon by Barr and Krosshaug (2005) may guide sports professionals. It is important for sports professionals to know why certain athletes may be at risk of injury risk factors and how injuries occur (injury mechanism), in order to understand the causes of sports injuries. Sports injuries are rarely the result of a single factor, and can generally be attributed to an association of circumstances. Also, keep in mind that an athlete's risk of injury is not a constant and is likely to change over time.

Risk Factors

Risk factors can be divided into intrinsic and extrinsic risk factors as well as modifiable and non-modifiable factors.

Intrinsic Risk Factors

Internal risk factors can be modifiable or non-modifiable. Modifiable factors such as skill level or fitness levels may be addressed through specific training methods. Non-modifiable factors such as sex may be used to create target interventions for athlete populations at an increased risk (think about female athletes with an increased risk for ACL injuries) These internal risk factors may include:

• Age (maturation, ageing)
• Sex
• Body composition (e.g. body weight, fat mass, BMI, anthropometry)
• Fitness level (e.g. muscle strength/power, VO₂ max, joint ROM)
• Health (previous injury, joint instability)
• Anatomy (alignment, intercondylar notch width)
• Skill level (e.g. sports-specific technique, postural stability)
• Psychological factors (e.g. competitiveness, motivation, perception of risk)

Extrinsic Risk Factors

These factors include the external factors that athletes are exposed to and include:

• Human factors (e.g. teammates, opponents)
• Sports factors (e.g. coaching, rules, referees)
• Protective equipment (e.g. helmet, mouth guard, shin guards)
• Sports equipment (e.g. shoes, ski's, racquets)
• Environmental factors (e.g. weather, snow and ice conditions, floor and turf type, maintenance of playing surface)

Interaction between the intrinsic and extrinsic risk factors may cause an athlete to be more or less susceptible to injury. A combination of external and internal risk factors acting simultaneously puts an athlete at a higher risk for injury.