Stress Fracture:
Definition:
Stress fracture, while relatively uncommon in the general population, is a common injury in athletic populations. Stress fractures are a form of overuse injury that occur when a bone is exposed to repetitive loading and mechanical stressors that exceed the bone’s ability to remodel and adapt [10] In essence, a stress fracture occurs when remodelling predominates over repair [31] Repetitive sub-maximal mechanical loading from weight-bearing exercise exposes bone to internal forces, causing micro – cracks. In a healthy person, with adequate recovery and nutrition, this will trigger physiologic bone adaption and the bone will remodel and adapt to forces applied. However, if the forces applied exceed the bone’s ability to remodel and repair, the imbalance between bone formation and resorption can cause these micro – cracks to become more severe, resulting in a bone stress injury, the most severe of which is a grade 4 stress fracture [5, 6].
Incidence:
Stress fracture is a relatively common injury among athletic and military populations. Varying incidences of stress fracture have been reported among these populations. Research states that stress fracture accounts for up to 20% of all athletic injuries. [2]. Bennell, et al, reported an overall incidence rate of 21.1%, with an incidence of 0.70 stress fractures per 1000 hours of training in their prospective study of track and field athletes. [9] They found that stress fractures made up 20% of the total musculoskeletal injuries sustained by track and field athletes. [9]. Reinking et. al conducted a prospective study and found the stress fracture incidence to be 15% among cross country / track athletes. The incidence rate for these athletes specifically was significantly higher than the rate reported in a mixed sport population (6%). [3]
Time Lost
Treatment of stress fracture involves a period of restricted weight – bearing activity and therefore necessitates removal from sports participation for a period of time. Time lost due to a stress fracture can be devastating for a competitive athlete. Rizzone et al. 2017 found that 21% of the stress fractures sustained in their study resulted in season – ending injuries. [32] Time lost from stress fracture in track and field can range from 6 weeks to over 6 months, depending on the site and severity of the injury [4, 5]. Dobrindt, Hoffmeyer et al. 2012 found that high risk fractures took a mean of 132 days before returning to sports, while a low risk fracture had a mean return to sports time of 119 days. [4] In a study of division 1 athletes, it was found that the mean time to return to unrestricted sports participation after a stress fracture diagnosis was 12 to 13 weeks for all injury sites. [33]
Recognised Risk Factors:
Due to the relative frequency of stress fracture in athletic populations, their significant recovery times and subsequent effect on athletic performance., many studies have been done on stress fractures and their risk factors. Both intrinsic and extrinsic risk factors have been identified in the research. Extrinsic factors are modifiable and can include, diet, weight, medication, training, footwear etc.[6, 7] Factors related to training load have been linked time and time again to stress fracture development. High training load / volume (mileage or hours spent training) has been shown to increase the risk for stress fracture [2, 7]. In addition, a sudden or rapid increase in training load often precedes a stress fracture. [7]. Previous history of stress fracture has been consistently linked with increased risk of stress fracture, in both men and women[7-10]. Numerous intrinsic risk factors have been assosciated with an increased risk of stress fracture in the literature, including female sex [2, 6-8, 10, 12]
Interestingly, intrinsic risk factors have only been seen consistently regarding female athletes. These intrinsic factors include, low energy availability [2, 11], low BMI [10], menstrual disturbances / irregularities [2, 6, 8, 10-13], low bone mineral density [2, 6, 8, 11, 12]. A combination of these factors has been recognised and called the “Female Athlete Triad”.
The Female Athlete Triad:
Definition:
The “Female Athlete Triad” was first coined in 1992 to describe a medical condition observed in physically active females. [8]. At that time, amenorrhea, osteoporosis and eating disorders were the components required for the diagnosis [14]. In 2007, it’s definition was modified to include a spectrum of dysfunction related to irregular menstrual function, reduced bone mineral density in place of osteoporosis and eating disorders were updated to low energy availability , with or without an eating disorder [2, 14]. The revised definition does not require an athlete to present with all of these features for diagnosis. [2]
RED-S
The concept of RED-S (Relative energy deficiency in sport) was proposed in 2014. RED-S is an umbrella term to describe the physiological and pathophysiological effects of energy deficiency in male and female athletes [15]. It states that a state of relative energy deficiency in all athletes, regardless of their sex, causes generalised adverse effects, resulting in decreased performance. [14] RED-S is said to be a more comprehensive, broader term for the overall syndrome which includes what has so far been called the “Female Athlete Triad”. [15]
Female Athlete Triad and Stress Fracture:
Increased risk of stress fracture has been seen in athletes who present with the Female Athlete Triad throughout the literature. Research has confirmed relationships between female athlete triad components and the development of musculoskeletal injury in most studies among adolescent athletes [34]. In addition, a dose – response relationship between female athlete triad components and the development of a stress fracture has been seen. Barrack et al, (2014) was the first to report this relationship, noting a higher incidence of bone stress injuries among participants meeting criteria for multiple triad – related risk factor variables compared to those who met the criteria for a single risk factor [5]. Edama et. Al (2021) found that the bone stress fracture rate was significantly higher in the high risk category (based on triad risk assessment score) than the low risk category [15]. Johnson et. al (2021)[11] noted that for female athletes who have one component of the female athlete triad, the risk of developing a stress fracture was 2.5 times more than an athlete with none. Furthermore, for those athletes presenting with two or more components, their risk of developing a stress fracture is 4.7 times higher than those with none[11]. It is clear now that the more components of the female athlete triad an athlete has, the more likely she is to incur a bone stress injury. [5]
Prevalence:
Athletes do not have to present with all 3 components of the female athlete triad in order to be diagnosed, athletes are categorised on a continuum from health to disease [17]. Studies have reported the prevalence of the triad in several different ways. A carefully conducted systematic review reported that the prevalence of 1 triad component ranged from 16 – 60%, the prevalence of any 2 triad components ranged from 2.7 – 27% and the prevalence of all 3 triad components presenting simultaneously ranged from 0 – 16% [16]. Tenforde et al (2017) identified that 29% of athletes were classified as having a moderate or high risk of stress fracture, based on the 2014 female athlete triad coalition guidelines. [17]. Results from studies indicate that while the number of athletes suffering from all 3 aspects of the triad concurrently is fairly low, there is a relatively high percentage of female athletes who are affected by some component of the spectrum of the disease [35].
Screening:
The importance of screening for and actively managing triad risk factors can not be underestimated. Early intervention may prevent long – term health consequences and injuries, including stress fractures in exercising women [17]. It has been suggested that all female athletes should be screened for the presence of the female athlete triad annually. The current standard pre-participation evaluation form has been endorsed by 6 medical societies and includes 9 questions related to the triad. Any athlete who is at risk for any Triad component should undergo a more in – depth evaluation [21]. Both the IOC and the Triad Coalition have introduced risk assessment tools intended to facilitate the clinical decision making process and guide the determination of an athlete’s eligibility to continue sports participation based on the calculated degree of risk [18]. Identifying athletes who are at increased risk helps to guide sports medicine providers to provide the most appropriate treatment and to ensure that the health of each athlete is addressed in a comprehensive manner [17].
Cumulative Risk Assessment – Female Athlete Triad Consensus Statement 2014.
The cumulative risk assessment provides an objective method of determining an athlete’s risk using risk stratification and evidence-based risk factors for the Female Athlete Triad [21]. Individuals are scored on a scale from 0 – 2 points (with 0 being no risk, 1 being moderate risk and 2 being high risk) on 6 individual risk factors.
Low EA (with or without disordered eating / eating disorder) :
Low EA with or without disordered eating or an eating disorder for the Triad Coalition is based on the presence of dietary restriction, disordered eating behaviours, and/or diagnosis of an eating disorder. . [21]. The coalition did not provide specific directions on how to assess this factor. As such, different papers have used different assessment tools, such as the “Three factor eating questionnaire”, the “eating disorder inventory” [18]. Other questionnaires such as the low energy availability in females questionnaire (LEAF – Q), a 25 item questionnaire, utilising subsets of gastrointestinal symptoms, injury frequency and menstrual dysfunction (validated in endurance athletes, 78% sensitivity / 90% specificity) [19, 22] and the eating disorder examination questionnaire (EDE – Q 6.0) have been used as a measure of low energy availability throughout the literature. [23, 24]
Low BMI:
· Low Risk: BMI ≥ 18.5 or ≥ 90% EW or weight stable.
· Moderate Risk: BMI 17.5 < 18.5 or < 90% or 5 to < 10% weight loss/month.
· High Risk: BMI ≤ 17.5 or < 85% EW or ≥ 10% weight loss / month.
Delayed menarche:
· Low Risk: Menarche < 15 years
· Moderate Risk: Menarche 15 to < 16 years
· High Risk: Menarche ≥ 16 years
Oligomenorrhea and/or amenorrhea:
· Low Risk : > 9 menses in 12 months.
· Moderate Risk: 6 – 9 menses in 12 months.
· High Risk: < 6 menses in 12 months.
When menstrual status cannot be assessed, such as during hormonal contraceptive use, low EA determined using self – report and disordered eating questionnaires was the best substitution, resulting in 80% of study participants being placed in the same clearance category. [1]
Low BMD
· Low Risk: Z – score ≥ -1.0
· Moderate Risk: Z – Score -1.0 < -2.0
· High Risk: Z – Score ≤ -2.0
Koltun et. al, 2020 [1] found that when BMD cannot be assessed, substituting delayed menarche was the best – fit replacement, resulting in 91% of participants being placed in the same clearance category. [1]
Stress reaction / fracture.
· Low Risk: 0
· Moderate Risk: 1
· High Risk: ≥2 ; ≥1 high risk or of trabecular bone sites. High risk sites include lumbar spine, femoral neck, sacrum, and pelvis.
Individual scores are then summed to calculate the cumulative risk assessment score which is used to classify the athlete into 3 categories. These categories are then used to determine their eligibility to continue sports participation.
· Low Risk (0 -1 points) = Full clearance
· Moderate Risk (2 – 5 points) = Provisionally cleared, clearance granted, but with modification in training as specified by physician (with possibility for status to change depending on clinical progress and new information gathered).
· High Risk (6+ points) = Restricted from training and competition [18, 21]
Koltun et. al, 2020 have made modifications to the cumulative risk assessment tool, to be used when certain factors cannot be assessed (e.g., BMD and menstrual function). In doing this, they have made the cumulative assessment tool more accessible to health practitioners and athletes. [1]
Discussion:
Stress fractures are a relatively common injury among athletic populations. Female athletes have consistently been shown to be more “at risk” than their male counterparts. The female athlete triad is a recognised risk factor for stress fracture development. Time lost to stress fracture can be devastating to a competitive athlete. Identifying risk factors and implementing preventative strategies to reduce their incidence is preferable over any other treatment option.
Unlike many other sports, individuals involved in athletics often do not have access to a team doctor, athletic therapist or other medical professional. The modifications suggested by Koltun et al. to the cumulative risk assessment have made it possible for athletes to self – administer. This potentially will give athletes the ability to assess their own risk and seek out whatever help is most appropriate prior to sustaining an injury. Ideally, the incidence of stress fracture in athletics would be reduced.
Additionally, as this risk assessment tool is more accessible, more health care professionals and coaches can implement it. Having an overview of an athlete’s health will allow healthcare professionals to provide a more holistic treatment plan through appropriate referrals etc.
References:
1. Barrack, M. T., et al. (2013). "Update on the female athlete triad." Current Reviews in Musculoskeletal Medicine 6(2): 195-204.
2. Barrack, M. T., et al. (2014). "Higher Incidence of Bone Stress Injuries With Increasing Female Athlete Triad–Related Risk Factors." The American Journal of Sports Medicine 42(4): 949-958.
3. Barrow, G. W. and S. Saha (1988). "Menstrual irregularity and stress fractures in collegiate female distance runners." The American Journal of Sports Medicine 16(3): 209-216.
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7. De Souza, M. J., et al. (2014). "2014 Female Athlete Triad Coalition Consensus Statement on Treatment and Return to Play of the Female Athlete Triad: 1st International Conference held in San Francisco, California, May 2012 and 2nd International Conference held in Indianapolis, Indiana, M." British Journal of Sports Medicine 48(4): 289-289.
8. Dobrindt, O., et al. (2012). "Estimation of return-to-sports-time for athletes with stress fracture – an approach combining risk level of fracture site with severity based on imaging." BMC Musculoskeletal Disorders 13(1): 139.
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