Trunk and Lower Extremity Movement Patterns, Stress Fracture Risk Factors, and Biomarkers of Bone Turnover in Military Trainees

Incidence and Risk Factors for Bone Stress Injuries in United States Air Force Special Warfare Trainees

OBJECTIVES

To determine (1) the incidence rate of lower extremity (LE) bone stress injuries (BSIs) in United States Air Force Special Warfare (AFSPECWAR) trainees during the first 120 days of training, and (2) factors associated with sustaining a LE BSI.

DESIGN

Retrospective cohort study.

METHODS

AFSPECWAR Airmen (n = 2,290, mean age = 23.7 ± 3.6 years) entering an intensive 8-week preparatory course "SW-Prep" between October 2017 and May 2021. We compared anthropometric measurements, previous musculoskeletal injury (MSKI), fitness measures, and prior high-impact sports participation in those that did and did not suffer a BSI during the 120-day observation period using independent t-tests and chi-square tests. A multivariable binary logistic regression was used to determine factors associated with suffering a BSI.

RESULTS

A total of 124 AFSPECWAR trainees suffered a BSI during the surveillance period, yielding an incidence proportion of 5.41% and an incidence rate of 1.4 BSIs per 100 person-months. The multivariate logistic regression revealed that lower 2-minute sit-up scores, no prior history of participation in a high-impact high-school sport, and a history of prior LE MSKI were associated with suffering a BSI. A receiver operator characteristic curve analysis yielded an area under the curve (AUC) of 0.727.

CONCLUSION

BSI incidence proportion for our sample was similar to those seen in other military settings. Military trainees without a history of high-impact sports participation who achieve lower scores on sit-ups tests and have a history of LE MSKI have a higher risk for developing a LE BSI during the first 120 days of AFSPECWAR training.

The Relationship Between Stress Fractures and Bone Turnover Markers Is Unclear in Athletic and Military Populations: A Critically Appraised Topic

Clinical Scenario: Having an indication of how bone is remodeling in response to training load could help identify athletes and military personnel at increased stress fracture (SFx) risk. Direct assessment of bone remodeling is impractical. Biochemical markers of bone turnover are used as an indirect measure of bone remodeling and have potential to inform prevention and treatment efforts. To date, the relationship between bone turnover markers and SFxs in athletes or military personnel remains unclear. Clinical Question: Are SFxs related to bone turnover markers in athletes and military personnel? Summary of Key Findings: Seven met eligibility criteria. In five studies, an association between SFxs and bone turnover markers existed. Clinical Bottom Line: The evidence supporting a relationship between SFxs and bone turnover markers in athletes and military personnel is mixed. While five of the seven studies reported some type of relationship, no studies prospectively measured bone turnover markers in a group of athletes or military personnel without an SFx or without SFx history and followed them over time to reassess bone turnover markers upon SFx occurrence. Strength of Clinical Recommendation: In accordance with the Strength of Recommendation Taxonomy, Grade C is the most appropriate strength of recommendation rating.

The Relationship between Landing Error Scoring System Performance and Injury in Female Collegiate Athletes

BACKGROUND

The Landing Error Scoring System (LESS) is a standardized tool used to identify aberrant biomechanical movement patterns during a jump-landing task. Prior authors have examined the value of the LESS in identifying ACL injury risk in athletic populations. Yet, no study has evaluated the association between LESS performance and incidence of any type of lower extremity injury in female collegiate athletes across multiple sports.

PURPOSE

The purpose of this study was to examine the association between LESS performance as measured with a markerless motion-capture system and lower extremity injury in female collegiate athletes.

STUDY DESIGN

Prospective cohort study.

METHODS

One hundred and ten DI female collegiate athletes (basketball, n=12; field hockey, n=17; gymnastics, n=14; lacrosse, n=27; softball, n=23; volleyball, n=17) completed a jump-landing test prior to the start of their sport seasons. The LESS was automatically scored using a Microsoft Kinect sensor and Athletic Movement Assessment software (PhysiMax®). Participants were tracked throughout one competitive season for incidence of time-loss lower extremity injury. A Receiver Operating Characteristic curve determined the optimal cutpoint for the total LESS score for predicting injury. Pearson's Chi squared statistics examined the association between injury and LESS total scores >5. The Fisher exact test evaluated group differences for the frequency of receiving an error on individual LESS test items.

RESULTS

Female collegiate athletes with LESS scores >5 were not more likely to be injured than those with scores ≤5 (χ2=2.53, p=0.111). The relative risk of injury to this group was 1.78 (95% CI=0.86, 3.68) while the odds ratio was 2.10 (95% CI=0.83, 5.27). The uninjured group was more likely to receive an error on lateral trunk flexion at initial contact than the injured group (p=0.023).

CONCLUSION

The LESS total score was not associated with an increased odds of lower extremity injury in this cohort of female collegiate athletes. Future studies to examine the association between individual LESS item scores and injury are warranted.

LEVEL OF EVIDENCE

1b.