Elsevier

Bone

Volume 73, April 2015, Pages 120-126
Bone

Original Full Length Article
Fundamental differences in axial and appendicular bone density in stress fractured and uninjured Royal Marine recruits — A matched case–control study,☆☆

https://doi.org/10.1016/j.bone.2014.12.018Get rights and content

Highlights

  • Stress fractures are common in male Royal Marine recruits in the 32-week programme.

  • We compare bone parameters of stress fractured recruits with matched controls.

  • Cases and controls underwent DXA, pQCT and BUA scanning.

  • Axial BMD and tibial diameter were lower in stress fracture cases than controls.

  • Skeletal differences predispose male military recruits to stress fracture.

Abstract

Stress fracture is a common overuse injury within military training, resulting in significant economic losses to the military worldwide. Studies to date have failed to fully identify the bone density and bone structural differences between stress fractured personnel and controls due to inadequate adjustment for key confounding factors; namely age, body size and physical fitness; and poor sample size. The aim of this study was to investigate bone differences between male Royal Marine recruits who suffered a stress fracture during the 32 weeks of training and uninjured control recruits, matched for age, body weight, height and aerobic fitness. A total of 1090 recruits were followed through training and 78 recruits suffered at least one stress fracture. Bone mineral density (BMD) was measured at the lumbar spine (LS), femoral neck (FN) and whole body (WB) using Dual X-ray Absorptiometry in 62 matched pairs; tibial bone parameters were measured using peripheral Quantitative Computer Tomography in 51 matched pairs. Serum C-terminal peptide concentration was measured as a marker of bone resorption at baseline, week-15 and week-32. ANCOVA was used to determine differences between stress fractured recruits and controls. BMD at the LS, WB and FN sites was consistently lower in the stress fracture group (P < 0.001). Structural differences between the stress fracture recruits and controls were evident in all slices of the tibia, with the most prominent differences seen at the 38% tibial slice. There was a negative correlation between the bone cross-sectional area and BMD at the 38% tibial slice. There was no difference in serum CTx concentration between stress fracture recruits and matched controls at any stage of training. These results show evidence of fundamental differences in bone mass and structure in stress fracture recruits, and provide useful data on bone risk factor profiles for stress fracture within a healthy military population.

Introduction

Stress fracture is a common overuse injury within military training, where a high level of physical activity involving impact is a key component of the physical training [1], [2]. The prevalence of stress fracture in Royal Marine (RM) recruits (males aged 16–32 y) has typically been of the order of 4–7% [3], [4]. These injuries result in significant morbidity, often requiring lengthy rehabilitation at a personal cost to an injured recruit, as well as considerable expense to the military medical services [5].

RM training is widely acknowledged to be one of the most arduous initial military training programmes in the world. The 32-week programme – which only recruits males – encompasses physical training, classroom-based learning and personal administration skills along with field exercises, weapons training and specific Commando skills such as the assault course and rope climbing. There is a progression of professional and physical assessments (or criterion tests) during the course, culminating in the Commando Tests in week-31.

In contrast with other military programmes – which tend to be of a shorter duration than the 32 weeks of RM training – the most common site of fracture during RM training is metatarsal rather than tibia [6], [7], [8]. Furthermore, fractures in RM training tend to be reported later during the military training programme than in much of the literature [1], [6], [9].

Published cohort studies have indicated gender, age, body weight, height, muscle size/strength, physical fitness, exercise history and smoking to be potential factors influencing stress fracture risk in male military recruits [6], [10], [11], [12], [13], [14], [15]. However, the small number of case–control studies exploring bone mineral density (BMD) and other bone parameters in military populations have been limited by the extent of the control for these risk factors and/or the small number of confirmed stress fractures per se [6], [8], [9], [10], [16], [17]. Furthermore, only one study investigating stress fractures in military personnel has employed Dual X-ray Absorptiometry (DXA), peripheral Quantitative Computer Tomography (pQCT) and Broadband Ultrasound Attenuation (BUA) [15]. Central DXA was only undertaken on seven males with stress fracture, limiting the power of these findings with respect to stress fracture risk.

Bone turnover markers represent a method of assessing the metabolic changes in bone associated with bone remodelling [18]. Previous studies have reported conflicting findings with regards to longitudinal changes in bone turnover markers during military training, as well as with respect to differences between stress fracture cases and controls [19], [20], [21], [22]. Therefore the relevance of bone turnover markers in predicting stress fracture risk remains unclear.

The principal aim of this case–control study therefore was to investigate differences in axial and appendicular BMD using three contrasting but complimentary methods of measurement for bone mass and bone structure (i.e. DXA, pQCT and BUA), and a marker of bone resorption (C-telopeptide of collagen cross-links, CTx), between stress fractured and non-injured RM recruits, that was adequately powered to detect any such differences and with identical matching for age, body weight, height and aerobic fitness.

Section snippets

Study participants

The present study was part of Surgeon General's Bone Health Project, which aimed to identify risk factors for illness and injury in recruits during RM training. Other measures including body girths, skinfolds and assessment of past and present dietary intake were also undertaken, but are not reported here. Recruits from a total of twenty troops, who commenced RM training at the Commando Training Centre (CTC), between Sept 2009 and July 2010, were invited to participate in the study

Stress fracture

From the 1090 recruits who volunteered for the study, a total of 78 recruits (7%) suffered one or more stress fractures. From the study sample, 62 matched pairs of stress fractured recruits and controls were assessed with DXA. Ten stress fractured recruits either opted out of training before it was possible to complete scan visits, or the injury was reported to the CTC Medical Centre in week-31 of training. (By week-31, a recruit would have completed all the criteria Commando Tests, such that

Main findings

This study in male Royal Marine recruits identified lower mean BMD at axial sites and structural differences in the tibiae of the stress fracture group compared with matched controls (P < 0.001). There were no differences in serum CTx concentration or BUA between stress fracture recruits and matched controls. The incidence of stress fracture (7%) was similar to that previously reported for this military population [3]. But this incidence was higher than that reported for male recruits in other

Authors' roles

Authors' roles: Study design: JLF, SLN, AA, TD. Study conduct: TD, JLF, AA. Data collection: TD, AS, RC, PT. Scan interpretation: PT, CC. Serum analysis and interpretation: MORH, TRA. Data analysis: TD. Data interpretation: TD, JLF, SLN. Drafting manuscript: TD, JLF. Revising manuscript content: TD, JLF, SLN, AA. Approving final version: TD, SLN, CC, MORH, TRA, AA, JLF. TD takes responsibility for the integrity of the data analysis.

Disclosures

All authors have no conflicts of interest.

Acknowledgments

The authors would like to thank colleagues at the Commando Training Centre Royal Marines, Lympstone, Devon, UK, for their cooperation and support with this study, and the imaging technicians at the Osteoporosis Centre, Southampton General for accommodating the recruit scans within a busy clinical schedule.

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    This work was funded by the UK Ministry of Defence.

    ☆☆

    TD was a recipient of a Young Investigator Award at the UK Osteoporosis Conference, Manchester, UK, 4–7th June 2012 for this work. Aspects of this work were presented in the Plenary Poster Session at the ASBMR Conference, Minneapolis, USA, 12–15th Oct 2012.

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