Background 

Lower extremity stress fractures result in lost time from work and sport and incur costs in the military when they occur in service members. Hypovitaminosis D has been identified as key risk factor in these injuries. An estimated 33% to 90% of collegiate and professional athletes have deficient vitamin D levels. Other branches of the United States military have evaluated the risk factors for stress fractures during basic training, including vitamin D deficiency. To the best of our knowledge, a study evaluating the correlation between these injuries and vitamin D deficiency in US Navy recruits and a cost analysis of these injuries has not been performed. Cutbacks in military medical staffing mean more active-duty personnel are being deferred for care to civilian providers. Consequently, data that previously were only pertinent to military medical providers have now expanded to the nonmilitary medical community.

Questions/purposes 

We therefore asked: (1) What proportion of US Navy recruits experience symptomatic lower extremity stress fractures, and what proportion of those recruits had hypovitaminosis vitamin D on laboratory testing? (2) What are the rehabilitation costs involved in the treatment of lower extremity stress fractures, including the associated costs of lost training time? (3) Is there a cost difference in the treatment of stress fractures between recruits with lower extremity stress fractures who have vitamin D deficiency and those without vitamin D deficiency?

Methods 

We retrospectively evaluated the electronic medical record at Naval Recruit Training Command in Great Lakes, IL, USA, of all active-duty males and females trained from 2009 until 2015. We used ICD-9 and ICD-10 diagnosis codes to identify those diagnosed with symptomatic lower extremity stress fractures. Data collected included geographic region of birth, preexisting vitamin D deficiency, vitamin D level at the time of diagnosis, medical history, BMI, age, sex, self-reported race or ethnicity, hospitalization days, days lost from training, and the number of physical therapy, primary care, and specialty visits. To ascertain the proportion of recruits who developed symptomatic stress fractures, we divided the number of recruits who were diagnosed with a stress fracture by the total number who trained over that span of time, which was 204,774 individuals. During the span of this study, 45% (494 of 1098) of recruits diagnosed with a symptomatic stress fracture were female and 55% (604 of 1098) were male, with a mean ± SD age of 24 ± 4 years. We defined hypovitaminosis D as a vitamin D level lower than 40 ng/mL. Levels less than 40 ng/mL were defined as low normal and levels less than 30 ng/mL as deficient. Vitamin D levels were obtained at the discretion of the individual treating provider without standardization of protocol. Cost was defined as physical therapy visits, primary care visits, orthopaedic visits, diagnostic imaging costs, laboratory costs, hospitalizations, if applicable, and days lost from training. Diagnostic studies and laboratory tests were incorporated as indirect costs into initial and follow-up physical therapy visits. Evaluation and management code fee schedules for initial visits and follow-up visits were used as direct costs. We obtained these data from the Centers for Medicare & Medicaid Services website. Per capita cost was calculated by taking the total cost and dividing it by the study population. Days lost from training is based on a standardized government military salary of recruits to include room and board.

Results 

We found that 0.5% (1098 of 204,774) of recruits developed a symptomatic lower extremity stress fracture. Of the recruits who had vitamin D levels drawn at the time of stress fracture, 95% (416 of 437 [95% confidence interval (CI) 94% to 98%]; p > 0.99) had hypovitaminosis D (≤ 40 ng/mL) and 82% (360 of 437 [95% CI 79% to 86%]; p > 0.99) had deficient levels (≤ 30 ng/mL) on laboratory testing, when evaluated. The total treatment cost was USD 9506 per recruit. Days lost in training was a median of 56 days (4 to 108) for a per capita cost of USD 5447 per recruit. Recruits with deficient vitamin D levels (levels ≤ 30 ng/mL) incurred more physical therapy treatment costs than did those with low-normal vitamin D levels (levels 31 to 40 ng/mL) (mean difference USD 965 [95% CI 2 to 1928]; p = 0.049).

Conclusion 

The cost of lost training and rehabilitation associated with symptomatic lower extremity stress fractures represents a major financial burden. Screening for and treatment of vitamin D deficiencies before recruit training could offer a cost-effective solution to decreasing the stress fracture risk. Recognition and treatment of these deficiencies has a role beyond the military, as hypovitaminosis and stress fractures are common in collegiate or professional athletes.

Level of Evidence 

Level III, prognostic study.

中文翻译：

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训练期间被诊断出有症状的应力性骨折的海军新兵比例以及这些伤害的经济影响

背景 

下肢应力性骨折会导致工作和运动时间的损失，并且当军人发生下肢应力性骨折时，会给军队带来费用。维生素 D 缺乏症已被确定为这些损伤的关键危险因素。据估计，33% 至 90% 的大学和职业运动员维生素 D 水平不足。美国军方的其他部门评估了基础训练期间应力性骨折的危险因素，包括维生素 D 缺乏症。据我们所知，尚未开展一项研究，评估这些损伤与美国海军新兵维生素 D 缺乏之间的相关性，并对这些损伤进行成本分析。军事医疗人员的削减意味着更多的现役人员将被推迟到民用医疗机构接受护理。因此，以前仅与军事医疗提供者相关的数据现在已扩展到非军事医疗界。

问题/目的 

因此，我们提出以下问题：(1) 有多少比例的美国海军新兵出现有症状的下肢应力性骨折，以及有多少比例的新兵在实验室测试中患有维生素 D 缺乏症？(2) 下肢应力性骨折的治疗涉及哪些康复费用，包括损失训练时间的相关费用？（3）维生素D缺乏和非维生素D缺乏的下肢应力性骨折新兵治疗应力性骨折的费用是否存在差异？

方法 

我们回顾性评估了美国伊利诺伊州五大湖海军新兵训练司令部 2009 年至 2015 年间接受训练的所有现役男性和女性的电子病历。我们使用 ICD-9 和 ICD-10 诊断代码来识别那些被诊断患有以下疾病的人：有症状的下肢应力性骨折。收集的数据包括出生地理区域、先前存在的维生素 D 缺乏症、诊断时的维生素 D 水平、病史、BMI、年龄、性别、自我报告的种族或民族、住院天数、训练损失天数以及参加训练的次数。物理治疗、初级保健和专科就诊。为了确定出现有症状的应力性骨折的新兵比例，我们将被诊断为应力性骨折的新兵人数除以该时间段内接受训练的总人数（204,774 人）。在本研究期间，被诊断患有症状性应力性骨折的新兵中，45%（1098 人中的 494 人）为女性，55%（1098 人中的 604 人）为男性，平均±标准差年龄为 24±4 岁。我们将维生素 D 缺乏症定义为维生素 D 水平低于 40 ng/mL。低于 40 ng/mL 的水平被定义为正常偏低，低于 30 ng/mL 的水平被定义为缺陷。维生素 D 水平由个体治疗提供者自行决定，无需标准化方案。成本被定义为物理治疗就诊、初级保健就诊、骨科就诊、诊断成像费用、实验室费用、住院费用（如果适用）以及培训损失的天数。诊断研究和实验室测试作为间接成本纳入初始和后续物理治疗就诊。首次访问和后续访问的评估和管理代码费用表被用作直接成本。我们从医疗保险和医疗补助服务中心网站获得这些数据。人均成本是通过将总成本除以研究人口来计算的。训练损失的天数是根据新兵的标准化政府军事工资计算的，包括食宿。

结果 

我们发现 0.5%（204,774 名新兵中的 1098 名）出现了有症状的下肢应力性骨折。在应力性骨折时测定维生素 D 水平的新兵中，95%（437 人中的 416 人[95% 置信区间 (CI) 94% 至 98%]；p > 0.99）患有维生素 D 不足 (≤ 40 ng/mL) ）和 82%（437 例中的 360 例 [95% CI 79% 至 86%]；p > 0.99）在评估时实验室测试中存在缺陷水平（≤ 30 ng/mL）。每名新兵的总治疗费用为 9506 美元。培训损失天数中位数为 56 天（4 至 108 天），每名新兵的人均成本为 5447 美元。维生素 D 水平不足（水平 ≤ 30 ng/mL）的新兵比维生素 D 水平正常较低（水平 31 至 40 ng/mL）的新兵需要更多的物理治疗费用（平均差 965 美元 [95% CI 2 至1928]；p = 0.049）。

结论 

与有症状的下肢应力性骨折相关的训练和康复损失是一项重大的经济负担。在新兵训练前筛查和治疗维生素 D 缺乏症可以为降低应力性骨折风险提供经济有效的解决方案。认识和治疗这些缺陷的作用超出了军队的范围，因为维生素缺乏症和应力性骨折在大学或职业运动员中很常见。

证据水平 

III级，预后研究。