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Correlation between femoral neck shaft angle and surgical management in trainees with femoral neck stress fractures.

The most common overuse injury that leads to the discharge of new military recruits is a stress fracture. (1) Stress fractures are associated with abrupt changes in physical activity level, such as the increase in activity some recruits are exposed to as part of military basic training. (1) Stress fractures result from repetitive, submaximal loads on normal bone that cause bone formation to lag behind bone resorption, leaving bone prone to microtrauma. (2) A subset of stress fractures, subject to high tensile forces and limited vascularity, are prone to delayed healing and are at risk for complete fracture, delayed, or nonunion, and require a more aggressive treatment approach. (3) One of the high-risk stress fractures is of the lateral femoral neck which risks osteonecrosis of the femoral head, the need for arthroplasty, and permanent disability. (4,5) Early surgical intervention for these high risk stress fractures is recommended to prevent fracture progression. (3-5) The cost of a recruit sustaining a femoral neck stress fracture that requires surgery is estimated to exceed $100,000 per injured recruit. At military treatment facilities (MTFs), surgical fixation is performed in about 25% of cases of femoral neck stress fractures. (6)

Femoral neck stress fractures make up less than 10% of all stress fractures. (4,5,7-10) These injuries are most common in female military recruits. (2,7) Overall, complications occur in 10% to 40% of all femoral neck stress fracture patients. Complication rates increase with displacement and varus surgical reduction. (11)

Both intrinsic and extrinsic factors have been associated with an increased risk of femoral neck stress fracture. Extrinsic factors may include the type of physical activity, prior training regimens, footwear, and environment. (7) Intrinsic factors include sex, bone density and size, muscle size, foot shape, leg length, and hip geometry. (5,7-9,12)

Hip geometry is an important intrinsic risk for stress fractures. Clinically, loads in the average loading direction will not cause a fracture, but loads of extreme magnitude or extreme orientation may. (13) In cases of altered femoral neck geometry, the joint load orientation becomes more vertical with coxa valga and more horizontal in coxa vara. (13) Coxa vara is defined as a femoral neck shaft angle of less than 120[degrees], coxa valga as an angle of greater than 140[degrees] average femoral neck shaft angle ranges from 125[degrees] to 131[degrees].13 Femoral neck stress fractures are associated with coxa vara (14) and compression side femoral neck stress fractures are more common. (3)

The treatment of femoral neck stress fractures should first focus on correcting predisposing intrinsic and extrinsic factors. Treatment of most compression side femoral neck stress fractures involves not bearing weight on the affected extremity for 6 weeks. (3) Compression side stress fractures that show chronic changes such as cysts or intramedullary sclerosis involve more than 50% of the neck on MRI, and those that are complete may require surgical fixation. (1,2) Sariyilmaz et al used coxa vara and the resulting mechanical abnormality as an additional indication for surgery. (15) Tension side femoral neck stress fractures should be treated with increased vigilance to prevent progression to complete fracture. (2,8) Nondisplaced stress fractures can be treated with cannulated screw fixation or Pauwel osteotomy; however, displaced fractures would require dynamic hip screw placement or arthroplasty. (15)

The purpose of this study is to determine if, in the presence of femoral neck stress fracture, there is a correlation between femoral neck shaft angle, surgical treatment, and outcomes.

METHODS

After approval from the MTF Institutional Review Board, we performed a retrospective study. Patients that had been evaluated by orthopaedics, had imaging of the hip, and diagnosed with a femoral neck stress fracture at the MTF between June 1, 2012 and May 31, 2014 were included. We reviewed hospital and clinic records and available imaging data from surgical scheduling, electronic medical records, and the Picture Archive and Communication System (PACS) application.

A potential subject list, shown in Table 1, was compiled using an electronic medical record search of ICD-9 codes which correspond to stress fractures of the femur, hip, and pelvis. Imagery available in PACS was reviewed to ensure the potential subjects did, in fact, have a femoral neck stress fracture and the necessary imaging studies were available for analysis. We then screened the potential subject list for other inclusion and exclusion criteria, shown in Table 2.

Each subject's femoral neck shaft angle was measured on the anteroposterior radiograph by calculating the angle formed by the intersection of a line bisecting the midpoint of the femoral neck and the midpoint of the femoral head, and the anatomic axis of the femur, illustrated in the Figure. Each subject's MRI was then examined in order to grade the severity of the femoral neck stress reaction as indicated by bone edema and a frank fracture line (Table 3). Each subject's electronic medical record was examined for details on the clinical course, provider recommended activity restrictions, and ability to perform full military duty. Each subject was searched on the surgical schedule to determine whether they underwent surgery for a femoral neck stress fracture.

Comparisons among groups were then made using unpaired student's t test and Pearson's correlation for continuous data, and 2-tailed Fisher's exact test for categorical data. All analysis was performed using GraphPad Prism 6 (GraphPad Software, Inc, La Jolla, CA).

RESULTS

Search of orthopaedic encounters within the electronic medical record found 205 uses of the queried ICD-9 codes in 185 individuals. Of those, diagnosis of femoral neck stress fracture was found in 72 individuals. Nineteen individuals were excluded from the study because an MRI was not obtained as part of their workup, they had been treated at their previous duty station, had pathologic fractures, were not active duty, or had no fracture on MRI. This left 53 individuals as study participants, with 10 individuals having bilateral femoral neck stress fractures (63 total stress fractures).

Review of the 53 included individuals found that all of the affected individuals were initial trainees, and 12 were male (23%). The average age of the included subjects was 22.9 years (range 18 to 39 years) and there was no difference in age between male and female subjects (P=.3820). Thirty of the 63 affected femurs were right side (48%). All of the evaluated femoral neck stress fractures were compression side. One male presented with a complete fracture. Women had a greater mean femoral neck shaft angle compared to men (132.2[degrees] [+ or -] 0.6[degrees] versus 129.0[degrees] [+ or -] 0.8[degrees], respectively; P=.0082). Normal is considered 125[degrees] to 131[degrees]. No correlation existed among femoral neck shaft angles, stress fracture grades, duration of symptoms, or pain scale results per hip.

Ten subjects (8 female, 2 male) had bilateral stress fractures. All bilateral stress fractures were noted on images obtained in a single encounter. In addition, the 7 patients who had surgical intervention for bilateral stress fractures had both sides fixed at one procedure. Having bilateral stress fractures did not affect surgery rates (P=.1563) or return to duty rates (P=.4639) compared to a unilateral stress fracture.

Twenty-four subjects (31 hips) underwent operative fixation. Percutaneous screw fixation was used in all 24 of the operative patients. One 19-year-old patient's course was complicated by chondrolysis and went on to total joint arthroplasty. Femoral neck shaft angles were not different between subjects who were not treated with surgery (131.6[degrees] [+ or -] 0.8[degrees]) and those who underwent percutaneous screw fixation (131.4[degrees] [+ or -] 0.7[degrees], P=.8759). However, subjects with operatively treated hips had higher stress fracture grades on MRI (3.4 [+ or -] 0.1) versus subjects who did not undergo surgery (2.9 [+ or -] 0.1, P=.0059). Subjects who underwent surgery also had higher mean pain scores on presentation to orthopaedics (4.8 [+ or -] 0.5) versus subjects who did not undergo surgery (3.4 [+ or -] 0.5, P=.0412).

Two-thirds of surgical patients did not return to full duty (16/24), and 48% of nonsurgical patients did not return to full duty (14/29, P=.2660). There was no difference between femoral neck shaft angles among subjects who were able to return to duty (132.0[degrees] [+ or -] 1.1[degrees]) and subjects who were not able to return to duty (131.2[degrees] [+ or -] 0.6[degrees], P=.5081). Stress fracture grade was also not different between those who returned to full military duty (3.1 [+ or -] 0.1) and those who did not (3.2 [+ or -] 0.1, P=.4701). There was a trend, though not significant, towards individuals who did not return to duty having higher mean pain scores on presentation to orthopaedics (4.6 [+ or -] 0.4 not return to duty versus 3.3 [+ or -] 0.6 return to duty, P=.0575).

Comment

The results of this study suggest there is no correlation between return to full military duty rates and treatment, femoral neck shaft angle, or fracture grade on MRI. There was a trend toward significance in higher pain level at presentation and lower return to duty rates. Patients who underwent surgical fixation had greater fracture grade and pain than those that did not have surgery. The femoral neck shaft angle was found to be more valgus in women. Additionally, the mean angle in this cohort was more valgus than the previously cited normal range of 125[degrees] to 131[degrees]. (13) Bilateral stress fractures were found in 19% of study participants.

In this study, all of the patients who had stress fractures were trainees. This suggests initial training places added stress on the femoral neck that either does not continue after conditioning or results in the attrition of trainees prone to these fractures. Individual preconditioning and dietary variance would affect how the trainee reacts to the increase in physical activities unique to initial training. The programs that have shown to decrease training injuries, such as command awareness, provider training, and the Army Physical Readiness Training (PRT) program, should be continued. (6)

This study found no tension-sided femoral neck stress fractures. This is not surprising because compression-sided fractures are more common; however, the proportion of surgically-treated fractures was 49%. This percentage is greater than previously presented in the literature (25%). (6) Although there was no statistically significant correlation between stress fracture grade and pain level, the stress fracture grade and pain level were higher for those operatively treated. While some literature supports treating compression side stress fractures with strict limitation of weight bearing, (3) our high operative rate is evidence that surgeon and facility considerations play a role in management of this condition. For example, surgeons at this MTF must consider whether strict nonweightbearing is reasonable for individuals with training demands within the military environment.

Clinically, providers should continue to have a high index of suspicion for femoral neck stress fractures in trainees presenting with hip pain. An MRI should be obtained if history warrants. When obtaining MRIs, the contralateral hip should be imaged to exclude asymptomatic stress reaction in the contralateral hip. (3,17) Care should also include identifying and treating any intrinsic factors that put the trainee at risk for stress fracture. (3) Treatment may need to include supplementation with calcium and vitamin D, or treatment of women with low-dose estrogen. (8) However, not all intrinsic factors are amenable to intervention and focus must remain on modification of extrinsic factors when possible. (8) Initial military training fitness programs that assess and gradually progress fitness levels are necessary for injury prevention. (8) These could include progressive resistance training and protective exercises such as the forward lunge, isokinetic hip extension, one-legged long jump, and isokinetic knee flexion. (8,18,19)

All retrospective studies have similar limitations including those imposed by querying records that differ in quality. Not all data that was desired was recorded in every medical record. Many lacked record of pain scale, duration of symptoms, and duration of restricted weight bearing. This study was unable to assess for female athlete triad due to the lack of records on the patient's menstrual cycle and diet. In post-hoc power analysis using Stata 13.1, we found we were adequately powered at 0.9519 for the comparison between return to full military duty and those that did not with regard to mean femoral neck shaft angle. A follow up study to obtain a power of 0.80 would require 424 subjects, with 212 subjects each in the surgical and nonsurgical groups, for the comparison between operatively treated hips and femoral neck shaft angles. So while we were adequately powered with this sample size to examine some dependent variables, we were not adequately powered to examine all of them. A study of such size would not be possible at this single medical facility.

CONCLUSION

Both intrinsic and extrinsic factors contribute to stress fracture. Extrinsic factors may include the type of physical activity, prior training regimens, footwear and environment. (7) Intrinsic factors include sex, bone density and size, muscle size, foot shape, leg length, and hip geometry. (5,7-9,12) Those charged with training design should work to minimize the contribution of modifiable factors to prevent stress fractures. Future studies that prospectively gather information on female athlete triad, metabolic work-up results, pretraining fitness levels, and seasonal differences in rates would be useful. Studies that randomize surgical treatment may not be possible, but nonoperative treatment modalities involving treatment of modifiable intrinsic and extrinsic factors would be helpful in helping care providers choose the best treatment to avoid the patient's separation. Stress modeling of the exercises preformed in initial training could also help tailor physical fitness program to prevent stress fractures. Future study is also necessary to limit the personal and financial effects of these costly fractures.

CPT Robyn L. Chalupa, SP, USA

MAJ Jessica C. Rivera, MC, USA

CPT David J. Tennent, MC, USA

LTC (P) Anthony E. Johnson, MC, USA

REFERENCES

(1.) Shin AY, Gillingham BL. Fatigue fractures of the femoral neck in athletes. J Am Acad Orthop Surg. 1997;5(6):293-302.

(2.) Boden BP, Osbahr DC, Jimenez C. Low-risk stress fractures. Am J Sports Med. 2001;29(1):100-111.

(3.) Boden BP, Osbahr DC. High-risk stress fractures: evaluation and treatment. J Am Acad Orthop Surg. 2000;8(6):344-353.

(4.) Pihlajamaki HK, Ruohola JP, Kiuru MJ, Visuri TI. Displaced femoral neck fatigue fractures in military recruits. J Bone Joint Surg Am. 2006;88(9):1989-1997.

(5.) Behrens SB, Deren ME, Matson A, Fadale PD, Monchik KO. Stress fractures of the pelvis and legs in athletes: a review. Sports Health. 2013;5(2):165-174.

(6.) Scott SJ, Feltwell DN, Knapik JJ, et al. A multiple intervention strategy for reducing femoral neck stress injuries and other serious overuse injuries in U.S. Army Basic Combat Training. Mil Med. 2012;177(9):1081-1089.

(7.) Cosman F, Ruffing J, Zion M, et al. Determinants of stress fracture risk in United States Military Academy cadets. Bone. 2013;55(2):359-366.

(8.) Jacobs JM, Cameron KL, Bojescul JA. Lower extremity stress fractures in the military. Clin Sports Med. 2014;33(4):591-613.

(9.) Kupferer KR, Bush DM, Cornell JE, et al. Femoral neck stress fracture in Air Force basic trainees. Mil Med. 2014;179(1):56-61.

(10.) Malhotra R, Meena S, Digge VK. Tensile type of stress fracture neck of femur: role of teriparatide in the process of healing in a high risk patient for impaired healing of fracture. Clin Cases Miner Bone Metab. 2013;10(3):210-212.

(11.) Lee CH, Huang GS, Chao KH, Jean JL, Wu SS. Surgical treatment of displaced stress fractures of the femoral neck in military recruits: a report of 42 cases. Arch Orthop Trauma Surg. 2003;123(10):527-533.

(12.) Carey T, Key C, Oliver D, Biega T, Bojescul J. Prevalence of radiographic findings consistent with femoroacetabular impingement in military personnel with femoral neck stress fractures. J Surg Orthop Adv. 2013;22(1):54-58.

(13.) Fischer KJ, Eckstein, F.; Becker C. Density-based load estimation predicts altered femoral load directions for coxa vara and coxa valga. J Musculoskelet Res. 1999;3(2):83-92.

(14.) Carpintero P, Leon F, Zafra M, Serrano-Trenas JA, Roman M. Stress fractures of the femoral neck and coxa vara. Arch Orthop Trauma Surg. 2003;123(6):273-277.

(15.) Sariyilmaz K, Ozkunt O, Sungur M, Dikici F, Yazicioglu O. Osteomalacia and coxa vara. An unusual co-existence for femoral neck stress fracture. Int J Surg Case Rep. 2015;16:137-140.

(16.) Arendt E, Agel J, Heikes C, Griffiths H. Stress injuries to bone in college athletes: a retrospective review of experience at a single institution. Am J Sports Med. 2003;31(6):959-968.

(17.) Moo IH, Lee YH, Lim KK, Mehta KV. Bilateral femoral neck stress fractures in military recruits with unilateral hip pain. J R Army Med Corps. June 17, 2015 [epub ahead of print].

(18.) Martelli S, Kersh ME, Schache AG, Pandy MG. Strain energy in the femoral neck during exercise. J Biomech. 2014;47(8):1784-1791.

(19.) Qian JG, Li Z, Zhang H, Bian R, Zhang S. Effectiveness of selected fitness exercises on stress of femoral neck using musculoskeletal dynamics simulations and finite element model. J Hum Kinet. 2014;41:59-70.

AUTHORS

CPT Chalupa is a physician assistant with the Orthopaedic Surgery Service, Department of Orthopaedics and Rehabilitation, Brooke Army Medical Center, JBSA Fort Sam Houston, Texas.

MAJ Rivera is with the US Army Institute of Surgical Research, Joint Base San Antonio Fort Sam Houston, Texas.

CPT Tennent is with the Department of Orthopaedics and Rehabilitation, San Antonio Military Medical Center, Joint Base San Antonio-Fort Sam Houston, Texas.

LTC (P) Johnson is Chairman, Department of Orthopaedics and Rehabilitation, Brooke Army Medical Center, JBSA Fort Sam Houston, Texas.

Table 1. The potential subject list of codes corresponding
to stress fractures of the femur, hip, and pelvis.

ICD-9                      Description

733.90   Disorder of the bone and cartilage unspecified
733.95   Stress fracture of other bone
733.96   Stress fracture of the femoral neck
733.97   Stress fracture of the shaft of the femur
733.98   Stress fracture of the pelvis
736.31   Coxa valga (acquired)
736.32   Coxa vara (acquired)
736.39   Other acquired deformities of the hip

Table 2. Additional inclusion and exclusion criteria for subject
screening.

Inclusion Criteria

Treated between June 1, 2012 and May 31, 2014
Diagnosis of a femoral neck stress fracture confirmed by MRI
Age: 18-45 years
Active duty
Treatment by orthopaedics
Available MRI and anteroposterior pelvis

Exclusion Criteria

Age < 18 years
Age > 45 years
Pathologic fracture
Electronic medical record not available
Imaging to evaluate stress fracture not available

Table 3. Criteria table used to grade severity of the femoral
neck stress reaction based on examination of the subject's
MRI imagery. Adapted from Arendt et al. (16
)

Grade   STIR *    T2 Signal   T1 Signal       Plain X-ray
        Signal     Change      Change            Film
        Change

1       Present   None        None        Negative
2       Present   Present     None        Negative
3       Present   Present     Present     Periosteal reaction
4       Present   Fracture    Fracture    Periosteal reaction
                    line        line        or fracture line

* Short T1 inverse recovery imaging
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Article Details
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Author:Chalupa, Robyn L.; Rivera, Jessica C.; Tennent, David J.; Johnson, Anthony E.
Publication:U.S. Army Medical Department Journal
Article Type:Report
Geographic Code:1USA
Date:Jan 1, 2016
Words:3168
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