Working Diagnosis:
Incomplete compression fracture of the proximal right femur.

Treatment:
The patient was made non-weight bearing on crutches and progressed to full weight bearing, pain free over a period of 10 weeks. Throughout her injury the patient continued to do hip and core rehabilitation with her trainer. She gradually progressed from bike and elliptical to Alter G running as tolerated.

Outcome:
Repeat X-ray one month after diagnosis showed early callus, with another X-ray two months later revealing consolidation of the fracture site. Three months after diagnosis the patient is pain free on full weight bearing and can run at 90% on the Alter G. The athlete will return to activity gradually as she continues to progress to full running and then onto soccer-related drills, such as cutting and kicking. She is expected to make a full return to her sport.

Author's Comments:
Femoral neck stress injuries can be classified based on injury severity or by location. Fredericson et al1 proposed a grading scale based on MRI findings to stratify the severity of stress injuries from Grade 1 to 4. They concluded that periosteal edema is likely the initial injury, seen in Grade 1, and if activity continues, will progress to a more serious injury characterized by bone marrow edema and ultimately cortical breakdown, resulting in a fracture, which is seen in Grade 41.

Femoral neck stress injuries can also be classified by location. If the stress reaction develops on the superior aspect of the femoral neck it is classified as the tension side, or Type I, while injuries on the inferior aspect are classified as the compression side, or Type II. Type III stress fractures occur when the femur is displaced. Conservative management can be used for incomplete compression stress injuries, as seen in our patient, while complete compression and tension femoral neck stress injuries require surgical fixation. Displaced femoral neck stress fractures require immediate reduction and surgical fixation2.

Time frame for returning to sport is dependent on the grade and location of the injury. Temporary discontinuation of weight-bearing activity is necessary to allow the bone to remodel and repair. Braces, crutches, or casting may be required in Grade 3 or 4 injuries to minimize weight-bearing activity1. Those with grade 1 injuries typically return to sport within 3 weeks, while those with grade 3 or 4 injuries can take up to five months4. Athletes should report being pain-free with full activity before returning to their sport. Return rates for incomplete compression injuries are as high as 100%, while return rates for displaced fractures are only 33%2. This emphasizes the importance of early diagnosis to allow for timely intervention.

Delayed diagnosis leads to a variety of consequences from worsening stress reaction, muscle atrophy, aerobic deconditioning, and psychological distress5. Delays in treatment increase the risks of chronic pain, femoral non-union, avascular necrosis, and long-term functional impairments3. It is essential that we have a high degree of suspicion for these types of injuries in athletes who present with persistent pain despite their atypical presentation.

Editor's Comments:
Femoral neck stress fractures present as a vague pain with insidious onset. Due to risk of progression of the injury, early diagnosis is important. Plain radiographs may initially be normal, so advanced imaging may be needed. Relative energy deficiency should be considered and addressed to promote overall bone health and prevent further injuries. While the athlete may not present with an overt eating disorder, there may be insufficient energy intake to offset a high energy expenditure.

References:
1. Fredericson M, Bergman AG, Hoffman KL, Dillingham MS. Tibial Stress Reaction in Runners: Correlation of Clinical Symptoms and Scintography with a New Magnetic Resonance Imaging Grading System. American Journal of Sports Medicine. 1995; 23 (4): 472-481. Available at: https://www.ncbi.nlm.nih.gov/pubmed/7573660
2. Robertson GA, Wood AM. Femoral Neck Stress Fractures in Sport: A Current Concepts Review. Sports Medicine International Open. 2017; 1: E58-E68. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6226070/
3. Cichy B, Roche SJ, Wozniak A. Atypical femoral neck stress fracture in a marathon runner: a case report and literature review. Irish Journal of Medical Science. 2012; 181: 427-429.
4. Kijowski R, Choi J, Shinki K, Del Rio AM, De Smet A. Validation of MRI Classification System for Tibial Stress Injuries. American Journal of Roentgenology. 2012; 198: 878-884.
5. Fukushima Y, Ray J, Kraus E, Syrop IP, Fredericson M. A Review and Proposed Rationale for the use of Ultrasonography as a Diagnostic Modality in the Identification of Bone Stress Injuries. J Ultrasound Med. 2018; 37: 2297-2307. Available at: https://onlinelibrary.wiley.com/doi/epdf/10.1002/jum.14588

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