Femoral neck stress fracture in an adolescent boy

Clinical History

A 13-year-old football playing adolescent boy presented to the Emergency Department with a 3-week history of right hip pain, which was increasing in intensity. No history of injury prior to the onset of symptoms was elicited. The pain was exacerbated both by activity and prolonged periods of sitting down.

Imaging Findings

A pelvic radiograph was performed. The image (Figure 1) showed a sclerotic line at the inferior margin of the right femoral neck in keeping with a stress fracture.

A pelvic MR exam was requested to confirm or refute the radiological diagnosis. A linear fracture line was seen extending from the inferior margin of the right femoral neck (low signal on both T1 and STIR), which did not extend to the lateral cortex (Figures 2, 3). Diffuse bone marrow oedema was also seen centred around this area (high signal on STIR). The study confirmed a stress fracture of the right femoral neck.

Our patient was advised to refrain from his usual sporting activities for a period of 6 weeks and permitted to weight bear with crutches. After 6 weeks his symptoms had resolved and a plain radiograph showed evidence of fracture healing (Figure 4).

Discussion

Stress fractures were first described in relation to the metatarsals in 1855 by Breithaupt, who documented foot pain in military recruits [1]. Stress fractures fall into two main categories; fatigue fractures (which occur with abnormal loading of normal bone), and insufficiency fractures (which occur with normal loading of abnormal bone) [2].
Stress fractures are more typically found in older children between the ages of 10-15 years [3], and have become increasingly common with the increase of repetitive training for sports. Stress fractures result from increased tensile forces on bone in the face of muscle fatigue, compounded by the fact that muscle strength develops faster than bone strength during training, leading to an imbalance of biomechanical forces [4].
Common sites for stress fractures in children include the tibia (greater than 50% of cases), the metatarsals and fibulae [5]. Femoral stress fractures make up 3% of stress fractures in children [4], usually affecting the inferior surface of the neck, the shaft or the distal metaphysis, particularly in adolescents [6]. Femoral neck stress fractures often have an insidious onset of symptoms, with worsening anterior hip pain on exertion and restricted movement. Such a vague presentation requires a high degree of suspicion, with one study quoting a delay of up to 14 weeks prior to diagnosis in this anatomical location [7].
Radiographs are usually performed in the first instance, as whilst they have low sensitivity (up to 50% of cases will never develop radiographic abnormalities) [5], they can rule out other important pathologies such as neoplasia or osteomyelitis. Features which may be identified on plain radiography in cases of stress fracture include; focal cortical lucencies, endosteal thickening, sclerosis of trabecular bone and periosteal reaction.
The gold standard for imaging for a suspected stress fracture is MRI, with a sensitivity and specificity approaching 100% [3, 5]. Bone marrow oedema results in low signal intensity on T1-weighted images, and high signal intensity on STIR and T2-weighted images. A fracture line appears as a well-defined, linear low signal intensity on STIR, T1- and T2-weighted images [3, 5, 6].
Treatment of femoral neck stress fractures often depends on the site, with compression-sided (inferior) stress fractures, as in our case, often managed conservatively. Tension-sided (superior) stress fractures warrant urgent referral to an orthopaedic team for consideration of operative intervention [7].
Our patient was advised to refrain from his usual sporting activities for a period of 6 weeks. Repeat radiograph showed evidence of fracture healing [Figure 4].

Differential Diagnosis List

Final Diagnosis

Right femoral neck stress fracture.

URL:	https://www.eurorad.org/case/13073
DOI:	10.1594/EURORAD/CASE.13073
ISSN:	1563-4086