Working Diagnosis:
Nondisplaced stress fracture of the proximal fibular shaft.

Treatment:
Patient was made non-weight bearing with crutches for 2 weeks. The importance of smoking cessation was discussed and encouraged. After period of non-weight bearing status she was instructed to start a 6 week course of physical therapy for altered gait mechanics.

Outcome:
She was able to return to regular activities.

Author's Comments:
Proximal fibular stress fractures are exceedingly rare, with cases documented only in athletes and military recruits involved in repetitive squat-jumping exercises. The proposed mechanism of injury involves a combination of compression loading, biceps femoris contraction, and shear fatigue from increased shearing force placed on the proximal fibula. Our patient, neither military recruit nor athlete, did have other risk factors for bone stress injury: female gender, Caucasian ethnicity, and cigarette smoking. An overload mechanism has also been thought to play a role and our patient did recall, upon further questioning, that 6 months prior to presentation she purchased a trampoline. She and her son had been jumping on it for approximately 3-4 months prior to presentation.
(1-6)

Editor's Comments:
Bone stress injuries are overuse injuries that occur due to repetitive stress. While they are typically thought of in relation to distance running, overuse injuries and the female athlete triad, there are additional risk factors that shouldn't be overlooked. Two important non-modifiable risk factors are female sex and race - with non-Hispanic whites having the highest risk of stress fracture (7). There are many modifiable risk factors for bone stress injury including repetitive activities, decreased physical physical, worn footwear, poor running biomechanics, decreased bone density, low BMI, smoking, and inadequate Vit D and calcium consumption (7). For this particular patient, it is possible decreased physical fitness in combination with the repetitive stress of trampoline jumping with altered biomechanics may have contributed to her bone stress injury.

Hong et al published a retrospective cohort analysis of Korean military recruits who presented with proximal leg pain aggravated by squatting (2). In their study of 12 recruits, the proximal-middle 1/3 of the fibula was the most common site of injury, in 10 out of the 12 recruits. All stress fractures were diagnosed with plain radiographs and responded well to conservative treatment of bed rest/immobilization, followed by graded return to activity over a period of approximately 4 weeks. While they did not comment on the significance, 6 of the 12 recruits were smokers. They postulated that the shearing forces placed on the proximal fibula with walking and jumping from a squatting position contributed to the development of these stress fractures. The exact mechanism for development of proximal fibula stress fractures remains poorly understood.

Little exists in the adult literature with regards to trampoline related injuries. In the pediatric literature, Kim et al noted that the knee/lower leg was the most frequently injured site in trampoline related injuries (8). They proposed that a varus shearing force in addition to compressive forces contributes to the pattern of lower extremity fractures noted in this pediatric population.

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