Background: Displaced fatigue fractures of the femoral neck are uncommon, but they can lead to substantial patient morbidity. This study was performed to examine the incidence, long-term consequences, radiographic findings, risk factors, and complications associated with this fracture.

Methods: Between 1975 and 1994, twenty-one military recruits sustained a displaced fatigue fracture of the femoral neck. Nineteen patients were followed for an average of eighteen years. Data regarding the population at risk, hospital records, initial and follow-up radiographs, and physical findings were analyzed. The impact of instructions from the Finnish Defense Forces, Department of Medical Services, provided in 1986 for prevention of femoral neck fatigue fractures was assessed.

Results: At our institution, the incidence of displaced fatigue fractures of the femoral neck was 5.3/100,000 service years from 1975 to 1986, prior to the introduction of the prevention regimen in 1986, and it was 2.3/100,000 service years (95% confidence interval, 0.11 to 1.31) from 1987 to 1994. The rate of Garden type-IV fractures decreased from 3.8 to 0/100,000 service years (95% confidence interval, 0 to 0.66) between the first and second time-periods. The detection of nondisplaced symptomatic fatigue fractures of the femoral neck increased from 15.5 to 53.2/100,000 service years (95% confidence interval, 2.27 to 5.21) between the two time-periods. Eighteen of the nineteen patients had had prodromal symptoms prior to the fracture displacement. Following fracture treatment, six patients had delayed union or nonunion of the fracture. Osteonecrosis of the femoral head developed in six patients and was significantly associated (p = 0.001) with shortening of the femoral neck. Severe osteoarthritis developed in eight patients.

Conclusions: A displaced fatigue fracture of the femoral neck leads to long-term morbidity in a high percentage of patients. Most patients have prodromal symptoms, which provide an opportunity to prevent fracture displacement. Our results indicate that, in a military setting, an educational program can diminish the incidence of fatigue fracture displacement by increasing the awareness of these fractures and their prodromal symptoms and by facilitating diagnosis in the early stages before displacement occurs.

Level of Evidence: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.