Atypical fractures do not have a thicker cortex.

Abstract

An association between atypical fractures and general cortical thickness of the femoral shaft is often suggested in the literature. Our radiographic measurements of 59 atypical and 218 ordinary fractures now exclude a difference larger than 10 % in mean femoral cortical thickness (sum of lateral and medial) with 95 % confidence. An increased general cortical thickness in patients with fatigue fracture of the femoral shaft (atypical fractures) is commonly suggested. However, there are scarce data to support this. In a published nationwide Swedish study, we identified by radiographic review 59 women with an atypical fracture during 2008. The femoral cortical thickness index (thickness/femoral diameter) of these women was now compared with the 218 ordinary fractures that occurred in the same region of the femur in a case-control design. The cortical thickness index 5 cm below the lesser trochanter was the primary variable. Patients with atypical fractures were younger. Without correction for age, they had a thicker cortex (i.e., higher index). However, the difference in cortical thickness disappeared after age correction. The 95 % CI excludes a group mean difference exceeding 10 % of total mean thickness. Similarly, there was no significant difference in cortical thickness between patients with or without bisphosphonate treatment or between the ipsi- and contralateral femurs in patients with an atypical fracture. The concept of a generally increased cortical thickness in patients with atypical fractures should be reconsidered.