The effect of long-term alendronate treatment on cortical thickness of the proximal femur

Abstract

Background: One of the radiographic hallmarks in patients with atypical femoral insufficiency fractures after prolonged bisphosphonate treatment is generalized cortical hypertrophy. Whether cortical thickening in the proximal femur is caused by long-term alendronate therapy, however, remains unknown.

Questions/purposes: We asked whether long-term alendronate use of 5 years or more results in progressive thickening of the subtrochanteric femoral cortices.

Patients and methods: We retrospectively evaluated changes in cortical thickness and cortical thickness ratio (ratio of cortical to femoral shaft diameter) at the subtrochanteric region of the proximal femur in baseline and latest hip dual-energy xray absorptiometry (DXA) scans of 131 patients. The mean followup was 7.3 years. Patients were divided into two groups: control (no history of alendronate, 45 patients) and alendronate (history of alendronate ≥ 5 years, 86 patients). We determined cortical thickness and cortical thickness ratio at 3.5 and 4.0 cm below the tip of the greater trochanter, representing the subtrochanteric region.

Results: After a minimum of 5 years followup, mean cortical thickness decreased approximately 3% in the alendronate and control groups. The cortical thickness at the subtrochanteric femoral region changed less than 1 mm in greater than 90% of the patients with long-term alendronate treatment. We observed no differences in mean changes of cortical thickness and percent changes of cortical thickness between the two groups.

Conclusions: Long-term alendronate treatment did not appear to cause thickened femoral cortices within the detection limits of our method. This finding contrasts with the notion that long-term alendronate treatment leads to generalized cortical thickening.

Fig. 1

A DXA scan that was uploaded to a PACS is shown. Measurements were obtained at 3.5 cm and 4.0 cm from the tip of the greater trochanter. Cortical thickness was calculated by subtracting the medullary diameter from the femoral shaft diameter (AD − BC). The cortical thickness ratio was defined as the percentage of the cortical thickness to its femoral shaft diameter [(AD − BC)/AD].

Fig. 2

A radiograph of a patient with an atypical subtrochanteric femoral insufficiency fracture is shown. The asterisks indicate cortical hypertrophy of the femoral cortices at the proximal and distal fragments.