Radiographic features of multifocal endosteal thickening of the femur in patients on long-term bisphosphonate therapy

To describe the characteristics of multifocal endosteal thickening in patients on bisphosphonate therapy. A retrospective study of 68 patients with atypical femoral fractures (as defined by ASBMR) whilst on bisphosphonate therapy was performed. Femoral radiographs were assessed for: focal endosteal thickening, number of lesions, lesion location, femoral bowing, periosteal beak and black line. Medical records were reviewed to obtain relevant clinical data. Forty-eight lesions with multifocal endosteal thickening were detected in seven patients (2 unilateral, 5 bilateral), affecting 11.8 % of femora. Location was mainly diaphyseal (95.8 %), upper (10.4 %), middle (58.3 %) and lower femur (31.3 %), involving the lateral (85.4 %), anterior (6.3 %), anterolateral (2.1 %) and posterior cortices (6.3 %). Femoral bowing was present in 85.7 %. Associated findings of a periosteal beak and/or a black line, seen in 14.6 %, were associated with increased fracture risk (100.0 % sensitivity, 93.2 % specificity). Multifocal endosteal thickening is a new finding seen in patients with low bone mineral density on bisphosphonate therapy. They are rare, frequently bilateral, predominantly diaphyseal in location involving the lateral cortex and often associated with bowing. Caution is advised when seen in association with periosteal beak and/or black line because of a high rate of progression to complete fracture.