Perilesional Sclerosis Associated with Dreaded Black Lines in Incomplete Atypical Femoral Fractures after Antiresorptive Therapy

Introduction: This study aimed to describe the demographic, clinical, and radiological features of sclerosis adjacent to 'dreaded black lines' or radiolucent fracture lines (RFLs) in atypical femoral fractures (AFFs) associated with antiresorptive therapy.Methods: We reviewed radiographs acquired in our institution in Singapore between 2004 and 2020 from 100 femurs with AFFs, assessing the appearance and location of lesions, and the presence of endosteal or periosteal thickening.Demographic data, type and duration of antiresorptive therapy, and progression to complete fracture or need for prophylactic stabilisation were analysed.The cohort was subdivided into three groups: Group 1A included AFFs with an RFL and perilesional sclerosis; Group 1B included AFFs with an RFL but without perilesional sclerosis; and Group 2 included AFFs without an RFL.Results: A total of 17 sclerotic RFLs were identified.The majority were non-linear in appearance.Most were located in the subtrochanteric (41.2%) and proximal diaphyseal regions (35.3%), and all were associated with endosteal or periosteal thickening.All sclerotic RFLs occurred in patients with a mean age of 69 years.Sixteen cases (94.1%) had a history of bisphosphonate use, while one case had received denosumab.The mean duration of antiresorptive therapy was 66 months.Three cases (17.6%) progressed to complete fractures and six (35.3%) required prophylactic fixation.No significant differences were observed among the three groups in terms of demographics, antiresorptive therapy, or surgical intervention.Conclusion: We describe perilesional sclerosis as a previously unrecognised radiological feature adjacent to RFLs in AFFs, with distinctive characteristics.It occurs in approximately one-third of RFLs.Further research is needed to elucidate its pathophysiological and prognostic implications.