bisphosphonate ( bp ) is a potent anti - resorptive agent and was proven to be effective in prevention and treatment of osteoporosis through many randomized prospective studies . reported nonunion after low - energy injury among patients who took bp for several years for treatment of osteoporosis . bone biopsy revealed lack of viable osteoblasts , osteocytes , and osteoclasts in the specimen . fractures were caused by minor injuries and were associated with periosteal callus at the lateral femoral cortex . as the number of reports of this type of fracture increased , the american society of bone and mineral research ( asbmr ) organized a task force team and reported the results on two occasions ( fig . however , in most of the cases , aff occurs in the patients who are taking or who took bp for several years for treatment of osteoporosis or other metabolic bone diseases . it is difficult to estimate the incidence of aff due to its low occurrence in bp users . the estimated incidence of aff is 5 to 100 per hundred thousand patient - years . it is time to declare that bp is the causative agent of aff although bp decreases the incidence of hip and vertebral fractures significantly . the incidence of aff increases significantly when the patient takes bp for 4 years or more than 4 years . prodromal symptoms such as dull pain and tenderness over the lateral aspect of the thigh are noted in 40% to 70% of the patients . it is recommended to check for prodromal symptoms if the patients are taking bp for more than 4 to 5 years . it is necessary to take a simple radiogram of the femur if aff is suspected . simple radiogram often reveals a beak or flare like periosteal and/or endosteal callus in the lateral femoral cortex . sometimes , the so - called ' dreaded black line ' can also be detected in the lateral cortex . if the simple radiogram appears looks normal even though the patient complains of prodromal symptoms , then bone scan or magnetic resonance imaging ( mri ) examination can identify tiny lesions in the lateral aspect of the femur . in korea , dual energy x - ray absorptiometry ( dxa ) examination of axial bone is performed every year to obtain reimbursement from national insurance . we may occasionally detect a tiny periosteal callus in the lateral aspect of the femoral cortex ( fig . 2 , 3 ) . bp should be stopped immediately after aff is diagnosed and calcium and vitamin d ( 1,000 to 2,000 iu ) should be administered . daily subcutaneous injection of recombinant human parathyroid hormone ( pth ; 1 - 34 ) is recommended if the patient can afford it . prophylactic femoral nailing is indicated when the dreaded black line is visible in the lateral femoral cortex , especially in the subtrochanteric area . however , excessive femoral bowing , which is often associated with aff , is an obstacle during femoral nailing . 4 ) delayed healing is reported in 28% of the cases , but the real incidence seems to be higher . in order to prevent delayed union or nonunion , restoration of correct anatomical alignment is recommended after intramedullary nailing . minor malreduction , which is acceptable in cases of ordinary fracture , occasionally causes nonunion and metal failure in aff . daily subcutaneous injection of recombinant human pth ( 1 - 34 ) is also recommended after surgical fixation . careful examination of the contralateral femur is recommended because of the high incidence of bilateral lesions .
bisphosphonate ( bp ) is a useful anti - resorptive agent which decreases the risk of osteoporotic fracture by about 50% . 
 however , recent evidences have shown its strong correlation with the occurrence of atypical femoral fracture ( aff ) . 
 the longer the patient takes bp , the higher the risk of aff . 
 also , the higher the drug adherence , the higher the risk of aff . 
 it is necessary to ask the patients who are taking bp for more than 3 years about the prodromal symptoms such as dull thigh pain . 
 simple radiography , bone scan , and magnetic resonance imaging ( mri ) are good tools for the diagnosis of aff . 
 the pre - fracture lesion depicted on the hip dual energy x - ray absorptiometry ( dxa ) images should not be missed . 
 bp should be stopped immediately after aff is diagnosed and calcium and vitamin d ( 1,000 to 2,000 iu ) should be administered . 
 the patient should be advised not to put full weight on the injured limb . 
 daily subcutaneous injection of recombinant human parathyroid hormone ( pth ; 1 - 34 ) is recommended if the patient can afford it . 
 prophylactic femoral nailing is indicated when the dreaded black line is visible in the lateral femoral cortex , especially in the subtrochanteric area .