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affected the interface stresses calculated. However, the results presented here clearlydemonstrate increasing tensile and shear stresses in substantial parts of the femoral implantcementbeneath the anterior flange during deep knee flexion. Based on the interface strengthexperiments the anterior interfacial stress-state calculated by the FE knee model leads to localinterface debonding during deep knee flexion, which increases the risk of femoral loosening.Proper anterior fixation of the femoral component is essential to reduce the risk of femoralloosening for high-flexion TKA.References[1] Han et al., J Bone Joint Surg Br, 89: 1457-61, 2007.[2] Dahlkvist et al., Eng Med, 11: 69-76, 1982.[3] Zelle et al., J Biomech, 42: 587-93, 2009.Saturday, October 9, 2010, 10:30-11:05Session B18: Pot Pourri!Bisphosphonate-Associated Subtrochanteric Stress Fractures: An EmergingEpidemic*William Ward - Wake Forest- Baptist Med Ctr - Winston-Salem, USAChristina J. Carter - Wake Forest University Health Sciences - Winston Salem, USA*Email: wgward@wfubmc.eduThe senior author has treated a series of patients with subtrochanteric and diaphyseal femoralstress fractures associated with long-term alendronate or other bisphosphonate usage. Severalpatients completely fractured their femurs prior to referral. Most patients had consulted otherphysicians and were referred for presumed neoplasms. All patients had been diagnosed withosteoporosis and had been treated with bisphosphonates. Their plane radiographs revealedabnormalities that are pathognomonic of bisphosphonate-associated stress fractures. However,due to the subtle nature of these new unfamiliar abnormalities, most were unrecognized as suchby clinicians (including experienced ISTA member hip surgeons) and radiologists. This series ispresented to illustrate this pattern of impending fracture.The authors have reviewed and will present a series (n=17) of femoral stress fractures inbisphosphonate-treated patients to illustrate the clinical and radiographic pattern of these stressfractures, and review their treatment.The most common lesion is a subtrochanteric lateral cortical thickening that in actuality is ahorizontal plane “dreaded black line” of a stress fracture with surrounding proximal and distalcortical thickening of the endosteal and periosteal bone. The stress fracture line is obscuredunless a near-perfect radiographic projection is obtained. The lesion is best seen with CTscans. MRI scans reveal the stress fracture lines with surrounding edema (Fig 1), which may befile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]