A novel diagnostic sign of hip fracture mechanism in ground level falls: two case reports and review of the literature

INTRODUCTION Most elderly hip fractures are the result of a ground level fall. Defining high risk falls and fracture mechanisms are important to develop successful hip fracture prevention programs. This case series presents a previously unreported diagnostic sign and for the first time documents a hip fracture mechanism for a knee impact injury from a ground level fall in two elderly patients. CASE PRESENTATION Case 1 was a 65-year-old Caucasian woman who fell forward with initial contact to her left knee, sustaining an impacted femoral neck fracture of her ipsilateral left hip. Case 2 was a 92-year-old Caucasian woman who fell bending forward, impacting her left knee and sustaining a comminuted intertrochanteric fracture of her ipsilateral left hip. The fractures occurred as a result of unprotected ground level falls in a forward direction with initial impact to the knee. The knee contusions were located near Gerdy's tubercle and appear characteristic of a direct impact injury. CONCLUSION The physical finding of a small localized site of impact and/or contusion in the anterior aspect of the knee in both of these patients with radiographic evidence of an ipsilateral hip fracture would strongly suggest that a knee impact injury can transmit enough energy to the proximal femur by axial loading to result in the hip fracture. The physical finding described is a reliable indicator of this hip fracture mechanism.