form the knee. Although this joint has three degrees of freedom, it is still stable due to the interaction of ligaments and cartilage. The labrum lines the circumference of the acetabulum to provide stability and shock absorption. Articular cartilage covers the concave area of acetabulum, providing more stability and shock absorption. Surrounding the entire joint itself is a capsule secured by the tendon of the psoas muscle and three ligaments. The iliofemoral, or Y, ligament is located anteriorly and serves to prevent hip hyperextension. The pubofemoral ligament is located anteriorly just underneath the iliofemoral ligament and serves primarily to resist abduction, extension, and some external rotation. Finally the ischiofemoral ligament on the posterior side of the capsule resists extension, adduction, and internal rotation. When considering the biomechanics of hip fractures, it is important to examine the mechanical loads the hip experiences during low energy falls. Biomechanics The hip joint is unique in that it experiences combined mechanical loads. An axial load along the shaft of the femur results in compressive stress. Bending load at the neck of the femur causes tensile stress along the upper part of the neck and compressive stress along the lower part of the neck. While osteoarthritis and osteoporosis are associated with bone fracture as we age, these diseases are not the cause of the fracture alone. Low energy falls from standing are responsible for the majority of fractures in the elderly, but fall direction is also a key factor. Elderly tend to fall to the side as instead of forward, and the lateral hip and strikes the ground first. During a sideways fall, the chances of hip fracture see a 15-fold and 12-fold increase in elderly males and females, respectively. Neurological factors Elderly individuals are also predisposed to hip fractures due to many factors that can compromise proprioception and balance, including medications, vertigo, stroke, and peripheral neuropathy. Diagnosis Physical examination Displaced fractures of the trochanter or femoral neck will classically cause external rotation and shortening of the leg when the patient is laying supine. Imaging Typically, radiographs are taken of the hip from the front (AP view), and side (lateral view). Frog leg views are to be avoided, as they may cause severe pain and further displace the fracture. In situations where a hip fracture is suspected but not obvious on x-ray, an MRI is the next test of choice. If an MRI is not