Excerpt from Fractures, Hip

Synonyms, Key Words, and Related Terms: hip fracture, fracture of the hip, femoral head fractures, femoral neck fractures, intertrochanteric fractures, trochanteric fractures, subtrochanteric fractures, hip joint, iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament, avascular necrosis, intracapsular fracture, extracapsular fracture, anterior dislocation, posterior dislocation, single fragment fracture, comminuted fracture, stress fracture, incomplete fracture, impacted fracture, partially displaced fracture, completely displaced fracture, single fracture lines, multiple fracture lines, nondisplaced fracture

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Background: Fractures of the hip are relatively common in adults and often lead to devastating consequences. Disability frequently results from persistent pain and limited physical mobility. Hip fractures are associated with substantial morbidity and mortality; approximately 15-20% of patients die within 1 year of fracture.

Most hip fractures occur in elderly individuals as a result of minimal trauma, such as a fall from standing height. In young, healthy patients these fractures usually result from high-velocity injuries, such as motor vehicle collisions or falls from significant heights. Despite comparable fracture locations, the differences in low- and high-velocity injuries in older versus younger patients outweigh their similarities. High-velocity injuries are more difficult to treat and are associated with more complications than minor trauma injuries.

Pathophysiology:

Skeletal anatomy

The hip joint is a large multiaxial ball-and-socket synovial joint, enclosed by a thick articular capsule. The hip joint is designed for stability and a wide range of movement. Next to the shoulder, it is the most moveable of all joints. During standing, the entire weight of the upper body is transmitted to the heads and necks of the femurs. The round head of the femur articulates with the cuplike acetabulum. The depth of the acetabulum is increased by the reinforcing fibrocartilaginous labrum, which “grasps” the femoral head, covering more than half of it. Articular cartilage covers the entire head of the femur, except for the pit (fovea) for the ligament of the femoral head.

The strong, loose fibrous capsule permits free movement of the hip joint, attaching proximally to the acetabulum and transverse acetabular ligament. The fibrous capsule attaches distally to the neck of the femur only anteriorly at the intertrochanteric line and root of the greater trochanter. Posteriorly, the fibrous capsule crosses to the neck proximal to the intertrochanteric crest without attaching to it. The fibrous capsule thickens to form 3 ligaments of the hip joint: the Y-shaped iliofemoral ligament (of Bigelow), the pubofemoral ligament, and the ischiofemoral ligament.

The hip joint is further supported by the femur and the muscles that cross the joint; this bone and these muscles are the largest and most powerful in the human body. The anatomy of the femur is shown in Image 1. The length, angle, and narrow circumference of the femoral neck permit substantial range of motion at the hip but also subject the femoral neck to incredible shearing forces. A fracture results when these forces exceed the strength of the bone. The intertrochanteric line is an oblique line that connects the greater and lesser trochanters, dividing the femoral neck from the shaft. Hip fractures involve fracture of any aspect of the proximal femur, from the head to the first 4-5 cm of the subtrochanteric area.

Vascular supply

The vascular supply to the proximal femur is tenuous and provided largely by two sources.

Branches of the medial and lateral circumflex femoral arteries, usually branches of the deep femoral artery, ascend on the posterior aspect of the femoral neck in the retinacula (reflections of the capsule along the neck of the femur toward the head). The branches of the medial and lateral circumflex arteries perforate the bone just distal to the head of the femur where they anastomose with branches from the foveal artery and with medullary branches located within the shaft of the femur.

The ligament of the head of the femur usually contains the artery of the ligament of the head of the femur (foveal artery), a branch of the obturator artery. The foveal artery enters the head of the femur only when the center of the ossification has extended to the pit (fovea) for the ligament of the head, around age 11-13 years. This anastomosis persists e .....