Displacement of a femoral neck fracture disrupts the blood supply of the femoral head. This leads to high rates of avascular necrosis (AVN), a condition in which a portion of the femoral head bone dies and collapses if attempts are made to realign and fix the fracture. Instead of realigning/fixing the fracture, the femoral head needs to be replaced by a hip prosthesis. Surgical options are a hemiarthroplasty and a total hip arthroplasty. In a hemiarthroplasty, a stem is placed into the proximal femur and a new ball is placed on the end of the stem. The acetabular articular cartilage is left in place and rubs against the metal femoral head of the hemiarthroplasty prosthesis. In a total hip arthroplasty, the articular cartilage of the acetabulum is removed and replaced by a cup, in addition to the femoral component that is placed in a hemiarthroplasty. The surgeon has a choice of different materials in a total hip arthroplasty to form the new acetabular bearing surface including polyethylene, ceramic, and metal. All of these materials provide better resistance to wear over time than articular cartilage.
The pressure of the metal femoral head on acetabular articular cartilage over time will lead to progressive degeneration of the acetabular side of the joint, increased pain, and decreased patient satisfaction. An elderly patient who has a displaced femoral neck fracture but whose ambulation is limited due to being walker-dependent can do well with just a hemiarthroplasty because of their age and activity level. Conversely, an active, healthier, younger patient who has a displaced femoral neck fracture will do better with a total hip arthroplasty due to the higher level of pain and increased acetabular cartilage breakdown if a hemiarthroplasty is placed. In multiple studies, hemiarthroplasty has been shown to have lower patient satisfaction scores and higher reoperation rates than total hip arthroplasty.
If a joint replacement wears out or loosens over time, a revision arthroplasty needs to be performed in which the old components are removed and new ones placed. Each time a component is removed from the surrounding bone, some of that bone is removed as well leaving less structural support for any new components that are implanted.
Displaced femoral neck fracture medical expert witness specialties include orthopaedic surgery and emergency medicine.