Home Study Program: primary total hip arthroplasty

AORN Journal,  Dec, 2003  by Jill Jasperson Branson,  Wayne M. Goldstein

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Since 2001, 17 manufacturers have produced and marketed 111 different cemented and cementless (ie, porous) femoral components and 56 different acetabular components for use in primary total hip arthroplasty (THA) procedures. (1) This myriad of implant systems poses a challenge for perioperative nurses working with numerous surgeons who perform THA. Surgeons select a specific implant system based on an implant's design characteristics and historical performance, each patient's pathology, and his or her training and experience. Some hospitals choose implants for surgeons to use in their facility based on standardization efforts. (2)

Regardless of the chosen system, a primary THA replaces the proximal femur, including the femoral head, and resurfaces the acetabulum, creating a new ball-and-socket joint. Surgeons must have a thorough knowledge and understanding of hip biomechanics to successfully perform arthroplasty procedures, manage problems, select appropriate components, and counsel patients regarding their activity levels. (3 (p300))

HIP ANATOMY AND MOTION

The hip joint contains the articulating surfaces of the spheroid femoral head and acetabulum cavity (Figure 1). These smooth cartilage surfaces absorb stress and allow the femoral head to glide easily in the acetabulum. The spherical head has approximately 40% coverage in the acetabulum in any position. It is one of the body's largest weight-bearing joints. The articulation in this joint allows a person to walk, squat, and turn without pain. Large muscles and tendons power the hip and allow movement. (4)

[FIGURE 1 OMITTED]

A normal femur extends and abducts 20[degrees] to 30[degrees], flexes 135[degrees], and has a combined arc rotation of 90[degrees]. (4) This joint must withstand many years of cyclic loading with as many as one million cycles per year equal to at least three to five times the body's weight. Cyclic loading forces act between the ball and socket with each step. Stepping down a curb or getting out of a chair may subject the hip to overloads of as much as 10 to 12 times the body's weight. (4)

Defects of the hip's cartilage can be caused by osteoarthritis, rheumatoid arthritis, avascular necrosis, and trauma. Cysts and bone pitting may occur at these defect sites, and reactive bone spurs may form as the body attempts to compensate for the damaged surface. With time, the cartilage will crack or wear away and cause pain as the ball and socket rub together in a bone-on-bone fashion. Bone spurs impinging on themselves and the thickened and inflamed hip capsule add to the patient's discomfort. Anterior-posterior (AP) and lateral x-rays of the hip of a patient who has these problems demonstrate a narrowed joint space, bone spurs, and deformities in the diseased hip. (4)

HISTORICAL PERSPECTIVE

During the early 1900s in the United States and Europe, surgeons used various tissues and inorganic materials as layers between diseased joint surfaces in the hip. After contouring deformed or ankylosed hip surfaces, fascia lata grafts, soft tissue, and even gold foil were used to provide a resurfacing layer in the joint in an effort to restore motion. Unpredictable results using these methods led Marius Smith-Peterson, MD, to perform a "mold arthroplasty" in 1923, in which he placed a mold between exposed surfaces of the femoral head and acetabulum. The original material for the mold was made from glass; over time this evolved to break-resistant glassware, phenolic resin, and cobalt-chrome-casting alloy in 1937. Austin Moore, MD, collaborated with Harold Bohlman, MD, in 1940 to treat a patient with severe hip disease and deformity by designing and implanting the first femoral prosthesis using chrome cobalt casting alloy.

Chrome cobalt casting alloy proved to be more durable than its fragile predecessors and was modified further by Smith-Peterson and Otto E. Aufranc, MD. (5)

A femoral head prosthesis, improved component materials, manufacturing capabilities, improved understanding of hip mechanics, and realization of the need to resurface the acetabulum helped THA evolve further. English orthopedic surgeon, Sir John Charnley, made several contributions to the evolution of THA, including development of a stainless steel femoral head to be used with a polyethylene acetabular cup. He termed this low friction arthroplasty. This design remains the standard for most systems to this day. Sir Charnley introduced the use of bone cement (ie, polymethylmethacrylate) as a grout to fix THA components. His techniques revolutionized the THA procedure, and by 1970, several surgeons in the United States reported pain relief and improved function for patients after using his technique. (5)

Cemented components that loosened over time led researchers to improve cement techniques with vacuum mixing, retrograde filling of the femoral canal, and pressurization. Porous coatings on the femoral stem and acetabular cup were developed in an attempt to create bone ingrowth and biological fixation. The combination of metal and polyethylene articulating in the hip has become the mainstay of THA. As improved fixation allowed implants to remain implanted longer, it became apparent that a method to reduce polyethylene wear, which results in osteolysis, was needed. (5) Osteolysis is a common complication in THA and is the most common cause of implant failure. It is an inflammatory reaction to polyethylene particles that are formed during wear as the metal surface rubs on the polyethylene surface during motion of the artificial joint. (6)