Surgery is done with the patient either lying down (supine) or on his or her side (lateral decubitus). Several surgical approaches can be made—anterior (from the front), posterior (from the back) or approaches closer to the side—anterolateral, posterolateral.
An incision is made through the skin and the fat layer beneath the skin. Depending on the approach, the muscles either in front or back of the hip are separated so that an interval or plane can be created that will lead to the joint. Sometimes some of the smaller muscles need to be divided in order to reach the joint. If surgery is by a posterior approach the sciatic nerve is identified so that it may be protected during the procedure.
The lining of the joint, the capsule, is exposed and an incision is made. At this point, joint fluid or synovial fluid usually extrudes from the joint. When the capsule is divided the hip joint can be seen. The femoral head can be visualized within the socket. The leg is then rotated so that the head of the femur is dislocated or comes out of the socket.
If surgery is being done for arthritis the damage to the articular cartilage, the surface of the joint, is evident. The neck of the femur below the femoral head is exposed. A saw is then used to cut the neck of the femur so that the femoral head can be removed.
Some-times the neck of the femur is cut when the femoral head is still in the acetabulum. The head is then removed from the socket after the neck is cut. Once the femoral head has been removed, the remaining part of the femoral neck can be retracted so that the joint surface of the acetabulum is exposed. Arthritic changes, if present, are visible in the socket as well.
The soft tissue lining around the rim of the socket, the labrum, is removed. The socket is then prepared to receive the acetabular component of the hip replacement. The remaining joint cartilage is removed and the acetabulum is prepared by round or spherical power driven reamers. The reamers remove some of the bone beneath the surface to create room for the implant.
Reaming is begun with a small diameter reamer. The reamers are then increased in size by one or two millimeters until there is a good tight fit of the reamer in the socket. An acetabular component may then be placed that is the same size as the reamer or one to two millimeters larger. This will insure that the component fits tightly.
The outer metal shell of the acetabular component can then be driven or impacted into place in the prepared socket. If there is a tight fit it may be left alone. If the component does not feel completely secure, one or two screws may be inserted through holes in the metal shell into the bone of the pelvis.
Once the metal shell is impacted and fixed in the bone, the polyethylene liner that fits inside the metal shell is placed. If the component is to be cemented, then the cement is mixed and pressed into the prepared socket. The component is then positioned inside the cement. Pressure is then maintained on the component until the cement is dry so that the position does not change.
The acetabular side of the joint replacement is complete. The surgeon can now begin to work on the femur. The neck of the femur is then brought back into the surgical field and retractors are positioned.
A surgical drill or an awl is then used to identify the canal of the femur which will receive the stem of the femoral component. Once the canal has been opened it may be widened with reamers in 1/2 to one millimeter increments. A special orthopaedic chisel called a rasp or broach is then used to carve a space in the area below the femoral neck called the metaphysis.
The rasp has the same shape as the actual femoral component and can be used as a trial component before the permanent component is implanted. Next, a trial femoral head and neck component is put on top of the rasp. The diameter of the head matches the diameter of the polyethylene liner of the socket. The neck lengths come in different sizes so that the surgeon can restore the joint to its proper height.
Once the trial components are positioned, the ball is put into the socket and the joint is tested. This is called a trial reduction. The surgeon moves the hip in several directions to make sure the joint stays in place and the ball does not come out of the socket. He also checks to see if the joint is too loose or too tight and to make sure that the length of both legs is equal. If there is a problem, he can make adjustments.
The trial femoral head and the rasp are removed. The permanent stem is driven into place or cemented in the femoral canal. The head and neck component is seated on the stem.
At this point, the field is checked to make sure that no loose pieces of bone or tissue are sitting in the socket. The hip joint is then permanently put into place or reduced. It is once more tested through a range of motion. The wound is washed out or irrigated with a saline solution and is checked to make sure there is no active bleeding.
A drainage tube may be placed deep in the wound and brought through a separate small skin puncture away from the incision. The tube is connected to an external suction drain and is removed the day after surgery. The deep muscle layers in the wound are closed together with sutures. The layer of fat or fascia beneath the skin is also closed. The skin edges are brought together either with sutures or small metal staples.
At the end of the procedure a dressing is applied to the wound. The patient is awakened if he or she has had general anesthesia. He is then transferred to a bed or stretcher.
A hip abduction pillow may be placed between the legs to prevent them from crossing and causing a dislocation. A skin traction boot may also be applied for this purpose. When the patient is safely awakened from anesthesia he is taken to the recovery room area on the bed or stretcher.