Posterior Hip Replacement

Posterior hip replacement is the most common approach used for performing a total hip replacement. The approach is also known as southern or Moore’s approach is popular as it does not involve cutting of the abductor group of muscles.

The abductors help a person to walk without limping on taking a step. The approach also offers a good exposure of the thigh bone during the surgery as compared to the anterior approach.

Hip replacement is the most successful surgery in the entire history of medicine. Hip replacements today last for 20 years or even a lifetime. A total hip replacement may be performed for a number of reasons but arthritis of the hip remains the most common cause.

The arthritis of the hip may lead to painful movements about the hip joint during walking, sitting, driving, etc. A hip replacement surgery recreates the motion of the natural joint by replacing the diseased parts with prosthetic parts.

Approaches

During the surgery, the surgeon gives a skin incision followed by cutting or separation of the tissue to reach the hip joint. The hip joint may be accessed through a number of different approaches. In the posterior approach, the surgeon accessed the hip joint through the back of the joint.

Similarly in the anterior approach, the surgeon accesses the joint from the front. Other less commonly used approaches are the anterolateral and lateral approaches. The hip joint is accessed from the side in the direct lateral approach and if the incision is made some distance from the side to the front, it is known as the anterolateral approach.

The choice of surgical approach is often dependent upon a number of factors. Any prior incision, the selection of the implant, the risk of dislocation, obesity, hip deformity, and surgeon training all influence the choice of hip replacement approach.

Posterior approach
The surgery is usually performed under general anesthesia or at times may be performed under spinal anesthesia. The surgeon positions the patient on their side with the affected hip facing up. The surgeon may bend the hip and the knee of the affected side with the other leg laying straight.

After cleaning and draping in the usual fashion, the surgeon gives an incision in the back of the buttock in mimicking the alphabet “J”. The surgeon separates and cuts the underlying tissue known as fascia. The fascia is a tough tissue that covers the muscles.

Next, the surgeon separates the major muscle forming the buttock known as the gluteus maximus. The surgeon separates the muscle while taking care not to disrupt the blood supply and the nerve supply of the muscle. The trochanteric bursae are cleared in the operative field.

The affected side is manipulated in a position in order to rotate the hip inward. The inward rotating action places the small external rotator muscles in tension so the surgeon can see them clearly. The short external rotator muscles attach behind the upper part of the thigh bone. The muscles help in moving the hip outward.

Two of the short external rotator muscles piriformis and the obturator internus muscles are tagged and cut just near the upper thigh bone. During the process, the surgeon also takes care to locate the sciatic nerve to prevent inadvertent injury.

The hip capsule is a tough tissue that surrounds the hip joint. The tissue is cut using a special “T” shaped incision. The surgeon is now able to see the diseased joint and the surgeon cuts the neck of the thigh bone (femur) to separate the head of the femur from the upper thigh bone.

The head of the thigh bone is removed from the bony socket (acetabulum) using a special instrument. The cutting of the neck with a bone saw is done keeping in mind the implant position. The surgeon then proceeds to remove osteophytes also known as bone spurs around the socket.

The acetabulum socket is freshened with help of a reamer. The freshening of the bone in the socket helps the bone to grow on and in the acetabulum implant (cup). The reaming of the acetabulum socket is done in a position that allows maximum movement of the joint while maintaining stability. The prosthetic cup is press-fitted and may be additionally fixed to the acetabulum using screws.

The surgeon then uses a drilling instrument to locate the canal of the upper thigh bone. Rasping instruments in the shape of the implant are then inserted and removed with a larger size each time. The rasps and broaches help to freshen the canal of the thigh bone and prepare the seat for the implant.

The last broach is left in place and the surgeon covers the neck of the trial broach with a trial head of the femur. The trail head is placed back in the socket using a maneuver and the surgeon checks for stability, range of motion, and length of the extremity.

Upon satisfaction with the size of the trial implants, the surgeon inserts the prosthetic femoral stem in the prepared upper thigh bone. The stem is press-fitted in the canal with a special emphasis on the direction and the angle of the final position. The stem is mostly press-fitted but may be fixed with bone cement in limited cases.

A prosthetic head made of metal alloy or ceramic is placed upon the neck. The metallic acetabulum socket is covered with a high-grade plastic liner. The head is placed back in the socket. The capsule as well as the cut short external rotators are repaired. The incision is closed in layers and a bandage is placed on the skin incision.

The patients are placed on deep vein thrombosis precaution in the form of blood-thinning medication such as aspirin. The patients are able to stand up and walk with assistance the next day of the surgery. The majority of the patients are able to walk without assistance (calipers/walkers) at the end of 3-4 weeks.

As with any surgery, there may be potential complications in the form of heart attack, blood clots, infection, bleeding, failure of hardware, leg length discrepancy, etc. Although rare, the complications are discussed at length with all patients undergoing hip replacement surgery. Hip replacement surgery has been a boon to millions of patients suffering from hip pain worldwide and is one of the most common surgeries performed by orthopedic surgeons.