Total hip arthroplasty is one of the most successful medical procedures ever invented. Approximately 300,000 such procedures are performed in the United States annually. This procedure can treat a wide variety of disorders that ultimately lead to severe arthritis of the hip. Arthritis is characterized by destruction of the articular cartilage and direct contact of the bony surfaces of the hip socket and femoral head. This can lead to pain, stiffness, inability to walk, difficulty sitting, and other disabilities. The main goal of total hip replacement is to relieve pain. However, many patients have the ability to walk farther after the procedure and often no longer require walking aids after the surgery.
The procedure is usually performed under a general or spinal anesthesia. The procedure can be performed with the patient either lying on their side or on their back. The hip can be approached from the front, the back, or the side. After the hip is exposed, the neck of the femur is cut at a specific angle and the femoral head is removed. This allows a good view into the hip socket. The arthritic hip socket often has lost its cartilage and has developed many bone spurs. A device known as a reamer is used to prepare the hip socket for a metal cup by machining it to a hemispherical shape and exposing a bleeding surface of bone to allow ingrowth of bone onto the hip socket component (acetabular component). Next, the component is impacted into place. Once the acetabular component has been applied, a second component or prosthesis is placed into the femoral shaft. The femoral component is usually composed of titanium or cobalt-chromium alloy. Depending on the specific design, it can be implanted with bone cement or with direct contact to the bone (press-fit).
The following case is an illustration of the steps involved in a total hip replacement performed in a 29 year old female with severe avascular necrosis of the femoral head and secondary arthritis.
1.This patient's hip radiograph (left) demonstrates the advanced avascular necrosis of the femoral head. This is shown as flattening and fragmentation of the upper aspect of the femoral head. At the time of the radiograph, we also notice that she has developed flattening at the edge of the hip socket (arrow). A normal hip radiograph is shown immediately below the patient's hip radiograph.
2.A special operating room table is used to position the leg in order to facilitate the surgical exposure. The table allows the leg to be bent toward the floor to allow direct access to the top of the femur (thighbone) through the incision in the front.
3.A specialized hook is attached to the table which helps to hold the femur up while a titanium stem is placed within the upper part of the femur. In this image the prosthesis or metal stem(long arrow) has been seated fully into the femur with the neck of the prosthesis coming out toward the camera(short arrow).
4.A ceramic femoral head component has been mounted onto the metal femoral component. The ceramic head component is spherical and measures 36mm in this case. The femoral head fits into a precisely matched ceramic insert which locks into the hip socket component (acetabular component). The combination of the femoral head and the insert makes up the "bearing surface" which in this case is ceramic on ceramic.
5.At this point the femoral head has been placed in the hip socket component. The hip is now "reduced" (put back in place). A final check of the position of the hip implants is performed. The leg is moved in extreme positions to be sure that the hip implants do not come apart due to dislocation. Potential reasons for the hip to dislocate would be abnormal contact between the implants, inaccurate positioning of the implants, or inadequate soft tissue (muscle) tension.
6.The final radiograph shows the implants to be in appropriate position.
What are current hip replacements made of?
Most contemporary metal hip replacements are made of titanium alloys or cobalt-chromium alloys. The best way to understand the implants used in current replacements is to divide them into two parts. First is the metallic components that are directly fixed to the bone. These can be either through the use of cement (mostly on the femur or thigh-bone) or through a cementless or ingrowth process where the bone actually grows onto the metal. The second part of the hip replacement is made of the parts that actually move relative to one another (the bearing). These can be made of either metal on polyethylene plastic (most common) or other bearings such as ceramic-on-ceramic or metal-on-metal.
How long will I be in the hospital?
In most cases, patients remain in the hospital at our facility for a minimum of 2 days and usually 3-4 days.
Would I go home or go to a nursing facility after the surgery?
This depends on how much help you have at home. The goal of physical therapy both in the hospital and at home is to get you to be independent. If this can not be acheived while you are in the hospital, a vigorous course of therapy in a skilled nursing facility is the best answer to continue to progress toward independence.
Can I put my full weight on the leg after a hip replacement?
In most cases of ingrowth prostheses, we restrict the amound of weightbearing on the leg for 4 to 6 weeks. This has been shown to lead to decreased risk of the stem collapsing into the femur
What does the term “bearing surface” mean?
Bearing surface refers to the surfaces that actually contact one another in a total hip replacement. The ideal bearing surface for a joint is cartilage. This is a result of its electrical properties, water content, and architecture. As a result, cartilage on cartilage has a lower friction than ice on ice. In total joint replacement, the goal is to achieve a low friction joint with production of as little debris as possible and provides long-term durability to last the patient’s lifetime. The various current options for bearing surfaces in joint replacement include metal-on-polyethylene, ceramic-on-ceramic, and metal-on-metal.
When do you use bone cement?
Bone cement has had a long history of use in total hip replacement. Over the past 15 years, its use has declined due to the risk associated with loosening of cemented joint replacements. In our efforts to improve on the results of the cemented joint replacements, a number of cementless implants have been developed. Cementless implants depend on the ingrowth or ongrowth of bone onto their surface. The various surfaces can be made of a roughened surface, a surface with small beads, or a fibrous metal mesh. The cementless implants on the socket side have performed exceedingly well. A number of earlier cementless implants on the femoral side did not perform as well as cemented femoral components. However, we have learned important lessons about factors that are associated with success in cementless femoral components. Currently, a number of published reports have shown that some cementless femoral and acetabular designs have a 98 to 100% success rate at 10 years. These are equal or better to many cemented designs at the same time intervals. We currently use predominantly cementless designs unless we are concerned about the fixation of such implants. In such cases, cemented implants offer immediate fixation to bone and permit immediate weightbearing for the patient.
Do hips wear out?
Total hip replacements can wear out. This has been associated with higher activity, with polyethylenes with poor mechanical properties, and with larger diameter femoral heads. Currently, with bearing surfaces such as highly cross-linked polyethylenes, metal-on-metal, and ceramic-on-ceramic, the rates of wear in hip replacements may finally be controlled.
Can I jog after my hip replacement?
No published study has documented the clinical outcome of hip replacements in patients who are runners. However, the association of higher failure rates with younger, more active patients suggest that such activities may lead to an earlier need for revision surgery.
Do I have to follow any other precautions after my surgery?
Depending on the approach, there will be certain precautions/positions to avoid after hip replacement. For most posterior approaches, the patient is asked to avoid bending their hip greater than 90 degrees, to avoid turning their knee in (internal rotation) during activities like picking up an object from the floor, and to avoid deep, cushioned couches. Anterior or lateral hip approaches often require anterior hip precautions (no turning out of the foot while standing or lying flat).
Will my leg lengths be equal after the surgery?
Your surgeon will make efforts to achieve equal leg lengths after the surgery. The most important factor in success after total hip replacement is the achievement of a stable hip (a hip that does not dislocate). The stability of the hip depends on the positioning of the implants, the tightness of the soft-tissues, and the bony anatomy. In some cases, the leg needs to lengthened slightly in order to achieve adequate soft-tissue tension.
What would happen if my hip dislocates?
A dislocated hip can occur during activities in which the precautions are not followed or as a result of soft-tissue laxity or impingement. Impingement is a situation where the component or bony structures contact each other in such a way that they push the hip out of socket.
What is the "anterior approach total hip replacement"?
The anterior approach for total hip replacement is a surgical approach to the hip that has been used for over 30 years for total hip replacement in Europe and more recently in the United States. The major advantage of the surgery is that it provides a truly "minimally invasive" way to perform the hip replacement. The muscular interval between the tensor fasciae latae muscle and the sartorius muscle is used. No muscle is cut with the operation, providing a very stable hip with minimal damage to the soft-tissues of the hip. There are no bending or positional precautions after the surgery. We use a special table called a "fracture table" to perform the operation. It allows us to position the leg during the operation and helps to expose both the socket and the femur.
What if I have a car accident with a hip replacement? Can the bone break around the replacement?
Yes, trauma of any kind after a hip replacement can lead to very severe fractures which are even harder to treat that a fracture without a hip replacement. The treatment of these injuries often requires either the use of plates and rods or the revision of the hip replacement entirely with placement of a new, long femoral component to span the fracture.
What is resurfacing total hip replacement?
Resurfacing total hip replacement is a type of hip replacement that places the femoral component on the neck of the femur rather than passing a stem down the shaft. The cup component in the hip socket is usually a one piece all metal component.
Do you have any cartilage replacement procedures for the hip?
At this point the experience with the treatment of cartilage defects in the hip is limited to a few scattered reports. These include the use of microfracture, mosaicplasty, and osteochondral allografting. The challenge in the hip is the difficulty in accessing the joint, the specific geometry of the ball and socket, and the limited blood supply of the head of the femur.