"The choice of one type of hip replacement over another has become one of the most important preoperative decisions made by both patient and surgeon. Choosing the artificial bearing surface of your implant is where most preoperative decision making comes into play. It is not uncommon to hear terms such as "metal-on-metal," or "porcelain hip," when discussing options in this area. Additional advances also may be discussed. For example, you may hear terms such as "capping the femur" or "minimally invasive surgery." Although these advances may work well in many people, not everyone is a suitable candidate for these types of hip replacements. The decision to proceed with one type of hip replacement over another should be based on the knowledge about past and current technology, its potential durability based on laboratory testing and clinical use, and the drawbacks of its use." (1)
What will the Hip Replacement be Made of?
Cross-Linked Polyethylene
The bearing component most commonly used for total hip replacement in the United States is a metal femoral head (ball) made of either stainless steel, cast or wrought cobalt, a metal-base alloy against a polyethylene (plastic)-lined acetabular cup.
Benefits
Cross-Linked Polyethylene
The bearing component most commonly used for total hip replacement in the United States is a metal femoral head (ball) made of either stainless steel, cast or wrought cobalt, a metal-base alloy against a polyethylene (plastic)-lined acetabular cup.
Benefits
- Durable and versatile
- Long, successful clinical history
- Not toxic to the human body
- Adequate toughness for most lifestyles
- May wear down over time, which can lead to inflammation, bone loss, and/or a revision procedure
Ceramic
Ceramic bearings are available in 2 configurations: a ceramic femoral head (ball) with a polyethylene liner, or a ceramic femoral head (ball) with a ceramic liner. No one material is right for every patient. Only a surgeon can determine what's right for your patient, but is beneficial to understand the difference.
Benefits
Ceramic bearings are available in 2 configurations: a ceramic femoral head (ball) with a polyethylene liner, or a ceramic femoral head (ball) with a ceramic liner. No one material is right for every patient. Only a surgeon can determine what's right for your patient, but is beneficial to understand the difference.
Benefits
- Reduced wear—improved lubrication and reduced friction (3)
- Performance—lower wear rates compared with polyethylene and metal (3)
- More prone to fracture
- Less forgiving in surgery
- More likely to require the removal of greater quantities of healthy bone due to size limitations
- More expensive than other bearing options
While hip implants are made of several different types of materials, the most common are titanium and cobalt chrome. The surgeon will choose the implant that best fits your patient's lifestyle, anatomy, and other needs. On average, a total hip system (stem, head, shell, and liner) weighs between 1 and 2 pounds, depending on the type of material that is used. Most systems consists of a combination of material. Keep in mind that the ball socket must be able to freely move, which also determines the materials most commonly used.
With hip replacement, an acetabular cup usually includes a metal shell and a plastic, metal, or ceramic liner to replace the acetabulum.
With hip replacement, an acetabular cup usually includes a metal shell and a plastic, metal, or ceramic liner to replace the acetabulum.
What Components are Replaced?
In a total hip replacement surgery, doctors replace the diseased or damaged hip with an implant consisting of a stem, ball, liner, and socket.
- The stem, made of metal, is inserted into the femur (thigh bone) and anchors the implant in place
- The ball is attached to the top of the stem
- The socket is anchored into the pelvis and the ball, which is attached to the top of the stem, then rotates within the liner (4)
Anterior Approach vs. Posterior Approach
Anterior
The Anterior Approach for total hip replacement is a tissue-sparing alternative to traditional hip replacement surgery that provides the potential for less pain, faster recovery and improved mobility because the muscle tissues are spared during the surgical procedure. The technique allows the surgeon to work between the muscles and tissues without detaching them from either the hip or thighbones - sparing these tissues from trauma.
Keeping the muscles intact may also help to prevent dislocations. With the Anterior Approach, the surgeon uses one small incision on the front (anterior) of the hip as opposed to the side or back. Since the incision is in front, patients avoid the pain of sitting on the incision site. (5)
Benefits of Anterior Approach
*Disadvantages to the mini anterior hip replacement are both practical and medical. For medical experts, a special operating table or specialized retractors and specific tools are required. Patients also run a slightly higher risk of experiencing femoral and ankle fractures if the special table is used. In addition, due to the approach, there is a substantial risk of a numb, tingling or burning sensation along the thigh, referred to as lateral femoral-cutaneous nerve damage. Patients who have implants or metal hardware in the hip from prior surgery, are muscular, those who have a wide pelvis, or who are very obese may not be well-suited for this procedure and if they do undergo it, it may require longer incisions.
Anterior
The Anterior Approach for total hip replacement is a tissue-sparing alternative to traditional hip replacement surgery that provides the potential for less pain, faster recovery and improved mobility because the muscle tissues are spared during the surgical procedure. The technique allows the surgeon to work between the muscles and tissues without detaching them from either the hip or thighbones - sparing these tissues from trauma.
Keeping the muscles intact may also help to prevent dislocations. With the Anterior Approach, the surgeon uses one small incision on the front (anterior) of the hip as opposed to the side or back. Since the incision is in front, patients avoid the pain of sitting on the incision site. (5)
Benefits of Anterior Approach
- Possible accelerated recovery time because key muscles are not detached during the operation. (Some other procedures require cutting or disturbing the important muscles at the side or back of the leg.) The Anterior Approach is known as a tissue-sparing procedure because it avoids cutting these key muscles and tissues and therefore minimizes muscle damage
- Potential for fewer restrictions during recovery. Although each patient responds differently, this procedure seeks to help patients more freely bend their hip and bear their full weight immediately or soon after surgery
- Possible reduced scarring because the technique allows for one relatively small incision
- Potential for stability of the implant sooner after the surgery, resulting in part from the fact that the key muscles and tissues are not disturbed during the operation.
- The hip is exposed in a way that does not detach muscles or tendons from the bone
- A high-tech operating table is often used to help improve access
- Intraoperative x-ray or computer navigation is typically used to confirm implant position and leg length
- Larger, heavier patients—may be candidates for minimally invasive hip surgery with this technique
- The Anterior Approach enters the body closer to the hip joint, with far less tissue between the skin and the bones of the hip, so more patients may be candidates, but there are important disadvantages* to understand.
*Disadvantages to the mini anterior hip replacement are both practical and medical. For medical experts, a special operating table or specialized retractors and specific tools are required. Patients also run a slightly higher risk of experiencing femoral and ankle fractures if the special table is used. In addition, due to the approach, there is a substantial risk of a numb, tingling or burning sensation along the thigh, referred to as lateral femoral-cutaneous nerve damage. Patients who have implants or metal hardware in the hip from prior surgery, are muscular, those who have a wide pelvis, or who are very obese may not be well-suited for this procedure and if they do undergo it, it may require longer incisions.
Posterior
The posterior approach, the dominant hip replacement surgical method for many years, is used in the majority of the hip replacements performed in the United States. It involves accessing the hip joint via an incision made close to the buttocks. This approach provides doctors with a good view of the hip capsule, allowing for optimum placement of implants.
Mini-posterior approaches
*Disadvantages include tissue damage: The surgeon must cut through the fascia lata, gluteus maximus, and external rotators. These muscles all prevent the femur from dislocating our of the back of the hip socket (posterior dislocation), and cutting them increases the chance of future dislocations.
The posterior approach, the dominant hip replacement surgical method for many years, is used in the majority of the hip replacements performed in the United States. It involves accessing the hip joint via an incision made close to the buttocks. This approach provides doctors with a good view of the hip capsule, allowing for optimum placement of implants.
Mini-posterior approaches
- The mini-posterior is considered a more straightforward approach then the anterior, resulting in lesser complication rates.
- There is significantly less bleeding with the mini-posterior approach, notably reducing the necessity of a blood transfusion after the surgery.
- The mini-posterior is more straightforward, many surgeons think it provides an increased margin of safety for the patient, because the incision can easily be extended if exposure is poor, or if a fracture occurs. Because of the straightforward exposure of the femur, there is less risk of femoral fracture or poor implant positioning. Should one of these events occur during a mini-posterior procedure, they are easier to recognize and correct. Because visualizing the femur is easier, an experienced surgeon can choose the most appropriate femoral implant rather than just the one that is easiest to implant, taking into account the patient’s bone quality, activity level and age.
- There is less risk of neurological injury.
- No special surgical equipment is required when performing a mini posterior.
*Disadvantages include tissue damage: The surgeon must cut through the fascia lata, gluteus maximus, and external rotators. These muscles all prevent the femur from dislocating our of the back of the hip socket (posterior dislocation), and cutting them increases the chance of future dislocations.
References
- http://healthletter.mayoclinic.com/editorial/editorial.cfm/i/262/t/choosingtherighttotalhipreplacement/
- Liao Y-S, Greer, et al. Effects of Resin and Dose on Wear and Mechanical Properties of Cross-linked Thermally Stabilized UHMWPE. Society for Biomaterials, the 7th World Biomaterials Congress, Sydney, Australia, 2004.
- Goldsmith A, et al. A comparative joint simulator study of the wear of metal-on-metal and alternative material combinations in hip replacements. Institution of Mechanical Engineers, Journal of Engineering in Medicine. 2000;214:39-47.
- https://www.hipreplacement.com/technology/implants/basics
- https://www.hipreplacement.com/about/about_surgery/anterior_surgery
- http://www.aaos.org/news/acadnews/2013/AAOS8_3_20.asp