Total Hip Replacement Implants
The implants used in the hip replacement may differ in a number of aspects. They may be made from different materials or may have different shapes. The type of implant best for the patient is usually decided by the surgeon after a discussion with the patient.
Total hip replacement is a surgical procedure to replace the diseased parts of the hip joint. The hip joint is formed by the upper end of the thigh bone (femur) and the bottom of the pelvis (acetabulum). The hip replacement surgery remains the most successful surgery in modern medicine.
Procedure
Different techniques can be used to access the hip joint. Most commonly, the hip joint is accessed from behind (posterior approach). It can also be accessed from the front (anterior approach) or the side (lateral approach).
A Minimally Invasive technique involves giving a smaller incision and less separation of tissues. Robotic Surgical assistance may be used in all these techniques. The merits and demerits of each technique are discussed with the patient so that the technique can be individualized.
- The damaged part of the acetabular socket is removed, and a cup made of metal alloy or ceramic is fixed with screws or press-fitted in the socket.
- The head of the femur is cut with a saw, and a stem made of metallic alloy is inserted in the upper part of the thigh bone.
- The stem may be press-fit or fixed using a special form of bone cement, allowing the bone to hold the implant.
- A prosthetic head made of metal alloy or ceramic is placed on the stem replacing the natural head of the femur.
- A special form of highly durable plastic called polyethylene is placed between the head and socket to allow smooth gliding.
Implants
An ideal implant should last duplicate the function of the natural joint. The artificial hip should allow natural movements for the patients to do the activities they enjoy. The implant should be non-allergic and have a good track record. The implant should have a low degree of friction and less generation of wear and tear particles.
An ideal implant should last a patient’s lifespan. Most implants last on an average for 15-20 years or more. The choice of implant used also depends upon the surgeon’s familiarity with the implant and expertise. Currently used implants may either be hard-on-soft bearing or hard-on-hard bearings.
Trial and Actual Implant (Head of femur and Acetabular Component)
Splined modular distal femoral component
The image shows a splined tapered modular distal femoral prosthetic component. The tapered end allows ease of insertion and the splined design provides rotational stability in the femoral canal. The modular implants are commonly used in revision hip replacement surgery. The special design allows to achieve greater stability in the event of encountering bone loss during extraction.
Hard-on-soft bearing
The ball is made of metal and the cup is made of specialized plastic called polyethylene. The polyethylene plastic is highly cross-linked to make it resistant to wear and tear. The metal may be made of a cobalt-chromium alloy or ceramic. The metal ball and a polyethylene liner is currently the most commonly used bearing surface.
Total Hip Replacement Components.
Ceramic is a harder surface than the cobalt-chromium alloy. The ceramic surface is ultra-smooth and scratch-resistant. Due to these properties, ceramic has extremely low generation of wear and tear particles.
Different types of acetabular liners and shells
There are different types of acetabular liners and shells. Neutral liners are commonly used in primary surgeries. Lateralized liners and acetabular liners with elevated rims may be used in revision surgeries to prevent dislocation. Constrained liners and dual mobility heads are used in cases of total hip replacement dislocation.
Hard-hard bearing
These bearing surfaces can either be a metal ball on a metal cup or ceramic ball on a ceramic cup. The surface of the metal/ceramic implants may be made rough to allow the bone to grow on the implant. The metal alloy may be highly carbonized to decrease the generation of wear and tear particles.
The advantage of hard-on-hard bearing surfaces is reduced chances of dislocation. The hard-on-hard bearing surfaces are able to accommodate a large size of the ball (femoral head). A larger size of the ball reduces the chance of dislocation.
Hard bearing acetabular liner
The hard bearing acetabular liner comes with an inserter ring to prevent micromotion. The large cavity of the metallic liner allows insertion of a large prosthetic head of femur therefore limiting the chances of dislocation.
A disadvantage of hard-on-hard metal alloy implants is the generation of wear and tear particles. The levels of the alloy (cobalt-chromium) may be increased in the blood. These implants are therefore avoided in patients with kidney failure. The implants are also avoided in patients of childbearing age group.
The metal alloy wear particles may cause aseptic vasculitis associated vascular lesion (ALVAL). The immune cells of the body may accumulate around the implant and cause erosion of the bone and inflammation of the tissues. These may also cause the formation of a solid mass known as a pseudotumor.
The ceramic hips are generally made of alumina ceramic. The alumina ceramic has a very high density and therefore has an extremely smooth surface. The smooth surface allows decreased friction. The implants are also hydrophilic (water retaining), that allows a small film of water on the surface leading to lubrication.
The ceramic implants are also scratch-resistant and are inert in the body. The ceramic implants are extremely sensitive to implant position. Malpositioned ceramic implants may lead to failure. Ceramic implants may also press against each other at the outer boundary to cause chip fracture. The implants may also produce a squeaking sound.
Conclusion
Although a number of different implant designs and hip systems may be used in joint replacement surgeries, the metal on polyethylene remains a very popular option. The type of implant and the material used may depend upon the patient’s anatomy and the orthopaedic surgeon’s experience.
Do you have more questions?
Are there different designs of total hip replacement implants available, and how do they vary in terms of stability and longevity?
Yes, there are various designs of total hip replacement implants, including cemented, uncemented, and hybrid designs, each with its advantages and considerations regarding stability and longevity.
Can total hip replacement implants be customized to fit a patient’s specific anatomy, or are they standardized?
Total hip replacement implants can be customized to some extent to fit a patient’s specific anatomy, with options for different sizes, shapes, and configurations to optimize fit and function.
What are the potential complications associated with total hip replacement implants, such as loosening or wear of the implant components?
Potential complications of total hip replacement implants include implant loosening, wear of the implant components, dislocation, infection, nerve or blood vessel injury, and allergic reactions to implant materials.
How long do total hip replacement implants typically last, and what factors influence their longevity?
The longevity of total hip replacement implants varies depending on factors such as patient age, activity level, implant type, surgical technique, and the presence of any complications or underlying conditions.
Can total hip replacement implants be revised or replaced if they wear out or fail over time?
Yes, total hip replacement implants can be revised or replaced through a surgical procedure known as revision hip replacement if they wear out or fail over time. This involves removing the old implants and replacing them with new ones.
Are there any restrictions on physical activities or movements for individuals with total hip replacement implants?
While total hip replacement implants can significantly improve mobility and function, some restrictions on high-impact activities or extreme ranges of motion may be advised to minimize the risk of implant wear or dislocation.
How does the surgical approach used for total hip replacement surgery impact the choice of implant design and fixation method?
The surgical approach used for total hip replacement surgery may influence the choice of implant design and fixation method, as different approaches may require specific implant configurations or fixation techniques for optimal outcomes.
What are the differences between cemented and uncemented total hip replacement implants, and how do they affect the surgical procedure and recovery?
Cemented total hip replacement implants are fixed to the bone using bone cement, while uncemented implants rely on bone ingrowth for stability. The choice between cemented and uncemented implants depends on factors such as patient age, bone quality, and surgeon preference.
Can total hip replacement implants be made of biocompatible materials to reduce the risk of adverse reactions or implant rejection?
Yes, total hip replacement implants are typically made of biocompatible materials such as titanium alloys, cobalt-chromium alloys, ceramic, or polyethylene to minimize the risk of adverse reactions or implant rejection.
How does the size and shape of total hip replacement implants impact their stability and performance in the hip joint?
The size and shape of total hip replacement implants are carefully selected to match the patient’s anatomy and optimize stability and performance in the hip joint, reducing the risk of implant-related complications.
What are the advantages and disadvantages of metal-on-metal, metal-on-polyethylene, ceramic-on-ceramic, and ceramic-on-polyethylene total hip replacement implants?
Each combination of materials for total hip replacement implants has its advantages and disadvantages in terms of wear resistance, durability, friction, and potential for adverse reactions or complications.
How does the cost of total hip replacement implants vary depending on the type of material and design chosen?
The cost of total hip replacement implants varies depending on factors such as the type of material, design complexity, manufacturer, and any additional features or customization options.
Are there any specific precautions or follow-up care instructions for individuals with metal or ceramic total hip replacement implants?
Individuals with metal or ceramic total hip replacement implants may be advised to undergo regular follow-up appointments, monitoring for signs of implant wear or failure, and to report any unusual symptoms or discomfort promptly.
Can total hip replacement implants be MRI-compatible, or are there limitations for patients with implants undergoing imaging studies?
Some total hip replacement implants are MRI-compatible, while others may have limitations or contraindications for patients undergoing imaging studies. Patients should inform healthcare providers of any implants before undergoing MRI scans.
How do advancements in implant technology and materials influence the outcomes and longevity of total hip replacement surgery?
Advancements in implant technology and materials continue to improve the outcomes and longevity of total hip replacement surgery by enhancing implant durability, wear resistance, biocompatibility, and overall performance in the hip joint.
Can total hip replacement implants be used in patients with osteoporosis or compromised bone quality, or are there alternative options available?
Total hip replacement implants can be used in patients with osteoporosis or compromised bone quality, but special considerations may be necessary to ensure adequate implant fixation and stability. Alternative options such as bone grafting or specialized implant designs may be considered in some cases.
How do total hip replacement implants affect joint biomechanics and function compared to the natural hip joint?
Total hip replacement implants aim to restore joint biomechanics and function as closely as possible to the natural hip joint, allowing for improved mobility, pain relief, and quality of life in patients with hip joint disease.
What are the potential risks and benefits of using modular total hip replacement implants compared to non-modular designs?
Modular total hip replacement implants offer advantages such as intraoperative flexibility and customization but may also pose risks such as component loosening or fretting corrosion. The choice between modular and non-modular designs depends on factors such as patient anatomy and surgeon preference.
How does the choice of bearing surface in total hip replacement implants impact wear rates and long-term implant survival?
The choice of bearing surface in total hip replacement implants, such as metal-on-metal, metal-on-polyethylene, ceramic-on-ceramic, or ceramic-on-polyethylene, can influence wear rates and long-term implant survival, with each combination having unique characteristics and considerations.
My name is Dr. Suhirad Khokhar, and am an orthopaedic surgeon. I completed my MBBS (Bachelor of Medicine & Bachelor of Surgery) at Govt. Medical College, Patiala, India.
I specialize in musculoskeletal disorders and their management, and have personally approved of and written this content.
My profile page has all of my educational information, work experience, and all the pages on this site that I've contributed to.
