The best expertise in Orthopaedic & Arthritis care
MS (ORTHO), DNB (ORTHO), FRCS (GLAS), FRCS (TR & ORTH)
FELLOWSHIP IN SHOULDER AND UPPER LIMB SURGERY, UK
FELLOWSHIP IN TRAUMA AND JOINT RECONSTRUCTION, TORONTO, CANADA
HIP REPLACEMENT: YOUR
I have been diagnosed with arthritis of the hip. What is this?
Arthritis is a condition in which the smooth surfaces of the joint become rough as a result of wearing away. Damage to the cartilage can be caused by degenerative process (osteoarthritis), inflammatory process (rheumatiod arthritis, ankylosing spondylarthropathy, connective tissue diseases, etc.) or incongruity of joint surfaces (post-traumatic arthritis, avascular necrosis, developmental dysplasia, etc.). This leads to pain, stiffness, deformity and limping.
If your hip pain is persistent and disabling you need hip replacement.
Hip replacement is an operation in which the damaged ball and socket are replaced by artificial device called prosthesis. This relieves the pain, restores movements and corrects the deformity at the hip.
You should think of hip replacement when your pain…
- Provides complete and lasting relief of pain
- Improves quality of life
- Abolishes the need for painkillers
- Restores movement to the hip
- Enables activities of daily living without help
- Restores independence
- Enables outdoor activities like travelling, shopping, attending social functions, etc.
- Enables gainful employment
- Improves walking ability which has a positive impact on control of diabetes, hypertension, ischemic heart disease and obesity
- Improves participation in social activities and mental outlook
In a total hip replacement, the worn out surfaces are replaced by artificial device (prosthesis). The socket is replaced by a hemispherical cup which has a metallic shell and an inner high-density polyethylene liner. The head is replaced by a metal sphere supported on a tapered stem which fits into the bony canal of the femur. The implants have specially textured surface which allows them to grip the bone. Sometimes acrylic bone cement is also used to fix the implants.
Advances in Hip Replacement
Metal on Polyethylene: The traditional bearing surface in hip replacement is metal ball (femoral head) and high-density polyethylene socket (acetabular cup). In spite of the high quality of the materials and manufacturing techniques, wear of polyethylene is inevitable. This results in attrition and failure of the bearing surface. Wear particles elicit an inflammatory reaction that leads to bone resorption and loosening of the prosthesis. In an effort to eliminate polyethylene wear, other bearing surfaces have been developed.
Ceramic articulations: Ceramic bearing surfaces have very smooth finish which reduces wear. They can be used in conjunction with polyethylene (ceramic-on-polyethylene) or ceramic (ceramic-on-ceramic). Oxynium is a proprietary material of ceramicised metal. It has properties similar to ceramic. These articulations are preferred in young patients.
Metal-on-metal articulations: In this type both the head and socket are made of metal. These have been almost entirely given up because of the risks of metallosis, granuloma formation and elevated metal ion levels in blood.
The design of hip prostheses matches the anatomy of the human bones. In complex hip deformities, this may not be the case. Modular prostheses – which consist of separate tip, body and neck portions – are helpful in such cases. These prostheses are assembled using different shapes and sizes of individual elements to match the shape of the deformed bone.
Bony defects especially in the socket do not allow a good fixation of the implant. These defects were traditionally filled with bone grafts obtained from the patient or from a bone bank. The problems with bones grafts are lack of availability, additional surgery to obtain graft, resorption, risk of infection, and transmission of diseases via banked bone. Augmented or custom-made metal implants suffered from lack of integration with bones – resulting in their loosening. The development of Trabecular metal has addressed these problems. Trabecular Metal is a unique, highly porous biomaterial made from elemental tantalum which resembles bone in structure and mechanical function and integrates very well with patient’s bone. It can be fashioned into various shapes to fill bone defects. There is no risk of resorption and transmission of disease. Trabecular Metal implants have revolutionized joint replacement surgery and made complex reconstructions possible.
Traditional hip replacement involves placing the femoral component in the marrow cavity of the thigh bone. This entails removal of the head and neck of the femur and a part of the bone from the marrow cavity.
In hip resurfacing, only the surface of the femoral head is removed and a cap-like prosthesis inserted. This preserves the bone from the neck and the marrow cavity. This is helpful if a future revision is required as more native bone is preserved. This also restores the bio-mechanics to near normal resulting in a more natural ‘feel’ after replacement. The motion regained is also near normal.
Hip resurfacing implants have metal-on-metal articulation. There are concerns about metallosis, granuloma formation and elevated blood metal ion levels. Hence resurfacing is done in very selected cases now-a-days.
During hip replacement, the joint is exposed from the front or the back side. Either approach involves making a skin incision about six inches long and detaching or splitting the muscles to give adequate access for the operation.
Minimally invasive approaches involve making smaller incisions in the skin and muscles. This leads to a faster recovery and better cosmetic outcome. This is generally done for slim patients with good flexibility. It is difficult in obese patients and those who have stiff hips. The procedure requires special instruments. X-ray or computer guidance is used by some surgeons but is not essential.
In practice, it is seen that the final result with a standard approach is the same as with minimally invasive approach, although a bit slower in the initial post-operative period.
The instruments and techniques employed in a joint replacement are very precise and allow a very accurate procedure to be performed. Since all surgical approaches are designed to perform the operation with minimum trauma to the tissues, only the hip joint and the adjacent bones are exposed. Most of the time, this exposure allows very accurate placement of the implants. However, in complex deformities, the traditional approaches may not be adequate to assess the alignment of the bones and the implants. In such cases computer navigation can provide the surgeon with additional help in performing the surgery.
Surgical navigation systems utilize an array of stereoscopic infra-red cameras; infra-red reflectors (tracking devices) which are placed on the bones and on specially calibrated instruments; and a computer. The computer generates a virtual 3-dimensional model of the bones. It displays the instruments, the dimensions of the bones and the size of the implants. This information is used to guide the placement of implants.
The advantages are improved accuracy and better surgeon feedback during the surgery. It is especially useful when there is a pre-existing deformity in the bones. The disadvantages are increased cost, increase in surgical time and a small extra incision.
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