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
YOUR QUESTIONS ANSWERED
YOUR QUESTIONS ANSWERED
If your knee pain is persistent and disabling you need knee replacement.
Knee replacement is an operation in which an artificial device (prosthesis) is implanted to replace the worn-out knee.
- Pain relief
- Restoration of movements of the knee
- Correction of deformities
- Improvement of activity level and functional status
- Provides complete and lasting relief of pain
- Improves quality of life
- Abolishes the need for painkillers
- Restores movement to the knee
- Enables activities of daily living without help
- Restores independence
- Enables outdoor activities like travelling, shopping, attending social functions, etc.
- Enables gainful employment
- Corrects bow-leg or knock-knee deformity
- 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
Total knee replacement involves removing the worn-out joint surfaces and implanting prosthetic device in place of the damaged surfaces. Only 8 -10 mm of the damaged bone surface is removed. The shape of the implants (prosthesis) closely matches the amount of bone removed. The femoral component is made of metal and has a bi-condylar shape. The tibial component consists of an oval-shaped metal tray with a highly cross-linked polyethylene inset. The patellar component is a circular polyethylene disc with convex surface. Resurfacing of the knee cap is optional. The implants are fixed using acrylic bone cement.
ADVANCES IN KNEE REPLACEMENT
Different manufacturers have introduced implants of varying designs and composition – multiple sizing options and gender-specific implants; mobile tibial tray; different alloys or surface finish, Vitamin E treated polyethylene, cruciate ligament retaining knee, etc. These design features confer certain additional advantages but are not absolutely essential. The choice of the implant depends upon the surgeon’s preference and training, the patient factors (age, activity level, expectations, etc.) and cost considerations.
In some patients, only one half of the knee is affected by arthritis (usually inner half). Replacing only the diseased half of the knee can treat this. The advantages are smaller incision, faster recovery, and preservation of natural kinematics of the knee. However, not all patients are suitable for unicompartmental replacement. The arthritis should be limited to only one side of the joint. Any arthritis affecting the other side of the knee will give rise to pain. The patient should not have severe deformity, contractures or ligament insufficiency. The procedure is not applicable for inflammatory types of arthritis.
The usual approach to knee replacement involves splitting the quadriceps muscle in the middle and reflecting the kneecap to one side. Minimally invasive knee replacement is done using an incision that splits a smaller portion (or none) of the muscle. This should lead to a faster recovery. This is generally done for slim patients with good flexibility in the knee. It is difficult in obese patients and those who have stiff knees. The procedure requires special instruments and is best done with computer navigation as there a possibility of component malpositioning. 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.
During knee replacement, 8-10 mm of bone is removed from the surface of femur and tibia to accommodate the implants. This is done manually with the help of sizing instruments, alignment guides, cutting jigs (guides) and tensioning devices. The surgeon relies on X-rays, scanograms and manual assessment for executing the procedure.
In a custom fit knee replacement, cutting guides are made for the patient before the operation. A 3-D model of the knee is generated using an MRI or CT scan. This is then used to create patient-specific cutting guides for bone resection. Advantages of this technique are improved accuracy, simplification of the procedure, shorter surgical times and decreased blood loss. The disadvantage is the cost and the time required to generate the cutting guides (about 10 days).
The instruments and techniques employed in a joint replacement are very precise and allow a very accurate procedure to be performed. However certain landmarks like the center of the ankle, and especially the center of the hip, cannot be determined precisely with these instruments. During minimally invasive surgery even the landmarks in the surgical field itself are less visible.
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. The position of the cutting guides and the path of the instruments is displayed. It also gives numerical values of the bony dimensions, the amount and angulation of bone resection and implant sizes. This information is used to guide the placement of implants. It also allows balancing of the ligaments. Simplified navigation systems, which are less complex, are also available.
The advantages are improved accuracy, better surgeon feedback during the surgery and decreased blood loss. It is especially useful when there is a pre-existing deformity in the femur or tibia. Computer navigation allows the surgeon to perform minimally invasive surgery. The disadvantages are increased cost, increase in surgical time and a small extra incision.
Robotic devices have also been developed to execute the bony part of the procedure with improved accuracy and reduction of blood loss.
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