Complex and Revision Knee Replacement
Total knee replacement is one of the most successful procedures in all of medicine. In the vast majority of cases, it enables people to live richer, more active lives free of chronic knee pain. During primary total knee replacement, the knee joint is replaced with an implant, or prosthesis, made of metal and plastic components. Although most total knee replacements are very successful, over time problems such as implant wear and loosening may require a revision procedure to replace the original components.
There are different types of revision surgery. In some cases, only one implant or component of the prosthesis has to be revised. Other times, all three components—femoral, tibial, and patellar—need to remove or replaced and the bone around the knee needs to be rebuilt with augments (metal pieces that substitute for missing bone) or bone graft. Damage to the bone may make it difficult for the doctor to use standard total knee implants for revision knee replacement. In most cases, he or she will use specialized implants with longer, thicker stems that fit deeper inside the bone for extra support.
When is revision knee replacement recommended?
Implant Loosening and Wear
Osteolysis has occurred around the tibial component, causing it to become loosened from the bone. For a total knee replacement to function properly, an implant must remain firmly attached to the bone. During the initial surgery, it was either cemented into position or bone was expected to grow into the implant's surface. In either case, the implant was firmly fixed. Over time, however, an implant may loosen from the underlying bone, causing the knee to become painful.
The cause of loosening is not always clear, but high-impact activities, excessive body weight, and wear of the plastic spacer between the two metal components of the implant are all factors that may contribute. Also, younger patients, when they undergo the initial knee replacement, may "outlive" the life expectancy of their artificial knee. There is a higher long-term risk for these patients that revision surgery will be needed due to loosening or wear.
In some cases, tiny particles that wear off the plastic spacer accumulate around the joint and are attacked by the body's immune system. This immune response also attacks the healthy bone around the implant, leading to a condition called osteolysis. In osteolysis, the bone around the implant deteriorates, making the implant loose or unstable.
Infection is a potential complication in any surgical procedure, including total knee replacement. Infection may occur while you are in the hospital or after you go home. It may even occur years later. If an artificial joint becomes infected, it may become stiff and painful. The implant may begin to lose its attachment to the bone. Even if the implant remains properly fixed to the bone, pain, swelling, and drainage from the infection may make revision surgery necessary.
An antibiotic spacer placed in the knee during the first stage of treatment for joint replacement infection.
Revision for infection can be done in two ways, depending on the type of bacteria, how long the infection has been present, the degree of infection, and patient preferences.
Debridement. In some cases, the bacteria can be washed out, the plastic spacer can be exchanged, and the metal implants can be left in place.
Staged surgery. In other cases, the implant must be completely removed. If the implant is removed to treat the infection, your doctor will perform the revision in two separate surgeries. In the first surgery, he or she will remove the implant and place a temporary cement spacer in your knee. This spacer is treated with antibiotics to fight the infection and will remain in your knee for several weeks. During this time, you will also receive intravenous antibiotics. When the infection has been cleared, your doctor will perform a second surgery to remove the antibiotic spacer and insert a new prosthesis. In general, removing the implant leads to a higher chance of curing the infection, but is associated with a longer recovery.
If the ligaments around your knee become damaged or improperly balanced, your knee may become unstable. Because most implants are designed to work with the patient's existing ligaments, any changes in those ligaments may prevent an implant from working properly. You may experience recurrent swelling and the sense that your knee is "giving way." If knee instability cannot be treated through non-surgical means such as bracing and physical therapy, revision surgery may be needed.
Sometimes a total knee replacement may not help you achieve the range of motion needed to perform everyday activities. This may happen if excessive scar tissue has built up around the knee joint. If this occurs, your doctor may attempt "manipulation under anaesthesia."In this procedure, you are given anaesthesia so that you do not feel pain. The doctor then aggressively bends your knee in an attempt to break down the scar tissue.
In most cases, this procedure is successful in improving range of motion. Sometimes, however, the knee remains stiff. If extensive scar tissue or the components' position in your knee is limiting your range of motion, revision surgery may be needed.
A periprosthetic fracture is a broken bone that occurs around the components of a total knee replacement. These fractures are most often the result of a fall and usually require revision surgery.
In determining the extent of the revision needed, your doctor will consider several factors, including the quality of the remaining bone, the type and location of the fracture, and whether the implant is loose. When the bone is shattered or weakened from osteoporosis, the damaged bone section may need to be completely replaced with a larger revision component.
Complex Knee Replacement
Complex knee replacement is, where patients have a painful arthritic knee with other conditions near or involving the knee joint, such as an old fracture of the lower femur or upper tibia which healed in a deformed or malunited position, or previous surgery with internal fixation devices(plates and screws),pronounced deformity due to significant bone stock loss and/ora grossly unstable knee due to stretching or tearing of ligaments, then a standard primary knee replacement may not suffice and a larger, complex primary knee replacement may be necessary.In this setting a variety of additional measures, including the use of more complex implants with longer stems, bone replacing metallic augments, bone grafting and larger plastic liners are often needed to restore the length and correct alignment of the lower limb and replace the missing bone stock, and adequately re-tension the collateral ligaments and other surrounding soft tissue structures.Where increasing degrees of deformity are corrected or previous trauma or surgery have resulted in attenuation of the collateral ligaments, if the degree of laxity is moderate, but there is adequate soft tissue such that,its likely with time and soft tissue healing, that the knee will develop some biological stability, then temporary balancing using a very stable tightly fitting or constrained plastic liner between the femoral and tibial components with a closely fitting cam-post articulation is apropriate.When significant bone stock loss from the shaft of the femur or tibia is present, such as after significant trauma, previous surgery or having to remove a bony or soft tissue tumour or address a non-correctable bony deformity, then a larger “endoprosthesis” may be needed to replace large segments of bone. These implants can be quite large and allow for reattachment of soft tissue structures such as the collateral ligaments and the patella tendons and require considerable preoperative planning and intra-operative attention to detail to try to correctly restore lower limb leg length and rotation of the femur and tibia to allow for adequate functioning of the extensor mechanism and lower limb nerves and blood vessels. Finally, where a combination of bony and soft tissue deficits exist, and it is not possible to achieve stability of the knee through the above described measures, it may be necessary to use a “rotating hinge” type knee replacement, where the mechanical device has a hinge that both flexes andextends and also rotates. These larger implants usually require a longer incision, a wider surgical approach and longer operative and recovery times. If consideration of an endoprosthesis or rotating hinge type implant isnecessary, many of the routine anatomical landmarks will often be absent, making it more difficult and less reliable to achieve the usually desirable range of motion and level of function in the knee, with a necessary shift in the overall goals of surgery away from a high level of function to achieving alower limb with approximately equal leg length with improved pain management and improved ability to stand and mobilise. Careful consideration is usually given to all patients being considered for knee replacements to help best identify in advance, who is likely to require such implants, but occasionally, unexpected intra-operative findings modify the selection of implants from the standard to a more constrained implant. It is still usually possible to achieve a good alignment, acceptable range of motion and stable, pain free or pain improved knee with these more complex knee replacements.