Knee replacement surgery was first performed in 1968. Since then, improvements in surgical materials and techniques have greatly increased its effectiveness. Total knee replacements are one of the most successful procedures in Orthopedics
The knee is the largest joint in the body and having healthy knees is required to perform most everyday activities. The knee is made up of the lower end of the thighbone (femur), the upper end of the shinbone (tibia), and the kneecap (patella). The ends of these three bones where they touch are covered with articular cartilage, a smooth substance that protects the bones and enables them to move easily.
Details of Surgery -
Knee replacement (also called knee arthroplasty) might be more accurately termed a knee "resurfacing" because only the surface of the bones are actually replaced. There are four basic steps to a knee replacement procedure.
There are four basic steps to a knee replacement procedure.
Prepare the bone : The damaged cartilage surfaces at the ends of the femur and tibia are removed along with a small amount of underlying bone.
Position the metal implants : The removed cartilage and bone is replaced with metal components that recreate the surface of the joint. These metal parts may be cemented or "press-fit" into the bone.
Resurface the patella : The undersurface of the patella (kneecap) is cut and resurfaced with a plastic button. Some surgeons do not resurface the patella, depending upon the case.
Insert a spacer : A medical-grade plastic spacer is inserted between the metal components to create a smooth gliding surface.
Deformity correction: During the operation any deformities must be corrected, and the ligaments balanced so that the knee has a good range of movement and is stable and aligned.
Total Knee Implant :- A) Components
There are three components to a knee implant, replacing three bone surfaces - femoral, tibial and patellar implants. The components weigh between 10 to 15 ounces in total.
Femoral Component :In a knee implant, the femoral component, made of metal, curves up arounds the end of the femur (or thighbone). It has a central groove allowing the patella (or kneecap) to move up and down smoothly as the knee joint bends and straightens.
Tibial Component : The tibial component of a knee implant is a flat metal platform with a polyethylene insert or spacer. These have a double dish configuration for the femoral condyles and also either a notch to accommodate the cruciate ligaments (cruciate sparing) or a cam structure to take their place (cruciate sacrificing).
Patellar Component: The patellar 'button' is a dome-shaped piece of ultrahigh molecular weight polyethylene that replicates the surface of the kneecap.
Fixed Bearing : The polyethylene cushion of the tibial component is fixed to the metal platform base.
Mobile Bearing : The difference between a fixed-bearing implant and a mobile bearing implant is in the bearing surface. They allow patients a few degrees of greater rotation to the medial and lateral sides of their knee.
Medial Pivot (also known as Rotating Platform): In a rotating platform, the polyethylene insert can rotate slightly around a conical post, thereby copying the activity of the natural knee joint.
Posterior Cruciate Ligament (PCL)-Retaining: Another important aspect of a total knee replacement is the treatment of the Posterior Cruciate Ligament which prevents the femur from shunting back on the top of the tibia when it is flexed - sometimes referred to as 'roll back'. Depending upon its condition, this ligament can be kept (retained) or sacrified.
C) Constrained - Hinge Type
Commonly available / used implant brands :-
Stryker - Knee Systms - Scorpio NRG, Scorpio Single Axis
Depuy - PFC Sigma, RPF
Smith Nephew - Genesis II, Journey, Technology
VERILAST-OXINIUM- alloy and a highly cross-linked polyethylene(XLPE)
VISIONAIRE - Patient Matched Instrumentation-uses the patient's own MRI and full leg X-Ray to design cutting blocks specific to that patient.
Variations in TKR
Minimal invasive TKR-have been developed in total knee replacement (TKR) that do not cut the Quadriceps-tendon. This technique has advantages of shorter incision length, retraction of the patella (kneecap) without eversion (rotating out), and specialized instruments.
UKR-Partial knee replacement
The knee is generally divided into three "compartments": medial (the inside part of the knee), lateral (the outside), and patellofemoral (the joint between the kneecap and the thighbone). patients having arthritis of all three compartments need total knee replacement .patients with wear confined primarily to one compartment, usually the medial, and may be candidates for unicompartmental knee replacement or High TIbial Osteotomy. Advantages of UKA compared to TKA include smaller incision, easier post-op rehabilitation, better post-operative range of motion, shorter hospital stay, less blood loss, lower risk of infection, stiffness, and blood clots.