knee replacement surgery video

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Total Knee Replacement Video

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total knee replacement

The key difference is the relative size of the end of the femur or thigh bone. For a given front-to-back or anterior-posterior (AP) width, the femurs of females tend to be narrower in the medial-lateral (ML) or side-to-side direction compared to males. An implant which is proportioned based on male anatomy would, therefore, be too wide on a similarly sized female. The result is that when a surgeon sizes the implant based on the AP width of the femur, the implant could “overhang” the narrower female bone and cause irritation of the surrounding soft-tissue. Faced with this situation, orthopaedic surgeons are sometimes forced to “downsize” the femoral component during total knee replacement surgery. In downsizing the femoral component, the doctor chooses a smaller implant, so that the implant does not overhang the sides of the bone.

There are, however, some potential disadvantages to downsizing depending upon the type of instrumentation system the surgeon is using during the knee replacement procedure. If the surgeon is using an implant system where the femoral component is placed at a particular distance relative to the anterior surface of the femur (anterior referencing), excessive laxity in flexion can occur with downsizing. Alternatively, if the doctor is using a system which references the posterior aspect of the femur, the resulting femoral preparation could “notch” or undercut the anterior aspect of the femur. This could, in turn, lead to fracture of the femur.

Recognizing that neither of the above scenarios is desirable, the makers of implants specifically designed for females have sought to remedy this by making the implants more narrow in the ML direction. On a male knee, the implant could “underhang” leaving some distal femoral bone exposed, but this is generally not a problem.

In the company announcements, both manufacturers noted that their new “Female” knee replacements are designed to address the more narrow female femur. Zimmer also noted that differences extend beyond femur width to things such as the angle of the femur in relation to the tibia. It will be interesting to see how these new implants fair clinically and whether the potential advantages are realized.

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total knee replacement surgery game online

http://www.edheads.org/activities/knee/

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Total knee replacement

The resected bone can be several millimeters thick (about 1/4-1/3 inch). The separate components work together to form the complete prosthetic device. In some cases the surgeon may choose not to replace the patella and let your native patella mate with the other artificial components (this is quite common in Europe, less common in the US).

The Femoral Component

Typically this is a Cobalt-Chrome metal component. The highly polished outer surface serves as the end of the femur, the other side is either “cemented” or “press-fit” onto the prepared bone surface.

Most implants in the US today are cemented. A polymer based compound is mixed in the OR forming a putty which hardens. The surgeon puts the putty in between the implant and bone to secure it.

In the “press-fit” variety, a roughened surface on the inside of the component has a porous 3-D structure designed to promote bony ingrowth.

There are pros and cons to each type of fixation. As mentioned, the cemented version is more common, but both have well established clinical histories

The Tibial Component

The tibial component is usually a two-piece metal and plastic implant although there are all plastic versions available.

The metallic portion of the implant can be titanium or cobalt-chrome and it is fixed to the tibial bone in much the same way as the femoral implant.

The plastic component is known as a “tibial bearing” or “tibial spacer” or simply “tibial insert.” It is a plastic component made of a special grade polyethylene (UHMWPE). Manufacturers have begun to “treat” the plastic with gamma radiation to improve wear properties.

The Patellar Component

The patellar component is typically an all plastic component that is fixed to the cut surface of the underside of the patella or knee cap.

The component is secured with bone cement and articulates or “joins up” with the femoral component, as it would with the normal knee.

Because the patella moves up and down across the surface of the femoral component, the relative alignment of the two components is critical. Patella problems are among the most common complications following total knee replacement, although the overall complication rate is small.

Primary Knee Replacement

Primary Knee Replacement, as the term suggests, the name given to a family of knee implants designed to be used as a first knee replacement. This type of knee replacement allows the remaining soft-tissue to provide some of the constraint to the knee joint and is usually implanted in patients who have not had a previous Total Knee. The term constraint, does not imply limiting movement, rather it simply allows some of the normal stabilizers in the knee (namely the collateral ligaments, and sometimes the PCL) to still perform their function.

Revision Knee Replacement

Revision Knee Replacement is designed to replace a worn-out and/or loosened Primary Knee Replacement. This type of knee replacement has more intrinsic constraint and can “play the role” of some of the natural stabilizers which may be absent or no longer functioning. In some cases, a revision knee implant may be used as a patient’s first knee implant if the disease is advanced enough.

PS Knee Implants

PS, Posteriorly Stabilized, or PCL Substituting Knee Implants are designed to be implanted with the Posterior Cruciate Ligament or PCL removed. In this type of knee replacement, a protrusion on the tibial insert is designed to mate with a specially shaped bar (cam) on the femoral component. This “cam and post” interaction substitutes for the normal function of the PCL by:

CR Knee Implants

CR or Cruciate Retaining Knee Implants are designed to be implanted with an intact Posterior Cruciate Ligament or PCL. Often this ligament is still functioning to some degree in patients with advanced osteoarthritis. In this type of knee replacement, the PCL is allowed to act as the primary stabilizer limiting anterior or “frontward” movement of the femur (thigh) relative to the tibia (shin). This is the primary function of the PCL in the normal knee. Another function of the PCL is to promote posterior or backward movement of the femur relative to the tibia as you bend or flex your knee. This movement is necessary to allow for deep flexion of the knee.

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A. The worn ends of the femur ( thigh bone), tibia (shin) and patella (knee cap) are removed with a saw and replaced with metal and plastic.

More on Knee Replacement Surgery

Q. What, is a Knee Replacement Implant made of?

A. Implants are typically made of a combination of Cobalt Chrome and/or Titanium metals and UHMWPE (ultra-high-molecular-weight polyethylene) plastic.

More on Knee Implants.

Q. Are there different kinds of implants?

A. Yes! There are many types of knee implants that fit into broad categories related to their interaction with the remaining natural soft tissue. For example a CR or Cruciate Retaining knee implant is designed to work with the PCL (posterior cruciate ligament) intact. Other types of implants are designed to work without it. In addition, there are many manufacturers of implants which create several brands of knees in each of the broad categories. Surgeons have many, many choices.

More onTypes of Knee Implants.
Links to Implant Manufacturers.

Q. How long will my Knee Replacement last?

A. There are many studies on this topic and the actual time an implant will survive before needing revision will vary on a case by case basis. Several studies demonstrate greater than 90% survivorship at 15 years (1)

Q. How are the implants held in place?

A. Total knee replacement implants implants are secured to the bone either with a special polymeric compound (”bone cement”) or are “press-fit” into place. Press fit implants have rough or porous undersurfaces into which bone will grow.

More on Knee Implants.

Q. What is a Uni (or Partial or Half-knee) Replacement?

A. A “Uni” or unicompartmental knee replacement replaces only the medial (inner) or lateral (outer) half of the knee joint (the tibio-femoral joint). The knee cap or patella is not replaced.

More on Unicompartmental Knee Replacement.

Q. What is MIS or Minimally Invasive Knee Replacement?

A. MIS or Minimally Invasive Knee Replacement is like standard knee replacement except that the incision is smaller, and care is taken not to resect the quadriceps muscle (also known as “quad sparing”). Also, the patella is not “everted” or “flipped” over This is all intended to result in less trauma and speed recovery.

More on Minimally Invasive Knee Replacement.

Q. What about recovery, pain etc?

A. Every case is unique and this discussion is best left for a medical professional. You can read about the experience of other recipients at a very interesting discussion forum at Robin’s Total Knee Replacement.

References
1) Dixon MC, Brown RR, Parsch D, Scott RD. Modular fixed-bearing
total knee arthroplasty with retention of the posterior cruciate
ligament. A study of patients followed for a minimum of fifteen years.
J Bone Joint Surg Am.
2005 Mar;87(3):598-603

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Osteoarthritis

Often the cartilage begins to wear in an area of the knee that is “overloaded.” This is most commonly seen on the medial or inside part of your knee. This “medial compartment” is the area of the knee between the medial condyle of the femur and the medial aspect of the tibial plateau. In medial compartment wear, the bone just below the joint surface can change and a varus deformity or “bow-legged” condition can occur. As the deformity worsens, the compartment sees more load, which in turn causes more degeneration. This “downward spiral” can eventually lead to a severe state and the need for surgical intervention.

If the damage is localized and not too severe, a Unicompartmental Knee Implant may be indicated. Otherwise a Total Joint Replacement may be used. Each case is different and only your doctor can determine what is indicated.

If the above scenario occurs on the opposite side (the lateral compartment) a valgus or “knock-kneed” deformity can result. In general a valgus condition is less common than a varus condition.

You can visit the sites below for general information on osteoarthritis

http://www.arthritis.org/conditions/DiseaseCenter/oa.asp http://www.brighamandwomens.org/patient/osteoarthritis.asp http://www.stoneclinic.com/osteoknee.htm

Total Knee replacement can offer independence and mobility for those suffering from Osteoarthritis or other forms of degenerative joint disease. It is, however, a major surgery and involves a significant recovery period.

For some insight into what that is like, you can visit:

http://www.hieran.com/knee/

The surgical experience, rehabilitation following knee surgery and recovery are discussed in a forum where patients share stories and discuss their experiences.

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The outline below is indicative of the “standard” approach. A minimally invasive technique is similar, but the incision and disruption to surrounding soft-tissue is reduced. An incision is made a few inches above the knee cap and extends just below the knee into the shin. The outer capsule of the joint is opened and the bones of the knee are inspected. In one type of procedure, both the ACL and PCL are removed (if present). The ACL (anterior cruciate ligament) and the PCL (posterior cruciate ligament) are the primary front-to-back stabilizers of the knee joint. In patients with advanced disease, these ligaments are compromised or absent. (See section on different types of implants) The link below is an excellent interactive overview of knee surgery - you get to be the surgeon! (it is animated so you do not have to worry if you are a bit squeamish). Having developed both implants and instrumentation, I was amazed at how “realistic” this is. They have some nice photos of actual surgery as well for those of you that are really curious.

http://www.edheads.org/activities/knee/index.htm

Femoral Preparation in Total Knee Replacement

A small hole is drilled in the end of the femur (at about the center of the knee joint.

A long rod is placed in the intramedullary canal of the femur (the hollow portion of the bone where the marrow is).

A cutting guide is placed on the rod and rotated so that it sets up a slot to make the femoral distal cut. This is a cut that created a plane that is roughly parallel to the floor if you were in a standing position. This cut is made such that it is perpendicular to a line connecting the center of the hip and the center of the ankle. This line is the mechanical axis of the lower extremity and it is important that the implant is aligned properly with respect to this. In doing so, the load distribution across the implant is optimized and the longevity of the implant maximized.

Next, a cutting guide is placed on the plane of the distal cut, it is aligned in rotation and 4 more cuts are made. The rotational alignment here (which is called internal/external rotation) is important in balancing the soft tissue and aligning the patella track of the implant. The patella track is literally a track or groove in the implant in which the patella moves during knee motion. Incorrect alignment of this track can lead to pain and/or accelerated wear of the patella component.

Once these cuts are made, the preparation is basically finished. Some implants have small fixation pegs on the distal surface so two holes are sometimes drilled for these. In the case of a PS implant (see PS implant post), a “box” is cut out from roughly the center of the prepared femur to make space for the cam/post mechanism of the PS implantThe outline below is indicative of the “standard” approach. A minimally invasive technique is similar, but the incision and disruption to surrounding soft-tissue is reduced.

Tibial Preparation in Total Knee Replacement

• Typically, the top surface of the tibia is resected creating a planar surface that is perpendicular to the shaft of the tibia. In a “PCL retaining” procedure, a “bony island” is preserved around the insertion site of the Posterior Cruciate Ligament in the tibia. In a “PCL sacrificing” procedure, the PCL and the insertion area are removed.
• About 8mm of bone is removed as measured off of the “good” side of the joint surface of the tibia known as the tibial plateau. In the arthritic knee, there is usually uneven wear of the joint surface. The joint basically collapses on the diseased side. The resection level is typically a couple of millimeters below the surface of the worn side of the joint, or 8mm off of the “good” side. Creating a flat tibial surface therefore requires a wedge shaped piece of bone to be removed.
• Once the resection is made, trial components are placed in the joint. With the femoral and tibial prep complete (and often the patella prep as well), and a trial femur and tibia implant in place, the surgeon basically moves and tenses the joint through a range of motion. The surgeon can use tibial insert trials (also called tibial bearings or tibial spacers) of various thicknesses until the correct stability is achieved. The tibial insert trial corresponds to the tibial insert implant that will eventually sit in between the metal femoral and tibial
  implant components.
• Often, the surgeon must make surgical corrections of certain soft-tissue structures to help align and stabilize the knee.
• Once trialing is complete, the appropriate “keel” preparation is made. The keel is a fin or cross shaped protrusion on the implant that helps it stay fixed and in
  the bone. This can be punched, chiseled, broached or cut into the tibia and a set of instruments is used so that the resulting shape matches the implant. Here, the surgeon must take care in aligning the keel preparation so that the correct rotation of the implant about the axis of the tibia is achieved. Correct rotational alignment of the implant promotes better distribution of load across
  the implant and better motion of the knee joint.
• Next, the “tibial baseplate” portion of the implant is simply pressed or cemented in place.
• A plastic tibial insert is then snapped into the tibial baseplate (see the Implant section for more details). The insert comes in the various thicknesses that correspond to the trial used previously.

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Polyethylene Wear and Osteolysis

Although there have been many advances in Total Knee Implants, they are still mechanical devices that can wear over time or if implanted improperly.

Modern knee replacements have been cited to have a greater than 90% survivorship at 15 years (1) however, over the long term, challenges still remain.

The “weak link” so to speak in a Total Knee is typically the tibial insert (or tibial bearing). The insert is made of ultra-high-molecular-weight-polyethylene or UHMWPE. As your knee moves (to the tune of 1 million steps or more/year!) the surface of the insert will wear and create tiny particles of UHMWPE.

The wear rate in modern knees that are implanted well is very small. But if a knee is unbalanced and/or of poor design, accelerated wear can occur. This accelerated wear, can in turn, lead to failure of the insert (i.e. cracking) or a biologic response to the wear particles known as osteolysis. In the presence of the small particles (recognized as foreign bodies) the bone can “resorb” or waste away around the implants leading to loosening of the implants from the bone.

Knee implant design is a balance between providing freedom of movement and congruity. The less congruity between the tibial insert and femoral component, the more movement can occur (sounds good, but…). However, to distribute forces over a wide enough area to minimize wear (forces at the knee can reach up to 5 times body weight!), a close mating of the femoral component and tibial insert is desired. These competing requirements lead to a design challenge that is constantly being optimized as new implants are developed. Also recent treatment to implant materials can also help.

Surgical technique is also important. The better aligned the components are, the more resistant they will be to wear. Modern instrumentation has made knee replacement very reproducible. In addition, new computer assisted techniques may also be improving accuracy. On the other hand, new “less invasive” techniques offer reduced scarring and quicker recovery, but as you might infer, could make it more challenging to obtain a well aligned knee and hence could lead to long term problems if done incorrectly.

As younger and more active patients wish to maintain active lifestyles in the face of debilitating joint pain, the issue of implant wear will continue to be at the forefront and inspire continued development of implant design and surgical technique.

(1)”Long-term followup of nonmodular total knee replacements.”
Keating EM, Meding JB, Faris PM, Ritter MA. Clin Orthop. 2002 Nov;
(404):34-9.

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• Stryker
• Zimmer
• JnJ Depuy
• Biomet
• Smith and Nephew

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