TotalKneeWeb.com – Article Index

A

Knee Replacement Allergies – Nothing to Sneeze At?

Arthritis, Osteoarthritis and Osteoporosis….What’s the Difference anyway?

B

What’s the “Best” Total Knee Replacement?

C

Knee Replacement Clicking

Patellar Clunk Syndrome: Complication Following Knee Replacement Surgery

F

Female Knee Replacement

G

General

Interesting Items from Around the Web October 11th 2010

Knee Replacement – Items from around the web – January 8th 2011

K

Knee Replacement-General

L

How Are the Ligaments Affected in Total Knee Replacement?

To Retain or Sacrifice the PCL (Posterior Cruciate Ligament)…That is the Question

M

Manipulation

Minimally Invasive (MIS)

Mobile Bearing

O

Osteoarthritis

Osteoporosis

P

Press-Fit Knee Replacement

Patellar Clunk Syndrome: Complication Following Knee Replacement Surgery

V

Video Showing a Traditional Total Knee Replacement Surgery?

Posted by admin | Filed Under Uncategorized | Leave a Comment 

Knee Replacement – Items from around the web – January 8th 2011

“Prehabilitation” and Knee Replacement.

In a recent article available at  LowerExtremityReview.com the concept of  “Prehabilitation” or exercise before Total Knee Replacement Surgery was reviewed.  It has been demonstrated that one of the predictors of post operative range of motion (ROM) is pre-operative ROM.  It stands to reason that exercises aimed at increasing pre-op ROM and knee function could positively impact post-op recovery and motion.  This article discusses this topic in detail and also includes a free-download for a recommended Pre-Op “Prehabilitation” regimen.

Click Here for the original article.

American Joint Replacement Registry becoming a reality

In countries like Sweden and Great Britain, hip and knee replacement procedures and outcomes are tracked in a national database or “registry.”  Such data is often useful in spotting trends and helping to reduce revision rates. Today, a similar set of data does not exist in the US, however a recent article in “Orthopedics Today”1 states that this is about to change. Beginning soon, data from 15 U.S.  “pilot” hospitals will begin to be collected and funneled into the registry.   Initially, things like the “mechanics” of the data collection and ensuring patient confidentially will be worked out.  An overview of the goals and anticipated impact of the registry can be found here

http://orthodoc.aaos.org/ajrr/AJRR%20Fact%20Sheet_AJRR.pdf at www.ajrr.net

1 “First Phase of U.S. Joint Replacement Registry Data Collection Set to Begin, Orthopedics Today, Nov 2010 online at: http://www.orthosupersite.com/view.aspx?rid=77205 ?

Posted by admin | Filed Under What's New? | 2 Comments 

The Impact of “High-Risk” Sports in Knee Replacement Patients

At the recent meeting of the American Academy of Orthopaedic Surgeons, a study was presented where survivorship of total knee replacements in patients who participated in certain “high-risk” sports was compared to those who did not participate in such activities.1

In this study, a group of 1500 patients that received the identical prosthesis were asked if they participated in certain high-risk activities. These are activities which place excessive load on the implant such as basketball, soccer or football. Within this group, 218 were identified as having participated in such “high-risk” sports. These patients were then “matched” against a control group so other factors such as BMI, age and sex could be eliminated.

What the researchers discovered was somewhat contrary to conventional wisdom. At roughly 7.5 years after surgery, the high-risk group had slightly superior function and slightly lower rates of failure (loosening, wear of the implant etc) compared to the control group. As stated in the study, “At a mean follow-up time of 7.5 years after modern condylar TKA in 218 patients no significant differences in implant durability could be demonstrated between those involved in not-recommended sports activities compared to matched controls.” Only time will tell if differences in implant longevity over longer periods will become apparent, so further study is warranted. Nonetheless, as increasingly younger and more active patients elect to have total knee replacement surgery, the limits on total knee replacement design and longevity will be tested and questioned.

References
1 Parratte S, Lynn Dahm DL, Stuart MJ, Pagnano MW, Berry DJ, Does Participation in Not-recommended Sports Impact Total Knee Arthroplasty Durability, AAOS Annual Meeting Podium Presentation, 2010

Posted by admin | Filed Under What's New? | 4 Comments 

Mobile Bearing Knee Replacement Offers no Benefits vs. Fixed Bearing

In a previous posting 1, the question was raised as to which is better, fixed or mobile bearing . In the end, the answer was not very clear. But in the view of one implant manufacture, the choice is simple: fixed bearing.

In a recent press release, a major U.S. Orthopedic implant company (Stryker Corporation) has decided not to offer their mobile bearing knee replacement in the U.S. market. Although the company has executed a clinical trial in an effort to gain FDA approval for the device, data gathered during the study has demonstrated no clinical advantages for the mobile bearing knee compared to a comparable fixed bearing design.

The company also cited higher costs and higher revision rates for mobile bearings as further reasons why the mobile bearing design will not be pursued in the U.S. market.

The original press release can be found here:
http://www.prnewswire.com/news-releases/us-ide-study-indicates-mobile-bearing-knees-offer-no-clinical-advantages-over-fixed-bearing-knees-86866577.html

More on Stryker can be found here:
http://www.stryker.com/en-us/products/Orthopaedics/KneeReplacement/index.htm

1 Is One Really Better? Fixed vs. Mobile Bearing Knee replacement

Posted by admin | Filed Under What's New? | Leave a Comment 

Press-Fit Total Knee Replacement: Working to Prevent Loosening and Bone Loss

In , the worn ends of the bones that make up the joint are replaced with metal and plastic implants. These implants are secured to the bone either with “bone cement” which the surgeon applies to the implant and bony surfaces or they are simply “press-fit” into place. In the press-fit scenario, the surface of the implant which contacts the bone is typically coated with a porous structure. This structure is designed to mimic the porous or sponge-like structure of the prepared bone in order to promote bony in-growth into the implant coating.

In addition to utilizing a bone-like porous structure for press-fit implant coatings, it is desirable that the “flexibility” or “elasticity” of the implant material also approach that of bone. This is because bone, which is a dynamic living tissue, actually responds and adjusts to the stresses placed upon it. If an implant is too stiff relative to the bone, then over time, the bone will become less and less dense, literally disappearing under the implant due to what the body perceives as lack of use (the old “use it or loose it” adage). This is known as “stress-shielding.” The resulting bone loss may eventually result in loosening of the implant.

It is possible that such bone loss and resulting implant failure can be avoided by using materials and coatings which better approximate the properties of real bone. This is because as the implant material properties approach that of normal bone, loads are better transferred through the implant to the bone, thus allowing the bone to perceive more normal use and encourage the continued maintenance of bone under the implant.

In a recent article in the Journal of Bone and Joint Surgery (American) Minoda et. al1. looked at how bone in the tibia (shin bone) responded to a particular type of press-fit implant. The implant utilized a tantalum porous coating. The property of the bone that was measured to gage how it responded to the implant was bone mineral density (BMD). In the study, a group of implanted knees (28) receiving the press-fit implant was followed and compared over a period of two years, two a group of knees (28) with a cemented implant. BMD scans taken were taken at various intervals.

The researchers found that BMD decreased in the tibia in both groups. However, in the press-fit (porous tantalum) group, the decrease was only 6.7% +/- 22.9% vs. 36.8% +/- 24.2% in the cemented group. So it appears that this particular porous coated implant may have been able to allow more natural loading of the tibia, thereby reducing bone loss compared to the cemented implant. Only time will tell if these apparent benefits continue long-term.

References:
1. Yukihide M, Kobayashi A, Iwaki H, Ikebuchi M,I nori F, Takaoka K. Comparison of Bone Mineral Density Between Porous Tantalum and Cemented Tibial Total Knee Arthroplasty Components. Journal of Bone and Joint Surgery (American). 2010;92:700-706

Posted by admin | Filed Under What's New? | 1 Comment 

Weight Gain After Knee Replacement?

A recent study out of the University at Delaware found that patients actually gained weight following knee replacement surgery. Conventional wisdom was that after suffering years of debilitating pain, formerly sedentary arthritis sufferers would resume activity and exercise following their knee replacement. However, researchers found that patients actually gained an average of 14 pounds after a two year follow up period…

Follow this link for more information on this topic

Posted by admin | Filed Under What's New? | 1 Comment 

Mobile Bearing Knee Replacement

A particular type of you may hear about is known as the “Rotating Platform” or “Mobile Bearing” knee. In this version the tibial insert (see the Implant post) is designed to move in between the Femoral component and the tibial component.

The femoral and tibial components are fixed to the thigh and shin bones respectively. This allows the insert to remain well mated against the femoral component while still allowing the necessary rotational movement of the tibia (shin) relative to the femur (thigh). The possible benefits are:

  • Increased wear resistance since the femur and tibial insert can be made to “match” more closely. Increasing the contact between the components reduces the pressure on the insert making it potentially last longer. In fixed bearing knees, the rotational movement of the femur relative to the tibia has to occur on top of the insert, so it can’t be made to match as closely.
  • The potential for more natural motion since it allows a greater degree of rotation about the knee compared to fixed designs.

Keep in mind though that since the insert can move it can also dislocate. In addition, the high conformity between the insert and femur of this implant can sometimes limit flexion of the knee compared to other designs. Basically, increased rotation at the knee (like during a golf swing) can come at the expense of increased flexion.

Note that traditional fixed bearing knees also allow rotation to occur, but in a different way. Rotation occurs on the plastic bearing surface between the femoral component and the tibial insert.

Several studies have shown that the long-term results of both implants are comparable.

The study below found similar results in patients who received one of each type of replacement (one in each leg of course!)

Chiu KY, Ng TP, Tang WM, Lam P. “Bilateral total knee arthroplasty: One mobile-bearing and one fixed-bearing”J Orthop Surg (Hong Kong). 2001 Jun;9(1):45-50

Posted by admin | Filed Under Uncategorized | Leave a Comment 

Knee Replacement Complications

(also known as total knee arthroplasty) is generally a highly successful procedure with excellent long-term results. In a recent study, 97% of patients remained “revision-free” at 10 years 1. Despite these favorable outcomes, complications may still occur. Listed below are some of the more common complications of total knee replacement surgery.

Infection

Several steps are taken to prevent infection. For example, antibiotics are often given before, during and after knee replacement surgery. Still, a small percentage of knee replacements become infected. In a recent study of over 3000 replacements, 2.9% experienced “superficial” infections while 0.8% of infections occurred within the joint. An increased rate of infection was observed in patients who experienced complex surgery or who had certain characteristics such as obesity or poor pre-operative health. 2

Loosening

Knee replacement components are affixed to the bone in two ways. In “press-fit” implants, long term fixation relies on the growth of bone into what is typically a porous surface or coating on the underside of the implant. Alternatively, the implants may be “cemented” into place with a strong polymer (PMMA) which is mixed and applied at the time of surgery. Both of these fixation methods can fail over time for a variety of reasons causing the implant to become loose and requiring revision (see Implant Poly Wear)

DVT

Deep Vein Thrombosis (DVT) is a rare but potentially very serious complication. Blood clots (thrombus) can sometimes form in the “deep” veins near the surgical site. This can cause pain, redness and swelling. Sometimes, the clot can become dislodged and travel through the bloodstream and into the lungs where it can become trapped. This is called a pulmonary embolism and can be fatal. Obviously, many, many precautions are taken to prevent this serious complication.

Patellar Clunk Syndrome

This complication involves interaction of the scar tissue at the top of the patella with the femoral component. See our article on Patellar Clunk Syndrome for more information.

Joint stiffness

Obviously, the joint will be soar and relatively stiff immediately after surgery, however, limited flexion after the immediate post-operative period is undesirable. To read more on stiffness following knee replacement surgery, visit our article joint stiffness following knee replacement surgery.

Allergic Reaction

A small number of patients may experience an allergic reaction or hypersensitivity to the metallic elements in the implants. A more detailed explanation of this complication can be found our article on this topic.

1 Barrington JW, SahA, Malchau H, Burke DW. Contemporary cruciate-retaining total knee arthroplasty with a pegged tibial baseplate. Results at a minimum of ten years. JBJS (Am.). 2009;91:874-878.

2. Jämsen E, Varonen M, Huhtala H, Lehto MU, Lumio J, Konttinen YT, Moilanen T. Incidence of Prosthetic Joint Infections After Primary Knee Arthroplasty.  J Arthroplasty.2008 Dec 3.

Posted by admin | Filed Under Uncategorized | Leave a Comment 

Patellar Clunk Syndrome: Complication Following Knee Replacement Surgery

In general, (TKR) is a highly successful procedure. However, complications, although relatively rare, can sometimes occur. One such complication is known as .

To understand this condition, it helps to first understand a little bit about knee anatomy and function (Figure 1). During knee flexion and extension, the patella (knee-cap) rides within a groove in the femur (thigh bone).

Knee Anatomy

Figure 1: Basic Knee Anatomy

In knee replacement the worn ends of the bones are “resurfaced” with metal and plastic implants. The patellar groove is part of the metal femoral component that is implanted onto the prepared femur during the total knee replacement procedure. At the end of this groove there is a transition between the metallic implant and the native bony surface.

Following knee replacement, scar tissue can sometimes form at the top or “superior pole” of the patella. During particularly deep flexion, this scar tissue may move below the end of the groove in the femoral component and then “catch” on the end of the groove as the patella moves back with knee extension. It is this catching and then forceful release with extension that results in the “clunk” and pain characteristic of this condition.

This condition is more prevalent in a type of knee replacement known as Posterior Stabilized, or “PS” knee replacement, although it has also been reported in Cruciate Retaining (CR) knee designs as well. 1 In PS knee designs, where the posterior cruciate ligament is removed, the patellar groove tends to be shorter to avoid contact (in extension) between the end of the groove and a plastic post on the tibial component found in these types of designs. Consequently, the patella can come off the end of the groove during lesser degrees of flexion.

The publication cited at the end of this article provides more detailed information and a review of some of the literature on patellar clunk.

1 Niikura T, Tsumura N, Tsujimoto K, Yoshiya S, Jurosaka M, Shiba R. Patellar Clunk Syndrome After TKA with Cruciate Retaining Design: A Report of Two Cases. Orthopedics. 2008: 31:90

Posted by admin | Filed Under What's New? | 71 Comments 

Is Knee Replacement in Your Future?

Most knee replacements are performed for the treatment of where the smooth cartilage in the knee joint breaks down resulting in pain, stiffness and swelling. The x-ray below is of a knee where osteoarthritis is present.  Note the close proximity of the upper (femur) and lower (tibia) bones.  In this knee the cartilage, which is not visible on an x-ray has worn away.  If this had been a healthy knee, there would be a distinct gap between the two bones.

intro-re-write-21-jan-09_html_2834b341

Osteoarthritis is usually progressive.  It often begins mildly, but over time, wear in the cartilage starts to result in an uneven distribution of weight across the knee joint; often with more damage observed on one side versus the other.  This in turn causes even more force to pass through the affected side, resulting in even faster degeneration of the joint.

This localized damage is most commonly found on the inside or “medial” part of the knee (), but it can also occur on the “lateral” or outside part of the knee (lateral compartment).  When it occurs on the medial side, the patient may have a varus or “bow-legged” deformity.  When lateral osteoarthritis is present, a distinct “knock-kneed” or valgus deformity is observed.

These deformities are usually corrected at the time of .

It is interesting to consider what, if anything, may initiate this cycle of uneven wear, worsening load distribution, and further wear.  Is it possible that some folks may be predisposed to this condition due to their bony anatomy?  A presentation at this years AAOS meeting looked to answer this very question. 1 The researchers examined the anatomy in patients receiving knee replacements whose pre-operative varus and valgus deformities were significant.  In those patients, they found that key functional axes in the knee were not aligned normally.  Specifically, they found that the alignment of the “mechanical axis” of the lower limb to the in the knee was not normal. To understand these axes and their observed relationship, a review of basic knee anatomy is required.

In the normal lower limb, the mechanical axis is defined as an imaginary line originating at the center of the femoral head (the “ball” on the “ball-and-socket hip joint) passing through the center of the knee and ending at the center of the ankle.  When the hip, knee and ankle line up in this way, the lower limb and knee joint alignment are considered “normal”.  In a varus or valgus knee, the center of the knee is no longer on this line and is pushed “outward” in varus and “inward”  in valgus.

The epicondylar axis is an imaginary line connecting the femoral (thigh-bone) origins of the medial collateral and lateral collateral ligaments (MCL and LCL).  One can think of these ligaments as the “ropes” or “chains holding a swing.  In this analogy, the epicondylar axis is like the top bar of the swing.  The tibia or thigh bone is the swing which rotates about the bar (epicondylar axis) during knee flexion and extension.

is-knee-replacement-in-your-future-23-mar-09_html_m53f606bc

In their study, the authors observed that in patients with severe varus or valgus deformities, the epicondylar axis was “misaligned” relative to the mechanical axis in the same direction (albeit smaller in magnitude) as in the knee joint deformity.  For example, if a patient had severe osteoarthritis in the medial or inside part of the knee, a significant bow-legged or varus deformity was observed and the epicondylar axis was “tilted” in the same direction.  In other words, the inherent bony anatomy appeared to predispose certain patients to uneven loading across the knee joint (a “crooked swing”), which, in turn appears to have made them more susceptible to the resulting osteoarthritic deformity.  The results were not statistically significant, but a noticeable trend was observed.  So to answer the question “is knee replacement in your future?” one may not have to look much further than one’s own bony anatomy.

1. Beyers-Thering MT, Krackow KA, Mihalko WM. “Relationship of the Femoral Epicondylar Axis to the Mechanical Axis in Deformed Osteoarthritic Knees.” 2009 AAOS Annual Meeting, Poster No. P201

Posted by admin | Filed Under What's New? | 2 Comments 

Next Page »