Total Knee Replacement (TKR) is a very successful surgery. Along with Total Hip Replacement, it has been one of the most dramatic break through for the last century.
In an effort to maintain that success, hospitals, surgeons and implant manufacturers have worked hard to provide patients with techniques, tools and implants to minimize the chances of errors.
Unfortunately, the success rate is not 100%.
In this pages, I want to go over some possible scenarios of why you might be in the unlucky percentage that have to go through a knee or hip revision surgery.
Again, TKR and THR are very successful surgeries that aim are relieving your pain. Motion and activity levels are mostly dependent on your pain relief but can also be limited by your physician. However, if your pain persist or comes back, it is usually the first sign that you need to have your knee or hip check by your orthopedic surgeon.
So what can cause this persistent pain or a new onset of pain?
A - Infection
Infection of a total joint is a bad complications. If severe enough, your implants will have to be taken out and a spacer will be placed instead so as to clear the infection and maintain your joint open while you heal. Once the infection cleared, another operation will be necessary to implant new prothesis.
Redness, swelling and pain are all possible symptoms of an infection. A needle aspiration might be necessary to confirm the diagnosis
B - Implant Fixation
Hip and knee implants are held in place by two mechanisms
|Pressfit: A 'porous" structure on the implant allows the bone to grow in and to secure the implants to your body. It is very effective and mostly used in hips.
Cement: A powder and a liquid are mixed together to create a doughy cement, commonly used in dentistry as well. It is applied to the surfaces of the implant and held in place against the bone until it hardens. The bond created is very solid and this technique has been successfully refined for the last 50 years.
How do implants hurt and possibly loosen?
Though some common reasons are associated with this problem, it is mostly a multifactorial issue and all options will be looked at by your physician.
Just like the tire on your car, implants have to be positioned in the proper alignment they were designed to work under. Very precise instruments are used by surgeons to reduce the chance of errors. Navigation or “GPS” system specifically made for these surgeries can help achieve a high level of accuracy (see Computer Assisted Surgery).
However, it does happen that your implants might have been misaligned in the initial surgery and, as a process of increased pressures and forces, have now loosened.
If your “God given” hip or knee wore out and you needed it replaced, chances are that your artificial ones can as well. Implant systems of today are built to last and function under higher activity levels than before, but if you have had a knee or hipreplaced 10 years ago, your plastic could wear out. Again this can be associated with many other factors, misalignment being a primary reason for early sign of wear.
Make sure to go see your surgeon at appropriate intervals so he can monitor how your artificial joint is doing. Catching wear early is important before more damage is done.
Wear creates particles, which the body wants to get rid off but can’t: it doesn’t have the tools to “digest” plastic or metal particles. A natural response of the body is to “eat itself” as a last option to get rid off these particles. This “suicide” mission causes the natural bone around the implants to reabsorb itself and thus slowly creating a a void.
It is that lack of bone around the implants that can cause an implant to slowly loosen. Thus the importance of continuous monitoring by your physician.
The good news, wear is a slow process but it can sneak up on you!
Notice how the red arrow points to a narrowing of the joint space compared to the other side? it indicates that the plastic has worn out. Also note the areas highlighted by the circle and the triangle which points to bone voids created by the body’s response to “eating itself”.
A complete knee revision was required. Waiting too long to treat wear issues can lead to a complex revision surgery.
Obviously, if you fall or get hurt near or in the area of your joint replacement, you can increase the chance of the shock to either break your implant or your bone next to it, or break the implant bond loose.
4 - Trauma
Severe trauma, which could occur during a car or motorcycle accidents, might require immediate surgery.
5 - Instability
Total Joint surgery is not just about bone hurting. It is also about the muscles and tendons and ligaments that surround the joint and help it function properly as a whole. The combination of these structures is generally called the “Soft Tissue” envelope.
Obtaining, maintaining or restoring balance of the soft tissue envelope is a critical part of a total joint. For example, it is what keeps the ball in the socket on a hip replacement and what makes your knee “feel” stable on a knee replacement.
It can happen that due to an injury or a slight malposition of the implants or for other factors that a part of the soft tissue envelope becomes looser or tighter than the rest. With time, this inequality can worsen and it will require to be fixed either conservatively with a brace and/or physical therapy or surgically with a revision procedure.
On the left, the implants are aligned (see green bars). On the right, the ligaments are failing to maintain the implants centered and laxity is causing pain and a feeling of constant instability.
In summary, continuous or sudden pain after knee or hip replacement can be caused by many factors. Though often not too alarming, any changes that causes repeated onset of pain should be a sign that you need to see your physician.
Revision surgery can be needed. First and foremost however is to make sure that the true problem is identified so your surgeon know exactly what to fix. Waiting too long might make fixing the problem much more difficult.
From my extensive training at the Mayo Clinic, my team and I are able to bring to Southeastern Idaho a range of skills in identifying and fixing complex cases of revision hip and knee.