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There are several different treatments available for patients with arthritis of the knee, including surgery. This article outlines 5 different things you should know about kneecap replacements (patellofemoral arthroplasty).

Patients with arthritis, a disease that is characterized by joint pain, inflammation and stiffness, have access to several different treatment methods that, while not able to cure the disease, can help ease symptoms and improve range of motion and functioning of a joint. One of the treatment methods for arthritis of the knee is a knee replacement surgery, which is a procedure that is conducted for patients who have worn out their cartilage (the cushioning surface that lines the knee joint). Knee replacement surgery replaces the worn out joint with components that are made of metal and plastic. Historically, knee replacement surgeries are successful in helping improve function and reduce pain.

Some patients don’t need to replace their whole knee as only a portion of their knee will be affected by the arthritis. In this case, patients undergo what is known as a partial knee replacement.

This type of surgery essentially just means that only a portion of your knee will be replaced. While most partial knee replacements tend to replace the inner (medial) or the outer (lateral) portion of the knee, sometimes, the partial knee replacement will be conducted to replace the cartilage under the kneecap. This portion of the knee is commonly known as the patellofemoral compartment. The implant that will replace the knee cap is made of a metal groove that fits at the end of the thighbone and has a plastic disc that is attached to the underside of the kneecap.

If you are considering undergoing kneecap replacement or patellofemoral arthroplasty, here are the five things you should know.

1. What happens in a patellofemoral kneecap replacement surgery?

In order to conduct a patellofemoral knee replacement, the surgeon will start by creating a surface on the underside of the kneecap, as well as at the grove that is at end of the thighbone which will hold the artificial joint or implant. Next, the surgeon will use cement to hold the implanted joint in position, which is similar to a total knee replacement. Finally, and most importantly, the surgeon will make sure that the kneecap is able to slide up and down the groove at the end of the thighbone so that you will be able to walk normally. If this last step is not properly conducted, the new implant can wear out quickly, causing you to need a revision surgery.

2. How does a patellofemoral kneecap replacement surgery compare to a total knee replacement surgery?

When it comes to knee replacement surgeries, the less that is replaced within the knee, the quicker your recovery will be. Thus, compared to a total knee replacement, the recovery from a partial knee replacement is much quicker. Furthermore, patients are able to begin the exercises and bend their knee right after surgery. However, while that full weight can be put on the knee, people generally use crutches or a walker for the first few weeks.

3. How long does the implant last?

Generally, knee implants can last as long as 20 years without needing a revision. However, it is difficult to know exactly how long a kneecap implant will last. There are several factors that can affect how long these implants last (such as weight and activity levels). Additionally, over the last decade, there have been significant changes to the design of these implants in the hope that these newly-designed implants will be more durable. At the moment, there not a lot of long-term data with regards to how long these implants last. There is short-term data which states that 80 to 90 percent of patients will have a good outcome in the first 10 years after a kneecap replacement. However, it is not currently known whether the kneecap replacement will last longer than that.

4. What are the complications associated with a patellofemoral kneecap replacement surgery?

One of the reasons that the kneecap replacement may not work is that there a problem with the knee joint. In some instances, arthritis can spread from one region to another. Therefore, while your arthritis was limited to the kneecap at one point and thus, you only required a kneecap replacement, If the arthritis spreads then you will need another replacement. In fact, studies show that about a quarter of patients who undergo a kneecap replacement will need to eventually get a total knee replacement as a result of their worsening arthritis.

5. Who benefits from a patellofemoral kneecap replacement surgery most?

The patients that get the biggest benefit from a kneecap replacement are those that actually have a very specific problem within their kneecap, such as a patella fracture or patellar tracking. These diseases are associated with wear and tear of the cartilage under the kneecap and so the condition is restricted to that region. Conversely, patients with generalized knee arthritis tend to eventually need a full knee replacement.

Conclusion

It is much less common to get a kneecap replacement compared to a total knee replacement or a partial knee replacement. A kneecap replacement only tends to work well when the patient has a disease that restricts their condition to the kneecap. Therefore, most patients with arthritis will eventually need a total knee replacement. However, a certain subset of patients will benefit from this procedure.

  • Mochizuki, ROBERT M., and D. J. Schurman. "Patellar complications following total knee arthroplasty." JBJS 61.6 (1979): 879-883.
  • Waters, T. S., and G. Bentley. "Patellar resurfacing in total knee arthroplasty: a prospective, randomized study." JBJS 85.2 (2003): 212-217.
  • Windsor, Russell E., Giles R. Scuderi, and John N. Insall. "Patellar fractures in total knee arthroplasty." The Journal of arthroplasty 4 (1989): S63-S67.
  • Photo courtesy of SteadyHealth

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