A Review of the Research on Knee Replacement Surgery

The number of surgeries to replace part or all of the knee joint has tripled in the last 10 years. Along with that increase has come many changes in the way reconstructive knee surgeries are done. In this specialty update, all aspects of knee surgery are researched and reviewed.

What can you expect to find in this article? First, an analysis of trends and costs associated with knee surgery. Then the authors present an update on surgical techniques and complications. These two sections are followed by a summary of outcomes (results) for each type of implant and in specific patient groups. Let's look at each one of these and see what's new.

Along with an increase in volume (number) of reconstructive knee surgeries has come a push to reduce costs. By studying data from hospitals, it looks like the time it takes to do a knee replacement has dropped by 20 minutes in the last 15 years. They say that "time is money" and that applies to hospitalizations. Longer operations cost more and increase the risk of complications.

There's been a trend away from hospital-based surgeries as more surgeons specialize in a particular procedure such as reconstructive knee surgery. That has led to high-volume specialty centers where surgeons perform many knee joint replacements each week. The result has been improved outcomes, fewer complications, and lower costs.

With improved technology, surgeons have been able to offer patients improved standard of care. For example, computer navigation and tools to make more specific cuts have reduced differences that occur from surgeon to surgeon. More careful attention to the mechanical axis of the implant has also improved how long the implants last. A natural outcome of that focus has been improved function for patients.

Another change in how surgeries are done has been the move from open incision to minimally invasive surgery. Many, many studies have been done comparing the two methods. Is one better than the other? With less cutting are there fewer complications? Does the surgery take less time with minimally invasive procedures and thereby save money?

Along with smaller incisions that preserve the soft tissues has come a concept called rapid recovery rehab. Patients are up and walking and putting weight on the knee right away. Everything in the rehab protocol is speeded up. Although the improved short-term results with a faster rehab cycle have been shown, there are still too many mixed or opposite results reported when comparing minimally invasive to open incision surgeries to say for sure that one is superior to the other.

Two other areas that were reviewed included patient outcomes and complications with each of the major types of joint implants. Let's start with types of implants. There's the standard (cruciate ligament retaining) knee design, high-flexion, mobile-bearing, fixed-bearing, and patellar replacement versus resurfacing. Each of these was developed with specific problems or patient factors in mind.

One way surgeons have to compare results with the various choices is to use one implant type in the left knee and a different implant in the right knee. Studies of this kind have helped show that the high-flexion implant really doesn't have any advantages over the standard design. Patients in both groups and who had one of each had the same long-term results in terms of motion and function.

When comparing the mobile-bearing implant with its movable, rotating platform to the fixed-bearing design, again, surgeons found no difference in results between the two groups. They looked at pain, motion, function, patient preference, and even survival of the implant (how long it lasted).

What about the patellar component (the kneecap)? Does knee pain improve if the back of the patella (next to the knee joint) is resurfaced? Resurfacing involves smoothing down the uneven spots and jagged edges of the cartilage behind the knee. The surgeon may put a thin plastic liner along the back of the patella as well. Is it better to leave the kneecap alone or replace it all together? This is one area where some differences were measured over time. Although it's still not clear if persistent knee pain is caused by the patella, reoperation rates are higher for patients who don't have the patella resurfaced.

And in the final area of analysis, the authors summarized their findings regarding patient complications and results in specific patient groups. It looks like patients who have other health issues have an overall higher rate of complications and increased risk of poor outcomes with their knee implant. Dislocations, deep infections, and implant loosening and failure were observed in the group at-risk due to poor health.

Implant failure requiring reoperation is most commonly linked with infection. Risk factors include male sex, patients with rheumatoid arthritis, and history of bone fracture anywhere around the knee. Infection is less likely when implants are put in place with cement that has antibiotic in it or when the patient is receiving intravenous (IV) antibiotics directly to the bloodstream.

Additional factors that increase the risk of infection include obesity (body mass index greater than 50), diabetes, and younger age. Diabetes was actually a major complicating factor. Patients with diabetes were more likely to suffer serious complications of surgery such as stroke, delayed wound healing, and amputation because of deep, uncontrolled infection.

In summary, there have been many changes in how total knee replacement surgeries are carried out. Type of incision made, type of implant used, and risk factors for failure have changed in the last 15 years. Advances in technology and high-volume specialty practices have contributed to improved outcomes for patients with reduced costs. The lack of convincing evidence to support one implant type over another has been an unexpected result of ongoing studies.

With the aging of America and increased incidence of obesity, surgeons expect the number of total knee replacements done in the U.S. each year to continue to escalate. Review studies like this one help surgeons and patients see where we are headed and make course corrections if necessary and as needed.

Reference: Carl A. Deirmengian, MD, and Jess H. Lonner, MD. What's New in Adult Reconstructive Knee Surgery. In The Journal of Bone and Joint Surgery. November 17, 2010. Vol. 92A. No. 16. Pp. 2753-2763.

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