Total or Mini: Will a New Hip Replacement Technique Take Over?

As I mentioned I would in my previous post, this week I used my linkroll to find a topic on which to write. What I found was quite interesting. There is a new orthopedic procedure for hip replacement known as a mini, or minimally invasive hip replacement. This is an alternative to the standard total hip replacement. The intriguing thing about this new procedure is that the surgeons performing it claim to be able to create the same end result as a traditional open hip replacement without the long hospital stay associated with such an operation. I feel that this is simply not the case. While it is true that the recovery time is shorter for patients who undergo the mini hip replacement, there are greater risks for long-term complications that negate any initial benefits of the less-invasive surgery.

The total hip replacement procedure is one of the oldest and most successful orthopedic operations performed today. No other joint can be replaced as easily or completely as the hip. The procedure is performed exactly the way it sounds. The entire hip joint is removed from its socket and sawn off of the top of the femur. An artificial prosthesis (image to the right) is then inserted into the core of the femur and locked into place with methyl methacrylate, a bony cement. Younger or more physically demanding patients can chose a cementless prosthesis which fuses naturally to the bone. Cementless prostheses have micropores that the femur can grow into and create a strong permanent bond. The other end of the prosthesis is inserted into an artificial cup that is placed within the socket of the existing joint in the pelvis.

There are several options for the material and design of the replacement hip. One common pairing is a metal and plastic combination wherein the replacement socket is plastic and the ball joint is metal. Stainless steel is often chosen for its low reactivity, although some patients opt for titanium instead. A newer option is a ceramic prosthesis, although these have not been around long enough to prove their longevity. They have a high standard to meet, though. Traditional total hip replacement with a stainless steel and plastic prosthesis can be expected to last well over twenty years. Eighty percent of all replacements last longer than twenty years, and over half last longer than thirty. Of course, the younger a patient is, the more physically demanding they will be on it and the longer they will need it to last. This is an inherent flaw in the process of joint replacement that can only be solved through the eventual replacement of the replaced joint. A second replacement is known as a revision hip replacement. Revisions do not last as long as the initial replacement, but it is rare for a patient to need more than one revision.

This is due to the fact that a typical candidate for total hip replacement surgery is older (above the age of fifty) with osteoarthritis of the hip. Osteoarthritis is caused by normal wear and tear on the joint as a component of the aging process, and is detailed in the image at left. In this common form of arthritis, the cartilage separating the two bones wears away and leaves the bones to rub against each other. This can be very painful and in some cases will render the joint immobile. Men around the age of forty-five begin to become candidates for osteoarthritis, and women catch up by around age fifty-five. With this in mind, it is easy to see how pretty much anyone could find themselves in need of a hip replacement at some point in their life. According to the Central Ohio Orthopedics Center, Over 166,000 hip replacements are done annually in the United States, with more than one third of those going to patients below the age of sixty-five.

Given that so many patients are elderly, it is imperative that infection and post-operative complications be kept to a minimum. This is where the mini hip replacement comes in. In the traditional surgery, a relatively large incision is made either posterior, lateral or anterior to the joint. This incision is made large enough to allow the surgeon full access to the joint and the surrounding muscle, tendons, and ligaments. With the entire area in full view, replacement and alignment is a fairly straightforward process. The mini hip replacement, on the other hand, involves two smaller incisions. One of these incisions is made posterior to the joint and the other is lateral. These smaller incisions reduce the risk of infection by limiting the amount of exposure to everything outside of the body. With the two access points it is possible for the surgeon to remove the deteriorated joint, insert the prosthesis, and cement it in place without ever actually seeing what is going on directly. Instead, x-rays and cameras help with the alignment of the prosthesis within the body.

As one can imagine, this is a difficult procedure. In spite of the fact that patients who undergo a mini hip replacement can be walking again the next day, not many surgeons are performing it because it is so much more difficult than the open procedure. Since the surgery itself is more difficult, there is a greater chance for error on behalf of the surgeon. These mistakes usually appear minor, such as a slight misalignment of the prosthesis, but they can lead to larger consequences later. Mini hip replacement recipients are at a greater risk for prosthesis dislocation than total hip replacement recipients. Dislocation of a prosthesis is a very serious problem that can only be corrected by a revision replacement.

From what I have read in the available literature, it seems to me that the mini hip replacement is not yet ready to completely replace the full hip replacement. The benefits of the mini procedure do not outweigh the possible consequences of a surgical mistake. After all, what good does it do to get out of the hospital a few days sooner if you may be setting yourself up for a revision ten years sooner? I cannot say that there is no hope for this new technique though. In the future, surgeons may very well become more proficient at the mini procedure. When they do it will be an excellent alternative for someone who needs a hip replacement but due to poor health cannot risk an open procedure.