Mini-Incision Joint Replacement: Shorter Incisions vs. Longer Term Results
Certainly you’ve heard about it. You may even know someone who had it done. You’ve probably seen it on the 10 o’clock news. The patient goes into the hospital to have a total joint replacement (probably a hip replacement) and walks out of the hospital the same day. That seems rather incredible since most patients you’ve heard of spend a few days in the hospital after such an operation. It just has to be a better operation, right? Well, it’s not quite that easy.
Total joint replacement has been done successfully since the 1970’s. Hundreds of thousands of them are done around the world annually. When done properly a total joint replacement has the potential to relieve pain, improve function and to last for a long time. Over 90% of total hips and total knees done today will last for at least 15 years, but that hasn’t always been the case. In earlier years the plastic might wear out too quickly. Early metal parts were known to break. But improvements in metallurgy and in manufacture of the polyethylene (plastic), and use of alternative materials such as ceramics have largely eliminated or at least minimized the issue of failure of the “parts”. So today, in the case of hip joint replacement, the majority of failures are due to infection, dislocation or loosening of the parts (failure of fixation of the part to the bone). So lets look at each of those issues.
Routine use of antibiotics and improvement in surgical techniques in general have resulted in an infection rate of approximately 1% for traditional total joint replacement surgery. That rate doubles for minimal incision joint replacements. Why? Operations done through smaller incisions often take more time to complete and it has long been known that longer surgical time is correlated with higher infection rates. More importantly, however, is the issue of damage to the tissues. In order to work on a joint the skin, fatty tissue and muscles have to be gotten out of the way. That can be accomplished either by cutting those tissues or (after making a smaller incision) by stretching the tissues. A clean incision through healthy tissue, regardless of length, will usually heal uneventfully in 7 to 14 days. But if that tissue is damaged then healing isn’t as reliable. Stretching tissues excessively can produce such damage, as can abrading the skin edges of excessively small incisions by the use of various instruments (drills, reamers, etc.). Early studies on minimal incision joint replacement indicate that stretching and abrasion of the soft tissues probably contribute to the observed higher incidence of poor skin healing and subsequent wound complications including infection.
The issues of dislocation and of failure of fixation (the artificial joint parts coming loose) are directly related to a number of things, but most consistently to proper positioning and sizing of the component parts. Improper positioning can result in less than optimal orientation between ball and socket, causing the ball to slip out of the socket (dislocation). While that can be a complication that can occur early or later after a hip replacement, many times it can be resolved without further surgery. More troubling, however, is the issue of the parts coming loose prematurely, because if that happens then the parts usually have to be replaced all over again. The quality of fixation is dependent upon many things including how “straight” the femoral component is implanted and how tight is the press fit. Once again, studies have shown that malposition of ball and/or socket components in hip replacement surgery is more frequent in mini-incision surgery and that there is a significantly higher percentage of poor fitting components in those mini-incision procedures. Since mini-incision surgery hasn’t been around too long we are not yet sure if these issues of sub optimal alignment and sizing will result in higher failure rates, but those issues are known to cause higher failure rates in traditional incision surgeries.
So where do we stand and what do we tell you, our patients? First, common sense dictates that a surgeon should use the smallest incision possible for any surgical procedure while assuring that the incision and the exposure of the joint must be sufficient to perform the procedure with precision and accuracy. In past years the incision for a total hip replacement used to be 6 to 10 inches routinely. Now, owing to improved instruments and techniques, such incisions are often reduced to 4 inches. Total knee incisions can also often be reduced in length. But thus far absolutely no one who is a proponent of mini-incision joint replacement has even suggested, much less proven, that these techniques might produce long term results equal to or greater than traditional techniques. And at this point it is of the utmost importance that the well-known and proven long term benefits of joint replacement not be compromised by a technique that offers only a short term benefit (a shorter scar or, sometimes, a shorter hospitalization).
We are constantly monitoring and studying changes in surgical techniques in orthopaedics. We consistently attend courses to exchange ideas with other experts in our field and to keep abreast of progress in our specialty. We adopt changes once they have been proven to be of benefit to you and not just because they have promise. Change for any other reason may be good marketing, but it might also be bad medicine.
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