Minimally Invasive Hip Joint Replacement

The topic of minimally invasive total hip replacement (a.k.a. minimally invasive total hip arthroplasty or THA) has received particular scrutiny in the orthopaedic literature, and it continues to attract the attention of the lay press. Increasingly, patients are asking questions about minimally invasive surgery (MIS), and they are seeking surgeons who can offer this type of service.

The purpose of any total hip replacement is to treat end-stage arthritis by removing the arthritic joint. The worn cartilage surface of the joint is cut away, along with a portion of the associated bone. Then, the joint is replaced by artificial prosthetic components made of ceramic, metal, or plastic. The hip joint is a ball and socket joint, and a total hip replacement includes a femoral component with a femoral head (the ball) and an acetabular component or cup (the socket). The cup is placed in the pelvis, and the femoral head and stem are attached to the femur (thigh bone). The aim is to eliminate pain, and the result is a dramatic improvement in hip function.

The essential difference between minimally invasive THA and conventional total hip replacement is the size of the skin incision. Minimally invasive THA is defined as a total hip replacement performed through skin incisions measuring 10 to 12 cm (4 inches) or less. Depending on the size of the patient, total hip replacement can be performed through even smaller incisions. A smaller skin incision is accompanied by decreased dissection of the underlying musculature and hip capsule. For this reason, minimally invasive total hip replacement has come to be known as a "tissue-sparing" procedure.

Depending on the surgeon, minimally invasive total hip replacement can be accomplished through a variety of incisions. It can be accomplished through a single posterior incision on the back of the buttocks. It can be accomplished through a single anterior incision on the front of the hip. Or, it can be accomplished using an approach that combines two small incisions, one on the front and one on the back: the so-called "two-incision" technique. While each of these approaches has its proponents, none has been proven to be clinically superior.

Over the past few years, as minimally invasive surgery has begun to increase in popularity, a significant number of orthopaedic surgeons have voiced their concern regarding the relative safety of minimally invasive total hip replacement. After all, total hip replacement performed through standard incisions has a demonstrated track record of success. The key to success of any total hip replacement is the accurate placement of the prosthetic components. If these components are not selected and positioned appropriately, then the patient may experience problems postoperatively. These problems include dislocation of the joint and limb length inequality. With smaller incisions, the surgeon has a restricted view of the anatomy, and some surgeons have argued that minimally invasive surgery may lead to poorly positioned components. Some critics have asked whether surgeons should risk additional complications for what seems to be only a cosmetic benefit.

Early reports in the orthopaedic literature document increased complications with minimally invasive THA compared to traditional total hip arthroplasty. However, a close inspection of these early reports will demonstrate that most of the complications of minimally invasive total hip replacement are associated with surgeons who have been unfamiliar with these newer techniques. By now, there have been multiple studies showing that minimally invasive THA is as safe as traditional THA when it is performed by surgeons with adequate training and experience using minimally invasive techniques. In fact, some studies show that there may be advantages particular to minimally invasive total hip replacement. Some of these advantages include better postoperative pain control, early hospital discharge, and quicker postoperative recovery.

It is important to note that minimally invasive total hip replacement does not improve long term functional results. So, at one year postoperatively, a patient treated with a standard total hip replacement and a patient treated with minimally invasive surgery will be expected to demonstrate the same improvement in hip function. Minimally invasive surgery marks a change in the surgical approach, but it does not improve the durability of the components. The functional benefits of minimally invasive surgery are limited to the early postoperative course.

It is thought that minimally invasive surgery produces less pain due to the fact that there is a lesser degree of soft tissue disruption. However, it is important to note that the same pioneers who developed minimally invasive THA also developed simultaneous improvements in the methods used for anesthesia and pain control. When general inhalational anesthetic agents are avoided, patients experience fewer of the complications traditionally associated with anesthesia, including problems with blood pressure, confusion, and nausea. Following surgery, patients recover quickly, and they feel more alert. They are ready to begin postoperative rehabilitation activities (including walking) within hours of the completion of their surgery. With newer anesthetic and pain management programs, patients feel better, and they have the best chance of maximizing the benefits of minimally invasive surgery. For some patients, same-day discharge is possible if appropriate postoperative milestones can be met.

Perhaps the most important benefits associated with minimally invasive total hip replacement are psychological in nature. No doubt, some patients prefer minimally invasive total hip replacement due to the improved cosmetic appearance of a smaller incision. In addition to the creation of a smaller surgical scar, minimally invasive total hip replacement aims to limit the amount deep dissection and to preserve the integrity of associated soft tissue structures. It is possible that patients treated with minimally invasive surgery feel that their bodies have been violated to a lesser extent. Whatever the case, compared to patients treated with larger standard incisions, patients treated with minimally invasive total hip replacement demonstrate superior satisfaction with their surgery.

Depending on the patient, minimally invasive surgery may not be possible. Some patients may have a deformity that requires a more extensive surgical approach, and larger patients require a larger incision for exposure of the hip. The size of the incision should be adjusted as necessary in order to ensure appropriate fixation and position of the prosthetic components. In most circumstances, with the appropriate surgical team, minimally invasive total hip replacement can be accomplished safely without compromising clinical outcome. With this in mind, minimally invasive total hip replacement will probably continue to gain popularity. It seems unlikely that patients would choose a larger incision when a smaller incision would suffice.