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Medical Author:

B Sonny Bal, MD

Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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During some minimally invasive hip replacement surgery procedures, the person lies on one side. However, in the MIS-2-incision hip replacement procedure, the person lies flat on his or her back. Fluoroscopy is used to precisely guide the placement of the incision. Special instruments are used to make the small incisions. Also, the implants are slightly different in design than the implants that are used during a standard hip replacement surgery.

Traditional Hip Replacement Surgery

Standard total hip surgery involves an 8- to 12-inch incision. This helps the surgeon to align the implants and assess leg lengths. The instruments are designed for an opening of this size. Once the skin is opened, the surgeon dissects between the muscles, tendons, and nerves to reach the joint. This is known as the surgical approach. In North America, two types of approaches are used: the posterior approach and the lateral (anterior) approach.

• The posterior approach is usually made by using an incision that curves backward into the buttock area. The hip is reached by creating an incision and splitting the buttocks muscle and cutting the tendons of the small rotator of the hip. The arthritic hip ball (femoral head) is then taken out from the socket (acetabulum) by twisting the leg. The ball is cut off. The thigh bone and socket are hollowed out for the artificial implants. At the end of the operation, the muscles, fat layer, and skin are stitched back together.



• In the lateral, or anterior, approach, the skin is cut over the bony prominence on the side of the hipbone, the part that lies against the mattress when one sleeps on one's side. The thick fibrous tissue layer, called the fascia lata, which envelops and contains the large muscles of the thigh, must be cut to reach the muscle layer. The lateral buttocks muscle is split, allowing access to the front of the hip joint. The hip ball is removed. The thigh bone and socket are hollowed out. The implants are placed. At the end of the operation, the muscle, fat layer, and skin are repaired with stitches.

Until the muscles and the fascia lata heal and scar tissue forms, a person whose hip is replaced using either approach will continue to have soreness and weakness in that hip.

The posterior and lateral standard approaches are reliable, predictable, and safe in the hands of most orthopedic surgeons. The long-term results of these traditional hip replacements are well recorded, and outcomes after newer hip replacement techniques must be measured against these results.

Minimally Invasive Hip Replacement Surgery

Both the posterior approach and the lateral (anterior) approach have been adapted for use in minimally invasive techniques. Using a standard approach, a surgeon can transition to a minimally invasive approach by gradually shortening the incision to 4 inches or less. As the incision is shortened, the surgeon adapts to more restricted views of the anatomy. The incision can be moved from one site to another site without enlarging the length of the cut. The surgeon must learn to use methods that accommodate the smaller incision.

• Special instruments that are lower in profile and can fit through smaller skin openings are needed.



• Computer navigation techniques and fluoroscopy facilitate implant orientation, limb alignment, and other critical factors associated with the operation through these smaller openings. The skin, fascia lata, and underlying muscles are not cut as extensively. However, the underlying structures must still be divided to replace the hip.

MIS-2-incision hip replacement does not require the cutting of muscles and tendons. In addition, the fascia is cut toward the front of the thigh, where it is usually weaker and less developed and, therefore, not as critical for walking, unlike the thick and well-developed fascia on the side of the thigh.

If a person is choosing minimally invasive surgery, the specific approach used by the surgeon is important for the patient to understand. If the surgeon uses the posterior or the lateral (anterior) approach, then the only differences between the minimally invasive surgery and the traditional surgery are the size of the incision and the extent of deep muscle trauma; the surgeries are nearly identical in every other way. If the surgeon specifically uses the MIS-2-incision technique, the muscle trauma is significantly less and the recovery is much quicker.

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