The “approach” is the incision used for hip replacement and the deep pathway taken through the soft tissues. “Anterior Approach” refers to the use of the Short Smith-Petersen Approach to the hip.
Simply choosing the anterior approach for hip replacement however, does not guarantee patient benefits. Other elements of the technique are also necessary for minimizing soft tissue disruption, enhancing accuracy of artificial hip components and minimizing the chance of complication. Specifically supine patient position, the orthopedic table, and intra operative checks with the image intensifier(x-ray) enhance safety and accuracy of anterior approach and make anterior approach applicable to essentially all patients.
Definitions: Supine means patient on their back rather than on their side (lateral). Orthopedic table refers to the HANA or PROfx table. An image intensifier is a low dose x-ray machine used during surgery that displays an enhanced image on a TV screen and will also make x-ray prints.
Most surgeons performing hip replacement are accustomed to placing the patient lateral on a standard flat table and not taking check x-rays during surgery. Anterior approach hip replacement as I describe it is therefore a departure in methods which is often initially resisted by the uninitiated surgeon.
Supine patient position: With the patient lying on his back during surgery, his skeletal position is more consistent which allows better anatomic references for accurate positioning of the acetabular (hip socket) component as well as assessment of leg length. Urgent or emergency patient problems that the anesthesiologist might face are also more easily handled.
The orthopedic table: Though anterior approach is an ideal soft tissue interval for hip surgery regarding muscle preservation, it presents problems with access to the femur. If the surgeon struggles for access, muscles can be damaged and the benefits of anterior approach lost. The orthopedic table’s unique positioning capabilities deliver the upper femur for surgeon access while minimizing muscle trauma. The table acts outside the sterile field, moving the leg with the parallel carbon fiber spar and also acts inside the wound by lifting the upper femur for access with the robotic femoral support hook.
The image intensifier: Final judgment of the accuracy of a hip replacement (acetabular position, leg length, femoral offset, and component fit) is judged by x-ray. I advocate strongly that this information should be obtained during surgery (with the image intensifier) prior to closing the wound. An advantage of the anterior approach is that with the patient supine on the carbon fiber table, accurate x-ray information is easily and immediately available. With the patient lateral however, x-rays are more difficult to obtain and less accurate because of variable patient position and less accurate control of the x-ray direction. It is standard practice among the large majority of hip replacement surgeons (using lateral position and standard tables) to use pre operative planning from x-rays, positioning guides, and bony landmarks to guide component placement. Their next step however is to close the wound and then get an x-ray following surgery to see if their judgment is correct. Though experienced surgeons will often get things right without a check x-ray, learning the truth after the fact tends to make surgeons accept inaccuracies and a return to the operating room is the only solution for large inaccuracies.
Patients who get hip replacement typically get hip and pelvis x-rays at a number of occasions: prior to surgery, possibly during surgery, following surgery and at long term follow-up visits. I would say however, that the most important time to take a check x-ray is during surgery. Artificial hip components that are placed inaccurately can lead to multiple and life long problems (hip dislocation, inaccurate leg length, accelerated wear, squeaking hips, repeat surgeries). The radiation dose to the patient from an anterior approach hip replacement utilizing a modern image intensifier is typically not greater than one or two standard pelvis x-rays and is therefore safe.
Computer guidance to position hip components is also helpful in enhancing accuracy. The computer however creates a virtual picture with some tolerance for error while x-ray is an actual picture. My impression is therefore that computer guided surgery is not quite as accurate as checks with the image intensifier. Also, the surgeon who uses the computer still needs to get an x-ray at some point to see if the computer is right.
Along with muscle preservation the orthopedic table and supine position enhance accuracy by facilitating accurate intra operative x-rays. Small adjustments of pelvis and hip position made and held with the orthopedic table maximize the accuracy of intra operative x-ray. This accuracy, I find is greater than that seen on after surgery x-rays.
Use of the anterior approach incision therefore does not by itself bring maximum patient benefit. Anterior approach combined with the technologies and methods of the supine position, theorthopedic table,and theimage intensifierdoes.
Be aware also that some surgeons erroneously refer to antero-lateral or lateral approaches as “anterior” (see also Surgical Approaches for Hip Replacement).
Joel Matta, MD