1. Field of the Invention
This invention relates to the field of minimally invasive surgical techniques for a joint replacement, and more particularly, methods for accurately positioning components for hip or knee joint replacement procedures.
2. Description of the Related Art
During the course of total hip arthroplasty, acetabular and femoral prostheses are placed. In order for the implants to function up to their capacity, generally meaning greater than twenty (20) years of clinical reliability, each component must be placed in a specific position in relation to the patient's native anatomy. Specifically, proper positioning of the acetabular component in a hip replacement procedure appears to be crucial to the long-term success of the surgery. What exactly constitutes proper positioning of the acetabular component is the subject of much debate. A commonly used range, established by Lewinnek et al., involves a cup position in which the abduction angle is within the range of 30° to 50° and in which the anteversion angle is within the range of 5° to 25°. Generally, surgeons use radiographic techniques to achieve these angles.
Studies have shown, however, that a substantially large percentage of surgeries result in cups that are not within this range. This is especially true with respect to minimally invasive surgical procedures. Callanan et al. surveyed 1952 hip replacements, observing several prediction factors, and found that only 48.7% resulted in acetabular cups within this range. Indeed, of the 93 hip replacements in Callanan's survey that used minimally invasive techniques, only 19.4% resulted in acetabular cups within this range.
This supports the proposition that traditional techniques have been considered by many to be unreliable for determining proper positioning of the acetabular cup or femoral component.
A variety of tools are available, however, to assist the surgeon in achieving correct component alignment. The so-called traditional guides, or line-of-sight, have been in use for over 40 years and are very helpful, but not as reliable as one would hope.
In the last 8-9 years, in an effort to improve reliability, there have been attempts at using so-called navigation or computer guidance systems relying on pre-operative CT scans to pre-load information pertaining to the patient's anatomy, intraoperative registration (a cumbersome and potentially tedious method to match the patient's anatomy to the preloaded image), the placement of multiple skeletal pins for orientation, and elaborate line-of-site transmitters relying on complex computer algorithms to guide component placement. Unfortunately, in spite of the promise of improved results, the reluctance of patients to be exposed to a significant amount of radiation during a CT scan, the significant cost of such a test against a simple intraoperative x-ray treatment, the total cost of the computer guidance system (many hundreds of thousands of dollars plus the ongoing cost of support annually as the machine is maintained and updated), the incalculable cost to the healthcare system, and the patient of an unpredictable workflow as system breakdown occurs frequently, add operation time and potential risk to the patient, as well as considerable cost. Consequently, this method has not been widely adopted.
Furthermore, in spite of the existence of such tools, the current success rate for acetabular component positioning is only sixty percent (60%). Therefore, there is still a need to improve the reliability and efficiency of instrumentation in achieving these specific recognized optimal component positions.