Orthopedic personnel roles in the OR for computer-assisted total knee arthroplasty

AORN Journal,  Oct, 2005  by M.L. Swank,  I.E. Lehnert

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As twenty-first century orthopedic OR equipment and techniques evolve, so do the roles of orthopedic OR personnel. The change from performing traditional orthopedic surgery to performing computer-assisted orthopedic surgery can be both challenging and rewarding. Computer-assisted surgery (CAS) shifts OR protocols away from traditional surgeon-focused procedures to a more integrated team approach because the surgeon relies more heavily on the skills and contributions of the entire surgical team. Accordingly, excellent rapport can develop between surgeons and staff members, particularly during the transition from performing traditional surgery to performing CAS, as the surgeon and other surgical team members learn to use the equipment side by side.

This article describes the current status of CAS for total knee arthroplasty (TIC, A) based on the experiences of the orthopedic surgical team at Jewish Hospital, Cincinnati. Methods and problems associated with traditional TKA surgery and the development and advantages of CAS are discussed, thus allowing the changing role of orthopedic OR personnel to be brought into perspective.

TRADITIONAL TKA

Patients with arthritis and mechanical abnormalities that result from fractures or hereditary conditions often require TKA. Every year, 250,000 people in the United States and 600,000 people worldwide undergo TKA procedures. (1) In addition, the ever-increasing population of older adults will expand the demand for arthroplasty; the overall market for knee replacements is predicted to reach sales of $925 million in 2009, representing a compound annual growth of 5.2%. (2) Furthermore, as a consequence of significant improvements in TKA clinical outcomes, younger patients are seeking to regain full mobility and an active lifestyle with TKA surgery earlier than ever before. (2)

Prosthetic knees generally are comprised of femoral, tibial, and patellar components. Implanting these components requires the surgeon to make an incision over the front of the knee and accurately resect the distal end of the femur and the proximal end of the tibia to accommodate the prosthesis. The surgeon must ensure that the prosthetic components are aligned correctly and that the ligaments are balanced. To achieve this, the surgeon uses preoperative radiographs with acetate templates and mechanical alignment jigs (ie, instruments used to make bone incisions intraoperatively) to plan and perform surgical reconstruction. Individual jigs are used to perform the distal femur, anterior/posterior femur, and chamfer cuts, thus allowing the prosthesis to be implanted.

PROBLEMS ASSOCIATED WITH TRADITIONAL METHODS

Accurate alignment of the femoral and tibial implant components in TKA surgery is a critical factor for the success of the procedure in terms of knee stability, reduced postoperative pain and complications, and the overall longevity of the prosthesis. Correct alignment of the knee relies on accurate and precise reconstruction of the patient's mechanical axis (ie, the line from the center of the femoral head through the center of the knee and ankle) and component-to-component alignment. Exact alignment occurs when these three points are collinear in the frontal (ie, coronal) plane.

Traditionally, alignment of the femoral and tibial incisions has been determined by using either an intramedullary rod inserted into the medullary canal of the femur or an extramedullary guide, which is attached to the tibia and adjusted by sight to obtain the correct alignment. These mechanical jigs only allow the surgeon to make alignment decisions based on the anatomical axes of the femur and tibia and not on the mechanical axis of the limb, which cannot be assessed accurately during surgery when the hip and ankle are trader drapes and not visible to the surgeon. Studies have demonstrated that these limitations caused 71% to 94% (ie, when using intramedullary rods) and 82% to 88% (ie, when using extramedullary guides) of prostheses inserted to be within two degrees of being perpendicular to the tibial axis. (3-6) Furthermore, use of intramedullary rods has been associated with a higher incidence of clinical and subclinical fat embolism, (7-9) and use of extramedullary guides has demonstrated considerably less accuracy than use of intramedullary rods (10) because of the degree of position accuracy required. (11) This is particularly problematic for surgeons who perform TKA procedures infrequently. Even using preoperative computerized tomography scans in planning can lead to as much as two-degrees variability in determining component alignment. (11)

One group of researchers determined that an inaccuracy as small as 2.5 mm in the position of the femoral component can result in as much as 20 degrees restricted range of motion. (12) Abnormal varus or valgus alignment has been reported as a major cause of implant loosening, (13) and posterior tilting of the tibial component also can affect range of motion and kinematics. (14) Another group of researchers noted that when the mechanical axis was outside the three-degree valgus-varus range, the loosening rate was 24%. (15) Consequently, 4% to 5% of patients require revision surgery within 10 years of implantation. (16,17) In fact, a substantial percentage of patients experience failed procedures as a result of poor component alignment and associated pain. (18) Other factors, such as gender, obesity, and age, also affect the Life span of knee replacements, (19,20) and infection causes approximately 5% of all primary arthroplasty failures. (21)