Accurate component placement in joint replacement cannot be overemphasized; despite many re-engineering efforts over the past 3 decades, failure rates at 10 years for total hip arthroplasty (THA) and total knee arthroplasty (TKA) remain constant. Intraoperative decisions with joint replacement have been facilitated with manual instrumentation and are affected by the surgeons intuition, instinct, and experience. Current technology allows the development and use of high-tech instrumentation, which, irrespective of surgeon-dependent variables, gives intraoperative quantitative information on which precise placement of hip and knee components can be done. Component placement is the single most important technical maneuver the surgeon accomplishes to prevent mechanical complications, which will nearly eliminate outliers from very good and excellent results and revision as a consequence of technical errors; computer navigation has almost made it possible. In knees it gives precise component placement in the coronal and sagittal planes, and in hips it particularly improves acetabular component position by numerical control of inclination, anteversion, and most importantly center of rotation. Precision is enhanced even more when computer navigation is elevated to the next level, which is robotic guidance. The preoperative plan set by the surgeon is executed by the robotic tool while the surgeon manually controls the robotic arm. Bone preparation cannot exceed the boundaries the surgeon has set, as the surgeons manual force will stop the robot and the error cannot be made. Robotic surgery has progressed in the unicompartmental knee, and this innovation is in the final stages of development in THA.
Progress in better outcomes in total hip arthroplasty (THA) and total knee arthroplasty (TKA) operations has been steady since 1970. In the 1970s, the cement technique was improved; in the 1980s, cementless fixation was developed; and in the 1990s, bearing-surface technology was refined. In the 2000s, patient care has improved so that pain management is superior, hospital discharge can occur within 24 hours, and recovery allows patients to return to work within 3 weeks.1,2 The last frontier now being studied is improvement in surgical technique.
No new implant designs have been developed in THA or TKA since 1990. Established designs have been re-engineered with theoretical benefits in patient outcomes, but studies have shown no changes. High-flexion knees, Gender Knees (Zimmer, Inc, Warsaw, Indiana), resurfacing hip designs, and large-head metal-on-metal bearing surfaces have shown no improvement in results to date. Failure rates at 10 years remain constant, dislocation is the main cause of hip revision, and rotational instability the main cause of knee revision. Improvement in patient outcomes by reduction of mechanical complications will only occur by improvement in surgeon technique, especially for component placement.
Surgeons have always operated using their intuition, instinct, and experience. Intraoperative decisions in THA and TKA have been facilitated with manual instrumentation. Current technology allows the development and use of high-tech instrumentation, which gives intraoperative quantitative information to the surgeon on which he or she can act. It guides precision component placement in THA and TKA. Component placement is the single most important technical maneuver the surgeon accomplishes to prevent mechanical complications. Prevention of mechanical complications will nearly eliminate outliers from very good and excellent results and revisions as a consequence of technical errors.
Computer navigation systems, both image-based and imageless, have improved surgeon control of component placement. Knee navigation systems give precise placement of femur and tibia components in the coronal and sagittal planes. Hip navigation particularly improves acetabular component position by numerical control of inclination, anteversion, and perhaps most importantly, center of rotation. Karachalios et al3 clearly showed that maintaining the cup center of rotation within 2 mm of the anatomic center was the most important factor of long-term durability. Adjusting the acetabular anteversion according to femoral stem anteversion rather than targeting it to a number such as 15° or 20°, allows the surgeon to reconstruct the hip with a combined anteversion within its safe zone of 25° to 50°, lower for men and higher for women.4 Controlling the medialization of the acetabulum allows inclination of the cup to remain below 45°, which is required for optimal wear.5
The control of component placement is even more accurate when computer navigation is elevated to the next level, which is robotic guidance. The advantage of the robot is the elimination of manual errors of bone preparation, which reduce operative time and ensure correct bone removal. The robot has software with the bone preparation planned from a computed tomography scan of the joint. The surgeon inputs where he or she wants to place the component, including the angles of the cuts. The robotic tool cuts the bone with the surgeon manually controlling the robotic arm. The preparation cannot exceed the boundaries the surgeon has set. If the surgeon attempts to push the robot arm beyond the established boundary, the robotic tool will stop cutting bone and the error cannot be made (Figure).
Figure: Intraoperative view showing preparation of the femoral side with a robotic arm with a burr tip (robot tool; A). Computer screen view showing real-time preparation of the femoral side while burring is in progress (based on preoperative planning; B).
Unicompartmental knees are now being implanted with robotic guidance (MAKO Surgical Corp, Ft Lauderdale, Florida) in 12 centers in the United States. The repeatability of the component placement is evident to surgeons who have used it. In these pioneering centers, the preoperative time of setup for the robot and the patient is being reduced. Early results have been published.6 This technology has made unicompartmental knees a precise operation for patients with unicompartmental arthritis, whereas prior to robotic guidance it was primarily a freehand operation with highly variable results depending on the surgeon.
A THA robot program is being developed with acetabular bone preparation accomplished with a single reamer, elimination of the need for trial implants, and correct placement of the cup. The femur is prepared first, and the femoral neck cut can be correctly made to reconstruct the hip angle and offset (which creates the correct leg length) because the center of rotation of the acetabulum is known from preoperative planning. The femoral stem anteversion is measured by broach/trial stem implantation so the acetabular anteversion can be mated to it to reconstruct the hip in the combined anteversion safe zone of 25° to 50° (mean, 37°).4 The THA will be optimal for the patient in each case. Dislocation could become a historical complication as well as accelerated wear, as both complications are caused by impingement.7
Precision surgery, with quantitative knowledge of device placement and hard and soft tissue surgery within safe boundaries, is becoming more prevalent in all specialties of surgery. The da Vinci System robot (Intuitive Surgical, Inc, Sunnyvale, California) led this progressive innovation with heart and prostate surgery. Orthopedic surgery will particularly benefit because devices are used for all bone operations. The challenge for common use will be surgeon acceptance, surgeon training, and cost control.
- Dorr LD, Maheshwari AV, Long WT, Wan Z, Sirianni LE. Early pain relief and function after posterior minimally invasive and conventional total hip arthroplasty. A prospective, randomized, blinded study. J Bone Joint Surg Am. 2007; 89(6):1153-1160.
- Maheshwari AV, Boutary M, Yun AG, Sirianni LE, Dorr LD. Multimodal analgesia without routine parenteral narcotics for total hip arthroplasty. Clin Orthop Relat Res. 2006; (453):231-238.
- Karachalios T, Hartofilakidis G, Zacharakis N, Tsekoura M. A 12- to 18-year radiographic follow-up study of Charnley low-friction arthroplasty. The role of the center of rotation. Clin Orthop Relat Res. 1993; (296):140-147.
- Dorr LD, Malik A, Dastane M, Wan Z. Combined anteversion technique for total hip arthroplasty. Clin Orthop Relat Res. 2009; 467(1):119-127.
- Patil S, Bergula A, Chen PC, Colwell CW Jr, DLima DD. Polyethylene wear and acetabular component orientation. J Bone Joint Surg Am. 2003; 85(Suppl 4):56-63.
- Conditt MA, Roche MW. Minimally invasive robotic-arm-guided unicompartmental knee arthroplasty. J Bone Joint Surg Am. 2009; 91 (Suppl 1):63-68.
- Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am. 2007; 89(8):1832-1842.
Drs Dorr and Deshmane are from the Arthritis Institute at Good Samaritan Hospital, Los Angeles, California.
Dr Dorr received funding from Good Samaritan Hospital, Los Angeles, California. Dr Deshmane has no relevant financial relationships to disclose.
Presented at Current Concepts in Joint Replacement 2008 Winter Meeting; December 10-13, 2008; Orlando, Florida.
Correspondence should be addressed to: Lawrence D. Dorr, MD, The Arthritis Institute at Good Samaritan Hospital, 637 S Lucas Ave, 5th Floor, Los Angeles, CA 90017.