Patient Specific Total Knee Replacement

What is the Patient-Specific Total Knee Replacement?


The contemporary total knee replacement has only been in existence since the 1970s.  Although diseased and painful joints have been problematic for as long as humans have walked upright, it wasn’t until November of 1959 that Sir John Charnley of England divined a reproducible method of replacing a joint (the hip) with a metal-on-plastic articulation utilizing components cemented into native bone.  In the ensuing decades, work progressed on translating Dr. Charnley’s work into replacing other major joints using the same premise. In the early 1970s, John Insall, MD and his team were able to publish reports on the encouraging results of their “total condylar knee replacement,” and the total knee arthroplasty was born.

Dr. Insall’s total condylar design called for sacrificing of the major ligaments stabilizing the anterior-to-posterior translation of the native knee and replace this function with a post and cam articulation to mimic native knee mechanics.  His design proved unique in that it also called for resurfacing of the patella (knee cap) in addition to both the femoral (thigh bone) and tibial (shin bone) articulating surfaces. Each of these three components was fixed to the host bone using the same dental bone cement championed by Dr. Charnley in his earlier hip replacement surgery.

Soon, surgical “guides” were developed to assist surgeons in improving the accuracy of bone cuts to improve fit and, subsequently, patient outcomes.  “Intramedullary “ cutting guides utilize a hole drilled into the bone to access the inner intramedullary canal into which a metal rod is positioned with cutting guide affixed to afford a set angle and depth of cut.  In contrast, “extramedullary” guides perform the same function but without the requirement to be placed within the bone as an alignment. Rather, they are aligned with surface bony landmarks to their best approximation and pinned in place to guide the surgeon’s cutting device.  These guides have enjoyed a long history of use in helping surgeons to improve outcomes and reduce operative time as well as complications inherent with total knee replacement surgery.


Tailoring Implants to Patient Anatomy

History has been witness to many improvements in the specialized field of total knee arthroplasty (TKA).  Although most joint replacement specialty surgeons template (measure) a patient’s knee in order to anticipate the size of implants required, most are provided a variety of size options to tailor implants to best fit the patient’s actual anatomy encountered in the operating room.  This has served well since the inception of knee replacement as to fit, but postoperative complications and patient dissatisfaction scores provided an incentive for continued improvement. Limitations in postoperative range of motion experienced by some patients were reasonably attributed to implant design, and so manufacturers sought to improve their implant options to allow for fuller flexion in order to address range of motion concerns.  An attempt was even made to market gender-specific knee implants in order to address the differences in male and female anatomy, but by 2015 convincing evidence of their benefit could still not be demonstrated.

In the past few years, custom cutting guides have been advanced as one possible solution to more accurate matching of implant to patient anatomy.  The size, angle, depth and breadth of the bone on a five-foot-two-inch female patient who was a former college professor will necessarily be different than that of a six-foot-four-inch male who retired as an NFL linebacker.  The custom cutting guides are fashioned from either CT or MRI images of the individual patient and allow the surgeon to assess and alter almost all aspects of the surgery well before the actual date of the knee replacement. An additional benefit of these custom guides is that they do not require intramedullary alignment and as such avoid the complications sometimes seen with additional bleeding into the joint after an intramedullary guide’s removal.

Additionally, computer-assisted “robotic” knee replacement implements are becoming increasingly available.  These “robots” add significant cost to knee replacement surgery but benefit from the patient’s unique anatomy similar to that of the custom cutting guides.  “Robots” is included in quotations because these machines actually constrain the cut in the surgeon’s hand rather than perform the procedure for the surgeon, as one might envision a true robot to do.  Still, the accuracy afforded by use of the surgical robot is of arguable benefit in accurate component placement, especially so in the application of unicondylar knee replacement surgery (replacement of only one part of the knee), where component placement is critical to superior outcomes.


So is a SuperPATH hip or a Direct Anterior Approach Better for Me?

A well done total hip replacement by any technique is a good surgery.  The problems that lead a patient to seek hip replacement are those of persistent and unrelenting pain not relieved by nonsurgical methods, a lack of function, and a lack of mobility.  In replacing the hip joint, the surgeon seeks to relieve pain, restore function and regain mobility for the patient. Regardless of the surgical technique selected, these goals should be the intended result.  Whether one surgical technique or another has to do with surgeon experience, patient satisfaction, and patient preference.

Sir John Charnley, MD, of England was the first to pioneer the modern total hip replacement in November of 1959.  Dr. Charnley was an engineer and a true scientist in addition to his superior abilities as a surgeon. Many orthopedic surgeons had sought to produce a surgical technique for replacement of the diseased hip, but it was Dr. Charnley who was able to advance a technique for a reproducible total hip replacement with his “low friction arthroplasty,” which utilized a cemented metal stem and ball articulating with a cemented plastic acetabular cup.  Dr. Charnley’s patients regained their ability to walk and were able to escape the rusty claws of chronic pain from diseased hip joints. Both patients and surgeons flocked to Dr. Charnley’s British hospital to benefit from his great discovery.

In the ensuing decades, others added to Dr. Charnley’s work by promoting new advances, including replacing the hip through different surgical approaches and directions, creating implants which did not require cement, and reducing many of the complications noted after these early total hip replacement surgeries.  

Early efforts at hip replacement using an anterior surgical approach date as far back as 1947, when French surgeon Robert Judet used the technique to replace a hip at Garches Hospital in Paris.  When Dr. Charnley’s work in England produced the first reproducible method of hip replacement, the surgeons who favored the anterior surgical approach began to assimilate the two techniques. In the late 1990s and throughout the turn of the most recent century, the direct anterior approach found favor among many surgeons seeking to further these advances in reducing patient pain and complications from hip replacement, and simultaneously reduce the time required for rehabilitation from hip replacement surgery.  Much was made in marketing regarding the benefits of the direct anterior approach, and many surgeons sought to assimilate the technique in their own busy practices with varying degrees of success. The surgeons who practice the SuperPATH technique believe that this most recent advance in hip replacement promises similar improvements over more traditional hip replacement while at the same time reducing the risks of complications unique to the direct anterior approach for hip replacement surgery.


What are the Potential Benefits of Patient-Specific Total Knee Replacement?

The goal of any total knee replacement are to reduce pain (ideally, eliminate it), restore function and to help the patient regain mobility.  Since the inception of the total knee replacement in the 1970s, both intramedullary and extramedullary cutting guides have included the prospect for error in the angle or amount of bone removed to which implants would be affixed.  Even a small error in these cuts and the subsequent alteration in biomechanics of the joint could play a large role in outcome and decreased satisfaction with the final product.

Patient-specific total knee replacement seeks to capitalize on improved patient outcomes through increased accuracy for the bone cuts required to remove the diseased and painful parts of the knee and application of prosthetic components.  The unique anatomy of a given patient serves as the ultimate template in prediction of the right component part, size, and even orientation that promises to provide the best chance for superior outcomes.


The Bottom Line

In the hands of any properly trained joint specialty surgeon, a well-done total knee replacement is a good surgery.  Replacement of a painful and increasingly limiting knee joint promises to rid a patient of worsening symptoms of pain, immobility and loss of function.  Inventive surgical approaches including subvastus, midvastus, and minimally invasive approaches to total knee replacement have yet to be proven in the surgical literature to convey improved outcomes compared to a standard midline approach for total knee arthroplasty.  Improved sizing and accuracy of component placing, however, holds the promise of accurate application of prosthetic parts and by extrapolation, the potential for improved pain scores, shorter rehabilitation, and improved functionality for patients following the surgery.

Dr. Blair believes that, in his hands, patient specific total knee replacement represents the latest advancement in the continuing evolution of knee replacement surgery; allowing patients to benefit from reduced postoperative pain, reduced time required for postoperative recuperation, and reduced risk for complications associated with knee replacement surgery.  With all of his experience and surgical knowledge, Dr. Blair describes the patient-specific total knee replacement as “the knee replacement surgery I would recommend for any member of my own family who needed to have a knee replaced.”


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