Mechanical Alignment Total Knee Arthroplasty: A Thoughtful Beginning With Unanticipated Limitations

The evolution of total knee replacement (TKR) from a novel and unreliable procedure to a highly reliable one is one of the major achievements of modern surgery over the past 50 years. Improvements in alignment theory, implant and instrument design, and surgical techniques have cumulatively contributed to this. That being said, serious surgeons all over the world can never accept what we do “now” as the ultimate solution. Every aspect of total knee surgery must be continuously subject to scrutiny for both incremental and disruptive change. The pursuit of perfection demands nothing less than acceptance of constant change. Although the focus of this book is on the role of kinematic alignment principles, it is important to put this in historical perspective and to acknowledge the roles played by perioperative patient management and implant and instrument design.

How did we get to where we are today, in 2021? The early phase of the modern era of artificial knee replacement began with the hinge prostheses in Europe by Börje Walldius of the Karolinska Institute in Stockholm, Sweden, and the interposition arthroplasty in the United States. The original Walldius prosthesis in 1951 was a hinge made of acrylic inserted without cement. The material was soon changed to the cobalt chrome alloy. His report of the technique and results in 1960 included an interesting reference to instrumentation: “No special instrument is required…” Although the early results were encouraging, fixed hinge designs of various types, including the Guepar, fell out of favor because of high failure rates. Aware of the work by Venable and Stuck on the use of Vitallium alloy in fracture surgery in the late 1930s, Marius Smith-Petersen, a Norwegian-born surgeon working at the Massachusetts General Hospital in Boston, used this material for his famous cup arthroplasty of the hip and experimented with an analogous cobalt-chrome resurfacing of the distal femur with a stem into the distal femur. In that same time frame, MacIntosh and Duncan McKeever developed interpositional metal hemiarthroplasties. ^‒ These were inserted without cement with a keel in the surface of the tibia for fixation and direct articulation against the bone of the femur. I was the assistant surgeon for several of these cases still being done occasionally by Richard (Dick) Scott in Boston in the late 1970s.

In the United Kingdom in 1962, Mr. John Charnley introduced the total hip with acrylic cement fixation. There were many materials tried on the acetabular side until the introduction of polyethylene after failures with other materials such as Teflon. The combination of polymethylmethacrylate acrylic cement and polyethylene as a bearing surface by Charnley for the hip was a game changer and ushered in the true modern era of total joint replacement. In the late 1960s, Gunston, a Canadian who had worked in Charnley’s lab, developed a bicompartmental knee arthroplasty with cemented poly on the tibia and round metal femoral components on the condyles. Charnley experimented with a hemiarthroplasty that had a poly component on the femoral side and metal on the tibial side (Load Angle Inlay, Thackeray). The success of this was short lived. I revised one of these knees 20 years ago in a rheumatoid patient with a combined varus supracondylar osteotomy and revision arthroplasty (see Fig. 1.1 ).

The further development of unicompartmental arthroplasty by Marmor, Murray, Goodfellow and O’Connor of the Oxford group, Scott and the Brigham Group in Boston, and many others is not a focus of this book and will not be covered further in this introduction; suffice to say that a uni is an example of an anatomic versus mechanical alignment-based procedure. Intact anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are prerequisites, and overcorrection is to be avoided. In some high-volume knee arthroplasty practices at this time (i.e., 2021), up to 60% of cases of primary knee osteoarthritis are being done with unis rather than full TKR.

In the late 1960s, also in England, Michael Freeman, surgeon, and SAV Swanson, engineer, developed a single radius of curvature, nonlinked prosthesis with a flat anterior femoral design. It was a “roller in trough” design—a virtual modular equivalent of the hinge prosthesis. Both cruciate ligaments were sacrificed. More important than the prosthesis, however, were Freeman’s important contributions to the history of surgical technique and instrumentation. It was Freeman who introduced parallel cuts of the two major bones that were perpendicular to the mechanical axis. Furthermore, he introduced intramedullary instrumentation to facilitate reproducibility of the cuts. Many of the knees in that era were associated with severe deformities from inflammatory arthropathies, particularly rheumatoid arthritis. He prioritized achievement of reproducible mechanical axis, rather than anatomic alignment.

A major leap forward was the development of the total condylar prosthesis by the English surgeon John Insall, working at the Hospital for Special Surgery in New York City in collaboration with the engineer Peter Walker and Drs. Ranawat and Ingless. Both cruciate ligaments were sacrificed. Further refinements by the engineer Burstein led to the Insall-Burstein total condylar prosthesis with an all-poly tibia with a post. This laid the foundation for all modern posterior cruciate–sacrificing knee replacements. Parallel with this major achievement was work in Boston by Sledge et al. on designs that preserved the posterior cruciate. These early generation knees had drawbacks of all-poly tibial components, which resulted in high stresses on the cement, particularly in larger sizes, and poor patellar tracking. The metal-backed modular tibia solved that problem, and posterior cruciate-retaining philosophy was established as a highly reliable alternative to the New York school, which requires posterior cruciate sacrifice in all cases with much greater femoral bone stock loss. Patellofemoral issues were serious problems with both the cruciate-sacrificing designs of the New York school and the posterior cruciate–retaining designs of the Boston school. Implant design improvements with a central trough in the femoral component and high profile of the anterior lateral femoral flange helped greatly to improve patellofemoral mechanics.

Some confusion exists in historic terminology. The Boston surgeons at the Brigham and engineer Peter Walker designed the posterior cruciate–retaining “Kinematic Knee Prosthesis,” manufactured by Howmedica and subsequently acquired by Stryker years later. The Kinematic prosthesis was inserted using mechanical alignment instrumentation and principles. Over time, the term “kinematic alignment” has come to mean principles of insertion that respect and reproduce to varying degrees the anatomic variations of individual knees.

No two knees are identical, even in the same individual. Think of the analogy to the human face. We all have faces, yet no two faces are the same. Imagine a facial plastic surgeon dealing with posttraumatic facial deformities or elective facial reconstruction. Is the goal to make every face look the same? Is it not important to respect individual variations that make each face unique? So, too, with the knee. It is clearly understood that the human knee has a few degrees of physiologic varus in the coronal plane, yet the mechanical axis principles require a perpendicular cut of the tibia with the goal of making “every knee the same.” The groundbreaking instrumentation of Freeman was adopted and improved by others. An alternative approach was introduced by Hungerford and Krakow, a more physiologic “kinematic alignment” that respected variations in anatomy of the knee. This was paired with the first U.S. Food and Drug Administration- (FDA)-approved cementless TKR in the United States in 1984, the porous-coated bead Porous Coated Anatomic (PCA). ^, That device went on to a much higher failure rate than expected, and porous bead technology is no longer used. This impact on alignment philosophy has lived on, however. It is important to recognize the contribution from Japan by Yamamoto, who reported on a cementless design with superior results to the cemented version in the late 1970s. This book explores the evolution and current status of kinematic alignment.

There is a major difference between the mindset of a surgeon and a bench scientist. A scientist postulates many ideas and seeks then to prove that the hypothesis is either wrong or right, without bias. A surgeon works with the burden and expectation of perfection in every operation. Acceptance of an error in planning or technique in any case is difficult for a surgeon to deal with. Accordingly, discarding a traditional and customary technique is difficult, even when data from a well-done study dictate that change is warranted. Consider how many years it took for the majority of surgeons to abandon the use of drains for knee replacements, even when published studies as early as 1998 showed no harm as well as benefits to doing so.

So how does adoption of kinematic alignment fit in? Mechanical alignment has served as a straightforward and easy-to-teach technique. Why change now? The real issue is that 6% to 14% of total knee patients are unhappy with their outcomes in the peer-reviewed literature. It is reported much higher, up to 30%, in the lay press. Can adoption of kinematic alignment lead to a significant improvement in patient satisfaction? The hypothesis that it will be superior is based on studies that show that the imposition of a rigid, “one size fits all” mechanical alignment approach actually reproduces the native anatomy for less than 5% of individual knees. Hungerford made an even stronger assertion in his chapter on alignment in a TKA book in 2005, when he wrote, “In single-leg stance the ankle must be brought directly under the center of gravity. This means that the lower leg and the mechanical axis are inclined toward the midline by 3 degrees. This can vary by as much as ±1.5 degrees depending on the breadth of the pelvis and the length of the femur…” In our experience of measuring this relationship in thousands of patients, we have seen only one patient in whom the joint line was actually perpendicular to the mechanical axis. The tibial shaft is normally parallel to the mechanical axis and is therefore 87 degrees to the joint line and not perpendicular to the joint line (see Fig. 1.2 ). Furthermore, in the peer-reviewed, Ranawat Award–winning paper by Bellemens et al. in 2012, it was reported that up to 32% of men and 17% of women have a native mechanical axis of 3 degrees or more. The kinematic alignment philosophy that recognizes and respects the bell curve distribution of “normal” for each individual has intuitive attractiveness. This is not a new concept, but enthusiasm for change has accelerated. However, it is important to include in the introduction that one prospective, randomized study by Young et al., also a Ranawat Award winner of the Knee Society, found no difference between kinematic technique with custom jigs and mechanical axis technique with computer-assisted technique. This must be taken into account in the overall equation of what really matters in the quest to make total knee patients as happy as those who get total hips. Is it possible that the way in which the kinematic alignment was performed in that study was significantly different from that proposed in this book? Regardless, the key to widespread acceptance of the principles and adoption of the kinematic technique by the majority of surgeons will hinge on successful results reported by independent surgeons performing similar studies. One study alone cannot be accepted as definitive, but it must be acknowledged and respected for its impact on the discussion. Other studies have shown improved flexion and improved patient-reported outcomes in kinematically aligned knees, including the prospective study by Dossett et al. This is a dynamic and evolving area of clinical practice and research.