By Daniel R. Cavazos, MD, FAAOS
The advancements in orthopaedic total joint arthroplasty have been quite successful. Studies report that total hip arthroplasty (THA) has patient satisfaction rates of 90 to 95%, with a 20-year survivorship of the implant. Contrarily, total knee arthroplasty (TKA) outcomes provide only 80 to 85% patient satisfaction, with satisfaction defined as relief from symptoms (pain, instability, stiffness) and the restoration of function, with a 10 to 15-year survivorship of the implants. Despite innovative technology and surgical techniques, the efforts to improve knee replacement outcomes have not markedly improved over the past several decades. This article discusses two aspects of TKA: conventional instruments or robotics and alignment philosophy, aiming to improve knee replacement surgery outcomes.
Most commonly, the surgeon will use conventional instruments to position the femoral and tibial components of a total knee arthroplasty in mechanical alignment (MA) on an anterior-posterior radiograph (coronal). Essentially, the goal of this technique is to establish a straight line between the centers of the femur and tibia shafts, or a zero-degree axis. One study revealed that surgeons derived mechanical axis deviated 9 degrees in 7% of patients and over 5 degrees in 34% of patients. These patients are considered outliers, according to a study in The Journal of Bone and Joint Surgery. Numerous studies have shown that a coronal MA of greater than 3 degrees resulted in poor patient outcomes and decreased prosthetic survivorship. The robotic technique achieved a zero-degree MA with zero outliers, according to a 2013 study in The Journal of Arthroplasty.
This precision of robotic technology was the primary reason surgeons adopted it. However, most total knee replacements still use conventional instruments because this precision in robot-assisted surgery has not improved the long-term performance and outcome in a TKA. Perhaps the alignment philosophy of MA, which changes the patient’s alignment and soft tissue tension, could be changed to a kinematic alignment (KA). The native alignment of the knee is restored with KA and the native tensioning of the knee soft tissues provides almost painless, normal motion. This alignment is difficult to achieve manually. Robotic technology is a more accurate tool for measuring and recreating the pre-arthritic, painless knee joint with KA.
According to a recent study in The Journal of Arthroplasty, high-volume manual instrument surgeons performing more than 50 TKAs per year report a high proportion of alignment outliers, at 11.8%. This level of imprecision may negatively impact the younger patient who needs excellent long-term survivorship of the implants or the very active older patient, such as a pickleball player who needs a painless range of motion and stability.
In the final analysis, the treating orthopaedic surgeon must feel confident using the best techniques to produce an excellent outcome of a TKA for the patient. Robotic technology has proven to be an accurate and precise tool to enable newer alignment philosophies that can lead to better outcomes.
Daniel Cavazos, MD, FAAOS, is an orthopaedic surgeon at Hampton Roads Orthopaedics Spine and Sports Medicine specializing in sports medicine, arthroscopic surgery and minimally invasive total joint replacements. hrosm.com
