Preserving Normal Kinematics in TKA
Dr. Jeffrey DeClaire promotes a new way of thinking about total knee arthroplasty that doesn’t sacrifice the ACL.
The ultimate goal of total knee arthroplasty (TKA) is restoration of normal knee anatomy and normal knee kinematics.
An impediment to this goal is the removal of the anterior cruciate ligament (ACL). Although the ACL is the most critical ligament of the knee, it is almost always sacrificed in TKA, and has been since the very first TKA. The importance of the ACL is evident by the history of ACL injuries and the number of individuals, including athletes, who have had their lives significantly altered by the absence of this ligament.
One of the first component designs for TKA sacrificed both the ACL and the posterior cruciate ligament (PCL). “This was largely due to severe deformities and advanced arthritis, requiring the removal of both ligaments to achieve exposure of the knee, making it easier to restore alignment and motion,” explained Jeffrey H. DeClaire, MD, of DeClaire Knee & Orthopaedic Institute and Crittenton Hospital Medical Center, Rochester Hills, Michigan.
As implants have evolved, the technique of TKA has still depended on altering the soft tissue environment to accommodate the mechanical device, which is designed to replace the degenerated arthritic surfaces of the knee. “Once any ligament of the knee is removed, especially the ACL, the normal kinematics is permanently altered,” Dr. DeClaire said.”
The Challenge of Altered Kinematics
This alteration of the kinematics has been a challenge for years, requiring orthopaedic surgeons to balance flexion-extension gaps and the release of soft tissue structures as they create the new soft tissue environment for the mechanically shaped implant.
It also fueled Dr. DeClaire’s interest in the knee, particular the role of the ACL. “For years,” he said, “I have devoted my career to protecting, restoring, and reconstructing the ACL, while at the same time sacrificing every normal, healthy ACL with every total knee I performed.”
He began to question the removal of the ACL, considering its importance in knee kinematics and clinical data showing that 60% to 70% of TKA patients have an intact ACL. With knee kinematics in mind, Dr. DeClaire proposed a new way of thinking: retain ligament balance rather than redefine it to match the design of the prosthesis.
“Restoring normal kinematics is necessary to allow a greater degree of functional ability,” Dr. DeClaire explained. “We need to not only preserve the ligaments, but also have a prosthesis with appropriately designed articular surfaces.”
An Option for Retaining Normal Kinematics
IIn March 2013, such a prosthesis – which Dr. DeClaire helped develop over the course of about 3 years – was cleared by the US Food and Drug Administration (Vanguard® XP Knee System; Biomet, Inc., Warsaw, Indiana). Combined with the surgical technique, this prosthesis allowing for retention of normal knee kinematics.
“The soft tissue envelope of functional motion is not disrupted as in traditional TKA,” Dr. DeClaire explained, “eliminating the need to re-balance or alter the soft tissues in order to fit the mechanical device.”
Bicruciate TKA requires a more detailed preoperative assessment of knee arthritis so the surgeon knows what is going on with the knee beyond worn surfaces, Dr. DeClaire said. When he examines patients, Dr. DeClaire looks for:
- Good preoperative range of motion (>100°)
- Little flexion contraction (<15°)
- Intact ligaments, as demonstrated by the Lachman’s test and pivot shift test
- Correctable varus or valgus
He also obtains true lateral views of the knee and stress views.
Before beginning the procedure, Dr. DeClaire does a thorough assessment under anesthesia to confirm his preoperative findings.
The only patients who would not be candidates for a bicruciate TKA, he said, are “those with complete deficiency of the ACL from previous injuries or deficiencies related to severe, advanced degenerative arthritis of the knee.”
The new implant is intended for replacement of a total knee joint and preservation of the ACL and/or PCL when used in conjunction with a femoral, tibial, and patellar component. Prospective studies are under way to further evaluate the clinical outcomes of this new design and new approach to TKA.
The response to the implant from Dr. DeClaire’s colleagues has been extremely positive. “There is absolutely no resistance or disadvantage to the preservation of normal knee anatomy in the performance of a TKA, especially the ACL,” Dr. DeClaire said. “And after all, more and more, patients today are expecting a high-performance knee.”