Scientific Evaluation of a New Alignment Method for Total Knee Arthroplasty

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PI: Hull, Maury L.Proposal Number: 1067527Goals and Objectives: The general aim of the proposed research is to use in vitro testing to determine whether kinematic alignment, which is a controversial new method of aligning components in total knee arthroplasty (TKA), gives better knee function than mechanical alignment, which is the traditional method of alignment. The two alignment methods will be assessed by determining which better restores the kinematic axes of the tibiofemoral joint to normal, the passive envelopes of motion to normal, more evenly balances and centers the medial and lateral contact forces on the tibial component. These four general categories of dependent variables are important determinates of knee function, which must be tested in vitro because the use of instrumentation with this level of sophistication in vivo is not possible. The proposed research will test the following four hypotheses: 1) Kinematically aligned TKA restores the position and orientation of both the transverse axis in the femur about which the tibia flexes and extends and the longitudinal rotational axis in the tibia about which the tibia internally and externally rotates closer to normal than mechanically aligned TKA. 2) Kinematically aligned TKA restores the neutral and bidirectional limits of the passive envelopes of motion of flexion-extension, varus-valgus, and internal-external rotations and anterior-posterior translation closer to normal than mechanically aligned TKA. 3) Kinematically aligned TKA better balances the contact forces in the medial and lateral compartments than mechanically aligned TKA. 4) Kinematically aligned TKA better centers the contact forces in the medial and lateral compartments than mechanically aligned TKA. Our research group is uniquely able to perform these studies because we have developed a new method for determining the axes of motion, we have experience using our custom built six degree-of-freedom load application knee testing system, and we have extensive developmental and clinical experience with kinematically and mechanically aligned TKAs. Intellectual Merit: The method of aligning a TKA is of keen interest to the patient and surgeon because alignment determines knee motion, stability, pain relief, patient satisfaction, durability, and revision rate. Mechanically aligned TKA, which strives to achieve a 0° mechanical axis, has good long-term durability, but several studies have shown that 20-25% of patients are less than satisfied due to persistent unexplained pain, stiffness, and instability. One reason for the less than satisfied outcome is that aligning the limb to a 0º mechanical axis changes the kinematics of the knee. The change in kinematics requires ligament releases to restore motion, which can cause instability. Kinematic alignment is a controversial but exciting new method that strives to restore the kinematics of the knee to normal in which case ligament releases are not required. Kinematically aligned TKA has increased patient satisfaction, shortened surgery, reduced transfusions, and quickened recovery compared to mechanically aligned TKA. The in vitro assessment of axes of motion, passive envelopes of motion, and contact forces will provide quantifiable explanations for the differences in clinical results between methods. Broader Impact: Total knee arthroplasty (TKA) is a surgical procedure used to reduce pain, restore joint function, and improve the quality of life of patients suffering from osteoarthritis (OA) of the knee. In 2006, 542,000 TKA procedures were performed in the US, and it has been projected that by 2030, 3.48 million TKA procedures will be performed annually. Because 20-25% of patients are less than satisfied [5, 45], there is a need to improve the clinical outcome and a need to reduce the morbidity and expense associated with revision surgery. If the proposed in vitro cadaveric study determines that kinematically aligned TKA better restores the transverse axis in the femur, passive envelopes of motion, distribution of contact forces, and better centers the contact forces, then the use of this alignment technique in vivo would be further justified. The broad impact of the increased use of kinematically TKA would likely translate into improved clinical outcome, a reduction in the revision rate, and reduction in the social and medical costs for the tens of millions of patients that will undergo TKA in the next two decades.