Total knee arthroplasty (TKA) is a common surgical procedure which reduces pain and restores joint function in patients with advanced knee osteoarthritis. In 2005, there were approximately 523,000 TKA surgeries performed in the US and this number is expected to increase to 3.48 million by 2030. Although TKA is an effective intervention, suboptimal outcomes do occur, causing many patients to have difficulty carrying out activities of daily living. Many of these suboptimal outcomes are believed to be the result of poor component alignment and soft tissue balancing during TKA. While surgeons have a keen sense of what is acceptable joint stability, there is no objective definition and they do not know precisely how their actions during surgery affect postoperative stability. The goal of my dissertation research is to determine the relationship between surgical technique and knee joint stability.

A successful TKA is dependent on many factors, but component alignment has been identified as particularly important. A variety of techniques exist to establish the rotation of the tibial component and the impact of this variability is unknown. To address this void, we performed a cadaver study to determine how tibial component rotation affects knee stability. We used a surgical navigation system and a custom stability device to measure knee stability and passive kinematics on 10 specimens with the tibial component aligned to 4 commonly used axes. Our study showed that for all rotations, TKA produces a “softer” knee, but showed little change based on the tibial alignment alone.

Knee stability during TKA is usually assessed as a surgeon manually manipulates the knee and decides if the joint has acceptable laxity and stiffness. This subjective method does not objectively quantify stability and has unknown repeatability. Using the navigation system and custom stability tool from the cadaver study, we are the first to group to intra-operatively characterized knee stability during a TKA by measuring the force applied by the surgeon and the resulting knee motion on 15 patients. Results from this initial cohort demonstrate that our system is reliable and that TKA generally results in a looser knee.

In addition to subjective assessments of stability, some surgeons use the “gap technique” to achieve a balanced joint which aims to establish equal gaps in flexion and extension between the bone cuts on the femur and the tibia. However, it is not thoroughly understood how TKA component alignment affects the gaps or the frontal plane biomechanics of the knee. Using a computer simulation that accurately models the stability testing done in the OR and in the lab, we varied TKA component alignment to determine the effect on the gaps between the bone cuts and the biomechanical behavior of the joint. Our model showed that alignments that achieve balanced gaps do not necessarily result in balanced frontal plane behavior.

This dissertation advances the understanding of how TKA changes the stability of the knee. The methodology presented in this dissertation lays the groundwork for future orthopaedic research involving the use novel measurement tools inside the OR and computer modeling.