Recent advances in 3D printing enable the use of custom patient-specific instruments to place drill guides and cutting slots for knee replacement surgery. However, such techniques limit the ability to intra-operatively adjust an implant plan based on soft-tissue tension and/or joint pathology observed in the operating room, e.g. cruciate ligament integrity. It is hypothesized that given the opportunity, a skilled surgeon will make intra-operative adjustments based on intra-operative information not captured by the hard tissue anatomy reconstructed from a pre-operative CT scan or standing x-ray. For example, tibiofemoral implant gaps measured intra-operatively are an indication of soft-tissue tension in the patient's knee, and may influence a surgeon to adjust implant position, orientation or size. This study investigates the frequency and magnitude of intra-operative adjustments from a single orthopedic surgeon during 38 unicondylar knee arthroplasty (UKA) cases. For each patient, a pre-operative plan was created based on the bony anatomy reconstructed from the pre-operative CT. This plan is analogous to a plan created with patient-specific cutting blocks or customized implants. With robotic technology that utilizes pre-operative imaging, intra-operative navigation and robotic execution, this “anatomic” plan can be fine-tuned and adjusted based on the soft tissue envelop measured intra-operatively. The relative positions of the femur and the tibia are measured intra-operatively under a valgus load (for medial UKA, varus load for lateral UKA) for each patient from extension to deep knee flexion and used to compute the predicted space between the implants (gaps) throughout flexion. The planned position, orientation and size of the components can then be adjusted to achieve an optimal dynamic ligament balance prior to any bony cuts. This is the plan that is then executed under robotic guidance. Intra-operative adjustments are defined as any size, position or orientation changes occurring intra-operatively to the pre-operative anatomic plan.Introduction
Methods
Kinematics of human joints have been studied using various methods of observation for millennia, including cadaver dissection, mechanical tests, and more recently photogrammetric gait analysis. For just over sixteen years, dynamic single-plane radiographic observations have been used to quantitatively characterize the motions of anatomic and prosthetically replaced joints. These observations have improved the understanding, in particular, of knee function and the influence of prosthetic design and surgical technique on knee kinematics and patient function. Other studies have reported the kinematics of the hip, shoulder, spine and foot/ankle. It is clear that advances in the technologies to acquire and quantify radiographic images of the skeleton in motion can have a major impact on joint mechanics research and, ultimately, clinical diagnosis. This lecture will highlight two avenues of development in our laboratory: open-source software for determining skeletal kinematics from radiographic images, and a novel robotic imaging platform for observing the skeleton in motion. Our group is working on an open-source shape-matching software application that will be freely available to anyone who wishes to use it (sourceforge.net/projects/jointtrack). This flexible platform will allow the modular addition of new capabilities as plug-in components written in a wide range of languages (C++, Python, Java, etc.), and makes heavy use of other open-source and public libraries (I.C.E., OpenGL, VTK, ITK). All of our future developments will use this platform so that the latest results will be available to all, and hopefully other users will share their advances collaboratively. We currently have created a graphical user interface for performing single-plane model-image registration, and are currently working to expand this to handle bi-plane imaging. We also are developing a robotic platform to permit radiographic imaging of human joints during normal, unrestricted, dynamic activities. This platform will move the x-ray source and sensor in response to the patient’s unconstrained motion, providing views with greater diagnostic potential than are acquired with fixed or c-arm imaging systems. This same imaging platform will also provide an extremely flexible platform for cone-beam tomography, so that a single system will be able to perform all imaging functions required for skeletal model-image registration based kinematic measurements. The goal of these endeavors is to advance the possibility that dynamic radiographic analysis of joint motion will soon be a useful, accurate, and routine diagnostic and measurement tool available to enhance the efforts of orthopaedic surgeons in the treatment of their patients.
