Karl D. Reinig

Three-Dimensional Mechanics, Kinematics, and Morphology of the Knee Viewed in Virtual Reality

T he premise of this article, and the scientific exhibit upon which it is based, is that the morphologic shape of the distal aspect of the femur and its relation to the tibia and the patella dictates the kinematics of the knee. The morphologic and kinematic characteristics of the knee presented in earlier exhibits1,2 at the 2001 and 2003 Annual Meetings of the American Academy of Orthopaedic Surgeons demonstrated the following relationships. The location and orientation of the femoral sulcus is lateral to the midplane between the femoral condyles and is oriented between the anatomic and mechanical axes of the femur (Figs. 1-A and 1-B). The center of the femur in cross section is offset, medial and anterior, to the center of the tibia, and these offset cross sections are rotated relative to each other in the pathologic knee (Fig. 2). A single, fixed flexion-extension axis of the knee is centered in the asymmetric cylindrical femoral condyles (Fig. 3). These and other observations1-8 of distal femoral morphology and their relationship to knee kinematics form the basis for the additional studies in the present article. These new studies relate the morphology of the femur (condyles and epicondyles) and the axis of the limb (mechanical axis) to the location and orientation of the flexion-extension axis of the knee in three-dimensional space. The clinical importance of this work is found in its application to ligament reconstruction and total knee arthroplasty. Despite improvements in design, implant alignment in total knee arthroplasty remains a crucial factor in the function and longevity of the implant9-11. It has been demonstrated that malalignment causes increased wear of the implant and premature failure of the construct11-14. Most contemporary implants are designed to be aligned to …

Three-dimensional Morphology And Kinematics Of The Distal Part Of The Femur Viewed In Virtual Reality: Part Ii

The purpose of this exhibit is to demonstrate, with conventional and virtual images, the three-dimensional shape of the naturally asymmetric distal part of the femur, illustrating the cylindrical axis of the femoral condyles relative to the conventional (mechanical, anatomic, and epicondylar) axes of the lower limb and knee. The relationships between morphologically and experimentally determined rotation axes are illustrated. This study provides kinematic and morphologic validation for a single cylindrical flexion-extension axis of the knee. The clinical implications of a single flexion axis of the knee for alignment and soft-tissue balance in total knee arthroplasty, as well as the position and tension of a graft in anterior cruciate ligament reconstruction, are demonstrated with the aid of illustrations from the Visible Human Project at the National Library of Medicine as well as images from the University of Colorado Center for Human Simulation. The morphologic shape of the distal part of the femur and its relation to the tibia and the patella dictate the kinematics of the knee. Work presented in an earlier American Academy of Orthopaedic Surgeons exhibit1 demonstrated that the lateral tracking of the patella is reflected in the trochlear groove lying lateral to the mid-plane and oriented between the mechanical and anatomic axes of the femur in the coronal plane2,3. The posterior-lateral offset of the tibia relative to the femur in the normal knee and the external rotation of the tibia relative to the femur in the abnormal knee were also documented in the transverse plane4-7. The asymmetric cylindrical morphology of the femoral condyles posterior to the coronal plane, another morphologic feature of the distal aspect of the femur demonstrated in the earlier exhibit1, dictates the location of the flexion-extension axis of the knee and drives the kinematics …

Three-Dimensional Morphology of the Distal Part of the Femur Viewed in Virtual Reality

The morphologic shape of the distal part of the femur dictates the shape, orientation, and kinematics of prosthetic total knee replacement. Traditional prosthetic designs incorporate symmetric femoral condyles with a centered trochlear groove. Traditional surgical techniques center the femoral component to the distal part of the femur and position it relative to various bone landmarks. However, failure patterns documented in retrieval studies1,2, case series3, and kinematic studies demonstrate how traditional designs and surgical techniques reflect a poor understanding of distal femoral morphology and knee kinematics. It has been shown that the flexion/extension axis of the knee is fixed within the femur and that the articular surfaces of the condyles are circular in profile4,5. Ligament length patterns are significantly altered by abnormal axial alignment when a hinged knee brace is used6. It is expected that a malaligned femoral component would have the same effect in total knee arthroplasty. The purpose of this report is to demonstrate, with conventional images and with interactive animations in virtual reality, the three-dimensional shape of the naturally asymmetric distal part of the femur, with illustration of the sulcus axis of the trochlear groove and the flexion/extension axis of the condyles relative to conventional axes (mechanical, anatomic, epicondylar, and posterior condylar). Correlations between the morphologically determined rotation axes and experimentally determined kinematic axes are illustrated. Eighty-five mummified cadaveric knees were measured with a stereotactic micrometer (Fig. 1)7. The location and orientation of the sulcus were obtained by repeated horizontal passes of the stereotactic stylus over the distal part of the femur, beginning at the top of the articular surface and progressing down to the intercondylar notch (Fig. 2). With each horizontal pass, the lowest depression of the trochlea (sulcus) was identified by …

Variability of landmark identification in total knee arthroplasty.

Virtual reality is new technology that is finding application in many facets of orthopaedics. We will describe an application of virtual reality in orthopaedic research. Component placement in total knee arthroplasty depends on identification of anatomic landmarks about the knee. We surmised significant interobserver variability occurs in the identification of landmarks of the distal femur used in total knee arthroplasty. The results tested in virtual space show that certain anatomic landmarks used in total knee arthroplasty are not reliable. The significance of this observation is that landmark identification, an integral component of computer- assisted surgical navigation in total knee arthroplasty, represents a source of method error in an otherwise accurate and precise computer-assisted technique.

Improving residency training in arthroscopic knee surgery with use of a virtual-reality simulator: A randomized blinded study

BACKGROUND There is a paucity of articles in the surgical literature demonstrating transfer validity (transfer of training). The purpose of this study was to assess whether skills learned on the ArthroSim virtual-reality arthroscopic knee simulator transferred to greater skill levels in the operating room. METHODS Postgraduate year-3 orthopaedic residents were randomized into simulator-trained and control groups at seven academic institutions. The experimental group trained on the simulator, performing a knee diagnostic arthroscopy procedure to a predetermined proficiency level based on the average proficiency of five community-based orthopaedic surgeons performing the same procedure on the simulator. The residents in the control group continued their institution-specific orthopaedic education and training. Both groups then performed a diagnostic knee arthroscopy procedure on a live patient. Video recordings of the arthroscopic surgery were analyzed by five pairs of expert arthroscopic surgeons blinded to the identity of the residents. A proprietary global rating scale and a procedural checklist, which included visualization and probing scales, were used for rating. RESULTS Forty-eight (89%) of the fifty-four postgraduate year-3 residents from seven academic institutions completed the study. The simulator-trained group averaged eleven hours of training on the simulator to reach proficiency. The simulator-trained group performed significantly better when rated according to our procedural checklist (p = 0.031), including probing skills (p = 0.016) but not visualization skills (p = 0.34), compared with the control group. The procedural checklist weighted probing skills double the weight of visualization skills. The global rating scale failed to reach significance (p = 0.061) because of one extreme outlier. The duration of the procedure was not significant. This lack of a significant difference seemed to be related to the fact that residents in the control group were less thorough, which shortened their time to completion of the arthroscopic procedure. CONCLUSIONS We have demonstrated transfer validity (transfer of training) that residents trained to proficiency on a high-fidelity realistic virtual-reality arthroscopic knee simulator showed a greater skill level in the operating room compared with the control group. CLINICAL RELEVANCE We believe that the results of our study will stimulate residency program directors to incorporate surgical simulation into the core curriculum of their residency programs.

Evaluation of skill level between trainees and community orthopaedic surgeons using a virtual reality arthroscopic knee simulator.

BACKGROUND Several virtual reality simulators have been developed to assist orthopaedic surgeons in acquiring the skills necessary to perform arthroscopic surgery. The purpose of this study was to assess the construct validity of the ArthroSim virtual reality arthroscopy simulator by evaluating whether skills acquired through increased experience in the operating room lead to improved performance on the simulator. METHODS Using the simulator, six postgraduate year-1 orthopaedic residents were compared with six postgraduate year-5 residents and with six community-based orthopaedic surgeons when performing diagnostic arthroscopy. The time to perform the procedure was recorded. To ensure that subjects did not sacrifice the quality of the procedure to complete the task in a shorter time, the simulator was programmed to provide a completeness score that indicated whether the surgeon accurately performed all of the steps of diagnostic arthroscopy in the correct sequence. RESULTS The mean time to perform the procedure by each group was 610 seconds for community-based orthopaedic surgeons, 745 seconds for postgraduate year-5 residents, and 1028 seconds for postgraduate year-1 residents. Both the postgraduate year-5 residents and the community-based orthopaedic surgeons performed the procedure in significantly less time (p = 0.006) than the postgraduate year-1 residents. There was a trend toward significance (p = 0.055) in time to complete the procedure when the postgraduate year-5 residents were compared with the community-based orthopaedic surgeons. The mean level of completeness as assigned by the simulator for each group was 85% for the community-based orthopaedic surgeons, 79% for the postgraduate year-5 residents, and 71% for the postgraduate year-1 residents. As expected, these differences were not significant, indicating that the three groups had achieved an acceptable level of consistency in their performance of the procedure. CONCLUSIONS Higher levels of surgeon experience resulted in improved efficiency when performing diagnostic knee arthroscopy on the simulator. Further validation studies utilizing the simulator are currently under way and the additional simulated tasks of arthroscopic meniscectomy, meniscal repair, microfracture, and loose body removal are being developed.

A haptic interface for the explorable virtual human

Haptic technology enhances a graphic user interface by allowing the user to interact in three dimensions with models on the screen, with force feedback giving the perception of touch. Recently several groups developed Internet based haptic systems that allow users in different parts of the world to interact with the same models simultaneously [Hikichi et al. 2002; Peterson 2002]. Although this system operates in real time, delay jitter caused by time required to transfer data inhibits the ability to apply realistic qualities to the individual models, as the lag in time is compensated by increasing the apparent weight of the model. Therefore, those users with greater lag times perceive the models as heavier than those with smaller lags [Hikichi et al. 2002]. While the required refresh rate of 1kHz suggests at least a portion of the interaction must be accomplished locally even on these other systems, transform updates must be handled at a server level. The haptic interface for the Explorable Virtual Human (EVH) we present allows the user to interact with various models taken from the Visual Human data set and the 100 micron knee. Our approach implements the PHANToM haptic device and can either incorporate single point collision as determined by the General Haptic Open Software Toolkit (GHOST®) SDK or calculate collision and force feedback information based on the shape and size of the haptic cursor and various properties of the models being viewed. In addition, collision detection allows deformations for those models representing soft tissues. Because the interaction occurs in real time, both the graphics and haptics run on the local computer while the browser enables the large data set to be managed by the server.