Donald G. Eckhoff

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 …

Early Neuromuscular Electrical Stimulation to Improve Quadriceps Muscle Strength After Total Knee Arthroplasty: A Randomized Controlled Trial

Background The recovery of quadriceps muscle force and function after total knee arthroplasty (TKA) is suboptimal, which predisposes patients to disability with increasing age. Objective The purpose of this investigation was to evaluate the efficacy of quadriceps muscle neuromuscular electrical stimulation (NMES), initiated 48 hours after TKA, as an adjunct to standard rehabilitation. Design This was a prospective, longitudinal randomized controlled trial. Methods Sixty-six patients, aged 50 to 85 years and planning a primary unilateral TKA, were randomly assigned to receive either standard rehabilitation (control) or standard rehabilitation plus NMES applied to the quadriceps muscle (initiated 48 hours after surgery). The NMES was applied twice per day at the maximum tolerable intensity for 15 contractions. Data for muscle strength, functional performance, and self-report measures were obtained before surgery and 3.5, 6.5, 13, 26, and 52 weeks after TKA. Results At 3.5 weeks after TKA, significant improvements with NMES were found for quadriceps and hamstring muscle strength, functional performance, and knee extension active range of motion. At 52 weeks, the differences between groups were attenuated, but improvements with NMES were still significant for quadriceps and hamstring muscle strength, functional performance, and some self-report measures. Limitations Treatment volume was not matched for both study arms; NMES was added to the standard of care treatment. Furthermore, testers were not blinded during testing, but used standardized scripts to avoid bias. Finally, some patients reached the maximum stimulator output during at least one treatment session and may have tolerated more stimulation. Conclusions The early addition of NMES effectively attenuated loss of quadriceps muscle strength and improved functional performance following TKA. The effects were most pronounced and clinically meaningful within the first month after surgery, but persisted through 1 year after surgery.

Difference between the epicondylar and cylindrical axis of the knee.

Locating the true flexion-extension axis of the knee can play an important role in component placement in a total knee arthroplasty, especially using contemporary computer-assisted surgical navigation. We determined if the commonly used transepicondylar axis is an accurate and reproducible substitute for the flexion-extension axis. Twenty-three fresh-frozen cadaveric distal femurs with intact soft tissue were imaged with computed tomography and reconstructed in three-dimensional virtual space. The transepicondylar axis was compared with a line equidistant from the articular surface of each femoral condyle. Measures were performed by three observers three times for each specimen. Interobserver and intraobserver variations were small, but the differences between axes were approximately 5°. The difference between axes decreased when projected from three-dimensional space to traditional two-dimensional planes (coronal and transverse), explaining why this discrepancy has not been previously documented. The greater difference in three-dimensional space may account for midrange instability reported in total knee arthroplasty. The increased accuracy afforded by computer-assisted surgical navigation in total knee arthroplasty may be lost and increased malposition of components may occur if this discrepancy between reference axes is not appreciated and addressed.

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 …

Femoral morphometry and anterior knee pain.

By computed tomography scan, morphology of the femur in 20 adult patients with anterior knee pain was compared with that of ten volunteers without knee pain to identify femoral characteristics associated with the painful patella. Anteversion, measured as the difference between the axis of the head-neck and the axis of the posterior condyles, was significantly greater in symptomatic adults (p < 0.01). Configuration of the distal femur and position of the patella relative to the femur were similar in each group. Adult anterior knee pain was, therefore, associated with increased anteversion without compensatory change in trochlear morphology or patellar orientation to the femur.

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 …

Version of the osteoarthritic knee

Version of normal and osteoarthritic knees is evaluated by computed tomography in this study. Version of the knee is defined as the static rotation of the tibia with respect to the femur in full knee extension. It is measured as the difference between the transverse axes of the femoral condyles and tibia. The average knee version, or external rotation of the tibia with respect to the femur across the normal knee, was 0 degree. Version of the osteoarthritic knee was 5 degrees. Rotation of the tibia with respect to the femur across the extended osteoarthritic knee is a relationship that will affect the placement of components in total knee arthroplasty. This relationship should be addressed in alignment instrumentation and technique to avoid component malalignment in total knee arthroplasty.

Femoral anteversion and arthritis of the knee

Anteversion and arthritic changes were recorded in 110 well-preserved femora to identify a correlation between knee osteoarthritis and anteversion. Arthritis was recorded as no change (grade 0), osteophytes (grade 1), cysts or erosions (grade 2), and burnishing or eburnation (grade 3). Anteversion was identified by measure of the angle between the axis of the head-neck and the axis of the posterior condyles. There was no relation between anteversion and proximal femoral arthritis but increased arthritis of the distal femur with decreased anteversion (p < 0.04) was identified, establishing a correlation between femoral anteversion and arthritis of the knee.

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.

Sulcus Morphology of the Distal Femur

Traditional images of the distal femur place the intercondylar groove midway between the condyles. The location of the sulcus of the intercondylar groove in a large Sudanese skeletal population was verified using a custom stereotactic device. The results of this study show that the femoral sulcus is lateral to the midplane between the 2 femoral condyles. This study also shows that the configuration of the sulcus is linear and is oriented between the traditional anatomic and mechanical axes of the femur.