Knee Axes of Rotation: Determination and Implications

A.M. Hollister, M.A. Kester, S.D. Cook, M.E. Brunet and R.J. Haddad, Jr., New Orleans, Louisiana

32nd Annual ORS, New Orleans, Louisiana, February 17-20, 1986

Abstract: Since the work of Fick it has been recognized that joints have axes that can be used to describe normal and pathologic joint mechanics. Inman showed that all the motion of the ankle could be explained by simple axes that described the ligamentous and bony joint anatomy. Agee has described a simple device capable of finding the in vivo and in vitro axes of the metacarpalphangeal joint. This data was used to describe joint mechanics and to design a prosthetic joint. It was the objective of this investigation to use a similar device in vivo and in vitro to demonstrate the longitudinal and sagittal axes of the human knee.

The Axes of Rotation of the Knee

Anne M. Hollister, M.D., Sanjay Jatana, M.D., Anoop K. Sing, F.R.C.S., William W. Sullivan, M.D., and Andrei G. Lupichuk, B.S.E.E., Torrance, California

Clinical Orthopaedics and Related Research, Number 290, May 1993, pp 259-268

Abstract: Knee motion is believed to occur about a variable flexion-extension (FE) axis perpendicular to the sagittal plane and a longitudinal rotation (LR) axis. The authors used a mechanical device to locate the FE and the LR axes of six fresh anatomic specimen knees. The motion of points on the LR axis produced circular, planar paths about the fixed FE axis. Magnetic resonance (MR) images in planes perpendicular to the FE axis showed a circular profile for the femoral condyles. The FE axis is constant and directed from anterosuperior on the medial side to posteroinferior on the lateral side, passing through the origins of the medial and lateral collateral ligaments and superior to the crossing point of the cruciates. The LR axis is anterior and not perpendicular to the FE axis, the anatomic planes. This offset produces the valgus and external rotation observed with extension. The implications of two fixed offset axes for knee motion on prosthetic design, braces, gait analysis, and reconstructive surgery are profound.

A Comparison of the Transepicondylar Line with the Optimal Flexion/Extension Axis of the Knee

D.L. Churchill, S.J. Incavo, C.C. Johnson, B.D. Beynnon, Burlington, Vermont

44th Annual Meeting, Orthopaedic Research Society, March 16-19, 1998, New Orleans, Louisiana

Abstract: Knee kinematics have historically been analyzed in the sagittal plane using the method of instantaneous centers of rotation (ICR). These centers are found to move within the femur during the flexion cycle suggesting that the knee has no single fixed axis of rotation. Studies using the helical axis method (the three-dimensional equivalent of the plane ICR method) support this finding.

In contrast, other authors argue that there is in fact a single axis of flexion/extension (the FE axis) which remains fixed in the femur. In addition, there is a second axis (the LR axis) which is fixed in the tibia approximately parallel to its long axis. Earlier work has demonstrated that if these two axes are properly located, the kinematics of the knee can be accurately accounted for by simultaneous rotations about them. All other motions of the knee are negligible. This implies that there are two distinct and fundamental components of knee motion essentially corresponding to flexion/extension (rotation about the FE axis) and internal/external rotation of the tibia (rotation about the LR axis). The FE axis can thus be considered the "optimal" flexion/extension axis of the knee joint, while the LR axis the "optimal" axis of internal/external tibial rotation. Both of these axes are fixed within their respective bones.

Previous work concentrated primarily on determining the location of the tibial LR axis. The focus of this work was on determining the location of the femoral FE axis relative to bony landmarks. Specifically, the hypothesis was that the FE axis, as determined by kinematic analysis, corresponds with the transepicondylar (TE) line. The TE line passes between the most prominent points on the femoral epicondyles and is easily identifiable intraoperatively and during routine examination.

Effect of Surgical Technique and Prosthetic Design on Extensor Mechanism Function Following Total Knee Arthroplasty Tibial Tray

O.M. Mahoney, C.D. McClung, C.A. Zahiri, Athens, Georgia, T.P. Schmalzried, and H.S. Tullos, Los Angeles, California

45th Annual Meeting, Orthopaedic Research Society, February 1-4, 1999, Anaheim, California

Abstract: Symptoms related to extensor mechanism or the patello-femoral articulation are the most common complaints following total knee replacement and can limit the function of an otherwise satisfactory arthroplasty (well-aligned, well-fixed, stable, and with good flexion).

Morphology of the Transepicondylar Axis and Its Application in Primary and Revision Total Knee Arthroplasty

James B. Stiehl, M.D., and Bruce D. Abbot, B.S., Milwaukee, Wisconsin

The Journal of Arthroplasty, Volume 10, Number 6, 1995, pp 785-789

Abstract: A morphologic anatomic study was done of the lower extremity to investigate various relationships of the transepicondylar axis (TEA). Thirteen cadaver specimens were dissected and mounted to a metal frame with a pin passing through the TEA. The center of the knee was determined as the depth of the anterior intercondylar groove. The ratio of the upper leg to lower leg measured from femoral head center and ankle center to TEA was 1.02. The mean distance of the TEA to the joint line was 3.08cm medial and 2.53cm lateral. The mean femoral angle comparing the TEA to mechanical axis was 0.61º varus. The mean tibial angle comparing the TEA to the mechanical axis was 0.4º varus in extension and 0.43º in flexion, with no signifcant difference in the lower extremity angle with flexion (P<.01). The TEA is an important landmark that, from this study, is virtually perpendicular to the mechanical axis of the lower extremity and parallels the knee flexion axis. Femoral component rotation and joint line positioning in total knee arthroplasty can be determined use the TEA.

Kinematics of Posterior Cruciate Ligament-retaining and -Sacrificing Mobile Bearing Total Knee Arthroplasties

Phillip J. Lewandowski, M.D., Michael J. Askew, Ph.D., Deborah F. Lin, B.S., Frank W. Hurst, LPN, and Arne Melby, M.D.

The Journal of Arthroplasty Vol 12 No. 7 1997

Abstract: The posterior cruciate ligament (PCL)-retaining, meniscal bearing and the PCL-sacrificing rotating platform designs of the LCS prosthesis (DePuy, Warsaw, IN) were designed to minimally constrain knee kinematics while minimizing bone-cement-prosthesis interface stresses and polyethylene wear. The kinematics and stability of the knee following arthroplasty with these devices rely on adequate tensioning of the remaining soft tissues by management of the flexion/extension gaps at the time of surgery. In this in vitro study, the knee kinematics and the function of the quadriceps mechanism for 8 cadaveric knees were measured quantitatively before and after implantation of these 2 prosthesis designs. Following implantation of the PCL-retaining, meniscal bearing prosthesis, anterior translations during anterior drawer testing were significantly greater (P < .05) than those seen in the intact knee. Implantation of the PCL-retaining, meniscal bearing prosthesis resulted in an increase in the extension gap of 2 mm. Quadriceps force needed to achieve full extension was increased by 30% over that needed in the intact knee. The PCL-sacrificing, rotating platform prosthesis constrained anterior translation such that nearly normal anterior knee stability was reestablished; however, the extension gap was increased by 4 mm and the quadriceps force needed to achieve full extension was 50% greater than that needed in the intact knee. Attempts to achieve joint stability by increases in the thickness of the tibial component to widen the flexion/extension gaps result in compromises of quadriceps efficiency, particularly in the absence of a functioning PCL, as demonstrated in this in vitro model. Patients receiving the PCL-sacrificing prosthesis may experience difficulty in those activities requiring quadriceps power near full extension, such as rising from a chair or ascending or descending stairs.

Muscle Strength After Successful Total Knee Replacement

Chun-HsiungHuang, M.D., Cheng-Kung Cheng, Ph.D., Yung-Ta Lee, B.S., and Kuang-Sheng Lee, M.D., Taiwan, Republic of China

Clinical Orthopaedics and Related Research, Number 328, pp 147-154

Abstract: This study investigated the long term results of muscle strength of the knee joint after total knee replacement. Isokinetic testings of 120 and 180º per second and isometric testings at 30º and 60º knee flexion were studied on 1 healthy group and 3 groups of patients 6 to 13 years after total knee arthroplasty with prosthesis designs of total condylar, low contact stress meniscal bearing, or low contact stress rotating platform. The total condylar and low contact stress rotating platform prostheses were designed for use with a cut posterior cruciate ligament, whereas the low contact stress with meniscal bearing type was designed for use with a retained posterior cruciate ligament. The muscle strength ratios of hanstring to quadriceps were compared among the prosthetic designs and there were no statistical differences among patient groups. Whether the posterior cruciate ligament was cut or retained did not affect the relative muscle strength of the quadriceps and hamstring. All hamstring to quadriceps ratios from the isokinetic testings of these 3 prostheses design groups were greater than those of the healthy group, but were quite close to those of patients with cut anterior cruciate ligaments or with lower levels of daily activity. The hamstring to quadriceps ratios after successful total knee replacement were not the same as those of the healthy gruop even after long term (6-13 years) functional adaptation.