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Scientific Articles   |    
Assessment of the Radii of the Medial and Lateral Femoral Condyles in Varus and Valgus Knees with Osteoarthritis
Stephen M. Howell, MD; Stacey J. Howell; Maury L. Hull, PhD
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors, or a member of his or her immediate family, received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from commercial entities (Biomet Sports Medicine and OtisMed, Inc.).

Investigation performed at Mechanical and Aeronautical Engineering, University of California at Davis, Davis, California

Copyright ©2010 American Society for Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2010 Jan 01;92(1):98-104. doi: 10.2106/JBJS.H.01566
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Abstract

Background: 

Understanding the relationship between the radii of the medial and lateral femoral condyles in varus and valgus knees is important for aligning the femoral component and for restoring kinematics in total knee arthroplasty. The purpose of this study was to test the hypothesis that the asymmetry between the radii of the medial and lateral femoral condyles in varus and valgus knees with osteoarthritis is small enough to be clinically unimportant.

Methods: 

A magnetic resonance imaging scan was obtained with use of a biplanar, rotational alignment protocol in a consecutive series of subjects with end-stage osteoarthritis prior to total knee arthroplasty. The alignment protocol oriented the scanning plane so that both condyles were imaged in a plane perpendicular to the primary femoral axis of the knee about which the tibia flexes and extends. The study included 155 varus knees and forty-four valgus knees. Radii were calculated from the area of the best-fit circle overlaid from 10° to 160° on the subchondral corticocancellous bone interface of the medial and lateral femoral condyles. The radius of a condyle was the average of the radii on four adjacent images that showed the femoral condyle with the largest curvature.

Results: 

In the 155 varus knees, the radius of the lateral condyle was an average of 0.1 mm larger than that of the medial condyle (p = 0.003). In the forty-four valgus knees, the radius of the lateral condyle was an average of 0.2 mm larger than that of the medial condyle (p < 0.006). There was a strong association between the radii of the medial and lateral femoral condyles in both the varus (r2 = 0.9210) and the valgus (r2 = 0.9129) knees.

Conclusions: 

As determined by imaging of the femoral condyles perpendicular to the primary femoral axis of the knee, the asymmetry between the radii of the medial and lateral femoral condyles in varus and valgus knees with end-stage osteoarthritis was =0.2 mm, which is small enough to be considered clinically unimportant when aligning a total knee prosthesis.

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    References

    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Stephen M. Howell, MD
    Posted on April 01, 2010
    Dr. Howell and colleagues respond to Drs. Schnurr and König
    University of California at Davis, Davis, California

    Thank you for your interest in our study and for restating the importance of studying the anatomy of the distal femur in the knee with varus and valgus deformities because of the impact the anatomy has on aligning the femoral component and restoring kinematics in total knee arthroplasty. We believe you are correct in pointing out that a difference in methods, or more precisely a difference in the ‘perspective’ of how our two studies viewed the anatomy of the distal femur, explains why our study found no clinically important asymmetry between the radii of the medial and lateral femoral condyles in either the varus or valgus knees and your study found a hypoplastic lateral femoral condyle in the valgus knee. We agree with you that the difference in the reference axes explains the difference in findings between our studies, which directly impacts how we prefer to align the femoral component in total knee arthroplasty.

    In our study, the difference between the radii of the medial and lateral femoral condyles was measured from the ‘kinematic’ perspective of how the knee moves 3-dimensionally. The most important kinematic axis of the knee passes through the center point of the best-fit circles of the medial and lateral femoral condyles, and is termed the primary femoral axis about which the tibia flexes and extends (1-5). Our study referenced the primary transverse axis in the femur about which the tibia flexes and extends. This axis is a line connecting the centers of circles fit to the bony articular surfaces of the condyles (2-8). The primary transverse axis of the knee has no relationship to the mechanical axis of the femur, the mechanical axis of the tibia, or the transepicondylar axis. The only intraoperative morphologic reference to guide the surgeon is the articular surface of the femoral condyles. No other morphologic feature of the knee or limb will lead the surgeon reliably and repeatedly to the primary transverse axis in the femur about which the tibia flexes and extends (3). We measured the largest radii of the femoral condyles from the primary transverse axis in the femur about which the tibia flexes and extends and in a plane perpendicular to this axis.

    In your study, the difference between the medial and lateral femoral condyles was measured from the ‘non-kinematic’ or a ‘mechanical’ alignment perspective as determined intraoperatively by computer navigation. Your study referenced a line drawn perpendicular to the mechanical axis of the femur in the coronal plane, and the transepicondylar axis in the axial plane.

    In the coronal plane, you constructed a line perpendicular to the mechanical axis of the femur, which is not a kinematic reference axis because the normal distal femoral joint line is not perpendicular to the mechanical axis of the femur in most knees. Studies have shown that the normal distal femoral joint line is not perpendicular to the mechanical axis of the femur because there is wide variability in the bow of the femur (8), and because 98% of normal subjects do not have a neutral hip- knee-ankle angle (4). The smaller resection from the lateral femoral condyle and the large resection from the medial femoral condyle in the valgus knee you mentioned you observe are caused by the line perpendicular to the mechanical axis of the femur being oblique to the primary transverse axis in the femur in most knees. Aligning the joint line of the femoral component perpendicular to the mechanical axis of the femur has undesirable consequences of changing the distal femoral joint line from normal and kinematically malaligning the knee resulting in ligament releases and mid-flexion instability (3,4).

    In the axial plane, you constructed a line connecting the ‘best’ point in the region of the medial and lateral epicondyles with a navigational probe, which is not a kinematic reference axis for several reasons. One reason the transepicondylar axis is not a kinematic reference axis is the 5° difference (range 2-110) between the primary transverse axis in the femur and the transepicondylar axis in 3-dimensional space (3,4). The transepicondylar axis passes through the distal femur proximal and anterior to the origin of the anterior and posterior cruciate ligaments with no apparent relationship to these important soft tissues of the knee. In contrast, the primary transverse axis in the femur about which the tibia flexes and extends remains equidistant from the surface of both posterior femoral condyles passing through the origins of the anterior and posterior cruciate ligaments (3). A second reason that the transepicondylar axis is not a kinematic reference is that precisely identifying the transepicondylar axis with navigational and conventional instruments is highly unreliable. Siston et al. showed a rotational error of placing the femoral component from 13° internal rotation to 16° external rotation when 11 highly-skilled surgeons constructed the transepicondylar axis by selecting the ‘best’ point in the region of the medial and lateral epicondyles with a navigational probe (9).

    To summarize, our observation that the valgus knee does not have a hypoplastic lateral femoral condyle remains true when the knee is studied from a kinematic perspective in a plane perpendicular to the primary transverse axis in the femur. Surgeons who view the knee from a mechanical perspective with navigational or conventional instruments need to understand that aligning the femoral component perpendicular to the mechanical axis of the femur and parallel to the transepicondylar axis kinematically malaligns most knees (2-8). Eckhoff has correctly warned that the use of navigation that does not incorporate reference axes that describe the kinematics of the knee, may “more accurately” align the limb but malalign the knee leading to altered kinematics and increased wear and, ultimately, to premature failure of the arthroplasty (4). We encourage those who use navigational instruments to investigate the use of kinematic alignment as it has the potential to improve motion, stability, and clinical outcome (7,10).

    The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors, or a member of his or her immediate family, received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from commercial entities (Biomet Sports Medicine and Stryker, Inc.). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

    References

    1. Churchill DL, Incavo SJ, Johnson CC, Beynnon BD. The transepicondylar axis approximates the optimal flexion axis of the knee. Clin Orthop Relat Res. 1998;356:111-8.

    2. Coughlin KM, Incavo SJ, Churchill DL, Beynnon BD. Tibial axis and patellar position relative to the femoral epicondylar axis during squatting. J Arthroplasty. 2003;18:1048-55.

    3. Eckhoff D, Hogan C, DiMatteo L, Robinson M, Bach J. Difference between the epicondylar and cylindrical axis of the knee. Clin Orthop Relat Res. 2007;461:238-44.

    4. Eckhoff DG, Bach JM, Spitzer VM, Reinig KD, Bagur MM, Baldini TH, Flannery NM. Three-dimensional mechanics, kinematics, and morphology of the knee viewed in virtual reality. J Bone Joint Surg Am. 2005;87 Suppl 2:71-80.

    5. Hollister AM, Jatana S, Singh AK, Sullivan WW, Lupichuk AG. The axes of rotation of the knee. Clin Orthop Relat Res. 1993;290:259-68.

    6. Eckhoff DG, Bach JM, Spitzer VM, Reinig KD, Bagur MM, Baldini TH, Rubinstein D, Humphries S. Three-dimensional morphology and kinematics of the distal part of the femur viewed in virtual reality. Part II. J Bone Joint Surg Am. 2003;85 Suppl 4:97-104.

    7. Howell SM, Hodapp EE, Kuznik K, Hull ML. In vivo adduction and reverse axial rotation (external) of the tibial component can be minimized. Orthopedics. 2009;32:319.

    8. Howell SM, Kuznik K, Hull ML, Siston RA. Longitudinal shapes of the tibia and femur are unrelated and variable. Clin Orthop Relat Res. 2010;468:1142-8.

    9. Siston RA, Patel JJ, Goodman SB, Delp SL, Giori NJ. The variability of femoral rotational alignment in total knee arthroplasty. J Bone Joint Surg Am. 2005;87:2276-80.

    10. Howell SM, Kuznik K, Hull ML, Siston RA. Results of an initial experience with custom-fit positioning total knee arthroplasty in a series of 48 patients. Orthopedics. 2008;31:857-63.

    Christoph Schnurr
    Posted on March 10, 2010
    Anatomy of the Distal Femoral Condyle in Valgus Deformities
    LVR Clinic of Orthopedic Surgery, Viersen, Germany

    To the Editor:

    We read the article by Howell et al. (1) with interest. Especially in valgus knee deformities, the alignment of the femoral total knee component remains a challenge. Therefore, studies concerning the anatomy of the distal femur in varus and valgus deformities are required. However, routinely we have perceived the lateral femoral condyle in valgus deformities to be smaller than the medial one - large resections of bone from the medial distal and posterior femoral condyle go together with small bone resections from the lateral femoral condyle. Similar concepts have been published by other groups (2-5). Recently, we analyzed the computer navigation data of our last 500 total knee arthroplasties. The most distal points of the femoral condyles were measured perpendicular to the mechanical femoral axis, and the most posterior points were measured parallel to the primary knee axis. Our analysis resulted in a significantly smaller lateral condyle in valgus deformities in comparison to varus deformities (the difference between the most distal point of the medial and lateral condyles: valgus 4.3mm, varus 0.2mm [p<0.001]; the difference between the most posterior point of the medial and lateral condyles: valgus 2.8mm, varus 1.5mm [p=0.033]). The inaccuracy of the imageless navigation device has been proven to be less than 1mm or 1° (6), hence we believe these results to be reliable. From our point of view, these results are not in line with the published study. Can methodical issues explain the discrepancy?

    The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors, or a member of his or her immediate family, received, in any one year, payments or other benefits of less than $10,000 or a commitment or agreement to provide such benefits from a commercial entity (BrainLAB, Feldkirchen, Germany).

    References

    1. Howell SM, Howell SJ, Hull ML. Assessment of the radii of the medial and lateral femoral condyles in varus and valgus knees with osteoarthritis. J Bone Joint Surg Am. 2010;92:98-104.

    2. Engh GA. The difficult knee: severe varus and valgus. Clin Orthop Relat Res. 2003;416:58-63.

    3. Elkus M, Ranawat CS, Rasquinha VJ, Babhulkar S, Rossi R, Ranawat AS. Total knee arthroplasty for severe valgus deformity. Five to fourteen-year follow-up. J Bone Joint Surg Am. 2004;86:2671-6.

    4. Favorito PJ, Mihalko WM, Krackow KA. Total knee arthroplasty in the valgus knee. J Am Acad Orthop Surg. 2002;10:16-24.

    5. Pape D, Kohn D. [Soft tissue balancing in valgus gonarthrosis]. Orthopade. 2007;36:657-8. German.

    6. Lustig S, Fleury C, Goy D, Neyret P, Donell ST. The accuracy of acquisition of an imageless computer-assisted system and its implication for knee arthroplasty. Knee. 2010 Jan 8. [Epub ahead of print]

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