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Can Normal Knee Kinematics Be Restored with Unicompartmental Knee Replacement?
Shantanu Patil, MD1; Clifford hW. ColwellJr., MD1; Kace A. Ezzet, MD1; Darryl D. D'Lima, MD1
1 Orthopaedic Research Laboratories, Scripps Clinic Center for Orthopaedic Research and Education, 11025 North Torrey Pines Road, Suite 140, La Jolla, CA 92037. E-mail address for D.D. D'Lima: ddlima@scripps.edu
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In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from DePuy, a Johnson and Johnson company, and from Alfred A. Smith and Susan Smith D. Richardson. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Orthopaedic Research Laboratories, Scripps Clinic Center for Orthopaedic Research and Education, La Jolla, California

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2005 Feb 01;87(2):332-338. doi: 10.2106/JBJS.C.01467
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Background: Unicompartmental replacement can be an alternative to tibial osteotomy in younger, active patients with unicompartmental knee disease. In unicompartmental replacement, the other compartments and knee ligaments are largely untouched. Therefore, it was hypothesized that the knee kinematics after unicompartmental replacement may also be unchanged. To test this hypothesis, knee kinematics and quadriceps tension were recorded before and after replacement with a unicompartmental design and then with a tricompartmental design.

Methods: Six human cadaver knees were tested before implantation, after implantation with a bicruciate-retaining unicompartmental knee prosthesis, and after implantation with a posterior cruciate-retaining tricompartmental knee prosthesis. The unicompartmental prosthesis was initially implanted, and it was then revised to a total condylar knee replacement. The knee kinematics were measured with use of an electromagnetic tracking device while the knee was put through dynamic simulated stair-climbing under peak flexion moments of approximately 40 N-m. Quadriceps tension was also measured for all three conditions.

Results: No significant differences in tibial axial rotation were noted between the intact and unicompartmental conditions. However, tricompartmental replacement significantly affected tibial axial rotation (p = 0.001). Femoral rollback was not significantly affected by either unicompartmental or tricompartmental arthroplasty. Quadriceps tension was also similar among all three conditions.

Conclusions: In this in vitro cadaver study, the tricompartmental replacement significantly changed knee kinematics while the unicompartmental replacement preserved normal knee kinematics.

Clinical Relevance: The results of this in vitro biomechanical cadaver study suggest that the unicompartmental design has the potential to restore (or preserve) normal kinematic function better than tricompartmental implants. Restoration of normal knee function may benefit patient rehabilitation, extensor function, implant survival, and wear.

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    Darryl D. D'Lima, M.D.
    Posted on March 16, 2006
    Dr. D'Lima et al respond to Dr. John
    Scripps Clinic Center for Orthopaedic Research and Education, La Jolla, CA 92037

    Dr. John may be right in his statement that translation of the mid- point of the transepicondylar axis would not by itself capture the differential rollback between the lateral and medial femoral condyles. However, differential rollback would be recorded as axial tibial rotation. In the knee biomechanics literature, kinematics are expressed differently depending on the type of motion analysis used. Typically, fluoroscopic studies assume that the lowest point on the femoral condyle represents the instantaneous tibiofemoral contact and report translation of this point as rollback. Motion analysis studies that use skin or bone mounted tracker systems typically use anatomic landmarks to define a coordinate system in the femur and report translation of the center of this coordinate system. We chose the latter for direct comparison of kinematics between our own previous studies and the large available body of knee kinematic literature.

    If differential rollback changed after unicompartmental arthroplasty this would be reflected in a change in translation of the mid- transepicondylar point and/or a change in axial tibial rotation. Defining rollback in either fashion would not change our conclusion. Dr. John is entitled to his opinion regarding the cause of relatively higher lateral unicompartmental replacement failure. However, if he wishes to support his speculation we would like to see evidence that increased rolling produces more wear that sliding. The use of term “translation” does not differentiate between rollback and sliding. Greater posterior translation of the lateral femoral condyle relative to the medial indicates greater rolling in the lateral compartment and greater sliding in the medial compartment. When we mention the advantages of normal kinematics, we were comparing it with the abnormal kinematics reported after total knee replacement which involve forward sliding of the femur with flexion (“reverse rollback”)(1).


    1. Dennis, D. A., Komistek, R. D., Colwell Jr, C. W., Ranawat, C. S., Scott, R. D., Thornhill, T. S., and Lapp, M. A.: In vivo anteroposterior femorotibial translation of total knee arthroplasty: a multicenter analysis. Clin Orthop Relat Res.47-57, 1998.

    Darryl D. D'Lima, M.D.
    Posted on March 16, 2006
    Dr.D'Lima et al respond to Drs. Joshi and Nagare
    Scripps Clinic Center for Orthopaedic Research and Education, LA Jolla, CA 92037

    In our publication we did not recommend performing unicompartmental replacement in ACL deficient knees. Our article states that we only tested knees without obvious defects. In these knees transection of the ACL would not simulate the entire clinical spectrum seen with traumatic or pathological ACL rupture. An ACL deficient knee with unicompartmental arthritis may have other associated abnormalities that could affect survivorship.

    One of our goals was to determine whether the change in knee kinematics after total knee arthroplasty could be attributed to the missing biomechanical support provided by the ACL. Since transecting the ACL did not change the kinematics after unicompartmental replacement, we concluded that resecting the ACL was not likely to be responsible for abnormal kinematics observed in total knee replacement. We can only repeat what we stated in our article: “This study only tested cadaver knees in controlled, closed-kinetic-chain knee extension. It is possible that the results may be different in other activities.”

    We strongly caution against unicompartmental replacement in ACL deficient knees until more definitive evidence is available.

    Joby John
    Posted on November 17, 2005
    Can Normal Knee Kinematics Be Restored with Unicompartmental Knee Replacement
    Royal Shrewsbury Hospital, UK

    To The Editor:

    I read with great interest the article by Patil, et al. I agree with the authors that preservation of anatomy in unicompartmental knees would produce a near normal kinetic and kinematic profile. However, the definition of roll-back as the translation of the mid point of the transepicondylar axis, would seem questionable. It is known that the lateral condyle translates substantially more than the medial condyle. Femoral condylar roll-back is said to occur only laterally.(1) Measuring roll-back with a point on an axis closer to the medial condyle would not be reflective of the true picture of roll-back, as small alterations in translation of tibiofemoral contact point on the lateral compartment may not be detected.

    This may be the reason why it seemed that ACL resection did not affect the knee kinematics in this study. Results from unicompartmental arthroplasty series have shown inferior results in ACL deficient knees.(2) This phenomenon is unlikely to happen if the kinematic profile of the knee was unaltered. I would also be skeptical about the conclusion that restoring normal kinematics of the knee would decrease the wear. Lateral unicompartmental knee replacements have not done as well as their medial counterparts, partly because of the decreased tibial slope and also increased tibiofemoral translation. It might actually be a case of the normal kinematics being partly responsible for the decreased survival of the lateral unicompartmental knee replacement.


    1. Pinskerova V., et al. Does femur roll-back with flexion? JBJS Br.2004 Aug;86-B(6):925-931.

    2. Goodfellow JW. The Oxford Knee for unicompartmental osteoarthritis. JBJS Br.1998 Nov;70(5):692-701.

    Avinash P Joshi
    Posted on March 17, 2005
    Can normal Knee kinematics be restored with unicompartmental Knee replacement ?
    Gloucester Royal Hospital, Great Western road, Gloucester, GL1 3NN, UK

    To the Editor:

    We read with great interest the recent article by Patil, et al. We agree with the authors that when compared to performing TKA for triccompartmental disease, there is 'lack of soft tissue abnormalities further reducing surgical variations' in a unicompartmental knee. However, we would like to stress that 'balancing of the soft tissue tension' in a Knee undergoing unicompartmental replacement is equally important and at times very difficult. In fact a minor change in the thickness of the polythelene spacer affects the tibio- femoral angle and hence also the tension around the medial collateral ligament in a unicompartmental Knee(1).

    We would also disagree with their conclusions that 'the role of ACL in antero-posterior stability and axial rotation is not important'. This is when we know the results of a unicompartmental Knee to have been inferior and to have been failed in a ACL deficient/lax Knee(2).

    The paper also states that resecting the ACL in a unicompartmental Knee arthroplasty did not change the kinematics of the Knee. Does one conclude from the findings that a unicompartmental Knee performed in a ACL deficient/lax Knee could give the same results and equal chance of success/failure as in a ACL intact Knee ?


    1) Hopgood.P et al. The effect of tibial implant size on post- operative alignment following medial unicompartmental knee replacement. Knee. 2004 Oct;11(5):385-8.

    2) Goodfellow JW. The Oxford Knee for unicompartmental osteoarthritis. JBJS Br.1998 Nov;70(5):692-701.

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