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Scientific Articles   |    
The Geometry of the Tibial Plateau and Its Influence on the Biomechanics of the Tibiofemoral Joint
Javad Hashemi, PhD1; Naveen Chandrashekar, PhD2; Brian Gill, MD3; Bruce D. Beynnon, PhD4; James R. Slauterbeck, MD4; Robert C. SchuttJr., MD3; Hossein Mansouri, PhD5; Eugene Dabezies, MD3
1 Department of Mechanical Engineering, 7th and Boston Streets, Lubbock, TX 79409-1021. E-mail address: javad.hashemi@ttu.edu
2 Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada
3 Department of Orthopaedic Surgery and Rehabilitation, Texas Tech University Health Sciences Center, 3601 4th Street Stop 9436, Lubbock, TX 79430-9436
4 Department of Orthopaedic Rehabilitation, University of Vermont, Burlington, VT 05405-008
5 Department of Mathematics and Statistics, Texas Tech University Health Sciences Center, Broadway and Boston Streets, Lubbock, TX 79409-1042
View Disclosures and Other Information
Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the National Institutes of Health (NIAMS/NIH), Grant Number R01AR050421. Neither they nor a member of their immediate families 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, 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.
Investigation performed at Texas Tech University, Lubbock, Texas, and the University of Vermont, Burlington, Vermont

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Dec 01;90(12):2724-2734. doi: 10.2106/JBJS.G.01358
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Abstract

Background: The geometry of the tibial plateau is complex and asymmetric. Previous research has characterized subject-to-subject differences in the tibial plateau geometry in the sagittal plane on the basis of a single parameter, the posterior slope. We hypothesized that (1) there are large subject-to-subject variations in terms of slopes, the depth of concavity of the medial plateau, and the extent of convexity of the lateral plateau; (2) medial tibial slope and lateral tibial slope are different within subjects; (3) there are sex-based differences in the slopes as well as concavities and convexities of the tibial plateau; and (4) age is not associated with any of the measured parameters.

Methods: The medial, lateral, and coronal slopes and the depth of the osseous portion of the tibial plateau were measured with use of sagittal and coronal magnetic resonance images that were made for thirty-three female and twenty-two male subjects, and differences between the sexes with respect to these four parameters were assessed. Within-subject differences between the medial and lateral tibial slopes also were assessed. Correlation tests were performed to examine the existence of a linear relationship between various slopes as well as between slopes and subject age.

Results: The range of subject-to-subject variations in the tibial slopes was substantive for males and females. However, the mean medial and lateral tibial slopes in female subjects were greater than those in male subjects (p < 0.05). In contrast, the mean coronal tibial slope in female subjects was less than that in male subjects (p < 0.05). The correlation between medial and lateral tibial slopes was poor. The within-subject difference between medial and lateral tibial slopes was significant (p < 0.05). No difference in medial tibial plateau depth was found between the sexes. The subchondral bone on the lateral part of the tibia, within the articulation region, was mostly flat. Age was not associated with the observed results.

Conclusions: The geometry of the osseous portion of the tibial plateau is more robustly explained by three slopes and the depth of the medial tibial condyle.

Clinical Relevance: The sex and subject-to-subject-based differences in the tibial plateau geometry found in the present study could be important to consider during the assessment of the risk of knee injury, the susceptibility to osteoarthritis, and the success of unicompartmental and total knee arthroplasty.

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    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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    Javad Hashemi, Ph.D.
    Posted on July 09, 2012
    Thank you for the opportunity to correct the error
    Department of Mechanical Engineering, Texas Tech University

    We appreciate Dr. Sessa’s thoughtful comments and the opportunity to provide a correction. Dr. Sessa has correctly raised an issue about our power analysis statement. The issue involves an undetected typographical error and should read as presented below with the added “non” (capitalized for emphasis). We acknowledge that we should have detected and fixed this typographical error and we apologize for this oversight.

    The sentence in question should read as follows:

    "A power analysis revealed the need for a minimum of twenty-two subjects of each sex to establish 80% power to protect against the undue NON-rejection of the null hypothesis."

    Regarding our power analysis and sample size calculation:

    The power analysis was done based on the two-sample t-test. Assuming μ12,σ to be the means and common standard deviation of the two populations, the power function is calculated based on the non-central t-distribution with non-centrality parameter that not only depends on the unknown parameters μ12,σ but also the sample sizes. In addition, the actual calculation also depends on the level of significance α.

    Sample size is determined by assuming specific values for the unknown parameters μ12,σ and the value of power[1]. Clearly, since we are never going to know the actual values of μ12,σ and in the absence of a large scale previous study in the case of this investigation, one of the authors (JH) used the results of our pilot study on coronal tibial slope (CTS) of eleven female and nine male subjects (a total of twenty subjects) to estimate the sample size[1].

     

    REFERENCE:
    [1]. http://www.dssresearch.com/KnowledgeCenter/toolkitcalculators/samplesizecalculators.aspx

    Pasquale Sessa, MD, PhD
    Posted on April 27, 2012
    Power Analysis in this Article

    I'd like to highlight that in this article there appears to be an error in the description of the power analysis. I refer to the statement in the 'Material and Methods' section: 'A power analysis revealed the need for a minimum of twenty-two subjects of each sex to establish 80% power to protect against the undue rejection of the null hypothesis'.

    The power analysis is generally carried out to protect against accepting the null hypothesis (of no association) when in fact the null hypothesis should be rejected (because an association is present).

    How was the power analysis carried out?

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