Reliability and Validity

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					Quantifying of avascular
necrosis of femoral head

       The clinical problem
Determining the risk of femoral head
  collapse in a patient with AVNFH
                Step 1.
     Asking an answerable question

n   In a 36-year-old woman with a 1-year
    history of avascular necrosis of femoral
    head, what is the risk for developing
    femoral head collaspse( Ficat stage III)?
                Step 2
    Selecting an evidence resource
n
 Quantifying the Extent of Femoral
Head Involvement in Osteonecrosis
n   By SEBASTIAN F. CHERIAN, MD, ALAN
        LAORR, MD, KHALED J. SALEH, MD,
    MSC,
        FRCSC, MICHAEL A. KUSKOWSKI, PHD,
        ROBERT F. BAILEY, LPN, AND EDWARD
    Y.
        CHENG, MD
n   Investigation performed at the Department of
    Orthopaedic Surgery, University of Minnesota,
    Minneapolis, Minnesota
       Quantifying the Extent of
               AVNFH
n   There are numerous methods for quantifying the
    extent of osteonecrosis of the femoral head.

n   However, there is no consensus regarding which
    method is the most reliable.

n   The purpose of this study was to determine the
    reliability and prognostic accuracy of “three”
    commonly used methods for quantifying the
    extent of osteonecrosis of the femoral head.
        Quantifying the Extent of
                AVNFH

n   The interobserver and intraobserver agreement
    was determined for each method

n   The ability of each method to predict the time to
    subchondral collapse was analyzed statistically.
        Quantifying the Extent of
                AVNFH
n   Joint-preserving surgical interventions
    ÞÞgenerally more successful at earlier stages of
    bone
          involvement (before the occurrence of a
    subchondral
          fracture).
n   The concept of quantifying femoral head
    involvement (important in determining prognosis)
    introduced by
    ÞÞ The staging system of Steinberg et al.
        Quantifying the Extent of
                AVNFH
n   Subchondral fracture is the most prognostically
    important variable indicating progression to
    osteoarthritis.

n   Several studies have demonstrated that the size
    of the necrotic lesion is important in determining
    whether a subchondral fracture will occur

n   Size = necrotic volume or the surface area or arc of
           subchondral bone affected ??
         Quantifying the Extent of
                 AVNFH
n   Methods:
    n    Thirty-nine hips in twenty-five patients who had stage
        -I or
          II osteonecrosis of the femoral head, according to
        the grading system of the Association Research
        Circulation Osseous, were independently examined
        on two separate occasions by three observers of
        different specialty backgrounds and experience.

    n   Each observer used three methods to quantify the
        extent of osteonecrosis of the femoral head:
        (1) the percentage of femoral head involvement.
        (2) the index of necrotic extent
        (3) the modified index of necrotic extent
         Materaial and methods
n   The three raters in this study :
    1. a third-year radiology resident
    2. an attending staff musculoskeletal radiologist
    3. an attending staff orthopaedic surgeon


n   The observers were blinded to both their
    previous evaluations and the evaluations
    of the other observers.
The percentage of femoral head
         involvement
n   first described in 1984
n   the abnormal signal on T1-weighted images
n   visually estimated on the basis of serial coronal
    and sagittal images
n   according to the estimated percentage of the
    area involved compared with the area of the
    entire femoral head, were grouped into three
    categories,
     as <15%, 15% to 30%, and >30%.
     The index of necrotic extent
n   developed by Koo and Kim in 1995

n   The necrotic arc angles on the midcoronal
    and midsagittal images were designated A
    and B, respectively.

n   The index of necrotic extent was calculated
    as (A/180) × (B/180) × 100
    The modified index of necrotic
               extent

n   The necrotic arc angle is measured on the
    image that demonstrates the maximal
    lesion size in the sagittal (A) and coronal
    (B) planes rather than on the midcoronal
    and midsagittal images.
          Result--- Reliability and
                   Validity
n   The interobserver agreement as defined by
    intraclass correlation coefficients
    n   The index of necrotic extent
        ÞÞ 0.58 (p < 0.001) for the first observation
              0.70 (p < 0.001) for the second observation.
    n   The modified index of necrotic extent
        ÞÞ 0.63 (p < 0.001) for the first observation
              0.81 (p < 0.001) for the second observation.
    n   The interobserver agreement of the percent
        involvement, as defined by Kendall coefficients of
        concordance,
        ÞÞ 0.71 (p < 0.001) for the first observation
              0.79 (p < 0.001) for the second observation.
         Result--- Reliability and
                  Validity
n   The intraobserver agreement---nearly perfect
    n   The index of necrotic extent
        ÞÞ 0.91 (p < 0.005) for the first rater
              0.83 (p < 0.005) for the second rater,
              0.93 (p < 0.005) for the third rater.
    n   The modified index of necrotic extent
         ÞÞ0.65 (p <0.005) for the first rater
              0.88 (p < 0.005) for the second rater
              0.91 (p < 0.005) for the third rater.
    n   The percent involvement
         ÞÞ 0.90 (p < 0.005) for the first rater
               0.89 (p < 0.005) for the second rater
               0.88 (p <0.005) for the third rater
Result--- Prognostic Ability (1)
 n   the percent involvement was significantly
     related to (log rank = 5.81, p < 0.05) the time
     to subchondral collapse
Result--- Prognostic Ability (2)
 n   index of necrotic extent (log rank = 7.17, p <
     0.007)
    The index of necrotic extent
n   (A/180) × (B/180) × 100 = 40
     A x B = 40 x 180 x 180 / 100 = 12960
     假設 A等於 B
     A2 = 12960
     A =Ö      12960        = 113.8 degree
Result--- Prognostic Ability (3)
 n   modified index of necrotic extent (log rank =
     4.05, p < 0.04)
              Critical Appraisal
n   Evidence level ?

n   Reliability and Validity
n   Reproducibility
n   Limitation
       Interobserver Agreement
n   Epidemiologists consider interobserver
    agreement of 0.6 to 0.8 to be substantial and 0.8
    to 1.0 to indicate nearly perfect agreement .
n   With the sample size used in this study (thirty-
    eight hips), a correlation coefficient of 0.44 could
    be detected as significant at the p = 0.05 level
    with 80% power.
n   Kendall coefficients of concordance : for a
    noncontinuous categorical variable ( groups)
          Reliability and Validity
n   The interobserver agreement as defined by
    intraclass correlation coefficients
    n   The index of necrotic extent
        ÞÞ 0.58 (p < 0.001) for the first observation
              0.70 (p < 0.001) for the second observation.
    n   The modified index of necrotic extent
        ÞÞ 0.63 (p < 0.001) for the first observation
              0.81 (p < 0.001) for the second observation.
    n   The interobserver agreement of the percent
        involvement, as defined by Kendall coefficients of
        concordance,
        ÞÞ 0.71 (p < 0.001) for the first observation
              0.79 (p < 0.001) for the second observation.
          Reliability and Validity
n   The intraobserver agreement---nearly perfect
    n   The index of necrotic extent
        ÞÞ 0.91 (p < 0.005) for the first rater
              0.83 (p < 0.005) for the second rater,
              0.93 (p < 0.005) for the third rater.
    n   The modified index of necrotic extent
         ÞÞ0.65 (p <0.005) for the first rater
              0.88 (p < 0.005) for the second rater
              0.91 (p < 0.005) for the third rater.
    n   The percent involvement
         ÞÞ 0.90 (p < 0.005) for the first rater
               0.89 (p < 0.005) for the second rater
               0.88 (p <0.005) for the third rater
                 Limitations
n   Only three observers
n   Sample size (38 hips)
n   Other variables ( surgical intervention,
    medication, weight bearing status etc…)
n   Configuration of the lesions
                        Results
n   There was significantly valid agreement among the
    observers for all three methods (p < 0.001 for all
    three).

n   The index of necrotic extent and the percent
    involvement → substantial agreement among raters
     The modified index of necrotic extent
     → nearly perfect agreement

n    Survivorship analysis revealed prognostically
    significant
     predictors of subchondral fracture.
       the percent involvement (p < 0.05)
      index of necrotic extent (p < 0.007)
      modified index of necrotic extent (p < 0.04)
                  Conclusions
n   index of necrotic extent, modified index of
    necrotic extent, and estimation of the percentage
    of involvement of the femoral head are
    reproducible and reliable methods for
    quantitatively evaluating the extent of
    osteonecrosis of the femoral head.

n   Furthermore, they are clinically useful for
    identifying hips at greatest risk for subchondral
    collapse.

				
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posted:11/27/2013
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