Quantifying of avascular necrQuantifying of avascular necrosis of femoral headosis of femoral head

The clinical problemThe clinical problemDetermining the risk of femoral Determining the risk of femoral head collapse in a patient with head collapse in a patient with

AVNFHAVNFH

Step 1. Step 1. Asking an answerable questionAsking an answerable question

In a 36-year-old woman with a 1-year hisIn a 36-year-old woman with a 1-year history of avascular necrosis of femoral heatory of avascular necrosis of femoral head, what is the risk for developing femorad, what is the risk for developing femoral head collaspse( Ficat stage III)?l head collaspse( Ficat stage III)?

Step 2 Step 2 Selecting an evidence resourceSelecting an evidence resource

Quantifying the Extent of Femoral Head Involvement in Osteonecrosis

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 Investigation performed at the Department of

Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota

Quantifying the Extent of AVNFH

There are numerous methods for quantifying the extent of osteonecrosis of the femoral head.

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

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

The interobserver and intraobserver agreement was determined for each method

The ability of each method to predict the time to subchondral collapse was analyzed statistically.

Quantifying the Extent of AVNFH

Joint-preserving surgical interventions generally more successful at earlier stages of bon

e involvement (before the occurrence of a subchon

dral fracture). The concept of quantifying femoral head involvemen

t (important in determining prognosis) introduced by

The staging system of Steinberg et al.

Quantifying the Extent of AVNFH

Subchondral fractureSubchondral fracture is the is the most prognostically most prognostically important variableimportant variable indicating progression to ost indicating progression to osteoarthritis.eoarthritis.

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

Size necrotic volume or the surface area or arc of subchondral bone affected ??

Quantifying the Extent of AVNFH

Methods: Thirty-nine hips in twenty-five patients who had stage-I or II osteonecrosis of the femoral head, according to the gradi

ng system of the Association Research Circulation Osseous, were independently examined on two separate occasions by three observers of different specialty backgrounds and experience.

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 methodsMateraial and methods The The three ratersthree raters in this study : in this study : 1.1. a third-year radiology resident a third-year radiology resident 2.2. an attending staff musculoskeletal radiologis an attending staff musculoskeletal radiologis

tt 3.3. an attending staff orthopaedic surgeon an attending staff orthopaedic surgeon The observers were The observers were blindedblinded to both their to both their

previous evaluations and the evaluations previous evaluations and the evaluations of the other observers. of the other observers.

The percentage of femoral head involvement

first described in 1984 the abnormal signal on T1-weighted images visually estimated on the basis of serial coronal

and sagittal images according to the estimated percentage of the ar

ea 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

developed by Koo and Kim in 1995

The necrotic arc angles on the midcoronal and midsagittal images were designated A

and B, respectively.

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

The modified index of necrotic extent

TThe necrotic arc angle is measured on thhe necrotic arc angle is measured on the image that demonstrates the e image that demonstrates the maximal maximal lesionlesion sizesize in the sagittal (A) and coronal in the sagittal (A) and coronal (B) planes rather than on the midcorona(B) planes rather than on the midcoronal and midsagittal images.l and midsagittal images.

Result--- Result--- Reliability and Validity

The The interobserver agreementinterobserver agreement as defined by as defined by intraintraclass correlation coefficientsclass correlation coefficients The index of necrotic extentThe index of necrotic extent 0.58 (p < 0.001) for the first observation 0.58 (p < 0.001) for the first observation 0.70 (p < 0.001) for the second observation. 0.70 (p < 0.001) for the second observation. The modified index of necrotic extentThe modified index of necrotic extent 0.63 (p < 0.001) for the first observation0.63 (p < 0.001) for the first observation 0.81 (p < 0.001) for the second observation.0.81 (p < 0.001) for the second observation. The interobserver agreement of The interobserver agreement of the percent involvemthe percent involvem

entent, as defined by , as defined by Kendall coefficients of concordancKendall coefficients of concordancee,,

0.71 (p < 0.001) for the first observation 0.71 (p < 0.001) for the first observation 0.79 (p < 0.001) for the second observation.0.79 (p < 0.001) for the second observation.

Result--- Result--- Reliability and Validity

The The intraobserver agreement---nearly perfectintraobserver agreement---nearly perfect The index of necrotic extent The index of necrotic extent 0.91 (p < 0.005) for the first rater 0.91 (p < 0.005) for the first rater 0.83 (p < 0.005) for the second rater,0.83 (p < 0.005) for the second rater, 0.93 (p < 0.005) for the third rater. 0.93 (p < 0.005) for the third rater. The modified index of necrotic extent The modified index of necrotic extent 0.65 (p <0.005) for the first rater0.65 (p <0.005) for the first rater 0.88 (p < 0.005) for the second rater0.88 (p < 0.005) for the second rater 0.91 (p < 0.005) for the third rater.0.91 (p < 0.005) for the third rater. The percent involvementThe percent involvement 0.90 (p < 0.005) for the first rater0.90 (p < 0.005) for the first rater 0.89 (p < 0.005) for the second rater0.89 (p < 0.005) for the second rater 0.88 (p <0.88 (p <0.005) for the third rater0.005) for the third rater

Result--- Result--- Prognostic Ability (1)

the percent involvement was significantly related to (log rank = 5.81, p < 0.05) the time to subchondral collapse

Result--- Result--- Prognostic Ability (2)

index of necrotic extent (log rank = 7.17, p < 0.007)

The index of necrotic extent

(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 = = 113.8 degree12960

Result--- Result--- Prognostic Ability (3)

modified index of necrotic extent (log rank = 4.05, p < 0.04)

Critical AppraisalCritical Appraisal

Evidence level Evidence level ??

Reliability and ValidityReliability and Validity ReproducibilityReproducibility LimitationLimitation

Interobserver AgreementInterobserver Agreement EpidemiologistsEpidemiologists consider interobserver agree consider interobserver agree

ment of ment of 0.6 to 0.8 to be substantial0.6 to 0.8 to be substantial and and 0.8 to 1.0.8 to 1.0 to indicate nearly perfect agreement0 to indicate nearly perfect agreement . .

With the sample size used in this study (thirty-With the sample size used in this study (thirty-eight hips), a correlation coefficient of eight hips), a correlation coefficient of 0.440.44 co could be detected as significant at the p = 0.05 leuld be detected as significant at the p = 0.05 level with 80% power. vel with 80% power.

Kendall coefficients of concordanceKendall coefficients of concordance : for a noncontinuous categorical variable ( groups)

Reliability and Validity The The interobserver agreementinterobserver agreement as defined by as defined by intraintra

class correlation coefficientsclass correlation coefficients The index of necrotic extentThe index of necrotic extent 0.58 (p < 0.001) for the first observation 0.58 (p < 0.001) for the first observation 0.70 (p < 0.001) for the second observation. 0.70 (p < 0.001) for the second observation. The modified index of necrotic extentThe modified index of necrotic extent 0.63 (p < 0.001) for the first observation0.63 (p < 0.001) for the first observation 0.81 (p < 0.001) for the second observation.0.81 (p < 0.001) for the second observation. The interobserver agreement of The interobserver agreement of the percent involvemthe percent involvem

entent, as defined by , as defined by Kendall coefficients of concordancKendall coefficients of concordancee,,

0.71 (p < 0.001) for the first observation 0.71 (p < 0.001) for the first observation 0.79 (p < 0.001) for the second observation.0.79 (p < 0.001) for the second observation.

Reliability and Validity The The intraobserver agreement---nearly perfectintraobserver agreement---nearly perfect

The index of necrotic extent The index of necrotic extent 0.91 (p < 0.005) for the first rater 0.91 (p < 0.005) for the first rater 0.83 (p < 0.005) for the second rater,0.83 (p < 0.005) for the second rater, 0.93 (p < 0.005) for the third rater. 0.93 (p < 0.005) for the third rater. The modified index of necrotic extent The modified index of necrotic extent 0.65 (p <0.005) for the first rater0.65 (p <0.005) for the first rater 0.88 (p < 0.005) for the second rater0.88 (p < 0.005) for the second rater 0.91 (p < 0.005) for the third rater.0.91 (p < 0.005) for the third rater. The percent involvementThe percent involvement 0.90 (p < 0.005) for the first rater0.90 (p < 0.005) for the first rater 0.89 (p < 0.005) for the second rater0.89 (p < 0.005) for the second rater 0.88 (p <0.88 (p <0.005) for the third rater0.005) for the third rater

LimitationsLimitations

Only three observersOnly three observers Sample size (38 hips)Sample size (38 hips) Other variables ( surgical Other variables ( surgical

intervention, medication, weight intervention, medication, weight bearing status etc…)bearing status etc…)

Configuration of the lesions

Results There was significantly valid agreement among the obs

ervers for all three methods (p < 0.001 for all three).

The index of necrotic extent and the percent involvement → substantial agreement among raters

The modified index of necrotic extent → nearly perfect agreement Survivorship analysis revealed prognostically significa

nt 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

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.

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