Validity and Reliability of measuring femoral anteversion and neck-shaft angle in patients

with cerebral palsy

Seoul National University Bundang HospitalSeoul National University Children’s Hospital *

Introduction

Increased femoral anteversion and coxa valga

are common deformities associated with intoe-

ing gait and unstable hips in CP, which need

surgical correction

Physical examination and neck shaft angle mea-

sured on hip radiographs are primary tools eval-

uating femoral anteversion and coxa valga

Introduction

Physical examinations measuring femoral antev-

ersion include Trochanteric prominence angle test (TPAT)

Hip internal rotation (IR)

Hip external rotation (ER)

CT measurement is accurate, but expensive and

involves radiation exposure

Purpose of Study

To assess the validity and reliability of physi-cal examinations measuring femoral antever-sion and neck shaft angle measured on hip AP radiographs Concurrent validity Intra- and interobserver reliability

Materials and methods Prospective study approved by IRB 36 consecutive patients with CP scheduled for

SEMLS Mean age 11.0 years (SD 1.3) M : F = 26 : 10 6 hemiplegia, 25 diplegia, and 5 quadriplegia GMFCS I / II / III / IV / V 5 / 11 / 11 / 7 / 2

Exclusion Previous Op, trauma, infection, etc.

TPAT

Hip IR

Hip ER

NSA on X ray

Femoral AV on CT

Standard method for concurrent validity of P/E

NSA on CT

Standard method for concurrent validity of NSA on X-ray

Validity

Physical exam measuring femoral AV Correlation with femoral anteversion measured on

2D CT

NSA measured on X ray Correlation with NSA measured on 3D MPR CT im-

age

Reliability Interobserver reliability of physical exam using

three orthopaedic surgeons on a single day

Intra- and interobserver reliability of NSA on X- ray Repeated measurements with an interval of 3 wks

Statistics Validity

Pearson’s correlation coefficients Reliability

Intraclass correlation coefficients (ICCs) 2 way random effects, single measurement & absolute

agreement Multiple regression test

To predict the accurate femoral anteversion (CT) from physical exam

Results

Summary of Measurements

Examiation Mean (deg) SD (deg) Range (deg)

TPAT 40 17 -20 to 70

Hip IR 60 17 10 to 85

Hip ER 38 14 10 to 70

Femoral AT on CT 36 18 -26 to 73

NSA on X ray 142 10 119 to 169

NSA on CT 139 8 118 to 162

Concurrent Validity of Physical exam and NSA on X ray

Examinations R value p-value

TPAT 0.862 <0.001

Hip IR 0.787 <0.001

Hip ER -0.480 <0.001

NSA on X ray 0.892 <0.001

Interobserver Reliability of Physical exam

Examination ICCs 95% CI

TPAT 0.809 0.695 to 0.890

Hip IR 0.889 0.817 to 0.937

Hip ER 0.530 0.338 to 0.702

Intra- and interobserver reliability of NSA on X ray

Reliability ICCs 95% CI

Intraobserver

1st examiner 0.973 0.947 to 0.986

2nd examiner 0.946 0.878 to 0.974

3rd examiner 0.929 0.694 to 0.974

Interobserver

1st session 0.937 0.825 to 0.973

2nd session 0.869 0.541 to 0.951

Overall 0.912 0.806 to 0.958

Femoval AV on CT= 0.92 x TPAT - 3.2 (R2=0.829)

Conclusions TPAT and NSA on X ray showed clinically rel-

evant validity and reliability compared with CT measurement

CT examination evaluating proximal femoral geometry could be replaced by physical exami-nation and X ray in patients with CP, avoiding unnecessary radiation exposure

This study has been published in JBJS-Am.

Thank you !