Ki Hyuk Sung, MD

Department of Orthopaedic SurgerySeoul National University Bundang Hospital

Rate of correction after asymmetrical physeal suppression in valgus deformity:

Analysis using a Linear mixed model application

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Introduction

• Coronal angular deformity of the lower limb is a

common finding in growing children

• Permanent (irreversible) hemiepiphysiodesis

• Temporary (reversible) hemiepiphysiodesis using

staples, percutaneous screws, or a tension band

plate (eight-plate)

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Introduction

• Measuring the rate of correction is necessary to predict

the time to end point

• The rate of angular correction has been calculated

simply by averaging.

• Other factors (age, surgical method, direction of

deformity, etiology, physis) must be considered while

estimating the rate of correction

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Introduction

• A linear mixed model (LMM) is useful in settings where

multiple correlated measurements are made on the

same statistical units

• LMM consists of fixed effects and random effects

• Estimation of the correction rate by using a mixed model

application may confer more practical information to

clinicians

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Purpose

• To estimate the rate of angular correction

after asymmetrical physeal suppression

• To analyze the factors that influence the rate

of correction by using a linear mixed model

application

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Material and methods

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Inclusion criteria

• Patients with valgus angular deformity of the

lower limb who underwent asymmetrical physeal

suppression

• A minimum follow-up of 3 months

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Exclusion criteria

• Patients who visited our hospital less than two

times

• Patients who had inadequate preoperative or

postoperative radiographs available for review

• Patients who underwent any other bony

procedures such as an osteotomy

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Radiographic measurements

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Building a linear mixed model

• Three groups

• Distal femoral, proximal tibial, and distal tibial

• The rate of angular correction was adjusted by

multiple factors by using LMM

• Age, gender, and surgical method as the fixed effects

• Each subject as the random effect

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Individual pattern of correction rate

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Building a linear mixed model

• The estimates were fitted using the restricted

maximum likelihood estimation (REML) method

• The final model

• Age and surgical method specific rate

• Sex and surgical method specific intercept

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Statistical Methods

• Univariate analysis

• LMM was used to model the correction rates and assess

covariate effects.

• Multivariate analysis

• For the final model to examine the significantly

contributing factor to the rate of valgus deformity

correction

• R (Version 2.13.1) using nlme package

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Results

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Patients’Demographics

Physis treated Distal femurProximal

tibiaDistaltibia

Total

No. of physes 72 70 33 175

No. of measurements 276 305 128 709

Gender (Male/ Female) 43/29 38/32 26/7 107/68

Limb (Left/ Right) 35/37 36/34 15/18 86/89

Age at surgery(years, mean±SD) 12.0±2.3 11.7±3.1 11.6±2.6 11.8±2.7

Surgical method

Staple/Screw/Permanent 24/44/4 20/47/3 0/28/5 44/119/12

Anatomical angle at initial(°, mean±SD) 76.1±4.5 85.0±5.0 77.9±5.1 80.0±6.3

Anatomical angel at final(°, mean±SD) 83.4±5.4 90.2±6.5 87.3±8.2 86.9±7.1

Mean amount of correction(°, mean±SD) 7.3±6.0 5.2±4.8 9.4±7.4 6.8±6.0

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Univariate analysis of the correction rate for distal femur

Factor CodingRate of

correction (°/month)

95% Confidence

intervalp-value

Sex Male (referent) 0.55 0.41 to 0.68 <0.001*

Female 0.75 0.54 to 0.97 0.062

Method Staple (referent) 0.64 0.46 to 0.82 <0.001*

Screw 0.64 0.42 to 0.87 0.968

Permanent 0.25 -0.24 to 0.74 0.124

Age F<12/M<14 (referent) 0.71 0.59 to 0.84 <0.001*

F≥12/M≥14 0.39 0.17 to 0.61 0.006*

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Univariate analysis of the correction rate for proximal tibia

Factor CodingRate of

correction (°/month)

95% Confidence

intervalp-value

Sex Male (referent) 0.36 0.25 to 0.47 <0.001*

Female 0.37 0.20 to 0.53 0.941

Method Staple (referent) 0.26 0.11 to 0.41 0.001*

Screw 0.42 0.24 to 0.60 0.085

Permanent 0.28 -0.12 to 0.69 0.909

Age F<12/M<14 (referent) 0.40 0.30 to 0.51 <0.001*

F≥12/M≥14 0.29 0.12 to 0.46 0.205

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Univariate analysis of the correction rate for distal tibia

Factor CodingRate of

correction (°/month)

95% Confidence

intervalp-value

Sex Male (referent) 0.52 0.39 to 0.64 <0.001*

Female 0.39 0.15 to 0.62 0.270

Method Screw (referent) 0.43 0.32 to 0.55 <0.001*

Permanent 0.63 0.39 to 0.86 0.101

Age F<12/M<14 (referent) 0.48 0.36 to 0.60 <0.001*

F≥12/M≥14 0.48 0.18 to 0.76 0.947

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Multivariate analysis of the correction rate for distal femur

Factor CodingRate of

correction (°/month)

95% Confidence

intervalp-value

Baseline Staple, F<12/M<14 0.79 0.60 to 0.97 <0.001*

Age F≥12/M≥14 0.51 0.27 to 0.75 0.025*

Method Screw 0.66 0.43 to 0.83 0.241

Permanent 0.58 0.06 to 1.11 0.441

* The difference in the rate of correction between the younger children and the older children is significant.

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Multivariate analysis of the correction rate for proximal tibia

Factor CodingRate of

correction (°/month)

95% Confidence

intervalp-value

Baseline Staple, F<12/M<14 0.29 0.14 to 0.44 <0.001*

Age F≥12/M≥14 0.14 -0.04 to 0.32 0.098

Method Screw 0.48 0.29 to 0.67 0.046*

Permanent 0.38 -0.03 to 0.79 0.660

* The difference in the rate of correction between the younger children and the older children is significant.

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Multivariate analysis of the correction rate for distal tibia

Factor CodingRate of

correction (°/month)

95% Confidence

intervalp-value

Baseline Staple, F<12/M<14 0.44 0.33 to 0.55 <0.001*

Age F≥12/M≥14 0.35 0.07 to 0.64 0.552

Method Permanent 0.68 0.44 to 0.92 0.057

* The difference in the rate of correction according to the age and the method is not significant.

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Conclusion

• Asymmetrical physeal suppression with staples,

percutaneous transphyseal screws, and permanent

method all are effective methods for treating

valgus deformity in growing children.

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Conclusion

• When we treat valgus deformity in growing

children, we should take into consideration the fact

that the rate of correction at the distal femur is

lower in older children.

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