The applicability of the Greulich & Pyle Atlas for bone age assessment in primary school-going children of Karachi, Pakistan.

OBJECTIVE
To assess the degree of applicability of bone age calculated by Greulich & Pyle Atlas in estimation of chronological age for therapeutic and medico legal purposes.


METHODS
Two Hundred and Twenty children (139 males, 81 females) between ages of 56 and 113 months (4.5 to 9.5 years) were randomly selected from 4 primary schools of Shireen Jinnah & Clifton, Karachi. Digital images of hand and wrist radiographs were obtained by a computed radiography at Ziauddin Hospital Clifton. Bone ages were computed using Greulich & Pyle Atlas by radiologists at Ziauddin Hospital, North Nazimabad, Karachi.


RESULTS
On average, the Greulich & Pyle Atlas underestimates chronological age by 6.65 ± 13.47 months in females and 15.78 ± 12.83 months in males (p-values < 0.001). High correlation was found between chronological age and bone age in both genders (Females r=0.778; p-value< 0.001, Males r=0.816; p-value < 0.001).


CONCLUSION
Bone age calculated by Greulich & Pyle Atlas should not be used for estimating chronological age in children of ages 56-113 months in situations where high accuracy is required (e.g. medicolegal cases). However, serial measurements of bone age by this atlas can be used in management of growth related endocrine disorders in these children.

developed by Dr. Wiliam Walter Greulich and Dr. Sarah Idell Pyle in 1959 6 using data collected from the "Brush foundation study of human growth and development" headed by Professor Wingate Todd 7 on Caucasian children of the upper socioeconomic class living in United states of America.The atlas comprises of reference radiographic images of left wrist and hand from birth till 19 years of age for males and 18 years of age for females.It is based on the fact that ossification centers in the hand and wrist bones appear in a sequential and fixed order.Bone age is calculated by comparing the degree of ossification in various hand and wrist bones with the nearest matching plate on the Greulich & Pyle Atlas separately for male and female children.
Due to the fixed ethnic and socioeconomic class of children selected for generation of this atlas, its applicability varies in different parts of the world.It is considered to compute a bone age which is comparable to chronological age in children from developed countries of West 8 and Middle east 9 but great difference exists between the two in children from developing countries such as Iran 10 and India. 11A couple of studies have been conducted to assess the reliability of Greulich & Pyle Atlas in Pakistani children.One of them has a retrospective study design which could result in recall bias, 12 the other has limited the cohort to older children of ages 8-18 years. 13Thus bringing about the need to assess the usability of this method in younger Pakistani children with a relatively accurate date of birth acquired from a valid source of data.

METHODS
School children between the ages 54 to 113 months (4.5 to 9.5 years) were randomly selected for the study from 4 different schools in the Clifton and Shireen Jinnah Colony Regions of Karachi.After approval from the school administration, camps were setup at school where parents and children were recruited.Consent forms were signed by parents, subsequently assent forms were signed by children and they were given an appointment at Ziauddin Hospital Clifton.At the hospital their height and weight were noted.Children with a major childhood illness lasting more than 3 months or height above 95 th percentile for age or height below 5 th percentile for age were excluded from the study.Information regarding the date of birth of the included subjects was obtained from school records.A total of 244 subjects underwent radiography of the left wrist and hand (Posterior Anterior view) using a SHIMADZU radiographic system.Exposure was obtained on an AGFA cassette and digitalized by AGFA 30-X CR Reader.220digital images of radiographs were selected and 24 were rejected due to inadequate exposure.Bone age was

RESULTS
The mean difference between chronological age and bone age was less in females as compared to males (6.65 & 15.75 months respectively; p-values < 0.001).However, a strong significant positive correlation (r= 0.788 & 0.816 respectively; p-values, 0.001) was noted between chronological age and bone age in both the genders (Table-I).
Bland Altman Plot of females shows a mean difference of +6.65 months between chronological age and bone age.95% of the points lie between -19.75 months and +33.05 months.3.7% points lie beyond ± 2 SD lines.(Fig.1).
Bland Altman Plot of males shows a mean difference of +15.78 months between chronological age and bone age.95% of the points lie between -9.37 months and +40.93 months.7.2% points lie beyond ± 2 SD lines.(Fig.2).
A mean difference of less than 6 months is noted between the chronological age and bone age of females aged 54-65 months, 78-89 months and 102-113 months.However, mean differences of more than 8 months are noted in females aged 66-77 months and 90-101 months.

(Table-II).
A mean difference of more than 13 months is observed between chronological age and bone age in all male age groups (minimum mean difference 13.9 months and maximum mean difference 18.9 months).(Table-II).

DISCUSSION
Our study indicates that there is a great variation in the chronological age and bone age calculated by the Greulich & Pyle Atlas.The degree of disparity between the two ages is less in females, with mean differences ranging from 4.4 to 8.9 months (Table-II) whereas it is markedly higher in males ranging from 13.2 to 18.9 months (Table-II).Various international studies have reported different results regarding the applicability of the Greulich & Pyle Atlas for estimation of chronological age.In Australia, bone ages of males are on average advanced by 0.4 years, whereas bone ages of females on average are skeletally delayed by 0.3 years when using this atlas. 14Another study found significant difference in chronological and bone ages in Israeli boys. 9However, statistically significant difference between the means and standard deviations of up to one year have been reported between chronological age and bone age of Turkish chidren. 15here is a paucity of literature from Pakistan regarding bone age assessment in children.However, our results are consistent with Shaikh et al 13 who performed a similar study on children aged 8-18 years at Chandka Medical College, Larkana, and reported a mean differences of ages in females and males as 0.5 and one years respectively.Zafar et al 12 who compared bone and chronological ages at the Agha Khan University Hospital, Karachi also found that the mean differences between the ages was less in females as compared to males in children of middle and late childhood.
The scatterplot graphs show that difference between chronological age and bone age by Greulich and Pyle method in 95% of females range from -19.75 months to +33.05 months(Fig.1)and in 95% of males range from -9.37 months to +40.93 months(Fig.2).This extreme discrepancy makes the Greulich & Pyle Atlas invalid for forensic application of bone age in the estimation of chronological age in Pakistani children.
However there is a high correlation between the two ages in both genders (Table -

AKNOWLEDGEMENTS
We would like to acknowledge the contributions of Ms. Nida, Biostatistician at Ziauddin University, Karachi, in statistical analysis of this study and Bilal Matin, 4th year medical student at Ziauddin University, in sample collection of this study.We are extremely thankful to the administration of the collaborating schools, as well as the children who acted as subjects in the study and their parents.
Source of funding: Ziauddin University.

Table -
II: Differences between chronological age (CA) and bone age by Greulich & Pyle Atlas (GP) in different age quartiles.*indicate significant at p<0.05.

Table - I
: Differences and relationship between chronological age (CA) and bone age by Greulich & Pyle Atlas (GP) in different genders.*indicate significant at p<0.05.
The mean difference between chronological age and bone age calculated by Greulich & Pyle Atlas is greater in boys compared to girls.This significant difference between the two ages limits use of Greulich & Pyle Atlas in estimating chronological age for medico legal purposes.However, a high correlation between chronological and bone age by Greulich & Pyle Atlas makes it suitable for followup use in growth disorder patients.