Bone of contention: The applicability of the Greulich-Pyle method for skeletal age assessment in South Africa

Background: The Greulich-Pyle (GP) method is one of the most commonly used radiographic techniques for skeletal age (SA) determination. The applicability of this method for populations outside of the United States has been questioned and this has been investigated in several recent studies around the world. Only limited data are available on the accuracy of the GP method for a South African population. Objective: To determine the accuracy and reliability of the GP method in a population from KwaZulu-Natal, South Africa. Method: A retrospective study was performed using a digital database consisting of 102 hand-wrist radiographs. The SA was estimated by two readers with different levels of experience, using the GP method. Differences between estimated SA and chronological age (CA) were analysed. Results: Skeletal age determined with the CP method was found to significantly differ from CA. For the population as a whole, the GP method underestimated age. The greatest mean underestimation between SA and CA was 11.5 +/- 17 months and 7.4 +/- 13.2 months for the 10.1 to 15 year age groups in male and female patients, respectively. The method was found to have excellent inter- and intra-observer reliability. Conclusion: The GP method generally significantly underestimates age for both genders. Overestimation is also possible with individuals as young as 16 years old found by the method to be skeletally mature. Until new SA assessment tools are developed for South Africa, use of supplementary means of determination of SA should be considered, especially in medico-legal cases.