ORIGINAL ARTICLE Multiplier Method for Prediction of Adult Height in Patients with Achondroplasia Dror Paley, MD, Alexander L. Matz, David B. Kurland, Bradley M. Lamm, DPM, and John E. Herzenberg, MD Abstract: To date, the only way to predict adult height in achon- droplastic dwarves has been to consult a growth chart. The purpose of this study was to ascertain whether the multiplier method of pre- dicting adult height at skeletal maturity in healthy persons can be applied to persons with achondroplasia. Previous studies have shown that the multiplier method can be applied to lower limb length, upper limb length, total height, foot length, and foot height. It is therefore reasonable to suggest that the growth pattern for total height in achondroplastic dwarves might also be characterized by a multiplier. Total height multipliers for achondroplastic dwarves (‘‘achondropla- sia height multipliers’’) were calculated from two separate databases by dividing height at maturity by height at each respective age for both genders. Little variability was found among multipliers for each age and among multipliers calculated from different databases. Upper torso (sitting height) multipliers and lower limb multipliers were also derived for achondroplastic dwarves. Lower limb and total height growth rates were slower in achondroplastic dwarves compared with healthy persons. However, sitting height multipliers for achondro- plastic dwarves were closely related to sitting height multipliers for healthy persons. Because these findings showed that the multiplier values were independent of population and percentile, the multiplier method may be a valid method for quickly predicting height at any age for achondroplastic dwarves. Key Words: achondroplasia, growth, height, height prediction, multiplier method (J Pediatr Orthop 2005;25:539–542) N ormal human growth patterns are commonly reported in the literature, whereas studies of abnormal human growth are rare: our literature search revealed only two studies evaluating achondroplastic growth. 1,2 Although achondropla- sia is the most common form of dwarfism, surprisingly little attention has been given to the growth patterns associated with this condition. Recently, the pattern of normal human growth has been characterized by the multiplier method, which determines the length or height at skeletal maturity by using an age- and gender-specific coefficient multiplied by the current length or height at that age. 3 Normal growth multipliers for each percentile are the same; therefore, short and tall people have the same multiplier for each age. Furthermore, multi- pliers have been found to be the same among different populations. 3 The multiplier method is a concise way to characterize growth patterns and predict lengths and heights of normal persons at maturity. Lower limb length, upper limb length, total height, foot length, and foot height have been char- acterized by the multiplier method. 3–5 Multipliers are different for each anatomic location, indicating that the growth pattern for each body segment is different. The purpose of this study was to derive total height multipliers for achondroplastic dwarves(‘‘achondroplasia height multipliers’’). We also com- pared achondroplastic growth patterns with normal growth patterns for total height, sitting height, and lower limb length. METHODS The most commonly used growth data for achondro- plastic dwarves were compiled by Horton et al 1 in a study of 403 participants (214 girls, 189 boys). This Horton database contains total height measurements for each age from birth to 18 years, presented as the mean, mean 6 1 SD, and mean 2 6 SD. We used the Horton database to calculate achondroplasia height multipliers for each percentile at each age by dividing height for boys and girls at skeletal maturity (H m ) by corresponding height at each year of age from birth to skeletal maturity (H). This converted every data point from the graphs presented by Horton et al to a multiplier (M) for height at skeletal maturity: M = H m /H (Tables 1 and 2). Conversely, current height can be multiplied by the age-specific multiplier to calculate height at skeletal maturity: HM = H m . The same method was used to calculate achondroplasia height multi- pliers based on a database presented by Nehme et al, 2 but the Nehme database lacked measures of variance and retained only average height. After the achondroplasia height multipliers were derived from both databases, they were compared and the variability was calculated by taking the absolute difference of the multiplier values. Achondroplasia height multipliers were then compared with total height multipliers for normal persons. In addition, we derived upper torso (sitting height) multipliers and lower limb multipliers from the Horton database by using the previously described method and compared them with From the Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, Baltimore, Maryland. Study conducted at Sinai Hospital of Baltimore, Baltimore, Maryland. None of the authors received financial support for this study. Reprints: Dr. Dror Paley, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, 2401 West Belvedere Avenue, Baltimore, MD 21215 (e-mail: dpaley@lifebridgehealth.org). Copyright Ó 2005 by Lippincott Williams & Wilkins J Pediatr Orthop  Volume 25, Number 4, July/August 2005 539