title: Achondroplasia: Really rhizomelic?
abstract: Achondroplasia is the most common form of short limb dwarfism in humans. The shortening of the limb lengths in achondroplasia is widely described as "rhizomelic." While this appearance may be convincing clinically, the description is not necessarily true or helpful radiologically. The aims of this study, were therefore, to determine whether rhizomelic shortening is a true feature of achondroplasia at diagnosis in infancy. Humeral, radial, femoral, and tibial diaphyseal lengths were recorded by two independent observers from 22 skeletal surveys of infants with achondroplasia and compared with 150 normal age-matched control subjects. Upper and lower limb bone length ratios (radial/humeral and tibial/femoral lengths, respectively) in both groups were compared using an unpaired t-test. Mean upper limb length ratios were statistically higher within the achondroplasia group at 0.87 ± 0.04 (n = 22, mean age 70 ± 94 days) compared to normal controls at 0.79 ± 0.02 (n = 150, mean age 113 days ± 88 days; P < 0.0001). Lower limb length ratios were not significantly different between groups (0.84 ± 0.04 vs. 0.83 ± 0.02, P = 0.46). There was good inter-observer agreement of limb length measurements, with an average measurement difference of 0.1 ± 1.4 mm. In conclusion, infants with achondroplasia demonstrate statistically significant rhizomelic shortening within the upper limbs, but not lower limbs at diagnosis, compared to normal controls. The term "rhizomelic shortening" in relation to achondroplasia should be reserved when describing upper limb proportions. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Diagnostic Imaging, The Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Susan Cheng
authors.initials: SC
authors.lastname: Shelmerdine
authors.affiliation: Department of Radiology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom.
authors.forename: Helen
authors.initials: H
authors.lastname: Brittain
authors.affiliation: Department of Radiology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom.|Institute of Child Health, University College London, London, United Kingdom.
authors.forename: Owen J
authors.initials: OJ
authors.lastname: Arthurs
authors.affiliation: Department of Radiology, Great Ormond Street Hospital for Children NHS Foundation Trust, London, United Kingdom.
authors.forename: Alistair D
authors.initials: AD
authors.lastname: Calder
mesh_terms: D000130:Achondroplasia / Q000175:diagnosis* / Q000235:genetics*; D001837:Body Weights and Measures; D001848:Bone Diseases, Developmental / Q000175:diagnosis*; D016022:Case-Control Studies; D005260:Female; D005269:Femur / Q000002:abnormalities*; D006579:Heterozygote; D006801:Humans; D006811:Humerus / Q000002:abnormalities*; D007223:Infant; D007231:Infant, Newborn; D035002:Lower Extremity / Q000473:pathology; D008297:Male; D009154:Mutation; D011859:Radiography; D051498:Receptor, Fibroblast Growth Factor, Type 3 / Q000235:genetics; D034941:Upper Extremity / Q000473:pathology
chemical_list: D051498:Receptor, Fibroblast Growth Factor, Type 3
keywords: achondroplasia; limb proportions; limb ratio; rhizomelic; skeletal dysplasia