The Nomenclature and Classification of Limb Anomalies

Ronan O'Rahilly, M.D.

This article originally appeared in Limb Malformations, ed. D. Bergsma, in Birth Defects Original Article Series, The National Foundation, New York, Vol. V, 3, 1969. It is reprinted with the permission of the author and publisher.

The history and principles of the classification of limb anomalies are outlined. The basic terminology was laid by Isidore Geoffroy Saint-Hilaire in 1837. The discovery of x-rays in 1895 rendered possible the precise delineation of the skeleton in vivo, so that an anatomic rather than a purely clinical classification became practicable. Consistency with the Nomina anatomica of 1955 is desirable and the author suggests that the time may be ripe for the establishment of an internationally acceptable Nomina teratologica.

Nomenclature and classification, both of which are important in teratology, are necessary for the precise reporting of malformations, the setting up of registries and the calculating of incidence.

The basis of a classification of deficiencies and duplications of the major long bones of the limbs was proposed more than a decade and a half ago10. The classification of the deficiencies was subsequently elaborated by providing numerous illustrated examples and suggesting a system of notation2. Further modifications and expansions have been undertaken by prosthetic experts and their consultants1. A study of the relevant publications is suggested, as it is not intended to propose a classification here but rather to exemplify the principles involved by discussing some of the complexities of selected anomalies.

The first comprehensive anatomic terminology was issued in 1895 in Basel and serves as the basis of our present nomenclature, which is known as the Nomina Anatomica and was issued in 1955 in Paris8. Among the principles adopted, the following are noteworthy: 1) that, with a very limited number of exceptions, each structure shall be designated by one term only; 2) that every term in the official list shall be in Latin, each country, however, to be at liberty to translate the official Latin terms into its own vernacular; 3) that the terms shall be primarily memory signs, but shall preferably have some informative or descriptive value and 4) that eponyms shall not be used.

Where teratologic descriptions or terms involve parts of the body, agreement with the Nomina Anatomica is naturally desirable. For example, the obsolete and pedantic term extremity in place of limb should be avoided. The terms arm and leg should be reserved for the appropriate subdivisions and not used for limbs as a whole. To refer to the carpal scaphoid or to the tarsal navicular suggests a lack of appreciation that the scaphoid is found only in the hand and the navicular only in the foot. To speak of the innominate bone is to appear unacquainted with the fact that the hip bone has long since been named. Again, to specify dorsal vertebrae implies a lack of understanding that all vertebrae are dorsal, although only a dozen of them are thoracic.

Much of the classification of congenital anomalies stems from the work of Isidore Geoffroy Saint-Hilaire in 1837. His classification of limb anomalies (Fig. 1 ) was as follows:


I. Ectroméliens Phocomèle
II. Syméliens Symèle


Despite the embryologic and anatomic interest of the syméliens, we are compelled to concentrate more on the ectroméliens because of their clinical importance. In the words of Geoffroy Saint-Hilaire4, the ectroméliens are characterized "by more or less complete malformation (avortement) of one or more limbs."

A. Phocomelia, which literally means "seal limb," is characterized by "hands or feet of usual size and commonly even completely normal, which, supported by excessively short limbs, usually appear to emerge directly from the shoulder or hips."4

It is relevant here to point out that most of the terms used for congenital limb anomalies were, as would be expected, based originally on clinical examination, that is, they were employed in a purely clinical sense, without special regard to the underlying anatomic configuration. Thus phocomelia was, and indeed still commonly is, used for "seal-like limbs" irrespective of the underlying anatomy. It is high time, however, to consider whether such imprecision should be allowed to continue.

The discovery of x-rays in 1895 gave a new dimension to the study of the skeleton in vivo and, within a decade, numerous skeletal abnormalities had been investigated by Röntgen's "new kind of rays." This made possible the determination of the exact skeletal arrangement in the living, and hence it became possible to classify limb anomalies with much greater precision and in far greater detail. Perhaps, indeed, the skeleton may have been overemphasized from the point of view of teratogenesis, but, in the practical order of diagnostic and orthopedic requirements, the osseous system inevitably occupies a commanding role.

Although the delineation of limb anomalies may be based, at least in some instances, on clinical, functional, teratogenic, embryologic or genetic criteria, the only satisfactory criterion of classification at the present time is the anatomic. In relatively few cases can an external causal agent such as thalidomide be pinpointed, and such disputed causal terms as amputation (which could at best apply to only a small minority) should be rigorously avoided. Moreover, even where a causal agent is known, etiologic classification supplements but does not replace the anatomic. Spina bifida has to be subdivided anatomically even where a given case may be attributable to a specified teratogen. Similarly, a genetic basis can be implicated in only some cases of anomalies and, in those, the genetic data supplement but do not replace the anatomic. Once an anatomic classification becomes established, however, the additional information can be superimposed. Thus, Temtamy11 has recently proposed that, for each anatomic category, a distinction be made according to whether the anomaly is isolated, i.e., confined to the limbs, or occurs as a part of a syndrome with other systems or regions involved. This has enabled Temtamy to provide a very detailed and valuable classification of hand anomalies that are found as a part of syndromes.

B. In hemimelia, which literally means "half limb," "the forearm or the leg, but particularly the hand or the foot ... is lacking ... or is represented by only some rudimentary parts." Thus the limb has "the form of a more or less short stump, either deprived of all sign of hand or foot, or, more commonly, ending in one or more imperfect and rudimentary digits."4

It should be recalled that the main parts of a limb are four in number: 1) the zonoskeleton (scapula and clavicle; hip bone); 2) the stylopodium (humerus; femur); 3) the zygopodium (radius and ulna; tibia and fibula); and 4) the auto-podium (hand; foot). It is the last two parts that are defective in typical hemimelia.

In the course of time, the German authors came to prefer the term peromelia to hemimelia. The term means literally merely a "malformed limb" but, in German clinical usage, it refers chiefly to a malformation "the main feature of which is a stump-like formation (Stummelbildung),"12 "a transverse or conical tapering stump (Stumpf)."6 However, the term peromelia is also extended to include even isolated absence of digits (adactylia). In other words, the term peromelia is purely clinical and has no sound anatomic basis.

Although typically hemimelia involves the presence of approximately only half a limb, in some instances only a longitudinal portion of the zygopodium and autopodium is deficient. Such clumsy designations as "congenital absence of the radius," however, do not serve the needs of present-day terminology and classification. To add to the confusion, the condition is sometimes regarded as a form of ectromelia6, or even of phocomelia.

The deficient portion may be on either the preaxial or the postaxial side of the limb and hence such a condition may be termed a paraxial hemimelia10. It has become established practice to label such cases on the basis of the missing portion. Hence, a limb in which only the radial side of the two distal segments is affected is known as radial hemimelia, by which is meant that the radial portion of the affected (distal) half of the limb is deficient. It is somewhat surprising to find that authors who seem to have no particular problems with other classically named conditions, such as mitral stenosis, seem so easily shocked by the idea that radial hemimelia should be given a Greek designation.

The imprecision of clinically based terms in limb anomalies has become very apparent in the case of malformations ascribed to thalidomide, where such conditions as radial hemimelia are sometimes labeled "phocomelia" (e.g., by Ingalls and Klingberg5). Radial defects and phocomelia may, of course, occur together in the same individual. Moreover, where inherited, these conditions may be found in various transitional grades among individuals of one pedigree11. Nevertheless, an anatomic distinction seems to be justified. If, on the other hand, phocomelia be included under radial defects11, it is difficult to see where a phocomelic but pentadactyl hand could be placed. As mentioned earlier, an anatomic reassessment of phocomelia seems to be overdue2.

The situation becomes more complicated when those cases are considered in which, although the radial portion of the affected half of the limb is involved, distal parts are more or less normal even on the radial side. For example, involvement may be confined to the styloid process of the radius, the adjacent carpals, and the first metacarpal, whereas the phalanges of the thumb may be present even if reduced9. Such conditions are called intercalary, meaning that a deficiency is interposed between more or less normal parts (phocomelia is the classical instance of an intercalary condition). The above case is an example of intercalary radial hemimelia7. On the other hand, were the features of the above case to include total absence of the thumb (as in a mother and daughter described by Fritzsche3), the condition would be an example of a terminal deficiency.

In terminal deficiencies, all distal elements of a bony column are absent, whereas, in intercalary deficiencies, only middle parts are absent from a proximodistal column (Fig. 2 ). Most limb deficiencies may be classified into one of the four following groups: 1) terminal transverse (e.g., amelia, hemimelia, acheiropodia, adactylia); 2) terminal longitudinal (e.g., radial hemimelia); 3) intercalary transverse (e.g., phocomelia) and 4) intercalary longitudinal (e.g., intercalary radial hemimelia).

C. Ectromelia, which literally means "aborted limb," is "characterized by the complete or almost complete absence of one or more limbs." It includes three chief types, "the limb being found ending in one or several imperfect digits, or presenting the form of a stump without a trace of digits, or, finally, lacking completely."4 The term ectromelia, however, is vague and largely, if not entirely, unnecessary. Many or most instances included come under the designation amelia, by which is meant absence of a free limb. In order to avoid the conflicting uses of such terms as ectromelia and peromelia, a new term, meromelia, was recently introduced to cover all deficiencies other than amelia1.

In conclusion, it may be suggested that the time has come to seek international agreement for the establishment of a Nomina teratologica. The procedures should follow those already used to considerable advantage in fields ranging from anatomy to cytogenetics. As a beginning, meetings might profitably be undertaken to establish an internationally acceptable classification of limb anomalies.

The Committee on Prosthetics Research and Development and its Subcommittee on Child Prosthetics Problems have for many years been interested in the establishment of an internationally acceptable system for the classification of congenital limb anomalies. Dr. O'Rahilly's penetrating discussion of the subject, which is reprinted here, concludes with the suggestion that the time has come to seek international agreement on a Nomina teratologica. We submit that the time is past due and urge that, under suitable auspices, the protagonists of different systems on both sides of the Atlantic be brought together to settle their differences and to apply their talents to the production of a mutually acceptable nomenclature.


Department of Anatomy, St. Louis University School of Medicine, St. Louis, Missouri

1. Burtch, R. L. (ed.), Classification Nomenclature for Congenital Skeletal Limb Deficiencies. Prosthetic and Orthotic Studies, New York University Post-Graduate Medical School, New York, 1965. 
2. Frantz, C. H., and R. O'Rahilly, Congenital skeletal limb deficiencies. J. Bone and Joint Surg., 43A: 1202-1224, 1961. 
3. Fritzsche, H., Kausalitätsbeurteilung einer Lunatummalazie bei Daumenaplasie, eine seltene Beobachtung einer symmetrischen Tetradaktylie bei Mutter und Tochter. Z. Unfallmed. Berufskr., 55:84-89, 1962. 
4. Geoffroy Saint-Hilaire, I., Histoire Générale et Particulière des Anomalies de l'Organisation chez l'Homme et les Animaux ... ou Traité de Tératologie. Société Belge de Librairie, Vol. 2. Brussels, 1838. 
5. Ingalls, T. H., and M. A. Klingberg, Implications of epidemic embryopathy for public health. Amer. J. Publ. Hlth., 55:200-208, 1965. 
6. Jentschura, G., E. Marquardt, and E.-M. Rudel, Behandlung und Versorgung bei Fehlbildungen und Amputationen der oberen Extremität. Thieme, Stuttgart, 1963. 
7. Klippel, M., and E. Rabaud, Sur une forme rare d'hemimelie radiale intercalaire. Nouv. Iconogr. Salpet., 16:238-251, 1903. 
8. Nomina Anatomica, third edition. Excerpta Medica Foundation, Amsterdam, 1966. 
9. O'Rahilly, R., Radial hemimelia and the functional anatomy of the carpus. J. Anat. (London), 80:179-183, 1946. 
10. O'Rahilly, R., Morphological patterns in limb deficiencies and duplications. Amer. J. Anat., 89:135-193, 1951. 
11. Temtamy, S., Genetic Factors in Hand Malformations. Ph.D. dissertation, Johns Hopkins University, Baltimore, 1966. 
12. Werthemann, A., Die Entwicklungsstorungen der Extremitäten. Springer, Berlin, 1952.