Congenital Differences of the Upper Extremity: Classification and Treatment Principles

Various classification systems are divided according to their basis of foundation; descriptive, anatomic or topographical, embryologic, teratologic sequencing, genetic, and different combinations of these.

Descriptive classification is based on findings of deformity, such as radial clubhand, which describes a radially deviated hand looking like a golf club, or camptodactyly, meaning a flexed finger. Although this system is intuitive and commonly used as a diagnosis in clinical practices, it depends on the confusing Greek and Latin terminology and has little scientific value.

A more developed system is the anatomic or topographical classification based on anatomic findings or the extent of involvement. Syndactyly is a kind of descriptive classification for a finger deformity, but complete, incomplete, simple or complex syndactyly is an anatomic classification and indicates the extent of involvement. This can guide treatment recommendations and sometimes prognosis. Similarly, most sub-classifications for various diagnostic conditions are based on anatomy, such as the Wassel classification for thumb polydactyly which is based on the level of thumb bifurcation.8) Frantz and O'Rahilly9, 10) further developed the anatomic or topographic classification and expanded the concept of intercalary deficiencies. They divided limb deficiencies into terminal and intercalary, and each into transverse and paraxial.

The anatomic classification system was further developed into embryologic classification by Swanson et al.11) in 1964, which was based on the concept that anomalies should be grouped according to the part that were affected during development. In the Swanson classification, each limb malformation is classified according to the most predominant anomaly and is placed into one of seven categories (Table 1). This system was accepted by the American Society for Surgery of the Hand (ASSH), the IFSSH, and the International Society for Prosthetics and Orthotics (ISPO), and is now termed as the IFSSH classification.6)

Table 1
The Classification System Developed by the International Federation of Societies for Surgery of the Hand6, 7)

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Recently, the Japanese Society for Surgery of the Hand (JSSH) suggested a modification of the IFSSH system, adding two groups; "Abnormal induction of rays" and "Unclassifiable cases."12) The category of "Abnormal induction of rays" includes syndactyly, the central polydactyly-cleft hand-osseous syndactyly complex, and triphalangeal thumb. This concept was based on recent embryologic studies supporting a common etiology for central polyactyly, syndactyly, and typical cleft hand.13) Although this makes sense from an embryologic standpoint, the new category separates central polydactyly from radial and ulnar polydactyly that are classified as "Duplication," resulting in the separation of morphologically similar congenital differences and creating a major contradiction to accept intuitively.5, 14) Tonkin14) points out that the difference between abnormal formation and abnormal induction appears to be one of semantics.

Congenital differences can be classified according to their severity of expression, which is called teratologic sequence classification. Although this classification is not comprehensive of all anomalies, this system is often used for classification for specific conditions, as the extent of pathology can determine function and guide treatment. For example, teratologic sequencing of thumb hypoplasia as used in Blauth and Manske's 5 category system classifies thumb hypoplasia according to the severity of hypoplasia and is helpful for directing the treatment (Table 2).15, 16)

Table 2
Classification of the Hypoplastic Thumb15, 16)

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Finally, there can be a classification system based on particular genetic or molecular abnormalities. For instance, defects in the HOXD13 have been implicated in several common congenital hand differences such as syndactyly and polydactyly.17) However, this type of classification may be cumbersome as the genetics are extremely complex and involve multiple steps and interactions between many genes and proteins, in addition to the interaction with environmental factors.5) Progress in understanding of these complex genetic and molecular interactions may contribute to a better classification scheme and guide potential genetic treatment options.

At present, the most widely accepted classification is the IFSSH classification. However, it has been criticized for its inherent limitations because it attempts to incorporate etiology into morphologically-based classificiation,4, 14) and is difficult to classify complex cases, especially with the complex spectrum of cleft hand and symbrachydactyly.18)

The IFSSH classification system separates "Failure of formation" from "Failure of differentiation" on the basis of timing of the causative insult, but creates separate groups for "Duplication," "Overgrowth," and "Undergrowth," although duplication is a kind of failure of formation and "Overgrowth" and "Undergrowth" are examples of differentiation or development failure (failure of differentiation).14)

In addition, the "cleft hand" is difficult to explain by the IFSSH system. Cleft hand can be divided into typical and atypical. A typical cleft hand (central deficiency) is not associated with forearm anomalies unlike radial or ulnar deficiencies, and is usually bilateral, familiar, and associated with polydactyly, syndactyly and clefting of the feet, while atypical cleft hand or symbrachydactyly is usually unilateral, not hereditary, and not associated with foot anomalies, suggesting different etiologies for similar conditions. In the original Swanson/IFSSH classification, typical cleft hand was classified under "Failure of formation" and symbrachydactyly was classified as "Undergrowth," suggesting that Swanson initially considered the etiologies of the two conditions as different. However, in the current modification of the IFSSH classification, symbrachydactyly is brought back to "Failure of formation" category,19, 20) highlighting the fact that the IFSSH classification is truly morphological and not etiologically based.5) Concerning the typical cleft hand, which is usually associated with central polydactyly and syndactyly, the JSSH modification tried to overcome the problem by introducing another category of "Abnormal induction of rays," but also has its own contradictions as we noted before.

I suggest a new classification for congenital differences of the upper extremity, which is modified after the current IFSSH classification system (Table 3). This classification is also an embryologic classification, and is based on the concept that an organ develops and matures through three distinct stages, which are formation, separation, and growth, and each stage can have two types of control failure, which are early control failure (resulting in under-formation, under-separation, or under-growth) and late control failure (resulting in over-formation, over-separation, or over-growth). These 6 control failures have three morphological types, which are longitudinal, transverse, and mixed. By having these morphological types for each control failure category, my classification system makes it easy to intuitively classify complex deformities.

Table 3
The Author's Classification of Congenital Differences of the Upper Extremity

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Concerning the "Generalized skeletal abnormalities" in the IFSSH system, my system classifies the conditions as "Structural failure" as opposed to "Control failure," because those anomalies have abnormal tissue from structural or cellular failures while conditions of "Control failure" have normal tissue quality. Therefore, congenital differences of the upper extremity can be first divided into "Control failure" (with normal tissue) and "Structural failure" (with abnormal tissue), and then the "Control failure" can be further classified into "Formation failure," "Separation failure," and "Growth failure," and the "Structural failure" into "Generalized structural failure" and "Localized structural failure."

The most significant difference of my classification from the IFSSH system is that it divides the concept of "Differentiation" of the IFSSH system into "Separation" and "Growth." This system has three large categories under "Control failure" and can avoid placing separate categories of "Overgrowth" and "Undergrowth" (embryologically failure of differentiation) at the same level of hierarchy. Furthermore, by placing "over-formation" and "under-formation" under the large category of "Formation failure," this system removes the redundant category of "Duplication," which is also embryologically a kind of formation failure. In addition, this classification system removes constriction band syndrome from the 7 categories of the IFSSH system and places it under the category of "Formation failure" ("transverse type under-formation"), because the main pathology of distal tissue agenesis or coalescence is a vascular compromise at some point of intra-uterine organ formation.

The advantage of my classification is that physicians can intuitively classify most of the congenital anomalies because the 3 stages (formation, separation, growth), the 3 types (longitudinal, transverse, and mixed) and the 2 prefixes (under-, over-) are anatomically or morphologically straightforward, although the system is based on embryology. For example, the complex symbrachydactyly, which has mixed longitudinal and transverse deficiency by the anatomical classification, and can be simply classified into "Mixed type under-formation" by my classification system, successfully including both anatomical and embryological concepts. In my experience, most of the congenital differences could be categorized reliably with some reasonable explanations.

In addition, my classification system can categorize some disease entities, which have not been included in any classification schemes previously, such as congenital laxity of joint, which is not included in the IFSSH system, can be classified as "Transverse type over-separation." Also, delta bone is not classified into any category in the IFSSH system, but it can be classified as "Longitudinal type under-separation," because the anomalous orientation of the growth plate causing coronal deviation is thought to be caused by incomplete separation of the epiphysis from the primary ossification center.

Lastly, my classification system can logically and intuitively guide the treatment principle for each category, such as "Under-formation" needs lengthening (or transplantation), and "Over-formation" needs resection (or amputation); "Under-separation" requires separation (or division), and "Over-separation" requires reduction (or arthroplasty or fusion); "Under-growth" needs augmentation and "Over-growth" needs resection (or debulking).

Treatment of upper extremity congenital differences should be initiated as soon as possible, because most anomalies tend to change with time and the human body is considered to maintain skeletal remodeling power until two to three years of age.

I have reviewed the current classification systems for congenital differences of the upper extremity, discussed the contradictions and limitations of the IFSSH classification, and presented a modified classification system. In addition, I provided treatment principles according to the suggested classification system. As our understanding of the etiology of congenital differences of the upper extremity increase and as experience of treating difficult cases accumulates, even an ideal classification system and optimal treatment strategies will undoubtedly continue to evolve.