Classification of congenital thumb hypoplasia and deformity

Wei Wang, Chuanchang Dai, Lu Zhang

Department of Plastic and Reconstructive Surgery, Shanghai Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China

Keywords:Classification Congenital thumb hypoplasia Deformity

ABSTRACT Background:Congenital thumb deformities account for one-third or more of all cases of congenital hand deformity.However, the current classification schemes of congenital thumb hypoplasia are no longer adequate due to their lack of adaptability to increasing knowledge in the field.Hence,a modified system with the potential to adapt to ongoing advances in knowledge and understanding is desperately needed.Methods: Based on the photographs collected from thousands of cases of congenital deformities of the hand and upper limb over multiple decades in our department,we subdivided thumb hypoplasia according to the variables of morphological characteristics, anatomical structures, functional status, the relationship between thumb deformity and hand deformity, the relationship between congenital hand deformity syndrome and thumb hypoplasia, and the selection of treatment methods.Results: A total of 10 types were presented, which were elucidated with nomenclatures as well as pathological feature and symptoms.Conclusion: This modified system may shed additional light on the classification of congenital thumb anomalies,which will assist in a more effective selection of treatment modalities and offers significant benefits to both patients and practice.

1.Introduction

Precise classification of thumb hypoplasia is the basis for understanding multiple diseases and selecting the most appropriate treatment strategies.The availability of a detailed classification also promotes the spread of information and knowledge.Because congenital thumb deformities account for one-third or more of all cases of congenital hand deformity,an accurate classification scheme is necessary.

Blauth1originally classified thumb hypoplasia into five grades, and many authors currently use a modified version of the Blauth classification for thumb hypoplasia.The Bayne classification of thumb hypoplasia2and the modified classification schemes proposed by Manske,3,4Abdel-Ghani,5and McDonald6combined the previous classification methods into 6 types and 7 groups.Subsequently, Upton7classified thumb hypoplasia into 10 types, and although this method was more practical and more comprehensive, it was not very accurate.Therefore,the current report details a collection of photographs from thousands of cases of congenital deformities of the hand and upper limb that were collected over multiple decades in our department, with the aim of modifying and supplementing the currently available classification schemes of congenital thumb hypoplasia.

2.Methods

The proposed modified classification for thumb hypoplasia is based on the following variables: (1) morphological characteristics; (2)anatomical structures, including the bone, joint, and supporting and stabilizing structures of ligaments, and the development of dynamic muscles and tendons;(3)functional status reflecting the defect in terms of degrees of flexion, extension, abduction, adduction, rotation, and opponensplasty of the thumb; (4) the relationship between thumb deformity and hand deformity; (5) the relationship between congenital hand deformity syndrome and thumb hypoplasia;and(6)the selection of treatment methods.

3.Results

The specific classification scheme is detailed in Table 1.

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3.1.Type I thumb hypoplasia

Nomenclature:Minor hypoplasia.

Pathology and symptoms:The thumb is short,small,and narrow,and the thumbnail is short and narrow; these features may be accompanied by mild adduction or abduction deformity with light functional damage.The supporting, dynamic, and stabilizing structures of the thumb are present, and their functions are approximately normal.Although there are different degrees of hypoplasia, the flexion, extension, abduction,adduction, rotation, and opponensplasty functions of the thumb are generally present;the muscle strength is rated at above grade 4.Type 1 thumb hypoplasia is a type of dysfunctional short thumb deformity.The morphological and functional defects are variable;for example,there are different degrees of extension and flexion and differences in the thenar muscle strength and normal thumb strength.However,the grasp,grip,2-finger pinch, 3-finger pinch, lateral prehension pinch, and opponensplasty tasks of the thumb are normal.Although insufficiencies are present, it is difficult to improve them by surgery; thus, this type of deformity generally does not receive treatment (Fig.1).Many short thumb deformities are categorized as syndromic short thumb deformities, which present more significant functional and morphological damage and will be discussed elsewhere.

3.2.Type II thumb hypoplasia

Nomenclature: Moderate thumb hypoplasia with thenar muscle hypoplasia and/or extensor and flexor pollicis brevis muscle hypoplasia.

Pathology and symptoms: These cases present clear thumb hypoplasia.The thumb is short and small with adduction deformity and demonstrates moderate morphological, structural, and functional damage.Because the degrees of deformity vary, this type can be further subclassified into the IIa, IIb, IIc, and IId subtypes of moderate thumb hypoplasia.

3.2.1.Type IIa thumb hypoplasia

Nomenclature:Thumb hypoplasia with thenar muscle hypoplasia.

Pathology and symptoms:Thumb adduction,the presence of defects in the first web space, and clear thenar muscle hypoplasia are evident(Fig.2).

3.2.2.Type IIb thumb hypoplasia

Nomenclature: Moderate thumb hypoplasia of the extensor pollicis brevis muscle.

Pathology and symptoms:There is thumb adduction,the presence of defects in the first web space, and extensor pollicis brevis muscle hypoplasia with or without thenar muscle hypoplasia.Type IIb thumb hypoplasia may be accompanied by minor hypoplasia of the supporting structures of the metacarpals and phalanges (Fig.3).

3.2.3.Type IIc thumb hypoplasia

Nomenclature:Moderate thump hypoplasia with flexor pollicis brevis muscle hypoplasia.

Pathology and symptoms:There is thumb adduction,the presence of defects in the first web space,and flexor pollicis brevis muscle hypoplasia with or without thenar muscle hypoplasia.Pollicis brevis flexor tendon hypoplasia and the presence of abnormal insertion points are also evident.Type IIc thumb hypoplasia may be accompanied by minor hypoplasia of the supporting structures of the metacarpals and phalanges(Fig.4).

3.2.4.Type IId thumb hypoplasia

Nomenclature: Moderate thumb hypoplasia with moderate hypoplasia of the supporting structures and stabilizing structures of the thumb bones.

Pathology and symptoms: There is moderate thumb phalanx or/and first metacarpal bone hypoplasia and moderately abnormal morphology and structure, with a thin and small phalanx and metacarpal bone.The flexion, extension, abduction, adduction, rotation, and opponensplasty functions of the thumb are present as well as differing degrees of muscle hypoplasia damage(Fig.5).

Fig.1. Type I thumb hypoplasia.Minor hypoplasia of the right thumb is evident.The thumb is short and small, the distal phalanx is short and small, and thumbnail hypoplasia is present.The patient’s grandmother exhibited the same deformity.The thumb function was almost normal,and there was no indication for surgery.An Xray film shows minor hyperplasia of the right thumb and hypoplasia of the distal phalanx.

Fig.2. Type IIa thumb hypoplasia with type IIa moderate left thumb hypoplasia.(A) X-ray film.(B) Type IIa moderate left thumb hypoplasia and thenar muscle hypoplasia.(C) The child demonstrates thenar muscle hypoplasia in the left hand.The thumb could not complete digital opposition functions.The completion of flexion and opposition functions of the left thumb required assistance from the right hand.

Fig.3. Type IIb moderate thumb hypoplasia.This case demonstrates adduction type right thumb hypoplasia.Thumb extensor tendon hypoplasia and thenar muscle hypoplasia are evident.

3.3.Type III thumb hypoplasia

Nomenclature:Severe thumb hypoplasia and/or severe hypoplasia of the dynamic structures, supporting structures,stabilizing structures and morphology of the thumb.

Pathology and symptoms:There is thumb hypoplasia accompanied by significant hypoplasia of the dynamic, supporting, stabilizing structures and the morphology of the thumb.These symptoms manifest as thumb adduction, thenar muscle hypoplasia, and hand hypoplasia of the extrinsic muscles.There is also significant hypoplasia of the thumb phalanx and first metacarpal bone and hypoplasia of some or most of the structures of the interphalangeal, metacarpophalangeal, and/or carpometacarpal joints.Although the thumb is oriented in the opponens position, the first metacarpal bone is occasionally finger-shaped.Severe hypoplasia and severe dysfunction of the first metacarpal bone are also evident.Due to the different degrees of hypoplasia and different components affected,type III thumb dysplasia can be subclassified into the a,b, and c subtypes.

Fig.4. Type IIc moderate thumb hypoplasia and a schematic diagram of the flexor pollicis longus muscle tendon showing thumb hypoplasia.The affected hand demonstrates a short and small thumb with adduction deformity.This is accompanied by deformity of the insertion point of the flexor pollicis longus muscle tendon of the thumb.The flexor pollicis longus muscle was divided into 2 sections,with insertion points at the flexor side and dorsal sides of the thumb.The flexor muscle tendon is present at the dorsal side as a membranous flexor tendon with insertion points at the distal metacarpophalangeal or distal interphalangeal joint.

3.3.1.Type IIIa severe thumb hypoplasia

Nomenclature:Type IIIa severe hypoplasia of the thumb and/or grade II thumb hypoplasia with severe hypoplasia of the first metacarpal bone.

Pathology and symptoms: The first carpometacarpal joint is present but demonstrates evidence of hypoplasia.There is also severe damage to the supporting and dynamic functions of the thumb(Fig.6,right).

3.3.2.Type IIIb thumb hypoplasia

Nomenclature: Type IIIb severe thumb hypoplasia and/or grade II thumb hypoplasia with severe hypoplasia of the first metacarpal bone and the first carpometacarpal joint.

Pathology and symptoms:There is severe hypoplasia or total absence of the first carpometacarpal joint, as well as severe damage to the supporting and dynamic functions of the thumb(Fig.6, left).

3.3.3.Type IIIc thumb hypoplasia

Nomenclature: Type IIIc abduction type severe thumb hypoplasia and/or grade II thumb hypoplasia with first metacarpal bone hypoplasia and severe hypoplasia of the first carpometacarpal joint and hypoplasia of thumb abduction.

Pathology and symptoms: Phalangeal hypoplasia as well as severe hypoplasia of the first metacarpal bone,metacarpophalangeal joint,and carpometacarpal joint are evident.Abnormal positioning; thumb adduction deformity; and severe damage to the position, morphology,and function of the thumb are also present(Fig.7).

3.4.Type IV thumb hypoplasia

Nomenclature:Severe hypoplasia with a floating thumb.

Pathology and symptoms:The floating thumb contains bone and soft tissues,but it demonstrates severe hypoplasia,and the metacarpal bone is absent.The thumb is very soft and is connected to the hand by only a very small skin bridge.There are nerves and blood vessels in the skin bridge,but the floating thumb does not possess any functionality(Fig.8).

3.5.Type V thumb hypoplasia

Nomenclature:Absence of the thumb and hypoplasia.

Pathology and symptoms:There is a 4-fingered hand,and a thumb at the opponens position is absent.The development of the remaining 4 fingers is normal, and the morphology and function of the fingers are normal or demonstrate minor hypoplasia (Fig.9).

3.6.Type VI thumb hypoplasia

Nomenclature:Absence of the thumb and hypoplasia of a multi-finger thumb.

Fig.5. Type IId moderate thumb hypoplasia.The right thumb is short and small and demonstrates flexion-adduction deformity.Thenar muscle hypoplasia and extensor pollicis hypoplasia are evident.This is accompanied by clear hypoplasia of the phalanx joints of the first metacarpal bone and thumb deformity, but most functions are intact.The opponens function of the deformed thumb is poor, and the thumb could not touch the little finger but could touch the ring finger, with reduced pinch strength of the thumb.X-ray film shows that the phalanx of the right thumb and the first metacarpal bone are thin and small and the metacarpal bones are finger-shaped.The epiphysis is visible at the distal metacarpal bone.Metacarpophalangeal joint deformity is evident, as are biphalangeal fingers and proximal phalanx deformity.This patient selected non-surgical treatment.

Fig.6. Type IIIa severe thumb hypoplasia of the right hand.Adduction deformity, thenar muscle hypoplasia,and extensor pollicis muscle hypoplasia are evident.The phalanx of the thumb and metacarpal bone are thin and small and demonstrate severe hypoplasia.A triphalangeal thumb and triangular structure of the middle phalanx and interphalangeal joint are evident.The left hand shows type IIIb severe thumb hypoplasia, with thumb adduction and hypoplasia of the thenar muscle and extensor halluces.Severe hypoplasia of the thumb phalanx and metacarpal bone and the absence of the proximal first metacarpal bone and carpometacarpal joint are evident.

Fig.7. Type IIIc severe thumb hypoplasia.Right thumb abduction hypoplasia and grade II thumb hypoplasia are evident with abnormal development of the phalanges,metacarpals,metacarpophalangeal joints,and carpometacarpal joint.A thumb abduction deformity, thenar muscle hypoplasia, and severe dysfunctional thumb hypoplasia are also evident.

Fig.8. Type IV thumb hypoplasia.A case of floating thumb hypoplasia.

Pathology and symptoms: There is a multi-finger thumb defect including 5, 6, 7, or 8 fingers.All fingers are at the same plane, and a thumb at the opponens position is absent.There is a thumb defect, but the morphology and function of the major fingers are normal.Some fingers may demonstrate hypoplasia or syndactyly.

3.6.1.Type VIa thumb hypoplasia

Nomenclature:Hypoplasia of the thumb on a 5-fingered hand.

Pathology and symptoms: This type can be further subclassified into the aa and ab subtypes.In type VIaa thumb hypoplasia,there are 5 fingers,and although the thumb demonstrates hypoplasia, the remaining fingers develop normally.In type VIab thumb hypoplasia,there are 5 fingers,with thumb hypoplasia and the remaining fingers appearing short and small.

3.6.2.Type VIb thumb hypoplasia

Pathology and symptoms: There are 6–8 fingers with thumb hypoplasia(Fig.10).

3.7.Type VII thumb hypoplasia

Nomenclature:Absence of the thumb and hypoplasia with syndactyly,polydactyly,or webbed hand deformity.

Pathology and symptoms: These cases present syndactyly and/or polydactyly of the hand.The thumb at the opponens position and the wide first web space are absent.The presentation can consist of 5,6,or 7 fingers; syndactyly; or finger flexion deformity.There is also thumb or finger hypoplasia(Fig.11).

3.8.Type VIII thumb dysplasia

Nomenclature:Whole-hand hypoplasia type thumb hypoplasia.

Pathology and symptoms: There is whole-hand dysplasia and thumb dysplasia, including many syndromic short thumbs and short hand hypoplasia,such as syndromic short skeletal thumb ray.The most common deformities include Apert syndrome,Poland syndrome,and spade hand deformity(Fig.12).

3.9.Type IX thumb hypoplasia

Nomenclature:Hypoplasia of the thumb with cleft hand.

Pathology and symptoms: Central ray longitudinal deficiencies are present, and the thumb is completely absent or deformed.Type IX hypoplasia can further be subclassified into the a, b, c, and d subtypes,which include thumb defects in a 4-fingered cleft hand,thumb defects in a 3-fingered cleft hand, thumb defects in a 2-fingered hand, and thumb defects in a 1-fingered cleft hand(Figs.13 and 14).

3.10.Type X thumb hypoplasia

Nomenclature:Thumb hypoplasia with constriction ring syndrome.

Fig.9. Type V thumb hypoplasia.Congenital absence of the thumb and thumb hypoplasia are evident.There are 4 well-developed fingers on the hand.Left: radial club hand deformity of type V thumb hypoplasia.

Fig.10. Type VI thumb hypoplasia.Congenital absence of the thumb and multi-finger thumb hypoplasia are evident.Middle:This child presented with a thumb defect and 6 fingers,which was classified as type VIb.Left:The left and right hands of the mother and grandmother,respectively,of the child with 5 fingers and the absence of the thumb(type VIaa with well-developed fingers).Right:Hypoplasia of the thumb with 6 fingers(type VIb)and finger hypoplasia with 5 fingers and absence of the thumb (type VIab) (right finger hypoplasia).

Fig.11. Type VII thumb hypoplasia showing absence of the thumb and hypoplasia of syndactyly, polydactyly, and webbed hand deformity.The top and bottom images show complete syndactyly with 5, 6, or 7 fingers; absence of the thumb; and finger hypoplasia.

Fig.12. Type VIII whole-hand hypoplasia type thumb hypoplasia.Left:Apert syndrome.Middle and right:Poland syndrome.Absence of the thumb with 4 or 5 fingers,thumb hypoplasia, and finger hypoplasia are evident.This is accompanied by 3–5 fingers, hand hypoplasia, short fingers with syndactyly hypoplasia, thumb hypoplasia, spade hand, or finger hypoplasia.

Fig.13. Type IX thumb hypoplasia.Type IXa showing a 4-fingered cleft hand with thumb hypoplasia and Type IXb showing a 3-fingered cleft hand with thumb hypoplasia.

Fig.14. Type IX thumb hypoplasia.Type IXd showing a 2-or 1-fingered cleft hand with thumb hypoplasia.Left:Type IXc showing a 2-fingered cleft hand and thumb hypoplasia on both hands.Middle: Single-finger cleft hand with thumb hypoplasia on both hands.Right: Single-finger cleft hand with thumb hypoplasia on the unilateral hand.

Pathology and symptoms: There is constriction ring deformity in the limbs, body, or skull.The thumb is short and small, and there are distal defects, constriction rings, and congenital broken thumb deformities(Fig.15).

4.Discussion

Classical thumb hypoplasia is the specific entity to which most surgeons working in the field of plastic and hand surgery are referred for the treatment of underdeveloped thumb.However, thumb hypoplasia accompanies many congenital conditions, including thumb duplication,transverse deficiencies and symbrachydactyly,brachydactyly,cleft hand complex and ulnar longitudinal deficiency, congenital constriction ring syndrome,and other miscellaneous conditions such as hypoplastic thumb in Apert or Poland syndrome.Each condition involves its own specific challenges,but the principles remain the same.In all cases,the ultimate goal is to provide a functional limb that can be integrated into the child’s overall development.This goal may be met surgically or through specialized therapy and rehabilitation.Every case is unique, and each patient and parent will have a different capacity to adapt.8These differences should be taken into account before embarking on a long,often difficult reconstructive course.It should be stressed that the child will never have a “normal” hand.Once realistic expectations have been set,reconstruction and rehabilitation can commence.

Fig.15. Type X thumb hypoplasia.There were two cases of constriction ring deformity of the proximal phalanx of the left thumb and fingers, minor thumb hypoplasia, and severe finger hypoplasia.

5.Conclusion

This modified system may shed additional light on the classification of congenital thumb anomalies, which will assist in a more effective selection of treatment modalities and offers significant benefits to both patients and practice.

Ethics declarations

Ethics approval and consent to participate

Ethical approval was waived due to the nature of this study.Written informed consent was obtained from all individual participants included in the study.

Consent for publication

All patients provided written informed consent to publish the data contained within this study.

Competing interest

The authors declare that they have no competing interests.

Authors’contributions

Wang W:Writing-Original draft preparation.Dai C:Photo collection.Zhang L:Writing-Reviewing and Editing.