The triphalangeal thumb has a different appearance than normal thumbs. The appearance can differ widely; the thumb can be a longer thumb, it can be deviated in the radio-ulnar plane (clinodactyly), thumb strength can be diminished. In the case of a five fingered-hand it has a finger-like appearance, with the position in the plane of the four fingers, thenar muscle deficiency, and additional length. There is often a combination with radial polydactyly.

Generally, triphalangeal thumbs are non-opposable. In contrast to most people with opposable thumbs, a person suffering from TPT cannot easily place his or her thumb opposite the other four digits of the same hand. The opposable thumb's ability to effortlessly utilize fingers in a "pinch" formation is critical in precision gripping. For the thumb to adequately grip, certain thumb criteria must be met (e.g. suitable position and length, stable joints and good thenar muscle strength). Because triphalangeal thumbs cannot easily oppose and do not possess many of the optimal qualities found in most opposable thumbs, they tend to cause the hand to be less effective in use and, therefore, prove to be more problematic in daily life.

Diagnosing the congenital clasped thumb is difficult in the first three to four months of life, as it is normal when the thumb is clutched into the palm in these first months.

Diagnoses that cause the same flexion or adduction abnormalities of the thumb are:

- Congenital clasped thumb

- Congenital Trigger thumb (flexion of the interphalangeal joint) - Trigger finger

- Spasticity: overstimulation of muscles

Syndrome associated flexion-adduction of the thumb:

- Freeman-Sheldon syndrome (a congenital, heritable affection of the face, the hands, the feet and some joints)

- Distal arthrogryposis

- MASA syndrome

- X-linked hydrocephalus

- Adducted thumb syndrome

- Waardenburg syndrome

- Whistling face syndrome (Freeman-Sheldon syndrome)

- Digitotalar dysmorphism

- Multiple pterygium syndrome

In general there are five types of thumb hypoplasia, originally described by Muller in 1937 and improved by Blauth, Buck-Gramcko and Manske.

- Type I: the thumb is small, normal components are present but undersized. Two muscles of the thumb, the abductor pollicis brevis and opponens pollicis, are not fully developed

. This type requires no surgical treatment in most cases.

- Type II is characterized by a tight web space between the thumb and index finger which restricts movement, poor thenar muscles and an unstable middle joint of the thumb metacarpophalangeal joint. This unstable thumb is best treated with reconstruction of the mentioned structures.

- Type III thumbs are subclassified into two subtypes by Manske. Both involve a less developed first metacarpal and a nearly absent thenar musculature. Type III-A has a fairly stable carpometacarpal joint and type III-B does not. The function of the thumb is poor. Children with type III are the most difficult patients to treat because there is not one specific treatment for the hypoplastic thumb. The limit between pollicization and reconstruction varies. Some surgeons have said that type IIIA is amenable to reconstruction and not type IIIB. Others say type IIIA is not suitable for reconstruction too. Based on the diagnosis the doctor has to decide what is needed to be done to obtain a more functional thumb, i.e. reconstruction or pollicization. In this group careful attention should be paid to anomalous tendons coming from the forearm (extrinsic muscles, like an aberrant long thumb flexor – flexor pollicis longus).

- Type IV is called a pouce flottant, floating thumb. This thumb has a neurovascular bundle which connects it to the skin of the hand. There’s no evidence of thenar muscles and rarely functioning tendons. It has a few rudimentary bones. Children with type IV are difficult to reconstruct. This type is nearly always treated with an index finger pollicization to improve hand function.

- Type V is no thumb at all and requires pollicization.

This is a very rare situation, in which the extra digit is on the ring, middle or index finger. Of these fingers, the index finger is most often affected, whereas the ring finger is rarely affected.

This type of polydactyly can be associated with syndactyly, cleft hand and several syndromes.

Polysyndactyly presents various degrees of syndactyly affecting fingers three and four.

Thumb hypoplasia is a spectrum of congenital abnormalities of the thumb varying from small defects to absolute retardation of the thumb. It can be isolated, when only the thumb is affected, and in 60% of the cases it is associated with radial dysplasia (or radial club, radius dysplasia, longitudinal radial deficiency). Radial dysplasia is the condition in which the forearm bone and the soft tissues on the thumb side are underdeveloped or absent.

In an embryo the upper extremities develop from week four of the gestation. During the fifth to eighth week the thumb will further develop. In this period something goes wrong with the growth of the thumb but the exact cause of thumb hypoplasia is unknown.

One out of every 100,000 live births shows thumb hypoplasia. In more than 50% of the cases both hands are affected, otherwise mainly the right hand is affected.

About 86% of the children with hypoplastic thumb have associated abnormalities. Embryological hand development occurs simultaneously with growth and development of the cardiovascular, neurologic and hematopoietic systems. Thumb hypoplasia has been described in 30 syndromes wherein those abnormalities have been seen. A syndrome is a combination of three or more abnormalities. Examples of syndromes with an hypoplastic thumb are Holt-Oram syndrome, VACTERL association and thrombocytopenia absent radius (TAR syndrome).

Common relevant features of acrocephalosyndactyly are a high-arched palate, pseudomandibular prognathism (appearing as mandibular prognathism), a narrow palate, and crowding of the teeth.

All acrocephalosyndactyly syndromes show some level of limb anomalies, so it can be hard to tell them apart. However, the typical hand deformities in patients with Apert Syndrome distinguish it from the other syndromes.

The hands in patients with Apert syndrome always show four common features:

1. a short thumb with radial deviation

2. complex syndactyly of the index, long and ring finger

3. symbrachyphalangism

4. simple syndactyly of the fourth webspace

The deformity of the space between the index finger and the thumb may be variable. Based on this first webspace, we can differentiate three different types of handdeformation:

- Type I: Also called a "spade hand". The most common and least severe type of deformation. The thumb shows radial deviation and clinodactyly, but is separated from the index finger. The index, long and ring finger are fused together in the distal interphalangeal joints and form a flat palm. During the embryonic stage, the fusion has no effect on the longitudinal growth of these fingers, so they have a normal length. In the fourth webspace, we always see a simple syndactyly, either complete or incomplete.

- Type II: Also called a "spoon" or "mitten" hand. This is a more serious anomaly since the thumb is fused to the index finger by simple complete or incomplete syndactyly. Only the distal phalanx of the thumb is not joined in the osseous union with the index finger and has a separate nail. Because the fusion of the digits is at the level of the distal interphalangeal joints, a concave palm is formed. Most of the time, we see complete syndactyly of the fourth webspace.

- Type III: Also called the "hoof" or "rosebud" hand. This is the most uncommon but also most severe form of hand deformity in Apert syndrome. There is a solid osseous or cartilaginous fusion of all digits with one long, conjoined nail. The thumb is turned inwards and it is often impossible to tell the fingers apart. Usually proper imaging of the hand is very difficult, due to overlap of bones, but physical examination alone is not enough to measure the severity of deformation

The classification of ulnar polydactyly exists of either two or three types. The two-stage classification, according to Temtamy and McKusick, involves type A and B. In type A there is an extra little finger at the metacarpophalangeal joint, or more proximal including the carpometacarpal joint. The little finger can be hypoplastic or fully developed. Type B varies from a nubbin to an extra, non-functional little finger part on a pedicle. According to the three-type classification, type I includes nubbins or floating little fingers, type II includes duplications at the MCPJ, and type III includes duplications of the entire ray.

Classification of radial dysplasia is practised through different models. Some only include the different deformities or absences of the radius, where others also include anomalies of the thumb and carpal bones. The Bayne and Klug classification discriminates four different types of radial dysplasia. A fifth type was added by Goldfarb et al. describing a radial dysplasia with participation of the humerus. In this classification only anomalies of the radius and the humerus are taken in consideration. James and colleagues expanded this classification by including deficiencies of the carpal bones with a normal distal radius length as type 0 and isolated thumb anomalies as type N.

Type N: Isolated thumb anomaly

Type 0: Deficiency of the carpal bones

Type I: Short distal radius

Type II: Hypoplastic radius in miniature

Type III: Absent distal radius

Type IV: Complete absent radius

Type V: Complete absent radius and manifestations in the proximal humerus

The term absent radius can refer to the last 3 types.

The thumb contains five groups of muscle and/or tendons:

1. Extensor tendons (to stretch the thumb)

2. Flexor muscles/tendons (to bend the thumb)

3. Abductor muscles/tendons (to move the thumb outwards)

4. Adductor muscle (to move the thumb inwards)

5. Opposing muscles (to move the thumb opposite the small finger)

In order for the thumb to maintain a normal position, a strict balance between these groups is required. Weak or absent extensors and/or abductors (the extensor pollicis brevis tendon, the extensor pollicis longus tendon or, rarely, the abductor pollicis longus tendon), can cause a disbalance, leading to an abnormal position of the thumb: congenital clasped thumb. There is also the possibility that two tendons are affected simultaneously.

The following tendon deviations can induce congenital clasped thumb:

- The flexor tendons are too short (the thumb is drawn into the palm)

- The abductor tendons are hypoplastic or absent

- The extensor tendons are hypoplastic or absent

Furthermore, a tight thumb web space (the area between thumb and index finger) can contribute to congenital clasped thumb. The thumb cannot be properly abducted (moved outwards), if the web space is too tight.

To summarize, the causes of congenital clasped thumbs may vary between patients and can sometimes be a combination of the preceding components. Treatment should be tailored to all occurring components in order to achieve good results.

Besides the clicking, snapping or triggering, a characteristic Notta nodule is commonly found on the palmar side at the metacarpophalangeal (MCP) joint. This nodule can be found by palpation. Children can also present a thumb which they cannot extend actively due to entrapment of the nodule to the A1 pulley. Some may even present with a fixed flexion deformity of the IPJ where no extension is possible.

Radial dysplasia, also known as radial club hand or radial longitudinal deficiency, is a congenital difference occurring in a longitudinal direction resulting in radial deviation of the wrist and shortening of the forearm. It can occur in different ways, from a minor anomaly to complete absence of the radius, radial side of the carpal bones and thumb. Hypoplasia of the distal humerus may be present as well and can lead to stiffnes of the elbow. Radial deviation of the wrist is caused by lack of support to the carpus, radial deviation may be reinforced if forearm muscles are functioning poorly or have abnormal insertions. Although radial longitudinal deficiency is often bilateral, the extent of involvement is most often asymmetric.

The incidence is between 1:30,000 and 1:100,000 and it is more often a sporadic mutation rather than an inherited condition. In case of an inherited condition, several syndromes are known for an association with radial dysplasia, such as the cardiovascular Holt-Oram syndrome, the gastrointestinal VATER syndrome and the hematologic Fanconi anemia and TAR syndrome. Other possible causes are an injury to the apical ectodermal ridge during upper limb development, intrauterine compression, or maternal drug use (thalidomide).

Ectrodactyly, split hand, cleft hand, derived from the Greek "ektroma" (abortion) and "daktylos" (finger) involves the deficiency or absence of one or more central digits of the hand or foot and is also known as split hand/split foot malformation (SHFM). The hands and feet of people with ectrodactyly are often described as "claw-like" and may include only the thumb and one finger (usually either the little finger, ring finger, or a syndactyly of the two) with similar abnormalities of the feet.

It is a rare form of a congenital disorder in which the development of the hand is disturbed. It is a type I failure of formation – longitudinal arrest. The central ray of the hand is affected and usually appears without proximal deficiencies of nerves, vessels, tendons, muscles and bones in contrast to the radial and ulnar deficiencies. The cleft hand appears as a V-shaped cleft situated in the centre of the hand. The digits at the borders of the cleft might be syndactilyzed, and one or more digits can be absent. In most types, the thumb, ring finger and little finger are the less affected parts of the hand. The incidence of cleft hand varies from 1 in 90,000 to 1 in 10,000 births depending on the used classification. Cleft hand can appear unilateral or bilateral, and can appear isolated or associated with a syndrome.

Split hand/foot malformation (SHFM) is characterized by underdeveloped or absent central digital rays, clefts of hands and feet, and variable syndactyly of the remaining digits. SHFM is a heterogeneous condition caused by abnormalities at one of multiple loci, including SHFM1 (SHFM1 at 7q21-q22), SHFM2 (Xq26), SHFM3 (FBXW4/DACTYLIN at 10q24), SHFM4 (TP63 at 3q27), and SHFM5 (DLX1 and DLX 2 at 2q31). SHFM3 is unique in that it is caused by submicroscopic tandem chromosome duplications of FBXW4/DACTYLIN. SHFM3 is considered 'isolated' ectrodactyly and does not show a mutation of the tp63 gene.

Congenital trigger thumb, (or Pediatric trigger thumb), is a trigger thumb in neonates and young children. Triggering, clicking or snapping is observed by flexion or extension of the interphalangeal joint (IPJ). In the furthest stage, no extension is possible and there is a fixed flexion deformity of the thumb in the IPJ. Cause, natural history, prognosis and recommended treatment are controversial.

The differential diagnosis includes;

- Symbrachydactyly

- Chorionic villus sampling

- Congenital amputations

- Hypoplasias of hand, digit, thumb

- Adams-Oliver syndrome

- ADAM complex

ADAM Complex; CRS is sometimes mislabeled as ADAM complex. ADAM is an abbreviation for Amniotic Deformity, Adhesions Mutilations. CRS is the malformation due to a constriction ring around mostly a limb. ADAM-complex is the association of limb defects (caused by constriction rings) and certain craniofacial clefts

“Adams-Oliver syndrome is often mislabeled as CRS and consists of cutis aplasia of the scalp in which a longitudinal defect can vary in size and can often be associated with full-thickness skullcap loss. The distal digital or toe hypoplasia-aplasia is often confused with CRS. Constriction rings with or without edema are not present. The digital or toe hypoplasia-aplasia usually contains diminutive nails or nail folds”.

The constriction ring syndrome is a complex collection of asymmetric congenital anomalies, in which no two cases are exactly alike. This is why a classification is difficult to make.

The most widely used classification system was proposed by Patterson. This classification system is based on the severity of the syndrome and is useful because, the different types require different treatments. Other clinicians have amended this scheme by separating the depth of the ring into mild, moderate, severe and amputation and by further defining the presence or absence of lymphedema or soft tissue loss distal to the ring. Expanding over subdivision in depth of the clefts for every classification is not necessary because the principles of treatment and technique for correction are the same

There are four categories:

1. simply constriction rings

2. constriction rings associated with deformity of the distal part with or without lymphedema

3. constriction rings associated with acrosyndactyly

4. uterine amputation

Patterson divided the constriction ring associated with acrosyndactyly into three types:

- Type I: conjoined fingertips with well-formed webs of the proper depth

- Type II: the tips of the digits are joined, but web formation is not complete

- Type III: joined tips, sinus tracts between digits and absent webs

Patterson I;

There are simple constriction rings which are strands most commonly around the distal extremities as fingers and toes. In general, the thumb is not likely to be affected by a constriction ring because the fetus typically holds the thumb in tight adduction flexion, making entanglement with strands less likely. These malformations need to be surgically removed which must be executed in different stages and can done by different techniques (see also treatment).

Patterson II;

The CRS involves strands which obstruct the lymphatic vessels and thus causing fluid retention, distal of the affected extremity. This utters itself with swollen parts distal of the constriction.

Patterson III;

In this form there is a complex form of syndactyly named acrosyndactyly, the fingers (or toes) were initially separated but due to the constriction they are formed back together. Sometimes multiple fingers can be involved. The distal fusion between digits or toes never initially involves a skeletal coalition. The digits are usually hypoplastic if multiple digits are involved. When the constriction cuts of the blood supply to the fingers, the fingers can form a peak with the most palmar digit being the index finger. Normal neurovascular bundles are not present in the distal parts. Hands with fused fingers need to be released in phases to preserve the distal blood supply.

Paterson IV;

One of the most severe consequence of constriction strains is probably intrauterine amputations, this is where the constriction goes as deep as the bone and cuts of the blood supply of the proximal extremity. The result will be that the developing toe or finger will become ischemic and will fall of. Because the end result is a transverse amputation that cuts off the vascular supply to the developing extremity, the actual constriction ring is not seen

This can result in different outcomes;

- complete resorption; this is the most common form of amputation. In this form the amputated digit is completely resorbed during intrauterine development and therefore the amputated digit can’t be found.

- recovery of the digit; the digit is recovered with the placenta during delivery.

- engraftment elsewhere; the amputated digit can be, in rare cases, engrafted somewhere on the fetus.

Intrauterine death;

In extremely rare cases a strain can form around the umbilical cord and cut off the blood supply to the fetus which will result in intrauterine death.

Malformation associated with constriction ring syndrome;

The percentage of associated anomalies varies from 40% to as high as 80%

Constriction ring deformities are as common on the lower extremity as on the upper, almost all of these involve the musculoskeletal system, with clubbed feet being the most common in up to 30% of reported cases

Large reported series reveal an incidence between 5% and 15% of craniofacial malformations with clefting of the lip or palate.

Radial aplasia is a congenital defect which affects the formation of the radius bone in the arm. The radius is the lateral bone which connects to the wrist via articulation with the carpal bones. A child born with this condition has either a short or absent radius bone in one or both of his or her arm(s). Radial aplasia also results in the thumb being either partly formed or completely absent from the hand. Radial aplasia is connected with the condition VACTERL association. The cause for radial aplasia in unknown, but it widely believed to occur within the first ten weeks of gestation.

This is characterized by hand and arm abnormalities. The following are specific characteristics:

- Malformed or absent (aplasia) thumb

- A thumb that looks more like a finger

- Partial or complete absence of a radius

- Shortening and radial deviation of the forearms

- Triphalangeal thumb

- Duplication of the thumb (preaxial polydactyly)

People with the combination of Duane anomaly and radial ray malformations may have a variety of other signs and symptoms. These features include:

- Unusually shaped ears

- Hearing loss

- Heart and kidney defects

- A distinctive facial appearance

- An inward- and downward-turning foot (a clubfoot)

- Fused vertebrae.

There are several classifications for cleft hand, but the most used classification is described by Manske and Halikis see table 3. This classification is based on the first web space. The first web space is the space between the thumb and the index.

Table 3: Classification for cleft hand described by Manske and Halikis

Ape hand deformity, also known as simian hand, is a deformity in humans who cannot move the thumb away from the rest of the hand. It is an inability to abduct the thumb. Abduction of the thumb refers to the specific capacity to orient the thumb perpendicularly to the ventral (palmar) surface of the hand. Opposition refers specifically the ability to "swing" the first metacarpal such that the tip of the thumb may touch the distal end of the 5th phalanx and if we put the hand on the table as the palm upward the thumb can not point to the sky. The Ape Hand Deformity is caused by damage to the distal median nerve (also called a Median Claw lesion), and subsequent loss of opponens pollicis muscle function. The name "ape hand deformity" is misleading, as apes have opposable thumbs.

It can occur with an injury of the median nerve either at the elbow or the wrist, impairing the thenar muscles and opponens pollicis muscle.

Ape hand deformity is one aspect of median nerve palsy, which is usually caused by deep injuries to the arm, forearm and wrist area.

Ape hand caused by median and ulnar nerve lesions

Additional findings that may be present in HFGS according to the latest research are:

- Limited metacarpophalangeal flexion of the thumb or limited ability to oppose the thumb and fifth finger

- Hypoplastic thenar eminences

- Medial deviation of the great toe (hallux varus), a useful diagnostic sign when present

- Small great toenail

- Fifth-finger clinodactyly, secondary to a shortened middle phalanx

- Short feet

- Altered dermatoglyphics of the hands; when present, primarily involving distal placement of the axial triradius, lack of thenar or hypothenar patterning, low arches on the thumbs, thin ulnar loops (deficiency of radial loops and whorls), and a greatly reduced ridge count on the fingers

Radiographic findings

- Hypoplasia of the distal phalanx and first metacarpal of the thumbs and great toes

- Pointed distal phalanges of the thumb

- Lack of normal tufting of the distal phalanges of the great toes

- Fusions of the cuneiform to other tarsal bones or trapezium-scaphoid fusion of the carpals

- Short calcaneus

- Occasional bony fusions of the middle and distal phalanges of the second, third, fourth, or fifth toes

- Delayed carpal or tarsal maturation

- Metacarpophalangeal profile reflecting shortening of the first metacarpal, the first and second phalanges, and the second phalanx of the second and fifth digits

Urogenital Defects

Females may have the following:

- Vesicoureteral reflux secondary to ureteric incompetence

- Ectopic ureteral orifices

- Trigonal hypoplasia

- Hypospadiac urethra

- Subsymphyseal epispadias

- Patulous urethra

- Urinary incontinence (related to structural anomalies and weakness of the bladder sphincter muscle)

- Small hymenal opening

- Various degrees of incomplete Müllerian fusion with or without two cervices or a longitudinal vaginal septum

Males may have the following:

- Retrograde ejaculation (related to structural anomalies and weakness of the bladder sphincter muscle)

Hand-foot-genital syndrome (HFGS) is characterized by limb malformations and urogenital defects. Mild bilateral shortening of the thumbs and great toes, caused primarily by shortening of the distal phalanx and/or the first metacarpal or metatarsal, is the most common limb malformation and results in impaired dexterity or apposition of the thumbs. Urogenital abnormalities include abnormalities of the ureters and urethra and various degrees of incomplete Müllerian fusion in females and hypospadias of variable severity with or without chordee in males. Vesicoureteral reflux, recurrent urinary tract infections, and chronic pyelonephritis are common; fertility is normal.

Some individuals have preaxial polydactyly in the feet (unilateral in one, bilateral in 13), consisting of a small extra biphalangeal toe, in most cases with an associated rudimentary extra metatarsal, lying in a soft tissue web between the hallux and second toe. In some cases, this was accompanied by hypoplasia of the head of the first metatarsal and absence of both phalanges of the hallux.