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.

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.

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.

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.

This is a less common situation, in which the affectation is on the side of the hand towards the thumb. Radial polydactyly refers to the presence of an extra digit (or extra digits) on the radial side of the hand. It is most frequent in Indian populations and it is the second most common congenital hand disorder. The incidence of radial polydactyly is reported as 1 in every 3,000 live births. The clinical features of radial polydactyly will depend upon the extent of duplication.

Radial polydactyly varies from a barely visible radial skin tag to complete duplication. Thumb polydactyly varies from barely visible broadening of the distal phalanx to full duplication of the thumb including the first metacarpal.

Radial polydactyly is frequently associated with several syndromes.

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).

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)

Characteristics are:

- A fibrous band instead of the fibula

- Short deformed leg

- Absence of the lateral part of the ankle joint (due to absence of the distal end of the fibula), and what is left is unstable; the foot has an equinovalgus deformity

- Possible absence of part of the foot requiring surgical intervention to bring the foot into normal function, or amputation.

- Possible absence of one or two toes on the foot

- Possible conjoined toes or metatarsals

Partial or total absence of fibula is among the most frequent limb anomalies. It is the most common long bone deficiency and is the most common skeletal deformity in the leg. It most often is unilateral (present only on one side). It may also present as bilateral (affecting both legs). Paraxial fibular hemimelia is the most common manifestation in which only the postaxial portion of the limb is affected. It is commonly seen as a complete terminal deficiency, where the lateral rays of the foot are also affected. Hemimelia can also be intercalary in which case the foot remains unaffected. Although the missing bone is easily identified, this condition is not simply a missing bone. Males are affected twice as often as females in most series.

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.

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.

The Wassel classification is used to categorise radial polydactyly, based upon the most proximal level of skeletal duplication.

Fibular hemimelia or longitudinal fibular deficiency is "the congenital absence of the fibula and it is the most common congenital absence of long bone of the extremities." It is the shortening of the fibula at birth, or the complete lack thereof. In humans, the disorder can be noted by ultrasound in utero to prepare for amputation after birth or complex bone lengthening surgery. The amputation usually takes place at six months with removal of portions of the legs to prepare them for prosthetic use. The other treatments which include repeated corrective osteotomies and leg-lengthening surgery (Ilizarov apparatus) are costly and associated with residual deformity.

People who are affected by Liebenberg Syndrome suffer from three main symptoms:

1. Dysplasia (improper formation) of the bony components of the elbow

2. Abnormal shape of carpal bones

3. Brachydactyly, a symptom where the fingers and toes are shorter than normal.

Schmitt Gillenwater Kelly syndrome is a rare autosomal dominant congenital disorder consisting of radial hypoplasia, triphalangeal thumbs, hypospadias, and maxillary diastema.

Hemimelia comprises

- Fibular hemimelia, Congenital longitudinal deficiency of the fibula or Fibular longitudinal meromelia

- Tibial hemimelia, Congenital longitudenal deficiency of the tibia, Congenital aplasia and dysplasia of the tibia with intact fibula, Congenital longitudinal deficiency of the tibia or Tibial longitudinal meromelia

- Radial Hemimelia, Congenital longitudinal deficiency of the radius, Radial clubhand, Radial longitudinal meromelia or Radial ray agenesis

- Ulnar hemimelia, Congenital longitudinal deficiency of the ulna, Ulnar clubhand or Ulnar longitudinal meromelia

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.

Cleidocranial dysostosis is a general skeletal condition so named from the collarbone (cleido-) and cranium deformities which people with it often have.

People with the condition usually present with a painless swelling in the area of the clavicles at 2–3 years of age. Common features are:

- Clavicles (collarbones) can be partly missing leaving only the medial part of the bone. In 10% cases, they are completely missing. If the collarbones are completely missing or reduced to small vestiges, this allows hypermobility of the shoulders including ability to touch the shoulders together in front of the chest. The defect is bilateral 80% of the time. Partial collarbones may cause nerve damage symptoms and therefore have to be removed by surgery.

- The mandible is prognathic due to hypoplasia of maxilla (micrognathism) and other facial bones.

- A soft spot or larger soft area in the top of the head where the fontanelle failed to close, or the fontanelle closes late.

- Bones and joints are underdeveloped. People are shorter and their frames are smaller than their siblings who do not have the condition.

- The permanent teeth include supernumerary teeth. Unless these supernumeraries are removed they will crowd the adult teeth in what already may be an underdeveloped jaw. If so, the supernumeraries will probably need to be removed to make space for the adult teeth. Up to 13 supernumarary teeth have been observed. Teeth may also be displaced. Cementum formation may be deficient.

- Failure of eruption of permanent teeth.

- Bossing (bulging) of the forehead.

- Open skull sutures, large fontanelles.

- Hypertelorism.

- Delayed ossification of bones forming symphysis pubis, producing a widened symphysis.

- Coxa vara can occur, limiting abduction and causing Trendelenburg gait.

- Short middle fifth phalanges, sometimes causing short and wide fingers.

- Vertebral abnormalities.

- On rare occasions, brachial plexus irritation can occur.

- Scoliosis, spina bifida and syringomyelia have also been described.

Other features are: parietal bossing, basilar invagination (atlantoaxial impaction), persistent metopic suture, abnormal ear structures with hearing loss, supernumerary ribs, hemivertebrae with spondylosis, small and high scapulae, hypoplasia of illiac bones, absence of the pubic bone, short / absent fibular bones, short / absent radial bones, hypoplastic terminal phalanges.

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.

Liebenberg Syndrome is a rare autosomal genetic disease that involves a deletion mutation upstream of the PITX1 gene, which is one that's responsible for the body's organization, specifically in forming lower limbs. In animal studies, when this deletion was introduced to developing birds, their wing buds were noted to take on limb-like structures.

The condition was first described by Dr. F. Liebenberg in 1973 while he followed multiple generations of a South African family, but it has since been noticed in other family lineages across the world.

The most common and defining features of BGS are craniosynostosis and radial ray deficiency. The observations of these features allow for a diagnosis of BGS to be made, as these symptoms characterize the syndrome. Craniosynostosis involves the pre-mature fusion of bones in the skull. The coronal craniosynostosis that is commonly seen in patients with BGS results in the fusion of the skull along the coronal suture. Because of the changes in how the bones of the skull are connected together, people with BGS will have an abnormally shaped head, known as brachycephaly. Features commonly seen in those with coronal craniosynostosis are bulging eyes, shallow eye pockets, and a prominent forehead. Radial ray deficiency is another clinical characteristic of those with BGS, and results in the under-development (hypoplasia) or the absence (aplasia) of the bones in the arms and the hands. These bones include the radius, the carpal bones associated with the radius and the thumb. Oligodactyly can also result from radial ray deficiency, meaning that someone with BGS may have fewer than five fingers. Radial ray deficiency that is associated with syndromes (such as BGS) occurs bi-laterally, affecting both arms.

Some of the other clinical characteristics sometimes associated with this disorder are growth retardation and poikiloderma. Although the presentation of BGS may differ between individuals, these characteristics are often observed. People with BGS may have stunted growth, short stature and misshapen kneecaps. Poikiloderma may also be present in people with this syndrome, meaning that their skin may have regions of hyperpigmentation and hypopigmentation, or regions where the skin is missing (atrophy).

Renal (kidney) defects are seen in approximately 50 percent of patients with VACTERL association. In addition, up to 35 percent of patients with VACTERL association have a single umbilical artery (there are usually two arteries and one vein) which is often associated with additional kidney or urologic problems. Renal abnormalities in VACTERL association can be severe, with incomplete formation of one or both kidneys or urologic abnormalities such as obstruction of outflow of urine from the kidneys or severe reflux (backflow) of urine into the kidneys from the bladder. These problems can cause kidney failure early in life and may require kidney transplant. Many of these problems can be corrected surgically before any damage can occur.

The following features are observed with VACTERL association:

- V - Vertebral anomalies

- A - Anorectal malformations

- C - Cardiovascular anomalies

- T - Tracheoesophageal fistula

- E - Esophageal atresia

- R - Renal (Kidney) and/or radial anomalies

- L - Limb defects

Although it was not conclusive whether VACTERL should be defined by at least two or three component defects, it is typically defined by the presence of at least three of the above congenital malformations.

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).

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.