Thumb hypoplasia

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Thumb hypoplasia is a spectrum of congenital abnormalities of the thumb varying from small defects to absolute retardation of the thumb. [1] It can be isolated, when only the thumb is affected, and in 60% of the cases [2] it is associated with radial dysplasia [1] (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. [3]

Contents

In an embryo the upper extremities develop from week four of the gestation. [1] During the fifth to eighth week the thumb will further develop. [4] In this period something goes wrong with the growth of the thumb but the exact cause of thumb hypoplasia is unknown. [1] One out of every 100,000 live births shows thumb hypoplasia. [2] In more than 50% of the cases both hands are affected, otherwise mainly the right hand is affected. [1] [2]

About 86% of the children with hypoplastic thumb have associated abnormalities. [1] [2] Embryological hand development occurs simultaneously with growth and development of the cardiovascular, neurologic and hematopoietic systems. [2] 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 [1] and thrombocytopenia absent radius (TAR syndrome). [2]

Classification

In general there are five types of thumb hypoplasia, originally described by Muller in 1937 and improved by Blauth, Buck-Gramcko and Manske. [1]

- Type I: the thumb is small, normal components are present but undersized. [3] Two muscles of the thumb, the abductor pollicis brevis and opponens pollicis, are not fully developed ,. [2] [3] This type requires no surgical treatment in most cases. [1] [5]

- Type II is characterized by a tight web space between the thumb and index finger which restricts movement, [5] poor thenar muscles and an unstable middle joint of the thumb metacarpophalangeal joint. [3] This unstable thumb is best treated with reconstruction of the mentioned structures. [1]

- Type III thumbs are subclassified into two subtypes by Manske. Both involve a less developed first metacarpal and a nearly absent thenar musculature. [2] Type III-A has a fairly stable carpometacarpal joint and type III-B does not. [1] [2] [3] The function of the thumb is poor. [2] 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. [4] 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). [3] [4] [5]

- Type IV is called a pouce flottant, floating thumb. [1] [2] [3] [5] This thumb has a neurovascular bundle which connects it to the skin of the hand. [1] [3] [5] There’s no evidence of thenar muscles and rarely functioning tendons. [4] [5] It has a few rudimentary bones. [4] [5] Children with type IV are difficult to reconstruct. [1] [4] This type is nearly always treated with an index finger pollicization to improve hand function. [1] [5]

- Type V is no thumb at all [2] [3] and requires pollicization. [1] [5]

Thumb hypoplasia type 2.png
Type II
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Type III-A
Thumb hypoplasia type 3b.jpg
Type III-B
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Type IV
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Type V

Cause

The cause is unknown, and likely related to genetic abnormalities.Children with Fanconi anemia can sometimes display hypoplasia of the thumb.[ citation needed ]

Diagnosis

Three main points in diagnosing thumb hypoplasia are: width of the first web space, instability of the involved joints and function of the thumb. [5] Thorough physical examination together with anatomic verification at operation reveals all the anomalies. [1] [5] An X-ray of the hand and thumb in two directions is always mandatory. [5] When the pediatrician thinks the condition is associated with some kind of syndrome other tests will be done. [1] More subtle manifestations of types I and II may not be recognized, especially when more obvious manifestations of longitudinal radial deficiency in the opposite extremity are present. Therefore, a careful examination of both hands is important. [3]

Treatment

When it comes to treatment it is important to differentiate a thumb that needs stability, more web width and function, or a thumb that needs to be replaced by the index finger. [4] Severe thumb hypoplasia is best treated by pollicization of the index finger. [3] [5] Less severe thumb hypoplasia can be reconstructed by first web space release, ligament reconstruction and muscle or tendon transfer. [3] [5]

It has been recommended that pollicization is performed before 12 months, but a long-term study of pollicizations performed between the age of 9 months and 16 years showed no differences in function related to age at operation. [3]

It is important to know that every reconstruction of the thumb never gives a normal thumb, because there is always a decline of function. [4] When a child has a good index finger, wrist and fore-arm the maximum strength of the thumb will be 50% after surgery in comparison with a normal thumb. [3] [4] The less developed the index finger, wrist and fore-arm is, the less strength the reconstructed thumb will have after surgery. [3] [4]

Related Research Articles

Finger Organ of manipulation and sensation found in the hands of humans and other primates

A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates. Normally humans have five digits, the bones of which are termed phalanges, on each hand, although some people have more or fewer than five due to congenital disorders such as polydactyly or oligodactyly, or accidental or medical amputations. The first digit is the thumb, followed by index finger, middle finger, ring finger, and little finger or pinkie. According to different definitions, the thumb can be called a finger, or not.

Polydactyly Physical anomaly involving extra fingers or toes

Polydactyly or polydactylism, also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly.

Median nerve Nerve of the upper limb

The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus.

Arthrogryposis congenital joint contracture in two or more areas of the body

Arthrogryposis multiplex congenita (AMC), or simply arthrogryposis, describes congenital joint contracture in two or more areas of the body. It derives its name from Greek, literally meaning "curving of joints".

Flexor pollicis brevis muscle muscle of the upper limb

The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three thenar muscles. It has both a superficial part and a deep part.

The flexor pollicis longus is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus.

In human anatomy, the abductor pollicis longus (APL) is one of the extrinsic muscles of the hand. As the name implies, its major function is to abduct the thumb at the wrist. Its tendon forms the anterior border of the anatomical snuffbox.

Adductor pollicis muscle muscle of the upper limb

In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique.

Opponens pollicis muscle muscle of the upper limb

The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb. It is one of the three thenar muscles, lying deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis.

Pollicization is a hand surgery technique in which a thumb is created from an existing finger. Typically this consists of surgically migrating the index finger to the position of the thumb in patients who are either born without a functional thumb or in patients who have lost their thumb traumatically and are not amenable to other preferred methods of thumb reconstruction such as toe-to-hand transfers.

Amastia refers to a rare clinical anomaly in which both breast tissue and nipple are absent. Amastia can be either isolated or complicated with other syndromes such as ectodermal dysplasia, syndactaly and lipoatrophic diabetes. This abnormity can be classified into various types and each could cause different pathologies. Amastia differs from amazia and athelia. Amazia refers to the absence of one or both mammary glands but the nipples remain present. While athelia refers to the absence of one or both nipples, but the mammary gland remains.

Muscles of the hand

The muscles of the hand are the skeletal muscles responsible for the movement of the hand and fingers. The muscles of the hand can be subdivided into two groups: the extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm. The intrinsic group are the smaller muscles located within the hand itself. The muscles of the hand are innervated by the radial, median, and ulnar nerves from the brachial plexus.

Median nerve palsy

Injuries to the arm, forearm or wrist area can lead to various nerve disorders. One such disorder is median nerve palsy. The median nerve controls the majority of the muscles in the forearm. It controls abduction of the thumb, flexion of hand at wrist, flexion of digital phalanx of the fingers, is the sensory nerve for the first three fingers, etc. Because of this major role of the median nerve, it is also called the eye of the hand. If the median nerve is damaged, the ability to abduct and oppose the thumb may be lost due to paralysis of the thenar muscles. Various other symptoms can occur which may be repaired through surgery and tendon transfers. Tendon transfers have been very successful in restoring motor function and improving functional outcomes in patients with median nerve palsy.

Triphalangeal thumb

Triphalangeal thumb (TPT) is a congenital malformation where the thumb has three phalanges instead of two. The extra phalangeal bone can vary in size from that of a small pebble to a size comparable to the phalanges in non-thumb digits. The true incidence of the condition is unknown, but is estimated at 1:25,000 live births. In about two-thirds of the patients with triphalangeal thumbs, there is a hereditary component. Besides the three phalanges, there can also be other malformations. It was first described by Columbi in 1559.

Congenital clasped thumb human disease

Infant’s persistent thumb-clutched hand, flexion-adduction deformity of the thumb, pollex varus, thumb in the hand deformity.

Ectrodactyly deficiency or absence of one or more central digits of the hand or foot

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 (ectrodactyls) are often described as "claw-like" and may include only the thumb and one finger with similar abnormalities of the feet.

Radial dysplasia Radial hemimelia is a congenital longitudinal deficiency of the radius bone of the forearm characterized by partial or total absence of the radius

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 stiffness 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.

Muscles of the thumb

The muscles of the thumb are nine skeletal muscles located in the hand and forearm. The muscles allow for flexion, extension, adduction, abduction and opposition of the thumb. The muscles acting on the thumb can be divided into two groups: The extrinsic hand muscles, with their muscle bellies located in the forearm, and the intrinsic hand muscles, with their muscles bellies located in the hand proper.

Linburg–Comstock variation is an occasional tendinous connection between the flexor pollicis longus and the flexor digitorum profundus of the index, the middle finger or both. It is found in around 21% of the population. It is an anatomical variation in human, which may be viewed as a pathology if causes symptoms. It was recognised as early as the 1800s, but was first described by Linburg and Comstock in 1979.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Riley, S.A. & Burgess, R.C. (2009). Thumb Hypoplasia. Journal of Hand Surgery, vol 34A, 1564–1573
  2. 1 2 3 4 5 6 7 8 9 10 11 12 Ashbaugh, H. & Gellman, H. (2009). Congenital Thumb Deformities and Associated Syndromes. Journal of Craniofacial Surgery, vol 20, number 4, 1039–1044
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Manske, P.R. & Goldfarb, C.A. (2009). Congenital Failure of Formation of the Upper Limb. Hand Clinics, 25, 157 – 170
  4. 1 2 3 4 5 6 7 8 9 10 Hovius, S., Foucher, G. & Raimondi, P.L. (2002). The Pediatric Upper Limb. London, United Kingdom: Informa Healthcare
  5. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Light, T.R. & Gaffey, J.L. (2010). Reconstruction of the Hypoplastic Thumb. Journal of Hand Surgery, vol 35A, 474 – 479