Metacarpal synostosis is a rare congenital difference which is characterized by the fusion of 2 (or, in rare cases, more)

metacarpals In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular skeleton, appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones (wrist, wris ...

of the hand, which are usually shortened. It is most commonly seen as a fusion of the

4th Fourth or the fourth may refer to: * the ordinal form of the number 4 * ''Fourth'' (album), by Soft Machine, 1971 * Fourth (angle), an ancient astronomical subdivision * Fourth (music), a musical interval * ''The Fourth'', a 1972 Soviet drama ...

and 5th metacarpals. It is a type of non-syndromic

syndactyly Syndactyly is a condition wherein two or more digits are fused together. It occurs normally in some mammals, but is an unusual condition in humans. The term is . Classification Syndactyly can be simple or complex. * In simple syndactyly, adja ...

synostosis Synostosis (; plural: synostoses) is fusion of two or more bones. It can be normal in puberty (e.g. fusion of the epiphyseal plate to become the epiphyseal line), or abnormal. When synostosis is abnormal it is a type of dysostosis. Examples of ...

. Autosomal dominant and X-linked recessive inheritance patterns have been reported.

Signs and symptoms

The fusion of two or more metacarpal bones is the characteristic feature of this malformation, however this itself causes more symptoms, such as

clinodactyly Clinodactyly is a medical term describing the curvature of a digit (a finger or toe) in the plane of the palm, most commonly the fifth finger (the "little finger") towards the adjacent fourth finger (the "ring finger"). It is a fairly common i ...

, shortening of the fused metacarpal bones, and reduced range of mobility of the fingers supported by the metacarpals.

Complications

There are usually no serious health complications associated with this condition, although severe cases which also involve syndactyly might interfere with hand function.

Causes

The variant of MS that fuses the

and 5th metacarpals is caused by X-linked recessive mutations (alterations or duplications) in the FGF16 gene, in

chromosome X The X chromosome is one of the two sex chromosomes in many organisms, including mammals, and is found in both males and females. It is a part of the XY sex-determination system and XO sex-determination system. The X chromosome was named for its u ...

. It is a feature of various rare disorders such as

Apert's syndrome Apert syndrome is a form of acrocephalosyndactyly, a congenital disorder characterized by malformations of the skull, face, hands and feet. It is classified as a branchial arch syndrome, affecting the first branchial (or pharyngeal) arch, the ...

, and can occur alongside other isolated congenital hand/foot malformations including

cleft hand Ectrodactyly, split hand, or cleft hand () 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 (ectr ...

, metatarsal synostosis, and

polydactyly Polydactyly is a birth defect that results in extra fingers or toes. The hands are more commonly involved than the feet. Extra fingers may be painful, affect self-esteem, or result in clumsiness. It is associated with at least 39 genetic mut ...

. A syndromic form of syndactyly known as ''syndactyly type V'' has metacarpal and metatarsal synostosis as symptoms.

Diagnosis

The following diagnostic methods can be used for metacarpal synostosis: *

Physical examination In a physical examination, medical examination, clinical examination, or medical checkup, a medical practitioner examines a patient for any possible medical signs or symptoms of a Disease, medical condition. It generally consists of a series of ...

Radiographs Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical ("diagnostic" radiography and "therapeu ...

Whole exome sequencing Exome sequencing, also known as whole exome sequencing (WES), is a genomic technique for sequencing all of the protein-coding regions of genes in a genome (known as the exome). It consists of two steps: the first step is to select only the subset ...

Sanger sequencing Sanger sequencing is a method of DNA sequencing that involves electrophoresis and is based on the random incorporation of chain-terminating dideoxynucleotides by DNA polymerase during in vitro DNA replication. After first being developed by Fred ...

Treatment

Treatment for this malformation typically involves the following: 1.

Osteotomy An osteotomy is a surgical operation whereby a bone is cut to shorten or lengthen it or to change its alignment. It is sometimes performed to correct a hallux valgus, or to straighten a bone that has healed crookedly following a fracture. It i ...

(for splitting/separating the synostosic metacarpals) 2.

Bone graft Bone grafting is a type of transplantation used to replace missing bone tissue or stimulate the healing of fractures. This surgical procedure is useful for repairing bone fractures that are extremely complex, pose a significant health risk to the ...

(for lengthening of shortened metacarpals, usually the fifth) 3. Ligament reconstruction 4. Tendon transposition (for the extensor digiti minimi quinti)

Epidemiology

This condition is thought to affect approximately 0.02% to 0.07% of the general population.

Associations

A large family has been described as having nonsense mutations of the FGF16 gene which resulted in metacarpal synostosis and, unexpectedly, in

heart disease Cardiovascular disease (CVD) is any disease involving the heart or blood vessels. CVDs constitute a class of diseases that includes: coronary artery diseases (e.g. angina pectoris, angina, myocardial infarction, heart attack), heart failure, ...

References

{{reflist Congenital disorders of musculoskeletal system