Carpal coalition the fifth to eighth weeks. The lunate and triquetral bones are the most common carpal bones to fuse together, resulting in a lunotriquetral coalition in 1% of people. 60% of patients with a lunotriquetral coalition will have it bilaterally. Among isolated incidents the capitate and hamate bones are the next most common to fuse followed by the pisiform-triquetrum, trapezium-trapezoid, scaphoid-capitate, and triquetrum-hamate. Carpal coalitions may further be divided into four subtypes: Generally since carpal-carpal fusions do not cause unease or discomfort for the patient, and do not impair wrist function, treatment is not needed. However, in the minority of cases
Supernumerary body part considered to have lost much or all of their original function through evolution. These body parts can be classed as additional to the required functioning of the body. In human anatomy the vermiform appendix is sometimes classed as a vestigial remnant. Prosthesis is an artificial extension that replaces a body part, and cybernetics is the study of computer technology in relation to organisms which can include replacement or additional body parts. Body integrity identity disorder (BIID) is a psychiatric disorder in which a person thinks that they have one or more additional limbs than they should, despite having two arms