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
Carpal bones or "distal surfaces" are articular, the superior generally convex, the inferior concave; the "medial" and "lateral surfaces" are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated. The structure in all is similar: cancellous tissue enclosed in a layer of compact bone. Occasionally accessory bones are found in the carpus, but of more than 20 such described bones, only four (the central, styloid, secondary trapezoid, and secondary pisiform bones) are considered to be proven accessory bones. Sometimes the scaphoid, triquetrum, and pisiform bones are divided into two. The carpal bones are ossified endochondrally