Synostosis

Synostosis is the fusion of two or more bones or cartilaginous elements into a single bone, reducing or eliminating the normal joint space. It can be a normal developmental occurrence in some populations or an abnormal condition arising from disease, injury, or abnormal bone formation. In synostosis, the tissues that normally separate adjacent bones ossify or fuse, leading to restricted movement at the affected site.

Common forms include craniosynostosis, where one or more of the skull sutures fuse prematurely, potentially altering skull shape and, in some cases, contributing to increased intracranial pressure. Other examples are radioulnar synostosis, in which the radius and ulna fuse and forearm rotation is limited, and tibiofibular synostosis, a fusion between the tibia and fibula that can affect ankle or leg mechanics. Vertebral synostosis or block vertebrae are congenital or acquired fusions of adjacent vertebrae that may limit spinal mobility and contribute to scoliosis or other deformities.

Causes and classification reflect the underlying biology: synostosis can be congenital, often associated with genetic syndromes or developmental errors, or acquired, resulting from trauma, infection, inflammatory disease, or heterotopic bone formation after an injury. Diagnosis relies on imaging such as X-ray, CT, or MRI to define the extent and location of fusion.

Management is individualized. Asymptomatic or incidental synostoses may require no treatment, while functional or cosmetic concerns, especially craniosynostosis, may warrant surgical intervention to restore growth potential or motion. Physical therapy and management of associated conditions are part of comprehensive care.