There are two main types of hereditary symphalangism: SYM1 (Cushing Symphalangism; OMIM #185800) which is stiffness of the PIP joints, the wrist and ankles and deafness. It is passed in an autosomal dominant fashion (50% chance of passing it on) and has been localized on the genome at 17q22. SYM1 There is also a SYM1b (OMIM #615298) has been localized to chromosomal 20q11 and relates to a defect in the GDF5 gene. SYM1b
The other inherited type of symphalangism is SYM2 (Distal Symphalangism, OMIM %185700). This includes stiffness of the DIP joints of the hands and feet. Less is known about this condition but it is also autosomal dominant. SYM2
Traditionally, attempts to surgically improve finger motion in symphalangism have had limited results. However, recently, Baek, et al reported reliably improved motion with surgical release. They also felt surgery in younger children may be more successful. Baek paper
Patients with symphalangism present with a stiff finger (or more than one, finger or toe). On examination, the stiff joint will not have the normal skin creases on the top or bottom. X-rays may appear similar to the normal fingers but often the two bones are fused on x-ray so that there is no joint.
Here is one example of a child with symphalangism and a single, stiff joint.
|Middle finger (long finger) symphalangism. Note the lack of skin creases over the PIP joint.|
|Symphalangism. Note the lack of finger flexion of the middle finger at the PIP joint.|
|The x- rays in symbrachydactyly look normal without clear evidence of the abnormality.|