Our five-year-old son has a bump on the tip of his finger and he can’t seem to straighten the joint. The pediatrician is sending us to an orthopedic surgeon for an evaluation. What could be causing something like this in a child so young?

No doubt you will soon have an answer to that question. The surgeon’s examination will likely include X-rays or some other type of imaging to see what’s affecting the bone and joint.

Two common problems that present with joint deformity and loss of motion in children are undiagnosed displaced (and possibly even healed by now) fracture or bone overgrowth. One of the most common causes of bone overgrowth in children is a benign bone tumor called osteochondroma.

Benign means the tumor isn’t cancerous and won’t travel elsewhere in the body causing harm. But it’s not benign in the sense that the loss of motion can affect hand function. And the deformity can lead to painful, limiting osteoarthritis.

The surgeon will also another possible diagnosis called Trevor disease. That’s a developmental disorder with excessive bone growth — usually just on one side of the bone. With any of these conditions, when the joint is involved, it is called an intraarticular (within the joint) problem. When the bone is affected without the joint, it is referred to as extraarticular (outside and not including the joint).