How to determine the Professional direction?

As a surgeon,I have worked for about 10 years.Now,I am an orthopaedist and my major is spine.As we know,the field of spine surgery,the Sub-professional of spine has cervical spine,upper cervical spine,lumbar spine,scoliosis,MISS(minimally invasive spine surgery ),and so on.

I am confused that how to determine the sub-professional direction?

How do you think about the question？