A physiotherapist will check that the degree of bow is within normal limits. The bow can be from several places (thigh to shin, just in the shin, just in the thigh, shin to ankle or all of the above). The degree of bow in each leg should be under a certain degree and symmetrical. There should be no dramatic bow in any one bone. The physiotherpist should also check gross motor skills for age and determine if the leg alignment is having any inpact on development. Bow legs is VERY normal for 17 months and in fact often at it's peak. A paediatrician can refer you to a specialist limb clinic if any of the above applies to your son.
Hope you have had a positive experience with the physiotherapist