Being concise is the key!!! They're trying to see if you really have interest in Osteopathic Medicine.
Besides, you'll get your opportunity to shine during your secondaries.... Trust me, they'll have room for you then. That was my first reaction to the primary application, but completely did a 180 once I saw the secondary apps questions.... Unlike, most allopathic schools, osteopathic med school do do an initial screening, thus you have to show in your primary statement that there is interest in the profession.... I'm not an expert, just my two cents....
Anyway, just wanted to let you know that you'll get your opportunity come secondaries to tell more. Good luck to your application and such...