The commercials for a variety of toning shoes make it look so easy to get in shape.   "I'm toning my muscles, strengthening my core …"  "Proven to tone your  hamstrings …"   But, as more people buy them, Consumer Reports medical adviser Dr. Orly Avitzur is hearing more frequently about injuries.    "One patient was breaking in a pair of toning sneakers, and less than 45 minutes after putting them on felt her ankle turn and a bone break."    Doctor Joel Buchalter, an orthopedic surgeon, says that's no big surprise. He says toning shoes are intentionally designed to create instability.    Dr. Joel Buchalter, "If you take a patient who is elderly or someone who has a balance issue and you put that shoe on them you're looking for disaster."   But even younger people complain of problems, including the physician's assistant in Dr. Buchalter's office who bought some Skechers Shape-Ups.   "I was scrubbed in surgery, wore them for several hours. Had back pain for probably three or four days."