Dogs typically carry 60 percent of their body wt on the front end so if there is a rear leg problem even more wt goes to the shoulders and neck thus causing secondary issues there. The pelvis has 2 important joints called the Sacroiliac Joints which allow your dog to walk, run, get up, sit down etc. Commonly these Sacroiliac joints lock up in motion thus inhibiting your dog from easily jumping up or down as well as walking and running. If the right side is locked in motion then the left front leg typically sees the affects since dogs walk and move in a diagonal. The neck aka cervical spine will also be affected since the muscles of the front leg tie into the neck.
Typically your vet will not be able to diagnose this since they are not trained in spinal biomechanics so the usual meds for pain and inflam will be given and the issue goes untreated.
Please call Dr Bruce at 781-337-1180 or email at firstname.lastname@example.org