Final answer:
A geriatric dog with chronic osteoarthritis should be evaluated every six months to monitor their condition and adjust their treatment plan as needed.
Step-by-step explanation:
A geriatric dog with chronic osteoarthritis should be evaluated every six months. Regular evaluations are important to monitor the dog's condition, assess pain levels, and make any necessary adjustments to their treatment plan. By evaluating the dog every six months, the veterinarian can ensure that the dog's arthritis is managed properly and any changes in medication or therapy can be made in a timely manner.