Injuries to a specific region can result in more than one diagnosis. The AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Sixth Edition, states that, in most cases, only one diagnosis in a region (eg, hip, knee, or foot/ankle) is appropriate. If a patient has two significant diagnoses (eg, ankle instability and posterior tibial tendonitis), the examiner should use the diagnosis with the highest impairment rating in that region that is causally related. The rationale for this principle is that the rating for the diagnosis with the highest impairment also encompasses the functional loss of diagnoses with lesser impairment; it also attempts to prevent the use of multiple diagnoses to inflate the impairment rating. In the Case Example, a 62-year-old female teacher was tripped and fell on her left knee at work; the diagnoses were osteoarthritis and medial collateral ligament sprain. Despite activity modification and extensive treatment, she reported only moderate improvement; an orthopedic surgeon was consulted and recommended total knee replacement (TKR), but the patient declined and decided to retire with the option to consider TKR later, if necessary. Causation is an issue because tricompartmental arthritis clearly was not caused by the fall, but one wonders about the role of the individual's arthritis is unclear. Evaluators should be aware that such apportionment varies by jurisdiction.