When claiming secondary service connection, is it necessary to demonstrate the secondary condition was incurred during service?

When claiming secondary service connection, the primary focus is on establishing a causal relationship between the secondary condition and an already recognized primary service-connected condition. Unlike direct service connection claims, where the condition must be linked to the veteran's service, secondary connections do not require that the secondary condition was incurred during service itself. Instead, the requirement is to demonstrate that the secondary condition is proximately due to or aggravated by the primary service-connected disability.

This means that as long as there is sufficient medical evidence to show that the secondary condition is a result of the existing service-connected disability, the claim can be valid. For instance, if a veteran is service-connected for a knee injury and subsequently develops arthritis in the other knee due to altered gait from that injury, they can claim secondary service connection for the arthritis without having to prove that the arthritis was directly incurred during military service. The key element is establishing that the secondary condition is a result of the primary service-connected condition.