What must be demonstrated for a secondary service connection to be established?

To establish a secondary service connection, it is essential to demonstrate a causal relationship between the primary and secondary conditions. This means that the secondary condition must result from or be aggravated by a service-connected primary condition. For instance, if a veteran has a service-connected disability such as a knee injury that leads to complications like arthritis in a nearby joint, the arthritis may be considered secondary to the primary condition. The critical factor is showing that there is a direct link in causation, which allows the veteran to receive benefits for the secondary condition as a result of the primary service-connected disability.

Other options do not correctly represent the requirements for a secondary service connection. Establishing a direct relationship to service pertains more to primary connections, where a disability is directly tied to military service. Evidence of treatment during service relates to how a claim is substantiated but does not pertain to the causal connection needed for secondary service connections. Likewise, while a recommendation from a medical provider can support a claim, it is not a necessary requirement for establishing secondary service connection on its own.