Secondary service connection under 38 CFR 3.310 allows a veteran to establish service connection for a condition that was caused or aggravated by an already service-connected disability. This is one of the most powerful and underutilized tools in VA claims strategy.
There are two types of secondary connection. Causation means the service-connected condition directly caused the new condition — for example, a service-connected back injury causing radiculopathy in the legs. Aggravation means the service-connected condition permanently worsened a non-service-connected condition beyond its natural progression — for example, service-connected knee instability aggravating pre-existing arthritis in the same knee.
To establish secondary service connection, you need: (1) a current diagnosis of the secondary condition, (2) evidence that the primary condition is already service-connected, and (3) a medical nexus opinion stating that the primary condition caused or aggravated the secondary condition, using the "at least as likely as not" standard.
Common secondary connections that veterans should consider include: depression or anxiety secondary to chronic pain conditions; radiculopathy secondary to spinal conditions; sleep disturbance secondary to PTSD or chronic pain; peripheral neuropathy secondary to diabetes; erectile dysfunction secondary to diabetes, medications, or PTSD treatment; migraines secondary to TBI; and knee or hip conditions secondary to altered gait from a service-connected foot or ankle condition.
The aggravation theory requires establishing a baseline level of the secondary condition before the aggravation occurred. The VA should rate the secondary condition at its current level minus the baseline — meaning the veteran is compensated only for the degree of worsening attributable to the service-connected condition.
A private nexus opinion specifically addressing secondary service connection is often the strongest evidence you can submit. The opinion should explain the medical mechanism by which the primary condition caused or worsened the secondary condition.
Note: This article references sections of the VA's M21-1 Adjudication Procedures Manual. The VA periodically reorganizes the M21-1 and section numbers may have changed since this article was written. For the most current section references, visit the VA's public M21-1 Web Automated Reference Material System (WARMS).