Knee Pain / Medial Compartment Osteoarthritis Secondary to Pes Planus (Flat Feet)

Yes. Under 38 CFR § 3.310(a), any disability proximately caused or chronically worsened by a service-connected condition is itself service-connected. Knee Pain / Medial Compartment Osteoarthritis is a documented secondary pairing for Pes Planus (Flat Feet) with moderate medical evidence. A nexus letter from a qualified physician linking the two conditions is the most reliable way to establish this connection.

The gold standard is a private nexus opinion stating — to at least a 50% probability ("at least as likely as not") — that the secondary condition was caused or aggravated by the primary service-connected condition. Peer-reviewed medical literature supporting the physiological mechanism strengthens the nexus. Treatment records documenting the onset or worsening of the secondary condition in temporal relation to the primary are supporting evidence.

The VA rates Knee Pain / Medial Compartment Osteoarthritis separately under its own 38 CFR Part 4 diagnostic code, then combines it with Pes Planus (Flat Feet) and all other service-connected ratings using the combined ratings formula under § 4.25. The formula applies the whole-person concept: a 50% combined existing rating plus a new 30% rating yields 65% (rounded to 70%), not 80%.

38 CFR § 3.310(a) states: "Disability which is proximately due to or the result of a service-connected disease or injury shall be service connected." The aggravation variant under § 3.310(b) applies where the primary condition permanently worsens a pre-existing disability beyond its natural progression. Both standards require a showing of nexus — a medical or scientific link between the primary condition and the secondary.

The medical evidence supporting Knee Pain / Medial Compartment Osteoarthritis as secondary to Pes Planus (Flat Feet) is rated moderate. Bilateral or unilateral pes planus (flat feet) is a recognized cause of knee pain and osteoarthritis through the lower extremity kinetic chain. Excessive subtalar pronation from collapsed medial longitudinal arches causes obligatory tibial internal rotation during stance, which shifts the knee from a neutral position into valgus and internal rotation. This altered mechanical alignment increases medial compartment joint stress and lateral patellofemoral contact pressure. Finite element analysis of gait in subjects with pes planus documents a 5–18% increase in medial knee compartment loading compared to normal-arch controls. Over years of ambulation, this supraphysiologic medial compartment loading accelerates articular cartilage degeneration at the knee.

The VA will not solicit nexus evidence on your behalf for secondary claims. In practice, a written nexus opinion from a private physician or independent medical examiner is essential — the VA's Compensation & Pension (C&P) examiner is not required to produce a favorable nexus opinion, and the VA has discretion to weigh competing opinions. Submitting a private nexus letter at the time of filing is the most reliable strategy.