DC 5276Musculoskeletal SystemLast verified: APR 22, 2026

Secondary Conditions for Flatfoot, acquired

Flatfoot, acquired is a service-connected condition that can cause or aggravate 6 additional disabilities under 38 CFR § 3.310. Common secondaries include Achilles Tendinitis / Tendinopathy, Posterior Tibial Tendon Dysfunction (PTTD), Shin Splints / Medial Tibial Stress Syndrome (MTSS). Each secondary requires medical nexus evidence linking it to the primary, documented in treatment records or a private nexus letter.

“Disability which is proximately due to or the result of a service-connected disease or injury shall be service connected.”
— 38 CFR § 3.310(a), Disabilities that are proximately due to, or aggravated by, service-connected disease or injury
Evidence Strength:STRONGMODERATEEMERGING

Which secondary conditions are most common after Flatfoot, acquired?

EMERGING

Medical Rationale

Service-connected pes planus produces a biomechanical chain of compensation that ultimately stresses the lumbar spine. Excessive subtalar pronation → tibial internal rotation → femoral internal rotation → anterior pelvic tilt → lumbar lordosis exaggeration. The increased lumbar lordosis from foot pronation increases compressive load on the posterior lumbar facet joints and intervertebral discs. Gait studies using pressure-sensitive insoles confirm that subjects with bilateral pes planus have significantly increased lumbar paravertebral muscle EMG activity compared to subjects with normal foot arches, as the muscles work harder to stabilize an unstable kinetic chain base. Long-term, this sustained paraspinal muscle overactivation produces myofascial pain, facet arthropathy, and accelerated disc degeneration.

Key Studies

Brantingham JW et al. (2012) J Manipulative Physiol Ther (foot orthotics and lumbar outcomes); Lee JH et al. (2015) J Phys Ther Sci (pes planus and lumbar spine); Bird AR et al. (2003) Gait Posture (arch height and pelvic mechanics); Menz HB et al. (2013) Rheumatology (foot disorders and low back pain).

Filing Tips

Standing full-spine radiograph can document the cascading alignment changes from flat foot to pelvis to lumbar spine. Lumbar MRI or X-ray documenting degenerative changes. Because this is an emerging-evidence nexus, a detailed Independent Medical Opinion (IMO) from a physiatrist or chiropractor experienced in kinetic chain analysis is important. Records of custom orthotics use and podiatry records supporting the pes planus diagnosis provide the foundation.

MODERATE

Medical Rationale

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.

Key Studies

Tiberio D (1987) Phys Ther (subtalar pronation and tibial rotation); Powers CM et al. (1996) J Orthop Sports Phys Ther (foot pronation and patellofemoral stress); Reilly DT & Martens M (1972) Acta Orthop Scand; Levinger P et al. (2010) Clin Biomech (pes planus and knee OA).

Filing Tips

Weight-bearing foot X-rays documenting pes planus (loss of medial longitudinal arch, hindfoot valgus). Knee X-rays or MRI documenting medial compartment arthritis or patellofemoral degeneration. A podiatrist or orthopedic surgeon nexus letter linking the arch collapse mechanism to knee joint loading is the critical evidence. Orthotics prescription records confirming treatment for pes planus support the flat feet diagnosis.

MODERATE

Medical Rationale

Pes planus creates excessive forefoot loading and abnormal metatarsal head pressure distribution during the push-off phase of gait. The pronated foot position causes hypermobility of the first ray and transfers weight laterally to the second and third metatarsal heads, compressing the interdigital nerves (particularly the third common digital nerve between the 3rd and 4th metatarsal heads). This chronic compression and traction on the nerve produces perineural fibrosis — Morton's neuroma. The collapsed medial arch also increases transverse metatarsal arch loading, further narrowing the intermetatarsal spaces. Pedobarographic studies show 40-60% higher peak pressures under the 2nd and 3rd metatarsal heads in pes planus compared to normal arches.

Key Studies

Roddy E et al. (2008) J Foot Ankle Res (foot deformity and forefoot pain); Wu KK (1996) J Foot Ankle Surg (Morton neuroma pathophysiology); Nix SE et al. (2012) J Foot Ankle Res (forefoot pressure distribution and arch height).

Filing Tips

Ultrasound or MRI documenting interdigital neuroma or metatarsal head pathology. Podiatrist nexus letter addressing the forefoot pressure redistribution from flat feet. Document numbness, burning, or shooting pain in the forefoot with weight-bearing. VA rates under DC 5279 (metatarsalgia, anterior) — typically 10%. If Morton's neuroma requires surgical excision, document post-surgical residuals for additional rating consideration.

STRONG

Medical Rationale

Pes planus causes excessive and prolonged pronation during the stance phase of gait, which places abnormal tensile and torsional loads on the Achilles tendon. The calcaneal eversion associated with flat feet increases the medial bowstringing force on the Achilles, creating non-uniform stress distribution across the tendon cross-section. This asymmetric loading exceeds the tendon's collagen remodeling capacity, leading to insertional tendinopathy, paratenon thickening, and intratendinous degeneration. Biomechanical studies using force plates and motion capture demonstrate 23-35% greater peak Achilles tendon strain in flat-footed individuals compared to neutral arch controls. Military populations with pes planus and high physical demands (running, rucking, jumping) have accelerated tendon degradation.

Key Studies

Kaufman KR et al. (1999) Med Sci Sports Exerc (biomechanical analysis of arch height and injury); Becker J et al. (2017) J Orthop Res (Achilles strain in overpronators); Van Ginckel A et al. (2009) Br J Sports Med (Achilles tendinopathy risk factors).

Filing Tips

MRI of the Achilles tendon documenting tendinosis, partial tear, or peritendinitis. Podiatrist or orthopedic nexus letter addressing the biomechanical chain from flat feet to abnormal Achilles loading. Document custom orthotics prescribed for pes planus — this demonstrates the VA already recognizes the foot dysfunction. VA rates Achilles tendinitis under DC 5024 (tenosynovitis) based on limitation of motion and pain.

STRONG

Medical Rationale

The posterior tibial tendon is the primary dynamic arch support structure, and in pes planus it is chronically overloaded as it attempts to maintain medial longitudinal arch integrity against excessive pronation forces. Progressive posterior tibial tendon dysfunction (PTTD) is the natural biomechanical consequence of flatfoot deformity — the tendon undergoes repetitive microtrauma, collagen degeneration, and eventual elongation or rupture. PTTD follows a staged progression: Stage I (tendinitis without deformity), Stage II (flexible flatfoot worsening), Stage III (rigid flatfoot), Stage IV (valgus tilting of the talus). Military service accelerates this cascade through high-impact training, heavy load carriage, and prolonged standing. PTTD is the leading cause of adult-acquired flatfoot deformity.

Key Studies

Johnson KA & Strom DE (1989) Clin Orthop Relat Res (PTTD staging classification); Myerson MS (1997) Foot Ankle Int (PTTD pathomechanics); Kohls-Gatzoulis J et al. (2004) J Bone Joint Surg Br (PTTD and pes planus progression).

Filing Tips

MRI showing posterior tibial tendon thickening, partial tear, or degeneration. Physical examination documenting positive "too many toes" sign and single-heel-rise inability. Podiatrist or foot/ankle specialist nexus letter is essential — PTTD secondary to pes planus is biomechanically straightforward. Document how military duties (running, marching, rucking) accelerated the tendon degeneration. VA rates under DC 5024; severe cases may qualify for surgical correction with separate rating.

STRONG

Medical Rationale

Pes planus causes excessive pronation that increases traction forces on the deep posterior compartment muscles (tibialis posterior, flexor digitorum longus, flexor hallucis longus) at their tibial periosteal attachments. This repetitive periosteal loading produces medial tibial stress syndrome — periostitis of the posteromedial tibial border. The flat foot morphology also increases ground reaction force transmission through the tibial shaft due to diminished shock absorption from the collapsed arch. Prospective military cohort studies consistently identify pes planus as the strongest independent risk factor for MTSS, with flat-footed recruits showing 3-4x higher incidence during basic training. Chronic MTSS can progress to tibial stress fractures if untreated.

Key Studies

Newman P et al. (2013) Sports Med (risk factors for MTSS — pronation strongest predictor); Yates B & White S (2004) Gait Posture (foot biomechanics and MTSS); Moen MH et al. (2009) Sports Med (MTSS pathophysiology and risk).

Filing Tips

Bone scan or MRI showing periosteal edema along the medial tibial border. Document history of shin pain during military service and continued symptoms. Orthopedic or sports medicine nexus letter connecting flat feet to abnormal tibial loading is well-supported by literature. VA rates under DC 5022 (periostitis) or as analogous to limitation of motion. If chronic, document impact on walking and standing tolerance.

How do I file a secondary service connection claim?

File VA Form 21-526EZ and list the secondary condition as a new claimed disability, noting it is secondary to Flatfoot, acquired. Submit a nexus letter at the time of filing — the VA does not request nexus evidence on your behalf. An effective date of Intent to File (VA Form 21-0966) protects your start date for up to 12 months while you gather medical evidence.

Common Questions About Secondary Service Connection

What is a secondary service-connected condition?

A secondary service-connected condition is a disability that is proximately caused or chronically worsened by an already service-connected condition. The VA rates secondary conditions separately and combines them with the primary rating using the combined ratings table under 38 CFR § 4.25.

What legal standard applies to secondary service connection?

38 CFR § 3.310(a) governs secondary service connection. It states: "Disability which is proximately due to or the result of a service-connected disease or injury shall be service connected." Aggravation claims — where the primary condition worsens a pre-existing disability — are covered under § 3.310(b).

Which secondary conditions are most common after Flatfoot, acquired?

The 6 secondary conditions documented for Flatfoot, acquired vary by evidence strength. The most strongly supported include: Achilles Tendinitis / Tendinopathy, Posterior Tibial Tendon Dysfunction (PTTD), Shin Splints / Medial Tibial Stress Syndrome (MTSS). Evidence strength reflects the volume and quality of medical literature linking each secondary to the primary condition.

What evidence proves a secondary condition is caused by the primary?

The most reliable evidence is a private nexus letter from a treating physician or independent medical examiner that: (1) acknowledges the service-connected primary condition, (2) diagnoses the secondary condition, and (3) states to at least a 50% probability ("as likely as not") that the primary caused or aggravated the secondary. Treatment records documenting the progression are supporting evidence, not a substitute.

How does the VA rate secondary conditions?

Secondary conditions are rated under the same 38 CFR Part 4 diagnostic codes as any other condition. The VA then combines the primary and all secondary ratings using the combined ratings formula under § 4.25 — not simple addition. For example, a 50% primary and a 30% secondary combine to 65% (rounded to 70%), not 80%.

How do I file a secondary service connection claim?

File VA Form 21-526EZ and list the secondary condition as a new claimed disability, specifically noting it is secondary to your already service-connected primary condition. Submit a nexus letter and all relevant treatment records at the time of filing. If your primary claim is already decided, you can file for the secondary as a new claim at any time — the effective date will be the date of the new claim.

Can I add secondary conditions to an existing claim after it has been decided?

Yes. Secondary conditions can be added at any time as a new claim. The effective date for the secondary will generally be the date VA receives your new claim (or the date of an Intent to File, if filed within the preceding 12 months). If the secondary was improperly denied in an earlier rating decision, a Supplemental Claim or Higher-Level Review may allow an earlier effective date.

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