By Dr. Drew Brennes, D.C. — The Nexus Letter Doctor
TL;DR — Quick Answer: A service-connected foot or ankle injury rarely stays "just" a foot or ankle injury. Over years of walking on a compromised base of support, the body develops compensatory movement patterns — altered gait — that transmit abnormal loads upward through the knees, hips, and low back. These compensatory loads cause measurable, durable damage to adjacent joints. The peer-reviewed orthopedic and biomechanical literature has thoroughly documented this cascade, and the VA's own secondary service connection framework (38 C.F.R. § 3.310) explicitly recognizes it. If you have a service-connected lower extremity condition and are now experiencing knee, hip, or back symptoms, you likely have a valid secondary claim. This article explains the science, the timeline, and the claim framework.
Every veteran who's had a service-connected ankle, foot, or lower-extremity condition for more than a few years eventually notices the same thing: the pain doesn't stay where it started. The bad ankle starts to affect the knee. The knee starts to affect the hip. The hip starts to affect the low back. What was one problem becomes three or four.
If that describes you, you're not imagining it. You're experiencing what orthopedic and biomechanical scientists call compensatory kinetic chain loading — the well-documented process by which dysfunction at one lower-extremity joint alters gait mechanics. It transmits abnormal stress to joints proximal (upward) and, sometimes, distal (downward) to the primary site of injury.
This isn't a fringe theory. It's foundational biomechanics, and it's why the VA's secondary service connection framework under 38 C.F.R. § 3.310 exists in the first place. This article walks through the science, the timeline, and how it maps onto VA secondary claims — so you understand what's happening in your body and what claim framework applies to your situation.
The lower extremity — foot, ankle, knee, hip, pelvis, and low back — is not a set of independent joints. It is a coupled kinetic chain. Every joint in the chain influences the mechanical environment of every other joint during standing, walking, and running.
When the chain is functioning normally, the loads produced by ground contact during gait are absorbed and distributed evenly. The foot rolls through pronation and supination. The ankle dorsiflexes and plantar flexes. The knee flexes and extends with rotational coupling. The hip rotates and abducts. And the pelvis and lumbar spine make small, symmetric adjustments to maintain balance.
When one joint in the chain is compromised — by chronic instability, tendonitis, ligamentous laxity, arthritis, or pain avoidance — the whole chain reorganizes to compensate. That reorganization is what biomechanists call altered gait kinematics, It is the mechanism by which a single service-connected lower extremity injury eventually damages the joints above and below it.
An injured or unstable ankle changes the way you walk in several measurable ways:
Each of these mechanisms is small on any given step. But an average adult takes 5,000 to 10,000 steps per day. Over years and decades of walking with compromised mechanics, small compensatory changes accumulate into structural damage at the adjacent joints.
For more on how a chiropractor evaluates altered gait mechanics and articulates the biomechanical case in a nexus letter, see Can a Chiropractor Write a Nexus Letter?
Once gait is altered by a foot or ankle disability, the mechanical consequences propagate upward through the kinetic chain. The specific pathologies that develop are predictable:
Contralateral compensation. When one side is chronically painful, the opposite limb is chronically overloaded. This is why unilateral primary conditions frequently produce bilateral secondary claims — the "good" leg wears out from having to do more of the work.
For veterans dealing with the aftermath of an ankle or foot service-connected condition, this cascade is the biomechanical explanation for the "everything hurts now" phenomenon that so many veterans describe.
The short answer: it varies, but expect years to decades before adjacent joint damage becomes clinically obvious.
The compensatory kinetic chain load is small on any single step. But it's cumulative. The typical timeline looks something like this:
The takeaway: if it's been years since your primary lower-extremity injury and your knees, hips, or back are now hurting, that is not coincidence. It is the expected biomechanical consequence of walking on a compromised base of support for that long.
Here's a subtlety that often makes or breaks a secondary claim: bilateral distribution of the primary condition typically produces bilateral distribution of the secondary condition.
When only one ankle is affected, the compensation pattern is asymmetric — The opposite limb takes more load. As a result, the secondary condition often develops most severely on the contralateral (opposite) side. When both ankles are affected — which is the case for many veterans with bilateral service-connected ankle disabilities from years of running, marching, or jumping in service — the compensation is symmetric. Both knees, both hips, and the midline low back all take the increased load simultaneously.
If you have a bilateral primary condition and are developing bilateral secondary symptoms, that bilateral-to-bilateral correspondence is powerful evidence of the compensatory kinetic chain mechanism at work. It's not degenerative aging (which is usually asymmetric). It's the biomechanical fingerprint of your primary condition operating symmetrically through the chain.
The kinetic chain mechanism I've described is not something I invented. It is thoroughly documented in the peer-reviewed orthopedic, biomechanical, and rehabilitation literature. Some of the foundational citations include:
These are foundational, widely cited papers. When a well-drafted secondary-claim nexus letter cites this literature and applies it to a specific veteran's clinical picture, it is not stating opinion or speculation. It is applying settled biomechanical science to the facts of the case.
The VA's own regulatory framework explicitly recognizes the secondary service connection concept. 38 C.F.R. § 3.310 provides that a disability that is "proximately due to or the result of a service-connected disease or injury" is itself service-connected. Aggravation of a non-service-connected condition by a service-connected condition is also compensable, with the level of compensation reflecting the degree of aggravation.
The three-prong test for secondary service connection was articulated by the United States Court of Appeals for Veterans Claims in Wallin v. West, 11 Vet. App. 509 (1998):
For a gait-compensation-driven secondary claim, the nexus is the biomechanical mechanism described in this article, supported by peer-reviewed literature, applied to the specific facts of your case. A well-drafted nexus letter walks the rater through each of the three prongs with objective evidence.
For more on the CFR 38 framework generally, see 38 CFR Explained: The Rulebook Every Veteran Should Know About Before They File a Claim.
2026 Update — §3.310 Causation Standard: Effective May 1, 2026, the VA updated the M-21-1 secondary service connection causation framework following Spicer v. McDonough. Nexus letters for secondary claims must now explicitly satisfy a "but for" standard under both 38 CFR §3.310(a) (causation) and §3.310(b) (aggravation). See The VA Changed the Rules on Secondary Claims: What the New 'But For' Standard Means for Your Nexus Letter (2026) for the full breakdown of what changed and how it affects kinetic chain secondary claims.
Many veterans who develop secondary joint pathology hear the same discouraging feedback: "It's just pain. There's no diagnosis, so there's no disability." That framing is legally outdated.
In Saunders v. Wilkie, 886 F.3d 1356 (Fed. Cir. 2018), the United States Court of Appeals for the Federal Circuit held that pain, in and of itself, can constitute a compensable disability under 38 U.S.C. § 1110 when the pain causes functional impairment of earning capacity.
Practically, this means that "bilateral knee pain" or "bilateral hip pain" — with documented functional impairment on walking, sleeping, or stair-climbing (as measured by the Patient Specific Functional Scale or similar tools) — is a compensable disability, even if the treating provider hasn't attached a pathological diagnosis like osteoarthritis or meniscal tear. If your VA physical therapist or primary care provider has documented pain plus functional impairment, that meets the current-disability element of the Wallin three-prong test.
Don't let a rater or a C&P examiner talk you out of a valid claim by saying "it's just pain." Saunders is settled law.
Based on my experience writing nexus letters for veterans, these are the most common gait-compensation-driven secondary claim pathways:
| Primary (Service-Connected) | Secondary Claim | Mechanism |
|---|---|---|
| Bilateral ankle instability / tendonitis | Bilateral knee pain, medial compartment stress | Altered frontal-plane gait → medial knee loading |
| Bilateral ankle instability / tendonitis | Bilateral gluteal tendinopathy / greater trochanteric pain syndrome | Reduced base of support → hip abductor overload |
| Unilateral ankle injury | Contralateral (opposite) knee or hip pathology | Compensatory overload of the unaffected limb |
| Chronic plantar fasciitis / foot pain | Knee, hip, or low back pain | Altered foot mechanics propagating upward through the chain |
| Pes planus (flat foot) | Knee patellofemoral pain, gluteal tendinopathy | Overpronation → altered tibial and femoral rotation |
| Service-connected knee | Ipsilateral hip, low back, or contralateral knee | Antalgic gait → asymmetric loading upward and across |
| Service-connected hip | Low back, contralateral hip, or knee | Pelvic asymmetry → lumbar and cross-limb overload |
If your situation is in this table, your secondary claim has a biomechanically valid pathway. What remains is documenting the current diagnosis (or Saunders-qualifying pain with functional impairment), tying it to peer-reviewed literature, and articulating the mechanism for the rater in a well-drafted nexus letter.
A strong secondary-claim nexus letter, in my view, does the following:
The letter also needs to be written by a medical provider whose training and licensure are within scope for the claim. For most gait-compensation secondary claims involving the lower extremity kinetic chain, a chiropractor whose training is squarely in musculoskeletal biomechanics is well within scope. For claims involving intra-articular imaging findings or surgical candidacy, an orthopedic surgeon's opinion may carry additional weight.
For more on what separates a strong nexus letter from a weak one, see What Makes an Effective Nexus Letter.
No. Secondary service connection has no time limit. Some of the strongest secondary claims are filed 15, 20, or 30 years after the primary injury, when the adjacent joint pathology has become clearly documented. The longer you have been ambulating on a compromised base of support, the more the cumulative biomechanical damage supports the claim.
That denial almost always reflects the absence of a properly drafted nexus letter — not the absence of a valid claim. Under the framework described in this article, virtually every gait-compensation-driven adjacent joint claim has a valid biomechanical pathway. A supplemental claim or Higher-Level Review supported by a nexus letter that cites the peer-reviewed literature and applies the Wallin three-prong test to your specific facts is the typical path forward. For more on the denial-and-appeal process, see Why VA Claims Get Denied (and How to Fix It).
Not necessarily. Age-related changes and gait-driven degeneration coexist. The relevant question under 38 C.F.R. § 3.310 is whether your service-connected primary condition has caused or aggravated beyond its natural progression the current adjacent joint pathology. A well-drafted nexus letter addresses age-related contribution honestly, then explains why the primary condition has aggravated the natural progression — often through the bilateral-symmetry principle discussed above, or through documented onset timing, or through the specific pattern of findings (e.g., disproportionately advanced medial compartment involvement in a young veteran).
Sometimes, but not fatally. If obesity or diabetes are themselves secondary to a service-connected condition (for example, medication-associated weight gain from SSRI treatment of service-connected depression, or pain-driven inactivity), they can be secondary predicates in a multi-step framework recognized by VAOPGCPREC 1-2017 (obesity as an intermediate step). A well-drafted nexus letter addresses these factors explicitly rather than pretending they don't exist.
If you're not sure whether to file, a free consultation with a nexus letter provider can help you decide. I offer a free records review before any invoicing — if I look at your records and don't think a nexus letter will move your claim, I say so before any money changes hands. See Why I Offer Free Nexus Letter Consultations.
Yes. Gait compensation and adjacent joint damage from lower extremity kinetic chain dysfunction are squarely within a chiropractor's scope of training and practice. Most of the peer-reviewed literature cited above is authored by physical therapists, biomechanists, and orthopedic surgeons, but the underlying subject matter — musculoskeletal biomechanics — is core chiropractic training. For more on this, see Can a Chiropractor Write a Nexus Letter?
A nexus letter provides the medical opinion connecting the primary and secondary conditions. A DBQ (Disability Benefits Questionnaire) documents the severity of the secondary condition for rating purposes. Most secondary claims benefit from both — a nexus letter to establish service connection, and a DBQ (either from your VA C&P exam or from an independent examiner) to establish the rating percentage. For more, see DBQ vs Nexus Letter: What's the Difference and Why Both Matter for Your VA Claim.
Three things you can do this week:
The kinetic chain is real. Gait compensation causes durable damage to adjacent joints over time. The VA's own secondary service connection framework was written precisely to compensate veterans for this cascade. If you have a service-connected lower extremity condition and are now dealing with knee, hip, or back symptoms, the science is on your side.
This article is for informational purposes only and is not legal or medical advice. It is intended to help veterans understand the biomechanical basis of secondary service connection claims for lower extremity kinetic chain conditions. Always verify any provider's credentials and consult with your treating providers about your specific medical situation.
