Friction Coefficients: Arthritis is Not a Disease; It’s a Mechanical Failure

Why treating your body well pays dividends... and how to do it.

We have a language problem in medicine. We tell patients they “have” arthritis, as if it’s a virus they caught or a genetic curse they inherited. We treat it like a disease.

But as an engineer, I don’t see a disease. I see a mechanical failure.

Your knees didn’t just “get old.” They failed because the load vectors crossing the joint were out of tolerance. They failed because the coefficient of friction, which in a healthy joint is five times slicker than ice on ice, was compromised by eccentric loading.

You aren’t sick. You are misaligned.

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The Physics of Failure

In a study we published on femoral stem fixation (Inadequate Metadiaphyseal Fill of a Modern Taper-Wedge Stem), we looked at what happens when an implant doesn’t perfectly match the geometry of the bone.

When a hip stem is undersized or misaligned, it doesn’t just sit there. It subsides. It moves. The axial load of walking isn’t transferred evenly; it creates shear forces that destroy the interface between metal and bone.

The exact same physics applies to your native knee.

A healthy knee is designed to distribute load across two compartments (medial and lateral). It is an optimized load-bearing system. But if you have a slight varus (bow-legged) deformity, you are no longer distributing load evenly. You are point-loading the medial compartment.

It’s the difference between driving a car with perfect alignment and driving one where the tires are angled inward. It doesn’t matter how expensive the tires are; they will blow out after 10,000 miles. That isn’t “tire disease.” That is mechanical reality.

Tolerance Stacking

In engineering, we talk about “tolerance stacking,” when small deviations in multiple parts add up to a catastrophic failure.

In the human machine, arthritis is often the result of tolerance stacking:

1. Static Alignment: You have a mild structural deformity (varus/valgus).

2. Dynamic Weakness: Your glutes are weak, causing your femur to rotate internally during gait.

3. Excess Load: You are carrying an extra 30 pounds.

Individually, the system might handle these. Stacked together, they exceed the material properties of the cartilage. The friction coefficient skyrockets. The surface degrades.

We call this “Osteoarthritis.” I call it Cycle-Dependent Fatigue Failure.

Re-Engineering Your Chassis

Why does this distinction matter? Because you can’t “cure” a mechanical failure with a pill. You have to fix the mechanics.

If you want to preserve your joints (or your replacement joints), you have to think like a structural engineer.

• Reduce the Axial Load: Every pound of body weight places 4 to 6 pounds of force on the knee joint. Losing 10 pounds isn’t just cosmetic; it reduces the mechanical load on your knees by 40,000 to 60,000 pounds per mile walked. That is massive structural relief.

• Balance the Tension: Your muscles are the guy-wires holding the mast straight. If your quadriceps are weak or your hamstrings are tight, the joint tracks poorly. You are grinding the gears every time you take a step. Strengthening the “engine” (muscle) protects the “chassis” (bone).

• Respect the Envelope: Just like the implants I design, your joints have a specific range of motion where they function optimally. Pushing them repetitively outside that envelope, through poor form in the gym or bad posture at your desk, is asking for failure.

The Bottom Line

Stop waiting for a “cure” for arthritis. The cure is physics.

If you treat your body like a machine that requires alignment, lubrication, and load management, you can extend its warranty significantly. If you ignore the mechanics, you will eventually end up on my operating table.

And while I am very good at replacing the parts, the original equipment, when properly maintained, is still the best engineering on the planet.

R. Michael Meneghini, MD

If you liked this, share it with someone who complains about their “bad knees” but hasn’t looked at their mechanics. Next, I’m discussing “The ‘Rust’ Inside Us”, why inflammation is actually biological corrosion.

Thanks for reading The Incision Point! Subscribe to help disrupt the status quo.