Then last month, I stumbled into the modulus of elasticity.
It sounded to me like a place on the far side of the Neutral Zone - the kind of place where descendants of the wrathful Khan might hide out to do mortal battle with James Tiberius Kirk and the crew of the U.S.S. Enterprise.
As it turns out, the modulus of elasticity is a scale for measuring the bendability - the elasticity - of a metal.
Dr. Matt Pigott told me about it.
He’s a surgeon with Springfield Orthopaedic and Sports Medicine Institute.
I asked him, because a recent experience made me curious about the pins, screws and other hardware with which bone doctors put Humpty back together again.
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And, during that experience, I saw a poster announcing his arrival said Pigott “has been published in the American Society for Testing and Materials Journal and the Journal of Surgical Orthopedic Advances.
I also asked him because I thought he might be more reliable than my friend Denny, who told me the screw he saw on a friend’s X-ray sure looked a lot more like a wood screw than a metal screw.
As annoying as it is, Denny appears to have been right.
“There are some that are more like wood screws, and some that look more like metal screws,” Pigott told me.
At $20 to $50, the screws surgeons use can’t compete in price with the ones at Lowe’s and Home Depot. But they do come in many threads, sizes, lengths and pitches.
And bone doctors love their screws as much as the old guys of my youth who stored all their nuts, bolt and screws in glass jars hanging from screw-on lids mounted on 2-by-4s above their work benches.
“Screws are our main tools,” the good doctor told me. “They’re useful in most situations.”
They’re sometimes “the sole implant to hold bone fragments together.” Other times they hold plates to bone, keep nail implants from rotating, anchor joint replacement implants and “can even act as rebar in cement constructs.”
Rebar. Cool.
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Pigott also told me the screws are produced along a span of the modulus of elasticity. The softer or more elastic ones are made of titanium and its alloys, the harder of cobalt, chrome and stainless steel.
As for pins?
Apparently they don’t like to be called pins.
They prefer the term “temporary fracture fixation wires.” Pigott said they “are usually stainless steel (so they won’t bend) and act like skewers to hold bone fragments in relative alignment during healing.”
In short, they are center stage at many a bone-kabob.
“The most common ways to use pins,” Pigott said, “are to hold a fracture for 6-8 weeks while it heals and then remove them once the bone is strong enough to hold itself.”
Done with that, I asked him questions that would allow me to be hip on replacement hips.
The replacements, he told me, use a combination of materials.
The socket or cup within which the ball rotates is made of a hard metal and is attached to the pelvis. The liner of the cup, where the action is, is made of polyethylene, a plastic.
The ball, which fits into the cup, is made of cobalt, chrome or ceramic; all three materials slide smoothly against the plastic liner of the socket or cup, which makes for a lasting relationship.
The stem that leads out of the ball and eventually attaches to the femur is also made of titanium alloy, because its strength is closest to that of bone. But at the point where it attaches to the femur bone, things get interesting.
So that the bone and the stem will bond strongly together, the surface of the stem that attaches to the femur bone is lined with a porous titanium coating, with a sponge-like surface - though still made of titanium.
Blood naturally fills the spongey structure after surgery, then turns into scar tissue, Pigott said. And the scar tissue stimulates cells in the bone to migrate into sponge-shaped area. In time, calcium follows, and, in the end, “cements” the bone and plate together.
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Whoda thunk it?
Dr. Pigott’s research, by the way, had to do with suspected problems with all-metal replacement hips. At one time, they were thought to be the best kind for young people because the strength of the metal could withstand the remaining years of their lives.
But there was a problem. The metal-on-metal contact caused tiny metal shavings that could potentially cause problems. The body recognized the shavings as being foreign material and sent lymphocytes to devour them.
Not unlike Klingons, “The lymphocytes got angry,” Pigott said. Only rarely did the anger result in patient symptoms like ear ringing and pain syndromes. More often, there was vasculitis or inflammation of the blood vessels in the area and sometimes caused “pseudo tumors.”
His research, done at the University of Pittsburg Medical Center, was to determine whether any of the young patients who had such replacement hips there ever returned for surgical repair.
“None in our series had to be redone,” he said.
Once Pigott settles in, he hopes to compile statistics of surgeries done at Ohio Valley so that results there can contribute to the large number of cases needed for researchers to study what works best in the joint replacement world.
A final note.
As a rule, I don’t trust anyone who isn’t totally geeked out about something.
Dr. Pigott met my standard with flying colors.
In a career of 40 years and climbing, he’s the only person ever to confess to me that he’s geeked out about “hind foot bio mechanics” - that is, the way the area near the heel works in working and absorbing the stresses of carrying weight around for its entire life.
So, you ask, how does one get geeked out about hind foot biomechanics?
During the course of his studies, “I had good mentors,” he told me.
And I’m sure they’re all very well-heeled.
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