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Trigger Finger: Anatomy of a Simple Machine - Part 1

By Alexander Germanis at


Classified by scientists during the Renaissance, a simple machine was defined to be any basic mechanism that used leverage to multiply force on a object. There were six simple machines placed in this category, one of which is used by everyone on a daily basis: the pulley.


Although that simple machine helps make up more complex compound machines, such as a car engine, it also helps operate perhaps the most complex machine of all: the human body.


Nestled within each finger is a system of these simple machines. Dr. Jerome Oakey, a hand and wrist orthopedic surgeon in Bloomington, describes the layout and anatomy of this system, "If you look at your hand, starting at the base of the finger, you'll see three creases,” he begins. “In between those creases, starting below that crease at the bottom of the finger is where the first pulley, called A1, runs. Below the next crease is where the second pulley runs; and at the top crease, just below the tip of the finger, is that third pulley."


The pulleys themselves are comprised of a tissue called fascia — “a similar tissue to gristle in a steak,“ the doctor explains. “The pulley sits on top of the hand bone, or metacarpal, in the palm. So, it's a tunnel comprised of bone on the bottom, and a pulley on the sides and the top.”


"The pulleys have 'ropes' running through them," Dr. Oakey continues. "The 'ropes' are the tendons that move the fingers. Those pulleys help increase the force of a contracture,"or shortening, of the tendon. This means the pulley/tendon machine in each finger multiplies force as a simple machine is meant to do. The leverage or mechanical advantage applied to the pulley system is applied by a set of "muscles way up in the forearm that attach to those tendons," the doctor explains. Their location "helps minimize how much bulk you have in your hand."


The finger pulleys perform another important function, perhaps less obvious, but equally important to normal, everyday function. "They help maintain the position of the tendons against the bones [in the fingers]," says Dr. Oakey, "so when you go to make a fist, the tendons don't bowstring. It makes it a lot easier to hold things if you don't have tendons knocking them out of your hand."


To complete the anatomical layout of the fingers, the doctor adds, "There's a lining around the tendon that allows it to glide past not only the pulley system, but also two other tendons that run through there." That lining or tendon sheath is often the anatomical source of the condition known as trigger finger.


Trigger finger, or stenosing tenosynovitis, is an inflammatory condition in the fingers or thumb of the hand, when the finger will get stuck in a curled position, as if squeezing a trigger. When pried open, the finger will then straighten, like a trigger being released. "What occurs in trigger finger is you get inflammation along the tendon," explains Doctor Oakey. "And you essentially form a knot in the rope as it runs through that pulley. It's one of the most common things that I see."


Although it can affect every digit of the hand, trigger finger most commonly affects the thumb, middle, and ring fingers. More prevalent in women than in men, it also heavily affects diabetics. "Diabetics are a unique population," says the doctor. "They tend to get trigger fingers more frequently, and they tend to have a worse response rate to non-surgical treatment."


This is news for the wary, as the condition can be quite painful, too. "It is one of the most painful things that I see," Doctor Oakey states. "When people have severe hand pain, this is one of the first diagnoses that comes to mind." Fortunately, there are both surgical and non-surgical treatments to follow that diagnosis.


To learn more about trigger finger, its causes, and treatments, read next month's issue of Healthy Cells Magazine.


For more information, you may contact Dr. Oakey at McLean County Orthopedics, 309-663-6461. McLean County Orthopedics treats all types of orthopedic conditions, and offers a comprehensive range of services. our office is located at 2502 E. Empire in Bloomington.


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