The Knee and the Canary In the Coal Mine
What is shared by the knee and the canary in the coal mine?
Both are small. Both are delicate. And both give a warning of danger in the environment.
For most of the 20th century, canaries were used by coal miners to reflect the health of the air in the mine. Then in the mid-1980s they were retired, officially replaced by “digital noses.” The knee, though, carries on. It reflects the health of the whole body.
The knee is a joint, one of many, important because they are the place where movement occurs.
What kind of movement do joints allow?
Since we live in a three-dimensional world, there are three possibilities: forward/back, left/right and up/down.
The type of joint determines which possibility takes place. The knee, for instance, has a single possibility. Functioning like a hinge, with the hinge set horizontally, it allows movement forward and back. And nothing more. In Engineer Speak, the knee has one degree of freedom. The wrist – if you place your hand right now on the table, you will see – can move so the fingers go side-to-side or up-and-down. But you cannot turn the hand around a central axis at the wrist. So, the wrist has two degrees of freedom. The hip joint gives all three possibilities; thus, it has three degrees of freedom. The ankle is similar to the wrist. The vertebrae of the spine are similar to the hip joint in having three degrees of freedom, though, depending on the location within the spine, usually two of the three are preferred.
Ha! It’s complicated.
“Degrees of freedom” becomes significant when you reflect on all the bumps and twists that the body goes through in any type of action, and the more so, in any type of rough action. This need-for-adjustments should be met by those versatile joints that have multiple degrees of freedom. But when those joints get gunked up and stiff – through lack of use – the demand for accommodation is channeled to the ever-faithful, single degree-of-freedom knee. And it suffers.
The way to improvement, with or without knee replacement, is to restore mobility to the rest of the body. Those other joints must be given opportunities to move so they can fulfill their own proper obligations. Then the knee can breathe freely.