Structure and function are highly interrelated. You may have heard the adage “form follows function”; in anatomy, it is often said in reverse—that structure determines function. The directions and degrees of joint movement are determined by many factors: One is the specific shapes of the two articulating bones, where they meet each other. A clear example is seen at the elbow.
The Elbow’s Joint Movement Is Limited
The hinge nature of the elbow joint is obvious just from looking at the structure of the articulating bones. The hook shape of the proximal ulna moves around the spool-shaped end of the distal humerus, allowing bending—or flexion—and straightening—known as extension.
The large pointed bony landmark—the olecranon process—at the proximal ulna prevents excessive movement in the opposite direction of flexion, called hyperextension. The normal shapes of the proximal ulna and distal humerus simply don’t allow for much in the way of backward movement beyond straightening the elbow in extension.
Another factor that can limit range of motion at a joint is simply the size of the muscles or the amount of body fat in the area. For instance, if a body builder has a huge biceps muscle, he or she may not be able to fully flex at the elbow. Likewise, people who are obese may not get the typical range of motion at some of their joints, because excess soft tissues are in the way of the movement.
People who can move in ways that most of us cannot—like contortionists, ballet dancers, or yogis—have trained their ligaments and joint capsules to be increasingly more loose or lax by repeatedly stretching those structures over time in a given direction. There’s really no such thing as being double-jointed—people don’t have multiple joints where others just have one.
Instead, these highly flexible people have naturally pliable ligaments, or have relaxed their ligaments by repeated stretching while practicing various movements. They could also have an underlying connective tissue disorder that makes their ligaments loose.
Move Those Joints
On the other hand, joints that don’t get moved and stretched can become increasingly less mobile—like the syndrome known as frozen shoulder, which is medically called adhesive capsulitis. That’s because it causes the capsule to thicken and tighten around the shoulder joint.
Frozen shoulder can occur when the arm is immobilized for a while, like following surgery or after a stroke, or due to painful conditions like a rotator cuff tear. It’s often a vicious cycle, because the more the shoulder hurts, the less the person tends to use it, and the less they use it, the tighter the shoulder gets.
Within reason, joint movement is a use-it-or-lose-it proposition. The good news is that most people can recover with treatment—such as using anti-inflammatory medications, steroid injections into the joint, and physical therapy—but it can take months or even years to resolve.
Still, other joint pathologies, like carpal tunnel of the wrist or pitcher’s elbow, can result from overuse.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Arthritis can also be an overuse syndrome—but that’s only true of regional arthritis, called osteoarthritis. That is what most would call the “wear-and-tear” form of arthritis. Regional means the problem is confined to the area that’s been overused—like arthritis that develops in the hands of someone who has spent a lifetime knitting, cleaning teeth as a dental professional, or playing a musical instrument.
Osteoarthritis can occur in the back and shoulders of a pipefitter, weightlifter, or construction worker. It can also happen in the knees and hips of a nurse or an athlete. So, regional arthritis can come from repetitive use of a body region over a career. That’s the “wear” in the “wear-and-tear” of osteoarthritis—but what about the “tear”?
Osteoarthritis can also follow an injury to a joint—especially if the damage changes the way in which the joint normally moved before it was injured. Let’s say an athlete damages her knee in high school playing volleyball, she could end up getting arthritis in that particular knee as she gets older.
And it isn’t limited to just tearing a ligament—arthritis can follow any injury to a joint. The damage can continue to progress and get so extensive as to erode away the articular disc—if that particular joint has one—and even wear off the articular cartilage on the ends of the bones involved in the joint. This results in bone rubbing on bone to the point of what is called eburnation, which results in a polishing effect on the adjacent surfaces.
What is Systemic Arthritis?
Now, in anatomy and physiology, while regional means “localized”—the opposite of regional is systemic, meaning something—such as a condition—that involves multiple organs or tissues within one or more body systems. Some types of arthritis are systemic varieties—this means they cause pain and disability throughout numerous joints of the musculoskeletal system. But these conditions can also affect other body tissues—especially other connective tissues.
At the root of systemic arthritis is the person’s immune system. These autoimmune disorders, as they’re called, include types such as rheumatoid arthritis, psoriatic arthritis, lupus, ankylosing spondylitis, and juvenile arthritis that affects children. In these conditions, the patient’s immune system turns its ability to attack foreign cells and tissues on the person’s own native cells and tissues. This misguided uptick of the immune system causes widespread inflammation, and the joints affected can vary, depending on the type.
For example, rheumatoid arthritis primarily affects the synovial membrane lining of small joints in the hands and feet, while ankylosing spondylitis affects the spine, pelvis, and rib cage—causing the connective tissues in those areas to ossify and turn to bone. Not only do these conditions damage joints and affect movement, but, depending on the type of systemic arthritis, they can cause anemia, fever, fatigue, gastrointestinal issues, skin problems, and complications of the eyes, kidneys, and lungs.
Common Questions about Joint Movement and Our Lifestyle
Joint movement is affected by many factors. Two examples are the shape of the bones that meet at the joint and the shape of the muscles or body fat that surround a joint.
Frozen shoulder syndrome happens when joint movement at the shoulder is kept at a minimum for too long. This immobility may be caused by surgery, a stroke, or a rotator cuff tear.
Regional arthritis is when joint movement is too much, meaning the joint has been overused.