By Elizabeth A. Murray, Mount St. Joseph University
Lever systems have been used throughout history to gain a mechanical advantage—and enhance the power or speed of a movement—such as to move heavy objects with a wheelbarrow or as used in a tool like a prybar, a bottle opener, or the oar of a boat. Our joints and their movements are also examples of leverage systems.
Lever System in Human Body
The bones serve as the levers—they are the elongated and inflexible parts of the system that move around a joint, which is the fixed point, or fulcrum. To get movement in the leverage system, the effort applied to one end of the lever has to overcome the resistance, or load, at the other end.
In the body, the effort is the force generated by muscle activity, since bones and joints can’t move themselves. The resistance is the weight of the body part distal to the fulcrum and any added weight on that body part, like a dumbbell in hand or a heavy box that one is carrying.
Prosthetic Joints
Of all of the elements of the musculoskeletal system, joints are the only components that are readily and frequently replaced by artificial substitutes, known as prosthetic joints. When a joint is worn out, a person might be a good candidate for arthroplasty, that’s the medical term for the surgical installation of a prosthetic joint.
Recent estimates indicate that each year, in the US alone, there are about 700,000 knee replacements and about 400,000 total hip replacements. One source suggests, “Total joint arthroplasty is one of the most cost-effective and successful interventions in medicine.”
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
History of Joint Replacement Surgery
The history of joint replacement surgery goes back to the 1800s in the United States, but so-called total joint replacements didn’t begin until about the 1970s. In those days, there were many limitations on how long the replacements might last, and different body sizes in patients weren’t so easily accommodated—some of the early models were one-size-fits-all.
Since then, rates of joint replacements have grown steadily—with many refinements in styles, durability, and success. These have given the human race restored range of motion and a more pain-free lifestyle.
Physical Therapy
Following arthroplasty, physical therapists and other clinicians step in to teach a patient how to safely return to function using their artificial joint—including what movements they can and should do to rehabilitate, as well as which motions the patient should avoid, especially while healing.
But, that’s not the only time people participate in physical therapy. Physical therapists are experts in restoring range of motion in all types of musculoskeletal issues. In fact, some of the basic practices of physical therapists are actually called range of motion activities and might be employed long before a joint replacement surgery or help stall or even prevent the need for arthroplasty. These can be broken down into subgroups, such as passive and active range of motion exercises.
Passive Versus Active Range of Motion Exercise
In passive range of motion exercises, the clinician moves a patient’s body parts when they cannot, whether the patient is immobile from paralysis or other pathology. This hands-on therapy helps loosen stiff joints, relaxes tense connective tissues, and stretches muscles to guide them hopefully back to normal function.
But in active range of motion physical therapy the physical therapist directs the patient to move their body—even if simply starting in bed after surgery. This might involve doing ankle pumps, by repeated dorsiflexion and plantar flexion, or heel slides where the person keeps the heel on the bed, but then alternates between flexion and extension of the knee.
Moving up to the hip, the therapist might have the patient alternate between abduction and adduction of the hip joints by sliding a lower limb laterally, then bringing it back medially. By working from the feet to the knees, and then to the hips, even a person who is bedridden can get blood flow moving and keep their muscles engaged. This will hopefully get the patient back on their feet faster, and out of the hospital quicker after an injury or following surgery.
Restoring Health of the Bodily Levers
Many of us have benefitted from physical therapy to improve range of motion or restore strength to an injured or recovering body part.
Restoring or gaining range of motion isn’t limited to physical therapy, of course, there are other methods like yoga or general stretching to improve the function of our joints and build strength in our muscles.
Common Questions about Prosthetics and Physical Therapy
The bones serve as levers—they are the elongated and inflexible parts of the system that move around a joint, which is the fixed point, or fulcrum. To get movement in the leverage system, the effort applied to one end of the lever has to overcome the resistance, or load, at the other end.
Of all of the elements of the musculoskeletal system, joints are the only components that are readily and frequently replaced by artificial substitutes, known as prosthetic joints. When a joint is worn out, a person might be a good candidate for arthroplasty, that’s the medical term for the surgical installation of a prosthetic joint.
Following arthroplasty, physical therapists and other clinicians step in to teach a patient how to safely return to function using their artificial joint—including what movements they can and should do to rehabilitate, as well as which motions the patient should avoid, especially while healing.
Some of the basic practices of physical therapists are actually called range of motion activities and might be employed long before a joint replacement surgery or help stall or even prevent the need for arthroplasty.
