25.1: Structure and Function
By the end of this section, you will be able to:
- Identify structures of the musculoskeletal system
- Recognize functions of the musculoskeletal system
- Recall effects of impaired function of the musculoskeletal system
The normal musculoskeletal configuration in individuals allows for normal posture and mobility. Abnormalities, such as genetic, congenital, or as a result from disease or injury, can have effects on musculoskeletal structure and function. Wherever the system is functionally impacted, alterations from normal abilities may be noticed by the affected patient and assessed by healthcare personnel, including postural or mobility variations, traumatic injuries, electrolyte imbalances, or hematologic abnormalities.
An assessment of the musculoskeletal system includes collecting data regarding the structure and movement of the body as well the patient’s mobility. This unit provides an overview of the structure and function of the musculoskeletal system and explores the effects of impaired function.
Structures of the Musculoskeletal System
The musculoskeletal system gives us the ability to move. It is composed of bones, muscles, joints, tendons, ligaments, and cartilage that support the body, allow movement, and protect vital organs (Figure 25.2). The next sections review the anatomy of the musculoskeletal system, including the skeleton, skeletal muscles, tendons, and joints.
Skeleton
The skeleton is composed of 206 bones that provide the internal supporting structure of the body (Figure 25.3). The bone , or osseous tissue , is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body. In the areas of the skeleton where bones move (e.g., the rib cage and joints), cartilage , a semirigid form of connective tissue, provides flexibility and smooth surfaces for movement. The skeletal system is the body system composed of bones and cartilage and performs the following critical functions for the human body:
- supports the body
- facilitates movement
- protects internal organs
- produces blood cells
- stores and releases minerals and fat
The bones of the lower limbs are adapted for weight-bearing support, stability, and walking. The upper limbs are highly mobile with a large range of movements, along with the ability to easily manipulate objects with our hands and opposable thumbs.
It may appear that bones are static, but bone undergoes ossification and resorption throughout the life span. In the early stages of embryonic development, the embryo’s skeleton consists of fibrous membranes and hyaline cartilage. By the sixth or seventh week of embryonic life, the actual process of bone development, or ossification , begins. Bone development continues until about the age of 25 years (Breeland et al., 2023). The three types of cells involved are osteoblasts, osteocytes, and osteoclasts. Osteoblasts are immature bone cells and primarily produce collagen. Osteocytes are mature cells and facilitate new bone development. On the other hand, bones are remodeled by osteoclasts as they resorb or remove existing bone (Figure 25.4). In normal circumstances, this ossification-resorption process is in an appropriate balance; there are situations where this equilibrium is lost, and for example, bone loss becomes excessive—this is explored later in the chapter.
A ligament is a band of tissue that connect bones to one another, provide support and stability, and enhance joint movements. While bones are well supplied with blood, which supplies oxygen and other nutrients, ligaments are not well perfused which makes for a slower healing process for injured ligaments.
Skeletal Muscles
There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. The skeletal muscle produces movement, assists in maintaining posture, protects internal organs, and generates body heat (Figure 25.5). Skeletal muscles are voluntary, meaning a person is able to consciously control them, but they also depend on signals from the nervous system to work properly. Other types of muscles are involuntary and are controlled by the autonomic nervous system, such as the smooth muscle within our bronchioles.
To move the skeleton, the tension created by the contraction of the skeletal muscles is transferred to the tendons, strong bands of dense, regular connective tissue that connect muscles to bones.
This short video illustrates how bones move muscles by the interaction of signals from the neurological system and the contraction of muscle fibers.
Tendons
A tendon is a band of fibrous collagenous tissue that provide a continuation of the muscle sheath to enable muscle attachment to the periosteum of bones (Figure 25.6). Tendons are both flexible and strong, and they enable movement by pulling the bone upon muscle contraction, using a lever action. Tendons also provide some shock absorption, as they take up some of the muscle impact associated with certain activities, such as jumping. The tensile strength of tendons provides resistance to injury, but certain events (e.g., traumatic injury, fluoroquinolone antibiotics) may cause tendon damage or rupture. Similar to ligaments, tendons are not perfused as efficiently as some tissues, so healing after a tendon is injured is a slow process.
Joints
A joint is a location where bones come together. Many joints allow for movement between the bones (Figure 25.7). Synovial joints are the most common type of joint in the body. A synovial joint has a fluid-filled joint cavity where the articulating surfaces of the bones contact and move smoothly against each other.
The articular cartilage is smooth, white tissue that covers the ends of bones where they come together and allows the bones to glide over each other with very little friction. Articular cartilage can be damaged by injury or normal wear and tear. Lining the inner surface of the articular capsule is a thin synovial membrane. The cells of this membrane secrete synovial fluid , a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint.
Some joints are relatively immobile but stable. Other joints have more freedom of movement but are at greater risk of injury. For example, the hinge joint of the knee allows flexion and extension, whereas the ball-and-socket joint of the hip and shoulder allows flexion, extension, abduction, adduction, and rotation. The knee, hip, and shoulder joints are commonly injured and commonly seen in clinical settings.
Functions of the Musculoskeletal System
The musculoskeletal system has five main functions:
- support the body
- facilitate movement
- protect internal organs
- produce blood cells
- store and release minerals and fat
These functions adjust throughout the life span, according to the body’s needs.
Support, Movement, and Protection
Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body. Without the skeletal system, you would be a limp mass of organs, muscle, and skin. Bones also facilitate movement by serving as points of attachment for your muscles. While some bones only serve as a support for the muscles, others also transmit the forces produced when your muscles contract. From a mechanical point of view, bones act as levers, and joints serve as hinges.
Bones also protect internal organs from injury by covering or surrounding them. For example, your ribs protect your lungs and heart, the bones of your vertebral column (spine) protect your spinal cord, and the bones of your cranium (skull) protect your brain (Figure 25.8).
Mineral Storage, Energy Storage, and Hematopoiesis
The most apparent functions of the skeletal system are the gross functions—those visible by observation. Simply by looking at a person, you can see how the bones support, facilitate movement, and protect the human body. On a metabolic level, bone tissue performs several critical functions. For one, the bone matrix acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium and phosphorus. These minerals, incorporated into bone tissue, can be released back into the bloodstream to maintain levels needed to support physiological processes. Calcium ions, for example, are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses.
Bone also serves as a site for fat storage and blood cell production. The softer connective tissue that fills the interior of most bone is referred to as bone marrow . There are two types of bone marrow: yellow marrow and red marrow (Figure 25.9). The yellow marrow contains adipose tissue; the triglycerides stored in the adipocytes of the tissue can serve as a source of energy. The red marrow is where hematopoiesis —the production of blood cells—takes place. Red blood cells, white blood cells, and platelets are all produced in the red marrow. For example, a child who has a history of bleeding, bruising, and fatigue might be tested for a bone marrow disorder.
This video provides an overview of the structure and function of bones and muscles as well as a selection of some of the abnormalities affecting the musculoskeletal system.
Effects of Impaired Function of the Musculoskeletal System
There are approximately 150 different diseases and conditions that affect the musculoskeletal system, and about 1.71 billion people have musculoskeletal conditions worldwide (World Health Organization [WHO], 2022). These conditions are the leading cause of disability (WHO, 2022). Changes to the musculoskeletal system can have physical and psychological effects on a person.
Physical Effects
The musculoskeletal system is susceptible to an array of causes for variance from normal function. Based on the normal functions of the system, the impact on the body is somewhat predictable, considering which aspect of the system is not functioning properly. Physical effects commonly include the following:
- Inflammation: Illness and injury initiate the inflammatory processes. Five classic signs include pain, heat, redness, swelling, and loss of function.
- Pain (acute, chronic, or acute-on-chronic): Pain is the result of several possible musculoskeletal disorders.
- Limited dexterity and decreased mobility: Agility, strength, and movement can be limited by many factors.
- Electrolyte abnormalities: Calcium and phosphorous are stored in skeletal structures; imbalances can affect other electrolytes and overall health status.
- Impaired blood cell production: Altered bone marrow function potentially affects production of blood cells.
- Weakness and fatigue: Lack of energy and strength can result from different sources associated with musculoskeletal function and malfunction.
- Limitations in completing activities of daily living (ADLs): Malfunctions of normal function can impact ADLs in many ways.
Nurse:
Margaret, RN
Clinical setting:
Intensive care unit
Years in practice:
5
Facility location:
Aurora, Colorado
The patient was in his midtwenties; he was a rancher and had been on a tractor when it overturned, tossing him and then landing on top of him. Surprisingly, his musculoskeletal injuries were minor, considering a tractor had toppled onto him: a couple of rib fractures and some scrapes and abrasions. Why were his injuries not worse? When he fell off the tractor, and it ended up over him, he was lying in a pile of manure, which is soft and allowed him to be pushed further down, rather than on a hard surface where any resistance would have had to come from his own body.
However, lying in a pile of manure is not without risks. After all, it is full of bacteria, and he had several open wounds, so the risk for challenges to his immune system were huge. As his nurses, we had to be vigilant for signs of immune response to infection, which were likely to manifest through inflammatory reactions. We assessed him frequently, looking for new developments in the classic signs of inflammation. He was already experiencing loss of function—he had been intubated to address oxygenation issues brought on by the broken ribs, and we monitored for any changes indicating worsening in oxygenation and perfusion. And for the likely source of infection, we watched his wounds—marking regions of swelling and redness in order to identify any advancement of the processes, palpating for local warmth, and watching his face as we touched him, for responses likely to result from pain.
Such vigilance paid off: rising oxygen needs, diminished pedal pulses, falling blood pressure, and spikes in temperature and heart rate alerted us quickly to sepsis. The providers were promptly notified as changes occurred, and orders were thorough to address and support his body through the various physiological reactions involved in a systemic and potentially deadly cascade of events. He survived, and after a lengthy hospital course was transferred to a rehabilitation facility to regain lost muscle strength; after several months, he was discharged back to his ranch.
Any deviation from normal in the intricate functions of the musculoskeletal system can cause significant effects. As presented, traumatic injury, degenerative changes, hematologic changes, and autoimmune disorders are all possible contributors. The subsequent consequences are not limited to physical but often also involve psychological effects.
Psychological Effects
As previously established, musculoskeletal disorders can impact patients through physical deformities or functional changes, and one of the most common issues is pain. Psychological effects of musculoskeletal problems frequently include the following:
- Pain (acute, chronic, or acute-on-chronic): Pain can be the result of many musculoskeletal disorders.
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Reduced participation in activities: This may include the following:
- Society/group events: church attendance, social affairs, shopping, travel
- Employment: may miss work, or need to retire early for psychophysiological reasons
- Weakness: This can be a consequence of several musculoskeletal disorders.
- Anxiety and/or depression: This may be experienced relative to pain and worry about pending procedures, potential missed time at work, or job loss and family strain (Garnæs et al., 2022).
- Insomnia: Sleep can be impacted by many factors, including discomfort or pain, anxiety, or depression (Garnæs et al., 2022).
Scenario: Mr. Adams is scheduled for total knee arthroplasty in a week and is meeting with the orthopedic nurse for preoperative assessment and education. The nurse, Albert, is conscientious about describing key factors of the Enhanced Recovery After Surgery protocol followed by the hospital where Mr. Adams’s will have the surgery. Mr. Adams is wringing his hands and tapping one foot rapidly on the floor.
Nurse: Mr. Adams, I want to go over some things to expect after your knee operation next week. But first, do you have any questions?
Patient: It’s not really a question. I’m really nervous about this operation. I’m afraid I’ll get hooked on pain medicine. But I know it’s going to hurt, what with having my knee cut up.
Nurse: I can see you’re anxious. Let’s see if I can help you be more comfortable about this. Since you’re worrying about addiction, I’ll start with that. You’re right that right after the surgery, you can expect pain, and pain medicine usually includes what we call, “opioids, or narcotics.” While these are drugs that can cause addiction, when you need them, like for the first few days after an operation, and you take them correctly, the chances of becoming addicted are minimal.
Patient: But you see on TV, there are so many addicts in the world. They won’t give me fentanyl, will they?
Nurse: Your team of doctors usually uses a nerve block, which will keep pain under control for the first day or so. This helps you need less pain medicine through your IV, or as a pill. Your nurses will also ask you how your pain is at least every hour, but you can push your call button, and let them know if it gets worse before that, or you need something else. Again, if you take the pain medicine as your doctor prescribes, it is very unlikely to become addicted. It is common to only need a few days of opioids, and you can probably successfully switch to an anti-inflammatory drug like ibuprofen on day three. Maybe just taking the opioid at bedtime for another day or two.
Patient: What about the fentanyl? So much is on the news about there being so many overdoses.
Nurse: Many people worry about this, but that is not the same fentanyl used in the hospital. It is made in questionable ways and places. If you’re given fentanyl, it is made carefully in a laboratory and is as safe as other pain medicines like morphine or Dilaudid. The nurses will also be sure you have ice packs to help with the pain and swelling.
Patient: Oh good, I get so worried about things on the news.
Nurse: That’s one of the reasons for an appointment like this, Mr. Adams.
Scenario follow-up: Albert continues patient education, with more details about how to take pain medicine to keep pain under control. He also reviews recommendations for correct positioning of the operative leg after surgery, and how important it is to ambulate, starting on the same day of the surgery, barring any complications. Albert is careful to include opportunities for Mr. Adams to ask questions and vent his fears and worries. Before completing the appointment, the nurse has Mr. Adams demonstrate understanding the information by teaching the key points to Albert. He is given written information to review.
The psychological effects can become pervasive and invade other aspects of patients’ lives, causing recurrent emotional signs and symptoms. As conditions become more complicated, it can be more difficult to identify the root of the problem and appropriately treat the multiple factors involved. Even medication therapies bring complexity as each drug prescribed or recommended brings its own desired and potentially undesired results.