The musculoskeletal system and medical assisting care

Assisting with the musculoskeletal system

Orthopedics is the healthcare specialty that deals with most skeletal disorders and associated muscle, joint, and ligament conditions. An orthopedist is a physician who is specially trained to diagnose and treat skeletal system disorders. Some orthopedists specialize in certain areas of the body, such as hand, ankle, and foot injuries. An orthopedic surgeon is a specially trained physician who medically, surgically, and physically treats musculoskeletal disorders. Podiatry is the branch of medicine that deals with the diagnosis, treatment, and prevention of foot disorders. A podiatrist is a physician who specializes in treating the foot and ankle.

Rheumatology is a specialty that deals with disorders of connective tissue, including bone and cartilage. Rheumatology also deals with many diseases that are classified as autoimmune disorders. A rheumatologist is a physician who specializes in internal medicine and rheumatology. A rheumatologist treats patients with diseases of joints, muscles, bones, and tendons.

Musculoskeletal system diseases and disorders are common in an ambulatory care facility. When they are not seen in the orthopedic department, patients with musculoskeletal concerns are seen in primary care and urgent care settings.

The anatomy of the skeletal system

The musculoskeletal system (MS) consists of bones, joints, muscles, and supportive connective tissues (cartilage, tendons, and ligaments). The musculoskeletal system is responsible for the following functions:

• Body movement
• Protection, support, and framework for the organ systems of the body
• Storage for important minerals such as calcium and phosphorus
• Continually forming new blood cells by the process of hematopoiesis, which occurs in the red bone marrow inside some bones. Red blood cells, white blood cells, and platelets are all made in the bone marrow.

In this chapter, the discussion of the anatomy, physiology, and pathology of the musculoskeletal system is divided into the skeletal system and the muscular system. Human bones appear in a variety of shapes and sizes that suit their function in the body. Bones generally are categorized by shape:

• Flat bones protect internal organs. Examples include the cranium, ribs, and sternum.

• Short bones provide stability with their cube shape. Examples include carpals and tarsals.

• Long bones support weight and help with movement. Examples include the humerus, radius, femur, and tibia.

  Irregular bones have an irregular shape and help protect internal organs. The vertebrae are an example of irregular bones.

• Sesamoid bones are embedded in the tendons and help protect the tendons. The patella is the largest sesamoid bone in the body.

The human skeleton is composed of more than 200 bones. Bones are divided into two categories: the axial skeleton and the appendicular skeleton.

Axial skeleton

The axial skeleton is composed of 80 bones:

• The skull is made up of the following structures:
  • Cranium, which encloses and protects the brain. The eight bones that make up the cranium include the frontal, parietal (2), temporal (2), occipital, sphenoid, and ethmoid bones.
  • Facial bones, which include the mandible and vomer bone, and two each of the following bones: nasal, zygomatic, lacrimal, palatine, inferior nasal conchae, and maxillary (also called the maxilla or upper jawbone)
  • Ossicles, or the three small bones of the middle ear that transmit sound vibrations from the eardrum to the inner ear. The small bones include the malleus (hammer), incus (anvil), and stapes (stirrup)
  • The hyoid bone, in the neck above the larynx, is the attachment point for the extrinsic tongue muscle and other mouth muscles.
• The spinal or vertebral column is divided into five regions: cervical, thoracic, lumbar, sacral, and coccygeal. The spinal column is composed of 26 vertebrae. Soft disks filled with a jelly-like substance are between the vertebrae to cushion and keep them in place.
• The rib cage is made up of these structures:
  • Sternum (breastbone), which is made up of the manubrium, body, and xiphoid process.
  • Seven pairs of true ribs, which attach to the sternum by costal cartilage.
  • Five pairs of false ribs. The first three pairs of false ribs attach to the seventh rib and indirectly to the sternum by costal cartilage. The last two pairs of false ribs are called floating ribs because they are not attached in the front of the body.

The ribs, thoracic vertebral column, and sternum form the thorax.

Image 052 Image of Axial Skeletal bones and appendicular bones

Appendicular skeleton

The appendicular skeleton is composed of 126 bones. It can be divided into the upper and lower extremities.

The upper extremities are made up of these structures:

• Clavicle (collarbone).
• Scapula (shoulder blade); the acromion process is the lateral tip of the scapula. The acromion process is used as a landmark when injections are given in the deltoid muscle.
• Humerus (upper arm bone).
• Radius and ulna (lower arm bones). The radius is the bone on the thumb side, and the ulna is the little finger side of the forearm.
• Carpals (wrist bones), metacarpals (in the palm of the hand), and the phalanges (finger bones).

The lower extremities are made up of these structures:

• Pelvic girdle (coxal bone), which includes the ilium, ischium, and pubis. The male pelvis is deep and narrow. The female pelvis is broad and shallow. The pelvic inlet is wider to accommodate the birth of the baby.
• Femur (thigh bone), which is the longest and heaviest bone in the body. The greater trochanter is a protrusion near the neck of the femur. The greater trochanter is used as a landmark when ventrogluteal injections are given.
• Patella (kneecap), which is the largest sesamoid bone.
• Tibia (shin bone) and fibula (lower leg bone). The tibia is larger and stronger than the fibula, which is on the outer side of the leg. The protrusions on the ankle are as follows:
• Medial malleolus, part of the tibia and located on the inner side of the ankle
• Posterior malleolus, part of the tibia and located on the back of the ankle
• Lateral malleolus, part of the fibula and located on the outer side of the ankle
• Tarsals, which form the heel and the posterior side of the foot. The tarsals include the calcaneus (heel bone), talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and the lateral cuneiform.
• Metatarsals (feet bones) and the phalanges (toe bones).

Anatomy of long bones

The outer covering of a long bone is called the periosteum, and the inner lining is called the endosteum. The long bone is composed of the following parts:

• Diaphysis: The long shaft, which is made of hard, compact bone.
• Medullary cavity: The hollow space inside the diaphysis. Yellow bone marrow is found in the medullary cavity. Yellow bone marrow is a soft, gelatinous tissue that consists mostly of fat cells and a small amount of primitive blood cells.
• Epiphysis: The end of the long bone, which is made of spongy bone. The epiphysis is covered with articular cartilage and is attached by ligaments to the epiphysis of another bone, forming a joint. Articular cartilage reduces the stress of weight bearing and the friction of movement. The thickness of the cartilage depends largely on the amount of stress placed on a particular joint.
• Metaphysis: The narrow strip between the diaphysis and epiphysis. The metaphysis contains the epiphyseal plates (also called growth plates). This is where bone growth normally occurs.

Compact bone is made up of structural units called osteons. Osteons are composed of osteocytes (bone cells) and calcified matrix. The matrix stores phosphorus and calcium for the body to use. The nutrient foramina are small passageways that contain blood vessels that supply osteocytes with nutrients.

Joints

Bones are connected to each other at junctions known as joints (articulations). The range through which a joint can extend and flex is called its range of motion (ROM). Joints can be classified by their ROM:

• Synarthroses: Immovable (no ROM) joints held together by fibrous cartilaginous tissue. An example of this joint is the suture lines of the skull.
• Amphiarthroses: Limited ROM joints, which are joined together by cartilage that is slightly movable. Examples of these joints include the vertebrae and the pubic bones of the pelvic girdle.
• Diarthroses (or synovial joints): Full ROM joints. Examples include the hinge joints in the knee and the ball-and-socket joint in the hip. The following section will provide more details on diarthrotic joints.

Diarthrotic joints

Many of the diarthroses, or synovial joints, have bursae. Bursae are sacs of synovial fluid located between the bones of the joint and the tendons that hold the muscles in place. Bursae help cushion and support the joints when they move. Synovial joints also have joint capsules that enclose the ends of the bones. A synovial membrane lines the joint capsules. This membrane secretes synovial fluid that lubricates the joint. Joints also have cartilage that covers and protects the bone. The meniscus consists of crescent-shaped cartilage in the knee joint that also cushions the joint. Ligaments are strong bands of white, fibrous connective tissue that connect one bone to another at the joints.

There are six classifications of diarthroses (or synovial joints). Each type has its own unique movement:

• Hinge joint: Permits flexion and extension. Examples include the elbow, knee, and finger joints.
• Pivot joint: Permits rotation. Examples of pivot joints include the joint found between the atlas and the axis (first and second cervical vertebrae) and the joint between the ulna and radius.
• Saddle joint: Allows for flexion, extension, and other movements. An example is the thumb crossing over the palm of the hand.
• Condyloid joint: Permits flexion, extension, and circular motion. An example would be the movement of the atlas.
• Ball-and-socket joint: Allows free movement (rotation). Examples include the shoulder and hip joints.
• Gliding joint: Allows a bone to slide over another bone. This occurs in the wrist and between the vertebrae.

Physiology of the skeletal system

The skeletal system has several important roles in the body:

• Protecting, supporting, and providing a framework for organ systems of the body
• Helping with movement
• Developing new bone
• Regulating the blood calcium level
• Hematopoiesis, the formation of blood cells and platelets

Development of new bone

Between the periosteum and the endosteum, the osteoclasts and osteoblasts continuously remodel bones. The osteoclasts are bone cells that break down bone. The osteoblasts, bone-forming cells, make the bones strong, durable, and able to heal. Because bones have a good blood supply, they easily heal after trauma or a break (fracture).

When a fracture occurs, a protective blood clot and callus form at the break. During the healing process, new bone cells start to grow on both sides of the break. Eventually, the new bone from both sides meets, closing the fracture, and the callus is absorbed.

Regulation of the blood calcium level

About 98% of the body’s calcium is stored in the bones. Calcium is moved between the blood and bones through the work of the osteoblasts and osteoclasts. It is removed from the blood as the osteoblasts form new bone. This lowers the blood calcium level. When the osteoclasts break down bone, calcium is released into the blood, thus increasing the blood calcium level.

Two hormones work to maintain the blood calcium level. The parathyroid hormone from the parathyroid gland increases the activity of the osteoclasts when the blood calcium level is decreased. Calcitonin, which is produced in the thyroid, helps lower the blood calcium level. Calcitonin promotes bone formation by the osteoblasts and inhibits the bone breakdown by the osteoclasts.

Hematopoiesis

Spongy bone is found at the center of most bones. It is less dense than compact bone and has a network of open spaces that contain red bone marrow. The red bone marrow is a soft, gelatinous tissue that consists of blood stem cells. These stem cells can become white or red blood cells or platelets.

Musculoskeletal disorders are common in primary care, urgent care, orthopedics, and rheumatology departments. Medical assistants help the provider with examinations, diagnostic procedures, and treatments.