Musculoskeletal System Practice Questions

Functions and Composition of the Skeletal System

• Functions of the Skeleton: The skeletal system provides more than just structure; its primary functions include:

  • Support: Providing a framework for the body.

  • Protection: Shielding internal organs from injury.

  • Movement: Acting as a lever system for muscle attachment and locomotion.

  • Mineral Storage: Serving as a reservoir for critical minerals, specifically storing approximately $99\%$ of the body’s calcium and the majority of its phosphorus.

  • Hematopoiesis: The production of blood cells, which occurs within the red marrow.

• Bone Remodeling: Bone is a living tissue that undergoes constant reconstruction. This process is managed by two primary cell types:

  • Osteoblasts: Cells responsible for building new bone tissue and forming the bone matrix.

  • Osteoclasts: Cells involved in the breakdown and resorption of bone tissue.

  • Lifespan: Bone remodeling does not stop after growth; it continues throughout an individual's entire life.

• Bone Count and Development:

  • Adult Skeleton: Contains exactly $206$ bones.

  • Infant Skeleton: Contains approximately $270$ bones. The higher count in infants is due to the presence of separate bones that eventually fuse during growth, particularly in the skull, sacrum, and coccyx.

Skeletal Divisions and Regional Anatomy

• Axial Skeleton: Consists of $80$ bones located along the central axis of the body. Key components include:

  • Skull: Contains $28$ total bones, subdivided into $8$ cranial bones, $14$ facial bones, and $6$ auditory ossicles.

  • Vertebral Column: The adult column contains $26$ bones ($7$ cervical, $12$ thoracic, $5$ lumbar, $1$ sacrum, and $1$ coccyx).

  • Thoracic Cage: Composed of $25$ bones, including the sternum and $24$ ribs ($12$ pairs).

  • Hyoid Bone: Located in the neck.

• Appendicular Skeleton: Consists of $126$ bones, including the limbs and the girdles that attach them to the axial skeleton.

  • Pectoral Girdle: Includes the clavicle and scapula.

  • Pelvic Girdle: Includes the hip bones (iliac crest is a landmark for ventrogluteal injections).

Detailed Vertebral and Thoracic Anatomy

• Cervical Region: Includes vertebrae $C1$ through $C7$, located in the neck.

• Thoracic Region: Consists of $12$ vertebrae, each of which articulates with a pair of ribs.

• Lumbar Region: Consists of $5$ vertebrae. These have the largest bodies because they bear the greatest amount of body weight. Consequently, they are common sites for low-back strain.

• Thoracic Cage and Ribs:

  • Floating Ribs: These are ribs $11$ and $12$. They are classified as "floating" because they attach posteriorly to the vertebrae but have no anterior attachment.

Classification and Microscopic Structure of Bone

• Bone Types by Shape:

  • Long Bones: Characterized by a shaft and two expanded ends (e.g., femur, humerus).

  • Short Bones: Generally cube-shaped (e.g., carpals in the wrist, tarsals in the ankle).

  • Flat Bones: Thin and often curved (e.g., sternum, ribs, scapulae, cranial bones).

  • Irregular Bones: Have complex shapes that do not fit other categories (e.g., vertebrae).

  • Sesamoid Bones: Embedded within tendons. The patella is the largest sesamoid bone, embedded in the quadriceps tendon.

• Bone Tissues and Growth:

  • Red Marrow: Located within spongy bone, this is the site of hematopoiesis. In adults, it is found in the sternum, ribs, ilium, vertebrae, and the proximal femur.

  • Epiphyseal Plate: The structure responsible for longitudinal bone growth (lengthening). Injuries here in children can interfere with future bone growth.

  • Periosteum: The outer covering of the bone.

Muscle Tissue and Contraction

• Types of Muscle Tissue:

  • Skeletal Muscle: Striated, attached to bone, and under voluntary control.

  • Cardiac Muscle: Striated, involuntary, and unique for its intercalated discs and self-excitable nature (automaticity).

  • Smooth Muscle: Nonstriated, involuntary, and found in the walls of hollow organs, blood vessels, and the gastrointestinal tract.

• Muscle Properties:

  • Excitability: Ability to receive and respond to stimuli.

  • Contractility: Ability to shorten forcibly.

  • Extensibility: Ability to be stretched.

  • Elasticity: Ability of the muscle to recoil and return to its original resting length after being stretched.

• Physiology of Contraction:

  • Neuromuscular Junction: The point where a motor neuron meets a muscle fiber.

  • Acetylcholine (ACh): The neurotransmitter that initiates skeletal muscle contraction by binding to receptors and causing depolarization.

  • Calcium: Released from the sarcoplasmic reticulum, calcium is essential for the interaction between actin and myosin.

  • Origin vs. Insertion: The attachment of a muscle to the more movable bone is the insertion; the attachment to the less movable bone is the origin.

Anatomical Landmarks and Specific Muscles

• Head and Neck:

  • Mandible: The only freely movable bone in the skull; it articulates at the temporomandibular joint.

  • Temporal Bone: The thin squamous portion above the ear is highly vulnerable to fracture and epidural bleeding.

  • Sternocleidomastoid: Rotates the head to the opposite side and flexes the neck.

• Upper Extremity:

  • Radius: Located on the lateral (thumb) side of the forearm.

  • Ulna: Located medially; the olecranon process forms the bony point of the elbow.

  • Deltoid: Large triangular muscle covering the shoulder; used for abduction and small-volume ($\le 1\,mL$) IM injections.

  • Biceps Brachii: Flexes the elbow and supinates the forearm.

• Lower Extremity:

  • Tibia: The larger, medial, weight-bearing bone of the lower leg.

  • Fibula: The smaller, lateral bone of the lower leg.

  • Calcaneus: The largest tarsal bone (the heel), and a common site for pressure injuries.

  • Quadriceps Femoris: Composed of the rectus femoris and three vastus muscles; it is the primary muscle for knee extension.

  • Gastrocnemius and Soleus: These calf muscles insert into the calcaneus via the Achilles (calcaneal) tendon to allow for plantarflexion.

Pathophysiology and Clinical Conditions

• Spinal Curvatures:

  • Scoliosis: Lateral curvature of the spine.

  • Kyphosis: Exaggerated thoracic curve (humpback).

  • Lordosis: Exaggerated lumbar curve (swayback).

• Osteoporosis: Characterized by reduced bone density. Risk reduction includes weight-bearing exercise and adequate intake of calcium and vitamin D. Clinical signs include loss of height and thoracic kyphosis.

• Infections and Autoimmune Disorders:

  • Osteomyelitis: A bacterial bone infection causing pain, fever, and swelling.

  • Myasthenia Gravis: Autoimmune destruction of acetylcholine receptors, leading to muscle weakness that worsens with activity and improves with rest.

  • Muscular Dystrophy: A group of progressive, inherited diseases causing the degeneration of skeletal muscle fibers.

• Arthritis and Gout:

  • Osteoarthritis: Degenerative joint disease characterized by pain in weight-bearing joints that worsens with activity and improves with rest.

  • Rheumatoid Arthritis: Inflammatory condition; acute flares are managed with rest, heat, and gentle range of motion.

  • Gout: Caused by uric acid deposition; patients should avoid high-purine foods like organ meats and shellfish.

Nursing Care and Emergency Management

• Fractures and Healing:

  • Stages: $1.$ Hematoma formation (bleeding), $2.$ Hard callus formation, $3.$ Remodeling.

  • Types: Open (compound) fractures pierce the skin and carry high infection risks. Greenstick fractures are incomplete breaks common in children due to flexible bones. Pathologic fractures occur in bones weakened by disease (e.g., osteoporosis).

• Acute Complications:

  • Fat Embolism Syndrome: Occurs within $24-72\,hours$ after a long-bone or pelvic fracture. Symptoms include dyspnea, chest pain, confusion, and a petechial rash.

  • Compartment Syndrome: Indicated by pain unrelieved by opioids and pain with passive stretch. Early neurovascular signs are pain and paresthesia; late signs include pulselessness, paralysis, and dusky extremities with capillary refill > 3 seconds.

• Injury Management (RICE): For acute soft-tissue injuries (sprains), use Rest, Ice, Compression, and Elevation for the first $24-48\,hours$.

• External Immobilization and Traction:

  • Cast Care: Handle new plaster casts with palms to prevent indentations; allow to air dry uncovered; do not insert objects.

  • Skeletal Traction: Weights must hang freely and never be lifted or removed without an order. Ropes must stay in pulleys.

Body Mechanics and Patient Safety

• Lifting Technique: Always bend at the hips and knees to use leg strength, keep the load close to the body, and avoid twisting the spine.

• Pressure Injury Prophylaxis:

  • Supine: Monitor sacrum and heels.

  • Sitting: Monitor ischial tuberosities.

  • Side-lying: Monitor greater trochanter, lateral malleolus, and ear.

• Immobility Risks: Prolonged bed rest leads to disuse atrophy, joint contractures, foot drop (prevented by high-top boots or foot-support devices that maintain dorsiflexion), and bone demineralization.

Pharmacological Administration

• Intramuscular (IM) Injection Sites:

  • Infants (< 12 months): Vastus lateralis is preferred.

  • Adults (Irritating/Large Volume): Ventrogluteal is preferred due to muscle mass and safety from nerves.

  • Small Volume/Vaccines: Deltoid (maximum volume $1\,mL$).

• Administration: All IM injections should be given at a $90$-degree angle.

Terminology and Movement

• Directional Terms:

  • Proximal: Closer to the trunk or point of attachment.

  • Anterior: Toward the front of the body.

• Joint Movements:

  • Flexion: Decreasing the joint angle.

  • Extension: Increasing the joint angle.

  • Abduction: Moving away from the midline.

  • Adduction: Moving toward the midline.

  • Supination: Turning the palm upward.

  • Pronation: Turning the palm downward.

  • Dorsiflexion: Pulling toes toward the shin.

  • Plantarflexion: Pointing toes downward.

  • Inversion: Turning the sole of the foot inward (medially).

  • Circumduction: Circular, cone-shaped movement (combination of flexion, abduction, extension, and adduction).