Domain 2.9Anatomy and Physiology

Musculoskeletal System And Common Diseases

Last updated June 16, 2026

Overview

Welcome to your study guide for the Musculoskeletal System! As a Medical Assistant (MA), this domain is essential because a significant number of patient visits relate to pain, injury, or mobility issues.

Why is this critical for your role?

Patient Intake: You will frequently document "Chief Complaints" related to pain, stiffness, and range of motion.
Safety & Mobility: You must know how to safely transfer patients (e.g., wheelchair to exam table) and instruct them on using assistive devices like crutches.
Procedural Assistance: You may assist with splinting, casting, or setting up for joint injections.
Injection Sites: Understanding muscle anatomy is required to safely administer intramuscular (IM) injections (e.g., locating the deltoid).

This guide covers the anatomy of movement, the diseases that limit it, and the diagnostic tools used to evaluate it.

1. Anatomy and Physiology Review

Before diving into diseases, let's review the "normal" structure and function derived from your foundational anatomy knowledge.

Key Structures and Functions

Bones: Provide the framework, protection, and produce blood cells.
- Diaphysis: The shaft of a long bone.
- Epiphysis: The rounded end of a long bone.
- Osteoblasts: Cells that build bone.
- Osteoclasts: Cells that break down bone (resorption).
Muscles: Contract to produce movement and generate heat.
- Microscopic: Actin and Myosin proteins slide past each other to create contraction.
- Neuromuscular Junction: The point where a nerve meets a muscle. The neurotransmitter Acetylcholine is required here to trigger movement.
- Calcium: The essential mineral required for muscle contraction.
Connective Tissues (The "Cables"):
- Tendons: Connect Muscle to Bone (Mnemonic: MTB).
- Ligaments: Connect Bone to Bone.
- Cartilage: Cushioning tissue found between vertebrae and at the ends of bones.

Joint Movements (Kinesiology)

You must use these terms when documenting Range of Motion (ROM).

Term	Definition	Example
Flexion	Decreasing the angle of a joint.	Bending the elbow (bicep curl).
Extension	Increasing the angle of a joint.	Straightening the arm.
Abduction	Moving a limb away from the midline.	Raising arms to the side.
Adduction	Moving a limb toward the midline.	Lowering arms to your side ("Adding" to the body).
Rotation	Turning a body part around its axis.	Turning the head side to side.
Pronation	Turning the palm downward.	Pouring a pitcher of water.
Supination	Turning the palm upward.	Holding a bowl of soup.

2. Diseases of the Bones and Joints

These conditions affect the structural framework of the body.

Osteoarthritis (OA)

Definition: A degenerative joint disease ("wear and tear" arthritis) where the cartilage at the ends of bones wears down over time.
Signs & Symptoms: Joint pain, stiffness (especially in the morning), grating sensation (crepitus), and bone spurs.
Risk Factors: Aging, obesity, previous joint injuries.
Diagnostic Findings: X-rays show narrowed joint spaces and bone spurs.
Treatment: NSAIDs (pain relievers), physical therapy, weight loss, corticosteroid injections, joint replacement surgery (arthroplasty).

Rheumatoid Arthritis (RA)

Definition: A chronic autoimmune disorder where the immune system attacks the synovium (lining of the membranes that surround joints).
Signs & Symptoms: Tender, warm, swollen joints; usually affects the same joint on both sides of the body (symmetrical). Can cause severe joint deformity.
Risk Factors: Family history, smoking, middle age, female gender.
Diagnostic Findings: Blood tests for Rheumatoid Factor (RF) and elevated Erythrocyte Sedimentation Rate (ESR) (indicates inflammation).
Treatment: DMARDs (Disease-Modifying Antirheumatic Drugs), immunosuppressants.

Exam Tip: Osteoarthritis is caused by friction/aging (wear and tear). Rheumatoid Arthritis is caused by the immune system attacking the body.

Osteoporosis

Definition: A condition in which bones become weak, brittle, and porous due to a loss of bone density.
Signs & Symptoms: Often asymptomatic until a fracture occurs (frequently in the hip, wrist, or spine). Loss of height over time.
Risk Factors: Post-menopausal women (drop in estrogen), low calcium/vitamin D intake, sedentary lifestyle, smoking.
Diagnostic Tests: DEXA Scan (Dual-Energy X-ray Absorptiometry) measures bone mineral density (T-score).
Treatment: Calcium and Vitamin D supplements, bisphosphonates (bone-building meds), weight-bearing exercise.

Gout

Definition: A complex form of arthritis caused by the accumulation of uric acid crystals in a joint.
Signs & Symptoms: Sudden, severe attacks of pain, swelling, redness, and tenderness. Most commonly affects the big toe (podagra).
Risk Factors: Diet high in purines (red meat, organ meats, alcohol/beer), obesity, male gender.
Diagnostic Findings: Joint fluid analysis (arthrocentesis) reveals uric acid crystals; elevated blood uric acid.
Treatment:
- Acute: Colchicine, NSAIDs.
- Chronic: Allopurinol (lowers uric acid production). Dietary changes (avoid alcohol/red meat).

Osteomyelitis

Definition: A severe infection of the bone, usually caused by bacteria (Staphylococcus aureus).
Signs & Symptoms: Fever, chills, severe pain in the affected bone, swelling, warmth, and redness over the infection site.
Risk Factors: Open fractures (compound fractures), surgery, diabetes (poor circulation), weakened immune system.
Diagnostic Findings: Bone scan, MRI, CBC (elevated white blood cells), Blood Culture.
Treatment: Long-term IV antibiotics, surgical debridement (removing dead bone).

Bursitis

Definition: Inflammation of the bursae (small, fluid-filled sacs that cushion the bones, tendons, and muscles near joints).
Signs & Symptoms: Achy or stiff joints, pain when moving or pressing on the joint, swelling/redness. Common in the shoulder, elbow, and hip.
Risk Factors: Repetitive motions (e.g., throwing a baseball, kneeling for work).
Treatment: R.I.C.E. (Rest, Ice, Compression, Elevation), NSAIDs, corticosteroid injections.

3. Spinal Deformities

These are curvatures of the spine that deviate from the normal alignment.

Condition	Description	Visual Appearance
Scoliosis	Abnormal lateral (sideways) curvature of the spine.	Spine looks like an "S" or "C". One shoulder may appear higher than the other.
Kyphosis	Exaggerated forward rounding of the upper (thoracic) back.	"Humpback" appearance. Common in osteoporosis.
Lordosis	Exaggerated inward curve of the lower (lumbar) back.	"Swayback" appearance. Common in pregnancy or obesity.

4. Muscle and Neuromuscular Conditions

These conditions affect the muscles or the nerves that control them.

Muscular Dystrophy (MD)

Definition: A group of genetic diseases that cause progressive weakness and loss of muscle mass. Duchenne MD is the most common form in children.
Signs & Symptoms: Frequent falls, difficulty rising from a lying position, waddling gait, large calf muscles (pseudohypertrophy).
Risk Factors: Family history (X-linked recessive trait, mostly affects males).
Treatment: No cure. Physical therapy, corticosteroids to slow muscle degeneration, assistive devices (braces/wheelchairs).

Fibromyalgia

Definition: A chronic disorder characterized by widespread musculoskeletal pain, fatigue, and tenderness in localized areas.
Signs & Symptoms: Widespread pain, "fibro fog" (cognitive difficulties), sleep disturbances, depression.
Diagnostic Findings: Diagnosis of exclusion. Patients often have specific "tender points" on the body.
Treatment: Pain management, antidepressants, anti-seizure drugs (e.g., pregabalin), stress management, exercise.

Myasthenia Gravis

Definition: A chronic autoimmune neuromuscular disease that causes weakness in the skeletal muscles. Antibodies block acetylcholine receptors at the neuromuscular junction.
Signs & Symptoms: Muscle weakness that worsens with activity and improves with rest. Ptosis (drooping eyelids), double vision, difficulty swallowing or speaking.
Risk Factors: Autoimmune history.
Treatment: Cholinesterase inhibitors, corticosteroids, thymectomy (removal of the thymus gland).

Muscle Strains, Sprains, and Cramps

You must know the difference between a sprain and a strain.

Condition	Tissue Affected	Description
Sprain	Ligament	Stretching or tearing of a ligament (Bone to Bone). Common in ankles.
Strain	Muscle/Tendon	Stretching or tearing of a muscle or tendon (Muscle to Bone). Common in the back or hamstring.
Cramps	Muscle	Sudden, involuntary contraction of a muscle. Often caused by dehydration or electrolyte imbalance (Magnesium/Potassium).

Mnemonic: Strain contains a T for Tendon. Sprain has a P for Partial tear of a ligament.

Tendonitis

Definition: Inflammation or irritation of a tendon.
Signs & Symptoms: Pain described as a dull ache, tenderness, and mild swelling.
Common Sites: Elbow (Tennis Elbow), Shoulder (Pitcher's Shoulder), Achilles heel.
Treatment: R.I.C.E., physical therapy, orthotics (braces).

5. Common Bone Fractures

A fracture is a broken bone. The classification depends on the nature of the break.

Fracture Type	Description	Key Characteristic
Closed (Simple)	Bone breaks but does not penetrate the skin.	No open wound.
Open (Compound)	Bone breaks and pierces through the skin.	High risk of infection (Osteomyelitis).
Greenstick	Bone bends and cracks but doesn't break completely.	Common in children because their bones are softer/more flexible.
Comminuted	Bone shatters into three or more pieces.	Usually caused by high-impact trauma (car accident).
Impacted	Broken bone ends are jammed into each other.	Force applied to both ends.
Stress	Tiny cracks in the bone.	Caused by repetitive force (overuse), common in runners (shin splints).

6. Diagnostic and Therapeutic Procedures

As an MA, you will assist with preparing patients for these tests or therapies.

Diagnostic Tests

X-Ray: Uses radiation to visualize dense tissue (bone). First line for fractures.
MRI (Magnetic Resonance Imaging): Uses magnets/radio waves. Best for visualizing soft tissues (ligaments, tendons, spinal cord).
- MA Role: Screen patient for metal implants (pacemakers, shrapnel) before entry.
CT Scan: 3D X-ray. Good for complex fractures.
Electromyography (EMG): Measures the electrical activity of muscle tissue. Used to diagnose ALS, Myasthenia Gravis, or carpal tunnel.
Arthrocentesis: Surgical puncture to remove fluid from a joint space (e.g., knee) for analysis (gout/infection) or pain relief.

Therapeutic Modalities

R.I.C.E. Therapy: The standard first-aid treatment for acute soft tissue injuries (sprains/strains).
- Rest: Stop the activity.
- Ice: Apply cold packs (20 mins on/off) to reduce swelling/inflammation (Vasoconstriction).
- Compression: Wrap with an ace bandage to limit swelling.
- Elevation: Raise injury above heart level to reduce swelling.
Heat Therapy: Used for chronic pain or muscle stiffness. Increases blood flow (Vasodilation) to relax muscles.
Splinting/Casting:
- MA Role: Assist provider. Instruct patient to keep cast dry, check for sensation/color in fingers/toes (circulation check), and never stick objects inside the cast to scratch.

7. Final Key Takeaways

Connective Tissue Rule: Tendons = Muscle to Bone (MTB). Ligaments = Bone to Bone.
Arthritis Difference: Osteoarthritis is wear-and-tear (aging). Rheumatoid Arthritis is autoimmune.
Gout Triggers: Associated with Uric Acid and rich diets (meat/alcohol). Usually hits the big toe.
Fracture Terminology: Compound fractures break the skin (infection risk). Greenstick fractures happen in kids.
Spine Shapes: Scoliosis is lateral (S-shape). Kyphosis is humpback.
Osteoporosis: Screened via DEXA scan. Risk factors include being female, post-menopausal, and low calcium.
Muscle Weakness: Myasthenia Gravis involves blocked acetylcholine receptors and droopy eyelids. Muscular Dystrophy is genetic wasting.
Injection Safety: When giving a Deltoid injection, avoid the acromion process and radial nerve.
Sprain vs. Strain: A Sprain is a ligament injury. A Strain is a tendon/muscle injury.
Emergency: Osteomyelitis is a bone infection that requires aggressive antibiotics.