The Skeletal System: Bones, Joints, and Landmarks

Why the Skeletal System Matters for PT Aides

As a physical therapy aide, you will assist licensed therapists in treating patients recovering from fractures, joint replacements, sprains, and movement disorders. Before you can position a patient correctly, apply a hot pack safely, or help a therapist document a treatment session, you need a working knowledge of the bones, joints, and surface landmarks that guide clinical hands-on work. This lesson builds that foundation.

The Skeleton: Overview

The adult human skeleton contains 206 bones. It is divided into two regions:

• Axial skeleton: the skull, vertebral column, ribs, and sternum — the central axis of the body.
• Appendicular skeleton: the upper and lower limbs plus the pectoral and pelvic girdles that attach them to the axial skeleton.

Bones are classified by shape — long (femur, humerus), short (carpals, tarsals), flat (scapula, parietal), irregular (vertebrae), and sesamoid (patella). Shape influences function: long bones act as levers for movement; flat bones protect organs.

Major Bones of the Upper Extremity

• Clavicle and scapula form the pectoral girdle.
• Humerus: the single bone of the upper arm.
• Radius and ulna: the two forearm bones. The radius is on the thumb side; the ulna is on the pinky side and forms the bony point of the elbow (olecranon).
• Carpals (8), metacarpals (5), phalanges (14): the hand.

Major Bones of the Lower Extremity

• Pelvis: formed by the two hip bones (each made of ilium, ischium, and pubis) fused to the sacrum.
• Femur: the longest bone in the body; the thigh.
• Patella: sesamoid bone at the knee.
• Tibia and fibula: the leg. The tibia is weight-bearing and has the tibial tuberosity on its anterior surface.
• Tarsals (7), metatarsals (5), phalanges (14): the foot.

Key Bony Landmarks for Palpation

Bony landmarks are surface projections or depressions you can feel through the skin. Knowing them allows the PT team to identify anatomical reference points, measure limb alignment, and position patients safely.

| Landmark | Location |

|---|---|

| Acromion | Most lateral point of the scapula; forms the top of the shoulder |

| Coracoid process | Anterior shoulder; just below the clavicle, medial to the humeral head |

| Medial epicondyle | Medial bony bump at the elbow (ulnar nerve runs here — "funny bone") |

| Lateral epicondyle | Lateral bony bump at the elbow |

| Olecranon | Posterior elbow; tip of the ulna |

| ASIS (anterior superior iliac spine) | Front of the pelvis; the forward-pointing bony projection of the ilium |

| Greater trochanter | Lateral hip; large projection of the proximal femur |

| Tibial tuberosity | Anterior proximal tibia; where the patellar tendon inserts |

| Medial and lateral malleoli | Bony prominences on each side of the ankle (tibia and fibula) |

Safety note — palpation: Always explain what you are about to do before touching a patient or lab partner. Use appropriate pressure — firm but gentle. Avoid pressing directly over open wounds, bruising, or areas the patient reports as acutely painful. Never palpate the anterior neck (carotid region) unless specifically trained. Respect privacy and drape appropriately in clinical settings.

Joints: Structure and Function

A joint (articulation) is where two or more bones meet. Joints are classified two ways:

By structure (what holds them together):

• Fibrous — joined by fibrous tissue; little or no movement (e.g., skull sutures).
• Cartilaginous — joined by cartilage; slight movement (e.g., pubic symphysis, intervertebral discs).
• Synovial — fluid-filled joint cavity; most moveable; the type seen at nearly every limb joint.

By function (how much they move):

• Synarthrosis — immovable.
• Amphiarthrosis — slightly moveable.
• Diarthrosis — freely moveable (all synovial joints).

Synovial joint subtypes — classified by shape of the articulating surfaces:

| Joint | Structural subtype | Movements permitted |

|---|---|---|

| Shoulder (glenohumeral) | Ball-and-socket | Flexion, extension, abduction, adduction, rotation, circumduction |

| Elbow (humeroulnar) | Hinge | Flexion, extension |

| Wrist (radiocarpal) | Condyloid (ellipsoid) | Flexion, extension, abduction (radial deviation), adduction (ulnar deviation) |

| Hip (femoroacetabular) | Ball-and-socket | Flexion, extension, abduction, adduction, rotation, circumduction |

| Knee (tibiofemoral) | Modified hinge | Flexion, extension; slight rotation when flexed |

| Ankle (talocrural) | Hinge | Dorsiflexion, plantarflexion |

| Spine (intervertebral) | Cartilaginous (amphiarthrotic) | Flexion, extension, lateral flexion, rotation |

Safety and Scope of Practice

As a PT aide, you observe and assist under the direct supervision of a licensed physical therapist (PT) or physical therapist assistant (PTA). You do not evaluate patients, make clinical judgments about joint pathology, or perform palpation outside of supervised training. If a patient reports sharp pain, numbness, or tingling during any hands-on activity, stop immediately and notify the supervising clinician. Knowing your anatomy protects both you and the patient.