Anatomy Block 4

Which type of joint allows the greatest movement?

Synovial joints.

What cavity is present in every synovial joint?

A joint cavity containing synovial fluid.

What are the functions of synovial fluid?

Lubricates joints, reduces friction, and nourishes articular cartilage.

What is a ball-and-socket joint?

A spherical head of one bone fits into a rounded socket of another.

What does multiaxial mean?

Movement around three axes: flexion/extension, abduction/adduction, and rotation.

What are examples of ball-and-socket joints?

Shoulder (glenohumeral) and hip.

What is a hinge joint?

A cylindrical bone surface fits into a trough-shaped surface, allowing primarily flexion and extension.

Why are hinge joints uniaxial?

They permit movement around one axis.

What are examples of hinge joints?

Elbow, ankle (talocrural), and interphalangeal joints.

What movement occurs at a pivot joint?

Rotation around one longitudinal axis; it is uniaxial.

What are examples of pivot joints?

Proximal radioulnar and median atlantoaxial joints.

What happens at the proximal radioulnar joint?

The radial head rotates within the annular ligament against the radial notch of the ulna during pronation and supination.

What movement occurs at the median atlantoaxial joint?

The atlas and head rotate around the dens of the axis, as when shaking the head “no.”

What are plane joints?

Joints with relatively flat articular surfaces permitting short, nonaxial gliding movements.

What are examples of plane joints?

Intercarpal and intertarsal joints.

What movements occur at condylar (ellipsoid) joints?

Flexion/extension, abduction/adduction, and circumduction; no independent axial rotation.

Why are condylar joints biaxial?

They allow movement around two axes.

What are examples of condylar joints?

Radiocarpal joint and MCP joints of digits 2–5.

What characterizes a saddle joint?

Each articular surface is concave in one direction and convex in the perpendicular direction; movement is biaxial.

What is the main saddle joint of the hand?

First carpometacarpal joint between trapezium and first metacarpal.

What is thumb opposition?

Movement bringing the thumb pad toward the finger pads through combined abduction, flexion, and rotation of the first metacarpal.

How does skeletal muscle produce movement?

Contraction pulls on bones across joints through muscle attachments.

What is flexion?

Movement decreasing the angle of a joint.

What is extension?

Movement increasing the angle of a joint.

What is abduction?

Movement away from the body’s midline; finger abduction is away from the middle finger’s axis.

What is adduction?

Movement toward the body’s midline; finger adduction is toward the middle finger’s axis.

Where are upper-limb flexors and extensors usually located?

Flexors anteriorly; extensors posteriorly. Brachioradialis is an elbow flexor with radial nerve innervation.

What is forearm supination?

Rotation turning the palm anteriorly in anatomical position or upward with the elbow flexed.

What is forearm pronation?

Rotation turning the palm posteriorly in anatomical position or downward with the elbow flexed.

How are the radius and ulna positioned in supination?

Parallel and uncrossed.

What happens to the radius during pronation?

It crosses anterior to the ulna.

What is the forearm position in anatomical position?

Supinated, with palms facing forward.

Where do pronation and supination occur?

At the proximal and distal radioulnar joints, not the wrist joint.

Which muscles supinate the forearm?

Biceps brachii and supinator.

Which muscles pronate the forearm?

Pronator teres and pronator quadratus.

What is a muscle origin?

The relatively less movable attachment.

What is a muscle insertion?

The relatively more movable attachment, usually moving toward the origin during contraction.

What is direct versus indirect muscle attachment?

Direct: connective tissue blends with periosteum with little intervening tendon. Indirect: attachment through a tendon or aponeurosis.

What is a prime mover (agonist)?

The muscle chiefly responsible for a particular movement.

What is an antagonist?

A muscle that opposes or reverses an agonist’s action.

Give an agonist–antagonist example during elbow flexion.

Brachialis is an agonist; triceps brachii is an antagonist.

What is a synergist?

A muscle assisting a prime mover by adding force or limiting unwanted movement.

What is a fixator?

A synergist stabilizing a bone or the origin of a prime mover.

Can a muscle be both agonist and antagonist?

Yes, depending on movement; triceps is an agonist for elbow extension and antagonist for flexion.

What is the diaphysis?

The shaft of a long bone.

What are epiphyses?

The expanded ends of a long bone.

What is the medullary cavity?

The hollow space within the diaphysis, usually containing yellow marrow in an adult long-bone shaft.

What is periosteum?

Vascular connective tissue covering external bone except articular surfaces; supports growth and repair and tendon/ligament attachment.

What anchors periosteum to bone?

Perforating collagen fibers called Sharpey’s fibers.

What is endosteum?

A thin membrane lining internal bone surfaces, including the medullary cavity.

Why is bone blood supply important?

It supplies oxygen and nutrients for maintenance, growth, and fracture healing.

Where is the bicipital (intertubercular) groove?

Between the greater and lesser tubercles of the proximal humerus.

What tendon passes through the bicipital groove?

The tendon of the long head of biceps brachii; the short head does not pass through it.

Where is the radial (spiral) groove?

On the posterior humeral shaft, running obliquely from medial to lateral.

What structures occupy the radial groove?

Radial nerve and deep brachial (profunda brachii) artery.

Which nerve is at risk in a surgical neck fracture of the humerus?

Axillary nerve.

What findings suggest axillary nerve injury?

Weak shoulder abduction especially 15–90°, deltoid wasting, and reduced sensation over the lateral shoulder.

Which nerve is at risk in a humeral midshaft fracture?

Radial nerve; injury can cause wrist drop and weak finger extension.

Which nerve is at risk in a supracondylar humeral fracture?

Median nerve, including its anterior interosseous branch.

What can median/anterior interosseous injury after a supracondylar fracture cause?

Weak finger flexion and an abnormal “OK” sign.

Which nerve is at risk in a medial epicondyle fracture?

Ulnar nerve, which passes behind the medial epicondyle.

What findings suggest ulnar nerve injury?

Weak finger abduction/adduction, sensory loss in the little finger and ulnar half of ring finger, and possible clawing.

What is proximal humeral epiphyseal separation?

A growth-plate injury separating the proximal epiphysis from the rest of the humerus before skeletal maturity.

Which nerve can be injured during anterior shoulder dislocation?

Axillary nerve.

What is a Colles’ fracture?

Distal radius fracture, usually just proximal to the wrist, with dorsal displacement or angulation of the distal fragment.

What commonly causes a Colles’ fracture?

A fall onto an outstretched hand with the wrist extended.

What deformity is associated with a Colles’ fracture?

Dinner-fork deformity.

What associated fracture can accompany a Colles’ fracture?

Ulnar styloid fracture or avulsion.

Is a Colles’ fracture an isolated radial styloid fracture?

No. An isolated radial styloid fracture is commonly called a chauffeur’s fracture.

How many carpals are in each wrist?

Eight, arranged in proximal and distal rows.

Name the proximal carpal row from thumb to little finger.

Scaphoid, lunate, triquetrum, pisiform.

What mnemonic recalls the proximal carpal row?

“Straight Line To Pinky”: scaphoid, lunate, triquetrum, pisiform; thumb to little finger.

Name the distal carpal row from little finger to thumb.

Hamate, capitate, trapezoid, trapezium.

What mnemonic recalls the distal row from little finger to thumb?

“Here Comes The Thumb”: hamate, capitate, trapezoid, trapezium.

Name the distal carpal row from thumb to little finger.

Trapezium, trapezoid, capitate, hamate.

Which carpal articulates with the first metacarpal?

Trapezium, forming the thumb’s saddle joint.

Which carpal lies between trapezium and capitate?

Trapezoid.

Which is the largest carpal?

Capitate, centrally located in the distal row.

Which carpal has a hook?

Hamate.

Which carpal is a sesamoid within the flexor carpi ulnaris tendon?

Pisiform, on the palmar surface of triquetrum.

Which carpal is most frequently fractured?

Scaphoid, usually at its waist.

Why can a scaphoid waist fracture cause avascular necrosis?

Much of its blood supply runs distal to proximal; a waist fracture can interrupt proximal pole perfusion and cause necrosis or nonunion.

Which carpal is classically associated with dislocation and median nerve compression?

Lunate; palmar dislocation can compress the median nerve.

How are metacarpals numbered?

I–V, from thumb to little finger.

What are the parts of a metacarpal?

Proximal base, shaft, and distal head.

How many phalanges are in one hand?

Fourteen: three in each finger and two in the thumb.

Which phalanx is absent from the thumb?

Middle phalanx.

Where are the thumb MCP sesamoids?

Within tendons on the palmar side of the first MCP joint.

What is the rotator cuff and its shared function?

Four muscles and tendons dynamically stabilizing the humeral head in the glenoid cavity and assisting shoulder movement.

What does SITS stand for?

Supraspinatus, infraspinatus, teres minor, subscapularis.

Supraspinatus: location, origin, insertion, action, innervation?

Above scapular spine; supraspinous fossa → superior facet of greater tubercle; initiates abduction about 0–15°; suprascapular nerve, primarily C5–C6.

Infraspinatus: location, origin, insertion, action, innervation?

Below scapular spine; infraspinous fossa → middle facet of greater tubercle; external rotation; suprascapular nerve C5–C6.

Teres minor: location, origin, insertion, action, innervation?

Lateral scapular border below infraspinatus; lateral border → inferior facet of greater tubercle; external rotation and weak adduction; axillary nerve C5–C6.

Subscapularis: location, origin, insertion, action, innervation?

Anterior scapula facing ribs; subscapular fossa → lesser tubercle; internal rotation and assists adduction; upper and lower subscapular nerves C5–C6.

Which rotator cuff muscle inserts on the lesser tubercle?

Subscapularis; the other three insert on the greater tubercle.

Which rotator cuff muscles externally rotate the arm?

Infraspinatus and teres minor.

What commonly causes rotator cuff injury?

Overuse, trauma, and age-related degeneration.

Teres major: location, origin, insertion, action, innervation?

Below teres minor near inferior scapular angle; posterior inferior angle → medial lip of intertubercular groove; adduction, internal rotation, extension; lower subscapular nerve, commonly C5–C6 (course slide lists C6–C7).

Is teres major a rotator cuff muscle?

No; teres minor is.

Pectoralis major: location and origins?

Superficial anterior chest; medial clavicle, sternum, upper costal cartilages, and abdominal contribution from external oblique aponeurosis/anterior rectus sheath region.