Accounting /USMLE - Musculoskeletal and Connective Tissue Part 1

USMLE - Musculoskeletal and Connective Tissue Part 1

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The Unhappy Triad is a common knee injury in contact sports, typically caused by a lateral force to a planted leg. It involves tears of the ACL, MCL, and meniscus (classically medial, though lateral is more often injured). Treatment often includes surgical ACL reconstruction.

Unhappy Triad

Context of injury?

What happens?

Tears?

Treatment

Common injury in contact sports
Lateral force applied to planted leg
Tear of ACL, MCL (medial or tibial collateral ligament) and Meniscus (classically medial but lateral more common)
Surgical ACL reconstruction

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Key Terms

Term
Definition

Unhappy Triad

Context of injury?

What happens?

Tears?

Treatment

Common injury in contact sports
Lateral force applied to planted leg
Tear of ACL, MCL (medial or tibial collateral ligament) and Meniscus (cl...

Positive anterior drawer sign

ACL tear

Abnormal passive abduction of the leg

MCL tear

ACL attachments and function

Lateral condyle of the femur to the anterior intercondylar area of the tibia
Prevents femur from shifting backwards

PCL attachments and function

Medial condyle of the femur to the posterior intercondylar area of the tibia
Prevents femur from shifting forward

Pudendal nerve block
Function
Location

Relieve pain of delivery
Ischial Spine

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TermDefinition

Unhappy Triad

Context of injury?

What happens?

Tears?

Treatment

Common injury in contact sports
Lateral force applied to planted leg
Tear of ACL, MCL (medial or tibial collateral ligament) and Meniscus (classically medial but lateral more common)
Surgical ACL reconstruction

Positive anterior drawer sign

ACL tear

Abnormal passive abduction of the leg

MCL tear

ACL attachments and function

Lateral condyle of the femur to the anterior intercondylar area of the tibia
Prevents femur from shifting backwards

PCL attachments and function

Medial condyle of the femur to the posterior intercondylar area of the tibia
Prevents femur from shifting forward

Pudendal nerve block
Function
Location

Relieve pain of delivery
Ischial Spine

Location of lumbar puncture in adults

Iliac Crest (L3-4 or L4-5)

Rotator Cuff Muscles
Function
Attachement
Innervation

“Superman Subsumes his Inferior Minors”
Supraspinatus - Abducts before deltoid. Most common injury. Attaches superiorly
Infraspinatus - Lateral rotation. Pinching injury. Attaches posteriorly
Teres Minor - Adducts and lateral rotation. Attaches posteriorly
Subscapularis - medial rotates and adducts. Attaches anteriorly
C5-C6

Writs Bones (Carpals)

"So Long To Pinky, Here Comes The Thumb"

Closest to arm, Thumb to Pinky

Scaphoid, Lunate, Triquetrum

Closest to fingers, Pinky to Thumb

Pisiform, Hamate, Capitate, Trapezoid

Most commonly fractured carpal? Other risks to this bone?

Scaphoid. Prone to avascular necrosis owing to retrograde blood supply

Cause of acute carpal tunnel syndrome

Dislocation of the lunate

Carpal Tunnel Syndrome
PathoPhys
Presentation

Entrapment of median nerve in carpal tunnel
Paresthesia, pain and numbness in median nerve area.

Median Nerve Sensation

Anterior: thumb side of hand, 1st, 2nd, and half of 3rd fingers
Posterior: 1st, 2nd, and half of 3rd fingers

Innervation of Palm of Hand

Thumb side - median nerve
Pinky side - Ulnar nerve

Innervation of Back of Hand

Thumb side - Radial nerve (superficial branch)
Pinky side - Ulnar nerve
1st, 2nd, and 3rd fingers - Median nerve

Innervation of top of shoulder?

C4

Innervation of lateral side of upper arm?

C5

Innervation of lateral side of lower arm?

C6

Innervation of medial side of lower and most of upper arm?

T1

Innervation of Axilla

T2

Injury to lower trunk of brachial plexus
What can cause it?
What does it produce?

Compressed by cervical rib or Pancoast tumor of lung
Produces Klumpke’s Palsy

How and where is Radial nerve injured

Roots of radial nerve?

Motor manifestation of injury?

Sensory manifestation of injury?

Manifestation of injury?

Compressed in axilla by incorrect use of a crutch
Lesioned by midshaft fracture of humerus in spiral groove
Deep branch stretched by subluxation of radius
Posterior cord (C5-T1)
“BEST extensors”
Brachioradialis, Extensor of wrist and fingers, Supinator, Triceps
Posterior arm and dorsal hand and thumb
Saturday night palsy (wrist drop)

How is upper trunk of brachial plexus injured?

Trauma

Axillary nerve?

How is it injured?

Roots?

Motor manifestation of injury?

Sensory manifestation of injury?

Sign of injury?

Lesioned by fracture of surgical neck of humerus, dislocation of humeral head, or intramuscular injections

Posterior cord (C5, C6)

Deltoid paralysis (problem with abduction at shoulder).

Sensory loss of deltoid muscle.

Deltoid atrophy

Where is the anterior interosseous nerve injured?


Compressed in deep forearm


What is the cause of injury to recurrent branch of the median nerve?


Lesioned by superficial laceration


Bones of arm


Humerus
Ulna (pinky side)
Radius (thumb side)

Attachments of Flexor Retinaculum

Scaphoid and Trapezium to Pisiform and Hook of hamate

Abductor Pollicis Brevis

Origin

Insertion

Innervation

Action

Flexor Retinaculum, Scaphoid, Trapezius
Lateral side of proximal phalanx of the thumb
Recurrent branch of median nerve
Abducts the thumb

How does the ulnar nerve enter the hand? Possible pathology?

Through Guyon's Canal

| Guyon's Canal Syndrome

Abductor digiti minimi

Origin

Insertion

Innervation

Action

Pisiform and tendon of flexor carpi ulnaris
Medial side of base of proximal phalanx of little finger
Ulnar nerve
Abducts little finger

hypothenar

Pinky side


Thenar

Thumb side

Flexor Pollicis Brevis

Origin

Insertion

Innervation

Action

FR and Trapezius
Base of proximal phalanx of thumb
Median nerve
Flexes thumb

Opponens Pollicis

Origin

Insertion

Innervation

Action

FR and Trapezius
1st metacarpal
Median
Opposes thumb to other digits

Adductor Pollicis

Origin

Insertion

Innervation

Action

Oblique head: Capitate and base of 2nd and 3rd metacarpals

Transverse head: 3rd metacarpal

Proximal phalanx of thumb

Ulnar nerve

Adducts thumb

Palmaris Brevis

Origin

Insertion

Innervation

Action

FR, Palmar aponeurosis

Skin of medial palm

Ulnar

Wrinkles skin

Flexor Digiti Minimi Brevis

Origin

Insertion

Innervation

Action

FR and hook of hamate
Proximal Phalanx of pinky
Ulnar
Flexes

Opponens Digiti Minimi

Origin

Insertion

Innervation

Action

FR and hook of hamate
5th metacarpal
Ulnar
Opposes pinky

Lumbriclas

#

Origin

Insertion

Innervation

Action

4

Tendons of Flexor Digitorum Profundus

Lateral sides of extensor expansions

Lateral 2: Median

Medial 2: Unlar

Flexes metacarpophalangeal joints and extends interphalangeal joints

Dorsal interossei

#

Description

Origin

Insertion

Innervation

Action

"DAB"

4

Bipennate

Adjacent sides of metacarpal bones

Lateral sides of proximal phalanges

Ulnar

Abducts fingers, flexes metacarpophalangeal joints and extends interphalangeal joints

Palmar Interossei

#

Description

Origin

Insertion

Innervation

Action

"PAD"

3

Unipennate

Medial side of 2nd metacarpal

Lateral sides of 4th and 5th metacarpals

Proximal phalanges

Ulnar

Adducts fingers, flexes metacarpophalangeal joints and extends interphalangeal joints

Divisions of the Brachial Plexus

"Real Texans Drink Cold Bear"

Roots

Trunks

Divisions

Cords

Branches

Upper trunk of the Brachial Plexus
Roots?
Injury?

C5-C6

| "Waiter's Tip" - Erb's Palsy

Lower Trunk of Brachial Plexus
Roots?
Injury?

C8, T1

| Claw hand - Klumpke's Palsy

Posterior Cord of Brachial Plexus
Roots?
Injury?

C5-T1

| Wrist Drop

Long Thoracic Nerve
Roots?
Muscles innervated w/ function?
Context and consequences of Injury?

C5-C7
Serratus Anterior anchors scapula to thoracic cage. Used for abduction above horizontal position
Injured in mastectomy --> Winged Scapula and ipsilateral lymphedema

Musculocutaneous nerve

Roots?

Cause of injury?

Motor deficit?

Sensor deficit?

Manifestation of injury?

C5-C7
Upper Trunk Compression
Biceps, Brachialis, Coracobrachialis, Flexion of arm at elbow
Lateral forearm
Difficulty flexing the elbow. Variable sensory loss

Median nerve

Causes of injury?

Roots

Motor deficit

Sensory deficit

Manifestation of injury?

Compressed in supracondylar fracture of humerus producing pronator teres syndrome
Compressed in carpal tunnel syndrome and by dislocation of lunate
C5-T1
Opposition of thumb, Lateral finger flexion, Wrist flexion
Lateral hand
Decreased Thumb Function (pope's blessing)

Ulnar Nerve

Causes of injury?

Roots?

Motor deficit

Sensory deficit?

Sign

Lesioned by repeat minor traumas, Fracture of medial epicondyle of humerus, Trauma to heel of the hand, Fracture to hook of hamate
C8, T1
Medial finger flexion, Wrist flexion
Pinky side of hand
Radial deviation of wrist upon wrist flexion, Ulnar Claw

What protects the brachial plexus when the clavicle is fractured?

Subclavius muscle


Muscles innervated by Dorsal Scapular Nerve

Rhomboids and Levator Scapulae


Suprascapular nerve
What muscles does it innervate?
Roots

Supra and Infra spinatus

| C5, C6

Lateral Pectoral Nerve
Roots?
Muscles innervated?

C5-C7

| Pectoralis Major

Thoracodorsal Nerve
Roots
Muscles innervated

C7, C8

| Latissimus Dorsi

Erb-Duchenne Palsy

Nickname

Site of lesion

Context of injury

Findings

Waiters Tip
Upper Trunk of Brachial Plexus (C5, C6)
Seen in infants following trauma during delivery
Limb hangs by side (paralysis of abductors - suprascapular and deltoid), Medially rotated (paralysis of lateral rotators), Forearm pronated (loss of biceps)

Klumpke's Palsy

Site of lesion

Context of injury

Complication

Findings

Lower trunk of brachial plexus (C8, T1)
Embryological or childbirth defect
Cervical rib can compress subclavian artery and Lower Trunk resulting in Thoracic Outlet Syndrome
Atrophy of thenar and hypothenar eminences, Atrophy of interosseous muscles, Sensory deficits on medial side of forearm and hand, Loss of radial pulse when head moved to ipsilateral side

Clawing


Loss of lumbricals which flexes the MCP joints and extends the DIP and PIP joints


Ulnar Claw
Cause of lesion
PathoPhys

Long standing injury to ulnar nerve at hook of hamate (falling)
Distal Ulnar lesion --> Loss of medial lumbricals --> inability to extend 4th and 5th digits

Medial Claw
Caused by
PathoPhys

Carpal Tunnel Syndrome or Dislocated Lunate
Distal median nerve injury (after branch containing C5-C7 branches off to feed forearm flexors) --> Loss of lateral lumbricals --> Clawing of 2nd and 3rd fingers

Pope's Blessing
PathoPhys
Findings

Proximal median nerve lesion causes loss of lateral finger flexion and thumb opposition.
When asked to make a fist, 2nd and 3rd fingers remain extended and thumb remains unopposed

Ape Hand

Proximal median nerve lesion --> loss of opponens pollicis muscle function --> unopposable thumb (cannot abduct the thumb)

Klumpke's Total Claw
Site of lesion
PathoPhys

Lesion to lower trunk (C8, T1) of Brachial plexus
Loss of function of all lumbricals --> Forearm finger flexors (fed by median nerve with C5-C7) and finger extensors (fed by Radial nerve) are unopposed --> clawing of all digits

Thenar eminence muscles

Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis

Hypothenar eminence mucles

Opponens digiti minimi, Abductor digiti minimi, Flexor digiti minimi

Obturator Nerve

Roots

Cause of injury

Motor deficit

Sensory deficit

L2-L4
Anterior hip dislocation
Thigh Adduction
Medial Thigh

Femoral Nerve

Roots

Cause of injury

Motor deficit

Sensory deficit

L2-L4
Pelvic fracture
Thigh flexion and leg extension
Anterior thigh and medial leg

Common Peroneal nerve

Roots

Cause of injury

Motor deficit

Sensory deficit

L4-S2
Trauma or compression of lateral aspect of leg or fibula neck fracture
"PED"
Foot eversion and dorsiflexion, toe extension, foot dropPED, foot slap, steppage gait (Peroneus longus and brevis)
Anterolateral leg and dorsal aspect of food

Tibial Nerve

Roots

Cause of injury

Motor deficit

Sensory deficit

L4-S3

Knee trauma

"TIP"

Foot inversion and plantarflexion (cannot stand on TIPtoes), toe flexion

Sole of foot

Superior Gluteal Nerve
Roots
Cause of injury
Motor deficit

L4-S1
Posterior hip dislocation or polio
Thigh abduction (positive trendelenburg sign)

Trendelenberg Sign
What is it?
What does it mean?

Contralateral hip drop when standing on leg ipsilateral to site of lesion
Sign of injury to Gluteus minimus or medius (abductors of the hip)

Inferior Gluteal Nerve
Roots
Cause of injury
Motor deficit

L5-S2
Posterior hip dislocation
Cant jump, climb stairs, rise from seated position, push inferiorly

Sciatic nerve
Roots
Sensory area
Branches

L4-S3
Posterior thigh
Splits into common peroneal and tibial nerve

Steps of Ca entrance into skeletal muscles

ACh binding --> muscle depolarization at motor end plate

Depolarization travels along T tubule

V gated Dihydrophyridine receptors mechanically coupled to Ryanodine receptors in SR

Ca from SR enters cell

How does Ca activate muscles

  1. Ca --> troponin C | 2. Troponin C moves tropomyosin out of myosin binding groove on actin filaments

Steps of skeletal and cardiac muscle contraction

  1. ATP hydrolysis cocks myosin head

  2. Tropomyosin displaced and myosin binds actin

  3. P released --> power stroke

  4. ADP released and ATP binds allowing separation of myosin and actin

During contraction, what happens to the bands in the skeletal muscle

Shortening H and I bands and between Z line (HIZ shrinkage)

| A band remains the same length (A always the same)

Type 1 Muscle

Speed

Length of contraction

Color

Primary Reaction

"1 Slow Red Ox"
Slow twitch, Sustained contraction
Red fibers (from ↑ mito and myoglobin)
Oxidative phosphorylation

Type 2 Muscle

Speed

Color

Primary Reaction

What kind of training affects them?

Fast twitch
White fibers (↓ mito and myoglobin)
Anaerobic glycolysis
Weight training --> hypertrophy

Z line

Where actin attaches to backbone

I band

I band

H band

Just Myosin

A band

Myosin + Where Myosin overlaps with Actin

M line

Center of myosin

Endochondral Ossification
Which bones form this way?
Process

Axial and appendicular skeleton and base of skull
Cartilaginous model of bone is made by chondrocytes. Osteoclasts and Osteoblasts later replace with woven bone and then remodel to lamellar bone

In adults, when does woven bone occur?

After fractures or in Paget's disease

Membranous ossification
Which bones form this way?
Process

Calavarium and facial bones

| Woven bone forms directly w/o cartilage. Later remodeled to lamellar bone

Osteoblasts
Function
Derived from?

Build Bone by secreting collagen and catalyzing mineralization
Differentiate from mesenchymal stem cells in periosteum

Osteoclasts
Histo
Function
Derived from?

Multinucleated cells
Dissolve bone by secreting acid and collagenases
Differentiate from monocytes/macrophages

Affects of PTH on Bone

At low, intermittent levels, exert anabolic affects (building bone) on osteoblasts and (indirectly) osteoclasts.
Primary hyperparathyroidism --> catabolic affects (osteitis fibrosa cystica)

Affects of Estrogen on Bone

Estrogen --/ apoptosis in bone forming osteoblasts and induces apoptosis in bone-resorbing osteoclasts


Achondroplasia

What is it?

PathoPhys

Genetics

Presentation

Failure of longitudinal bone growth (endochondral ossification) --> short limbs. Membranous ossification not affected --> Large head relative to limbs.
Constitutive activation of Fibroblast Growth Factor Receptor 3 (FGFR3) inhibits chondrocyte proliferation
More than 85% of mutations are sporadic and associated with advanced paternal age. Condition also shows Autosomal Dominant inheritance
Dwarfism. Normal lifespan and fertility

Osteoporosis
What is it?
Lab Values
What can in lead to?

Trabecular (spongy) bone loses mass and interconnections despite normal bone mineralization
Normal lab values (serum Ca and PO4)
Vertebral Crush Fractures (Acute back pain, Loss of height, Kyphosis)

Osteoporosis Type 1
Context
PathoPhys
Areas affected

Postmenopausal
↑ bone resorption due to ↓ estrogen
Femoral neck fracture, distal radius (Colles' fracture)

Osteoporosis Type 2

Context

Prophylaxis

Treatment

Contraindications

Men and Women > 70 years old
Regular weight bearing exercise, Ca and Vit D intake
SERMs (estrogen) +/or Calcitonin, Bisphosphonates or pulsatile PTH for severe cases
Glucocorticoids are contraindicated

Osteopetrosis

AKA

PathoPhys

Description of bones

Consequences of bone pathology?

Marble Bone Disease
Failure of normal bone resorption due to defective osteoclasts. Mutations (Carbonic Anhydrase II) impairs ability of osteoclasts to generate acidic environment necessary for bone resorption
Thickened, dense bones that are prone to fracture.
Bone fills marrow space causing pancytopenia, extramedullary hematopoiesis

Osteopetrosis
XR
Complications
Treatment

Bone-in-bone appearance
Cranial nerve impingement and palsies b/c of narrow foramina
Bone marrow transplant because osteoclasts derived from monocytes

Osteomalacia/Rickets
Population affected
PathoPhys
Findings

Adults: Osteomalacia, Children: Rickets
Defective mineralization/calcification of osteoid. ↓ VitD --> ↓ serum Ca --> ↑ PTH --> ↓ serum Phosphate
Hyperactive osteoblasts --> ↑ AlkPhos (osteoblasts require alkaline environment)

Paget's Disease of Bone

AKA

Frequency

PathoPhys

Findings

Description of bone

Fractures?

Complications

Presentation

Osteitis Deformans
Common
Localized bone remodeling disorder causes by ↑ in osteoblasts and osteoclasts
Serum Ca, PO4, and PTH normal. ↑ ALP
Mosaic (woven) bone pattern
Long bone chalk-stick fractures
↑ blood flow from ↑ arteriovenous shunts --> high output heart failure
↑ risk of osteogenic sarcoma
Hat size ↑, hearing loss (auditory foramen narrowing)

Osteoporosis

Serum Ca

Serum PO4

ALP

PTH

Bone description

-
-

-
-
↓ Bone Mass