USMLE - Musculoskeletal and Connective Tissue Part 1
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
Key Terms
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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Term | Definition |
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Unhappy Triad Context of injury? What happens? Tears? Treatment | Common injury in contact sports |
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 |
PCL attachments and function | Medial condyle of the femur to the posterior intercondylar area of the tibia |
Pudendal nerve block | Relieve pain of delivery |
Location of lumbar puncture in adults | Iliac Crest (L3-4 or L4-5) |
Rotator Cuff Muscles | “Superman Subsumes his Inferior Minors” |
Writs Bones (Carpals) |
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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 | Entrapment of median nerve in carpal tunnel |
Median Nerve Sensation | Anterior: thumb side of hand, 1st, 2nd, and half of 3rd fingers |
Innervation of Palm of Hand | Thumb side - median nerve |
Innervation of Back of Hand | Thumb side - Radial nerve (superficial branch) |
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 | Compressed by cervical rib or Pancoast tumor of lung |
| Compressed in axilla by incorrect use of a crutch |
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 |
Attachments of Flexor Retinaculum | Scaphoid and Trapezium to Pisiform and Hook of hamate |
Abductor Pollicis Brevis Origin Insertion Innervation Action | Flexor Retinaculum, Scaphoid, Trapezius |
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 |
hypothenar | Pinky side |
| Thumb side |
Flexor Pollicis Brevis Origin Insertion Innervation Action | FR and Trapezius |
Opponens Pollicis Origin Insertion Innervation Action | FR and Trapezius |
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 |
Opponens Digiti Minimi Origin Insertion Innervation Action | FR and hook of hamate |
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 | C5-C6 | "Waiter's Tip" - Erb's Palsy |
Lower Trunk of Brachial Plexus | C8, T1 | Claw hand - Klumpke's Palsy |
Posterior Cord of Brachial Plexus | C5-T1 | Wrist Drop |
Long Thoracic Nerve | C5-C7 |
Musculocutaneous nerve Roots? Cause of injury? Motor deficit? Sensor deficit? Manifestation of injury? | C5-C7 |
Median nerve Causes of injury? Roots Motor deficit Sensory deficit Manifestation of injury? | Compressed in supracondylar fracture of humerus producing pronator teres syndrome |
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 |
What protects the brachial plexus when the clavicle is fractured? | Subclavius muscle |
| Rhomboids and Levator Scapulae |
Suprascapular nerve | Supra and Infra spinatus | C5, C6 |
Lateral Pectoral Nerve | C5-C7 | Pectoralis Major |
Thoracodorsal Nerve | C7, C8 | Latissimus Dorsi |
Erb-Duchenne Palsy Nickname Site of lesion Context of injury Findings | Waiters Tip |
Klumpke's Palsy Site of lesion Context of injury Complication Findings | Lower trunk of brachial plexus (C8, T1) |
Clawing | Loss of lumbricals which flexes the MCP joints and extends the DIP and PIP joints |
Ulnar Claw | Long standing injury to ulnar nerve at hook of hamate (falling) |
Medial Claw | Carpal Tunnel Syndrome or Dislocated Lunate |
Pope's Blessing | Proximal median nerve lesion causes loss of lateral finger flexion and thumb opposition. |
Ape Hand | Proximal median nerve lesion --> loss of opponens pollicis muscle function --> unopposable thumb (cannot abduct the thumb) |
Klumpke's Total Claw | Lesion to lower trunk (C8, T1) of Brachial plexus |
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 |
Femoral Nerve Roots Cause of injury Motor deficit Sensory deficit | L2-L4 |
Common Peroneal nerve Roots Cause of injury Motor deficit Sensory deficit | L4-S2 |
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 | L4-S1 |
Trendelenberg Sign | Contralateral hip drop when standing on leg ipsilateral to site of lesion |
Inferior Gluteal Nerve | L5-S2 |
Sciatic nerve | L4-S3 |
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 |
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Steps of skeletal and cardiac muscle contraction |
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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" |
Type 2 Muscle Speed Color Primary Reaction What kind of training affects them? | Fast twitch |
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 | Axial and appendicular skeleton and base of skull |
In adults, when does woven bone occur? | After fractures or in Paget's disease |
Membranous ossification | Calavarium and facial bones | Woven bone forms directly w/o cartilage. Later remodeled to lamellar bone |
Osteoblasts | Build Bone by secreting collagen and catalyzing mineralization |
Osteoclasts | Multinucleated cells |
Affects of PTH on Bone | At low, intermittent levels, exert anabolic affects (building bone) on osteoblasts and (indirectly) osteoclasts. |
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. |
Osteoporosis | Trabecular (spongy) bone loses mass and interconnections despite normal bone mineralization |
Osteoporosis Type 1 | Postmenopausal |
Osteoporosis Type 2 Context Prophylaxis Treatment Contraindications | Men and Women > 70 years old |
Osteopetrosis AKA PathoPhys Description of bones Consequences of bone pathology? | Marble Bone Disease |
Osteopetrosis | Bone-in-bone appearance |
Osteomalacia/Rickets | Adults: Osteomalacia, Children: Rickets |
Paget's Disease of Bone AKA Frequency PathoPhys Findings Description of bone Fractures? Complications Presentation | Osteitis Deformans |
Osteoporosis Serum Ca Serum PO4 ALP PTH Bone description |
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