MSK physiology Flashcards
Rotator cuff muscles
Shoulder muscles that form the rotator cuff:
Supraspinatus (suprascapular nerve)— abducts arm initially (before the action of the deltoid); most common rotator cuff injury (trauma or degeneration and impingement–> tendinopathy or tear, assessed by “empty/full can” test.
Infraspinatus (suprascapular nerve)— externally rotates arm; pitching injury.
teres minor (axillary nerve)—adducts and externally rotates arm.
Subscapularis (upper and lower subscapular nerves)—internally rotates and adducts arm. Innervated primarily by C5-C6.
arm abduction
supraspinatus (0-15degrees),
deltoid (15-100 degrees),
trapezius (>90 degrees),
serratus anterior inverated by long thoracic (>100 degrees)
wrist region
Scaphoid, Lunate, Triquetrum, Pisiform, Hamate, Capitate, Trapezoid, Trapezium (A) . (So Long To Pinky, Here Comes The Thumb).
Scaphoid (palpable in anatomic snuff) is the most commonly fractured carpal bone, typically due to a fall on an outstretched hand. Complications of proximal scaphoid fractures include avascular necrosis and nonunion due to retrograde blood supply. Fracture not always seen on initial x-ray. Dislocation of lunate may cause acute carpal tunnel syndrome.
Hand muscles
Thenar (median)—Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis, superficial head (deep head by ulnar nerve).
Hypothenar (ulnar)—Opponens digiti minimi, Abductor digiti minimi, Flexor digiti minimi brevis.
Dorsal interossei (ulnar)—abduct the fingers.
Palmar interossei (ulnar)—adduct the fingers.
Lumbricals (1st/2nd, median; 3rd/4th, ulnar)— flex at the MCP joint, extend PIP and DIP joints
Both groups perform the same functions: Oppose, Abduct, and Flex (OAF).
DAB = Dorsals ABduct.
PAD = Palmars ADduct.
Axillary (C5-C6)-caused of injury: Fractured surgical neck of humerus Anterior dislocation of humerus. presentation:
Flattened deltoid
Loss of arm abduction at shoulder (> 15°)
Loss of sensation over deltoid muscle and lateral arm
Musculocutaneous (C5-C7)- caused of injury: Upper trunk compression, Presentation:
Loss of forearm flexion and supination
Loss of sensation over lateral forearm
Median (C5-T1)-cause of injury: Supracondylar fracture of humerus (proximal lesion), Carpal tunnel syndrome and wrist laceration (distal lesion),
presentation:
“Ape hand” and “Pope’s blessing”
Loss of wrist flexion,
loss of flexion of lateral fingers,
loss of thumb opposition,
loss of lumbricals of 2nd and 3rd digits
Loss of sensation over thenar eminence and dorsal and palmar aspects of lateral 3 1 ⁄2 fingers with proximal lesion
Ulnar (C8-T1): caused of injury: Fracture of medial epicondyle of humerus “funny bone” (proximal lesion) Fractured hook of hamate (distal lesion) from fall on outstretched hand,
presentation :
“Ulnar claw” on digit extension
Radial deviation of wrist upon flexion (proximal lesion)
Loss of wrist flexion, flexion of medial fingers,
loss of abduction and adduction of fingers (interossei),
loss of actions of medial 2 lumbrical muscles
Loss of sensation over medial 1 1 /2 fingers including hypothenar eminence
Recurrent branch of median nerve (C5-T1): caused of injury: Superficial laceration of palm,
presentation:
“Ape hand”
Loss of thenar muscle group: opposition, abduction, and flexion of thumb
No loss of sensation
Erb palsy (“waiter’s tip”)-injury: Traction or tear of upper (“Erb-er”) trunk: C5-C6 roots, causes: Infants—lateral traction on neck during delivery, Adults—trauma, muscle deficit:Deltoid, supraspinatus, Infraspinatus, Biceps brachii
functional deficit: Abduction (arm hangs by side),
Lateral rotation (arm medially rotated),
Flexion, supination (arm extended and pronated)
Klumpke palsy-injury: Traction or tear of lower trunk: C8-T1 root, causes Infants—upward force on arm during delivery Adults—trauma (eg, grabbing a tree branch to break a fall), muscle deficit: Intrinsic hand muscles: lumbricals, interossei, thenar, hypothena,
functional deficit:
Total claw hand:
lumbricals normally flex MCP joints
and extend DIP and PIP joints
Thoracic outlet syndrome-injury: Compression of lower trunk and subclavian vessels, causes: Cervical rib (arrows in A ), Pancoast tumor, muscles deficit: same as Klumpke,
functional deficit: Atrophy of intrinsic hand muscles; ischemia, pain, and edema due to vascular compression
Winged scapula-injury: Lesion of long thoracic nerve, roots C5-C7 (“wings of heaven”), causes: Axillary node dissection after mastectomy, stab wounds, muscles deficit: Serratus anterior.
functional deficit: Inability to anchor scapula to thoracic cage –> cannot abduct arm above horizontal position (B)
At rest, a balance exists between the extrinsic flexors and extensors of the hand, as well as the intrinsic muscles of the hand—particularly the lumbrical muscles (flexion of MCP, extension of DIP and PIP joints).
“Clawing”—seen best with distal lesions of median or ulnar nerves. Remaining extrinsic flexors of the digits exaggerate the loss of the lumbricals –> fingers extend at MCP, flex at DIP and PIP joints.
Deficits less pronounced in proximal lesions; deficits present during voluntary flexion of the digits
Note: Atrophy of the thenar eminence (unopposable thumb–> “ape hand”) can be seen in median nerve lesions, while atrophy of the hypothenar eminence can be seen in ulnar nerve lesions.
Lateral femoral condyle to anterior tibia: ACL.
Medial femoral condyle to posterior tibia: PCL.
Anterior drawer sign
procedure: Bending knee at 90° angle, increase anterior gliding of tibia (relative to femur) due to ACL injury. Lachman test also tests ACL, but is more sensitive (increase anterior gliding of tibia [relative to femur] with knee bent at 30° angle).
Posterior drawer sign
Bending knee at 90° angle, increased posterior gliding of tibia due to PCL injury.
Abnormal passive abduction
Knee either extended or at ∼ 30° angle, lateral (valgus) force –> medial space widening of tibia –> MCL injury.
Abnormal passive adduction
Knee either extended or at ~ 30° angle, medial (varus) force –> lateral space widening of tibia –> LCL injury.
McMurray test
During flexion and extension of knee with rotation of tibia/foot:
Pain, “popping” on external rotation
–> medial meniscal tear (external rotation stresses medial meniscus)
Pain, “popping” on internal rotation
–> lateral meniscal tear (internal rotation stresses lateral meniscus)
Iliohypogastric (T12-L1): innervation: Sensory—suprapubic region Motor—transversus abdominis and internal oblique, cause of injury: Abdominal surgery, presentation:
Burning or tingling pain in surgical incision site radiating to inguinal and suprapubic region
Genitofemoral nerve (L1-L2): innervation: Sensory—scrotum/labia majora, medial thigh Motor—cremaster, cause of injury: Laparoscopic surgery,
presentation:
decrease anterior thigh sensation beneath inguinal ligament; absent cremasteric reflex
Lateral femoral cutaneous (L2-L3): innervation:Sensory—anterior and lateral thigh. cause of injury: Tight clothing, obesity, pregnancy, pelvic procedures, presentation:
decrease thigh sensation (anterior and lateral)
Obturator (L2-L4): innervation: Sensory—medial thigh Motor—obturator externus, adductor longus, adductor brevis, gracilis, pectineus, adductor magnus, cause of injury: Pelvic surgery,
presentation:
decrease thigh sensation (medial) and adduction
Femoral (L2-L4): innervation: Sensory—anterior thigh, medial leg Motor—quadriceps, iliacus, pectineus, sartorius, cause of injury: Pelvic fracture, presentation:
decrease thigh flexion and leg extension
Sciatic (L4-S3): innervation: Motor—semitendinosus, semimembranosus, biceps femoris, adductor magnus, cause of injury: Herniated disc, posterior hip dislocation,
presentation:
Splits into common peroneal and tibial nerves
Common peroneal (L4-S2): innervation: Superficial peroneal nerve: Sensory—dorsum of foot (except webspace between hallux and 2nd digit) Motor—peroneus longus and brevis Deep peroneal nerve: Sensory—webspace between hallux and 2nd digit Motor—tibialis anterior, cause of injury: Trauma or compression of lateral aspect of leg, fibular neck fracture,
presentation:
PED = Peroneal Everts and Dorsiflexes; if injured, foot dropPED
Loss of sensation on dorsum of foot
Foot drop—inverted and plantarflexed at rest, loss of eversion and dorsiflexion; “steppage gait”
Tibial (L4-S3): innervation: Sensory—sole of foot Motor—biceps femoris (long head), triceps surae, plantaris, popliteus, flexor muscles of foot, cause of injury:Knee trauma, Baker cyst (proximal lesion); tarsal tunnel syndrome (distal lesion),
presentation:
TIP = Tibial Inverts and Plantarflexes; if injured, can’t stand on TIPtoes Inability to curl toes and loss of sensation on sole;
in proximal lesions, foot everted at rest with loss of inversion and plantarflexion
Superior gluteal (L4-S1): innervation: Motor—gluteus medius, gluteus minimus, tensor fascia latae, cause of injury: Iatrogenic injury during intramuscular injection to superomedial gluteal region (prevent by choosing superolateral quadrant, preferably anterolateral region),
presentation:
Trendelenburg sign/gait— pelvis tilts because weightbearing leg cannot maintain alignment of pelvis through hip abduction Lesion is contralateral to the side of the hip that drops, ipsilateral to extremity on which the patient stands
Inferior gluteal (L5-S2): innervation: Motor—gluteus maximus, cause of injury: Posterior hip dislocation,
presenation:
Difficulty climbing stairs, rising from seated position; loss of hip extension
Pudendal (S2-S4): innervation: Sensory—perineum Motor—external urethral and anal sphincters, cause of injury: Stretch injury during childbirth,
presentation:
decrease sensation in perineum and genital area; can cause fecal or urinary incontinence
Can be blocked with local anesthetic during childbirth using ischial spine as a landmark for injection
Abductors Gluteus medius, gluteus minimus
Adductors Adductor magnus, adductor longus, adductor brevis
Extensors Gluteus maximus, semitendinosus, semimembranosus
Flexors Iliopsoas, rectus femoris, tensor fascia lata, pectineus, sartorius
Internal rotation Gluteus medius, gluteus minimus, tensor fascia latae
External rotation Iliopsoas, gluteus maximus, piriformis, obturator
Ankle sprains
Anterior TaloFibular ligament—most common ankle sprain overall, classified as a low ankle sprain. Due to overinversion/supination of foot. Always Tears First.
Anterior inferior tibiofibular ligament—most common high ankle sprain.
Signs of lumbosacral radiculopathy
Paresthesia and weakness related to specific lumbosacral spinal nerves. Usually, the intervertebral disc herniates into central canal, affecting the inferior nerves (eg, herniation of L3/4 disc affects L4 spinal nerve, but not L3).
Intervertebral discs generally herniate posterolaterally, due to the thin posterior longitudinal ligament and thicker anterior longitudinal ligament along the midline of the vertebral bodies.
L3–L4: Weakness of knee extension, patellar reflex
L4–L5: Weakness of dorsiflexion, difficulty in heelwalking
L5-S1:Weakness of plantar flexion, difficulty in toewalking, Achilles reflex
Neurovascular pairing-Nerves and arteries are frequently named together by the bones/regions with which they are associated. The following are exceptions to this naming convention.
Axilla/lateral thorax: nerve: Long thoracic, artery: Lateral thoracic
Surgical neck of humerus: nerve: Axillary, artery: Posterior circumflex
Midshaft of humerus: Nerve: radial, artery: Deep brachial
Distal humerus/ cubital fossa: nerve: Median, artery: Brachial
Popliteal fossa: nerve: Tibial, artery: Popliteal
Posterior to medial malleolus: nerve: Tibia, artery: Posterior tibia
Motoneuron action potential to muscle contraction-T-tubules are extensions of plasma membrane in contact with the sarcoplasmic reticulum, allowing for coordinated contraction of striated muscles.
- Action potential opens presynaptic voltagegated Ca2+ channels, inducing acetylcholine (ACh) release.
- Postsynaptic ACh binding leads to muscle cell depolarization at the motor end plate.
- Depolarization travels over the entire muscle cell and deep into the muscle via the T-tubules.
- Membrane depolarization induces conformational changes in the voltagesensitive dihydropyridine receptor (DHPR) and its mechanically coupled ryanodine receptor (RR) –> Ca2+ release from the sarcoplasmic reticulum into the cytoplasm.
- Tropomyosin is blocking myosin-binding sites on the actin filament. Released Ca2+ binds to troponin C (TnC), shifting tropomyosin to expose the myosin-binding sites
- The myosin head binds strongly to actin, forming a crossbridge. Pi is then released, initiating the power stroke.
- During the power stroke, force is produced as myosin pulls on the thin filament. Muscle shortening occurs, with shortening of H and I bands and between Z lines (HIZ shrinkage). The A band remains the same length (A band is Always the same length). ADP is released at the end of the power stroke.
- Binding of new ATP molecule causes detachment of myosin head from actin filament. Ca2+ is resequestered.
9 ATP hydrolysis into ADP and Pi results in myosin head returning to high-energy position (cocked). The myosin head can bind to a new site on actin to form a crossbridge if Ca2+ remains available.
types of muscle fibers
Type 1 muscle-Slow twitch; red fibers resulting from increased mitochondria and myoglobin concentration (increased oxidative phosphorylation) –> sustained contraction. Proportion increased after endurance training.
type 2 muscle: Fast twitch; white fibers resulting from decrease mitochondria and myoglobin concentration (increase anaerobic glycolysis). Proportion increase after weight/resistance training, sprinting.
bone formation
Endochondral ossification-Bones of axial skeleton, appendicular skeleton, and base of skull. Cartilaginous model of bone is first made by chondrocytes. Osteoclasts and osteoblasts later replace with woven bone and then remodel to lamellar bone. In adults, woven bone occurs after fractures and in Paget disease. Defective in achondroplasia.
Membranous ossification-Bones of calvarium, facial bones, and clavicle. Woven bone formed directly without cartilage. Later remodeled to lamellar bone.
cell biology of bones
Osteoblast-Builds bone by secreting collagen and catalyzing mineralization in alkaline environment via ALP. Differentiates from mesenchymal stem cells in periosteum. Osteoblastic activity measured by bone ALP, osteocalcin, propeptides of type I procollagen
Osteoclast -Dissolves (“crushes”) bone by secreting H+ and collagenases. Differentiates from a fusion of monocyte/macrophage lineage precursors. RANK receptors on osteoclasts are stimulated by RANKL (RANK ligand, secreted by osteoblasts). RANK receptors blocked by OPG (osteoprotegerin, a RANKL decoy receptor) –> decreased osteoclast activity.
Parathyroid hormone At low, intermittent levels, exerts anabolic effects (building bone) on osteoblasts and osteoclasts (indirect). Chronically increased PTH levels (1° hyperparathyroidism) cause catabolic effects (osteitis fibrosa cystica).
Estrogen Inhibits apoptosis in bone-forming osteoblasts and induces apoptosis in bone-resorbing osteoclasts. Causes closure of epiphyseal plate during puberty. Estrogen deficiency (surgical or postmenopausal) –> increased cycles of remodeling and bone resorption –> increased risk of osteoporosis.
muscle proprioceptors
muscle spindle- sense length and speed of stretch. facilitates muscle agonist contraction and antagonist relaxation to prevent overstretching. increased length (stretch) –> muscle resistance
location: body of muscle/type 1a and 2 sensory
Golgi tendon: senses tension. facilitates inhibition of muscle activation to reduce tension within the muscle and tendon. increase tendon–> muscle relaxation
location: tendons/type Ib sensory axons
