Musculoskeletal, Skin, and Connective Tissue - First Aid Flashcards
Arm Abduction
Rotator Cuff Muscles
Shoulder muscles that form the rotator cuff (SItS):
-
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.
Overuse Injuries of the Elbow:
- repetitive flexion (forehand shots)
- idiopathic
Medial Epicondylitis
(golfer’s elbow)
Overuse Injuries of the Elbow:
- repetitive extension (backhand shots)
- idiopathic
Lateral Epicondylitis
(tennis elbow)
Wrist Region:
So Long To Pinky, Here Comes The Thumb.
- Scaphoid
- Lunate
- Triquetrum
- Pisiform
- Hamate
- Capitate
- Trapezoid
- Trapezium
- Scaphoid (palpable in anatomic snuff box) 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.
Wrist Region:
- also called boxer’s fracture
- common fracture caused by direct blow with a closed fist (eg. from punching a wall or individual)
- most commonly seen in 4th and 5th metacarpals
Metacarpal Neck Fracture
Wrist Region:
- entrapment of median nerve in carpal tunnel (between transverse carpal ligament and carpal bones)
- nerve compression → paresthesia, pain, and numbness in distribution of median nerve
- thenar eminence atrophies but sensation spared, because palmar cutaneous branch enters hand external to carpal tunnel
- suggested by ⊕ Tinel sign (percussion of wrist causes tingling) and Phalen maneuver (90° flexion of wrist causes tingling)
- associated with pregnancy (due to edema), rheumatoid arthritis, hypothyroidism, diabetes, acromegaly, and dialysis-related amyloidosis
- may be associated with repetitive use
Carpal Tunnel Syndrome
Wrist Region:
- compression of ulnar nerve at wrist
- classically seen in cyclists due to pressure from handlebars
Guyon Canal Syndrome
Common Pediatric Fractures:
- incomplete fracture extending partway through width of bone following bending stress
- bone fails on tension side
- compression side intact
- bone is bent like a green twig
Greenstick Fracture
Common Pediatric Fractures:
- axial force applied to immature bone → cortex buckles on compression side and fractures
- tension side (other side of cortex) remains intact
Torus (buckle) Fracture
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 (OAF).:
- Oppose
- Abduct
- Flex
DAB = Dorsals ABduct
PAD = Palmars ADduct
Upper Extremity Nerves
- Axillary (C5-C6)
- Musculocutaneous (C5-C7)
- Radial (C5-T1)
- Median (C5-T1)
- Ulnar (C8-T1)
- Recurrent Branch of Median Nerve (C5-T1)
Upper Extremity Nerves:
- Causes 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
Axillary (C5-C6)
Upper Extremity Nerves:
- Causes of Injury:
- upper trunk compression
- Presentation:
- loss of forearm flexion and supination
- loss of sensation over lateral forearm
Musculocutaneous (C5-C7)
Upper Extremity Nerves:
- Causes of Injury:
- compression of axilla, eg. due to crutches or sleeping with arm over chair (“Saturday night palsy”)
- midshaft fracture of humerus
- repetitive pronation/supination of forearm, eg. due to screwdriver use (“finger drop”)
- Presentation:
- wrist drop: loss of elbow, wrist, and finger extension
- ↓ grip strength (wrist extension necessary for maximal action of flexors)
- loss of sensation over posterior arm/forearm and dorsal hand
Radial (C5-T1)
Upper Extremity Nerves:
- Causes 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, flexion of lateral fingers, thumb opposition, lumbricals of 2nd and 3rd digits
- loss of sensation over thenar eminence and dorsal and palmar aspects of lateral 31⁄2 fingers with proximal lesion
Median (C5-T1)
Upper Extremity Nerves:
- Causes 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, abduction and adduction of fingers (interossei), actions of medial 2 lumbrical muscles
- loss of sensation over medial 1 1/2 fingers including hypothenar eminence
Ulnar (C8-T1)
Upper Extremity Nerves:
- Causes of Injury:
- superficial laceration of palm
- Presentation:
- “ape hand”
- loss of thenar muscle group: opposition, abduction, and flexion of thumb
- no loss of sensation
Recurrent Branch of Median Nerve (C5-T1)
Humerus fractures, proximally to distally, follow the _____.
ARM
Axillary → Radial → Median
Brachial Plexus
Randy Travis Drinks Cold Beer:
- Roots
- Trunks
- Divisions
- Cords
- Branches
Brachial Plexus Lesions
① Erb palsy (“waiter’s tip”)
② Klumpke palsy (claw hand)
③ wrist drop
④ winged scapula
⑤ deltoid paralysis
⑥ “saturday night palsy” (wrist drop)
⑦ difficulty flexing elbow, variable sensory loss
⑧ decreased thumb function, “pope’s blessing”
⑨ intrinsic muscles of hand, claw hand
Brachial Plexus Lesions:
- Injury:
- traction or tear of upper 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)
Erb palsy (“waiter’s tip”)
Brachial Plexus Lesions:
- 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
- hypothenar
- Intrinsic Hand Muscles:
- Functional Deficit:
- Total Claw Hand:
- lumbricals normally flex MCP joints and extend DIP and PIP joints
- Total Claw Hand:
Klumpke palsy
Brachial Plexus Lesions:
- Injury:
- compression of lower trunk and subclavian vessels
- Causes:
- cervical rib
- Pancoast tumor
- Muscle Deficit:
- same as Klumpke palsy
- Functional Deficit:
- atrophy of intrinsic hand muscles
- ischemia, pain, and edema due to vascular compression
Thoracic Outlet Ssyndrome
Brachial Plexus Lesions:
- Injury:
- lesion of long thoracic nerve
- roots C5-C7
- Causes:
- axillary node dissection after mastectomy
- stab wounds
- Muscle Deficit:
- serratus anterior
- Functional Deficit:
- inability to anchor scapula to thoracic cage → cannot abduct arm above horizontal position
Winged Scapula
Distortions of the Hand
- 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.
- 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.
Knee Exam
LAMP:
- Lateral femoral condyle to anterior tibia: ACL
- Medial femoral condyle to posterior tibia: PCL
Knee Exam:
- bending knee at 90° angle, ↑ anterior gliding of tibia (relative to femur) due to ACL injury
- Lachman test also tests ACL, but is more sensitive (↑ anterior gliding of tibia [relative to femur] with knee bent at 30° angle)
Anterior Drawer Sign
Knee Exam:
bending knee at 90° angle, ↑ posterior gliding of tibia due to PCL injury
Posterior drawer sign
Knee Exam:
knee either extended or at ∼ 30° angle, lateral (valgus) force → medial space widening of tibia → MCL injury
Abnormal Passive Abduction
Knee Exam:
knee either extended or at ~ 30° angle, medial (varus) force → lateral space widening of tibia → LCL injury
Abnormal Passive Adduction
Knee Exam:
- 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)
McMurray Test
Common Hip and Knee Conditions:
- Inflammation of the gluteal tendon and bursa lateral to greater trochanter of femur
- treat pain with NSAIDs, heat, stretching
Trochanteric Bursitis
Common Hip and Knee Conditions:
- common injury in contact sports due to lateral force applied to a planted leg
- classically, consists of damage to the ACL, MCL, and medial meniscus (attached to MCL); however, lateral meniscus injury is more common
- presents with acute knee pain and signs of joint injury/instability
“Unhappy Triad”
Common Hip and Knee Conditions:
- inflammation of the prepatellar bursa in front of the kneecap
- can be caused by repeated trauma or pressure from excessive kneeling (also called “housemaid’s knee”)
Prepatellar Bursitis
Common Hip and Knee Conditions:
popliteal fluid collection in gastrocnemius-semimembranosus bursa commonly communicating with synovial space and related to chronic joint disease (eg. osteoarthritis, rheumatoid arthritis)
Baker Cyst
Ankle Sprains
-
Anterior TaloFibular ligament
- Always Tears First—most common ankle sprain overall, classified as a low ankle sprain
- due to overinversion/supination of foot
- Anterior Inferior Tibiofibular ligament
- most common high ankle sprain
Lower Extremity Nerves
- Iliohypogastric (T12-L1)
- Genitofemoral(L1-L2)
- Lateral Femoral Cutaneous (L2-L3)
- Obturator (L2-L4)
- Femoral (L2-L4)
- Sciatic (L4-S3)
- Common Peroneal (L4-S2)
- Tibial (L4-S3)
- Superior Gluteal (L4‑S1)
- Inferior Gluteal (L5-S2)
- Pudendal (S2-S4)
Lower Extremity Nerves:
- 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
Iliohypogastric (T12-L1)
Lower Extremity Nerves:
- Sensory—scrotum/labia majora, medial thigh
- Motor—cremaster
- Cause of Injury:
- laparoscopic surgery
- Presentation:
- ↓ anterior thigh sensation beneath inguinal ligament
- absent cremasteric reflex
Genitofemoral (L1-L2)
Lower Extremity Nerves:
- Sensory—anterior and lateral thigh
- Cause of Injury:
- tight clothing
- obesity
- pregnancy
- pelvic procedures
- Presentation:
- ↓ thigh sensation (anterior and lateral)
Lateral Femoral Cutaneous (L2-L3)
Lower Extremity Nerves:
- Sensory—medial thigh
- Motor—obturator externus, adductor longus, adductor brevis, gracilis, pectineus, adductor magnus
- Cause of Injury:
- pelvic surgery
- Presentation:
- ↓ thigh sensation (medial) and adduction
Obturator (L2-L4)
Lower Extremity Nerves:
- Sensory—anterior thigh, medial leg
- Motor—quadriceps, iliacus, pectineus, sartorius
- Cause of Injury:
- pelvic fracture
- Presentation:
- ↓ thigh flexion and leg extension
Femoral (L2-L4)
Lower Extremity Nerves:
- Motor—semitendinosus, semimembranosus, biceps femoris, adductor magnus
- Cause of Injury:
- herniated disc
- posterior hip dislocation
- splits into common peroneal and tibial nerves
Sciatic (L4-S3)
Lower Extremity Nerves:
- Superficial:
- Sensory—dorsum of foot (except webspace between hallux and 2nd digit)
- Motor—peroneus longus and brevis
- Deep:
- 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:
- loss of sensation on dorsum of foot
- Foot Drop—inverted and plantarflexed at rest, loss of eversion and dorsiflexion; “steppage gait”
Common Peroneal (L4-S2)
PED = Peroneal Everts and Dorsiflexes; if injured, foot dropPED
Lower Extremity Nerves:
- 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:
- inability to curl toes and loss of sensation on sole
- in proximal lesions, foot everted at rest with loss of inversion and plantarflexion
Tibial (L4-S3)
TIP = Tibial Inverts and Plantarflexes; if injured, can’t
stand on TIPtoes
Lower Extremity Nerves:
- 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 weight-bearing 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
Superior Gluteal (L4‑S1)
Lower Extremity Nerves:
- Motor—gluteus maximus
- Cause of Injury:
- posterior hip dislocation
- Presentation:
- difficulty climbing stairs and rising from seated position
- loss of hip extension
Inferior Gluteal (L5-S2)
Lower Extremity Nerves:
- Sensory—perineum
- Motor—external urethral andanal sphincters
- Cause of Injury:
- stretch injury during childbirth
- Presentation:
- ↓ 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
Pudendal (S2-S4)
Hip Muscles:
Abductors
- gluteus medius
- gluteus minimus
Hip Muscles:
Adductors
- adductor magnus
- adductor longus
- adductor brevis
Hip Muscles:
Extensors
- gluteus maximus
- semitendinosus
- semimembranosus
Hip Muscles:
Flexors
- iliopsoas
- rectus femoris
- tensor fascia lata
- pectineus
- sartorius
Hip Muscles:
Internal Rotation
- gluteus medius
- gluteus minimus
- tensor fascia latae
Hip Muscles:
External Rotation
- iliopsoas
- gluteus maximus
- piriformis
- obturator
Common Musculoskeletal Conditions:
- overuse injury of lateral knee that occurs primarily in runners
- pain develops 2° to friction of iliotibial band against lateral femoral epicondyle
Iliotibial Band Syndrome
Common Musculoskeletal Conditions:
- also called shin splints
- common cause of shin pain and diffuse tenderness in runners and military recruits
- caused by bone resorption that outpaces bone formation in tibial cortex
Medial Tibial Stress Syndrome
Common Musculoskeletal Conditions:
- ↑ pressure within a fascial compartment of a limb (defined by compartment pressure to diastolic blood pressure gradient of < 30 mm Hg) → venous outflow obstruction and arteriolar collapse → anoxia and necrosis
- causes include significant long bone fractures, reperfusion injury, and animal venoms
- presents with severe pain and tense, swollen compartments with limb flexion
- motor deficits are late sign of irreversible muscle and nerve damage
Limb Compartment Syndrome
Common Musculoskeletal Conditions:
inflammation of plantar aponeurosis characterized by heel pain (worse with first steps in the morning or after period of inactivity) and tenderness
Plantar Fasciitis
Common Musculoskeletal Conditions:
- noninflammatory thickening of abductor pollicis longus and extensor pollicis brevis tendons characterized by pain or tenderness at radial styloid
- ⊕ Finkelstein test (pain at radial styloid with active or passive stretch of thumb tendons).
De Quervain Tenosynovitis
Common Musculoskeletal Conditions:
- fluid-filled swelling overlying joint or tendon sheath, most commonly at dorsal side of wrist
- arises from herniation of dense connective tissue
Ganglion Cyst
Childhood Musculoskeletal Conditions:
- abnormal acetabulum development in newborns
- results in hip instability/dislocation
- commonly tested with Ortolani and Barlow maneuvers (manipulation of newborn hip reveals a “clunk”)
- confirmed via ultrasound (x-ray not used until ~4–6 months because cartilage is not ossified)
- Treatment: splint/harness
Developmental Dysplasia of the Hip
Childhood Musculoskeletal Conditions:
- idiopathic avascular necrosis of femoral head
- commonly presents between 5–7 years with insidious onset of hip pain that may cause child to limp
- more common in males (4:1 ratio)
- initial x-ray often normal
Legg-Calvé-Perthes Disease
Childhood Musculoskeletal Conditions:
- classically presents in an obese ~12-year-old child with hip/knee pain and altered gait
- increased axial force on femoral head → epiphysis displaces relative to femoral neck (like a scoop of ice cream slipping off a cone)
- diagnosed via x-ray
- Treatment: surgery
Slipped Capital Femoral Epiphysis
Childhood Musculoskeletal Conditions:
- overuse injury caused by repetitive strain and chronic avulsion of the secondary ossification center of proximal tibial tubercle
- occurs in adolescents after growth spurt
- common in running and jumping athletes
- presents with progressive anterior knee pain
Osgood-Schlatter Disease (Traction Apophysitis)
Childhood Musculoskeletal Conditions:
- common elbow injury in children < 5 years
- caused by a sudden pull on the arm → immature annular ligament slips over head of radius
- injured arm held in flexed and pronated position
Radial Head Subluxation (Nursemaid’s Elbow)
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.
Signs of Lumbosacral Radiculopathy:
- weakness of knee extension
- ↓ patellar reflex
L3–L4
Signs of Lumbosacral Radiculopathy:
- weakness of dorsiflexion
- difficulty in heel-walking
L4–L5
Signs of Lumbosacral Radiculopathy:
- weakness of plantar flexion
- difficulty in toewalking
- ↓ Achilles reflex
L5-S1
Neurovascular Pairing
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.
① Action potential opens presynaptic voltage-gated Ca2+ channels, inducing acetylcholine
(ACh) release.
② Postsynaptic ACh binding leads to muscle cell depolarization at the motor end plate.
③ Depolarization travels over the entire muscle cell and deep into the muscle via the T-tubules.
④ Membrane depolarization induces conformational changes in the voltage-sensitive dihydropyridine receptor (DHPR) and its mechanically coupled ryanodine receptor (RR) → Ca2+ release from the sarcoplasmic reticulum into the cytoplasm.
⑤ 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.
⑥ The myosin head binds strongly to actin, forming a crossbridge. Pi is then released, initiating the power stroke.
⑦ 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.
⑧ 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:
- slow twitch
- red fibers resulting from ↑ mitochondria and myoglobin concentration (↑ oxidative phosphorylation) → sustained contraction
- proportion ↑ after endurance training
Type 1
1 slow red ox
Types of Muscle Fibers:
- fast twitch
- white fibers resulting from ↓ mitochondria and myoglobin concentration (↑ anaerobic glycolysis)
- proportion ↑ after weight/resistance training or sprinting
Type 2
Smooth Muscle Contraction and Relaxation
Bone Formation:
- 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
Endochondral Ossification
Bone Formation:
- bones of calvarium, facial bones, and clavicle
- woven bone formed directly without cartilage
- later remodeled to lamellar bone
Membranous Ossification
Bone Histology:
- builds bone by secreting collagen and catalyzing mineralization in alkaline environment via ALP
- differentiates from mesenchymal stem cells in periosteum
- activity is measured by bone ALP, osteocalcin, and propeptides of type I procollagen
Osteoblast
Bone Histology:
- dissolves bone by secreting H+ and collagenases differentiates from a fusion of monocyte/macrophage lineage precursors
- RANK receptors on _____ are stimulated by RANKL (RANK ligand, secreted by osteoblasts)
- RANK receptors blocked by OPG (osteoprotegerin, a RANKL decoy receptor) → ↓ osteoclast activity
Osteoclast
Bone Endocrinology:
- at low, intermittent levels, exerts anabolic effects (building bone) on osteoblasts and osteoclasts (indirect)
- chronically ↑ levels (1° hyperparathyroidism) cause catabolic effects (osteitis fibrosa cystica)
Parathyroid Hormone
Bone Endocrinology:
- inhibits apoptosis in bone-forming osteoblasts and induces apoptosis in bone-resorbing osteoclasts
- causes closure of epiphyseal plate during puberty
- deficiency (surgical or postmenopausal) → ↑ cycles of remodeling and bone resorption → ↑ risk of osteoporosis
Estrogen
Musculoskeletal Pathologies:
- failure of longitudinal bone growth (endochondral ossification) → short limbs
- membranous ossification is affected → large head relative to limbs
- constitutive activation of fibroblast growth factor receptor (FGFR3) actually inhibits chondrocyte proliferation
- > 85% of mutations occur sporadically
- autosomal dominant with full penetrance (homozygosity is lethal)
- associated with ↑ paternal age
- most common cause of dwarfism
Achondroplasia
Musculoskeletal Pathologies:
- Trabecular (spongy) and cortical bone lose mass and interconnections despite normal bone mineralization and lab values (serum Ca2+ and PO43−).
- Most commonly due to ↑ bone resorption related to ↓ estrogen levels and old age
- Can be 2° to drugs (eg. steroids, alcohol, anticonvulsants, anticoagulants, thyroid replacement therapy) or other medical conditions (eg. hyperparathyroidism, hyperthyroidism, multiple myeloma, malabsorption syndromes).
- Diagnosed by bone mineral density measurement by DEXA (dual-energy X-ray absorptiometry) at the lumbar spine, total hip, and femoral neck, with a T-score of ≤ −2.5 or by a fragility fracture (eg. fall from standing height, minimal trauma) at hip or vertebra.
- One time screening recommended in women ≥ 65 years old.
Osteoporosis
Osteoporosis Prophylaxis
- regular weight-bearing exercise
- adequate Ca2+ and vitamin D intake throughout adulthood
Osteoporosis Treatment:
- Bisphosphonates
- Teriparatide
- SERMs
- Calcitonin
- Denosumab (monoclonal antibody against RANKL)
Osteoporosis can lead to _____—acute back pain, loss of height, kyphosis. Also can present with fractures of femoral neck, distal radius (Colles fracture).
Vertebral Compression Fractures
Musculoskeletal Pathologies:
- Failure of normal bone resorption due to defective osteoclasts → thickened, dense bones that are prone to fracture.
- Mutations (eg. carbonic anhydrase II) impair ability of osteoclast to generate acidic environment necessary for bone resorption.
- Overgrowth of cortical bone fills marrow space → pancytopenia, extramedullary hematopoiesis.
- Can result in cranial nerve impingement and palsies due to narrowed foramina.
- X-rays show diffuse symmetric sclerosis (bone-in-bone, “stone bone”).
- Bone marrow transplant is potentially curative as osteoclasts are derived from monocytes.
Osteopetrosis
Musculoskeletal Pathologies:
- Defective mineralization of osteoid (osteomalacia) or cartilaginous growth plates (rickets, only in children).
- Most commonly due to vitamin D deficiency.
- Children have pathologic bow legs (genu varum), bead-like costochondral junctions (rachitic rosary), craniotabes (soft skull).
- ↓ vitamin D → ↓ serum Ca2+ → ↑ PTH secretion → ↓ serum PO43−
- hyperactivity of osteoblasts → ↑ ALP
Osteomalacia/Rickets
Musculoskeletal Pathologies:
xrays show osteopenia and “Looser zones” (pseudofractures)
Osteomalacia
Musculoskeletal Pathologies:
x-rays show epiphyseal widening and metaphyseal cupping/fraying
Rickets
Musculoskeletal Pathologies:
- Common, localized disorder of bone remodeling caused by ↑ osteoclastic activity followed by ↑ osteoblastic activity that forms poor-quality bone
- Serum Ca2+, phosphorus, and PTH levels are normal
- ↑ ALP
- Mosaic pattern of woven and lamellar bone (osteocytes within lacunae in chaotic juxtapositions); long bone chalk-stick fractures.
- ↑ blood flow from ↑ arteriovenous shunts may cause high-output heart failure.
- ↑risk of osteogenic sarcoma.
- Hat size can be increased due to skull thickening.
- Hearing loss is common due to auditory foramen narrowing.
- Treatment: bisphosphonates
Paget Disease of Bone (Osteitis Deformans)
Stages of Paget Disease
- Lytic—osteoclasts
- Mixed—osteoclasts + osteoblasts
- Sclerotic—osteoblasts
- Quiescent—minimal osteoclast/osteoblast activity
Musculoskeletal Pathologies:
- infarction of bone and marrow
- usually very painful
- most common site is femoral head (watershed zone) due to insufficiency of medial circumflex femoral artery
Osteonecrosis (Avascular Necrosis)
Causes of Osteonecrosis (Avascular Necrosis)
CAST Bent LEGS:
- Corticosteroids
- Alcoholism
- Sickle cell disease
- Trauma
- “the Bends” (caisson/decompression disease)
- LEgg-Calvé-Perthes disease (idiopathic)
- Gaucher disease
- Slipped capital femoral epiphysis
Bone Disorders:
- — Serum Ca2+
- — PO43−
- — ALP
- — PTH
- ↓ bone mass
Osteoporosis
Bone Disorders:
- —/↓ Serum Ca2+
- — PO43−
- — ALP
- — PTH
- dense, brittle bones
- Ca2+ ↓ in severe, malignant disease
Osteopetrosis
Bone Disorders:
- — Serum Ca2+
- — PO43−
- ↑ ALP
- — PTH
- abnormal “mosaic” bone architecture
Paget Disease of Bone
Bone Disorders:
- ↑ Serum Ca2+
- ↓ PO43−
- ↑ ALP
- ↑ PTH
- “brown tumors” due to fibrous replacement of bone
- subperiosteal thinning
- idiopathic or parathyroid hyperplasia, adenoma, carcinoma
Osteitis Fibrosa Cystica
- Primary Hyperparathyroidism