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pathology
Musculoskeletal, skin, and connective tissue ` anatomy and physiology Don’t delete section iii 459
Musculoskeletal, skin, and connective tissue ` pathology
Cell biology of bone
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, expressed on osteoblasts). OPG (osteoprotegerin, a RANKL decoy
receptor) binds RANKL to prevent RANK-RANKL interaction osteoclast activity.
Parathyroid hormone At low, intermittent levels, exerts anabolic effects (building bone) on osteoblasts and osteoclasts
(indirect). Chronically 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) cycles of remodeling and bone resorption risk of osteoporosis.
` mUsCUlosKElEtal, sKin, and ConnECtiVE tissUE—pathology
Overuse injuries of the elbow
Medial epicondylitis Repetitive flexion (forehand shots) or idiopathic pain near medial epicondyle.
(golfer’s elbow)
Lateral epicondylitis Repetitive extension (backhand shots) or idiopathic pain near lateral epicondyle.
(tennis elbow)
Wrist and hand injuries
Metacarpal neck Also called boxer’s fracture. Common fracture
fracture caused by direct blow with a closed fist (eg,
from punching a wall). Most commonly seen
A
in 4th and 5th metacarpals A .
Carpal tunnel Entrapment of median nerve in carpal tunnel Suggested by ⊕ Tinel sign (percussion of wrist
syndrome (between transverse carpal ligament and carpal causes tingling) and Phalen maneuver (90°
bones) nerve compression paresthesia, flexion of wrist causes tingling).
B
pain, and numbness in distribution of median Associated with pregnancy (due to edema),
nerve. Thenar eminence atrophies B but rheumatoid arthritis, hypothyroidism, diabetes,
sensation spared, because palmar cutaneous acromegaly, dialysis-related amyloidosis; may
branch enters hand external to carpal tunnel. be associated with repetitive use.
Guyon canal Compression of ulnar nerve at wrist. Classically
syndrome seen in cyclists due to pressure from
handlebars.
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