TBL12 Flashcards
Vertebral column derived from?
somite-derived
Scapula, clavicle, and bones of the upper extremities derived from?
parietal mesoderm
What forms the cartilaginous replicas of embryonic bones?
chondrocytes and the noncalcified, avascular extracellular matrix
What surrounds the chondrocytes + matrix
perichondrium; oxygen and nutrients diffuse from the perichondrial capillaries
Bony collar
forms around the diaphysis and blocks diffusion from the perichondrial capillaries into the avascular space -> degradation of chondrocytes
Periosteum
covers the bony collar and eventually the whole bone except at the joints
What happens after the bony collar forms?
periosteal capillaries, osteoblasts, and macrophages invade the degrading replica to initiate endochondral ossification (i.e., replacement of the replica by bone); clusters of fused macrophages form osteoclasts that aggressively phagocytize the degrading cartilage -> primary ossification center
Osteoblasts
produce thick, randomly organized collagen fibers that enclose the osteoblasts within lacunae (i.e., the osteoblasts become osteocytes); osteocytes induce the deposition of hydroxyapatite crystals on the thick collagen fibers, which subsequently align in parallel rows that separate the osteocyte-filled lacunae.
Trabecular bone. Purpose of collagen and hydroxyapatite?
osteocytes and mineralized matrix organize into a meshwork of trabeculae; collagen fibers provide strength and the hydroxyapatite crystals provide hardness to the matrix. Osteoblasts that cover the surface of the trabeculae are essential for continued bone maturation
What section of the bone becomes trabecular bone first?
trabecular bone occupies the diaphysis and cartilaginous epiphyses (not labeled) reside at both ends of the diaphysis
How do epiphyseal growth plates form?
epiphyseal chondrocytes near the diaphysis proliferate to form cellular columns that align parallel with the long axis of the developing bone
Growth plate organization
chondrocytes immediately adjacent to the diaphysis degenerate and concurrent growth of the trabecular bone replaces the eroded cells (i.e., progressive replacement of eroded chondrocytes with trabecular bone enables lengthening of the developing bone).
Secondary ossification center
As trabecular bone at the periphery of the diaphysis is transformed into compact bone, formation of trabecular bone occurs in the epiphyses; trabecular bone at the periphery of the epiphyses is transformed into compact bone by age 10
When do bones stop growing?
growth plates remain active throughout puberty and bony union of the diaphysis with the epiphyses occurs at skeletal maturity.
Why is achondroplasia associated with skeletal dysplasia (e.g., dwarfism)?
mutation in FGFR3; normally has a negative regulatory effect on bone growth but mutation has receptor constitutely on -> shortened long bones
Structure of mature bone
compact (aka dense) bone at the periphery and the trabecular bone in the center
What initiates transfomration of trabecular bone into compact bone
primary osteons (i.e., oval profiles of trabecular bone at the periphery of the developing bone)
Structure of primary osteons
capillaries are centrally positioned and osteoblasts on the surface of the trabeculae create the peripheral boundaries
How do primary osteons become secondary osteons?
continued, inward deposition of bony matrix by the osteoblasts encloses the capillaries with concentric rows of lacunae separated by parallel, mineralized collagen fibers (i.e., primary osteons of trabecular bone become secondary osteons of compact bone)
Structure of secondary osteons (or Haversian system)
capillaries reside in osteoblast-lined central (ignore Haversian) canals; the concentric dotted lines represent osteocyte-filled lacunae separated by bony matrix. Oriented parallel to the long axis of the bone.
Canaliculi structure
tiny canals in the bony matrix that interconnect the concentric rows of lacunae and connect the innermost row to the central canal
Canaliculi function
enable capillary filtrates to spread from the central canals into the lacunae to sustain the osteocytes; connect the lacunae to the surface of the trabeculae to enable filtrates from capillaries in the bone marrow to sustain the osteocytes
Volkmann canals
join the central canals at right angles to enable continuity of the periosteal capillaries with the capillaries of the secondary osteons
Intersitial lamellae
separates adjacent osteons; remnants of secondary osteons after bone remodeling that occurs throughout life to adapt bones to changing physical stresses (e.g., after weight gains or new physical training regimens)
Effect of bone vascularity
ensures good regenerative potential for remodeling and deposition rates must match resorption rates to maintain skeletal integrity
Central trabecular bone of mature bones is occupied with?
bone marrow
Glenohumeral (shoulder joint) structure
the humerus articulates with the scapula
Glenoid cavity of scapula accept % of the humeral head at the joint
a third
Glenoid labrum
concentric rings of collagen fibers that attaches to the rim of the cavity to slightly but effectively deepen it
tonus of the rotator cuff muscles
essential for holding the humeral head in the glenoid cavity
Acromioclavicular (AC) joint structure
the lateral end of the clavicle articulates with the acromion
AC joint function
enables the clavicle to act as a strut (rigid support) that suspends the scapula and allows it to slide along the posterior thoracic wall
Coracoclavicular ligament (2)
prevents dislocation of the AC joint
Coracoacromial arch
coracoid process, acromion, and coracoacromial ligament -> prevents superior displacement of the humeral head from the glenoid cavity.
When does dislocation of the acromioclavicular joint occur and why is it described as a shoulder separation?
Occurs from a hard fall on the shoulder/outstretched upper limb, driven into the boards, severe blow to superolateral part of the back; “shoulder separation” because shoulder separates from the clavicle and falls because of the weight of the upper limbb
Why do most dislocations of the humeral head occur in an inferior direction, and why are such dislocations commonly described clinically as anterior dislocations?
Coraco-acromial arch prevents upward dislocation; anterior dislocation because hard blow when glenohumeral joint is fully abduted tilts the head of the humerus inferiorly onto the inferior weak part of the joint capsule
Intrinsic shoulder muscle attachements (generally)
attach to the scapula and clavicle proximally and to the humerus distally; thus, the muscles act on the glenohumeral joint (i.e., a muscle or its tendon must cross a joint to act upon it)
Adduction vs abduction
abduction - move arm to 90 degrees
Flexion vs extension
flexion - forward (arm), upward (wrist, elbow)
Location of greater and less tubercules, intertubercular sulcus, surgical neck, deltoid tuberosity
know it
Deltoid attachment
proximal attachment of the anterior, middle, and posterior parts of the deltoid begins at the lateral end of the clavicle and continues onto the scapular spine. Recognize all three parts attach to the deltoid tuberosity distally
Deltoid function
simultaneous contraction of all three parts of the deltoid with assistance from the supraspinatus muscle (assessed below) abducts the upper limb to 90 degrees
Teres major
which attaches to the inferior angle of the scapula proximally and to the medial surface of the humerus distally, medially rotates the arm
Location of supraspinous and infraspinous fossae, superior and inferior angles
know it
What attaches to the superior angle distally?
levator scapulae
Supraspinatus muscle
attaches to supraspinous fossae proximally and to the greater tubercle of the humerus distally; induces the first 15 degrees of abduction
Infraspinatus muscle
attaches to infraspinous fossae proximally and to the greater tubercle of the humerus distally; laterally rotates the arm
Teres minor
attaches to the lateral border of the scapula proximally and to the greater tubercle of the humerus distally; thus, it assists the infraspinatus during lateral rotation of the arm
Subacromial bursa
thin, fluid filled; cushions the tendon of the supraspinatus as it passes between the humeral head and coracoacromial arch to reach the greater tubercle
Subscapularis
attaches to the anterior surface of the scapula proximally and to the lesser tubercle of the humerus distally, medially rotates the arm
Suprascapular nerve
innervates the supraspinatus and infraspinatus
Axillary nerve
innervates the teres minor and courses across the surgical neck on the posterior surface of the humerus to innervate the deltoid
Subscapular nerve
innervates both the subscapularis and the teres major
Why is the upper extremity pulled into medial rotation after an avulsion fracture of the greater tubercle?
muscles (especially the subscapularis) that remain attached to the humerus pull the limb into the medial rotation
How is the axillary nerve commonly injured at the surgical neck of the humerus, and where does loss of sensation occur after the injury?
axillary nerve injuried by fracture at the surgical neck, dislocation of the glenohumeral joint, and by compression from the incorrect use of crutches; loss of sensation occurs over the lateral side of the proximal part of the arm, the area supplied by the superior lateral cutaneous nerve of the arm, the cutaneous branch of the axillary nerve
How would you test for degenerative tendinitis of the rotator cuff?
patient is asked to lower the fully abducted limb slowly and smoothly. From approximately 90 degrees abduction, the limb will suddenly drop to the side in an uncontrolled manner if the rotator cuff is diseased and/or torn
Location of supraglenoid and infraglenoid tubercles
know it
Locataion of the radial groove and olecranon
know it
Long head of triceps attachment
attaches to the infraglenoid tubercle proximally and to the olecranon of the ulna distally
Lateral head attachment
attaches proximally to the posterior humerus above the radial groove and and to the olecranon of the ulna distally
Medial head attachment
attaches proximally to the posterior humerus below the radial groove and to the olecranon of the ulna distally
Triceps function
extends the forearm at the elbow joint (the joint will be studied later)
Radial nerve
courses along the radial groove on the posterior surface of the humerus. Innervates the long and lateral heads of the triceps before entering the radial groove and the medial head is innervated after the nerve enters the groove.
Why is forearm extension weakened but not lost after fracture along the radial groove of the humerus?
long and lateral heads of the triceps are innervated before entering the radial groove
