Muscle, bone, and fractures Flashcards
Define muscle proprioreceptors
specialized sensory receptors that relay info about muscle dynamics
Describe the neuronal pathway in muscle stretch receptors
- Increased length & speed of stretch
- Afferent pathway via dorsal root ganglion
- Activation of inhibitory interneuron and alpha motor neuron
- Simultaneous inhibition of antagonist muscle (prevents overstretching) & activation of agonist muscle (contraction)
Type of innervation of muscle stretch receptors + location
Type Ia and II sensory axons
Located in the body of muscle
What activates muscle stretch receptors
Increased muscle stretch
Responsible for deep tendon reflexes
Describe the nerve pathway for Golgi tendon organ
- Increased tension
- Afferent pathway via DRG
- Activation of inhibitory interneuron
- Inhibition of agonist muscle (reduced tension within muscle and tendon
Type of innervation of Golgi tendon organ + location
Type Ib sensory axons
Tendons
What activates Golgi tendon organ
Increased muscle tension
Location of endochondral ossification
Bones of axial & appendicular skeleton, base of skull
Describe the process of endochondral ossification
- Cartilagenous model of bone is made by chondrocytes
- Osteoblasts/clasts later replace woven bone and remodel to lamellar bone
When does woven bone occur in adults
After fractures and in Paget disease
In what disease is endochondral ossification defective
Achondroplasia
Where does membranous ossification occur
Bones of calvarium, facial bones, clavicle
Describe the process of membranous ossification
Woven bone formed directly wo cartilage, then remodeled to lamellar
Describe the function of osteoblasts
Builds bone by secreting collagen & catalyzing mineralization in alkaline environments via ALP
Differentiation of osteoblasts
From mesenchymal stem cells in periosteum
What factors regulate osteoblast activity
Bone ALP, osteocalcin, propeptides of type I collagen
Describe the function of osteoclasts
Dissolves bone by secreting protons and collagenases
Differentiation of osteoclasts
Fusion of monocyte/macrophage lineage precursors
How is osteoclast activity regulated
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 = reduction in activity
Describe the function of PTH in bone formation
At low, intermittent levels, exerts anabolic effects (building bone) on osteoblasts and osteoclasts (indirect)
What are the chronic effects of high PTH levels
Primary hyperparathyroidism
cause catabolic effects (osteitis fibrosa cystica)
Function of estrogen in bone formation
Inhibits apoptosis in osteoblasts and induces apoptosis in osteoclasts
Causes closure of epiphyseal plate during puberty
What does estrogen deficiency cause to bones
(Surgical/postmenopausal)
Increases cycles of remodeling and bone resorption = risk of osteoporosis
Describe medial epicondylitis
Golfer’s elbow
due to repetitive flexion or idiopathic = pain near medial epicondyle
Describe lateral epicondylitis
Tennis elbow
Repetitive extension (backhand shots) or idiopathic = pain near lateral epicondyle
Who are found to commonly have clavicle fractures
Children and as birth trauma
Causes of clavicle fractures
fall on outstretched hand or by direct trauma to shoulder
Weakest point of clavicle
at the junction of middle and lateral thirds
Common location of clavicle fracture
middle third segment
Presentation of clavicle fracture
Presents as shoulder drop, shortened clavicle (lateral fragment is depressed due to arm weight and medially rotated by arm adductors [eg, pectoralis major])
Define Guyon canal syndrome and who are they seen in
Compression of ulnar nerve at wrist
Classically seen in cyclists due to pressure from handlebars
May also be seen with fracture/dislocation of the hook of hamate
Define carpal tunnel syndrome
Entrapment of median nerve in carpal tunnel (between transverse carpal ligament and carpal bones) = nerve compression causing paresthesia, pain, and numbness in distribution of median nerve
Clinical findings of carpal tunnel syndrome
Thenar eminence atrophies but sensation spared (bc palmar cutaneous branch enters hand external to carpal tunnel)
Tests for carpal tunnel syndrome
Tinel sign (percussion of wrist causes tingling) and Phalen maneuver (90° flexion of wrist causes tingling)
Associations of carpal tunnel syndrome
Pregnancy (due to edema), RA, hypothyroidism, diabetes, acromegaly, dialysis-related amyloidosis
May be associated with repetitive use
Define metacarpal neck fracture, seen commonly in which metacarpal
Also called boxer’s fracture
Common fracture caused by direct blow with a closed fist (eg, from punching a wall). Most commonly seen in the 5th metacarpal
Define iliopsoas abscess and pathology
Collection of pus in iliopsoas compartment
May spread from blood (hematogenous) or from adjacent structures (eg, vertebral osteomyelitis, tuberculous spondylitis/Pott disease, pyelonephritis)
What is iliopsoas abscess associated with
Crohn disease, diabetes, and immunocompromised states
Microbiological cause of iliopsoas abscess
Staphylococcus aureus most commonly isolated, but may also occur 2° to tuberculosis
Clinical (physical) findings of iliopsoas abscess
flank pain and bulge, fever, inguinal mass
Positive psoas sign (hip extension exacerbates lower abdominal pain)
Lab findings of iliopsoas abscess
Imaging (CT/MRI) will show focal hypodense lesion within the muscle plane
Tx of iliopsoas abscess
Antibiotics based on culture, CT-guided percutaneous drainage (PCD), or surgical drainage
