Week 2 Flashcards
There are two nuclear imaging studies commonly used for the musculoskeletal system. What are they and why would they be ordered?
- Bone densitometry, typically assessed by Dual X-ray Absorptiometry (DEXA), measures bone mineral density – the most important factor predicting bone fragility. DEXA is low radiation exposure and used to monitor bone density in patients with risk factors for osteoporosis/fracture (menopausal women, women with history of low-trauma fractures, individuals with long-term glucocorticoid use, etc.).
- Bone scintigraphy measures bone turnover – can be abnormal for many reasons. The most common circumstance for scintigraphy use vs. MRI in current practice is in the monitoring of prostate/breast cancer patients for blastic metastases.
In bacterial arthritis, where do the bacteria typically originate? How does untreated bacterial arthritis result in irreversible joint damage?
Bacterial arthritis usually stems from hematogenous spread (i.e. bacteria deposit in joint during bacteremia), though it can originate from direct inoculation (trauma, surgery, etc.). The mechanism by which untreated bacterial joint infections can result in severe and irreversible joint damage is indirect. Acute inflammation increases the local concentration of proteases and inflammatory cytokines, damaging cartilage, and the joint inflammation reduces capillary blood flow by increasing intra-articular pressure. Together, the inflammatory response results in rapid destruction of intra-articular cartilage.
How can rheumatologists attain disease remission (versus just symptom control) for patients with rheumatoid arthritis?
RA is thought to stem from a chronic autoimmune reaction in which cytokines play a critical role. The inflammatory effect promoted by certain cytokines are targeted with monoclonal antibodies, soluble receptors, or receptor antagonists. Alternatively, inflammatory signaling proteins (e.g. JAK) can be inhibited by small molecules to reduce cytokine production. Critically, these agents modulating the underlying inflammatory disease and don’t only serve to reduce symptoms.
What genetic risk factor exists for many disorders under the umbrella of seronegative spondyloarthritis, and what type of protein does this encode? What are some shared clinical features of these disorders?
HLA-B27: a variant of the class I human leukocyte antigen which presents antigenic peptides to T-cells. Common clinical features include arthritis, enthesitis (inflammation at tendon insertion), sacroiliitis, uveitis, inflammatory bowel disease, and psoriasis.
What is the most commonly fractured bone in the hand? What vascular structure is located nearby, and what recess/compartment houses these structures?
The scaphoid bone (classically, from a fall on an outstretched hand) and the radial artery. The recess is the anatomical snuffbox, the area between thumb extensor tendons when the thumb is extended. Bonus food for thought: what are the implications of this relationship for avascular necrosis?
A 16-year-old boy with maternal family history of retinoblastoma presents with distal thigh pain. X ray reveals a tumor. What tumor do you suspect and what will you see on histology?
Osteosarcoma – microscopic appearance of osteoblasts osteoid-producing cells and woven bone. Osteosarcoma and retinoblastoma are common cancerous manifestations of Li-Fraumeni syndrome (germline heterozygous p53 mutation), so the family history of cancer is a common “hint” to osteosarcoma. But, in general, osteosarcoma is most common in boys in their second decade of life and classically affects the metaphysis of the distal femur.
What is the treatment for severely increased pressure in an anatomical compartment? What about open fractures?
Full compartment fasciotomy for compartment syndrome. Operative irrigation, debridement, and fixation for open fractures.
After a difficult delivery, a newborn is observed to have a limb hanging in medial rotation/pronation with a flexed wrist. What is the likely mechanism of injury during the delivery and which specific structure(s) are injured?
Pulling on the head of a baby whose arm is caught in the birth canal can cause an upper brachial plexus tear at the superior trunk (C5-6). From LG: waiter’s tip hand is caused by loss of flexion, abduction and lateral rotation of the arm (biceps, deltoid, supraspinatus, infraspinatus and teres minor); loss of flexion of the forearm and weakness of supination (biceps, brachialis and brachioradialis); and weakness of wrist extension (wrist extensors are innervated in part by C6).
Lupus is an autoimmune disease diagnosed clinically – i.e. there is no defining test or symptom. According to the EULAR/ACR criteria, what is the “entry criterion” for further lupus workup and what are some of the more powerfully predictive additive criteria (e.g. sx, lab results)?
Antinuclear antibody positivity is the entry criteria. There are many additive criteria which are scored numerically, where a total score of 10 or more meets classification criteria for SLE. Some highly weighted criteria are a renal biopsy consistent with lupus nephritis (10), anti-dsDNA or -Smith antibodies (6), acute pericarditis (6), joint involvement (6), or acute cutaneous lupus (6).
Match the bone disease with the appropriate classification.
Classifications: inadequate bone resorption, too little matrix, excessive resorption, too little mineralization, or abnormal matrix.
Diseases: Paget Disease of bone, Rickets/osteomalacia, osteopetrosis, senile osteoporosis, osteogenesis imperfecta.
Inadequate resorption: osteopetrosis.
Too little matrix: senile osteoporosis.
Excessive resorption: Paget Disease.
Too little mineralization: Rickets/osteomalacia.
Abnormal matrix: osteogenesis imperfecta.
