APMLE Part I cheat sheet

The tibial nerve passes behind the medial malleolus within the tarsal tunnel beneath the flexor retinaculum, then divides into medial and lateral plantar nerves; medial calcaneal branches arise proximal to the retinaculum.

The dorsalis pedis artery continues the anterior tibial artery and is palpated between the extensor hallucis longus and extensor digitorum longus tendons; it gives off the arcuate and first dorsal metatarsal arteries.

The lateral plantar nerve supplies abductor digiti minimi and quadratus plantae; its deep branch supplies the interossei, adductor hallucis, and lateral three lumbricals.

The common fibular nerve winds around the fibular neck; the superficial fibular nerve supplies the lateral compartment, and the deep fibular nerve supplies the anterior compartment and first dorsal web space.

Femoral triangle borders are the inguinal ligament superiorly, sartorius laterally, and adductor longus medially; the floor includes iliopsoas and pectineus.

The popliteal artery ends at the lower border of popliteus, dividing into the anterior tibial artery and the tibioperoneal trunk, which gives the posterior tibial and fibular arteries.

Lower limb buds appear in week 4 and rotate medially about 90 degrees, moving extensor compartments anteriorly and the great toe medially; digits separate by apoptosis in the apical ectodermal ridge.

Thick (plantar) skin contains five epidermal strata (basale, spinosum, granulosum, lucidum, corneum) and lacks hair follicles and sebaceous glands but has abundant eccrine sweat glands.

The sural nerve is formed by the medial sural cutaneous (tibial) and lateral sural cutaneous (common fibular) branches and supplies sensation to the lateral foot and heel.

Net glycolysis yields 2 pyruvate, 2 ATP, and 2 NADH per glucose; phosphofructokinase-1 is the committed step, activated by AMP and fructose-2,6-bisphosphate and inhibited by ATP and citrate.

Pyruvate dehydrogenase requires thiamine pyrophosphate, lipoic acid, coenzyme A, FAD, NAD+, and magnesium; deficiency produces lactic acidosis and neurologic dysfunction.

Each acetyl-CoA oxidized in the TCA cycle yields 3 NADH, 1 FADH2, and 1 GTP; isocitrate dehydrogenase is the rate-limiting enzyme.

Oxidative phosphorylation yields roughly 2.5 ATP per NADH and 1.5 ATP per FADH2; ATP synthase harnesses the proton gradient across the inner mitochondrial membrane.

Glucose-6-phosphate dehydrogenase of the hexose monophosphate shunt generates NADPH and ribose-5-phosphate; deficiency causes oxidative hemolysis with Heinz bodies.

Carbamoyl phosphate synthetase I is the rate-limiting urea cycle enzyme, activated by N-acetylglutamate; ornithine transcarbamylase deficiency causes hyperammonemia with orotic aciduria.

ALA synthase is the rate-limiting step of heme synthesis and requires pyridoxine; lead inhibits ALA dehydratase and ferrochelatase, causing sideroblastic anemia.

Hydroxylation of proline and lysine in procollagen requires vitamin C, and lysyl oxidase crosslinking requires copper; defects cause scurvy and connective tissue fragility.

Vitamin B12 is a cofactor for methionine synthase and methylmalonyl-CoA mutase, linking deficiency to homocysteine elevation and methylmalonic acid accumulation.

Normal gait requires about 65-75 degrees of first metatarsophalangeal dorsiflexion at pre-swing; loss of this range (hallux rigidus) forces compensations such as early heel rise.

The windlass mechanism: hallux dorsiflexion tensions the plantar fascia around the first metatarsal head, elevating the medial longitudinal arch and inverting the rearfoot.

Subtalar pronation is triplanar dorsiflexion, eversion, and abduction; supination is plantarflexion, inversion, and adduction, both about an oblique axis.

Vertical ground reaction force peaks near 1.1-1.3 times body weight in walking and 2-3 times body weight in running.

Moment equals force times perpendicular distance; stress equals force divided by area; strain equals change in length divided by original length.

Subtalar joint neutral is the position in which the foot is neither pronated nor supinated with the plantar forefoot perpendicular to the rearfoot; it is the reference for orthotic casting.

During stance the center of pressure progresses from the lateral heel, along the lateral midfoot, to the first metatarsal head and hallux.

Ankle dorsiflexion of about 10 degrees is needed for normal gait; equinus limits tibial advancement and promotes midfoot pronation or forefoot compensation.

First ray dorsiflexion range and position determine whether the foot compensates in the sagittal plane during late midstance.

Gram-positive cocci in clusters that are catalase positive are staphylococci; coagulase positivity identifies Staphylococcus aureus.

Pseudomonas aeruginosa is oxidase positive, a non-lactose fermenter, forms blue-green pigment, has a grape-like odor, and is intrinsically resistant to many antibiotics.

Diabetic foot infections are often polymicrobial: S. aureus predominates, while chronic or previously treated wounds add gram-negative bacilli and anaerobes; deep tissue culture is preferred over superficial swabs.

IgM is the first antibody of a primary response, a pentamer that strongly activates classical complement; IgG crosses the placenta, IgA is mucosal, and IgE binds mast cells.

The classical complement pathway is initiated by C1q binding IgG or IgM, the alternative pathway by microbial surfaces and endotoxin; C3b is an opsonin and C5b-9 forms the membrane attack complex.

Clostridium perfringens is a gram-positive, spore-forming anaerobic rod whose alpha-toxin (lecithinase) causes myonecrosis and gas gangrene.

Methicillin resistance in staphylococci is mediated by mecA, which encodes penicillin-binding protein 2a with low affinity for beta-lactams.

S. aureus virulence factors include toxic shock syndrome toxin-1 (a superantigen), exfoliative toxins, and Panton-Valentine leukocidin.

Hepatitis B virus is a partially double-stranded DNA virus spread by blood, sexual contact, and perinatally; an effective vaccine is available.

Acute inflammation involves vasodilation and increased vascular permeability, followed by neutrophil margination, selectin-mediated rolling, integrin-mediated adhesion, and transmigration.

Granulomas consist of epithelioid macrophages and Langhans giant cells with a lymphocyte rim; causes include tuberculosis, sarcoidosis, histoplasmosis, and foreign bodies.

Healing by primary intention occurs in clean approximated wounds; secondary intention involves more granulation tissue, contraction, and scarring; type III collagen is replaced by type I during remodeling.

Acute osteomyelitis shows neutrophil-rich suppuration and bone necrosis; chronic disease produces a necrotic sequestrum, reactive involucrum, and Brodie abscess.

Diabetes produces non-enzymatic glycation with advanced glycation end products, hyaline arteriolosclerosis of small vessels, and distal symmetric axonal peripheral neuropathy.

Malignant features include pleomorphism, hyperchromasia, increased nuclear-to-cytoplasmic ratio, atypical mitoses, invasion, and metastasis.

Necrosis types: coagulative (ischemia except brain), liquefactive (brain, abscess), caseous (tuberculosis), fat (pancreatitis), and fibrinoid (vasculitis).

Amyloid deposits show apple-green birefringence under polarized light after Congo red staining.

Monosodium urate crystals are needle-shaped and negatively birefringent; calcium pyrophosphate crystals are rhomboid and positively birefringent.

Vancomycin is a glycopeptide that binds D-Ala-D-Ala peptidoglycan precursors, covering MRSA and other gram-positives; monitor levels because of nephrotoxicity and watch for infusion-related flushing.

Aminoglycosides bind the 30S ribosomal subunit, are bactericidal with concentration-dependent killing, and carry nephrotoxic and ototoxic risk.

Fluoroquinolones inhibit DNA gyrase (topoisomerase II) in gram-negatives and topoisomerase IV in gram-positives; adverse effects include tendinopathy and QT prolongation.

Beta-lactams inhibit transpeptidase (penicillin-binding proteins) and are bactericidal; adding an aminoglycoside gives synergy in enterococcal endocarditis.

Aspirin irreversibly acetylates platelet cyclooxygenase-1, suppressing thromboxane A2 for the platelet lifespan of about 7-10 days; other NSAIDs inhibit reversibly.

Warfarin inhibits vitamin K epoxide reductase, reducing factors II, VII, IX, and X; effect is monitored by INR and reversed with vitamin K, fresh frozen plasma, or prothrombin complex concentrate.

Acetaminophen overdose generates NAPQI via CYP2E1; N-acetylcysteine replenishes glutathione and is most effective within 8-10 hours of ingestion.

Clindamycin inhibits the 50S ribosomal subunit, covers anaerobes above the diaphragm, and carries a notable risk of Clostridioides difficile colitis.

Glucocorticoids inhibit phospholipase A2 and thereby arachidonic acid release; chronic use causes osteoporosis, hyperglycemia, and adrenal suppression.

Cardiac output equals heart rate times stroke volume; mean arterial pressure approximates cardiac output times total peripheral resistance.

Frank-Starling relationship: increased preload stretches myocardial fibers and increases stroke volume up to a physiologic limit.

GFR equals the filtration coefficient times net filtration pressure (glomerular capillary pressure minus Bowman space pressure minus glomerular oncotic pressure); autoregulation involves afferent arteriolar myogenic tone and tubuloglomerular feedback.

Rightward shifts of the oxyhemoglobin curve occur with increased CO2, hydrogen ion, temperature, and 2,3-bisphosphoglycerate, reducing oxygen affinity.

A typical neuron rests near -70 mV and fires when depolarization reaches about -55 mV, driven by sodium influx and repolarized by potassium efflux.

Nerve conduction velocity rises with myelination and larger fiber diameter; A-alpha fibers are fastest, while unmyelinated C fibers carry slow pain and temperature signals.

The thick ascending limb is water impermeable and uses the Na-K-2Cl cotransporter to drive the countercurrent multiplier; ADH inserts aquaporin-2 in the collecting duct.

Insulin promotes GLUT4 translocation in skeletal muscle and adipose tissue, while glucagon raises blood glucose through glycogenolysis and gluconeogenesis.

Parathyroid hormone raises serum calcium via bone resorption, renal calcium reabsorption, and activation of 1-alpha-hydroxylase; calcitonin lowers serum calcium.

Hallux valgus is lateral deviation of the great toe with medial prominence of the first metatarsal head; an intermetatarsal angle above 9 degrees is considered abnormal.

Charcot neuroarthropathy presents as a warm, swollen, erythematous foot in a neuropathic patient and progresses through Eichenholtz stages of development, coalescence, and remodeling; treatment is offloading and immobilization.

The Wagner classification grades diabetic foot ulcers 0 through 5 by depth, presence of osteomyelitis, and extent of gangrene.

Tinea pedis is a dermatophyte infection; potassium hydroxide preparation shows septate branching hyphae, and topical azoles or terbinafine are first-line.

Plantar fasciitis causes medial heel pain worst with the first steps after rising, with tenderness at the medial calcaneal tubercle; stretching, orthoses, and night splints are conservative options.

Onychocryptosis (ingrown toenail) is treated with partial nail avulsion; chemical matrixectomy with phenol reduces recurrence by destroying the germinal matrix.

Annual comprehensive diabetic foot examination includes 10-g monofilament testing, vibration perception, and pedal pulse assessment.

Morton neuroma typically affects the third interdigital space and produces a Mulder click on lateral metatarsal head compression; padded orthoses or injections are used.

The nail matrix has a proximal germinal portion producing most of the nail plate and a distal sterile portion adhering to the plate.

Transtheoretical model stages: precontemplation, contemplation, preparation, action, maintenance, with relapse cycling common; counseling should match the patient's current stage.

Classical conditioning pairs an unconditioned stimulus with a neutral conditioned stimulus (Pavlov); operant conditioning increases behavior with reinforcement and decreases it with punishment.

Piaget stages: sensorimotor (0-2 years), preoperational (2-7), concrete operational (7-11), and formal operational (11 and older).

Defense mechanisms range from mature (sublimation, humor) to neurotic (repression, rationalization) to immature (projection, splitting, denial).

Parsons sick role: the ill person is exempt from normal responsibilities but is obliged to seek competent help and to want to recover.

Transference is the patient's unconscious redirection of past relational feelings onto the clinician; countertransference is the clinician's analogous reaction to the patient.

Incidence counts new cases per person-time, whereas prevalence counts all existing cases at a point or over a period.

Sensitivity is the proportion of diseased persons correctly identified as positive; specificity is the proportion of healthy persons correctly identified as negative.

Valid informed consent requires decision-making capacity, disclosure of risks, benefits, and alternatives, comprehension, and voluntariness; life-threatening emergencies permit treatment without consent.

The four principles of biomedical ethics are autonomy, beneficence, nonmaleficence, and justice.

HIPAA permits use of protected health information for treatment, payment, and health care operations, subject to the minimum necessary standard.

Confidentiality may be breached for mandated reporting of child or elder abuse, certain communicable diseases, and serious imminent threats to an identifiable person (Tarasoff duty).

Withholding and withdrawing life-sustaining treatment are ethically equivalent when the treatment is judged futile or disproportionately burdensome.

Research ethics require institutional review board approval and adherence to the Belmont principles: respect for persons, beneficence, and justice.

Emancipated minors and specific state exceptions (emergency care, sexually transmitted infection treatment, contraception) may permit treatment without parental consent.

Physicians must disclose harmful medical errors to patients and institutions; disclosure is an autonomy and truth-telling obligation.

Conflicts of interest must be disclosed, and acceptance of industry gifts should be limited to items of minimal value that benefit patients.