This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Question 7441
Topic: Infection, Pharmacology & VTE
What is the most common organism responsible for acute hematogenous osteomyelitis in healthy children?
Correct Answer & Explanation
. Escherichia coli
Explanation
Staphylococcus aureus is by far the most common causative organism for acute hematogenous osteomyelitis across all age groups, including healthy children. While Kingella kingae is increasingly recognized in young children, S. aureus remains the dominant pathogen. E. coli and Pseudomonas are more common in neonates or immunocompromised patients. Streptococcus pyogenes is less common in bone infections.
Question 7442
Topic: Surgical Anatomy & Approaches
Which nerve is most commonly injured in fractures of the midshaft humerus?
Correct Answer & Explanation
. Median nerve
Explanation
The radial nerve courses in the spiral groove (radial groove) of the humerus, making it particularly susceptible to injury in fractures of the midshaft humerus. Median and ulnar nerves are more commonly injured around the elbow. The axillary nerve is vulnerable with proximal humerus fractures. The musculocutaneous nerve is less commonly involved in humeral shaft fractures.
Question 7443
Topic: Biology, Genetics & Bone Healing
What is the characteristic histological feature seen in Paget's disease of bone?
Correct Answer & Explanation
. Increased number of inactive osteoblasts
Explanation
Paget's disease (osteitis deformans) is characterized by highly disorganized bone remodeling, leading to a 'mosaic' or 'jigsaw' pattern of woven and lamellar bone. There is increased, chaotic osteoclastic resorption followed by rapid, disorganized osteoblastic bone formation. It does not involve decreased osteoclast activity, fibrous tissue replacement, or unmineralized osteoid accumulation primarily.
Question 7444
Topic: Biology, Genetics & Bone Healing
A 70-year-old female presents with acute onset back pain and a vertebral compression fracture. Which of the following is the most effective pharmacologic agent for preventing future osteoporotic fractures by inhibiting osteoclast function?
Correct Answer & Explanation
. Calcium and Vitamin D supplements
Explanation
Denosumab is a monoclonal antibody that targets RANKL, preventing osteoclast formation and function, leading to a potent antiresorptive effect and significant reduction in fracture risk. Bisphosphonates also inhibit osteoclast function and are first-line. Teriparatide is an anabolic agent. Calcium/Vitamin D are essential supplements but not direct anti-osteoporosis agents alone. Strontium ranelate has dual action but is less commonly used. Calcitonin has modest efficacy.
Question 7445
Topic: Infection, Pharmacology & VTE
The most important factor in preventing surgical site infections (SSIs) in orthopedic surgery is:
Correct Answer & Explanation
. Strict perioperative glycemic control in diabetic patients.
Explanation
While all options except for prolonged broad-spectrum antibiotics play a role in SSI prevention, the appropriate timing and selection of prophylactic antibiotics is widely considered the single most important intervention. Antibiotics should be administered within 60 minutes prior to incision and cover anticipated pathogens. Prolonged post-operative antibiotics are generally not recommended due to resistance concerns. Glycemic control, normothermia, and DVT prophylaxis are important adjuncts.
Question 7446
Topic: 1. General Principles & Basic Science
Regarding local anesthetics, which property determines the duration of action?
Correct Answer & Explanation
. pKa
Explanation
The duration of action of a local anesthetic is primarily determined by its protein binding. Higher protein binding allows the drug to remain at the nerve membrane for longer, extending its effect. Lipid solubility influences potency and speed of onset. pKa influences the speed of onset. Concentration affects the intensity and onset of the block. Vasoconstrictor additives prolong duration by reducing systemic absorption.
Question 7447
Topic: 1. General Principles & Basic Science
What is the primary function of the periosteum in adult long bones?
Correct Answer & Explanation
. Hematopoiesis
Explanation
The periosteum, particularly its inner cambium layer, contains osteoprogenitor cells vital for bone repair and appositional growth (increase in bone width). It also contains blood vessels that supply the outer one-third to one-quarter of the cortical bone. Hematopoiesis occurs in the bone marrow. Bone growth in length occurs at the epiphyseal plates.
Question 7448
Topic: 1. General Principles & Basic Science
Which zone of the epiphyseal plate is responsible for the proliferation of chondrocytes, leading to longitudinal bone growth?
Correct Answer & Explanation
. Zone of resting cartilage
Explanation
The Zone of Proliferation contains rapidly dividing chondrocytes arranged in columns. These cells increase in number, pushing the epiphysis away from the diaphysis and thus contributing to longitudinal bone growth. The zone of resting cartilage anchors the plate. Hypertrophy involves cell enlargement. Calcification is where the matrix calcifies, and ossification is where bone replaces cartilage.
Question 7449
Topic: Infection, Pharmacology & VTE
A patient with a history of intravenous drug use presents with acute pain and swelling in the knee. Arthrocentesis reveals purulent fluid. Which organism is a common cause of septic arthritis in this population, besides Staphylococcus aureus?
Correct Answer & Explanation
. Neisseria gonorrhoeae
Explanation
In intravenous drug users (IVDUs), Pseudomonas aeruginosa is a common cause of septic arthritis, particularly affecting large joints like the knee or sternoclavicular joint, in addition to Staphylococcus aureus. Neisseria gonorrhoeae is common in sexually active young adults. Streptococcus pneumoniae is less common. Borrelia burgdorferi causes Lyme arthritis. Salmonella spp. can cause osteomyelitis in sickle cell patients but is less common for septic arthritis in IVDUs.
Question 7450
Topic: Infection, Pharmacology & VTE
Which of the following is a recognized complication of using indomethacin for prophylactic ossification after total hip arthroplasty?
Correct Answer & Explanation
. Increased risk of deep vein thrombosis
Explanation
Indomethacin, a non-selective NSAID, can inhibit prostaglandin synthesis, which is crucial for early stages of fracture healing and bone formation. Therefore, a recognized complication of its use (e.g., for heterotopic ossification prophylaxis) is delayed fracture healing, especially in fresh fractures. It is not typically associated with increased DVT risk (aspirin is used for DVT prophylaxis), hypertension crisis, or auditory disturbances as its main adverse effects.
Question 7451
Topic: Infection, Pharmacology & VTE
Which imaging feature on plain radiographs is most indicative of chronic osteomyelitis?
Correct Answer & Explanation
. Soft tissue swelling and periarticular effusion
Explanation
The presence of a sequestrum (a fragment of necrotic bone that has separated from the healthy bone) and an involucrum (a sheath of new bone laid down by the periosteum around the infected, dead bone) are classic radiographic signs of chronic osteomyelitis. Soft tissue swelling and periarticular effusion are nonspecific. Periosteal elevation and lucent lesions can be seen in acute osteomyelitis but are less specific for chronicity. Early stages can be normal.
Question 7452
Topic: Biomechanics & Biomaterials
What is the primary advantage of uncemented (press-fit) components in total joint arthroplasty?
Correct Answer & Explanation
. Lower risk of infection
Explanation
The primary advantage of uncemented components is the potential for long-term biological fixation through osteointegration, where the patient's own bone grows directly onto or into the implant's porous surface. This can provide durable fixation. While it eliminates PMMA heat, it does not provide immediate biological fixation (mechanical press-fit is immediate), and revision surgery can be more complex due to bone ingrowth. Infection risk is not inherently lower.
Question 7453
Topic: 1. General Principles & Basic Science
Which of the following describes the effect of chronic denervation on skeletal muscle?
Correct Answer & Explanation
. Hypertrophy and increased strength.
Explanation
Chronic denervation of skeletal muscle leads to progressive atrophy, significant decrease in force production, and ultimately the replacement of muscle fibers with fibrous and adipose tissue. It also causes reduced metabolic activity and vascularity, and the neuromuscular junction degenerates. Muscle fibers generally convert towards a more 'slow-twitch' phenotype initially, but ultimately severe atrophy dominates, not hypertrophy.
Question 7454
Topic: Biology, Genetics & Bone Healing
Which type of fracture healing involves direct apposition of fracture ends with minimal callus formation, typically seen with absolute stability provided by rigid internal fixation?
Correct Answer & Explanation
. Secondary healing
Explanation
Primary (or direct) bone healing occurs when there is absolute stability and direct contact between the fracture ends, typically achieved with rigid internal fixation. This process involves direct remodeling by osteoclasts and osteoblasts, with minimal or no external callus formation. Secondary healing involves a callus, and endochondral ossification is part of secondary healing. Stress fractures heal like secondary fractures. Nonunion is a failure of healing.
Question 7455
Topic: Biology, Genetics & Bone Healing
A surgeon utilizes a structural cortical allograft to manage a massive diaphyseal bone defect during a revision total femur arthroplasty. Which of the following best describes the classical biological sequence of graft incorporation for this specific type of structural graft?
Correct Answer & Explanation
. Osteoblastic apposition occurs on dead trabeculae prior to osteoclastic resorption
Explanation
Cortical bone grafts incorporate via creeping substitution, but unlike cancellous grafts, the sequence is uniquely osteoclastic first. Osteoclasts must bore out the existing Haversian canals to allow vascular ingrowth before osteoblasts can lay down new bone. This initial resorptive phase leads to a temporary, significant decrease in the mechanical strength of cortical allografts. In contrast, cancellous grafts undergo initial osteoblastic apposition on dead trabeculae, followed by remodeling.
Question 7456
Topic: Biomechanics & Biomaterials
In optimizing the mechanical fixation of a non-locking plate for a diaphyseal osteoporotic humerus fracture, which of the following geometrical modifications to the cortical screw will most significantly increase its pullout strength?
Correct Answer & Explanation
. Increasing the core (minor) diameter while maintaining the outer diameter
Explanation
Pullout strength is the force required to pull a screw out of the bone and is proportional to the shear area of the bone engaged by the threads. The formula for pullout strength shows that it is most highly correlated with the major (outer) diameter of the screw. Increasing the core diameter increases the bending strength of the screw itself but does not increase pullout strength. Decreasing pitch increases the number of threads engaged, which helps, but is less impactful than increasing the major diameter.
Question 7457
Topic: Biology, Genetics & Bone Healing
A 45-year-old male is treated with a minimally invasive bridge plate for a severely comminuted midshaft tibia fracture. According to Perren's strain theory, direct (primary) bone healing with lamellar bone formation can only occur when the interfragmentary strain is kept below which of the following thresholds?
Correct Answer & Explanation
. 2%
Explanation
Perren's strain theory dictates that a specific tissue type can only form if the local mechanical strain does not exceed the strain tolerance of that tissue. Lamellar bone is highly rigid and can tolerate strains up to only 2%; thus, primary bone healing requires absolute stability (<2% strain). Woven bone tolerates up to 10% strain, cartilage tolerates up to 10%, and granulation tissue can tolerate up to 100% strain.
Question 7458
Topic: Physiology & Rehabilitation
A competitive long-distance marathon runner sustains an acute hamstring strain. Biopsies of the uninjured hamstrings in this athlete would reveal a predominance of muscle fibers characterized by which of the following physiologic profiles?
Correct Answer & Explanation
. High glycogen content, rapid fatigue, and extremely high myosin ATPase activity
Explanation
Endurance athletes like marathon runners have a predominance of Type I (slow-twitch) muscle fibers in their continuously acting skeletal muscles. Type I fibers are uniquely adapted for prolonged, sustained contractions. They are characterized by a high density of mitochondria, high myoglobin content (giving them a 'red' appearance), abundant capillary supply, preferential aerobic (oxidative) metabolism, and slow contraction speeds that resist fatigue.
Question 7459
Topic: Biomechanics & Biomaterials
During open reduction and internal fixation of a periprosthetic femur fracture, an inexperienced surgeon opts to use a standard stainless steel cortical screw to secure a commercially pure titanium locking plate. Which of the following best explains why this combination of dissimilar metals increases the risk of premature implant failure?
Correct Answer & Explanation
. Titanium has a lower modulus of elasticity, causing profound stress shielding of the adjacent stainless steel screw
Explanation
Mixing dissimilar metals (e.g., titanium and stainless steel) in the electrolytic environment of human tissue fluid creates a galvanic cell. Because the metals have different electrochemical potentials, electrons flow from the less noble metal (anode) to the more noble metal (cathode), resulting in accelerated galvanic corrosion of the anodic metal. This compromises structural integrity and releases potentially toxic metallic ions into the surrounding tissues.
Question 7460
Topic: Biology, Genetics & Bone Healing
Following a primary flexor tendon repair in Zone II of the hand, a structured early active mobilization protocol is initiated. At the cellular and tissue level, what is the primary biological advantage of this protocol during the early stages of tendon healing?
Correct Answer & Explanation
. It promotes intrinsic over extrinsic healing, leading to improved collagen alignment and a reduction in restrictive adhesion formation
Explanation
Flexor tendons heal through both intrinsic (proliferation of epitenon and endotenon cells) and extrinsic (ingrowth of fibroblasts from the surrounding tendon sheath) mechanisms. Extrinsic healing is largely responsible for the formation of motion-limiting peritendinous adhesions. Early controlled mobilization heavily suppresses extrinsic healing and favors intrinsic healing. It also applies mechanical stress that aligns the newly synthesized collagen fibrils longitudinally, greatly improving the tendon's tensile strength and functional gliding capacity.
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