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1. General Principles & Basic Science MCQs

Practice Set 53 of 789

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 1041

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with acute limp and fever of 38.8 C (101.8 F). ESR is 45 mm/hr, serum WBC is 14,000/mm3, and he refuses to bear weight. According to Kocher's criteria, what is the approximate probability that this child has septic arthritis?

. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria for pediatric septic arthritis of the hip include non-weight bearing, temperature >38.5 C, ESR >40, and WBC >12,000. Having all 4 predictors yields a 99% predictive probability for septic arthritis.

Question 1042

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, the transition from a soft cartilaginous callus to a hard bony callus is primarily mediated by which of the following processes?

. Intramembranous ossification
. Endochondral ossification
. Creeping substitution
. Haversian remodeling
. Osteoclastic resorption

Correct Answer & Explanation

. Endochondral ossification

Explanation

In secondary fracture healing, the soft callus composed primarily of cartilage is converted into a woven bone hard callus via endochondral ossification. This process is dependent on adequate mechanical stability and blood supply.

Question 1043

Topic: Surgical Anatomy & Approaches

During an anterolateral (Watson-Jones) approach to the hip, the superficial surgical interval is developed between which two muscles?

. Tensor fasciae latae and Sartorius
. Tensor fasciae latae and Gluteus medius
. Gluteus medius and Gluteus minimus
. Sartorius and Rectus femoris
. Rectus femoris and Pectineus

Correct Answer & Explanation

. Tensor fasciae latae and Gluteus medius

Explanation

The Watson-Jones (anterolateral) approach utilizes the muscular interval between the tensor fasciae latae and the gluteus medius. Although both are innervated by the superior gluteal nerve, it is a safe and widely used plane for hip exposure.

Question 1044

Topic: Biomechanics & Biomaterials

Which of the following metallic orthopedic implant materials has a modulus of elasticity closest to that of cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Alumina ceramic
. Solid Tantalum

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a modulus of elasticity of approximately 110 GPa, which is closest to cortical bone (15-20 GPa) among standard solid implant metals. This reduces the effect of stress shielding compared to stiffer metals like cobalt-chromium (210 GPa) or stainless steel (200 GPa).

Question 1045

Topic: 1. General Principles & Basic Science

Which of the following descriptions is more characteristic of tuberculosis than pyogenic spondylitis:

. Disc space is narrowed before significant bony changes occur.
. Involvement of multiple contiguous levels is uncommon.
. Bony erosions seen on computerized tomography are usually small and focal.
. Vertebral destruction exceeds disc destruction.
. Magnetic resonance imaging rarely shows significant soft tissue swelling.

Correct Answer & Explanation

. Vertebral destruction exceeds disc destruction.

Explanation

Vertebral destruction exceeds disc destruction in tuberculosis. Bony changes occur earlier in tuberculosis than in pyogenic spondylitis. Involvement of multiple contiguous levels is more common in tuberculosis than pyogenic spondylitis. Bony erosions seen on computerized tomography are large in tuberclosis and small in pyogenic spondylitis. Magnetic resonance imaging often shows significant soft tissue involvement in both disorders.

Question 1046

Topic: 1. General Principles & Basic Science

Which of the following statements is true of demineralized bone matrix:

. Demineralized bone matrix is osteogenic.
. Demineralized bone matrix is strongly osteoinductive.
. Demineralized bone matrix is weakly osteoinductive.
. Demineralized bone matrix is consistent between forms and different sterilization methods.
. Demineralized bone matrix is not osteoconductive.

Correct Answer & Explanation

. Demineralized bone matrix is weakly osteoinductive.

Explanation

Demineralized bone matrix is weakly osteoinductive. The term osteogenic refers to direct transmittal of cells capable of making bone. Demineralized bone matrix is not osteogenic. Demineralized bone matrix varies in efficacy between different forms and different methods of sterilization. The term osteoconduction refers to provision of a favorable scaffold and environment for bone formation. Demineralized bone matrix is osteoconductive.

Question 1047

Topic: 1. General Principles & Basic Science

Which of the following is not a specific feature in making the diagnosis of a dystrophic curve in neurofibromatosis 1:

. Penciling of the ribs
. Scalloping of the vertebrae
. Widening of the foramen
. Thinning of the transverse processes
. Right convex apex

Correct Answer & Explanation

. Penciling of the ribs

Explanation

Right convex apex is not a specific characteristic of dystrophic curves. It is more common in dystrophic curves than in nondystrophic curves, but it is commonly present in both types of curves. Penciling of the ribs is one of the features specific for dystrophic curves in neurofibromatosis 1. Scalloping of the vertebrae anteriorly and posteriorly is characteristic of dystrophic curves in neurofibromatosis 1. Widening of the neural foramen is specific for dystrophic curves in neurofibromatosis 1. Widening of the neural foramen is due to tumorous masses passing through the foramen. Thinning of the transverse process is a characteristic of dystrophic curves in neurofibromatosis 1.

Question 1048

Topic: 1. General Principles & Basic Science

Which of the following is a parameter that should be used in positioning arthrodesis of the hip in a young person:

. Flexion of 45°
. Abduction of 15° if there is shortening
. Adduction of 0°
. External rotation of 25°
. Shortening of at least 3 cm

Correct Answer & Explanation

. Adduction of 0°

Explanation

Neutral abduction is important in preventing back pain. The flexion should be between 25° and 35°. Any abduction beyond neutral poses increases risk of back pain. External rotation beyond approximately 5° is not needed. Arthrodesis often produces some mandatory shortening; therefore, intentional shortening is not needed.

Question 1049

Topic: 1. General Principles & Basic Science

When applying a halo for postoperative immobilization in a skeletally mature teenager, which of the following is the proper torque for the pins:

. 2 inch-pounds
. 4 inch-pounds
. 8 inch-pounds
. 10 inch-pounds
. 12 inch-pounds

Correct Answer & Explanation

. 8 inch-pounds

Explanation

Eight inch-pounds is the currently recommended torque to provide optimal biomechanical fixation while minimizing pin penetration. This is also recommended for adults. In young children, 4- to 6-inch-pounds are preferred.

Question 1050

Topic: 1. General Principles & Basic Science

Which of the following statements is true about bone marrow transplantation in mucopolysaccharidoses:

. Bone marrow transplantation is contraindicated.
. Bone marrow transplantation does not affect the orthopedic problems.
. Bone marrow transplantation reverses the orthopedic manifestations.
. Graft-versus-host disease is rare.
. Bone marrow transplantation should be deferred until skeletal maturity.

Correct Answer & Explanation

. Bone marrow transplantation does not affect the orthopedic problems.

Explanation

Bone marrow transplantation is effective in preventing the deposition of mucopolysaccharides in solid organs. Transplantation should be done early to prevent organ damage. Because the lysosomal enzyme does not cross the cell membrane of osteocartilaginous cells, it does not affect the orthopedic aspects. The risk of graft-versus-host disease is high but may be treated in most cases. Survival rate is 61% at 2 years for Hurler disease, which is otherwise fatal before maturity.

Question 1051

Topic: 1. General Principles & Basic Science

Regardless of age, the tonsils of the cerebellum should not extend more than this distance below the foramen magnum:

. 1 mm
. 2 mm
. 3 mm
. 5 mm
. Any protrusion is abnormal

Correct Answer & Explanation

. 5 mm

Explanation

Displacement of the cerebellar tonsils below the foramen magnum is termed a C hiari malfomation. A C hiari I malformation is an isolated malformation; a C hiari II malformation is associated with a syrinx. Symptoms may include headache, vomiting, and nystagmus. Although the normal protrusion allowed decreases with age, 5 mm is abnormal at any age.

Question 1052

Topic: 1. General Principles & Basic Science

When applying a halo, the use of six pins instead of four has which of the following effects:

. Increase in the infection rate
. Increased rate of pin loosening
. Increased rate of dural puncture
. Increase in load to failure by 50%
. Increase in risk of injury of the supraorbital nerve

Correct Answer & Explanation

. Increase in load to failure by 50%

Explanation

With an increase from four to six pins, the load to failure is increased by more than 50%. Additional pins decrease many of the complications, such as loosening and pin tract infection. The risk of dural puncture is not measurably increased because it is a rare complication.

Question 1053

Topic: 1. General Principles & Basic Science
The false profile radiographic view of the hip is taken with the patient in which of the following positions?
. The affected hip is against the film and the pelvis is rotated 65° away from the plane of the film.
. The unaffected hip is against the film and the pelvis is rotated 65° away from the plane of the film.
. The patient is supine and the beam is angled 45° cephalad.
. The patient is supine and the beam is angled 45° caudally.
. The patient is supine and the affected hip is maximally internally rotated.

Correct Answer & Explanation

. The affected hip is against the film and the pelvis is rotated 65° away from the plane of the film.

Explanation

The false profile radiographic view assesses anterior coverage and is obtained with the affected hip against the film and the pelvis rotated 65° away from the plane of the film.

Question 1054

Topic: Infection, Pharmacology & VTE

A 15-year-old boy has a history of excessive bleeding when he is cut. His maternal uncle passed away during a tonsillectomy. The boy presents with severe hip pain (worse in extension than in flexion) and some weakness in his knee extension. The most likely cause of the patients symptoms is:

. Septic arthritis of the hip
. Psoas abscess
. Lumbar epidural hematoma
. Iliopsoas hematoma
. Hip hemarthrosis

Correct Answer & Explanation

. Iliopsoas hematoma

Explanation

The patient has features suggesting mild hemophilia A or B including x- linked inheritance and occasional bleeding episodes. Iliopsoas hematoma is a complication of hemophilia. Bleed into the hip or the lumbar epidural space is less common and there are no signs to suggest infection.

Question 1055

Topic: Surgical Anatomy & Approaches

A patient with hemophilia A has a hematoma of the iliopsoas. He has a partial femoral nerve palsy. Treatment involves continuous factor replacement and:

. Open drainage
. Decompression of the fascia over the femoral nerve
. Percutaneous insertion of a drainage tube
. Embolization of feeder vessels by interventional radiologist
. Observation

Correct Answer & Explanation

. Observation

Explanation

The standard treatment of a psoas abscess is continuous factor replacement. Surgery is usually unnecessary, but it may be considered in cases of acute palsy with severe pain unresponsive to medical therapy. A percutaneous drainage tube is not recommended because the hematoma may be difficult to locate or drain.

Question 1056

Topic: 1. General Principles & Basic Science

Which of the following methods has the highest sensitivity in detecting skeletal lesions in patients with Langerhans cell histiocytosis:

. Physical examination
. Skeletal survey
. Ultrasound
. Bone scan
. Indium labeled white blood cell study

Correct Answer & Explanation

. Skeletal survey

Explanation

Skeletal survey is the most sensitive means of detecting lesions of eosinophilic granuloma (Langerhans cell histiocytosis). Bone scan detects most, but not all, of the lesions. Some lesions lack enough osteoblastic activity to appear on bone scan. Lesions are not detected on physical exam unless they are large enough to cause pain or tenderness. Indium labeled white cell studies are not used in this condition.

Question 1057

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue divided into distinct structural zones. Which of the following best describes the characteristics of the deep zone of articular cartilage?

. Highest water content, lowest proteoglycan content
. Lowest water content, highest proteoglycan content
. Randomly oriented collagen fibers
. Highest concentration of chondrocytes
. Collagen fibers parallel to the joint surface

Correct Answer & Explanation

. Lowest water content, highest proteoglycan content

Explanation

The deep zone of articular cartilage possesses the lowest water content and the highest proteoglycan concentration. Its collagen fibers are oriented perpendicular to the joint surface, anchoring the cartilage to the subchondral bone.

Question 1058

Topic: Biology, Genetics & Bone Healing

Bone formation occurs primarily via two distinct developmental pathways: endochondral ossification and intramembranous ossification. Which of the following skeletal structures forms exclusively through intramembranous ossification?

. Femur
. Tibia
. Clavicle
. Radius
. Fibula

Correct Answer & Explanation

. Clavicle

Explanation

The clavicle, mandible, and flat bones of the skull develop via intramembranous ossification, a process where mesenchymal stem cells differentiate directly into osteoblasts without a cartilage model. Long bones develop via endochondral ossification.

Question 1059

Topic: Biology, Genetics & Bone Healing

Denosumab is frequently used as a neoadjuvant or primary medical management for unresectable giant cell tumors of bone. What is the precise mechanism of action of this medication?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of osteoblast-like mononuclear cells
. Monoclonal antibody against RANK ligand (RANKL)
. Inhibition of the mTOR pathway
. Selective estrogen receptor modulation

Correct Answer & Explanation

. Monoclonal antibody against RANK ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds to and inhibits RANK ligand (RANKL). This prevents the activation of osteoclast-like giant cells, thereby reducing osteolysis and promoting tumor ossification.

Question 1060

Topic: Biology, Genetics & Bone Healing

In the process of endochondral ossification during secondary fracture healing, the cartilaginous callus is ultimately replaced by woven bone. Which of the following transcription factors is considered the master regulator strictly required for hypertrophic chondrocyte differentiation and subsequent vascular invasion in this pathway?

. SOX9
. RUNX2
. HIF-1 alpha
. Osterix (Sp7)
. Beta-catenin

Correct Answer & Explanation

. RUNX2

Explanation

RUNX2 (Cbfa1) is the essential master transcription factor for osteoblast differentiation and is required for the maturation of hypertrophic chondrocytes during endochondral ossification. Without RUNX2, vascular invasion and subsequent replacement of cartilage with bone fail to occur.

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