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1. General Principles & Basic Science MCQs

Practice Set 54 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 1061

Topic: 1. General Principles & Basic Science
Which of the following is an appropriate position for 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 increased risk of back pain. External rotation beyond approximately 5° is not needed. Arthrodesis often produces some shortening; therefore, intentional shortening is not needed.

Question 1062

Topic: 1. General Principles & Basic Science
A 12-year-old girl is brought into the office for an examination because of hip pain. She is able to bear weight on the involved limb while using crutches for stability. Radiographs reveal a grade III slip of the capital femoral epiphysis. Recommended treatment for this patient is:
. Skeletal femoral traction in order to improve the position
. Manipulate the hip under anesthesia in order to improve the position of the head
. Osteotomy of the femoral neck to improve the alignment
. Application of a hip spica
. In situ fixation

Correct Answer & Explanation

. In situ fixation

Explanation

In situ fixation provides the best results no matter what the grade of slip.

Question 1063

Topic: 1. General Principles & Basic Science
In classic hemophilia, a natural factor-VIII level of less than what percentage will lead to severe bleeding and complications?
. 50%
. 25%
. 15%
. 10%
. 5%

Correct Answer & Explanation

. 5%

Explanation

A surprisingly small amount of circulating factor-VIII (approximately 5%) is necessary to protect a patient from severe bleeding complications.

Question 1064

Topic: Infection, Pharmacology & VTE

A 1-week-old female infant with arthrogryposis multiplex congenital has hips that are stiff in flexion and abduction, and her knees have a range of flexion from 20° to 40°. In addition, her right thigh has become swollen and tender. The most likely cause of this latter problem is:

. Osteomyelitis of the femur
. Septic arthritis of the hip
. Dislocation of the hip
. Deep vein thrombosis
. Fracture of the femur

Correct Answer & Explanation

. Fracture of the femur

Explanation

Fracture is common in this condition because of osteopenia and the stress concentration due to joint stiffness. Osteomyelitis is uncommon in the diaphysis and much less common in this scenario than fracture. Septic arthritis of the hip is uncommon in this disease. Dislocation of the hip would not cause pain and swelling in this setting. Deep vein thrombosis is uncommon at this age.

Question 1065

Topic: 1. General Principles & Basic Science

Which of the following is a true statement regarding the results of surgery for a contracted joint in arthrogryposis:

. The joint range of motion can easily be doubled.
. The joint cannot be changed.
. The beginning and end of the range may change, but the total amount of motion remains about the same.
. The joint usually becomes stiffer.
. There is not an indication for such surgery.

Correct Answer & Explanation

. The beginning and end of the range may change, but the total amount of motion remains about the same.

Explanation

The beginning and end of the range may change, but the total amount of motion remains about the same. The amount of the range cannot be significantly increased. The endpoint can change, but not the amount of the range. The joint does not usually become stiffer. There may be an indication for surgery to put the joints in a functional position.

Question 1066

Topic: 1. General Principles & Basic Science

What percentage of the human genome represents the actual genes:

. 80%
. 66%
. 50%
. 20%
. 5%

Correct Answer & Explanation

. 5%

Explanation

The percentage of the genome that represents the sequence of our genes is approximately 5%. The rest of the genome codes are for initiator and termination sequences, maintenance functions, and unknown functions.

Question 1067

Topic: 1. General Principles & Basic Science
In studying a newly recognized disorder using a large population of affected individuals, geneticists discover that although the disorder often affects siblings, it is rarely found in any of their ancestors. This disorder most closely follows which pattern of inheritance?
. Autosomal dominant
. Autosomal recessive
. Sex-linked
. Multifactorial
. Anticipation

Correct Answer & Explanation

. Autosomal recessive

Explanation

Autosomal recessive conditions classically show horizontal inheritance. Ancestors do not display the gene because they would likely have only one copy of the mutant allele. Only when two carriers reproduce is the phenotype manifest in approximately one-fourth of their offspring. Autosomal dominant inheritance is characterized by vertical transmission. Many generations manifest the trait because it takes only a single copy of a mutant allele to display the phenotype. Sex-linked conditions are often traced back in a family. Normally the males are affected and the females are carriers. Multifactorial conditions are thought to result from the combination of different genes. Although the risk of recurrence in kindred is somewhat greater than the population as a whole, it is still quite low (only a few percent). It is rare for siblings to be affected. Anticipation refers to the phenomenon in which successive generations are likely to display more severe forms of a given disorder. Myotonic dystrophy is a classic example of this phenomenon.

Question 1068

Topic: 1. General Principles & Basic Science

Diseases caused by enzyme deficiency are commonly inherited by which of the following patterns:

. Autosomal dominant
. Autosomal recessive
. X-linked dominant
. Multifactorial
. Non-mendelian

Correct Answer & Explanation

. Autosomal recessive

Explanation

Two copies of a mutant allele are required to reduce enzyme function to levels that cause clinical impairment. Enzyme defects are rarely inherited by an autosomal dominant pattern because even half of the normal activity of most enzymes is adequate to maintain normal function. Enzyme defects are rarely inherited in an X-linked dominant pattern because one copy of a mutant allele is usually sufficient. Multifactorial inheritance refers to the interaction of multiple, or different genes, to produce a disorder. Enzyme deficiencies are typically the result of a defect in a single gene. Because enzymes are typically coded by a single gene, they follow mendelian patterns.

Question 1069

Topic: 1. General Principles & Basic Science

Polymerase chain reaction (PC R) is best characterized by which of the following descriptions:

. Use of enzymes to link chains of deoxyribonucleic acid (DNA) together
. Use of viral vectors to insert new DNA into a cell
. Denaturing and reannealing DNA multiple times with known primers
. Use of high temperatures to create ultra-high molecular weight polyethylene
. The process by which a cell-surface receptor turns on the transcription process

Correct Answer & Explanation

. Denaturing and reannealing DNA multiple times with known primers

Explanation

Polymerase chain reaction refers to denaturing DNA, isolating a segment of interest with known primers, and reannealing the strands multiple times to produce exponential copies of a segment.

Question 1070

Topic: 1. General Principles & Basic Science

Which of the following is the most definitive means of making a diagnosis of active skeletal tuberculosis:

. Positive tuberculin tine test
. Negative tuberculin tine test
. Positive culture and histological exam
. Magnetic resonance imaging
. Enzyme linked immunosorbent assay (ELISA) test

Correct Answer & Explanation

. Positive culture and histological exam

Explanation

An early histology confirmed later by a culture is considered the definitive means of diagnosis for active skeletal tuberculsosis. The tuberculin tine tests do not indicate active disease, only exposure. Magnetic resonance imaging is not specific for a particular infectious organism. The enzyme linked immunosorbent assay (ELISA) test is used to diagnose Lyme disease.

Question 1071

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with multiple fractures and recurrent osteomyelitis of the mandible. Radiographs demonstrate diffusely sclerotic bones and a "rugger-jersey" spine. Which cellular defect is the primary cause of this condition?

. Defective osteoblast differentiation
. Absence of alkaline phosphatase
. Inability of osteoclasts to acidify Howship's lacunae
. Defective Type I collagen synthesis
. Overactive osteocytes

Correct Answer & Explanation

. Inability of osteoclasts to acidify Howship's lacunae

Explanation

Osteopetrosis is characterized by defective osteoclast function, commonly due to a deficiency in carbonic anhydrase II. This prevents the acidification of Howship's lacunae, halting bone resorption and remodeling.

Question 1072

Topic: Biology, Genetics & Bone Healing

A newborn infant with 46,XY karyotype but female external genitalia presents with severe bowing of the tibiae and femurs, and respiratory distress. Which genetic mutation is primarily responsible for this disorder?

. SOX9
. RUNX2
. COL1A1
. FGFR3
. FLNB

Correct Answer & Explanation

. SOX9

Explanation

Campomelic dysplasia is an autosomal dominant condition caused by mutations in the SOX9 gene. It is characterized by severe bowing of the long bones, respiratory distress due to tracheobronchomalacia, and sex reversal.

Question 1073

Topic: 1. General Principles & Basic Science

A 10-year-old boy presents with bilateral knee pain, mild short stature, and a waddling gait. Radiographs show delayed and irregular ossification of the femoral and tibial epiphyses. A lateral knee radiograph prominently demonstrates a double-layered patella. What is the most likely diagnosis?

. Chondrodysplasia punctata
. Pseudoachondroplasia
. Multiple epiphyseal dysplasia
. Spondyloepiphyseal dysplasia congenita
. Dysplasia epiphysealis hemimelica

Correct Answer & Explanation

. Multiple epiphyseal dysplasia

Explanation

Multiple epiphyseal dysplasia (MED) primarily affects the epiphyses, causing joint pain, stiffness, and early osteoarthritis. The presence of a double-layered (or double-contour) patella on a lateral radiograph is a classic pathognomonic sign for MED.

Question 1074

Topic: Biology, Genetics & Bone Healing

A neonate presents with failure to thrive, severe anemia, and hepatosplenomegaly. Radiographs reveal a uniform, extreme increase in bone density with a "bone-within-a-bone" appearance in the spine. The pathogenesis of this malignant recessive disorder is primarily due to a defect in:

. Osteoblast proliferation
. Type I collagen synthesis
. Osteoclast function
. Chondrocyte hypertrophy
. Enchondral ossification

Correct Answer & Explanation

. Osteoclast function

Explanation

Malignant infantile osteopetrosis is caused by defective osteoclast function, often due to a deficiency in carbonic anhydrase II or TCIRG1 mutations. This prevents normal bone resorption and remodeling, obliterating the medullary canal and causing extramedullary hematopoiesis.

Question 1075

Topic: 1. General Principles & Basic Science

A 3-year-old girl is diagnosed with anterolateral bowing of the tibia and an impending pseudarthrosis. Physical exam reveals six axillary freckles and multiple Lisch nodules. The mutated gene responsible for this underlying condition is located on which chromosome?

. Chromosome 4
. Chromosome 11
. Chromosome 15
. Chromosome 17
. Chromosome 22

Correct Answer & Explanation

. Chromosome 17

Explanation

The clinical findings of anterolateral tibial bowing, axillary freckling, and Lisch nodules indicate Neurofibromatosis Type 1 (NF1). The NF1 gene produces neurofibromin and is located on chromosome 17.

Question 1076

Topic: Biology, Genetics & Bone Healing

A 14-year-old female presents with recurrent patellar dislocations, extreme skin hyperextensibility, and fragile tissues that bruise easily. She has wide, atrophic "cigarette paper" scars over her knees and elbows. Which of the following collagen types is most commonly defective in the classic form of this syndrome?

. Type I collagen
. Type II collagen
. Type IV collagen
. Type V collagen
. Type X collagen

Correct Answer & Explanation

. Type V collagen

Explanation

The classic type of Ehlers-Danlos syndrome is characterized by severe skin hyperextensibility, wide atrophic scars, and joint hypermobility. It is most commonly caused by mutations in the COL5A1 or COL5A2 genes, resulting in defective Type V collagen.

Question 1077

Topic: Biology, Genetics & Bone Healing
A 16-year-old tall, thin male presents with anterior chest pain and shortness of breath. He has a history of bilateral upward lens subluxation, arachnodactyly, and a recent diagnosis of protrusio acetabuli. Mutation in which of the following proteins is the primary cause of his condition?
. Elastin
. Fibrillin-1
. Cartilage oligomeric matrix protein
. Collagen type I
. Collagen type III

Correct Answer & Explanation

. Fibrillin-1

Explanation

This patient has Marfan syndrome, characterized by skeletal (tall stature, arachnodactyly, protrusio acetabuli), ocular (ectopia lentis), and cardiovascular (aortic root dilation) anomalies. It is an autosomal dominant disorder caused by mutations in the FBN1 gene, which encodes fibrillin-1.

Question 1078

Topic: Biology, Genetics & Bone Healing

A 9-year-old boy of Ashkenazi Jewish descent presents with chronic bone pain and a pathologic fracture of the distal femur. Radiographs reveal an "Erlenmeyer flask" deformity of the distal femurs. Laboratory tests show anemia, thrombocytopenia, and hepatosplenomegaly. What is the standard medical treatment for the underlying disorder?

. Bone marrow transplantation
. Bisphosphonate therapy
. Enzyme replacement therapy with imiglucerase
. High-dose vitamin D supplementation
. Growth hormone therapy

Correct Answer & Explanation

. Enzyme replacement therapy with imiglucerase

Explanation

Gaucher disease is a lysosomal storage disorder caused by a deficiency in glucocerebrosidase, leading to accumulation of glucocerebroside in the bone marrow and reticuloendothelial system. The standard treatment for non-neuronopathic (Type 1) Gaucher disease is enzyme replacement therapy, such as imiglucerase.

Question 1079

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy presents with profound bowing of the legs and short stature. Laboratory evaluation demonstrates normal serum calcium, low serum phosphate, and elevated alkaline phosphatase. Parathyroid hormone (PTH) levels are normal. A mutation in the PHEX gene is confirmed. What is the primary mechanism of hypophosphatemia in this condition?

. Decreased intestinal absorption of phosphate
. Impaired renal tubular reabsorption of phosphate
. Excessive skeletal deposition of phosphate
. Chronic diarrhea and intestinal phosphate loss
. Defective vitamin D 25-hydroxylation in the liver

Correct Answer & Explanation

. Impaired renal tubular reabsorption of phosphate

Explanation

X-linked hypophosphatemic rickets (XLH) is caused by a PHEX mutation, which leads to elevated levels of FGF23. FGF23 acts on the kidneys to severely decrease phosphate reabsorption in the proximal tubules, leading to renal phosphate wasting and hypophosphatemia.

Question 1080

Topic: Biology, Genetics & Bone Healing

A 10-month-old infant fed exclusively boiled cow's milk presents with severe irritability, bleeding gums, and pseudoparalysis of the lower extremities. Radiographs of the knee show a dense zone of provisional calcification, a radiolucent band just metaphyseal to it, and a ring of increased density around the epiphysis. The defective biochemical process is:

. Carboxylation of osteocalcin
. Cleavage of procollagen peptides
. Hydroxylation of proline and lysine residues
. Cross-linking of elastin
. Mineralization of osteoid matrix

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

This infant has scurvy (Vitamin C deficiency) resulting from an inadequate diet. Vitamin C is a necessary cofactor for prolyl hydroxylase and lysyl hydroxylase, enzymes responsible for the hydroxylation of proline and lysine during the synthesis of normal collagen.

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