Achondroplasia MCQs | Orthopedic Surgery Board Review

Question 1

A couple with normal stature has a child diagnosed with achondroplasia. They are concerned about the genetics of this condition and ask about the likelihood of this occurring. Based on the epidemiology of achondroplasia, what is the most accurate genetic explanation?

Explanation

Correct Answer: De novo mutation of a gene on chromosome 4

Achondroplasia is inherited in an autosomal dominant manner. However, over 80% of individuals with achondroplasia have parents with normal stature. In these cases, the condition is the result of a 'de novo' (new) mutation of a gene localized to the distal short arm of chromosome 4.

Question 2

Review the AP and lateral radiographs of the lumbar spine in this patient with short-limb dwarfism. Which of the following is the characteristic radiographic finding shown?

Explanation

Correct Answer: Interpediculate distance decreases from the upper to lower lumbar spine

The provided radiograph demonstrates the classic spinal findings in achondroplasia. The interpediculate distance abnormally decreases from the upper to the lower lumbar spine (AP view), and characteristic short pedicles are seen on the lateral view, which predisposes these patients to spinal stenosis.

Question 3

A 4-year-old boy presents with delayed motor milestones and the facial features shown below. What is the most likely diagnosis?

Explanation

Correct Answer: Achondroplasia

The clinical image shows a child with a head that is disproportionately large in relation to height, a prominent forehead (frontal bossing), and a broadened, depressed nasal bridge. These are the hallmark craniofacial features of achondroplasia, the most common human chondrodysplasia.

Question 4

A patient with the most common human chondrodysplasia presents for orthopedic evaluation. Based on the clinical photograph provided, which combination of physical findings is most characteristic of this condition?

Explanation

Correct Answer: Exaggerated lumbar lordosis, limitation of elbow extension, and genu varum

As seen in the clinical image and described in the text, patients with achondroplasia typically present with exaggerated lumbar lordosis, limitation of elbow extension and rotation, and genu varum. Hyperextension of the knees and most other joints is also common.

Question 5

An infant is diagnosed with achondroplasia shortly after birth. The parents are counseled regarding potential life-threatening complications during infancy. Which of the following represents the greatest risk of mortality in this age group?

Explanation

Correct Answer: Spinal cord compression and upper airway obstruction

In infancy, patients with achondroplasia are at an increased risk of death primarily due to compression of the spinal cord (often at the foramen magnum) and upper airway obstruction.

Question 6

The image below compares a patient with a specific skeletal dysplasia to an age-matched individual of normal stature. Which of the following statements accurately describes the anthropometric differences seen in this condition?

Explanation

Correct Answer: There is no difference in trunk height, but the chest and shoulders are narrower

Achondroplasia is a disproportionate short-limb dwarfism. As demonstrated in the comparative clinical image, there is no significant difference in the height of the trunk between an achondroplastic patient and a normal individual; however, the chest and shoulders are notably narrower.

Question 7

A 12-month-old infant with achondroplasia is brought to the clinic. The parents are concerned because the child is not yet walking and seems 'floppy.' Which of the following is the most appropriate counseling regarding the child's development?

Explanation

Correct Answer: Hypotonia and delayed motor milestones are typical, but intelligence is usually normal

In infancy, hypotonia is typical in achondroplasia, and the acquisition of developmental motor milestones is often delayed. However, intelligence and life span are usually normal, and parents should be reassured regarding cognitive development.

Question 8

A 10-year-old girl with achondroplasia asks about her expected final adult height. According to established growth data for this condition, what is the mean adult height for females?

Explanation

Correct Answer: 124 cm

According to the clinical data for achondroplasia, the mean adult height in males is 131 ± 5.6 cm, and in females, it is 124 ± 5.9 cm.

Question 9

The clinical photograph below shows the hands of a patient with achondroplasia. Which of the following statements best describes the hand manifestations in this specific dysplasia compared to other short-limb dwarfisms?

Explanation

Correct Answer: The fingers are not as short as in many other short-limb dwarfisms

As shown in the clinical image and noted in the text, the fingers in achondroplasia are not as short as in many other forms of short-limb dwarfism. They often present with a 'trident' appearance, though their relative length is better preserved than in other severe dysplasias.

Question 10

Achondroplasia is caused by a mutation that affects endochondral ossification. The responsible gene is localized to which of the following chromosomal regions?

Explanation

Correct Answer: Distal short arm of chromosome 4

Achondroplasia is the result of a mutation of a gene (FGFR3) localized to the distal short arm of chromosome 4. This mutation leads to a gain of function that inhibits chondrocyte proliferation, resulting in disproportionate short-limb dwarfism.

Question 11

A 5-year-old boy with short stature presents for evaluation. An AP and lateral radiograph of the lumbar spine is shown below. What is the characteristic radiographic finding demonstrated in this condition?

Explanation

Correct Answer: Decrease in interpediculate distance from upper to lower lumbar spine

In achondroplasia, a hallmark radiographic finding is the narrowing of the interpediculate distance from the upper to the lower lumbar spine, which is the opposite of the normal widening seen in unaffected individuals. Short pedicles are also characteristically seen on the lateral view.

Question 12

A child presents with the facial features shown below. Which of the following genetic mutations is most likely responsible for this phenotype?

Explanation

Correct Answer: Mutation on the distal short arm of chromosome 4

The clinical image demonstrates a disproportionately large head, prominent forehead, and a broadened, depressed nasal bridge typical of achondroplasia. This condition is caused by a mutation localized to the distal short arm of chromosome 4 (specifically the FGFR3 gene).

Question 13

A patient with the condition shown below presents to the clinic. Which of the following joint findings is typically associated with this disorder?

Explanation

Correct Answer: Limitation of elbow extension and rotation

Patients with achondroplasia typically exhibit exaggerated lumbar lordosis, genu varum, hyperextension of the knees and most other joints, but characteristically have a limitation of elbow extension and rotation.

Question 14

A couple with normal stature has a child diagnosed with achondroplasia. They are concerned about the risk of having another child with the same condition. What percentage of achondroplasia cases are the result of a de novo mutation in parents with normal stature?

Explanation

Correct Answer: Over 80%

Over 80% of individuals with achondroplasia have parents with normal stature. In these cases, the condition is the result of a spontaneous 'de novo' mutation.

Question 15

An infant is diagnosed with achondroplasia. Which of the following is a typical finding during the first year of life in this patient population?

Explanation

Correct Answer: Hypotonia and delayed motor milestones

In infancy, patients with achondroplasia typically present with hypotonia, and the acquisition of developmental motor milestones is often delayed. Intelligence and overall life span are usually normal.

Question 16

While life span in achondroplasia is usually normal, there is an increased risk of death in infancy. Which of the following is a primary cause for this increased mortality risk?

Explanation

Correct Answer: Upper airway obstruction and spinal cord compression

Compression of the spinal cord (often at the foramen magnum) and upper airway obstruction are critical complications in infants with achondroplasia that significantly increase the risk of death during infancy.

Question 17

A 12-year-old boy with achondroplasia is compared to his unaffected peer. Based on the clinical appearance shown below, which of the following statements regarding his trunk and chest is accurate?

Explanation

Correct Answer: The chest and shoulders are narrower compared to an unaffected peer.

In achondroplasia, there is no significant difference in the height of the trunk compared to unaffected individuals; however, the chest and shoulders are characteristically narrower.

Question 18

A family asks about the expected adult height for their male child recently diagnosed with achondroplasia. According to standard growth data for this condition, what is the mean adult height for males?

Explanation

Correct Answer: 131 +/- 5.6 cm

The mean adult height in males with achondroplasia is 131 +/- 5.6 cm, whereas in females it is 124 +/- 5.9 cm.

Question 19

The hands of a patient with a skeletal dysplasia are shown below. In achondroplasia, how do the fingers typically present compared to many other short-limb dwarfisms?

Explanation

Correct Answer: They are not as short as in many other short-limb dwarfisms.

While achondroplasia is a short-limb dwarfism, the fingers are characteristically not as short as those seen in many other forms of short-limb dwarfism.

Question 20

A 25-year-old male with achondroplasia is planning to start a family with a female of normal stature. What is the inheritance pattern of his condition, and what is the risk of passing the mutation to his offspring?

Explanation

Correct Answer: Autosomal dominant; 50% risk

Achondroplasia is inherited in an autosomal dominant manner. An affected individual has a 50% chance of passing the mutated gene to each offspring, regardless of the child's sex.

Question 21

A 12-year-old boy with disproportionate short stature presents with back pain. The AP and lateral radiographs of the lumbar spine are shown below. Which of the following is the characteristic radiographic finding demonstrated in this condition?

Explanation

Correct Answer: Decreasing interpediculate distance from L1 to L5

In achondroplasia, the interpediculate distance characteristically decreases from the upper to the lower lumbar spine, which is the opposite of the normal spine where it widens. This, combined with short pedicles seen on the lateral view, contributes to the high risk of spinal stenosis in these patients.

Question 22

A couple with normal stature has a child diagnosed with achondroplasia. They are concerned about the risk of having another child with the same condition. What is the most likely genetic mechanism responsible for their child's condition?

Explanation

Correct Answer: De novo mutation on the distal short arm of chromosome 4

Achondroplasia is inherited in an autosomal dominant manner. However, over 80% of individuals with achondroplasia have parents with normal stature, meaning the condition is the result of a 'de novo' (new) mutation. This gene is localized to the distal short arm of chromosome 4 (FGFR3 gene).

Question 23

A 5-year-old child presents to the orthopedic clinic. Clinical photographs are shown below. Examination of the upper extremities in this patient is most likely to reveal which of the following findings?

Explanation

Correct Answer: Limitation of elbow extension and rotation

The clinical images demonstrate a patient with achondroplasia, characterized by exaggerated lumbar lordosis and genu varum. A classic upper extremity finding in these patients is the limitation of elbow extension and rotation, despite hyperextension being common in most other joints like the knees.

Question 24

An infant is diagnosed with the most common form of human chondrodysplasia. While life span is generally normal, there is an increased risk of death in infancy. Which of the following is the primary cause of this increased mortality risk?

Explanation

Correct Answer: Compression of the spinal cord and upper airway obstruction

In achondroplasia, intelligence and life span are usually normal. However, compression of the spinal cord (often at the foramen magnum) and upper airway obstruction significantly increase the risk of death during infancy.

Question 25

A 3-year-old boy is evaluated for delayed motor milestones. His clinical appearance is shown below. Which of the following best describes the craniofacial characteristics associated with this syndrome?

Explanation

Correct Answer: Disproportionately large head, prominent forehead, and depressed nasal bridge

The image shows the classic facial features of achondroplasia. The head is disproportionately large in relation to height (macrocephaly), the forehead is prominent (frontal bossing), and the nasal bridge is broadened and depressed.

Question 26

A pediatrician refers a 9-month-old infant with achondroplasia to the orthopedic clinic due to concerns about delayed motor milestones. The parents are highly anxious about the child's future cognitive development. What is the most appropriate counseling to provide regarding this child's developmental trajectory?

Explanation

Correct Answer: Motor delays are typical due to hypotonia, but intelligence is usually normal.

In infancy, hypotonia is typical in achondroplasia, and the acquisition of developmental motor milestones is often delayed as a result. However, intelligence and overall life span are usually normal.

Question 27

The hands of a patient with a disproportionate short-limb dwarfism are shown below. According to the specific characteristics of this condition, how do these digits typically compare to other forms of short-limb dwarfism?

Explanation

Correct Answer: They are not as short as in many other short-limb dwarfisms.

While achondroplasia is a short-limb dwarfism and features a characteristic 'trident hand' deformity, the fingers themselves are actually not as short as those seen in many other forms of short-limb dwarfism.

Question 28

A 10-year-old female with achondroplasia and her parents are inquiring about her expected final adult height. Based on epidemiological data for this condition, what is the mean adult height for females?

Explanation

Correct Answer: 124 cm

In achondroplasia, the mean adult height in males is 131 +/- 5.6 cm, and in females, it is 124 +/- 5.9 cm.

Question 29

A clinical comparison between a patient with achondroplasia and an age-matched individual of normal stature is shown below. Which of the following statements accurately describes the axial skeletal proportions in the affected individual?

Explanation

Correct Answer: There is no difference in trunk height, but the chest and shoulders are narrower.

Achondroplasia is a disproportionate short-limb dwarfism. As demonstrated in the clinical comparison, there is no significant difference in the height of the trunk between an achondroplastic patient and a normal individual; however, the chest and shoulders are notably narrower in achondroplasia.

Question 30

A 45-year-old male with achondroplasia presents with neurogenic claudication. Radiographic evaluation of his lumbar spine is performed. Which of the following anatomical abnormalities of the vertebrae is most responsible for his spinal stenosis?

Explanation

Correct Answer: Characteristic short pedicles

Spinal stenosis is a hallmark complication of achondroplasia in adulthood. It is primarily driven by the characteristic short pedicles (seen on lateral radiographs) and the decreasing interpediculate distance in the lumbar spine, which severely narrows the spinal canal.

Question 31

A 5-year-old boy with disproportionate short stature presents for evaluation. The AP and lateral radiographs of the lumbar spine are shown below. Which of the following best describes the classic radiographic finding seen in the AP view of this condition?

Explanation

Correct Answer: The interpedicular distance decreases from L1 to L5.

In achondroplasia, a hallmark radiographic finding on the AP view of the spine is the narrowing of the interpedicular distance from the upper to the lower lumbar spine (L1 to L5). In a normal spine, this distance widens caudally. Anterior beaking is more characteristic of mucopolysaccharidoses (like Morquio or Hurler syndrome), and severe platyspondyly is seen in conditions like thanatophoric dysplasia or spondyloepiphyseal dysplasia.

Question 32

A 3-year-old child presents with the facial features shown in the clinical photograph below. Which of the following genetic mechanisms is most likely responsible for this patient's condition?

Explanation

Correct Answer: De novo mutation of a gene on the distal short arm of chromosome 4.

The clinical image shows a child with a disproportionately large head, prominent forehead (frontal bossing), and a broadened, depressed nasal bridge, which are classic facial features of achondroplasia. Achondroplasia is caused by a mutation in the FGFR3 gene, localized to the distal short arm of chromosome 4. Over 80% of cases are the result of a de novo (new) mutation in individuals with parents of normal stature.

Question 33

In infants diagnosed with the most common human chondrodysplasia, which of the following complications poses the greatest risk of mortality during the first year of life?

Explanation

Correct Answer: Cervicomedullary compression and upper airway obstruction.

Achondroplasia is the most common chondrodysplasia. In infancy, compression of the spinal cord (specifically cervicomedullary compression at the narrowed foramen magnum) and upper airway obstruction significantly increase the risk of sudden death. Atlantoaxial instability is more characteristic of Down syndrome or Morquio syndrome, while a bell-shaped thorax causing severe restrictive lung disease is classic for asphyxiating thoracic dystrophy (Jeune syndrome) or thanatophoric dysplasia.

Question 34

A 7-year-old patient presents with the clinical posture and lower extremity alignment shown below. Upon physical examination of the upper extremities, which of the following findings is most commonly associated with this syndrome?

Explanation

Correct Answer: Limitation of elbow extension and rotation.

The image demonstrates exaggerated lumbar lordosis, genu varum, and hyperextension of the knees, typical of achondroplasia. While many joints in achondroplasia exhibit hyperextensibility (like the knees), the elbow is a notable exception. Limitation of elbow extension and rotation is a very common and classic clinical finding in patients with achondroplasia.

Question 35

A couple with normal stature brings their newborn child to the orthopedic clinic. The child has been diagnosed with achondroplasia. The parents are concerned about the risk of having another child with the same condition. What is the most accurate counseling regarding the etiology of their child's condition?

Explanation

Correct Answer: It is the result of a de novo mutation in over 80% of cases, making the recurrence risk for this couple very low.

Achondroplasia is inherited in an autosomal dominant manner. However, over 80% of individuals with achondroplasia have parents with normal stature. In these cases, the condition is the result of a spontaneous 'de novo' mutation. Therefore, the recurrence risk for parents of normal stature who have one affected child is extremely low (though slightly higher than the general population due to the rare possibility of germline mosaicism).

Question 36

The clinical photograph below demonstrates the hands of a patient with the most common disproportionate short-limb dwarfism. Which of the following statements regarding the hand anatomy in this condition is true?

Explanation

Correct Answer: The fingers are not as short as in many other short-limb dwarfisms.

In achondroplasia, the hands often exhibit a 'trident' appearance due to the inability to approximate the tips of the middle and ring fingers. However, as noted in the clinical description, the fingers in achondroplasia are actually not as short as they are in many other forms of short-limb dwarfism. Syndactyly is characteristic of Apert syndrome, and triphalangeal thumbs are seen in conditions like Holt-Oram syndrome.

Question 37

A 12-month-old infant with achondroplasia is brought to the clinic by his parents, who are concerned that he is not yet walking or pulling to stand. Which of the following is the most appropriate response regarding his development?

Explanation

Correct Answer: This is likely due to typical infantile hypotonia, and motor milestones are often delayed, though intelligence is usually normal.

In infancy, patients with achondroplasia typically present with hypotonia. As a result, the acquisition of developmental motor milestones (such as sitting, standing, and walking) is often delayed. However, their intelligence and life span are usually normal. While spinal cord compression is a risk, delayed motor milestones alone in a 12-month-old are expected due to hypotonia and altered biomechanics, not necessarily an acute cord compression.

Question 38

The clinical photograph compares a patient with achondroplasia (left) to an age-matched child with normal stature (right). Based on the typical anthropometric features of this condition, which of the following statements is correct regarding the patient's torso?

Explanation

Correct Answer: The trunk height is similar to the normal child, but the chest and shoulders are narrower.

Achondroplasia is a disproportionate short-limb dwarfism. The shortening primarily affects the appendicular skeleton (rhizomelic shortening). As demonstrated in the clinical image, there is no significant difference in the height of the trunk between an achondroplastic patient and a normal-statured peer; however, the chest and shoulders are characteristically narrower in achondroplasia.

Question 39

An 18-year-old male with achondroplasia presents for a final growth evaluation. According to standard growth curves for this specific skeletal dysplasia, what is the expected mean adult height for males?

Explanation

Correct Answer: 131 cm

In achondroplasia, the mean adult height for males is approximately 131 +/- 5.6 cm. For females, the mean adult height is slightly lower, at approximately 124 +/- 5.9 cm.

Question 40

Review the lateral lumbar spine radiograph of the patient shown below. The characteristic anatomical abnormality seen on this view directly predisposes the patient to which of the following clinical conditions in adulthood?

Explanation

Correct Answer: Lumbar spinal stenosis.

The lateral radiograph demonstrates characteristically short pedicles. Combined with the decreased interpedicular distance seen on the AP view, these short pedicles result in a congenitally narrow spinal canal. In adulthood, even mild degenerative changes (such as disc bulging or facet hypertrophy) can precipitate severe symptomatic lumbar spinal stenosis, which is a hallmark complication of achondroplasia.

Question 41

A 5-year-old boy with disproportionate short stature presents for evaluation. An anteroposterior and lateral radiograph of the lumbar spine is obtained, as shown below. Which of the following is the hallmark radiographic finding in the lumbar spine for this condition?

Explanation

Correct Answer: Interpediculate distance decreases from upper to lower lumbar spine

In achondroplasia, a classic radiographic feature is that the interpediculate distance decreases from the upper to the lower lumbar spine, which is the opposite of the normal spine. Additionally, characteristic short pedicles are seen on the lateral view, contributing to spinal stenosis.

Question 42

A couple with normal stature has a child diagnosed with achondroplasia. They are concerned about the risk in future pregnancies and ask how this occurred. What is the most accurate statement regarding the genetics of this condition in their child?

Explanation

Correct Answer: It represents a de novo mutation in over 80% of such cases

Achondroplasia is inherited in an autosomal dominant manner. However, over 80% of individuals with achondroplasia have parents with normal stature, meaning the condition is the result of a 'de novo' (new) mutation.

Question 43

A 3-year-old child presents to the orthopedic clinic. Based on the clinical photograph below, which of the following craniofacial features is characteristic of this patient's underlying skeletal dysplasia?

Explanation

Correct Answer: Disproportionately large head with a prominent forehead and depressed nasal bridge

As seen in the provided clinical image and described in the text, patients with achondroplasia typically have a head that is disproportionately large in relation to their height, a prominent forehead (frontal bossing), and a broadened, depressed nasal bridge.

Question 44

While evaluating an infant with achondroplasia, the orthopedic surgeon must be vigilant about potential life-threatening complications. Which of the following conditions significantly increases the risk of death during infancy in these patients?

Explanation

Correct Answer: Upper airway obstruction and spinal cord compression

According to the clinical text, compression of the spinal cord (often at the foramen magnum) and upper airway obstruction are the primary factors that increase the risk of death in infancy for patients with achondroplasia.

Question 45

A 12-year-old boy with achondroplasia presents for a routine follow-up. The clinical photograph below demonstrates his typical standing posture. Which combination of physical findings is most consistent with this condition?

Explanation

Correct Answer: Exaggerated lumbar lordosis, limitation of elbow extension, and genu varum

The clinical image and text highlight that exaggerated lumbar lordosis, limitation of elbow extension and rotation, genu varum, and hyperextension of the knees and most other joints are common findings in achondroplasia.

Question 46

Achondroplasia is the most common of the human chondrodysplasias. The genetic mutation responsible for this condition is localized to which of the following chromosomal regions?

Explanation

Correct Answer: Distal short arm of chromosome 4

Achondroplasia is caused by a mutation in the FGFR3 gene, which is localized to the distal short arm of chromosome 4.

Question 47

A pediatrician refers a 9-month-old infant with achondroplasia to the orthopedic clinic due to concerns about delayed walking and poor head control. What is the typical developmental and cognitive profile for a child with this condition?

Explanation

Correct Answer: Hypotonia and delayed motor milestones with normal intelligence

In infancy, hypotonia is typical in achondroplasia, and the acquisition of developmental motor milestones is often delayed. However, intelligence and life span are usually normal.

Question 48

A clinical photograph of the hands of a patient with a skeletal dysplasia is shown below. In the context of achondroplasia, how do the fingers typically present compared to many other short-limb dwarfisms?

Explanation

Correct Answer: They are not as short as in many other short-limb dwarfisms

As noted in the text accompanying the clinical image, the fingers in achondroplasia are not as short as in many other forms of short-limb dwarfism, often presenting with a characteristic 'trident' appearance (though the relative length is the key distinguishing feature mentioned).

Question 49

A 14-year-old male with achondroplasia asks about his expected final adult height. According to established growth data for this condition, what is the mean adult height for males?

Explanation

Correct Answer: 131 +/- 5.6 cm

The mean adult height in males with achondroplasia is 131 +/- 5.6 cm, whereas in females it is 124 +/- 5.9 cm.

Question 50

Two individuals are shown in the clinical photograph below. The patient on the right has achondroplasia. When comparing the trunk and shoulder dimensions of a patient with achondroplasia to an individual of normal stature, which of the following statements is most accurate?

Explanation

Correct Answer: There is no difference in trunk height, but the chest and shoulders are narrower

Achondroplasia is a disproportionate short-limb dwarfism. As demonstrated in the clinical comparison image, there is no difference between the patients in the height of the trunk; however, the chest and shoulders are narrower in achondroplasia.

Question 51

A 2-year-old child with achondroplasia is noted to have a persistent thoracolumbar kyphosis measuring 35 degrees. Which of the following is the most appropriate next step in management?

Explanation

Most thoracolumbar kyphosis in achondroplasia resolves once the child begins walking and develops lumbar lordosis. However, if the kyphosis persists beyond the walking stage or exceeds 30 degrees, bracing with a custom TLSO is indicated to prevent rigid deformity.

Question 52

Achondroplasia is caused by a mutation in the FGFR3 gene. What is the specific effect of this mutation on the physeal growth plate?

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in FGFR3. This results in the suppression of chondrocyte proliferation and hypertrophy, primarily affecting the proliferative zone of the physis.

Question 53

A 35-year-old male with achondroplasia presents with neurogenic claudication. Radiographs show severe lumbar spinal stenosis. What anatomical feature primarily accounts for the spinal stenosis in this condition?

Explanation

Spinal stenosis in achondroplasia is primarily due to congenitally short pedicles and a characteristic narrowing of the interpedicular distance from L1 to L5. This decreases both the anteroposterior and transverse diameters of the spinal canal.

Question 54

An 8-month-old infant with achondroplasia presents with hypotonia, central sleep apnea, and hyperreflexia. What is the most critical next step in evaluation?

Explanation

These symptoms strongly suggest foramen magnum stenosis causing cervicomedullary compression, a life-threatening complication in infants with achondroplasia. MRI of the cervicomedullary junction is the modality of choice to assess the degree of compression.

Question 55

A 7-year-old child with achondroplasia presents with symptomatic genu varum. Which of the following is the primary pathophysiological driver of this lower extremity deformity?

Explanation

Genu varum in achondroplasia is predominantly caused by the relative overgrowth of the fibula compared to the tibia. This leads to lateral bowing and a varus thrust at the knee, which may require surgical realignment if progressive.

Question 56

Two individuals with achondroplasia are expecting a child and request genetic counseling regarding the risk of homozygous achondroplasia. What is the probability that their child will inherit this fatal form of the condition?

Explanation

Achondroplasia is an autosomal dominant condition. Therefore, two affected parents (who are heterozygotes) have a 25% chance of having a child with homozygous achondroplasia, which is typically lethal in the perinatal period.

Question 57

Which of the following best describes the classic radiographic appearance of the pelvis in a patient with achondroplasia?

Explanation

The classic pelvic radiographic findings in achondroplasia include squared, shortened iliac wings and horizontal acetabular roofs. This creates a wide, flat pelvic inlet commonly described as resembling a 'champagne glass'.

Question 58

A 12-year-old boy with achondroplasia is evaluated for upper extremity joint mobility. Which of the following joint abnormalities is most commonly observed in this patient population?

Explanation

Patients with achondroplasia typically experience limited elbow extension and supination due to structural changes in the distal humerus and radial head. Despite this limitation, it rarely causes significant functional impairment.

Question 59

A 4-year-old child presents with short-limbed dwarfism. Which of the following clinical findings best differentiates pseudoachondroplasia from achondroplasia?

Explanation

Pseudoachondroplasia is characterized by normal craniofacial features and head circumference. This distinguishes it from achondroplasia, which classically features frontal bossing and midface hypoplasia.

Question 60

A 45-year-old patient with achondroplasia undergoes a lumbar laminectomy for severe spinal stenosis. What crucial anatomical consideration must be addressed during decompression to ensure success while preventing iatrogenic instability?

Explanation

Due to the short pedicles and narrow interpedicular distance, the lateral recesses are particularly stenotic in achondroplasia. A wide laminectomy extending to the medial facets is required for adequate decompression, taking care to preserve the pars interarticularis to avoid instability.

Question 61

Reviewing an anteroposterior (AP) radiograph of the lumbar spine in a patient with achondroplasia, what is the expected change in interpedicular distance from L1 to L5?

Explanation

In achondroplasia, the interpedicular distance progressively decreases from L1 to L5. This is the opposite of a normal spine, where the distance widens caudally, and is a major contributor to lumbar spinal stenosis.

Question 62

A 5-year-old child with achondroplasia develops signs of cor pulmonale. What is the most likely underlying etiology of this condition?

Explanation

Cor pulmonale in achondroplasia is most commonly a complication of chronic hypoxemia secondary to severe obstructive sleep apnea. This condition is exacerbated by midface hypoplasia, a small pharynx, and relatively enlarged tonsils and adenoids.

Question 63

Parents of a 6-month-old infant with achondroplasia are concerned about a prominent bump on the child's back when sitting. Clinical exam reveals a flexible thoracolumbar kyphosis. What is the most appropriate advice for the parents?

Explanation

Thoracolumbar kyphosis is present in over 90% of infants with achondroplasia due to hypotonia and a heavy head. Avoiding unsupported sitting and using a firm mattress typically allows the kyphosis to spontaneously resolve once the child develops lumbar lordosis and begins walking.

Question 64

A couple of normal stature has a child diagnosed with achondroplasia. Which of the following factors is most strongly associated with the de novo mutation seen in this patient?

Explanation

Over 80% of achondroplasia cases are the result of a de novo mutation in the FGFR3 gene. This sporadic genetic event is strongly correlated with advanced paternal age.

Question 65

Which of the following hand deformities is considered a hallmark clinical finding in patients with achondroplasia?

Explanation

The 'trident hand' is a classic feature of achondroplasia. It is characterized by short, stubby fingers with a widened space between the third and fourth digits.

Question 66

Achondroplasia is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. This mutation directly affects which zone of the growth plate?

Explanation

Achondroplasia results from an activating mutation in FGFR3, which inhibits chondrocyte proliferation. This primarily affects the proliferative zone of the physis, leading to defective endochondral ossification.

Question 67

Approximately 80% of achondroplasia cases arise from de novo mutations. Which of the following is the most significant risk factor for these sporadic occurrences?

Explanation

De novo mutations in the FGFR3 gene accounting for achondroplasia are strongly associated with advanced paternal age. The mutations occur almost exclusively in the father's germline.

Question 68

A 9-month-old infant with achondroplasia presents with central sleep apnea, hypotonia, and brisk lower extremity reflexes. What is the most appropriate next step in management?

Explanation

These symptoms suggest cervical myelopathy due to foramen magnum stenosis, a potentially lethal complication in infants with achondroplasia. An MRI of the craniovertebral junction is indicated to evaluate for brainstem compression.

Question 69

A 45-year-old male with achondroplasia presents with bilateral leg pain and weakness after walking 50 meters, which is relieved by sitting. Which anatomic abnormality is the primary driver of this patient's pathology?

Explanation

Neurogenic claudication in adult achondroplastic patients is primarily caused by severe spinal stenosis. This is anatomically driven by congenitally short, thickened pedicles and decreased interpedicular distances.

Question 70

The parents of an 8-month-old infant with achondroplasia are concerned about a prominent curve in the child's lower back when sitting unsupported. Radiographs confirm a flexible thoracolumbar kyphosis. What is the recommended initial management?

Explanation

Infantile thoracolumbar kyphosis in achondroplasia is largely postural due to hypotonia and macrocephaly. Initial management involves preventing unsupported sitting; the deformity usually resolves once the child begins to stand and walk.

Question 71

A 4-year-old child presents for evaluation of short stature. Pelvic radiographs display classic findings associated with achondroplasia. Which of the following accurately describes these expected radiographic features?

Explanation

Classic pelvic radiographic findings in achondroplasia include a 'champagne glass' pelvis. This is characterized by squared iliac wings, narrow sacrosciatic notches, and flat, horizontal acetabular roofs.

Question 72

When reviewing the AP lumbar spine radiograph of a patient with achondroplasia, what classic finding differentiates their anatomy from an individual with normal stature?

Explanation

In a normal spine, the interpedicular distance progressively widens from L1 to L5. In achondroplasia, the interpedicular distance classically narrows from L1 to L5, predisposing the patient to spinal stenosis.

Question 73

Patients with achondroplasia frequently develop symptomatic genu varum. What is the primary anatomic cause of this deformity?

Explanation

Genu varum in achondroplasia is typically caused by disproportionate growth between the tibia and fibula. The fibula outgrows the tibia, exerting a varus bowing force on the lower extremity.

Question 74

A 6-year-old boy presents with disproportionate short stature. The orthopedic surgeon suspects pseudoachondroplasia rather than achondroplasia. Which of the following physical examination findings most strongly supports pseudoachondroplasia?

Explanation

Unlike achondroplasia, patients with pseudoachondroplasia have a normal facial appearance and head circumference. They also typically present later in childhood (ages 2-3) when growth delay becomes apparent.

Question 75

Achondroplasia is characterized by a failure of normal endochondral ossification. Consequently, which of the following skeletal structures typically attains a normal size in these patients?

Explanation

The clavicle and cranial vault develop primarily via intramembranous ossification, which is unaffected in achondroplasia. Long bones (like the humerus and femur) rely on endochondral ossification and are therefore shortened.

Question 76

A major cause of sudden death in the first year of life for infants with achondroplasia is respiratory arrest. This is primarily attributed to which of the following?

Explanation

Foramen magnum stenosis can lead to severe brainstem and upper cervical cord compression. This can result in central sleep apnea, respiratory arrest, and sudden infant death if not decompressed surgically.

Question 77

A 6-year-old with achondroplasia is found to have a rigid, progressive thoracolumbar kyphosis measuring 50 degrees. Lateral spine radiographs are most likely to show which associated finding at the apical vertebra?

Explanation

If infantile thoracolumbar kyphosis persists and becomes fixed, the apical vertebrae (typically L1 or L2) fail to develop normally anteriorly. This results in anterior wedging and a classic 'bullet-shaped' vertebra.

Question 78

What is the underlying pathophysiological mechanism of the genetic mutation seen in achondroplasia?

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This mutation abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis, severely affecting endochondral ossification while intramembranous ossification remains normal.

Question 79

A 6-month-old infant with achondroplasia presents with hypotonia, central sleep apnea, and poor head control. Which of the following is the most critical next step in management?

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis, which can present with central sleep apnea, hyperreflexia, or marked hypotonia. An MRI of the cervicomedullary junction is essential to evaluate for cord compression that may require urgent neurosurgical decompression.

Question 80

A 14-month-old child with achondroplasia has a prominent thoracolumbar kyphosis. Neurological examination is completely normal. What is the recommended initial management?

Explanation

Thoracolumbar kyphosis in infants with achondroplasia is highly prevalent and typically resolves once the child begins walking and developing active lumbar lordosis. Initial management involves avoiding unsupported sitting; bracing is reserved for kyphosis that persists beyond walking age or is progressive.

Question 81

Which of the following is the hallmark radiographic finding in the lumbar spine of a patient with achondroplasia?

Explanation

The classic radiographic feature of achondroplasia in the lumbar spine is the narrowing (or failure to normally widen) of the interpedicular distance from L1 to L5. Combined with short pedicles, this dramatically decreases the spinal canal volume and leads to symptomatic spinal stenosis later in life.

Question 82

An 8-year-old child with achondroplasia presents with progressive, symptomatic genu varum. Radiographs show significant mechanical axis deviation. What is the primary underlying skeletal cause of this specific deformity?

Explanation

Genu varum in achondroplasia is primarily caused by relative fibular overgrowth compared to the tibia, leading to a varus bending moment at the knee. Management often involves guided growth or corrective osteotomies depending on skeletal maturity and symptom severity.

Question 83

The genetic defect in achondroplasia primarily affects which specific zone of the growth plate?

Explanation

The FGFR3 gain-of-function mutation in achondroplasia primarily inhibits the proliferation of chondrocytes. Therefore, the proliferative zone of the physis is the most directly affected area, resulting in defective endochondral ossification and short-limb dwarfism.

Question 84

A 45-year-old male with achondroplasia presents with severe, progressive neurogenic claudication and lower extremity weakness. MRI confirms severe multi-level lumbar spinal stenosis. What is the most appropriate surgical approach?

Explanation

Spinal stenosis in achondroplasia is caused by short, thickened pedicles and severely decreased interpedicular distance. Effective decompression requires wide laminectomies often extending into the lateral recesses, which necessitates facetectomies and concomitant instrumented fusion to prevent iatrogenic instability.

Question 85

When evaluating an AP pelvis radiograph of a child with achondroplasia, which constellation of findings is most characteristic?

Explanation

The classic pelvic radiographic findings in achondroplasia include a broad 'champagne glass' pelvic inlet, squared (elephant ear) iliac wings, and horizontal acetabular roofs. The greater sciatic notch is also typically narrow and small.

Question 86

A 38-year-old healthy male and a 35-year-old healthy female have a newborn diagnosed with achondroplasia. What is the approximate recurrence risk for their future pregnancies?

Explanation

Approximately 80% of achondroplasia cases result from spontaneous de novo mutations, which are strongly associated with advanced paternal age. Since both parents are unaffected, the recurrence risk for future pregnancies is negligible (<1%), accounting only for rare instances of germline mosaicism.

Question 87

A patient with achondroplasia demonstrates a classic hand deformity. Which of the following describes the typical hand appearance in these patients?

Explanation

Achondroplasia is classically characterized by a 'trident hand' deformity. This consists of short, stubby fingers with an abnormally wide separation between the middle and ring fingers, making the patient unable to approximate those fingertips.

Question 88

A 3-year-old child presents with rhizomelic shortening, frontal bossing, and a trident hand. Genetic testing reveals a mutation in the FGFR3 gene. Which zone of the physis is primarily affected by this specific mutation?

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene, which inhibits chondrocyte proliferation in the proliferative zone of the growth plate. This leads to defective endochondral ossification.

Question 89

A 6-month-old infant with achondroplasia presents with a history of central sleep apnea, hypotonia, and brisk deep tendon reflexes. What is the most appropriate next step in management?

Explanation

Foramen magnum stenosis is a potentially fatal complication in infants with achondroplasia, presenting with central sleep apnea and myelopathy. An MRI is required to evaluate for cervicomedullary compression, which may necessitate urgent suboccipital decompression.

Question 90

A 14-month-old boy with achondroplasia has a flexible thoracolumbar kyphosis of 35 degrees. He has not yet begun walking independently. Neurological examination is normal. What is the recommended orthopedic management?

Explanation

Thoracolumbar kyphosis in infants with achondroplasia usually resolves once they begin walking and develop lumbar lordosis. Management consists of avoiding unsupported sitting; bracing is only considered if kyphosis persists or worsens after walking age.

Question 91

A 45-year-old male with achondroplasia presents with progressive neurogenic claudication and lower extremity weakness. MRI reveals severe lumbar spinal stenosis from L1 to L4. What is the most appropriate surgical intervention?

Explanation

Spinal stenosis in achondroplasia is caused by short pedicles and narrowing interpedicular distances. Multilevel wide laminectomy is the treatment of choice, taking care to preserve the pars and facets to avoid iatrogenic instability.

Question 92

Which of the following radiographic features of the pelvis is classic for a patient with achondroplasia?

Explanation

The classic pelvic radiographic findings in achondroplasia include a "champagne glass" pelvic cavity (wider than deep), squared iliac wings, and horizontal acetabular roofs. The greater sciatic notch is typically small and narrow.

Question 93

Review the AP radiograph of the lumbar spine in a patient with suspected skeletal dysplasia.

What is the characteristic finding of the lumbar pedicles in achondroplasia?

Explanation

In a normal spine, the interpedicular distance increases from L1 to L5. In achondroplasia, the classic radiographic finding is a progressive narrowing of the interpedicular distance from L1 to L5, contributing to spinal stenosis.

Question 94

A 7-year-old girl with achondroplasia presents with progressive genu varum.

What is the primary underlying mechanical cause of genu varum in patients with this condition?

Explanation

Genu varum in achondroplasia is largely driven by a length discrepancy between the tibia and fibula. The relatively longer fibula exerts a tethering and bowing effect on the tibia, leading to varus deformity.

Question 95

A 30-year-old pregnant woman with achondroplasia requires a Cesarean section. Which of the following is the most significant anesthetic consideration for her neuraxial anesthesia?

Explanation

Patients with achondroplasia have severe spinal canal stenosis and a reduced epidural space volume. Regional anesthetic doses must be significantly reduced to avoid unexpectedly high spinal blockade and associated respiratory compromise.

Question 96

A patient with achondroplasia presents to the clinic for a routine evaluation. Which of the following upper extremity abnormalities is most commonly associated with this condition?

Explanation

Upper extremity anomalies in achondroplasia characteristically include rhizomelic shortening and limited elbow extension, often lacking up to 30 degrees. Radial head dislocation is more characteristic of conditions like multiple hereditary exostoses.

Question 97

A male patient with achondroplasia marries a female of normal stature. What is the probability that their first child will inherit achondroplasia?

Explanation

Achondroplasia is inherited in an autosomal dominant pattern with essentially 100% penetrance. A heterozygous affected parent and an unaffected parent have a 50% chance of passing the mutant FGFR3 allele to each offspring.

Question 98

Two individuals with achondroplasia are expecting a child and undergo genetic counseling. What is the chance of the fetus inheriting homozygous achondroplasia, and what is its expected clinical course?

Explanation

When both parents have achondroplasia, there is a 25% risk of homozygous achondroplasia. This condition is universally lethal in the neonatal period, typically due to severe rib cage hypoplasia and subsequent respiratory failure.

Question 99

Parents of a 5-year-old boy with achondroplasia inquire about growth hormone (GH) therapy to improve his adult height. According to current literature, what is the expected outcome of GH therapy in achondroplasia?

Explanation

Growth hormone therapy in achondroplasia can initially increase growth velocity during the first few years of treatment. However, it does not correct the underlying skeletal dysplasia and has a negligible effect on final adult height.

Question 100

A new targeted pharmacological therapy, Vosoritide, has been approved for pediatric patients with achondroplasia whose epiphyses are not yet closed. What is the mechanism of action of this medication?

Explanation

Vosoritide is a C-type natriuretic peptide (CNP) analog. It binds to the natriuretic peptide receptor-B (NPR-B), activating a signaling cascade that inhibits the overactive MEK/ERK pathway caused by the FGFR3 mutation, thereby promoting endochondral bone growth.

Arab Board Orthopedic B Review | Dr Hutaif General Orth -...

Achondroplasia Orthopedic MCQs - Arab Board Exam Prep

Achondroplasia Orthopedic MCQs - Arab Board Exam Prep

Chapter Index