This practice set contains high-yield board review questions covering key concepts in 4. Pediatrics. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Question 5361
Topic: 4. Pediatrics
A newborn is diagnosed with achondroplasia. This condition is caused by an activating mutation in the FGFR3 gene. Which specific histological zone of the physis is primarily inhibited by this mutation?
Correct Answer & Explanation
. Proliferative zone
Explanation
Achondroplasia results from a gain-of-function mutation in FGFR3, which pathologically inhibits chondrocyte proliferation. This defect manifests primarily in the proliferative zone of the growth plate.
Question 5362
Topic: 4. Pediatrics
Achondroplasia, the most common form of short-limbed dwarfism, is characterized by a failure of endochondral ossification caused by a specific genetic mutation. Which of the following describes this defect?
Correct Answer & Explanation
. Gain-of-function mutation in FGFR3
Explanation
Achondroplasia is caused by an autosomal dominant, gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation continuously inhibits chondrocyte proliferation in the proliferative zone of the physis.
Question 5363
Topic: Pediatric Upper Extremity & Spine
A neonate is evaluated for bilateral radial deviation of the hands. Radiographs reveal complete absence of the radii bilaterally. However, the child has well-formed, pentadactyl hands with fully functional thumbs bilaterally. Laboratory evaluation is notable for a profoundly low platelet count. This clinical picture is pathognomonic for which of the following syndromes?
Correct Answer & Explanation
. TAR (Thrombocytopenia-Absent Radius) syndrome
Explanation
TAR (Thrombocytopenia-Absent Radius) syndrome is classically characterized by bilateral absence of the radius combined with thrombocytopenia. A pathognomonic and differentiating feature of TAR syndrome is that the thumb is uniformly present and often functional, unlike other radial longitudinal deficiencies (such as Fanconi anemia, Holt-Oram syndrome, and VACTERL association) where the thumb is typically absent or severely hypoplastic.
Question 5364
Topic: Pediatric Upper Extremity & Spine
A newborn is evaluated for a right radial clubhand and an absent thumb. To rule out the most life-threatening associated condition in this patient, which of the following screening tests must be obtained?
Correct Answer & Explanation
. Chromosomal breakage analysis with diepoxybutane (DEB)
Explanation
Radial longitudinal deficiency is associated with several syndromes, including VATER/VACTERL, Holt-Oram, TAR, and Fanconi anemia. Fanconi anemia is the most life-threatening of these due to its high risk of aplastic anemia and leukemia. It is diagnosed via chromosomal breakage testing induced by diepoxybutane (DEB) or mitomycin C. While echocardiogram and renal ultrasounds are also part of the workup for VACTERL and Holt-Oram, ruling out Fanconi anemia is paramount.
Question 5365
Topic: Pediatric Upper Extremity & Spine
A newborn is evaluated for a right radial longitudinal deficiency. Physical exam shows an absent right thumb and radius. Complete blood counts are entirely normal at birth, but the pediatrician is concerned about a condition that commonly presents with aplastic anemia later in childhood. Which of the following tests is used to definitively diagnose this genetic condition?
Correct Answer & Explanation
. Chromosomal breakage test with diepoxybutane (DEB)
Explanation
The patient is suspected of having Fanconi anemia, an autosomal recessive disorder characterized by radial ray anomalies (absent radius and thumb) and progressive bone marrow failure. The definitive diagnostic test is chromosomal breakage analysis using clastogenic agents like diepoxybutane (DEB) or mitomycin C. Normal complete blood counts at birth are common, as pancytopenia typically develops between ages 5 and 10.
Question 5366
Topic: 4. Pediatrics
A 6-month-old infant presents with a bilaterally absent thumb and radial deviation of the wrists. Radiographs reveal complete absence of the radius bilaterally. Which of the following laboratory screening tests is essential to rule out a life-threatening condition associated with this deformity?
Correct Answer & Explanation
. Chromosomal breakage test with diepoxybutane (DEB)
Explanation
Radial longitudinal deficiency is highly associated with systemic syndromes, particularly Fanconi anemia, Holt-Oram syndrome, TAR (Thrombocytopenia Absent Radius) syndrome, and VACTERL. Fanconi anemia is a fatal aplastic anemia if unrecognized and is diagnosed via the chromosomal breakage test using diepoxybutane (DEB). All patients with radial longitudinal deficiency require a DEB test, echocardiogram (Holt-Oram), and renal ultrasound (VACTERL) to rule out life-threatening anomalies.
Question 5367
Topic: Pediatric Upper Extremity & Spine
A neonate is evaluated for bilateral congenital forearm anomalies. Radiographs demonstrate bilateral absent radii, but both thumbs are present and well-formed. Which of the following diagnostic tests is the most urgent next step in the workup of this patient?
Correct Answer & Explanation
. Complete blood count
Explanation
This presentation is highly characteristic of Thrombocytopenia-Absent Radius (TAR) syndrome. A key distinguishing feature of TAR syndrome compared to Fanconi anemia and Holt-Oram syndrome is that the thumbs are present despite the absent radii. A complete blood count is crucial to evaluate for thrombocytopenia, which can be life-threatening in early infancy. Fanconi anemia (requires chromosomal breakage analysis) presents with absent radii AND absent thumbs. Holt-Oram syndrome (requires echocardiogram) involves heart defects and variable radial/thumb deficiencies.
Question 5368
Topic: 4. Pediatrics
A pediatric patient is diagnosed with achondroplasia, the most common form of short-limb dwarfism. This condition is classically caused by a specific mutation in which of the following genes?
Correct Answer & Explanation
. FGFR3 (Fibroblast growth factor receptor 3)
Explanation
Achondroplasia is an autosomal dominant disorder caused by a gain-of-function mutation in the FGFR3 gene. This mutation results in an exaggerated inhibitory effect on chondrocyte proliferation in the proliferative zone of the physis, leading to diminished longitudinal bone growth.
Question 5369
Topic: Pediatric Hip
A 12-year-old boy presents with left knee pain and a limp. Radiographs confirm a slipped capital femoral epiphysis (SCFE). Which of the following is the most widely accepted absolute indication for prophylactic in situ pinning of the contralateral, asymptomatic hip?
Correct Answer & Explanation
. Presence of an underlying endocrine or metabolic disorder
Explanation
Prophylactic pinning of the contralateral hip in SCFE is highly recommended in patients with an underlying endocrine or metabolic disorder (e.g., hypothyroidism, renal osteodystrophy) due to the extremely high risk (up to 100%) of bilateral involvement. Other indications include prophylactic treatment in patients under 10 years of age or those who cannot be reliably followed.
Question 5370
Topic: 4. Pediatrics
A 5-year-old girl sustains a displaced Gartland Type III supracondylar humerus fracture. On initial presentation, she has a pulseless but pink, well-perfused hand. She is taken to the operating room for closed reduction and percutaneous pinning. Post-operatively, her hand remains pulseless but pink and warm. What is the most appropriate next step in management?
Correct Answer & Explanation
. Observe closely with admission and serial examinations
Explanation
In pediatric supracondylar humerus fractures, the 'pulseless, pink' hand implies absent radial pulse but intact collateral capillary perfusion. Current AAOS guidelines and pediatric orthopaedic consensus recommend that if the hand remains pulseless but pink and well-perfused after anatomic closed reduction and percutaneous pinning (CRPP), the most appropriate management is close observation. Vascular exploration is primarily indicated for a 'pulseless, white' (ischemic) hand that does not improve after reduction.
Question 5371
Topic: Pediatric Hip
A 10-year-old boy presents with bilateral slipped capital femoral epiphyses (SCFE). His weight is in the 40th percentile. Which of the following endocrine disorders is most commonly associated with this presentation?
Correct Answer & Explanation
. Hypothyroidism
Explanation
Hypothyroidism is the most common endocrine disorder associated with SCFE, particularly in patients presenting outside the typical age range (under 10 or over 16) or with atypical body habitus (e.g., non-obese). Endocrine workup is highly recommended for SCFE in these patient demographics or when bilateral involvement is present at initial presentation.
Question 5372
Topic: 4. Pediatrics
A 2-year-old child presents with bilateral genu varum. Standing radiographs reveal a metaphyseal-diaphyseal angle (Drennan angle) of 20 degrees. Based on this finding, what is the most appropriate management?
Correct Answer & Explanation
. KAFO (Knee-Ankle-Foot Orthosis) bracing
Explanation
The patient has infantile Blount's disease. The metaphyseal-diaphyseal (Drennan) angle helps differentiate physiological bowing (<11 degrees) from infantile Blount's. An angle > 16 degrees suggests a very high likelihood of progression to Blount's disease. For a child under 3 years old with early Langenskiöld stages (I-II) and a high Drennan angle, bracing (KAFO) is the initial treatment of choice. Surgery is indicated if bracing fails or if the child is > 3-4 years old.
Question 5373
Topic: 4. Pediatrics
A 4-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). At the follow-up visit, the parents report that the child has stopped kicking the leg on the affected side. On examination, the infant lacks active knee extension on that side. This complication is most likely due to which of the following improper harness settings?
Correct Answer & Explanation
. Excessive flexion
Explanation
The infant has developed a femoral nerve palsy, which presents as a loss of active knee extension (decreased kicking). In the setting of Pavlik harness treatment, this is almost exclusively caused by excessive flexion of the hip (hyperflexion), which compresses the femoral nerve against the inguinal ligament. The treatment is to loosen the anterior straps or temporarily remove the harness until nerve function returns. Excessive abduction, conversely, leads to avascular necrosis of the femoral head.
Question 5374
Topic: Pediatric Upper Extremity & Spine
A 12-year-old girl with adolescent idiopathic scoliosis (AIS) presents with a right thoracic curve. Which of the following factors is the most reliable predictor of future curve progression in this patient?
Correct Answer & Explanation
. Magnitude of the curve at initial presentation
Explanation
The two most important overall predictors of curve progression in adolescent idiopathic scoliosis (AIS) are the magnitude of the curve at the time of diagnosis and the growth potential of the patient (indicated by age, menarchal status, and Risser sign). A larger curve magnitude at initial presentation correlates directly with a higher risk of relentless progression.
Question 5375
Topic: 4. Pediatrics
A child with short-limbed dwarfism, frontal bossing, and midface hypoplasia is diagnosed with the most common form of skeletal dysplasia. This condition involves a mutation in a gene that primarily affects which zone of the physis?
Correct Answer & Explanation
. Proliferative zone
Explanation
Achondroplasia is caused by an activating mutation in the FGFR3 gene. This mutation specifically inhibits chondrocyte proliferation, thereby disrupting the proliferative zone of the physis and impairing endochondral ossification.
Question 5376
Topic: 4. Pediatrics
A child presents with short-limbed dwarfism, frontal bossing, and midface hypoplasia. Genetic testing identifies a gain-of-function mutation in the FGFR3 gene. Which zone of the physis is primarily affected by this mutation?
Correct Answer & Explanation
. Proliferative zone
Explanation
Achondroplasia is caused by a gain-of-function mutation in Fibroblast Growth Factor Receptor 3 (FGFR3). FGFR3 normally inhibits chondrocyte proliferation. Overactivity severely suppresses the proliferative zone of the physis, leading to decreased endochondral bone formation.
Question 5377
Topic: Pediatric Hip
A 12-year-old obese male is diagnosed with a unilateral stable slipped capital femoral epiphysis (SCFE). In which of the following scenarios is prophylactic in situ pinning of the contralateral asymptomatic hip most strongly indicated?
Correct Answer & Explanation
. Age greater than 14 years at presentation
Explanation
Prophylactic pinning of the contralateral hip in SCFE is indicated in patients with a high risk of bilateral disease. Risk factors include endocrinopathies (e.g., hypothyroidism, renal osteodystrophy, growth hormone supplementation), prior radiation therapy, or presentation at an abnormally young age (typically under 10 years).
Question 5378
Topic: Pediatric Hip
An infant treated with a Pavlik harness for Developmental Dysplasia of the Hip (DDH) is noted to have an absent patellar reflex and decreased spontaneous extension of the knee on the affected side. This complication is most likely due to which of the following improper harness adjustments?
Correct Answer & Explanation
. Excessive flexion of the hips
Explanation
The clinical signs point to a femoral nerve palsy. In the context of a Pavlik harness, femoral nerve palsy is typically caused by hyperflexion of the hips, which acutely compresses the femoral nerve against the inguinal ligament. Excessive abduction is instead associated with an increased risk of avascular necrosis of the femoral head.
Question 5379
Topic: Pediatric Upper Extremity & Spine
In a 12-year-old female with Adolescent Idiopathic Scoliosis (AIS), which of the following combinations of clinical and radiographic parameters is associated with the highest statistical risk of curve progression?
Correct Answer & Explanation
. Risser 0, curve of 30 degrees, open triradiate cartilage
Explanation
The risk of curve progression in AIS is highest during the adolescent peak height velocity. Markers of significant remaining skeletal growth include a low Risser stage (0), open triradiate cartilage, and pre-menarchal status. A curve of 30 degrees combined with Risser 0 and an open triradiate cartilage indicates a nearly 100% risk of progression.
Question 5380
Topic: Pediatric Hip
According to the lateral pillar classification for Legg-Calvé-Perthes disease described by Herring, during which radiographic stage of the disease should the classification be applied to most accurately determine prognosis?
Correct Answer & Explanation
. Fragmentation stage
Explanation
The Herring lateral pillar classification evaluates the height of the lateral pillar of the capital femoral epiphysis (Group A >100%, Group B >50%, Group C <50%). It is most accurately assessed and most prognostic when applied during the fragmentation stage of Legg-Calvé-Perthes disease, when the full extent of the structural collapse is evident.
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