Question 1

Which of the following problems is most common in achondroplasia:

Explanation

Symptomatic stenosis of the thoracic and lumbar spine is seen in almost half of all achondroplastic patients, although not all patients require surgery. Atlantoaxial instability is rare in achondroplasia, although it is not uncommon in other dysplasias. Basilar invagination is not present in achondroplasia. Kyphosis is often transient in achondroplasia and rarely persists beyond the second year. Kyphosis is rarely symptomatic. Spondylolisthesis is rare in achondroplasia.

Question 2

A 2-year-old girl with diastrophic dysplasia is brought into the office for an overall examination. A lateral radiograph of the spine shows a kyphosis of 35° from C 3 to C 6. A neurologic exam is normal, although she does have stiff joints. The patient is not yet walking. For management of this kyphosis, recommended treatment includes:

Explanation

Many of these kyphoses will correct spontaneously if the curve does not exceed 50°. In this patient, the inability to walk is most likely due to other skeletal factors. There is no evidence that orthosis will change the natural history of the disorder. There is no need for traction given the high chance of spontaneous resolution and the dangers of traction. Posterior fusion is only indicated if the kyphosis is continually progressive, or if neurologic signs or symptoms develop. Anterior and posterior surgery is only indicated in cases with severe pre- existing neurologic deficit.

Question 3

A baby born with diastrophic dysplasia today may eventually require all of the following orthopedic procedures during childhood or adulthood except:

Explanation

Patients with diastrophic dysplasia rarely have instability of the upper cervical spine. Babies with diastrophic dysplasia often have rigid equinovarus feet that require surgery to become plantigrade and wear normal shoes. A number of patients with diastrophic dysplasia develop progressive scoliosis that requires surgical treatment. Degenerative disease of the hips is common and often requires arthroplasty in early adulthood. Degenerative disease of the knees is common and often requires arthroplasty in early adulthood.

Question 4

A patient with spondyloepiphyseal dysplasia congenita reaches the age of 5 without being able to walk with a walker. She has five beats of clonus in both ankles. Her reflexes are brisk and her toes are upgoing. The most likely problem that accounts for these conditions is:

Explanation

Atlantoaxial instability, sometimes combined with stenosis of the atlas, is a frequent cause of myelopathy in spondyloepiphyseal dysplasia congenita. Scoliosis does not account for developmental delay or myelopathy. Foramen magnum stenosis is rare in spondyloepiphyseal dysplasia congenita. Lumbar stenosis is rare with spondyloepiphyseal dysplasia congenita and would not account for myelopathy. Thoracolumbar kyphosis severe enough to cause myelopathy is rare in spondyloepiphyseal dysplasia congenita condition.

Question 5

Scoliosis in cleidocranial dysplasia is frequently associated with which of the following conditions:

Explanation

Scoliosis with cleidocranial dysplasia (C C D) is frequently associated with syringomyelia. Cervical instability is rare in C C D. Spondylolisthesis is rare in C C D. Spinal stenosis is rare in C C D. Spinal decompensation is rare in C C D.

Question 6

A 3-year-old girl with Larsen syndrome is brought into the office for examination. A spinal radiograph demonstrates a 50° kyphosis of the cervical spine. Her neurologic examination is normal. Recommended treatment includes:

Explanation

Posterior cervical fusion has been proven effective in curves of 60Â°or less, in preventing progression, and allowing correction with anterior growth. This curve is much more likely to worsen than to spontaneously improve, so preventive surgery is indicated. There is no role for halo traction in this situation. Bracing has not been proven effective in helping patients with Larsen syndrome. Addition of anterior fusion is not needed for this degree of curve in a neurologically normal child.

Question 7

A 10-year-old patient with Hurler syndrome has undergone a bone marrow transplant and is currently medically stable. He has developed a painful thoracolumbar kyphosis that measures 50° with 25% subluxation T12 on L1. Recommended treatment includes which of the following:

Explanation

Anterior and posterior fusion will correct the translation, instability, and ensure a solid fusion. Exercises will not correct the subluxation, which is the cause of the pain. A thoracolumbar orthosis is not corrective or well tolerated. There is no need for halo traction. Posterior fusion alone is not enough to control this focal instability if the patient is well enough to tolerate a more involved procedure.

Question 8

Aneurysmal bone cyst of the spine is most common in which of the following regions:

Explanation

Aneurysmal bone cyst of the spine is most common in the lumbar spine, followed by the cervical spine. Aneurysmal bone cyst of the spine is treated with embolization and/or surgical resection and reconstruction.

Question 9

Aneurysmal bone cyst of the spine is most likely in this age group:

Explanation

The most common age is the second decade; the mean age is 13 years old.

Question 10

A 14-year-old girl is examined because of a pain in her left flank. The radiographs of the lumbar spine show loss of the pedicle with expansion of the lateral wall of the third lumbar vertebral body. Magnetic resonance imaging shows multiple fluid levels in the vertebral body with no additional areas of involvement. She is neurologically normal. The least invasive, effective treatment is which?

Explanation

This patient has an aneurysmal bone cyst of the vertebra. Selective arterial embolization is a minimally invasive treatment that often succeeds in arresting the lesions. Many times it is the only treatment needed. Selective arterial embolization can also be used as part of a strategy to be followed by curettage and reconstruction to decrease operative bleeding. This lesion will continue to expand and might cause neurologic compromise or mechanical instability. Radiation therapy poses risks of later malignant degeneration. There are other ways of treating this lesion. Radical en bloc resection may unnecessarily injure neurologic structures. While curettage is often necessary, there is no reason to introduce the risk of radiation therapy.

Question 11

A 15-year-old girl has severe hip pain 3 years after a slipped capital femoral epiphysis that was complicated by avascular necrosis. Recommended treatment is a hip arthrodesis. In response to questions about late effects, after surgery the patient should be told that she is most likely to experience:

Explanation

Low back pain, followed closely by ipsilateral knee pain, is the most common late effect of hip arthrodesis in young patients. The tolerable pain usually occurs much later but may be treated by conversion to arthroplasty, if needed. Ipsilateral hip pain should be minimal or absent if the fusion is successful. Activity following arthrodesis is not significantly limited. Sports and heavy physical activities are feasible. The limp is usually minimal because the loss of hip motion is masked by lumbar motion. Pain in the contralateral hip is rare and is often minimal after hip arthrodesis.

Question 12

Which of the following is an appropriate position for arthrodesis of the hip in a young person:

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 5Â° is not needed. Arthrodesis often produces some shortening; therefore, intentional shortening is not needed.

Question 13

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:

Explanation

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

Question 14

A 9-year-old boy with cerebral palsy has trouble sitting. His mother states that whenever his diapers are changed or his hips are moved, he begins to cry. Radiographs demonstrate high dislocations of both femoral heads. The femoral heads have an ovoid shape and superolateral flattening. Recommended treatment is:

Explanation

Bilateral proximal femoral resection is the recommended treatment. Femoral head dislocations may become painful in cerebral palsy at a much earlier age than in nonspastic individuals. Botulinum toxin or adductor tenotomy will not solve the problem. Replacing the deformed femoral heads into the acetabulum will not achieve the long-term goal of good hip range of motion.

Question 15

A 9-year-old boy is examined due to a closed distal forearm fracture. The radius and ulna are both fractured and translated 100%. After manipulation twice with sedation, the translation cannot be reduced. There is 10-mm shortening of the radius and 5- mm shortening of the ulna. The distal radial angulation on the anteroposterior view is 5Â° less than normal. The least invasive treatment which would produce acceptable results is:

Explanation

The translation and shortening are not problems and the amount of angulation will easily remodel with this fracture. There is nothing to be gained from operative reduction.

Question 16

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

Explanation

This patient should be treated like an adult. Eight inch-pounds is the currently recommended torque to provide optimal biomechanical fixation while minimizing pin penetration.

Question 17

A posterior spine fusion with segmental hook fixation from T4-L4 is performed for idiopathic scoliosis in a 15-year-old girl. Somatosensory evoked potential monitoring is normal throughout the procedure. The patient awakens and is unable to move either lower extremity, but she does have some sensation in the lower extremities. Recommended treatment includes:

Explanation

Spinal cord injury occurs in approximately 1% of patients operated upon for idiopathic scoliosis. In some cases, sensory spinal cord monitoring may be unchanged, especially if the injury preserves the dorsal columns. The instrumentation should be removed as soon as possible in case spinal traction or derotation or implant protrusion is producing effects on the cord or its blood supply. Corticosteroids should be administered at spinal cord injury doses, but this should not be the only measure. Obtaining a myelogram may delay the removal of instrumentation and should not be the first step. Heparinization has no proven effect.

Question 18

A 12-year-old boy with achondroplasia has a gradual 40Â° thoracolumbar kyphosis. He is unable to walk more than two blocks. Magnetic resonance imaging reveals spinal stenosis, and the patient is scheduled to undergo posterior decompression from T12- S1. In addition to this procedure, you recommend:

Explanation

Extensive posterior decompression poses a high risk of postoperative increase in kyphosis because of both the patientâ s age and pre-existing kyphosis. Observation would not be a good idea because the risk is already known to be high. Neither a brace nor an uninstrumented fusion would prevent the deformity from developing. Corpectomy is not indicated because the kyphosis is not focal. Posterior instrumented fusion at the time of decompression is indicated.

Question 19

Which of the following is true regarding brace treatment for Scheuermann kyphosis:

Explanation

Brace treatment is effective for Scheuermann kyphosis. Unlike idiopathic scoliosis, permanent improvement of the deformity is the goal. The Milwaukee brace is often indicated. Brace treatment is ineffective for curves over 74°. The brace should be worn until skeletal maturity.

Question 20

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

Explanation

Bone marrow transplantation is effective in minimizing 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 21

A 7-year-old boy is brought in for an examination due to back pain. He has limited forward bending. Neurologic examination is normal. Radiographs reveal a uniform flattening of the third lumbar vertebra to 10% of its normal height. His temperature is 37.1° C and his white blood count is 11,000. The erythrocyte sedimentation rate is 18. The most likely diagnosis is:

Explanation

Eosinophilic granuloma often produces complete flattening of a single vertebral body in the absence of trauma or neurologic deficit. Osteogenesis imperfecta produces a more uniform flattening of the vertebrae but not by this degree. Tuberculosis rarely produces this much flattening of a single vertebra. The erythrocyte sedimentation rate is elevated in this condition. Bacterial infection rarely produces this much flattening of a single vertebral body without associated disk changes. The lab studies should suggest an inflammatory process. C ompression fracture produces less complete flattening of the vertebral bodies.

Question 22

A 12-year-old patient with osteogenic sarcoma metastatic to the spine is noted to have new onset of weakness of both lower extremities. Magnetic resonance imaging shows a mass expanding posteriorly and encroaching on the spinal cord. The recommended initial step is:

Explanation

Radiation therapy combined with steroids should be tried first to try to halt progression of the tumor. Unfortunately, the prognosis for this child is extremely poor. Increasing the dose of chemotherapy is not likely to work because the metastasis has already progressed despite initial treatment. Surgical resection must be tried if radiation does not produce improvement. Steroids are an adjunct to treatment but not sufficient alone. The patient is likely to have progressive paraparesis and loss of bowel function. In order to improve the quality of life remaining, surgical resection should be offered to the patient.

Question 23

The primary purpose of osteotomy in the closure of classic exstrophy of the bladder is to:

Explanation

The primary purpose of osteotomy is to improve the chance of a successful urologic reconstruction. This is achieved by decreasing the tension on the closure of the abdominal wall and bladder. The strain on the sacroiliac joints has not been measured with or without closure; this is not a primary purpose of the osteotomy. There is no conclusive evidence that the hips are at increased risk of degenerative disease in patients with exstrophy, or that osteotomy will alter the condition. In patients with exstrophy, the gait progressively normalizes over time. It is not possible to reconstruct a normal symphysis pubis in exstrophy.

Question 24

Which of the following is not a common finding in cloacal exstrophy:

Explanation

Hydrocephalus is rare because most patients have lipomeningocele, not myelomeningocele. Omphalocele is common in cloacal exstrophy. Most patients with cloacal exstrophy have a lipomeningocele that is a form of spinal dysrhaphism. Many patients have malformations of the sacroiliac joints. Approximately 25% of patients have dislocations of at least one hip.

Question 25

The thickness of a flexible intramedullary nail used in pediatric femur fractures should be which of the following percentages of the diameter of the femoral isthmus:

Explanation

It is recommended that the intramedullary nail be 40% of the diameter of the femoral isthmus.

Question 26

An infant is born with fibular hemimelia and has 20% shortening of the involved below-knee segment. Four rays are present on the foot, and the ankle is in slight valgus. Limb lengthening is likely to be superior to Syme disarticulation in which of the following parameters:

Explanation

The cost of prosthetics is greater in the disarticulation group. Pain is greater in the lengthened group. Function is equal to or better in the group who had disarticulation. Psychological acceptance is greater in the disarticulation group. The lengthened group requires more than twice the number of procedures.

Question 27

Which of the following is the best discriminator for risk of nonaccidental (child abuse) injury in young children with femoral shaft fractures:

Explanation

Nonaccidental injury was a factor in 29% of patients who were unable to walk vs 3% for patients who were able to walk. The fracture pattern and level of fracture do not help determine nonaccidental injury. Socioeconomic class is not the best discriminator and, generally, should not be factored into the decision process. Coexisting disability is not a significant discriminator.

Question 28

A 12-year-old boy with hemophilia A has a painless mass in his thigh. The femur is eroded anterolaterally and there is a large overlying soft tissue mass. Magnetic resonance imaging shows a 5 cm x 7 cm mass arising from the bone. The most likely diagnosis is:

Explanation

A pseudotumor is a hemophilic subperiosteal hematoma. The pseudotumor expands by repeated bleeds and increasing osmotic pressure. There was no periosteal reaction or intralesional calcification. The bone wall itself is not expanded as in aneurysmal bone cyst. There is nothing in the physical examination or patient history to point to infection.

Question 29

In classic hemophilia, a natural factor-VIII level of less than what percentage will lead to severe bleeding and complications:

Explanation

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

Question 30

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:

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 31

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

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 32

Which of the following statements is true regarding scoliosis in cerebral palsy (C P):

Explanation

Curves greater than 50° usually progress. Scoliosis is most common in totally involved C P patients. Scoliosis is rare in patients with hemiplegia. Braces rarely halt curves in CP. Surgery has no proven effect on prolonging life expectancy. The complication rate is higher in CP.

Question 33

A 12-year-old girl is referred because of a positive school scoliosis screen. She has a curve of 16° from T5 to T12, convex to the right. She incidentally also complains of mild back pain over the region of the curve several times per month. Neurologic examination is normal. Recommended treatment includes:

Explanation

Home exercises and re-examination in follow-up is the most appropriate treatment in view of lack of any worrisome features. If this child had severe pain or significant night pain, then further imaging studies would be warranted. The magnetic resonance imaging is not indicated in this situation. The bone scan has a low likelihood of being positive. Bracing is not indicated for the curve or the pain. Computer tomography is unlikely to demonstrate any pathology.

Question 34

A 10-year-old boy undergoes biopsy of a spinal cord tumor through a laminectomy of C7-T2. The most likely complication of this procedure is:

Explanation

The removal of posterior restraints in the young and growing flexible spine usually leads to cervicothoracic kyphosis.

Question 35

A patient with neurofibromatosis and a 55° scoliosis may be treated with a posterior fusion and instrumentation alone in which of the following situations:

Explanation

He has a kyphosis of 35°. This degree of kyphosis increases the risk of pseudarthrosis with posterior fusion alone. The laminectomy increases the risk of pseudarthrosis. Anterior fusion should be added when there is a history of pseudarthrosis. A 9-year-old boy has a high risk of crankshift phenomenon with posterior fusion alone.

Question 36

Which of the following statements is true regarding school screening for scoliosis:

Explanation

All children should be screened at age 11. The AAOS still recommends school screening for scoliosis. The AAOS recognizes that yearly screening is counterproductive. Screening at age 9 is too early.. Screening at age 16 is too late.

Question 37

Treatment of a patient with lumbar level myelomeningocele who has a vertical talus should consist of:

Explanation

Open reduction of the vertical talus will most likely prevent problems. With observation only, the patient is likely to stand or walk and develop pressure problems. Talectomy will not produce the most usable foot. Achilles tenotomy will not produce significant correction by itself. Triple arthrodesis will concentrate stress and lead to ulcers.

Question 38

What percentage of the human genome represents the actual genes:

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 39

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:

Explanation

Autosomal recessive conditions classically show â horizontalâ 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 onefourth 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 40

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

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 41

Morquio syndrome is caused by a deficiency in:

Explanation

Morquio syndrome is a member of the family of mucopolysaccharidoses. Morquio syndrome is a deficiency in the enzyme galactose-6-sulfatase. A deficiency in galactose-6-sulfatase results in increased urinary excretion of keratosulfate. Alpha-L-iduronidase is deficient in Hurler syndrome. Beta-glucuronidase is deficient in some rare mucopolysaccharidoses. Fibroblast growth factor receptor protein is deficient in achondroplasia. Sulfate transport protein is deficient in diastrophic dysplasia.

Question 42

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

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 43

Pleiotropy is demonstrated by which of the following examples:

Explanation

The term pleiotropy refers to a disease taking different shapes in various patients. Variation in the severity of a given problem is better termed "variable expressivity." Target joints are not genetically determined. Hurler syndrome usually not being present in prior generations of an affected patient is an example of autosomal recessive inheritance. The term pleiotropy refers to a disease taking different shapes in different subjects, whereas the cause of patients with Ollier disease having more involvement on one side of the body is unknown.

Question 44

Which of the following is the most common concern regarding anesthesia for a patient with juvenile rheumatoid arthritis:

Explanation

Stiffness and mandibular hypoplasia are fairly common in juvenile rheumatoid arthritis (JRA) due to inflammation of the temporomandibular joint that affects the growth plates of the mandibles. Basilar invagination is rare in JRA. Rotatory subluxation of C 1-C 2 is rare in JRA. Subaxial subluxation is rare in JRA. Cervical stenosis is not a clinical problem in JRA.

Question 45

A 4-year-old boy is brought to a clinic because he has been fussy, febrile, and unable to bend over for the past 4 days. In the office, his temperature is 38.2Â° C and his neurologic examination is normal. His lumbar lordosis is flattened and he resists flexion or extension. He has normal range of hip motion. Plain films of the lumbar spine are normal. The next imaging study should be:

Explanation

Magnetic resonance imaging should be the next step to rule out pyogenic spondylitis. Ultrasound has not been proven effective in evaluation of anterior spinal pathology. Computed tomograms do not have a greater sensitivity than plain films in early diagnosis of infection. An indium labeled scan may yield diagnostic information but would not be the preferred test because of the time needed and inability to provide other diagnostic information. Hip arthrogram would not be the next step because the hip range of motion is normal. Even if hip pathology were suspected, the next step would be a plain film and an ultrasound.

Question 46

A 6-year-old child suffers a displaced fracture of the distal humerus in the supracondylar region. The surgeon decides to reduce and pin the fracture. Which of the following risks increases if the procedure is delayed more than 8 hours?

Explanation

A retrospective comparison study has shown no increase of risks in delayed treatment of supracondylar fractures as long as the neurovascular examination is within normal limits.

Question 47

Which of the following statements is true regarding the growth plates around the ankle:

Explanation

The distal tibia grows more than the distal fibula. The anterolateral portion of the tibial physis ceases growing last, thus explaining the phenomenon of the Tillaux fracture. The physis of the distal fibula is always located more distally than the distal tibia. The two physes are not conjoined.

Question 48

Which of the following is the most common final attribution of back pain in children and adolescents after all appropriate diagnostic studies are performed:

Explanation

The majority of children and adolescents do not have an identifiable cause of back pain after all appropriate tests are performed. Many times the diagnosis is "musculo-ligamentous strain." the most common identified cause is spondylolysis.

Question 49

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

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 50

The most common region of the spine affected by tuberculosis is:

Explanation

The lower thoracic-upper lumbar spine is most commonly affected by tuberculosis. Multiple vertebrae are often involved in tuberculosis spondylitis.

Question 51

A 5-year-old boy presents with short stature, a short trunk, and a barrel chest. Radiographs show delayed ossification of the epiphyses and a hypoplastic odontoid. What is the genetic mutation associated with this condition?

Explanation

Spondyloepiphyseal dysplasia congenita (SEDC) is caused by a mutation in the COL2A1 gene. It is characterized by short-trunk dwarfism, coxa vara, and atlantoaxial instability due to odontoid hypoplasia.

Question 52

A 9-year-old boy presents with bilateral knee pain and a waddling gait. Radiographs show a "double-layer" patella. Which of the following genes is most commonly mutated in this condition?

Explanation

A double-layer patella is a classic radiographic sign of multiple epiphyseal dysplasia (MED). The most common mutation in MED is in the COMP gene (Cartilage Oligomeric Matrix Protein).

Question 53

A 6-year-old child with normal intelligence presents with short stature, corneal clouding, and severe genu valgum. Radiographs reveal atlantoaxial instability and platyspondyly with central anterior beaking of the vertebral bodies. What accumulated substance is expected in the urine?

Explanation

Morquio syndrome (MPS IV) is characterized by the accumulation of keratan sulfate. Orthopedic manifestations include severe genu valgum, odontoid hypoplasia, and platyspondyly with central anterior beaking.

Question 54

A 14-year-old female presents with broad shoulders and the ability to appose her shoulders in the midline anteriorly. She has delayed closure of her cranial sutures. Which orthopedic condition is she at highest risk of developing?

Explanation

Cleidocranial dysplasia is caused by a RUNX2 (CBFA1) mutation. Patients classically have hypoplastic or absent clavicles and are at high risk for developing progressive coxa vara.

Question 55

A 1-year-old child with multiple cafe-au-lait spots is noted to have isolated anterolateral bowing of the tibia. What is the recommended initial management to prevent fracture and progression to pseudarthrosis?

Explanation

Anterolateral bowing of the tibia is associated with Neurofibromatosis Type 1 and often progresses to congenital pseudarthrosis of the tibia (CPT). A total contact orthosis is initially used to brace the limb and delay or prevent fracture.

Question 56

A patient with osteogenesis imperfecta type I is undergoing intramedullary rodding of the femur. Which of the following anesthetic considerations is uniquely crucial for this patient population?

Explanation

Patients with OI, especially severe types, frequently have basilar invagination and cervical instability. Extreme care must be taken during neck extension for intubation to avoid spinal cord compression.

Question 57

An infant with achondroplasia presents with sleep apnea, hypotonia, and hyperreflexia. An MRI reveals stenosis of the foramen magnum. Which of the following mechanisms best explains this pathophysiology?

Explanation

Achondroplasia is caused by an FGFR3 mutation that inhibits endochondral ossification. The cranial base forms via endochondral ossification, leading to premature synchondrosis closure and foramen magnum stenosis.

Question 58

A newborn presents with bilateral knee dislocations, hip dislocations, and bilateral clubfeet. Physical examination reveals a depressed nasal bridge, prominent forehead, and spatulate thumbs. What spine abnormality is most critically associated with this condition?

Explanation

Larsen syndrome (FLNB mutation) is characterized by multiple large joint dislocations and classic facial features. Cervical kyphosis is the most critical spinal abnormality and can lead to severe myelopathy if not stabilized.

Question 59

A 9-year-old girl presents with precocious puberty, irregular hyperpigmented macules, and a limp. Radiographs of her femur reveal a ground-glass appearance and a "shepherd's crook" deformity. Which of the following best describes the underlying genetic defect?

Explanation

The patient has McCune-Albright syndrome, defined by polyostotic fibrous dysplasia, coast of Maine cafe-au-lait spots, and endocrine abnormalities. It is caused by a somatic activating mutation in the GNAS1 gene.

Question 60

A 6-year-old child presents with a short, webbed neck and a low posterior hairline. Radiographs show multiple fused cervical vertebrae. Which of the following organ systems must be evaluated as a priority in this patient?

Explanation

Klippel-Feil syndrome is associated with renal anomalies in up to 30% of patients, including unilateral renal agenesis. Renal ultrasonography is a critical part of the initial screening protocol.

Question 61

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?

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 62

A 4-year-old boy presents with recurrent, painful soft tissue swellings on his back that eventually turn into hard masses. He has a history of congenital bilateral hallux valgus and shortened great toes. What is the most appropriate management?

Explanation

This clinical picture describes Fibrodysplasia Ossificans Progressiva (FOP), caused by an ACVR1 mutation. Any trauma, including biopsy or surgery, will trigger explosive heterotopic ossification, making avoidance of trauma paramount.

Question 63

A 10-year-old Jewish boy presents with right hip pain. Radiographs show an Erlenmeyer flask deformity of the distal femurs and avascular necrosis of the right femoral head. A defect in which of the following enzymes is responsible?

Explanation

Gaucher disease is a lysosomal storage disorder caused by a deficiency in glucocerebrosidase. Classic orthopedic manifestations include the Erlenmeyer flask deformity of the distal femur, bone pain crises, and avascular necrosis of the femoral head.

Question 64

A 4-year-old child presents with short-limb dwarfism and a waddling gait. Unlike typical achondroplasia, this child has a completely normal facial appearance and head circumference. Radiographs show small, irregular epiphyses and metaphyseal flaring. What gene is mutated?

Explanation

Pseudoachondroplasia is caused by mutations in the COMP gene. Unlike achondroplasia, patients with pseudoachondroplasia have a normal facies and normal intelligence, along with severe epiphyseal and metaphyseal dysplasia.

Question 65

A newborn presents with short ribs, short stature, and postaxial polydactyly of the hands. An echocardiogram reveals a single atrium. What is the most likely diagnosis?

Explanation

Ellis-van Creveld syndrome is a chondroectodermal dysplasia characterized by short-limb dwarfism, postaxial polydactyly, dysplastic nails, and congenital heart defects (most commonly an atrial septal defect or single atrium).

Question 66

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?

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 67

A 3-year-old child presents with coarse facial features, severe mental retardation, corneal clouding, and hepatosplenomegaly. Radiographs reveal thick, spatula-like ribs and hypoplastic vertebral bodies with inferior beaking. Which enzyme is deficient?

Explanation

Hurler syndrome (MPS I) is caused by a deficiency in alpha-L-iduronidase. Radiographically, it demonstrates dysostosis multiplex, including inferior vertebral beaking, contrasting with Morquio syndrome's central beaking.

Question 68

An asymptomatic 25-year-old man undergoes pelvic radiographs after a minor fall. The x-rays show numerous small, well-defined circular radiodensities clustered around the pelvic joints and proximal femurs. A mutation in the LEMD3 gene is suspected. What is the most appropriate management?

Explanation

Osteopoikilosis ("spotted bone disease") is an asymptomatic, benign bone dysplasia caused by LEMD3 mutations. It requires no treatment and is typically found incidentally on radiographs.

Question 69

A child with diastrophic dysplasia presents with a classic "hitchhiker thumb" deformity. This deformity is primarily caused by which of the following anatomic abnormalities?

Explanation

The "hitchhiker thumb" in diastrophic dysplasia is caused by a severely shortened, oval-shaped first metacarpal and radial subluxation at the trapeziometacarpal joint. It is a hallmark of this sulfate transporter defect.

Question 70

A 1-year-old infant with achondroplasia exhibits a 40-degree thoracolumbar kyphosis when sitting. Neurological examination is normal. What is the most appropriate initial management for this spinal deformity?

Explanation

Thoracolumbar kyphosis in infantile achondroplasia is common and largely resolves when the child begins walking and develops lumbar lordosis. The primary initial management is to avoid unsupported sitting to prevent progression into a fixed structural deformity.

Question 71

A 6-year-old boy presents with disproportionate short-limb dwarfism and a waddling gait. His facial features are entirely normal. Radiographs reveal delayed, fragmented epiphyseal ossification and anterior tongue-like projections of the vertebral bodies. Which of the following genes or proteins is most likely mutated in this patient?

Explanation

The clinical presentation is characteristic of pseudoachondroplasia, which features short-limb dwarfism but normal facies, differentiating it from achondroplasia. It is caused by mutations in the COMP gene, leading to accumulation of mutant protein in the rough endoplasmic reticulum of chondrocytes.

Question 72

A 4-year-old child presents with a widened cranial vault, frontal bossing, and delayed closure of the fontanelles. On examination, he is able to bring his shoulders together anteriorly without discomfort. Which of the following orthopedic conditions is most frequently associated with this syndrome?

Explanation

This patient has cleidocranial dysplasia, an autosomal dominant condition caused by a RUNX2 (CBFA1) mutation resulting in clavicular hypoplasia. Coxa vara is the most common and significant orthopedic manifestation, occurring in up to one-third of these patients.

Question 73

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?

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 74

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:

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 75

A 5-year-old child with normal intelligence presents with short trunk dwarfism, severe genu valgum, and a barrel chest. Radiographs reveal severe platyspondyly with anterior central beaking of the vertebrae and marked hypoplasia of the odontoid. What enzyme is most likely deficient in this patient?

Explanation

The patient has Morquio syndrome (Mucopolysaccharidosis Type IV), characterized by normal intelligence, severe skeletal dysplasia, and potentially lethal atlantoaxial instability due to odontoid hypoplasia. It is caused by a deficiency in N-acetylgalactosamine-6-sulfatase (Type IVA) or beta-galactosidase (Type IVB).

Question 76

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?

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 77

A 4-year-old boy with disproportionate short-trunk dwarfism is evaluated in the clinic. He has a history of a cleft palate and severe myopia. Radiographs reveal delayed ossification of the pubic bones, severe coxa vara, and platyspondyly. This condition is caused by a mutation affecting which of the following?

Explanation

Spondyloepiphyseal dysplasia congenita (SEDC) is characterized by short-trunk dwarfism, coxa vara, cleft palate, and visual impairments like myopia or retinal detachment. It is an autosomal dominant disorder caused by a mutation in the COL2A1 gene, affecting Type II collagen.

Question 78

A 7-year-old girl presents with precocious puberty and a large cafe-au-lait macule with an irregular "coast of Maine" border. Radiographs of her proximal femur show a lytic, expansile, "ground-glass" lesion with a shepherd's crook deformity. What is the underlying genetic mechanism of this disease?

Explanation

McCune-Albright syndrome consists of polyostotic fibrous dysplasia, precocious puberty, and cafe-au-lait spots. It is caused by a somatic activating mutation in the GNAS1 gene, leading to overproduction of cAMP.

Question 79

A 6-year-old boy has an enlarged right lower extremity compared to the left. Examination reveals a lateral port-wine stain and extensive superficial varicose veins. If his projected leg length discrepancy at skeletal maturity is 3 cm, what is the most appropriate initial orthopedic management?

Explanation

This patient has Klippel-Trenaunay syndrome, characterized by the triad of a capillary malformation (port-wine stain), venous malformations, and soft tissue/bony hypertrophy. A predicted limb length discrepancy of 2 to 5 cm at maturity is best treated with a timed contralateral epiphysiodesis.

Question 80

A newborn infant presents with asymmetric limb shortening, bilateral cataracts, and ichthyosis. Radiographs reveal multiple stippled, punctate calcifications in the unossified epiphyses of the long bones. This clinical and radiographic presentation is most characteristic of:

Explanation

Chondrodysplasia punctata (such as the Conradi-Hunermann X-linked dominant type) is characterized by "stippled epiphyses" on radiographs in infancy. Associated clinical findings typically include asymmetric limb shortening, cataracts, and skin changes like ichthyosis.

Question 81

A 4-year-old boy presents with a painless, hard mass on the medial aspect of his right knee, causing a progressive asymmetric valgus deformity. Radiographs show an irregular, ossified mass arising from the medial half of the distal femoral epiphysis. What is the most likely diagnosis?

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is an osteochondroma-like overgrowth of an epiphysis, typically affecting one side (usually medial) of a joint, most commonly the knee or ankle. It leads to asymmetric joint deformity and restricted range of motion.

Question 82

A 10-year-old boy with a history of multiple fractures, blue sclerae, and dentinogenesis imperfecta presents with progressive weakness in his upper extremities, hyperreflexia, and gait instability. What is the most likely cause of his new neurologic symptoms?

Explanation

Patients with Osteogenesis Imperfecta (OI) have softened cranial bones that can lead to basilar invagination (settling of the skull onto the cervical spine). This can compress the brainstem and upper cervical cord, causing upper motor neuron signs, weakness, and cranial nerve deficits.

Question 83

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?

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 84

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?

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 85

A 3-year-old boy presents with painful soft tissue swellings on his back and neck. Physical exam reveals bilateral short great toes with marked hallux valgus. Radiographs show early heterotopic ossification in the paraspinal muscles. What is the most appropriate next step in management?

Explanation

Fibrodysplasia ossificans progressiva (FOP) features short great toes and progressive heterotopic ossification of skeletal muscles. Trauma or surgery (including biopsy or excision) severely exacerbates the ossification; therefore, the diagnosis should be confirmed non-invasively via genetic testing for the ACVR1 mutation.

Question 86

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?

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 87

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?

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 88

A 14-year-old boy with end-stage renal disease complains of generalized, severe bone pain. Radiographs of the spine show dense bands of sclerosis at the superior and inferior endplates of the vertebral bodies, producing a "rugger jersey" appearance. What laboratory profile is most consistent with his condition?

Explanation

Renal osteodystrophy is driven by secondary hyperparathyroidism due to renal failure. Failing kidneys cannot excrete phosphate or produce sufficient 1,25-dihydroxyvitamin D, leading to hyperphosphatemia, hypocalcemia, and a compensatory marked elevation in parathyroid hormone (PTH).

Question 89

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:

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.

Question 90

A 5-year-old boy presents with disproportionate short stature, a waddling gait, and joint laxity. His facial features are entirely normal, and his intelligence is intact. Radiographs reveal delayed epiphyseal ossification and metaphyseal irregularities. What is the most likely genetic mutation responsible for this condition?

Explanation

Pseudoachondroplasia is an autosomal dominant skeletal dysplasia caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene. Unlike achondroplasia, patients have a normal craniofacial appearance and normal intelligence.

Question 91

A 6-year-old child with a known skeletal dysplasia presents with neck pain and mild myelopathic symptoms. He is noted to have a short trunk, barrel chest, and severe myopia. Hand and foot radiographs show normal bone length and morphology. Which of the following is the most likely diagnosis?

Explanation

Spondyloepiphyseal dysplasia congenita is a type II collagen disorder (COL2A1) characterized by short-trunk dwarfism, normal hands and feet, and a high risk of myopia and retinal detachment. Cervical spine instability (atlantoaxial) is a critical complication requiring careful monitoring.

Question 92

A 12-year-old girl is diagnosed with Multiple Epiphyseal Dysplasia (MED). She complains of knee pain and a waddling gait. Which of the following radiographic findings is uniquely characteristic of this condition?

Explanation

A double-layered, or fragmented, patella observed on a lateral knee radiograph is a classic finding in Multiple Epiphyseal Dysplasia (MED). MED is caused by mutations in genes such as COMP, MATN3, and type IX collagen.

Question 93

An infant is born with a distinctly narrowed, bell-shaped thorax, shortened limbs, and polydactyly. The neonatologist notes severe respiratory distress requiring intubation shortly after birth. Pelvic radiographs show a "trident" appearance of the acetabular roof. What is the most likely diagnosis?

Explanation

Jeune syndrome (asphyxiating thoracic dystrophy) presents with a narrow, bell-shaped thorax leading to severe respiratory distress, shortened limbs, and occasionally polydactyly. Radiographs characteristically show a "trident" acetabulum with spurs on the sciatic notch.

Question 94

A 4-year-old boy with Morquio syndrome (Mucopolysaccharidosis Type IV) presents for orthopedic evaluation. Which of the following spinal abnormalities is the most critical and potentially life-threatening complication associated with this disorder?

Explanation

Morquio syndrome is frequently associated with profound odontoid hypoplasia and ligamentous laxity, leading to severe atlantoaxial instability. This represents the most critical orthopedic complication, often requiring early cervical fusion to prevent lethal myelopathy.

Question 95

A 9-year-old boy presents with unusually wide cranial sutures, delayed closure of the fontanelles, and the ability to bring his shoulders together in the midline anteriorly. Which of the following best describes the underlying pathophysiology of his condition?

Explanation

The clinical picture describes Cleidocranial Dysplasia, which is caused by a mutation in the RUNX2 (CBFA1) gene. This gene is critical for osteoblast differentiation, leading primarily to defective intramembranous ossification of the clavicles, cranium, and pelvis.

Question 96

In a newborn diagnosed with achondroplasia, what is the most common cause of mortality during the first year of life?

Explanation

The most common cause of mortality in infants with achondroplasia is sudden death due to central apnea, resulting from cervicomedullary compression at a stenotic foramen magnum. Early screening with MRI or CT of the craniocervical junction is essential.

Question 97

A 10-year-old girl with neurofibromatosis type 1 (NF1) presents with a severe scoliotic curve. Radiographs demonstrate a sharp, short-segmented structural kyphoscoliosis in the thoracic spine with marked vertebral wedging and "penciling" of the ribs. What is the most appropriate management?

Explanation

Dystrophic scoliosis in NF1 is characterized by short, sharp curves, vertebral wedging, and a high risk of pseudoarthrosis and curve progression. Given the aggressive nature and high failure rate of single-approach procedures, combined anterior and posterior spinal fusion is the treatment of choice.

Question 98

A neonate presents with multiple fractures, blue sclerae, and profound osteopenia on radiographs. Genetic testing confirms Osteogenesis Imperfecta (OI) type II. Which of the following mutations is typically responsible for this specific, lethal form of OI?

Explanation

Osteogenesis Imperfecta Type II is typically caused by a qualitative defect (often a missense mutation causing a glycine substitution) in the COL1A1 or COL1A2 genes, resulting in structurally abnormal collagen and early perinatal lethality. In contrast, the milder Type I OI typically results from a quantitative decrease (null mutation).

Question 99

A 6-month-old infant is evaluated for failure to thrive, hepatosplenomegaly, and cranial nerve palsies. Radiographs show a generalized, uniform increase in bone density with a "bone-within-a-bone" appearance in the spine. What is the primary cellular defect responsible for this condition?

Explanation

The patient has malignant infantile osteopetrosis, a condition characterized by osteoclast failure (often due to carbonic anhydrase II or TCIRG1 mutations). The inability to resorb bone leads to excessively dense but brittle bones, marrow obliteration, and secondary hepatosplenomegaly from extramedullary hematopoiesis.

Orthopedic Prometric Exam Preparation MCQs - Part 1

Orthopedic Prometric Exam Preparation MCQs - Part 17

Orthopedic Prometric Exam Preparation MCQs - Part 17

Chapter Index