Orthopedic Board Review: Skeletal Dysplasias MCQs

Question 1

A 12-year-old boy presents with bilateral shoulder hypermobility, allowing him to touch his shoulders in the midline. Radiographs reveal partial absence of the clavicles and multiple wormian bones in the skull. Which gene mutation is most likely responsible for this condition?

Explanation

Correct Answer: B

The clinical presentation is classic for Cleidocranial Dysplasia (CCD). CCD is caused by a mutation in the RUNX2 gene (also known as CBFA1), which is essential for osteoblast differentiation and intramembranous ossification. Key features include hypoplastic or absent clavicles, delayed closure of cranial sutures, wormian bones, and dental abnormalities (supernumerary teeth).

Question 2

In a patient diagnosed with Nail-Patella Syndrome (Hereditary Osteo-onychodysplasia), which of the following extra-skeletal manifestations is most critical to monitor due to its impact on long-term survival?

Explanation

Correct Answer: C

Nail-Patella Syndrome is characterized by the tetrad of nail hypoplasia, patellar hypoplasia/aplasia, iliac horns, and elbow dysplasia. However, up to 40% of patients develop nephropathy (proteinuria and hematuria), which can progress to end-stage renal disease. Monitoring renal function is vital for these patients.

Question 3

A 7-year-old girl presents with short stature and a 'hitchhiker thumb' deformity. Radiographs show a first metacarpal that is short and proximally placed. What is the primary defect in this skeletal dysplasia?

Explanation

Correct Answer: B

Diastrophic Dysplasia is caused by a mutation in the SLC26A2 gene, which encodes a sulfate transporter protein. This leads to undersulfation of proteoglycans in the cartilage matrix. Characteristic features include short-limbed dwarfism, 'hitchhiker thumbs' (due to a shortened first metacarpal), cauliflower ears, and severe clubfeet.

Question 4

Which radiographic finding is considered pathognomonic for Nail-Patella Syndrome, even in the absence of clinical symptoms at that site?

Explanation

Correct Answer: B

Bilateral iliac horns (Fong's sign) are posterior processes of the ilium and are considered pathognomonic for Nail-Patella Syndrome. They are present in approximately 80% of cases and are rarely found in any other condition.

Question 5

A patient with Pseudoachondroplasia presents with significant genu varum. Unlike Achondroplasia, which of the following clinical features is typically ABSENT in Pseudoachondroplasia?

Explanation

Correct Answer: C

Pseudoachondroplasia is caused by mutations in the COMP gene. While it shares short stature with Achondroplasia, patients with Pseudoachondroplasia have a normal craniofacial appearance (no frontal bossing or midface hypoplasia). They also exhibit significant joint laxity and severe epiphyseal/metaphyseal changes leading to early arthritis.

Question 6

A 5-year-old child is evaluated for asymmetric swelling and restricted motion of the medial aspect of the ankle. Radiographs show an osteochondromatous overgrowth arising from the medial epiphysis of the talus. What is the most likely diagnosis?

Explanation

Correct Answer: C

Dysplasia Epiphysealis Hemimelica (Trevor's disease) is a rare developmental disorder characterized by asymmetric osteochondromatous overgrowth of one or more epiphyses. It most commonly affects the lower limb (distal femur, proximal tibia, or talus) and is usually confined to one side of the joint (medial more common than lateral).

Question 7

In Spondyloepiphyseal Dysplasia Congenita (SEDC), what is the most critical preoperative assessment required before any surgical intervention involving general anesthesia?

Explanation

Correct Answer: C

Patients with SEDC (Type II collagenopathy) frequently have odontoid hypoplasia, leading to atlantoaxial instability (C1-C2). This poses a significant risk of spinal cord injury during intubation. Preoperative cervical spine clearance with dynamic films is mandatory.

Question 8

A patient presents with short stature, sparse hair, and a bulbous 'pear-shaped' nose. Radiographs of the hands show cone-shaped epiphyses of the middle phalanges. This constellation of findings is most consistent with:

Explanation

Correct Answer: A

Langer-Giedion Syndrome (Trichorhinophalangeal Syndrome Type II) is characterized by the triad of sparse hair, a bulbous nose, and multiple exostoses. Radiographically, cone-shaped epiphyses of the phalanges are a hallmark finding.

Question 9

Kniest Dysplasia is characterized by a 'Swiss cheese' appearance of the cartilage on histology. Which clinical finding is frequently associated with this condition and requires early screening?

Explanation

Correct Answer: A

Kniest Dysplasia is a type II collagenopathy. Along with 'dumbbell-shaped' long bones and coronal clefts in vertebrae, patients are at high risk for ophthalmologic issues, specifically severe myopia and a high incidence of retinal detachment, as well as hearing loss.

Question 10

A 4-year-old child presents with a waddling gait. Radiographs show delayed ossification of the femoral heads with a fragmented appearance, but the acetabulum is normal and the child is otherwise healthy and of normal height. What is the most likely diagnosis?

Explanation

Correct Answer: C

Meyer's Dysplasia (dysplasia of the femoral capital epiphysis) is a benign variant of epiphyseal development. It often mimics Legg-Calvé-Perthes disease but occurs in younger children (2-4 years), is often bilateral, and typically resolves spontaneously without the significant collapse or deformity seen in Perthes.

Question 11

A 12-year-old boy presents with delayed eruption of permanent teeth and the ability to approximate his shoulders anteriorly. Radiographs reveal bilateral absence of the clavicles and patent cranial sutures. Which gene mutation is most likely responsible for this condition?

Explanation

Correct Answer: B

The clinical presentation describes Cleidocranial Dysplasia (CCD). This condition is characterized by hypoplasia or aplasia of the clavicles, delayed closure of cranial sutures (fontanelles), and multiple supernumerary teeth. It is caused by a mutation in the RUNX2 (also known as CBFA1) gene on chromosome 6, which is essential for osteoblast differentiation and intramembranous ossification.

Question 12

In Nail-Patella Syndrome (Hereditary Osteo-onychodysplasia), which of the following radiographic findings is considered pathognomonic?

Explanation

Correct Answer: B

Nail-Patella Syndrome is characterized by the clinical triad of nail hypoplasia, patellar hypoplasia/aplasia, and iliac horns (Fong's sign). Iliac horns are bilateral, symmetrical bony outgrowths from the posterior surface of the iliac wings and are considered pathognomonic for this condition, which is linked to the LMX1B gene mutation.

Question 13

A 25-year-old male presents with chronic pain and stiffness in his right lower extremity. Radiographs show linear, dense cortical thickening along the medial aspect of the femur and tibia, resembling 'dripping candle wax.' This condition typically follows which distribution pattern?

Explanation

Correct Answer: C

The description of 'dripping candle wax' on radiographs is classic for Melorheostosis. This rare non-hereditary sclerosing bone dysplasia typically follows a sclerotomal distribution (the area of bone supplied by a single spinal sensory nerve). It often presents with pain, joint contractures, and limb deformity.

Question 14

A patient is incidentally found to have multiple small, well-defined, circular radiopaque spots (3-10 mm) clustered in the periarticular regions of the pelvis and long bones. The patient is asymptomatic. What is the most appropriate next step in management?

Explanation

Correct Answer: C

The radiographic findings are characteristic of Osteopoikilosis ('spotted bone disease'). This is a benign, autosomal dominant condition that is usually asymptomatic. The bone scan in osteopoikilosis is typically normal, which helps differentiate it from osteoblastic metastases or Paget's disease. No treatment is required.

Question 15

Camurati-Engelmann Disease (Progressive Diaphyseal Dysplasia) is characterized by which of the following clinical and radiographic features?

Explanation

Correct Answer: B

Camurati-Engelmann Disease is a rare autosomal dominant condition caused by a mutation in the TGFB1 gene. It presents with symmetric, progressive cortical thickening of the diaphyses of long bones (femur, tibia, humerus). Patients often present with limb pain, a waddling gait, and muscle weakness.

Question 16

A 14-year-old girl presents with a 'Shepherd's crook' deformity of the proximal femur and a 'ground-glass' appearance on radiographs. Genetic testing reveals a somatic mutation in the GNAS gene. Which of the following is the most likely diagnosis?

Explanation

Correct Answer: B

Fibrous dysplasia is caused by a somatic mutation in the GNAS gene, leading to the replacement of normal bone with fibrous tissue and immature trabecular bone (ground-glass appearance). The 'Shepherd's crook' deformity is a classic varus deformity of the proximal femur seen in polyostotic fibrous dysplasia.

Question 17

In patients with Multiple Hereditary Exostoses (MHE), what is the estimated lifetime risk of malignant transformation of an osteochondroma into a secondary chondrosarcoma?

Explanation

Correct Answer: B

While solitary osteochondromas have a less than 1% risk of malignant transformation, patients with Multiple Hereditary Exostoses (MHE) have a higher risk, generally cited between 1% and 5%. A sudden increase in size or the onset of pain in a previously stable lesion after skeletal maturity should raise suspicion.

Question 18

A 7-year-old child presents with asymmetric overgrowth of the medial aspect of the distal femoral epiphysis. The lesion appears as an osteocartilaginous mass arising from the epiphysis. What is the most likely diagnosis?

Explanation

Correct Answer: B

Trevor's Disease, or Dysplasia Epiphysealis Hemimelica (DEH), is a rare developmental disorder characterized by asymmetric overgrowth of one or more epiphyses. It most commonly affects the lower limb (talus, distal femur, or proximal tibia) and is usually confined to one side of the joint (medial more common than lateral).

Question 19

Which of the following conditions is characterized by the association of multiple enchondromas and soft tissue hemangiomas?

Explanation

Correct Answer: C

Maffucci Syndrome is characterized by multiple enchondromas and soft tissue cavernous hemangiomas (often containing phleboliths). It carries a significantly higher risk of malignant transformation (chondrosarcoma and visceral malignancies) compared to Ollier disease (which features enchondromas without hemangiomas).

Question 20

A 10-year-old girl presents with precocious puberty, large 'cafe-au-lait' spots with irregular 'coast of Maine' borders, and polyostotic fibrous dysplasia. What is the underlying pathophysiology?

Explanation

Correct Answer: B

The triad of polyostotic fibrous dysplasia, cafe-au-lait spots, and hyperfunctioning endocrinopathies (like precocious puberty) defines McCune-Albright Syndrome. It is caused by a post-zygotic somatic mutation in the GNAS1 gene, which leads to constitutive activation of the Gs-alpha protein, stimulating adenylate cyclase and increasing intracellular cAMP.

Question 21

A 14-year-old girl presents with bilateral wrist pain and restricted range of motion. Radiographs demonstrate a V-shaped proximal carpal row, dorsal prominence of the distal ulna, and excessive volar and ulnar tilt of the distal radius. A mutation in which of the following genes is most strongly associated with this isolated skeletal dysplasia?

Explanation

The patient has Madelung deformity, which is characterized by premature closure of the volar-ulnar distal radial physis. It is strongly associated with mutations in the SHOX gene, especially in the context of Léri-Weill dyschondrosteosis or Turner syndrome.

Question 22

A 5-year-old boy presents with left shoulder asymmetry. Physical examination reveals an elevated and hypoplastic left scapula with restricted shoulder abduction. If an omovertebral bone is identified on radiographs, which of the following associated regional anomalies must be most carefully evaluated?

Explanation

This patient has Sprengel deformity, a congenital failure of scapular descent. It is highly associated with Klippel-Feil syndrome, characterized by congenital fusion of the cervical vertebrae.

Question 23

A newborn is evaluated for a right lower extremity deformity. Examination reveals a shortened right leg, anteromedial bowing of the tibia, skin dimpling over the anterior crest, and a foot with three toes in marked equinovalgus. What is the most likely diagnosis?

Explanation

Fibular hemimelia is the most common congenital long bone deficiency and classically presents with anteromedial tibial bowing, absent lateral rays (toes), and an equinovalgus foot. Tibial hemimelia typically presents with a varus foot and preaxial polydactyly.

Question 24

In a patient diagnosed with Proximal Focal Femoral Deficiency (PFFD), which of the following clinical factors is the most critical determinant when deciding between a reconstructive limb-lengthening program versus an early amputation with rotationplasty?

Explanation

The predicted limb length discrepancy (LLD) at skeletal maturity dictates surgical management in PFFD. A predicted LLD greater than 20 cm typically necessitates amputation or rotationplasty, whereas discrepancies less than 20 cm may be amenable to staged lengthening procedures.

Question 25

A 3-year-old girl presents with a painless, palpable midshaft mass over her left clavicle. Radiographs reveal a complete defect with smooth, rounded, and sclerotic bone ends. If surgical intervention is deferred, what systemic or organic condition MUST be ruled out given the laterality of this lesion?

Explanation

Congenital pseudarthrosis of the clavicle almost exclusively occurs on the right side due to normal subclavian artery pulsation affecting embryonic development. If it occurs on the left side, dextrocardia or situs inversus must be investigated.

Question 26

A newborn has bilateral radially deviated hands and shortened forearms. Radiographs show bilateral absent radii. On physical examination, the thumbs are present and morphologically normal. Which underlying hematologic abnormality is most closely associated with this specific presentation?

Explanation

Thrombocytopenia Absent Radius (TAR) syndrome is distinguished from other radial longitudinal deficiencies (like Fanconi anemia) by the presence of a normal thumb. It is associated with severe, often transient, thrombocytopenia in infancy.

Question 27

A 30-year-old man complains of progressively worsening deep bone pain and joint contractures in his right leg. Radiographs display dense, eccentric, undulating cortical hyperostosis along the femur and tibia, classically described as resembling "flowing candle wax." Which gene mutation is primarily associated with this sporadic localized dysplasia?

Explanation

Melorheostosis is a rare, sporadic sclerosing bone dysplasia characterized by "dripping candle wax" hyperostosis, typically affecting a single limb. It is most commonly driven by somatic mutations in the MAP2K1 gene or loss-of-function in the LEMD3 gene.

Question 28

A newborn exhibits a significantly shortened left lower leg. Clinical examination shows a rigid varus foot deformity and duplication of the great toe. Radiographs demonstrate a completely absent tibia but an intact, relatively normally developed fibula. What is the most common genetic inheritance pattern for the familial form of this deficiency?

Explanation

Congenital tibial hemimelia often presents with a varus foot and preaxial polydactyly (duplication of the great toe). While many cases are sporadic, familial forms are typically inherited in an autosomal dominant pattern, frequently linked to the GLI3 gene or the ZRS enhancer of SHH.

Question 29

A 4-year-old boy is brought in for a unilateral chest wall asymmetry and a right hand deformity. Examination reveals absence of the sternocostal head of the right pectoralis major muscle and ipsilateral short, webbed fingers (symbrachydactyly). What is the most likely diagnosis?

Explanation

Poland syndrome is classically characterized by the unilateral absence of the sternocostal head of the pectoralis major muscle and ipsilateral hand anomalies, most commonly symbrachydactyly. It is thought to result from a transient interruption of the embryonic subclavian artery.

Question 30

An 8-month-old infant is referred for a noticeable anterolateral bow of the distal tibia. Radiographs demonstrate focal diaphyseal sclerosis and cortical thickening at the apex of the curve without an obvious fracture. To prevent the most dreaded complication associated with this deformity, what is the best initial management strategy?

Explanation

Anterolateral bowing of the tibia is highly associated with Neurofibromatosis type 1 and frequently progresses to congenital pseudarthrosis of the tibia if a fracture occurs. Prophylactic total contact bracing is the initial standard of care to protect the bone from fracturing.

Question 31

A neonate is born with a posteromedial bow of the left tibia and a severe calcaneovalgus positioning of the left foot. The parents are highly anxious about the child's future mobility. What represents the natural history of this specific condition?

Explanation

Unlike anterolateral bowing, posteromedial bowing of the tibia does not progress to pseudarthrosis and the angular deformity typically resolves spontaneously with growth. However, the affected limb will reliably demonstrate a limb-length discrepancy (usually 3-4 cm) at skeletal maturity.

Question 32

A 6-year-old girl is evaluated for a disproportionately large index and middle finger on her right hand. MRI reveals extensive fibroadipose tissue proliferation infiltrating the median nerve territory, accompanied by osseous enlargement. What somatic mutation is most commonly implicated in this localized gigantism?

Explanation

Macrodystrophia lipomatosa is a form of localized gigantism characterized by fibrofatty overgrowth, classically restricted to the territory of a major nerve (median or plantar). It is a part of the PIK3CA-related overgrowth spectrum (PROS) caused by somatic mosaic PIK3CA mutations.

Question 33

A 10-year-old boy presents with marked hypertrophy of his left leg compared to his right. Examination reveals a large, lateral cutaneous capillary malformation (port-wine stain) extending from the hip to the foot, along with prominent superficial varicosities. Which of the following is the most likely diagnosis?

Explanation

Klippel-Trenaunay syndrome is clinically diagnosed by the triad of a capillary malformation (port-wine stain), venous malformations (varicosities), and soft-tissue or bony hypertrophy of an extremity. Unlike Parkes Weber syndrome, it lacks clinically significant high-flow arteriovenous fistulas.

Question 34

A 4-year-old boy demonstrates a painless, bilateral inability to supinate his forearms. Radiographs reveal an osseous connection between the proximal radius and ulna. This congenital anomaly is a result of a failure of longitudinal segmentation during which period of embryonic development?

Explanation

Congenital radioulnar synostosis results from a failure of longitudinal segmentation of the common cartilaginous precursor of the radius and ulna. This embryological differentiation normally occurs between the 5th and 8th weeks of gestation.

Question 35

A 6-year-old boy is evaluated for painless, limited forearm rotation. Radiographs demonstrate an isolated posterior dislocation of the radial head. Which of the following radiographic features most strongly supports a congenital rather than a traumatic etiology?

Explanation

Congenital dislocation of the radial head is typically posterior and characterized by adaptive changes from a lack of normal articulation. These include a domed or convex radial head, a hypoplastic or flattened capitellum, and bowing of the ulna.

Question 36

A 5-year-old boy presents with a hard, painless swelling on the medial aspect of his right ankle and a progressive varus deformity. Radiographs show an irregular, multicentric radiopaque mass arising as an asymmetric overgrowth from the medial epiphysis of the distal tibia. What is the most likely diagnosis?

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is a rare developmental disorder characterized by an osteochondroma-like asymmetric overgrowth of the epiphysis. It most commonly affects the medial side of the ankle or knee in young boys.

Question 37

A newborn presents with a severe upper extremity anomaly featuring no thumb, seven triphalangeal digits, two ulnas, and an absent radius. This mirror-hand deformity (ulnar dimelia) is primarily caused by abnormal embryological signaling from which of the following?

Explanation

Ulnar dimelia (mirror hand) results from a duplication of the Zone of Polarizing Activity (ZPA). The ZPA expresses Sonic Hedgehog (SHH) protein, which is responsible for the radioulnar (anterior-posterior) patterning of the developing limb.

Question 38

A 4-year-old boy presents with painless, localized swelling on the medial aspect of his ankle. Radiographs reveal an asymmetric, irregular ossification mass arising from the medial half of the distal tibial epiphysis. What is the most likely diagnosis?

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is an osteochondroma-like overgrowth of an epiphysis. It is typically unilateral, primarily involves the medial half of the lower extremity joints, and causes localized deformity.

Question 39

A 13-year-old girl is evaluated for mesomelic short stature and a bilateral wrist deformity characterized by dorsal bowing of the distal radius and limited forearm rotation. Which gene mutation is responsible for this condition?

Explanation

Leri-Weill dyschondrosteosis is caused by a pseudoautosomal SHOX gene mutation. It classically presents with mesomelic dwarfism and Madelung deformity of the wrists.

Question 40

A 35-year-old male presents with chronic, aching pain and stiffness in his left lower extremity. Radiographs reveal a dense, irregular, eccentric cortical hyperostosis extending linearly along the femoral diaphysis. What is the genetic basis of this disorder?

Explanation

Melorheostosis is a sclerosing bone dysplasia presenting with a "dripping candle wax" appearance on radiographs, typically affecting a single limb. It is associated with somatic mutations in MAP2K1 or germline mutations in LEMD3.

Question 41

A 15-year-old female presents with an aching pain in her right thigh. Radiographs demonstrate a radiolucent, ground-glass expansile lesion in the proximal femur resulting in a shepherd's crook deformity. If café-au-lait spots with irregular borders are also present, which endocrine abnormality must be screened for?

Explanation

Monostotic or polyostotic fibrous dysplasia combined with café-au-lait spots and endocrine dysfunction defines McCune-Albright syndrome. The most common endocrine manifestation is precocious puberty, driven by an activating somatic mutation in GNAS.

Question 42

A 6-year-old girl is brought in because her left shoulder sits higher than her right, with limited glenohumeral abduction. A palpable bony bridge connects the cervical spine to the scapula. This deformity results from a failure of which developmental process?

Explanation

Sprengel deformity results from a failure of the scapula to descend from its embryonic cervical position to the thorax between the 9th and 12th weeks of gestation. An omovertebral bone tethers the cervical spine to the scapula in approximately 30% of cases.

Question 43

A 2-year-old boy presents with unilateral tibia vara. Radiographs reveal a well-defined radiolucency with surrounding cortical sclerosis in the medial cortex of the proximal tibial metaphysis. What is the most appropriate next step in management?

Explanation

Focal fibrocartilaginous dysplasia is a benign condition characterized by a radiolucent lesion in the medial tibial cortex causing unilateral bowleg. The vast majority of cases resolve spontaneously with observation as the child grows.

Question 44

In idiopathic Madelung deformity, premature fusion of the volar-ulnar aspect of the distal radial physis occurs due to mechanical tethering. Which anomalous structure is responsible for this tether?

Explanation

Madelung deformity is characterized by an abnormal volar tether known as Vickers ligament. This structure is a thickened, dysplastic short radiolunate ligament that bridges the radius and lunate, restricting the growth of the volar-ulnar distal radius.

Question 45

A 5-year-old boy presents with isolated, disproportionate overgrowth of the 2nd and 3rd toes of his left foot, accompanied by thick plantar soft tissue. Which nerve territory is classically involved and hypertrophied in this specific pedal presentation?

Explanation

Macrodactyly in the foot is a localized overgrowth condition that most frequently involves the medial plantar nerve territory, affecting the 1st through 3rd digits. The condition is often linked to somatic activating mutations in the PIK3CA gene.

Question 46

A patient with delayed cranial suture closure and bilateral clavicular hypoplasia is diagnosed with a RUNX2 gene mutation. Which of the following is the most common orthopedic complication in this condition that may require surgical correction?

Explanation

Cleidocranial dysplasia involves defective intramembranous ossification but also has enchondral defects, particularly in the pelvis. Coxa vara is a frequent, progressive complication that often requires surgical correction via a valgus-producing proximal femoral osteotomy.

Question 47

A 14-year-old female diagnosed with an LMX1B mutation presents with knee pain. Radiographs demonstrate absent patellae and posterior iliac horns. Which joint anomaly is also classically expected in this patient?

Explanation

Nail-patella syndrome classically presents with hypoplastic nails, absent or small patellae, pathognomonic iliac horns, and elbow abnormalities. The elbow issues typically include radial head subluxation, capitellar hypoplasia, and prominent medial epicondyles.

Question 48

An 8-year-old boy presents with a short neck, low posterior hairline, and restricted cervical motion. Cervical radiographs confirm congenital fusion of C3-C4. What is the most critical screening evaluation to perform upon initial diagnosis?

Explanation

Klippel-Feil syndrome is defined by congenital fusion of cervical vertebrae and is heavily associated with significant visceral anomalies. Genitourinary tract abnormalities occur in up to 30% of patients, making a screening renal ultrasound mandatory.

Question 49

A newborn is evaluated for severe posteromedial bowing of the left tibia and a calcaneovalgus foot deformity. What is the expected natural history of the lower limb deformity if managed conservatively?

Explanation

Congenital posteromedial bowing of the tibia generally demonstrates spontaneous improvement of the angular deformity over time. However, it typically results in a residual limb length discrepancy of 3 to 7 cm at skeletal maturity, distinguishing its benign course from anterolateral bowing.

Question 50

A newborn is evaluated for bilateral absent thumbs and severe radial longitudinal deficiency. Which genetic condition should be suspected, and what specific systemic screening is indicated?

Explanation

Holt-Oram syndrome (TBX5 mutation) is characterized by upper limb anomalies, notably absent or hypoplastic thumbs, along with congenital heart defects like atrial septal defects. The absence of thumbs clearly distinguishes it from TAR syndrome, where the thumbs are classically present.

Question 51

A newborn infant presents with a "mirror hand" deformity characterized by duplication of the ulna, an absent radius, and seven fingers. What developmental signaling center is duplicated to cause this condition?

Explanation

Ulnar dimelia is a rare congenital anomaly resulting from duplication of the Zone of Polarizing Activity (ZPA). The ZPA secretes Sonic hedgehog (SHH) protein, which directs the anterior-posterior (radioulnar) axis formation of the developing limb.

Question 52

A 5-year-old boy presents with an asymmetric, painless swelling on the medial side of his ankle. Imaging shows an asymmetric cartilaginous overgrowth originating from the medial distal tibial epiphysis. Which of the following best describes the typical histological appearance of this lesion?

Explanation

Trevor disease (dysplasia epiphysealis hemimelica) is characterized by an osteochondroma-like overgrowth of a portion of the epiphysis, typically on the medial side of the lower extremity. Histologically, it is virtually indistinguishable from a classic osteochondroma.

Question 53

A 13-year-old girl presents with bilateral wrist deformities and mesomelic short stature. Radiographs demonstrate volar and ulnar bowing of the distal radius with a prominent dorsal distal ulna. A mutation in which of the following genes is predominantly associated with this presentation?

Explanation

Leri-Weill dyschondrosteosis is characterized by a Madelung deformity and mesomelic short stature. It is caused by a haploinsufficiency mutation or deletion in the SHOX gene, located on the pseudoautosomal region of the sex chromosomes.

Question 54

A 30-year-old man presents with chronic, deep, aching pain in his right thigh and stiffness in his knee. Radiographs reveal an irregular, linear area of cortical thickening running along the medial aspect of the femur, resembling flowing wax. Which gene mutation is classically implicated in the sporadic pathogenesis of this condition?

Explanation

Melorheostosis presents with a flowing, "dripping candle wax" appearance on radiographs, usually confined to a single sclerotome. It is classically associated with loss-of-function mutations in the LEMD3 gene (also called MAN1).

Question 55

A newborn infant is noted to have a painless, mobile swelling over the middle third of the right collarbone. There is no history of birth trauma. Radiographs show a distinct gap in the mid-clavicle with smooth, rounded bone ends. What is the most appropriate initial management for this condition?

Explanation

Congenital pseudarthrosis of the clavicle is almost exclusively right-sided and presents with smooth, rounded bone ends without callus formation. Management is initially observational; if the patient develops symptoms or significant deformity, excision, bone grafting, and fixation are typically performed around 3 to 5 years of age.

Question 56

A 6-year-old boy is brought in for cosmetic evaluation of a right-sided chest wall asymmetry and ipsilateral short, webbed fingers. Examination reveals absence of the sternocostal head of the pectoralis major muscle. Which of the following upper extremity anomalies is most frequently associated with this patient's syndrome?

Explanation

Poland syndrome classically presents with unilateral hypoplasia or complete absence of the sternocostal head of the pectoralis major. The most commonly associated upper limb anomaly is ipsilateral symbrachydactyly (short, webbed fingers).

Question 57

A 4-year-old boy presents with anterior bowing of the left tibia. Radiographs reveal an expansile, osteolytic lesion confined to the anterior cortex of the tibial diaphysis with sclerotic margins. Immunohistochemical staining of a biopsy from this lesion is most likely to be positive for which of the following markers, helping distinguish it from fibrous dysplasia?

Explanation

Osteofibrous dysplasia occurs almost exclusively in the tibia and fibula, often presenting with anterior bowing. Unlike fibrous dysplasia, the spindle cells in osteofibrous dysplasia consistently stain positive for cytokeratin.

Question 58

A 4-year-old girl is evaluated for neck asymmetry and limited shoulder abduction. Examination reveals a highly positioned, hypoplastic left scapula. During surgical correction via the Woodward procedure, which structure is typically excised to facilitate inferior mobilization of the scapula?

Explanation

Sprengel deformity is a congenital failure of scapular descent, often tethered by an omovertebral connection. The Woodward procedure involves excising the omovertebral bone or fibrous band and relocating the muscular origins to move the scapula inferiorly.

Question 59

A neonate presents with severe bilateral foreshortening of the forearms and clubhands. Clinical examination reveals the absolute absence of the thumbs bilaterally. Echocardiography shows an atrial septal defect. Which of the following is the most likely genetic mutation associated with this presentation?

Explanation

Holt-Oram syndrome is characterized by radial longitudinal deficiency with absent or hypoplastic thumbs and congenital heart defects, primarily atrial septal defects. It is caused by an autosomal dominant mutation in the TBX5 gene.

Question 60

A 2-week-old infant is diagnosed with bilateral radial agenesis. Unlike many other syndromes with radial deficiencies, the infant has perfectly normal thumbs on both hands. Blood work reveals severe thrombocytopenia. Which of the following best describes the inheritance pattern and implicated gene for this condition?

Explanation

Thrombocytopenia-absent radius (TAR) syndrome is unique among radial deficiencies because the thumb is remarkably preserved. It is inherited in an autosomal recessive manner and is caused by mutations in the RBM8A gene.

Question 61

A 3-year-old child presents with disproportionate enlargement of the right index and middle fingers. The overgrowth involves both soft tissue and bone, and the fingers exhibit palmar deviation. The overgrowth in this condition is most classically distributed along the territory of which of the following structures?

Explanation

Macrodystrophia lipomatosa is a rare, localized form of congenital gigantism characterized by fibrofatty overgrowth that follows the distribution of a specific nerve. In the upper extremity, it most commonly follows the territory of the median nerve.

Question 62

A 14-year-old boy presents with a painless limp. Pelvic radiographs display a well-defined, radiolucent lesion with a ground-glass appearance in the proximal femur, causing a shepherd's crook varus deformity. A somatic activating mutation in which of the following genes is responsible for this lesion?

Explanation

Fibrous dysplasia is caused by a sporadic, somatic activating mutation in the GNAS gene. This leads to increased intracellular cAMP, causing abnormal proliferation and differentiation of osteoblasts.

Question 63

A 2-year-old boy presents with an established pseudarthrosis of the middle and distal thirds of the tibia. There is prominent anterolateral bowing, and he has multiple café-au-lait spots. Which of the following surgical techniques is most associated with obtaining union and preventing refracture in this challenging condition?

Explanation

Congenital pseudarthrosis of the tibia (often associated with NF1) has a notoriously high failure rate. Contemporary surgical management aims for complete resection of the hamartomatous tissue, stabilization with intramedullary rodding, and creation of a tibiofibular cross-union to maximize mechanical stability.

Question 64

A 5-year-old boy presents with a painless, progressively enlarging swelling on the medial aspect of his right ankle. Radiographs demonstrate an asymmetric, irregular mass of ossifying cartilage arising from the medial epiphysis of the distal tibia. What is the most likely diagnosis?

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is a rare developmental disorder characterized by an asymmetrical, osteochondroma-like overgrowth of cartilage in an epiphysis, most commonly affecting the medial side of the ankle or knee.

Question 65

A 4-year-old child presents with disproportionate overgrowth of the index and middle fingers. Imaging shows massive enlargement of the fibrofatty tissue and phalanges strictly localized within the distribution of the median nerve. What is the primary underlying genetic etiology?

Explanation

Macrodystrophia lipomatosa is a localized form of congenital gigantism associated with somatic mosaic mutations in the PIK3CA gene. It typically causes fibrofatty overgrowth along a specific nerve territory, most often the median nerve.

Question 66

A 35-year-old presents with chronic pain and stiffness in the right lower extremity. Radiographs show dense, undulating cortical hyperostosis resembling "flowing candle wax" along the medial cortex of the femur and tibia. Which somatic mutation is classically linked to this sporadic condition?

Explanation

Sporadic melorheostosis is characterized by "flowing candle wax" hyperostosis strictly involving a single limb or sclerotome. Recent evidence shows it is primarily driven by somatic mutations in the MAP2K1 gene.

Question 67

A newborn male is noted to have a hypoplastic right hand with symbrachydactyly. On examination, there is an absent anterior axillary fold on the ipsilateral side. What is the most widely accepted vascular etiology for this congenital anomaly?

Explanation

Poland syndrome presents with unilateral chest wall hypoplasia (absence of the sternocostal head of the pectoralis major) and ipsilateral hand anomalies. It is theorized to result from a disruption or hypoplasia of the embryonic subclavian artery.

Question 68

A 3-year-old girl has congenital absence of the right thumb and a hypoplastic radius. An echocardiogram reveals an atrial septal defect. Which gene mutation is responsible for this autosomal dominant condition?

Explanation

Holt-Oram syndrome (cardio-melic syndrome) is caused by mutations in the TBX5 gene. It classically presents with radial ray anomalies and congenital heart defects, most commonly an atrial septal defect (ASD).

Question 69

A neonate is evaluated for bilateral absence of the radius, but uniquely, both thumbs are fully formed and present. Laboratory analysis reveals profound thrombocytopenia. Which genetic anomaly is characteristic of this syndrome?

Explanation

Thrombocytopenia-Absent Radius (TAR) syndrome is distinct from other radial deficiencies because the thumb is classically preserved. It is associated with a microdeletion on chromosome 1q21.1 affecting the RBM8A gene.

Question 70

A 5-year-old child with severe Sprengel deformity is scheduled for a Woodward procedure to improve shoulder abduction and cosmesis. Which structures are typically detached from the spinous processes and translated inferiorly during this surgery?

Explanation

The Woodward procedure for Sprengel deformity involves detaching the origins of the trapezius, rhomboids, and levator scapulae from the spinous processes. This allows the muscular sheet and the attached scapula to be translated inferiorly.

Question 71

A 10-year-old boy presents with a short neck, low posterior hairline, and severely limited cervical motion. Radiographs confirm multiple fused cervical vertebrae. Which of the following evaluations is most critical in the initial workup of this patient to rule out a common associated anomaly?

Explanation

Klippel-Feil syndrome is associated with various visceral anomalies. Renal anomalies, such as unilateral renal agenesis, occur in approximately 30% of patients, making a baseline renal ultrasound essential.

Question 72

A 14-year-old female presents with bilateral wrist pain and a "fork-like" deformity. Radiographs show a shortened radius, volar bowing, and dorsal subluxation of the distal ulna. She is noted to have disproportionate mesomelic short stature. What is the genetic basis of this condition?

Explanation

Léri-Weill dyschondrosteosis is characterized by mesomelic dwarfism and Madelung deformity of the wrists. It is caused by a pseudoautosomal dominant haploinsufficiency of the SHOX gene.

Question 73

A 2-year-old child presents with unilateral tibia vara. Radiographs reveal a sharply demarcated, radiolucent defect in the medial cortex of the proximal metaphysis of the tibia with surrounding sclerosis. What is the recommended initial management for this specific lesion?

Explanation

Focal fibrocartilaginous dysplasia (FFCD) is a benign condition of the proximal medial tibia that mimics early Blount's disease. Most cases resolve spontaneously with observation as the child grows.

Question 74

A 4-year-old boy presents with an asymmetric, painless swelling on the medial aspect of his left ankle. Radiographs reveal irregular ossification centers arising from the medial epiphysis of the distal tibia, resembling an intra-articular osteochondroma. What is the most likely diagnosis?

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is a localized developmental abnormality characterized by asymmetric osteochondral overgrowth of an epiphysis. It most commonly affects the medial side of the lower extremity joints, particularly the ankle or knee.

Question 75

A 5-year-old girl presents with disproportionate overgrowth of her right index and middle fingers. Histological examination reveals extensive fibrofatty infiltration along the digital nerve sheaths. Which of the following genetic mutations is primarily implicated in this localized dysplasia?

Explanation

Macrodystrophia lipomatosa is a rare, localized congenital gigantism typically following a specific nerve territory, most commonly the median nerve. It is associated with somatic mosaic mutations in the PIK3CA gene, leading to excessive fibrofatty overgrowth.

Question 76

A 14-year-old girl presents with bilateral wrist pain and restricted motion. Radiographs show pronounced volar and ulnar curvature of the distal radius with dorsal subluxation of the distal ulna. If this is part of a syndromic condition, which gene is most likely mutated?

Explanation

Madelung deformity is caused by premature closure of the volar-ulnar distal radial physis. When bilateral and associated with mesomelic short stature, it is characteristic of Léri-Weill dyschondrosteosis, which is caused by a mutation in the SHOX gene.

Question 77

A 6-year-old boy is evaluated for a high-riding left scapula and restricted shoulder abduction. Imaging confirms a fibrous connection between the superior angle of the scapula and the cervical spine. During surgical correction via the Woodward procedure, which muscle origin is detached and moved inferiorly?

Explanation

In the Woodward procedure for Sprengel deformity, the origins of the trapezius and rhomboid muscles are detached from the spinous processes. The scapula is then mobilized inferiorly, and the muscles are reattached at a more caudal level.

Question 78

A 35-year-old man complains of chronic dull aching pain and stiffness in his right thigh and knee. Radiographs reveal undulating cortical hyperostosis extending along the femur, resembling dripping candle wax. This disorder is classically associated with loss-of-function mutations in which gene?

Explanation

Melorheostosis is characterized by irregular, sclerotic bone formation following a sclerotomal distribution, giving a 'dripping candle wax' appearance. It is classically linked to somatic or germline mutations in the LEMD3 gene (also known as MAN1).

Question 79

An infant is diagnosed with unilateral fibular hemimelia. Which of the following associated clinical findings is most likely to be present in the affected limb?

Explanation

Fibular hemimelia is the most common congenital long bone deficiency and is typically associated with anteromedial tibial bowing, absent lateral (postaxial) rays, and a ball-and-socket ankle joint. Anterolateral bowing is instead characteristic of congenital pseudarthrosis of the tibia.

Question 80

A 3-year-old child is brought to the clinic due to an inability to supinate the right forearm. Radiographs reveal bony continuity between the proximal radius and ulna. At what stage of embryonic development does the failure of longitudinal segmentation occur to cause this localized anomaly?

Explanation

Congenital radioulnar synostosis results from a failure of longitudinal segmentation of the common cartilaginous precursor of the radius and ulna. This failure typically occurs during the 5th to 8th week of embryonic gestation.

Question 81

A 2-year-old child presents with an anterolateral bowing of the left tibia that recently fractured. Radiographs show severe narrowing of the medullary canal at the fracture site. A thorough clinical examination should specifically look for which of the following?

Explanation

Congenital pseudarthrosis of the tibia with anterolateral bowing is highly associated with Neurofibromatosis type 1 (NF1). Therefore, the child must be closely examined for signs of NF1, such as café-au-lait spots, axillary freckling, and Lisch nodules.

Question 82

A 15-year-old girl is incidentally found to have an expansive, radiolucent, 'ground-glass' lesion in the proximal femur with endosteal scalloping. An incisional biopsy is performed. What is the classic histopathological hallmark of this localized skeletal condition?

Explanation

The lesion described is monostotic fibrous dysplasia. Histologically, it is characterized by irregular trabeculae of woven bone that resemble 'Chinese characters' embedded in a fibrous stroma, classically lacking osteoblastic rimming.

Question 83

A newborn presents with a shortened right lower extremity, an adducted and supinated foot, and preaxial polydactyly. Radiographs demonstrate complete absence of the tibia with a normal fibula and intact distal femoral epiphysis. According to the Jones classification, which type of tibial hemimelia is this, and what is its most common inheritance pattern if familial?

Explanation

Complete absence of the tibia with a present distal femoral epiphysis represents a Type 1a tibial hemimelia. When familial, such as in tibial hemimelia-polydactyly syndrome, it is classically inherited in an autosomal dominant pattern.

Question 84

A 1-year-old boy presents with an isolated limb length discrepancy. Radiographs show a shortened right femur with a normally articulated hip and knee, but with significant coxa vara (neck-shaft angle of 85 degrees). There is no pseudoarthrosis. Which of the following is the most appropriate initial management for the coxa vara?

Explanation

In congenital short femur with severe coxa vara (neck-shaft angle < 90 degrees or a progressively decreasing angle), a subtrochanteric valgus osteotomy is indicated to correct biomechanics and prevent progression. This realignment must precede any future limb lengthening procedures.

Question 85

A neonate is diagnosed with bilateral radial clubhand and profoundly low platelets. Interestingly, the child's thumbs are present. What is the typical natural history of the thrombocytopenia in this specific syndrome?

Explanation

Thrombocytopenia-Absent Radius (TAR) syndrome is unique among radial deficiencies because the thumb is classically present. The associated severe thrombocytopenia is most critical during infancy but generally improves and normalizes after the first 1-2 years of life.

Question 86

A 10-year-old girl with a low posterior hairline and short, webbed neck is diagnosed with Klippel-Feil syndrome. She also has a unilateral undescended scapula. What is the approximate reported incidence of Sprengel deformity in patients with Klippel-Feil syndrome?

Explanation

Sprengel deformity (congenital high scapula) is a frequently associated musculoskeletal anomaly in patients with Klippel-Feil syndrome. It is seen in approximately 25% to 35% of these individuals due to an interrelated arrest in embryologic development.

Question 87

A 14-year-old girl presents with a painless, progressive flexion contracture of the proximal interphalangeal (PIP) joint of her right little finger. Passive extension of the PIP joint is possible when the metacarpophalangeal (MCP) joint is held in flexion. Abnormal insertion of which structure is most commonly implicated in this localized condition?

Explanation

Camptodactyly most commonly affects the little finger. The dynamic nature of the contracture (improving with MCP flexion) typically points to an anomalous lumbrical muscle insertion or an abnormal flexor digitorum superficialis (FDS) anatomy.

Question 88

A newborn is evaluated for a sharp posteromedial angulation at the junction of the middle and distal thirds of the left tibia. The foot is held in a severe calcaneovalgus position. What is the expected natural history of the tibial angulation and the limb length discrepancy (LLD)?

Explanation

Congenital posteromedial bowing of the tibia is associated with a calcaneovalgus foot posture. While the angular deformity typically remodels and improves spontaneously over the first few years, the limb length discrepancy persists and often requires equalisation surgery at maturity.

Question 89

A 13-year-old girl presents with wrist pain and limited range of motion. Examination reveals a prominent distal ulna and volar subluxation of the hand. Radiographs show increased volar and ulnar tilt of the distal radius. Which gene mutation is responsible for her primary skeletal manifestation?

Explanation

Léri-Weill dyschondrosteosis is characterized by disproportionate short stature and Madelung deformity. It is an autosomal dominant condition caused by mutations or deletions of the SHOX gene located on the pseudoautosomal region of the sex chromosomes.

Question 90

A 5-year-old boy presents with a painless, asymmetric swelling over the medial aspect of his right ankle. Radiographs demonstrate an irregular, multicentric ossification center arising from the medial epiphysis of the distal tibia. What is the most appropriate initial management for this condition?

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is a rare focal skeletal dysplasia presenting as asymmetrical epiphyseal overgrowth, pathologically identical to an osteochondroma. Asymptomatic lesions are observed, while surgery is reserved for pain, progressive deformity, or mechanical mechanical restriction.

Question 91

A 3-year-old child presents with a history of recurrent, painful soft tissue swellings in the neck and back that eventually harden. On physical examination, there is noticeable shortening and valgus deviation of the bilateral great toes. Which of the following gene mutations is the primary cause of this condition?

Explanation

Fibrodysplasia ossificans progressiva (FOP) classically presents with congenital hallux valgus malformations and progressive heterotopic ossification of soft tissues. It is caused by a gain-of-function mutation in the ACVR1 gene, which encodes a bone morphogenetic protein (BMP) type I receptor.

Question 92

A 35-year-old man presents with progressive joint stiffness and localized pain in his right lower extremity. Radiographs reveal unilateral, undulating cortical hyperostosis along the medial aspect of the femur and tibia, resembling "dripping candle wax." What is the underlying genetic mutation associated with this specific radiologic finding?

Explanation

Melorheostosis is a rare, focal sclerosing bone dysplasia characterized by linear cortical hyperostosis resembling dripping candle wax. It is associated with somatic loss-of-function mutations in the LEMD3 gene, affecting the inner nuclear membrane protein MAN1.

Question 93

A 3-month-old infant is brought to the clinic with excessive crying, fever, and a noticeably swollen jaw. Radiographs exhibit pronounced subperiosteal new bone formation exclusively along the mandible. The parents are reassured that symptoms typically resolve spontaneously by age 2. Which collagen gene defect is implicated in this self-limiting condition?

Explanation

Caffey disease (infantile cortical hyperostosis) presents with a triad of soft tissue swelling, hyperirritability, and periosteal new bone formation most commonly affecting the mandible, clavicles, and ulna. The familial form is caused by an autosomal dominant missense mutation in the COL1A1 gene.

Question 94

An asymptomatic 20-year-old woman undergoes lower extremity radiographs following minor trauma. The X-rays incidentally reveal bilateral, multiple dense longitudinal striations in the metaphyses and diaphyses of the distal femurs and proximal tibias. Her skull appears normal, and she has no hearing deficits. What is the most likely diagnosis?

Explanation

Osteopathia striata (Voorhoeve disease) is a benign, asymptomatic bone dysplasia characterized by distinctive longitudinal linear densities in the metaphyses of long bones. It typically requires no specific treatment but must be differentiated from more severe sclerosing dysplasias like osteopathia striata with cranial sclerosis.

Question 95

A 4-year-old boy presents with disproportionate focal enlargement of his right index and middle fingers, noticeable since birth. The overgrowth is prominent on the volar aspect, causing dorsal deviation, and MRI reveals substantial fibrofatty infiltration along the median nerve territory. Which signaling pathway is typically altered in this focal overgrowth condition?

Explanation

Macrodystrophia lipomatosa is a focal, congenital overgrowth of an extremity driven by fibrofatty proliferation along a specific nerve territory. It is caused by somatic mosaic mutations in the PIK3CA gene, which leads to upregulation of the PI3K/AKT/mTOR cellular signaling pathway.

Pediatric Orthopaedics: Comprehensive MCQ Question Bank & Exam Prep

Skeletal Dysplasias: Single Site Involvement MCQs

Skeletal Dysplasias: Single Site Involvement MCQs

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