AAOS Pediatric Orthopedics MCQs: Board Review Set 4

Question 1

A 4-year-old boy sustained a nondisplaced, but complete, fracture of the left proximal tibial metaphysis 1 year ago. The fracture healed uneventfully in an anatomic position. Examination of the injured extremity now reveals 18 degrees of valgus compared with 3 degrees of valgus on the opposite side. Management should now include

Explanation

The development of a valgus deformity after this type of fracture is a well-known occurrence, and the patient's parents should be informed about this risk. In a patient who is age 4 years, the natural history is one of gradual correction by the development of a physiologic varus deformity at the distal tibial physis; therefore, no active intervention is needed at this time. Bracing has no effect on the deformity, and the child is too young for any procedure on the growth plate. Proximal tibial osteotomy is reserved until the patient nears skeletal maturity because of the risk of recurrence of the deformity. Lateral stapling can be done near skeletal maturity if the deformity persists, but this is unlikely to be necessary. Zionts LE, MacEwen GD: Spontaneous improvement of posttraumatic tibia valga. J Bone Joint Surg Am 1986;68:680-687.

Question 2

A 16-year-old boy with spastic quadriplegic cerebral palsy has been referred for evaluation and management of scoliosis. His parents report increasing problems with sitting balance, positioning, and hygiene because of the deformity. The radiograph shown in Figure 46 reveals a lordoscoliosis of 105 degrees with marked pelvic obliquity. Attempts at correcting the pelvic obliquity on supine bending radiographs show significant rigidity. Management should consist of

Explanation

Spinal stabilization is the treatment of choice in patients with severe scoliosis who have progressive positioning, sitting balance, and/or hygiene problems despite maximal nonsurgical management. Pelvic rigidity and marked frontal plane deformity necessitate anterior and posterior procedures so as to maximize correction and fusion. Weinstein SL (ed): The Pediatric Spine: Principles and Practice. New York, NY, Raven Press, 1994, pp 977-997.

Question 3

A 10-year-old boy reports a gradual onset of weakness; however, he is fully ambulatory. History reveals that he has a 17-year-old brother who has just stopped walking because of a similar condition. Laboratory studies show a creatine kinase level of 5,480 IU/L (normal 25 to 232 IU/L), and examination shows a slightly positive Gower sign. What is the most likely diagnosis?

Explanation

The patient has Becker muscular dystrophy. Patients with this condition have a slower rate of progression of disease compared with patients who have Duchenne muscular dystrophy, and walking may continue into the late teens. The creatine kinase level is not as high as in Duchenne muscular dystrophy, which can range from 20,000 to 30,000 IU/L. Becker muscular dystrophy is allelic to Duchenne muscular dystrophy, resulting in a mutation in the dystrophin gene. Myotonic dystrophy is characterized by a progressive inability to relax the muscles after contracture. The Gower sign is not helpful in this disease. Patients with Charcot-Marie-Tooth disease, one type of which is also known as HMSN type II, do not have elevated creatine kinase levels and usually present with a foot deformity. Spinal muscular atrophy, type II, usually presents with severe weakness in the second year of life. Matsuo M: From molecular diagnosis to gene therapy. Brain Dev 1996;18:167-172. Darras BT: Molecular genetics of Duchenne and Becker muscular dystrophy. J Pediatr 1990;117:1-15.

Question 4

Figure 47 shows the radiograph of a 2-day-old girl who has been referred for swelling and limited use of the right upper extremity. The second of twins, the infant was breech and delivered with forceps at age 38 weeks, weighing 5.37 lb. Difficulty in moving the arm was noted shortly after birth. Examination shows no active motion of the shoulder, elbow, or wrist. Active finger flexion and extension are present. The elbow is mildly swollen, and passive motion shows lack of full extension of 20 degrees, lack of full flexion of 15 degrees, and no restriction of pronation or supination. What is the most likely diagnosis?

Explanation

Fractures involving the entire distal humeral physis may be a complication of a difficult delivery. Basing the diagnosis on radiographs can be difficult at this age because the secondary ossification center of the lateral condyle has not developed. The key to the diagnosis is the constant relationship of the radius and ulna, with medial and posterior displacement of the forearm relative to the humerus. An ultrasound can be obtained to confirm the diagnosis in newborns. Because the fracture is through cartilage, examination may reveal only mild swelling, and crepitation may be muffled or not apparent. The lack of apparent active motion of the shoulder, elbow, and wrist is secondary to pseudoparalysis. Child abuse is a common mechanism of this injury in a child who is age 1 month to age 3 years. Beaty JH, Wilkins KE: Fractures involving the entire distal humeral physis, in Rockwood CA, Wilkins KE, Beaty JH (eds): Fractures in Children, ed 4. Philadelphia, Pa, Lippincott-Raven, 1996, vol 3, pp 790-801. Dias JJ, Lamont AC, Jones JM: Ultrasonic diagnosis of neonatal separation of the distal humeral epiphysis. J Bone Joint Surg Br 1988;70:825-828.

Question 5

Examination of a 12-year-old girl with a painful flatfoot deformity reveals tenderness in the region of the sinus tarsi and no appreciable subtalar motion. Radiographs are shown in Figures 48a through 48c. Two attempts to relieve her symptoms by cast immobilization fail to relieve the pain. Management should now consist of

Explanation

Surgical treatment is indicated for a symptomatic tarsal coalition that has failed to respond to nonsurgical management. In this patient, the radiographs reveal a calcaneonavicular coalition and no degenerative changes. The patient is symptomatic, and two attempts at use of a short leg walking cast have failed to provide relief. For calcaneonavicular coalitions, good results have been reported following resection and interposition of the extensor digitorum brevis. A retrospective study of this procedure achieved good to excellent results in 58 of 75 feet (77%). Degenerative arthritis or persistent pain following resection of a coalition is a reasonable indication for a triple arthodesis. A medial closing wedge osteotomy of the calcaneus may be indicated for a rigid flatfoot with severe valgus deformity. There are no studies documenting the long-term effectiveness of a manipulation under general anesthesia for this condition. Gonzalez P, Kumar SJ: Calcaneonavicular coalition treated by resection and interpostion of the extensor digitorum brevis muscle. J Bone Joint Surg Am 1990;72:71-77.

Question 6

When counseling a patient with hypophosphatemic rickets, which of the following scenarios will always result in a child with the same disorder?

Explanation

Hypophosphatemic rickets is an inherited disorder that is transmitted by a unique sex-linked dominant gene. Therefore, if a male patient has a female offspring, his affected X chromosome will be transmitted and all of his female children will have hypophosphatemic rickets. All male offspring of a male patient will be unaffected. All offspring of a female patient have a 50% chance of having the disorder. Understanding the inheritance of hypophosphatemic rickets facilitates early diagnosis and early treatment. Medical treatment with phosphorus and some types of vitamin D (most authors recommend calcitriol) improves, but does not fully correct, the mineralization defect in hypophosphatemic rickets. However, if medical treatment is begun before the child begins walking, the growth plate is then adequately protected and a bowleg deformity will most likely be prevented. Evans GA, Arulanantham K, Gage JR: Primary hypophosphatemic rickets: Effect of oral phosphate and vitamin D on growth and surgical treatment. J Bone Joint Surg Am 1980;62:1130-1138.

Question 7

A 15-year-old boy with Duchenne muscular dystrophy has a progressive scoliosis that now measures 55 degrees. He is in foster care and is no longer ambulatory. Because posterior spinal fusion with instrumentation is the recommended treatment, the patient participates in a thorough discussion of the risks and benefits of the procedure. However, he refuses the surgery. The physician should now

Explanation

Traditionally, patients have been viewed as ignorant about medical matters and ill-equipped to determine what is in their best interest. This has been especially true for minors. However, recent informed consent policies are now based on the patient's right to self-determination. While most spinal surgeons would agree that spinal fusion improves pulmonary function, sitting balance, and comfort, they would also agree that this comes at considerable risk in a patient with compromised pulmonary function and ultimately, a terminal condition. With increasing frequency, young people older than age 14 years are gaining greater autonomy in decision making about their health care matters. This includes do not resuscitate orders when young patients are terminally ill, as well as in less serious situations. Surgery could be performed with the permission of the legal guardians; however, in this situation it is preferable to follow the patient clinically until he consents to surgery along with the legal guardians. Bracing is contraindicated. Reich WT (ed): Encyclopedia of Bioethics. New York, NY, Simon and Schuster, 1995, pp 1256-1265. Confidential health services for adolescents. Council on Scientific Affairs, American Medical Association. JAMA 1993;269:1420-1424.

Question 8

Figure 49 shows the radiograph of a 3-year-old child with progressive bowlegs. Laboratory studies show a calcium level of 9.5 mg/dL (normal 9.0 to 11.0 mg/dL), a phosphorus level of 4.2 mg/dL (normal 3 to 5.7 mg/dL), and an alkaline phosphatase level of 305 IU/L (normal 104 to 345 IU/L). What is the most likely diagnosis?

Explanation

The patient has bowlegs associated with very wide physes, particularly noted at the hips. The widening of the growth plates is a classic sign of rickets; however, the normal levels of calcium, phosphorus, and alkaline phosphatase rule out both nutritional and hypophosphatemic rickets. Patients with nutritional rickets or hypophosphatemic rickets have hypophosphatemia and increased alkaline phosphatase levels. Jansen metaphyseal dysostosis has very severe radiographic findings that are not found in this patient; however, these radiographic findings are classic for Schmid metaphyseal dysostosis. This disorder is caused by a mutation in the gene for type X collagen, which is found only in the growth plates of growing children. Lachman RS, Rimoin DL, Spranger J: Metaphyseal chondrodysplasia - Schmid type: Clinical and radiographic delineation with a review of the literature. Pediatr Radiol 1988;18:93-102.

Question 9

Figures 50a and 50b show the standing clinical photographs of a 12-year-old boy who has had increasing pain in the left foot for the past 9 months. He reports that the pain is activity related, aching in nature, and localized to the medial aspect of the midfoot and hindfoot. History reveals that he sustained a puncture wound located superior and posterior to the medial malleolus from a plate glass window 18 months ago. Examination reveals no restriction of ankle or subtalar motion, normal neurovascular status, no masses, and a well-healed 1.5-cm laceration posterior to the superior aspect of the medial malleolus. Inversion strength of the foot is decreased to grade 3/5. Radiographs of the foot show no bony abnormalities. Treatment should consist of

Explanation

The photographs show a planovalgus posture of the foot. The foot deformity and decreased inversion strength are secondary to laceration of the posterior tibial tendon 18 months ago. If the injury had been recognized acutely, optimal treatment would have consisted of repair of the tendon; however, contracture now precludes that possibility. Therefore, transfer of the flexor digitorum longus or flexor hallucis longus is the preferred treatment. In adults with posterior tibial dysfunction, the entire tendon is typically degenerated and the transfer must be anchored through a drill hole in the navicular. In this patient, the distal end of the posterior tibial tendon is a satisfactory insertion site. Lengthening osteotomy of the calcaneus could be combined with the tendon transfer if the patient had a fixed deformity of the foot. UCBL orthoses and an ankle-foot orthosis are not considered good long-term solutions for a 12-year-old patient. Mosca VS: Flexible flatfoot and skewfoot, in Drennan JC (ed): The Child's Foot and Ankle. New York, NY, Raven Press, 1992, pp 355-376.

Question 10

Which of the following clinical scenarios represents an appropriate indication for convex hemiepiphysiodesis/hemiarthrodesis in the treatment of a child with a congenital spinal deformity?

Explanation

Convex hemiarthrodesis and hemiepiphysiodesis are procedures designed to gradually reduce curve magnitude in congenital scoliosis because of hemivertebrae. They are used to surgically create an anterior and posterior bar to arrest growth on the convexity of the existing deformity. Success of the technique is predicated on continued growth on the concave side of the deformity. Prerequisites for this procedure include curves of limited length (less than or equal to five vertebrae), curves of reasonable magnitude (less than 70 degrees), absence of kyphosis, concave growth potential, and appropriate age (younger than age 5 years).

Question 11

Figures 51a through 51c show the radiographs of a 7-year-old soccer player who reports a gradual onset of midfoot pain that began shortly after the start of soccer season. He states that the pain is worse with activity and is partially alleviated by rest. Examination reveals soft-tissue swelling, and tenderness and warmth in the region of the talonavicular and navicular cunieform joints. Management should consist of

Explanation

Osteochondrosis of the tarsal navicular (Kohler disease) is an infrequent cause of midfoot pain in children, and the etiology is unknown. The typical radiographic findings include flattening and irregular ossification of the tarsal navicular. The medial cunieform and talus maintain their normal articular contours. The acute process is best treated with rest and immobilization. A short leg walking cast results in relief of pain and a quicker return to activity compared with orthotics, although long-term success is similar with either method of treatment. Children may return to activities when the symptoms subside. The radiographic appearance of the talus begins to normalize by about 8 to 10 months following the onset of symptoms.

Question 12

A 10-year-old child with cerebral palsy undergoes bilateral hamstring lengthening for severe knee flexion contractures, and knee immobilizers are applied postoperatively. Examination at the initial postoperative check 2 hours after surgery reveals that she can dorsiflex her toes on the right foot, but not on the left foot. The physician should now

Explanation

Children with cerebral palsy are often difficult to examine. However, this patient clearly has a peroneal nerve deficit, most likely from the acute stretch after the hamstring lengthening. The nerve has the best chance of recovery if it is relaxed by flexing the knee. Once the nerve has recovered, gradual knee extension can be accomplished. Aspden RM, Porter RW: Nerve traction during correction of knee flexion deformity: A case report and calculation. J Bone Joint Surg Br 1994;76:471-473.

Question 13

Figures 52a and 52b show the plain radiographs of a 12-year-old girl who has right distal leg pain. She reports that symptoms are present with weight-bearing activities and improve with rest. Examination reveals diffuse tenderness over the distal tibial metaphysis and mild swelling. A photomicrograph of the biopsy specimen is shown in Figure 52c. What is the most likely diagnosis?

Explanation

This lytic lesion is in the epiphyseal-metaphyseal region of the distal tibia. The most common lesion in this area is a giant cell tumor. Although these lesions are most commonly seen in adults, they can also occur in the skeletally immature patient. The photomicrograph shows a lesion with multiple giant cells, the nuclei of which are similar to those in the background stroma; this finding is characteristic of giant cell tumors. Giant cells can be seen in many benign lesions, including aneurysmal bone cysts, Brown tumors, and eosinophilic granuloma. These lesions usually have fewer giant cells with less nuclei. The location of this lesion in the epiphyseal-metaphyseal area is not seen in aneurysmal bone cysts, unicameral bone cysts, Ewing's sarcoma, or eosinophilic granuloma.

Question 14

A 15-year-old boy with epilepsy who is treated with phenytoin sustains a vertebral compression fracture during a breakthrough seizure. Radiographs of the spine reveal generalized osteopenia. What is the most likely cause of the osteopenia?

Explanation

As a side effect of treatment, phenytoin induces osteomalacia, or rickets, in growing children, through interference with metabolism of vitamin D. Oral supplementation of vitamin D can minimize this effect in patients who are undergoing prolonged treatment with phenytoin.

Question 15

Figure 53 shows the pedigree of a family with an unusual type of muscular dystrophy. This pedigree is most consistent with what type of inheritance pattern?

Explanation

The pedigree documents involvement of male offspring only, and it also shows transmission through an uninvolved female carrier. This inheritance pattern is most consistent with a x-linked recessive inheritance. It would be inconsistent with a dominant inheritance pattern unless there was incomplete penetrance. Autosomal-recessive inheritance would be possible only if the family member labeled II.F was also a carrier of the same gene; however, this is unlikely. Mitochondrial inheritance is possible, but as with autosomal patterns, mitochondrial inheritance normally affects both male and female offspring. It is transmitted only through the maternal line.

Question 16

Which of the following is considered the most accurate test to determine the amount of limb-length discrepancy in a patient with a knee flexion contracture of 35 degrees?

Explanation

Flexion contractures and angular deformities of a limb cause inaccurate limb-length measurement results with most clinical methods. A CT scanogram is more accurate than standard scanograms for determining limb length in patients with knee flexion contractures of 30 degrees or more. The cost and time necessary to complete the examinations are comparable, but the CT scanogram delivers only 20% of the radiation needed for standard scanograms. Aaron A, Weinstein D, Thickman D, Eilert R: Comparison of orthoroentgenography and computed tomography in the measurement of limb-length discrepancy. J Bone Joint Surg Am 1992;74:897-902.

Question 17

Figures 54a and 54b show the radiograph and MRI scan of a 7-year-old boy who has a painful right thoracic scoliosis that measures 35 degrees. Neurologic examination is normal. Management should consist of

Explanation

Because hydrosyringomyelia, with or without an Arnold-Chiari malformation, is now being recognized as the etiology of many infantile and juvenile idiopathic scolioses, management should consist of a neurosurgical consultation. Observation with follow-up radiographs is not an option in curves of this magnitude. A technitium Tc 99m bone scan is unnecessary because the etiology of the curve has been identified. Although spinal fusion may be needed in the future, it should not be undertaken before the neurosurgical problem has been addressed. Zadeh HG, Sakka SA, Powell MP, Mehta MH: Absent superficial abdominal reflexes in children with scoliosis: An early indicator of syringomyelia. J Bone Joint Surg Br 1995;77:762-767. Schwend RM, Hennrikus W, Hall JE, Emans JB: Childhood scoliosis: Clinical indications for magnetic resonance imaging. J Bone Joint Surg Am 1995;77:46-53.

Question 18

A 10-month-old girl has the spinal deformity shown in Figures 55a and 55b with no apparent neurologic finding. The next step in evaluation should be to obtain

Explanation

Approximately 60% of patients with a congenital spine abnormality have associated malformations outside the spinal column. Genitourinary abnormalities are probably the most common, occurring in up to 37% of patients. These are usually anatomic anomalies, such as renal agenesis, duplication, fusion, and ectopia. A genitourinary ultrasound is the least invasive screening tool. Other associated anomalies include cervical vertebral abnormalities, VATER syndrome, and intraspinal abnormalities such as diastematomyelia. An MRI scan is not recommended as part of the screening examination; however, if the patient had neurologic signs or symptoms, an MRI scan would be indicated. Beals RK, Robbins JR, Rolfe B: Anomalies associated with vertebral malformations. Spine 1993;18:1329-1332.

Question 19

A 12-year-old girl has scoliosis at T5-T10 that measures 62 degrees. A clinical photograph of the axilla is shown in Figure 56. Management should consist of

Explanation

Neurofibromatosis type 1 (NF-1) is an autosomal-dominant disorder affecting about 1 in 4,000 people. NF-1 causes tumors to grow along various types of nerves and affects the development of non-nervous tissues, such as bone and skin. The gene for NF-1 is located on the long arm of chromosome 17 and codes the protein neurofibromin. Research indicates that NF-1 acts as a tumor-suppressor gene and, as such, plays an important role in the control of cell growth and differentiation. Axillary and inguinal freckling is considered a good diagnostic marker for NF-1. The hyperpigmented spots that measure from 2 mm to 4 mm may be congenital, but these typically appear and increase later in life. Scoliosis is the most common musculoskeletal disorder of NF-1. The curves are frequently dystrophic, kyphotic, and have a high risk of pseudarthrosis following spinal fusion. Anterior and posterior spinal fusion with rigid posterior segmental instrumentation is the treatment of choice. Goldberg Y, Dibbern K, Klein J, Riccardi VM, Graham JM Jr: Neurofibromatosis type 1: An update and review for the primary pediatrician. Clin Pediatr 1996;35:545-561.

Question 20

A 12-year-old girl has bilateral developmentally dislocated hips. History reveals no previous treatment, and she reports no discomfort. Good long-term clinical results are most likely to occur with

Explanation

The natural history of complete developmental dislocation of the hip is dependent on two factors: bilaterality and the presence or absence of a false acetabulum. Patients with bilateral dislocations may have low back pain because of hyperlordosis, but they tend to have less disability than patients with unilateral dislocations who have secondary problems related to limb-length inequality. Degenerative joint disease and clinical disability are most likely to develop in patients with completely dislocated hips and well-developed false acetabula. In a 12-year-old child who has bilateral developmental hip dislocations, it would be difficult to obtain surgical treatment results that are better than the natural history of the disorder. Abductor strengthening exercises are unlikely to influence the long-term outcome in this disorder. Surface replacements are not indicated in young asymptomatic patients. Weinstein SL: Natural history of congenital hip dislocation (CDH) and hip dysplasia. Clin Orthop 1987;225:62-76.

Question 21

Thyroid hormone regulates skeletal growth at the physis by stimulation of

Explanation

Children with hypothyroidism have delayed bone age, reduced thickness of the physis, disorganization of the cartilage columns of the physis, and impaired differentiation of proliferating chondrocytes into hypertrophic cells. As a result, these children have severe growth retardation, and slipped capital femoral epiphysis may develop because of mechanical weakening of the physis. Thyroid hormone regulates terminal differentiation of the growth plate chondrocytes, with a resultant increase in type X collagen and alkaline phosphatase. These substances are important factors in matrix mineralization. Insulin-like growth factors and FGF-2 appear to act synergistically to stimulate mitotic activity of the growth plate chondrocytes. TGF-beta= and PTHrP stimulate proteoglycan synthesis and mitotic activity of the chondrocytes and inhibit type X collagen and alkaline phosphatase activity. Ballock RT: Regulation of skeletal growth and maturation by thyroid hormone, in Buckwalter JA, Ehrlich MG, Sandell LJ, Trippel SB (eds): Skeletal Growth and Development: Clinical Issues and Basic Science Advances. Rosemont, Ill, American Academy of Orthopaedic Surgeons, 1998, pp 301-317. Rosier RN, O'Keefe RJ, Reynolds PR, Hicks DG, Puzas JE: Expression and function of TGF-beta= and PTHrP in the growth plate, in Buckwalter JA, Ehrlich MG, Sandell LJ, Trippel SB (eds): Skeletal Growth and Development: Clinical Issues and Basic Science Advances. Rosemont, Ill, American Academy of Orthopaedic Surgeons, 1998, pp 285-299.

Question 22

A newborn has an anterolateral bow of the tibia and a duplication of the great toe. Which of the following conditions will develop as the infant grows?

Explanation

Anterolateral bowing of the tibia is normally associated with congenital pseudarthrosis of the tibia. This, in turn, is associated with neurofibromatosis. Posterior bowing is more benign and usually corrects spontaneously. However, anterolateral bowing also corrects spontaneously, and the limb-length discrepancy may be the only remaining sequela when associated with duplication of the great toe. Lisch nodules and axillary freckling are pathognomonic findings in neurofibromatosis but would not be expected in this patient because this type of tibial deformity is not associated with neurofibromatosis.

Question 23

During stabilization of a slipped capital femoral epiphysis, the screw penetrates into the joint. The screw is repositioned so that it is within the femoral head. This transient penetration of the hip joint will most likely lead to

Explanation

Chondrolysis may be associated with unrecognized permanent penetration of the joint space by a pin or screw. However, transient penetration by the guide wire or screw is not associated with this problem. One study described 11 hips in which there was transient intraoperative penetration of the joint space by a guide wire or screw. These patients were followed for at least 2 years, with none showing any clinical or radiographic evidence of chondrolysis. Another retrospective study of 55 slipped epiphyses described 11 hips with transient intraoperative pin penetration, with none showing development of chondrolysis. There are no studies to suggest that transient pin penetration leads to osteonecrosis, stiffness, or premature physeal closure. Zionts LE, Simonian PT, Harvey JP Jr: Transient penetration of the hip joint during in situ cannulated-screw fixation of slipped capital femoral epiphysis. J Bone Joint Surg Am 1991;73:1054-1060.

Question 24

The mother of a 3-month-old infant states that she has difficulty positioning the infant's legs during diaper changes. Examination reveals limited abduction of both hips and a negative Ortolani sign. A radiograph reveals bilaterally dislocated hips. Initial management consists of guided reduction in a Pavlik harness, with weekly follow-up. Figures 57a and 57b show the radiograph and CT scan obtained after 6 weeks in the harness. Management should now consist of

Explanation

In an infant younger than age 6 months with a complete dislocation of the hip that is not initially reducible, the Pavlik harness may be used for a trial of guided reduction. When the harness is used in these patients, the infant should be followed at weekly intervals to see if reduction has been achieved. If the hip does not reduce after 3 to 4 weeks of harness wear, the harness should be discontinued, and closed or open reduction should be considered to avoid secondary deformation of the posterolateral acetabulum, also known as Pavlik harness pathology. Changing to other abduction braces is not indicated. Jones GT, Schoenecker PL, Dias LS: Developmental hip dysplasia potentiated by inappropriate use of the Pavlik harness. J Pediatr Orthop 1992;12:722-726. Atar D, Lehman WB, Grant AD: Pavlik harness pathology. Isr J Med Sci 1991;27:325-330.

Question 25

A 6-year-old boy with severe spastic quadriplegic cerebral palsy is nonambulatory. Examination reveals 10 degrees of hip abduction on the left and 30 degrees on the right with the hips and knees extended. The Thomas test shows 20 degrees of flexion bilaterally, and Ely test results are 3+/4 bilaterally. Radiographs show a center edge angle of 0 degrees on the left and -10 degrees on the right. The neck shaft angles are 170 degrees bilaterally. Which of the following procedures would offer the best results?

Explanation

The patient has bilateral subluxated hips, with nearly vertical neck shaft angles; therefore, the treatment of choice is varus derotation osteotomy. Shortening of the bone on one or both sides may be necessary to allow adequate range of motion postoperatively. In patients this age and with this degree of bony deformity, soft-tissue releases are not likely to lead to hip stability. Botulinum toxin has been shown to be effective in the treatment of ankle equinus, but its efficacy in other areas has not been demonstrated as yet. The indications for obturator neurectomy are unclear at present. Proximal femoral resection is a salvage procedure for long-standing hip dislocations that are symptomatic and not reconstructable. Tylkowski CM, Rosenthal RK, Simon SR: Proximal femoral osteotomy in cerebral palsy. Clin Orthop 1980;151:183-192.

Question 26

A 6-week-old female infant is currently being treated for developmental dysplasia of the hip (DDH) with a Pavlik harness. During a follow-up visit, the parents report that the child has stopped kicking her right leg. Examination reveals decreased active extension of the right knee, while ankle movements and toe flexion are intact. Which nerve is most likely affected?

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment, typically resulting from hyperflexion of the hips. It presents with decreased active knee extension and usually resolves completely when the harness is removed or adjusted.

Question 27

A 5-year-old boy sustains a Gartland type III extension-type supracondylar humerus fracture. On initial presentation, his hand is pink but pulseless. Following a satisfactory closed reduction and percutaneous pinning, the hand remains pink with brisk capillary refill, but the radial pulse remains unpalpable. What is the most appropriate next step in management?

Explanation

A "pink, pulseless" hand following adequate reduction and pinning of a supracondylar fracture generally has adequate collateral circulation and can be safely observed. The pulse typically returns within a few days, avoiding the need for immediate vascular exploration.

Question 28

According to the Loder classification, which of the following defines an unstable slipped capital femoral epiphysis (SCFE)?

Explanation

The Loder classification defines an unstable SCFE as the inability to ambulate, even with the use of crutches. Unstable slips are associated with a significantly higher rate of avascular necrosis compared to stable slips.

Question 29

A 6-year-old boy presents with an extension-type supracondylar humerus fracture. Radiographs demonstrate posterolateral displacement of the distal fragment. Which of the following neurologic structures is at greatest risk of injury?

Explanation

Posterolateral displacement of the distal fragment in an extension-type supracondylar humerus fracture tethers the anterior/medial structures, placing the anterior interosseous nerve (AIN) at greatest risk. Posteromedial displacement places the radial nerve at risk.

Question 30

A 4-week-old female infant undergoes a screening ultrasound of the hips due to a breech presentation. The coronal view reveals an alpha angle of 52 degrees and a beta angle of 65 degrees. According to the Graf classification, what does this alpha angle indicate?

Explanation

An alpha angle between 50 and 59 degrees corresponds to a Graf Type II hip, which indicates physiologic immaturity or mild dysplasia. An alpha angle greater than 60 degrees is considered normal (Type I).

Question 31

Which of the following patient profiles represents the strongest absolute indication for prophylactic in situ pinning of the contralateral hip in a patient presenting with a unilateral slipped capital femoral epiphysis (SCFE)?

Explanation

Endocrinopathies, such as hypothyroidism or renal osteodystrophy, are strong indications for prophylactic contralateral pinning in SCFE. These patients have a significantly elevated risk of developing bilateral disease.

Question 32

In the operative management of pediatric supracondylar humerus fractures, biomechanical studies have shown that which of the following pin configurations provides the greatest torsional stability?

Explanation

Crossed medial and lateral pins provide the greatest torsional stability for supracondylar humerus fractures. However, lateral-only pin constructs are often preferred clinically to eliminate the risk of iatrogenic ulnar nerve injury.

Question 33

In the closed or open reduction of late-presenting developmental dysplasia of the hip (DDH), which of the following factors is most strongly associated with an increased risk of developing avascular necrosis (AVN) of the femoral head?

Explanation

Immobilization of the hip in excessive abduction (the "frog-leg" position) causes mechanical compression of the retinacular vessels against the acetabular rim. This is the primary iatrogenic risk factor for AVN in the treatment of DDH.

Question 34

A 13-year-old boy undergoes single-screw in situ pinning for a stable slipped capital femoral epiphysis (SCFE). Seven months postoperatively, he complains of worsening hip stiffness and global pain. Radiographs reveal symmetric hip joint space narrowing to less than 2 mm with no signs of hardware failure. What is the most likely diagnosis?

Explanation

Chondrolysis is a devastating complication of SCFE characterized by acute cartilage necrosis, presenting with marked stiffness, pain, and symmetric joint space narrowing on radiographs. It is strongly associated with unrecognized joint penetration by the hardware.

Question 35

An 8-year-old boy is evaluated for a cosmetic deformity of his elbow three years after sustaining a supracondylar humerus fracture that was treated nonoperatively. He has full range of motion and normal neurology. What is the most common long-term deformity following this injury, and what is its primary functional consequence?

Explanation

Cubitus varus (gunstock deformity) is the most common malunion following a pediatric supracondylar humerus fracture. It is primarily a cosmetic deformity that rarely causes functional impairment or tardy nerve palsies.

Question 36

A newborn presents with bilateral, rigid, and irreducible hip dislocations. Physical examination also reveals bilateral clubfeet and fixed knee extension contractures. The infant otherwise has normal spinal anatomy on ultrasound. What is the most likely diagnosis?

Explanation

Teratologic hip dislocations are present at birth, typically rigid and irreducible, and associated with underlying neuromuscular or syndromic conditions such as arthrogryposis multiplex congenita or myelomeningocele.

Question 37

A 14-year-old boy with a severe, chronic slipped capital femoral epiphysis presents with severe impingement. The surgeon plans a corrective osteotomy at the apex of the deformity to restore anatomy. Which of the following procedures is an intracapsular osteotomy of the femoral neck that provides excellent correction but historically carries the highest risk of avascular necrosis?

Explanation

The Dunn procedure is an intracapsular, cuneiform osteotomy performed directly at the femoral neck to reduce a severe SCFE. Because it is intracapsular, it disrupts the retinacular blood supply and historically has a high risk of avascular necrosis.

Question 38

A 4-week-old female infant is being treated with a Pavlik harness for a dislocated left hip. At the 2-week follow-up, the mother notes the child is not moving her left leg. On exam, the infant lacks active knee extension but has normal ankle movement. What is the most likely cause?

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment, typically due to hyperflexion of the hip. Treatment involves adjusting the harness to reduce flexion, which usually leads to spontaneous recovery.

Question 39

An 18-month-old girl presents with a limp and a leg length discrepancy. Radiographs confirm a high, untreated dislocation of the right hip. What is the most appropriate initial management?

Explanation

In a child older than 18 months with a high dislocation, open reduction with a concomitant pelvic osteotomy and femoral shortening osteotomy is typically required to reduce the hip safely and minimize the risk of avascular necrosis.

Question 40

A 12-year-old obese boy presents to the emergency department unable to bear weight on his right leg after a minor fall. Radiographs reveal a severe, posterior slip of the right capital femoral epiphysis. What is the recommended definitive management?

Explanation

Unstable SCFE has a high risk of AVN. Recent literature supports open reduction and internal fixation utilizing a surgical hip dislocation approach (modified Dunn procedure) to decompress the intracapsular hematoma and restore anatomy.

Question 41

A 13-year-old boy undergoes in-situ pinning for a left-sided SCFE. Which of the following is the strongest indication for prophylactic pinning of the contralateral asymptomatic hip?

Explanation

Endocrine disorders, such as hypothyroidism or renal osteodystrophy, strongly predispose patients to bilateral SCFE. Prophylactic pinning of the contralateral hip is highly recommended in this population.

Question 42

A 5-year-old boy sustains a completely displaced, extension-type supracondylar humerus fracture. On presentation, the hand is pink and warm, but the radial pulse is absent. After urgent closed reduction and percutaneous pinning, the hand remains pink and warm, and the pulse remains absent. What is the most appropriate next step in management?

Explanation

A 'pulseless pink hand' after reduction of a supracondylar fracture indicates adequate collateral perfusion. Observation and close monitoring are appropriate, as the pulse often returns within a few days to weeks.

Question 43

A 6-year-old girl falls from monkey bars and sustains a displaced extension-type supracondylar humerus fracture with posteromedial displacement of the distal fragment. Which nerve is most commonly injured in this specific fracture pattern?

Explanation

Posteromedial displacement of the distal fragment in an extension-type supracondylar humerus fracture puts the radial nerve at the greatest risk of stretch or entrapment over the proximal fragment.

Question 44

According to the American Academy of Pediatrics (AAP) and AAOS, which of the following infants should routinely undergo a screening ultrasound for DDH at 6 weeks of age, regardless of clinical exam findings?

Explanation

Routine ultrasound screening at 6 weeks is recommended for infants with strong risk factors for DDH, specifically female sex with breech presentation, or a positive family history regardless of sex.

Question 45

When evaluating a pelvic radiograph of a 12-month-old child for developmental dysplasia of the hip, an abnormal acetabular index would typically be greater than:

Explanation

In a normal infant around 1 year of age, the acetabular index should be less than 25 degrees. Values greater than 30 degrees are considered dysplastic and warrant intervention or close monitoring.

Question 46

A 14-year-old boy with a history of a chronic, stable slipped capital femoral epiphysis pinned in-situ 1 year ago presents with increasing hip pain and stiffness. Radiographs show joint space narrowing and subchondral cysts in both the femoral head and acetabulum. What is the most likely diagnosis?

Explanation

Chondrolysis is a severe complication of SCFE characterized by progressive joint space narrowing and stiffness. It is strongly associated with unrecognized intra-articular hardware penetration during pinning.

Question 47

On an AP pelvis radiograph of a 12-year-old patient with suspected early SCFE, which line is drawn along the superior margin of the femoral neck to check for intersection with the lateral epiphysis?

Explanation

Klein's line is drawn along the superior aspect of the femoral neck on an AP radiograph. In a normal hip, it should intersect the lateral aspect of the femoral epiphysis.

Question 48

When evaluating the adequacy of a closed reduction for a pediatric supracondylar humerus fracture, Baumann's angle is primarily used to assess:

Explanation

Baumann's angle is used to evaluate coronal plane alignment. It helps ensure correct reduction and prevent cubitus varus deformity.

Question 49

A 10-year-old boy has a visible cubitus varus deformity 3 years after a supracondylar humerus fracture. Which of the following statements regarding this deformity is true?

Explanation

Cubitus varus following a supracondylar humerus fracture is usually due to malunion, not physeal arrest. It is primarily a cosmetic deformity without significant functional limitation.

Question 50

A 16-year-old girl presents with hip pain. Radiographs reveal acetabular dysplasia. Which of the following lateral center-edge angles (of Wiberg) is considered diagnostic for frank dysplasia in a skeletally mature patient?

Explanation

A lateral center-edge angle (LCEA) of Wiberg less than 20 degrees is generally considered diagnostic for acetabular dysplasia. A normal LCEA is typically 25 to 40 degrees.

Question 51

In which of the following scenarios is the use of a Pavlik harness absolutely contraindicated for the treatment of a dislocated hip?

Explanation

Teratologic hip dislocations are rigid and do not respond to Pavlik harness treatment. Attempts to use it can lead to severe complications like iatrogenic fractures or avascular necrosis.

Question 52

In a slipped capital femoral epiphysis, the displacement of the femoral neck relative to the capital epiphysis is typically in which direction?

Explanation

In SCFE, the epiphysis stays relatively fixed in the acetabulum while the femoral neck displaces anteriorly, laterally, and externally rotates relative to the epiphysis.

Question 53

A 4-year-old falls on an outstretched hand. Radiographs show a supracondylar humerus fracture with an intact posterior cortex but an anterior humeral line that passes anterior to the capitellum. How is this fracture classified?

Explanation

A Gartland Type II fracture is characterized by displacement (extension) with an intact posterior hinge (cortex). The anterior humeral line will pass anterior to the middle third of the capitellum.

Question 54

Which of the following is true regarding flexion-type supracondylar humerus fractures compared to extension-type fractures?

Explanation

Flexion-type supracondylar fractures frequently require open reduction because the reduction is often blocked by interposed tissue. They are immobilized in relative extension, and the ulnar nerve is most commonly injured.

Question 55

While performing a closed reduction and spica casting for a 9-month-old with DDH, what is the optimal "safe zone" of Ramsey to ensure joint stability while minimizing the risk of avascular necrosis?

Explanation

The safe zone of Ramsey is the arc of abduction between the angle where the hip redislócates and the angle of maximal abduction. Extreme abduction dramatically increases the risk of avascular necrosis.

Question 56

When performing in-situ percutaneous pinning of a severe slipped capital femoral epiphysis, the starting point for the guide wire on the lateral femur should be:

Explanation

Because the femoral neck displaces anteriorly and externally rotates, the starting point for the screw must be more anterior and proximal on the femoral neck to achieve the correct trajectory.

Question 57

A 6-year-old child presents with a displaced extension-type supracondylar fracture. On neurologic examination, the child is unable to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Which nerve is injured?

Explanation

The anterior interosseous nerve (AIN) innervates the flexor pollicis longus and the radial half of the flexor digitorum profundus. Injury is indicated by the inability to make an 'OK' sign.

Question 58

A 4-month-old girl is currently being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). Her mother reports that the infant has stopped actively extending her knee on the treated side. Which of the following is the most appropriate next step in management?

Explanation

Decreased active knee extension in a Pavlik harness suggests a femoral nerve palsy, typically caused by hyperflexion of the hip. The harness should be temporarily removed or adjusted to decrease flexion until neurologic function returns.

Question 59

A 13-year-old boy presents to the emergency department with acute-onset left hip pain after tripping. He is completely unable to bear weight on the left leg, even with crutches. Radiographs confirm a severe slipped capital femoral epiphysis (SCFE). Based on the Loder classification, what is the most significant complication risk associated with this specific presentation?

Explanation

According to the Loder classification, a SCFE is unstable if the patient cannot bear weight even with crutches. Unstable slips carry a significantly higher risk of avascular necrosis (AVN), historically reported to be up to 47%.

Question 60

A 6-year-old boy sustains a severe extension-type supracondylar humerus fracture (Gartland Type III). On examination, he cannot flex the interphalangeal joint of his thumb or the distal interphalangeal joint of his index finger. Which nerve is most likely injured?

Explanation

The anterior interosseous nerve (AIN), a branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures. Injury presents as an inability to form the 'A-OK' sign due to weakness of the flexor pollicis longus and flexor digitorum profundus.

Question 61

A 2-year-old girl is diagnosed with untreated developmental dysplasia of the left hip. Radiographs show a dislocated left hip with a false acetabulum and an acetabular index of 42 degrees. Which of the following surgical strategies is most appropriate for achieving a stable, concentric reduction?

Explanation

In a child older than 18-24 months, open reduction is typically required. Due to secondary adaptive changes like severe acetabular dysplasia and capsular laxity, a concomitant pelvic osteotomy (and often femoral shortening) is necessary to maintain stability.

Question 62

An 11-year-old girl with chronic kidney disease secondary to focal segmental glomerulosclerosis presents with a unilateral slipped capital femoral epiphysis (SCFE). Which of the following is the strongest indication for prophylactic pinning of the contralateral, asymptomatic hip in this patient?

Explanation

Patients with underlying metabolic or endocrine disorders (such as renal osteodystrophy, hypothyroidism, or growth hormone therapy) have a high rate of bilateral SCFE. Prophylactic pinning of the contralateral hip is highly recommended in these populations.

Question 63

A 5-year-old boy presents with a Gartland Type III supracondylar humerus fracture. The hand is pink, but the radial pulse is absent. After a satisfactory closed reduction and percutaneous pinning, the hand remains pink and well-perfused, but the radial pulse remains absent. What is the most appropriate next step in management?

Explanation

In a 'pink, pulseless' hand after satisfactory reduction of a supracondylar fracture, capillary refill indicates adequate collateral circulation. The standard of care is careful observation and hospital admission; surgical exploration is generally reserved for a white, pulseless hand.

Question 64

A 6-week-old female infant, born breech, undergoes a screening hip ultrasound. The coronal view reveals an alpha angle of 48 degrees and a beta angle of 80 degrees on the right side. The femoral head is subluxated. What is the most appropriate initial management?

Explanation

An alpha angle less than 60 degrees indicates acetabular dysplasia. The standard first-line treatment for an infant under 6 months of age with a reducible dysplastic or dislocated hip is a Pavlik harness.

Question 65

During the percutaneous pinning of a stable slipped capital femoral epiphysis (SCFE), the surgeon uses the approach-withdraw technique under fluoroscopy. Unrecognized pin penetration into the joint space most directly increases the risk of which of the following complications?

Explanation

Unrecognized hardware penetration into the joint space is a major risk factor for chondrolysis. Fluoroscopic evaluation with continuous internal-external rotation (approach-withdraw technique) is critical to confirm the pin is completely within the bone.

Question 66

A 7-year-old girl falls directly onto a flexed elbow. Radiographs reveal a flexion-type supracondylar humerus fracture. Which of the following nerve injuries is most strongly associated with this specific fracture pattern?

Explanation

While the anterior interosseous nerve is most commonly injured in extension-type fractures, flexion-type supracondylar humerus fractures are uniquely associated with a higher incidence of ulnar nerve injury due to the nerve's posterior position.

Question 67

A newborn boy with arthrogryposis multiplex congenita is found to have bilateral teratologic hip dislocations. Which of the following statements regarding the management of his hips is most accurate?

Explanation

Teratologic dislocations, such as those seen in arthrogryposis or myelomeningocele, do not respond well to Pavlik harness treatment. Its use is typically contraindicated due to high failure rates and risk of iatrogenic injury, necessitating open reduction.

Question 68

A 12-year-old obese boy is diagnosed with a slipped capital femoral epiphysis (SCFE). Histologic and biomechanical studies demonstrate that the slippage occurs through a specific zone of the physis. Through which zone of the growth plate does the primary failure occur in SCFE?

Explanation

SCFE is characterized by a mechanical failure through the hypertrophic zone of the physis. This zone is mechanically the weakest, especially under the increased shear stress associated with obesity during the adolescent growth spurt.

Question 69

When stabilizing a Gartland Type III supracondylar humerus fracture with percutaneous pins, a surgeon debates between placing crossed pins (medial and lateral) versus two lateral divergent pins. What is the primary biomechanical and clinical trade-off of using a crossed-pin configuration?

Explanation

Crossed pinning provides superior torsional stability compared to isolated lateral pinning. However, the placement of a medial pin carries an increased, albeit small, iatrogenic risk to the ulnar nerve.

Question 70

A 5-year-old child with residual developmental dysplasia of the hip undergoes a Pemberton osteotomy. Unlike a Salter osteotomy, the Pemberton osteotomy hinges on which of the following anatomic structures to achieve acetabular redirection?

Explanation

The Pemberton osteotomy is an incomplete pericapsular osteotomy that hinges on the flexible triradiate cartilage in children. In contrast, the Salter osteotomy is a complete innominate osteotomy that hinges on the pubic symphysis.

Question 71

A 6-year-old boy falls on an outstretched hand and sustains a widely displaced extension-type supracondylar humerus fracture. On examination, he is unable to actively flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Which of the following nerves is most likely injured?

Explanation

The anterior interosseous nerve (AIN) is the most commonly injured nerve in extension-type supracondylar humerus fractures. Injury presents with the inability to make an "OK" sign due to weakness of the flexor pollicis longus and flexor digitorum profundus to the index finger. Most AIN palsies in this setting are neuropraxias that resolve with observation.

Question 72

A 6-week-old female has been treated with a Pavlik harness for 2 weeks for Developmental Dysplasia of the Hip (DDH). Her mother reports that the baby is no longer kicking her right leg. Examination reveals decreased active extension of the right knee, while toe and ankle movements remain normal. What is the most appropriate next step in management?

Explanation

Femoral nerve palsy is a known complication of the Pavlik harness, typically caused by excessive hip hyperflexion compressing the nerve against the pelvis. The appropriate management is to temporarily discontinue the harness or significantly loosen the flexion straps until active quadriceps function returns, which usually occurs within a few days.

Question 73

A 13-year-old boy presents to the emergency department with severe acute hip pain after a minor fall and is completely unable to bear weight. Radiographs confirm a severe, displaced slipped capital femoral epiphysis (SCFE). According to the Loder classification, what is the most significant long-term risk associated with this specific presentation?

Explanation

The inability to bear weight, even with crutches, defines an unstable SCFE according to the Loder classification. Unstable SCFE carries a significantly high risk of avascular necrosis (AVN), historically reported to be between 20% and 50%.

Question 74

A 5-year-old girl sustains a Gartland type III supracondylar humerus fracture. After a successful closed reduction and percutaneous pinning in the operating room, her hand is warm and well-perfused with brisk capillary refill, but the radial pulse remains non-palpable. What is the most appropriate management?

Explanation

A "pink, pulseless" hand after successful reduction and pinning of a supracondylar fracture indicates adequate collateral circulation. Current guidelines recommend observation and close inpatient monitoring rather than immediate vascular exploration.

Question 75

An 11-year-old boy presents with a unilateral stable slipped capital femoral epiphysis (SCFE). His medical history is significant for panhypopituitarism, for which he receives growth hormone replacement. After treating the affected hip, what is the most appropriate management for the asymptomatic contralateral hip?

Explanation

Prophylactic pinning of the contralateral hip is highly recommended in patients with endocrine disorders (such as hypopituitarism or hypothyroidism) or renal failure. These patients have a significantly higher risk of developing bilateral SCFE compared to idiopathic cases.

Question 76

A 14-month-old girl presents with a painless limp since she began walking. Radiographs demonstrate a dislocated left hip. On the AP pelvis radiograph, displacement of the femoral head lateral to which of the following radiographic lines indicates abnormal lateralization?

Explanation

Perkins' line is drawn vertically downwards from the lateral edge of the acetabulum, perpendicular to Hilgenreiner's line. In a normal hip, the femoral head should sit entirely in the inferomedial quadrant created by these intersecting lines; lateral displacement crosses Perkins' line.

Question 77

An 8-year-old boy is brought to the clinic 2 years after undergoing closed reduction and percutaneous pinning of a Gartland III supracondylar humerus fracture. The parents are concerned about the cosmetic appearance of his arm, which shows a marked cubitus varus deformity. What is the most common cause of this deformity?

Explanation

Cubitus varus following a supracondylar fracture is almost always secondary to malunion rather than growth arrest. Failure to adequately correct medial impaction or residual internal rotation at the time of initial reduction leads to this common cosmetic deformity.

Question 78

A 12-year-old boy with a BMI in the 98th percentile presents with a 3-month history of ill-defined knee pain. The knee examination is unremarkable, but the affected hip exhibits obligate external rotation during passive flexion. Which radiographic finding on the AP pelvis is most characteristic of this condition?

Explanation

The clinical presentation is classic for a stable slipped capital femoral epiphysis (SCFE), demonstrating the Drehmann sign. Radiographically, Trethowan's sign is positive when the line of Klein (drawn along the superior femoral neck) fails to intersect the lateral aspect of the femoral epiphysis.

Question 79

A 2-year-old girl with neglected developmental dysplasia of the hip is scheduled for an open reduction via an anterior (Smith-Petersen) approach. Which of the following structures is NOT considered a primary anatomic obstacle to reduction in this condition?

Explanation

Primary obstacles to reduction in DDH include an inverted limbus, tight iliopsoas tendon, hypertrophied ligamentum teres, fibrofatty pulvinar, constricted inferior capsule, and a contracted transverse acetabular ligament. The gluteus medius is not an obstacle to concentric reduction.

Question 80

During preoperative planning for percutaneous pinning of a Gartland type III supracondylar humerus fracture, the biomechanical properties of different pin configurations are reviewed. Compared to two divergent lateral pins, a crossed-pin configuration (one medial, one lateral) provides statistically significant increased resistance to which of the following forces?

Explanation

Biomechanical studies have consistently shown that crossed pins offer superior resistance to torsional forces compared to two lateral pins. However, lateral pins are often preferred clinically to eliminate the risk of iatrogenic ulnar nerve injury associated with medial pin placement.

Question 81

A 14-year-old girl is 6 months post-operative from in situ pinning of a stable slipped capital femoral epiphysis (SCFE). She now presents with a stiff, painful hip. Examination reveals significant global restriction of range of motion. Radiographs demonstrate severe joint space narrowing, but the hardware is well-seated without joint penetration. What is the most likely diagnosis?

Explanation

Chondrolysis is a severe complication of SCFE characterized by acute cartilage necrosis, presenting with a painful, stiff hip and diffuse joint space narrowing on radiographs. While unrecognized pin penetration is a known cause, chondrolysis can also occur idiopathically after SCFE.

Question 82

A 4-week-old female infant, born breech, has a normal clinical hip examination. A screening ultrasound reveals an alpha angle of 45 degrees and a beta angle of 65 degrees. Based on the Graf classification, what is the most appropriate next step in management?

Explanation

An alpha angle of 45 degrees in a 4-week-old represents a Graf Type IIc or worse (alpha < 50 degrees), indicating significant dysplasia. Treatment with a Pavlik harness is indicated to promote proper acetabular development.

Question 83

A 7-year-old boy sustains a flexion-type supracondylar fracture of the humerus after falling onto a flexed elbow. Radiographs show anterior displacement of the distal fracture fragment. Which nerve is most commonly injured in this specific fracture pattern?

Explanation

Flexion-type supracondylar humerus fractures account for approximately 2-5% of cases and involve anterior displacement of the distal fragment. They are uniquely associated with a higher incidence of ulnar nerve injury, unlike extension types which typically injure the anterior interosseous nerve.

Question 84

The biomechanical failure that leads to a slipped capital femoral epiphysis (SCFE) occurs predominantly through which specific microscopic zone of the physis?

Explanation

In a slipped capital femoral epiphysis (SCFE), the mechanical slippage primarily occurs through the hypertrophic zone of the physis. This zone is structurally the weakest, especially during adolescent growth spurts when it becomes widened.

Question 85

A 9-month-old infant is undergoing a closed reduction and spica casting for developmental dysplasia of the hip (DDH). Intraoperatively, the surgeon establishes Ramsey's "safe zone" to minimize the risk of complications. This safe zone is defined by the arc of motion between the angle of maximum abduction and the angle of:

Explanation

Ramsey's safe zone for closed reduction in DDH is defined as the arc between the angle of maximum abduction (limited by adductor tightness) and the angle of minimum abduction where the hip redislocates. Maintaining the hip within this zone, while avoiding abduction greater than 60 degrees, minimizes the risk of avascular necrosis.

Question 86

A 13-year-old obese boy presents with severe left hip pain and inability to bear weight after a minor fall 2 days ago. Radiographs show a posterior and inferior displacement of the proximal femoral epiphysis. According to the Loder classification, what is the primary determinant of a poor prognosis in this patient?

Explanation

The Loder classification defines unstable SCFE by the inability to ambulate even with crutches. Unstable slips have a significantly higher risk of avascular necrosis (up to nearly 50%) compared to stable slips.

Question 87

A 6-week-old female is being treated with a Pavlik harness for a dislocated left hip. During a follow-up visit at 2 weeks, the mother notes the child is no longer kicking the left leg. Examination reveals decreased active knee extension on the left. What is the most appropriate next step in management?

Explanation

Decreased active knee extension indicates a femoral nerve palsy, a known complication of extreme hyperflexion in a Pavlik harness. The harness should be discontinued temporarily until neurologic function returns.

Question 88

A 6-year-old boy sustains a Gartland type III extension-type supracondylar humerus fracture. On presentation, his hand is pink and warm, but the radial pulse is nonpalpable. After closed reduction and percutaneous pinning, the hand remains pink and warm, but the pulse is still absent. What is the most appropriate next step in management?

Explanation

A "pink, pulseless" hand after reduction of a supracondylar fracture typically indicates adequate collateral circulation. The standard of care is close clinical observation rather than immediate surgical exploration if perfusion is adequate.

Question 89

A 12-year-old boy with chronic renal failure presents with a stable right slipped capital femoral epiphysis (SCFE). Which of the following is the strongest indication for prophylactic pinning of the contralateral, asymptomatic hip in this patient?

Explanation

Endocrine disorders and chronic renal failure are strong risk factors for bilateral SCFE. Prophylactic fixation of the contralateral hip is highly recommended in these populations due to the high risk of subsequent slip.

Question 90

A 5-year-old girl falls from monkey bars and sustains a displaced extension-type supracondylar humerus fracture. Examination reveals she is unable to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Which nerve is most likely injured?

Explanation

The anterior interosseous nerve (AIN), a branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures. Injury presents as the inability to make an "OK" sign due to loss of FPL and FDP function to the index finger.

Question 91

An 18-month-old girl presents with a painless limp. Examination reveals a positive Galeazzi sign and limited abduction of the right hip. Radiographs confirm a developmental dislocation of the right hip. What is the most appropriate initial surgical management?

Explanation

In children over 18 months of age with a completely dislocated hip, open reduction is generally required. Pelvic and/or femoral osteotomies are frequently added to correct secondary bony dysplasia and stabilize the joint.

Question 92

A 14-year-old boy complains of vague right knee pain for 3 months. Hip examination reveals that as the right hip is passively flexed, it obligately moves into external rotation and abduction. This clinical finding is most consistent with which of the following diagnoses?

Explanation

The Drehmann sign is the obligate external rotation and abduction of the hip during passive flexion. It is a classic physical examination finding in patients with a slipped capital femoral epiphysis.

Question 93

A 7-year-old boy presents with a severely displaced supracondylar humerus fracture. The overlying skin on the anterior distal arm exhibits a distinct dimple or "pucker" sign. This finding strongly suggests interposition of which of the following structures?

Explanation

An anterior skin pucker sign indicates that the proximal fracture fragment has penetrated the brachialis muscle and is tethering the deep dermis. This often makes closed reduction difficult and suggests a higher risk of neurovascular entrapment.

Question 94

In the radiographic evaluation of an infant treated for developmental dysplasia of the hip (DDH), the acetabular index is monitored sequentially. By what age should the acetabular index typically normalize to less than 20 degrees in a successfully treated child?

Explanation

The acetabular index measures the slope of the cartilaginous acetabular roof. It should steadily decrease with successful reduction and typically normalizes to less than 20-25 degrees by 2 years of age.

Question 95

A 9-year-old boy healed from a supracondylar humerus fracture sustained at age 5 but developed a prominent cubitus varus deformity. Which of the following statements regarding cubitus varus following supracondylar humerus fractures is true?

Explanation

Cubitus varus ("gunstock deformity") is usually caused by malunion (internal rotation and medial tilt), not growth arrest. While cosmetically displeasing, it rarely affects elbow range of motion or function.

Question 96

A 15-year-old boy is evaluated for worsening hip stiffness and pain 6 months after in situ pinning of a slipped capital femoral epiphysis (SCFE). Radiographs reveal concentric narrowing of the hip joint space to less than 3 mm and subchondral sclerosis. What is the most likely cause of these findings?

Explanation

Chondrolysis is characterized by acute cartilage destruction and concentric joint space narrowing (typically <3 mm) following SCFE. It presents with stiffness and pain and is heavily associated with unrecognized intra-articular hardware penetration.

Question 97

A newborn girl with arthrogryposis multiplex congenita is found to have bilateral rigid, high-riding hip dislocations. Unlike typical developmental dysplasia of the hip (DDH), what is the most appropriate initial management for her hip pathology?

Explanation

Teratologic hip dislocations in conditions like arthrogryposis are extremely rigid and do not respond to a Pavlik harness. Management is complex and often delayed until walking potential is clearer, frequently requiring open reduction later in life.

Question 98

A 12-year-old boy presents with an acute, unstable slipped capital femoral epiphysis (SCFE). The surgeon is planning surgical fixation. Which of the following maneuvers is strictly contraindicated during the surgical positioning and fixation of this patient?

Explanation

Forceful or non-gentle closed reduction of an unstable SCFE is contraindicated as it significantly increases the risk of avascular necrosis (AVN) by disrupting the tenuous epiphyseal blood supply. Most surgeons accept the deformity or allow only incidental reduction.

Question 99

A 6-year-old boy undergoes crossed-pin fixation (one lateral, one medial) for a displaced supracondylar humerus fracture. Postoperatively, he exhibits clawing of the ring and small fingers and numbness over the volar aspect of the fifth digit. The most likely etiology of this deficit is:

Explanation

Ulnar nerve injury is the most common iatrogenic nerve injury during crossed-pin fixation of supracondylar fractures, typically caused by the medial pin. Failing to protect the nerve through a mini-open incision increases this risk.

Question 100

During a closed reduction of a developmental dysplasia of the hip (DDH) under general anesthesia, an arthrogram is performed. The hip reduces in flexion and abduction but re-dislocates when adducted past 40 degrees of abduction. The hip cannot be safely abducted past 55 degrees due to significant adductor tension. Which of the following best describes this situation?

Explanation

The "safe zone of Ramsey" is the arc between the angle of re-dislocation and the angle of maximal safe abduction. A narrow safe zone (<20 degrees) increases the risk of AVN if immobilized in extreme abduction; performing an adductor tenotomy widens the safe zone.

AAOS Pediatric Orthopedic MCQs (Set 2): DDH, SCFE & Spinal Deformities | Board Review

AAOS Pediatric Orthopedics MCQs (Set 4): DDH, SCFE & Supracondylar Humerus | Board Review

Key Takeaway

AAOS Pediatric Orthopedics MCQs (Set 4): DDH, SCFE & Supracondylar Humerus | Board Review

Chapter Index