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1. General Principles & Basic Science MCQs

Practice Set 163 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 3241

Topic: 1. General Principles & Basic Science
Figures 25a and 25b show the radiograph and MRI scan of a 7 1/2-year-old boy who has been limping for 1 year. His pain has worsened over the past 2 weeks, and his parents note swelling over the dorsum of the foot for the past 4 days. Examination reveals no fever, and laboratory studies show a WBC of 6,700/mmยณ, an erythrocyte sedimentation rate of 26 mm/h, and a normal C-reactive protein level. What is the most likely diagnosis?
. Acute hematogenous osteomyelitis
. Kohlerโ€™s disease
. Tarsal coalition
. Tuberculosis
. Lisfranc fracture-dislocation

Correct Answer & Explanation

. Tuberculosis

Explanation

DISCUSSION: The diagnosis of tuberculous osteomyelitis in children is often delayed. In one series of 23 children, the average interval between the onset of symptoms and definite diagnosis was 4.3 months. In these patients, the presenting signs and symptoms were found to be mild, with the most common signs being localized swelling (69.6%) and a painful disability of the involved limbs (65.2%). A mild elevation of the erythrocyte sedimentation rate may be present, but the C-reactive protein level is usually normal. In patients who have osteoarticular tuberculosis, an MRI scan generally shows large intra-articular effusions, periarticular osteoporosis, and gross thickening of the synovial membrane. Differential diagnosis between tuberculosis and pyogenic arthritis is difficult, and an accurate diagnosis usually requires biopsy of synovial tissue. Aspiration of synovial fluid often results in insufficient information to make a diagnosis. Treatment generally consists of surgical debridement and combined antituberculous chemotherapy with isoniazid, ethambutol, and rifampin. REFERENCES: Wang MN, Chen WM, Lee KS, Chin LS, Lo WH: Tuberculous osteomyelitis in young children. J Pediatr Orthop 1999;19:151-155. Watts HG, Lifeso RM: Tuberculosis of the bones and joints. J Bone Joint Surg Am 1996;78:288-298.

Question 3242

Topic: Biology, Genetics & Bone Healing

Receptor activator of nuclear factor kappa b (RANKL) and macrophage colony stimulating factor (MCSF) signaling pathways are necessary for the formation of multinucleated osteoclasts that resorb bone. Which of the following cells are known to produce RANKL?

. Macrophages
. Osteoclasts
. Osteoblasts
. Monocytes
. Histiocytes

Correct Answer & Explanation

. Osteoclasts

Explanation

Osteoclast differentiation and function depend on the establishment of specific patterns of gene expression achieved through networks of transcription factors activated by osteoclastogenic cytokines such as RANKL and MCSF. RANKL and MCSF are produced by osteoblasts and T cells. Key transcriptional factors responsible for osteoclatogenesis require activation of transcriptional factors such as PU.1, NF-kappaB, AP-1, NFATc1, Mitf, Myc, and Src in osteoclast precursors that are of monocyte/macrophage origin.

Question 3243

Topic: 1. General Principles & Basic Science
Figures 34a and 34b show the axial and sagittal MRI scans of a 36-year-old man who reports the insidious onset of pain in the right shoulder. What is the most appropriate description of the acromial morphology?
. Type I acromion
. Type III acromion
. Meso os acromiale
. Meta os acromiale
. Pre os acromiale

Correct Answer & Explanation

. Meso os acromiale

Explanation

DISCUSSION: The MRI scans reveal a meso os acromiale with edema at the site in a skeletally mature patient. REFERENCES: Sher JS: Anatomy, biomechanics, and pathophysiology of rotator cuff disease, in Iannotti JP, Williams GR (eds): Disorders of the Shoulder: Diagnosis and Management. Philadelphia, PA, Lippincott Williams & Wilkins, 1999, p 23. Sammarco VJ: Os acromiale: Frequency, anatomy, and clinical implications. J Bone Joint Surg Am 2000;82:394-400.

Question 3244

Topic: Infection, Pharmacology & VTE

What is the most common causative bacteria in septic arthritis in children? Review Topic

. Staphylococcus aureus
. Brucella melitensis
. Haemophilus influenzae
. Kingella kingae
. Streptococcus pneumonia

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

The spectrum of causative bacteria and frequency of occurrence of specific pathogens in septic arthritis are similar to those seen in osteomyelitis, with Staphylococcus aureus being the most common. Other common causative organisms include Kingella Kingae, Streptococcus pneumonia, Klebsiella species, Salmonella, Brucella melitensis, and Haemophilus influenzae.

Question 3245

Topic: 1. General Principles & Basic Science

Implants composed of polylactic acid are excreted by what system after they are absorbed?

. Hepatic
. Renal
. Respiratory
. Gastrointestinal

Correct Answer & Explanation

. Respiratory

Explanation

Polylactic acid suture and suture anchors are popular bioabsorbable orthopaedic implants. This material undergoes hydrolysis of the ester background in vivo. Resulting lactic acid enters the tricarboxylic acid (Krebs) cycle and is excreted as carbon dioxide by the lungs. Polyglycolic acid and poly(p-dioxanone) may also be excreted by the kidneys.

Question 3246

Topic: Biology, Genetics & Bone Healing

An 11-year-old boy reports the acute onset of elbow pain and swelling after pushing his brother. The patient's mother and a younger sibling have experienced numerous fractures. You note that the patient and his mother have blue sclera and normal-appearing teeth. A radiograph of the elbow is shown in Figure 60. This patient's disorder is most likely the result of Review Topic

. parental abuse.
. abnormal osteoclast function.
. defective N-Ac-Gal-6 sulfate sulfatase enzyme.
. a quantitative defect of type I collagen synthesis.
. vitamin D deficiency.

Correct Answer & Explanation

. a quantitative defect of type I collagen synthesis.

Explanation

Osteogenesis imperfecta (OI) is a genetically determined disorder of type I collagen synthesis characterized by bone fragility. This patient sustained a displaced fracture of the olecranon apophysis after relatively minor trauma. Physical examination reveals distinctly blue sclera. His mother and younger sibling have experienced numerous fractures suggesting a family history of bone fragility. The patient's history, clinical features, and family history are consistent with a diagnosis of Sillence type I-A OI. Type I OI is the mildest and most common form. Inheritance is autosomal dominant.Type I is subclassified into the A type (absence of dentinogenesis imperfecta) and B type (presence of dentinogenesis imperfecta). These individuals have blue sclerae, and although the initial fracture usually occurs in the preschool years, it may occur at any age. Furthermore, olecranon apophyseal fractures that occur after relatively minor trauma have been associated with type I OI. Cells from individuals with type I OI largely demonstrate a quantitative defect of type I collagen; they synthesize and secrete about half the normal amount of type I procollagen. In this patient, there are no indications that the child has been subjected to abuse. Radiographs of the elbow show no evidence of osteopetrosis (due to abnormal osteoclast function) or rickets (due to a deficiency of vitamin D). Morquio syndrome (characterized by a defect of the enzyme N-Ac-Gal-6 sulfate sulfatase) is not associated with blue sclera.

Question 3247

Topic: Biology, Genetics & Bone Healing

A 35-year-old male is undergoing tibial bone transport with a circular external fixator for a 6 cm segmental defect. The transport segment has successfully reached the docking site. After 8 weeks, radiographs show a persistent lucency at the docking site with no bridging callus. What is the most appropriate next step to stimulate union?

. Increase the daily rate of bone transport
. Systemic administration of bisphosphonates
. Iliac crest bone grafting and compression at the docking site
. Immediate exchange to an intramedullary nail
. Perform a partial fibulectomy to allow settling

Correct Answer & Explanation

. Iliac crest bone grafting and compression at the docking site

Explanation

In distraction osteogenesis / bone transport, delayed union or nonunion at the docking site is a common complication. The standard of care to achieve union when the transport segment reaches the target but fails to consolidate is preparation of the docking site ends, autologous bone grafting (e.g., from the iliac crest), and applying compression across the docking site.

Question 3248

Topic: 1. General Principles & Basic Science
A surgeon performs a medial opening wedge high tibial osteotomy (HTO) to correct genu varum. During the procedure, the anterior and posterior cortices of the medial wedge are distracted equally using identical wedges. Given the triangular cross-sectional anatomy of the proximal tibia, what unintended sagittal plane change will occur?
. Decreased posterior tibial slope
. Increased posterior tibial slope
. Conversion to an anterior tibial slope
. No change in the sagittal slope
. Severe coronal plane translation

Correct Answer & Explanation

. Increased posterior tibial slope

Explanation

The proximal tibia is triangular, being wider posteriorly than anteriorly. If a medial opening wedge is opened equally anteriorly and posteriorly, the anterior opening is proportionally larger relative to the narrow anterior dimension. This effectively flexes the proximal fragment, leading to an unwanted INCREASE in the posterior tibial slope. To maintain the native slope, the osteotomy gap must typically be opened twice as much posteriorly as anteriorly.

Question 3249

Topic: 1. General Principles & Basic Science

When planning a multiplanar deformity correction using a 6-axis hexapod circular external fixator (such as a Taylor Spatial Frame), the computer software requires accurate 'mounting parameters' to calculate the strut adjustments. Which of the following correctly defines the mounting parameters?

. The position of the deformity apex relative to the joint line
. The size and length of the specific struts used in the frame construction
. The spatial relationship between the reference ring and the true mechanical axis of the bone segment
. The linear distance between the proximal and distal fixation rings
. The daily rate and rhythm of strut adjustment required for correction

Correct Answer & Explanation

. The spatial relationship between the reference ring and the true mechanical axis of the bone segment

Explanation

In hexapod circular frame software, 'mounting parameters' define the exact position and orientation of the reference ring in three-dimensional space relative to the corresponding reference bone fragment. This includes AP view translation, lateral view translation, and axial plane rotation relative to the bone's true mechanical/anatomical axis.

Question 3250

Topic: Biomechanics & Biomaterials

In the process of manufacturing highly cross-linked polyethylene (HXLPE) for total joint arthroplasty, the material is irradiated to create cross-links. Following irradiation, the polyethylene undergoes a thermal treatment known as 'remelting' (heating above the melting point of 135ยฐC). What is the primary mechanical or chemical trade-off of the remelting process compared to 'annealing' (heating below the melting point)?

. Remelting eliminates all residual free radicals but decreases fatigue strength and fracture toughness
. Remelting preserves residual free radicals but significantly increases yield strength
. Remelting increases the crystallinity of the polyethylene, making it highly resistant to crack propagation
. Remelting prevents oxidation but severely increases the adhesive wear rate
. Remelting has no effect on free radicals but increases the melting point of the material

Correct Answer & Explanation

. Remelting eliminates all residual free radicals but decreases fatigue strength and fracture toughness

Explanation

Irradiation of polyethylene generates free radicals that cause long-term oxidative degradation. Remelting (heating above the melting point) effectively extinguishes all free radicals, yielding excellent oxidation resistance. However, it decreases the crystallinity of the polymer, which reduces its yield strength, ultimate tensile strength, and fatigue crack propagation resistance. Annealing (below melting point) preserves crystallinity and mechanical strength but leaves some free radicals, risking future oxidation.

Question 3251

Topic: Biomechanics & Biomaterials

During deep flexion of a healthy, native human knee, distinct kinematic patterns are observed between the medial and lateral compartments. Which of the following best describes the normal kinematics of the femorotibial joint as the knee moves from extension into deep flexion?

. Symmetrical posterior rollback of both the medial and lateral femoral condyles
. Anterior translation of the lateral femoral condyle with external rotation of the tibia
. Minimal AP translation of the medial femoral condyle with significant posterior rollback of the lateral femoral condyle, resulting in internal tibial rotation
. Posterior translation of the medial femoral condyle while the lateral condyle acts as a fixed pivot, resulting in external tibial rotation
. Symmetrical anterior sliding of the femoral condyles to prevent impingement

Correct Answer & Explanation

. Minimal AP translation of the medial femoral condyle with significant posterior rollback of the lateral femoral condyle, resulting in internal tibial rotation

Explanation

In the native knee during flexion, the medial femoral condyle moves very little in the anteroposterior plane (often termed a 'medial pivot'), while the lateral femoral condyle undergoes significant posterior translation (rollback). Because the lateral side rolls back much more than the medial side, this relative movement causes the tibia to internally rotate relative to the femur during flexion.

Question 3252

Topic: Biology, Genetics & Bone Healing

A 40-year-old male is undergoing tibial lengthening via distraction osteogenesis using a circular Ilizarov external fixator. Following the corticotomy, there is a required waiting period before the commencement of distraction. What is the optimal 'latent period' in adults, and what is its primary biological purpose?

. 1-3 days; to prevent premature consolidation of the regenerate bone
. 7-10 days; to allow early capillary ingrowth and primitive callus formation before applying tension
. 14-21 days; to ensure full bridging of the periosteum prior to lengthening
. 24 hours; to maximize the local release of bone morphogenetic proteins (BMPs)
. 0 days (immediate distraction); to stimulate maximum inflammatory response

Correct Answer & Explanation

. 7-10 days; to allow early capillary ingrowth and primitive callus formation before applying tension

Explanation

The latent period is the time between the corticotomy/osteotomy and the initiation of distraction. In an adult undergoing tibial lengthening, the optimal latent period is typically 7 to 10 days. This allows the initial inflammatory phase to subside and permits the ingrowth of delicate capillaries and primitive mesenchymal tissue (early soft callus). If distraction begins too early (e.g., 0-3 days), the tissue is torn, leading to poor regenerate (hypotrophic). If it is too long, premature consolidation occurs.

Question 3253

Topic: 1. General Principles & Basic Science

According to Paley's rules of deformity correction, if the axis of correction (hinge) is placed at the Center of Rotation of Angulation (CORA) but the osteotomy is performed at a different level, which of the following describes the resulting geometric alignment?

. Pure angular correction without any translation of the bony fragments
. Angular correction combined with translation of the bony fragments, maintaining a colinear mechanical axis
. Angular correction combined with translation of the mechanical axis (axis deviation)
. Pure translation without angular correction
. Creation of a secondary CORA with paradoxical malalignment

Correct Answer & Explanation

. Angular correction combined with translation of the bony fragments, maintaining a colinear mechanical axis

Explanation

Paley's Rule 2 states that if the hinge (axis of correction) is placed at the CORA but the osteotomy is performed at a different level, the mechanical axis will be perfectly realigned, but the bony ends at the osteotomy site will undergo translation. Rule 1 (hinge and osteotomy at CORA) results in pure angulation. Rule 3 (hinge away from CORA) results in mechanical axis deviation.

Question 3254

Topic: 1. General Principles & Basic Science

When utilizing a Taylor Spatial Frame (hexapod external fixator) for complex deformity correction, accurate data entry into the software is critical. What do the 'mounting parameters' specifically describe?

. The location of the hardware origin relative to the Center of Rotation of Angulation (CORA)
. The position of the reference ring relative to the origin of the reference bone fragment
. The desired daily rate of angular correction and distraction
. The strut lengths required to achieve final hardware removal
. The anatomic location of the osteotomy site relative to the joint line

Correct Answer & Explanation

. The position of the reference ring relative to the origin of the reference bone fragment

Explanation

In the software of a hexapod circular fixator like the Taylor Spatial Frame, 'mounting parameters' dictate exactly where the hardware (specifically the reference ring) is located in 3D space relative to the reference bone fragment (origin). The other parameters include deformity parameters (describing the bone segments relative to each other) and frame parameters (size of rings and struts).

Question 3255

Topic: 1. General Principles & Basic Science

A 12-year-old boy undergoes resection of a symptomatic calcaneonavicular coalition. To minimize the risk of coalition recurrence, the surgeon plans to interpose tissue into the resection gap. Which of the following is the most commonly utilized autogenous tissue for this specific interposition?

. Extensor digitorum brevis (EDB) muscle belly
. Flexor hallucis brevis (FHB) muscle belly
. Abductor hallucis muscle belly
. Peroneus brevis tendon slip
. Plantaris tendon

Correct Answer & Explanation

. Extensor digitorum brevis (EDB) muscle belly

Explanation

Following resection of a calcaneonavicular coalition, interposition of the extensor digitorum brevis (EDB) muscle belly or a free fat graft into the resection defect is the gold standard technique to prevent postoperative hematoma organization and recurrent ossification (re-coalition).

Question 3256

Topic: 1. General Principles & Basic Science

When utilizing a Taylor Spatial Frame (TSF) for complex limb deformity correction, the computer software requires the definition of a 'Reference Ring'. Which of the following best defines the reference ring in the planning process?

. The ring attached to the longest bone segment
. The ring that is mounted exactly orthogonal (90 degrees) to the reference bone segment
. The ring closest to the joint line
. The master ring that is always placed distally on the tibia
. The ring that requires the most strut adjustments during the turning schedule

Correct Answer & Explanation

. The ring that is mounted exactly orthogonal (90 degrees) to the reference bone segment

Explanation

In the TSF system, the Reference Ring is defined as the ring that is mounted orthogonally to the reference bone fragment. Deformity parameters and strut calculations are all based relative to this ring's position.

Question 3257

Topic: Infection, Pharmacology & VTE

A 30-year-old man has had severe knee pain and swelling for 1 week. He reports he previously had acromioclavicular joint pain that disappeared. He denies any fever. Aspiration of a cloudy fluid from the knee reveals a WBC count of greater than 50,000 with 90% polymorphonucleocytes. While awaiting culture results, what is the most appropriate action?

. Cortisone injection
. Open surgical debridement
. Immediate arthroscopic lavage
. Intravenous vancomycin for presumptive MRSA infection
. Obtain sexual activity history and select appropriate antibiotic

Correct Answer & Explanation

. Obtain sexual activity history and select appropriate antibiotic

Explanation

The patient has polyarticular gonococcal arthritis. Acute septic arthritis in adults can be separated into two major patient groups: young (age 15 to 40 years) healthy, sexually active patients with gonococcal pyogenic arthritis and elderly or immunocompromised patients with nongonococcal septic arthritis. In gonococcal septic arthritis, the infecting organism is Neisseria gonorrhea. It is the most common cause of acute joint infection in persons 15 to 40 years of age in the U.S. The clinical presentation is variable, but typically includes migratory polyarthralgias, fever, rash, urethral or vaginal discharge, and tenosynovitis. A patient with disseminated gonococcal infection may report few genital symptoms. More than 50% of these infections are polyarticular. Because patients with gonococcal septic arthritis are healthy, prompt antibiotic treatment results in a generally good prognosis. MRSA septic arthritis would be associated with fever, more rapid onset of symptoms, and is rarely polyarticular.

Question 3258

Topic: Biology, Genetics & Bone Healing

Smoking has been associated with lower fusion rates in both cervical and lumbar fusion. Which of the following statements best describes an explanation for these findings?

. Nicotine impairs osteoblast activity, thus interfering with bone remodeling.
. The effects of smoking on bone healing are multifactorial and not yet fully understood.
. The vasoconstrictive and platelet-activating properties of nicotine inhibit fracture healing.
. Nicotine inhibits the function of fibroblasts, red blood cells, and macrophages.
. Hydrogen cyanide inhibits oxidative metabolism at the cellular level.

Correct Answer & Explanation

. The effects of smoking on bone healing are multifactorial and not yet fully understood.

Explanation

Tobacco smoking is now the leading avoidable cause of morbidity and mortality in the United States. The musculoskeletal effects of smoking have been implicated in osteoporosis, low back pain, degenerative disk disease, poor wound healing, and delayed fusion and fracture healing. A number of studies have demonstrated the relationship between smoking and development of pseudarthrosis. Numerous studieshave been performed to offer an explanation of the mechanism mediating this effect. Whereas all of the above have been postulated as explanations, more recent studies have demonstrated that nicotine delivered via a transdermal patch significantly enhanced posterior spinal fusion in rabbits. Thus it appears that the effects of smoking on fracture healing are multifactorial and not yet fully understood.

Question 3259

Topic: Surgical Anatomy & Approaches
A patient wakes up with a foot drop following open reduction internal fixation of a posterior wall/posterior column acetabular fracture. What position of the leg causes the highest intraneural pressure in the sciatic nerve?
. hip and knee extension
. hip flexion to 90, knee extension
. hip internal rotation, knee flexion to 90
. hip and knee flexion to 90
. hip extension, knee flexion to 90

Correct Answer & Explanation

. hip flexion to 90, knee extension

Explanation

DISCUSSION: Borrelli et al examined the intraneural pressure of the sciatic nerve with the hip and knee in various different positions. They found that the "sciatic nerve appeared to exceed published critical thresholds for alterations of blood flow and neural function only when the hip was flexed to 90 degrees and the knee was fully extended." As a result, the leg is typically positioned with the hip in extension (or minimal flexion) and the knee in about 90 degrees of flexion when performing acetabular surgery via a posterior approach.

Question 3260

Topic: Surgical Anatomy & Approaches
Figure 44 shows the AP radiograph of the hip of a patient who underwent screw fixation of the acetabulum. Which of the following structures is at least risk for injury during screw placement in the acetabular component?
. Common iliac artery
. Superior gluteal artery
. Obturator artery
. Sciatic nerve
. External iliac vein

Correct Answer & Explanation

. Common iliac artery

Explanation

DISCUSSION: Acetabular screws are inserted to supplement fixation. The acetabular component can be divided into four quadrants. Anatomic studies have shown that screws placed in the anterior superior and anterior inferior quadrants of the cup may injure the external iliac vein and obturator artery, respectively. Posterior superior and posterior inferior placement (in screws greater than 25 mm) may injure the sciatic nerve or the superior gluteal artery. The common iliac artery is proximal to the acetabulum and is at least risk for injury from acetabular screw placement. REFERENCE: Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 207-215.

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