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1. General Principles & Basic Science MCQs

Practice Set 182 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 3621

Topic: Biomechanics & Biomaterials

What mechanism is most likely responsible for the initiation of mechanical failure seen at the midstem modular junction of modular revision hip stems?

. Fretting fatigue
. Etching
. Crevice corrosion
. Abrasive wear

Correct Answer & Explanation

. Fretting fatigue

Explanation

The junction fracture is initiated in a fretting-fatigue mechanism and completed by a bending moment. Fretting fatigue occurs when contacting components experience cyclic loads while small oscillatory motion occurs between them. This increases tensile and shear stress, leading to small flaws that result in crack propagation. In the referenced study no evidence of corrosion was seen because there was no etching, pitting, corrosion products, or chloride formation. Etching is a finding seen in corrosion. Abrasive wear occurs when a rough surface glides against a softer surface. It is generally seen in polyethylene wear from bone or cement in third-body wear. Risk factors for stem breakage include high body mass index and lack of proximal bone support at the modular stem-junction area.

Question 3622

Topic: Biology, Genetics & Bone Healing
A healthy 52-year-old woman is seeking professional advice about management of osteoporosis. She has no risk factors for osteoporosis. What is the best recommendation for bone health for this patient?
. Bone mineral density testing performed semiannually
. No treatment
. A healthy diet high in calcium
. 1,000 to 1,500 mg calcium supplement plus 400 to 800 IU vitamin D per day
. Estrogen therapy

Correct Answer & Explanation

. 1,000 to 1,500 mg calcium supplement plus 400 to 800 IU vitamin D per day

Explanation

Women older than age 50 years should receive daily supplementation with calcium and vitamin D to help preserve bone density. Bone mineral density testing is recommended for women age 65 years or older and postmenopausal women with at least one risk factor for osteoporotic fractures: prior fragility fracture, low estrogen levels, premature menopause, long-term secondary amenorrhea, glucocorticoid therapy, maternal history of hip fracture, or low body mass index. Hormone therapy is not approved for the treatment of osteoporosis.

Question 3623

Topic: 1. General Principles & Basic Science

In articular cartilage, Interleukin 1 (IL-1) increases

. matrix metalloproteinase.
. proteoglycan synthesis.
. collagen production.
. nitric oxide synthetase.

Correct Answer & Explanation

. matrix metalloproteinase.

Explanation

IL-1 stimulates matrix metalloproteinase that directly degrade cartilage. It also stimulates enzymes such as cyclooxygenase 2 and nitric oxide synthetase, which further cause tissue catabolism and damage. Glucosamine has anabolic effects on proteoglycan synthesis and can also prevent tissue catabolism by preventing an IL-1 beta-induced decrease in proteoglycan synthesis. Transforming growth factor beta has chondroprotective functions and has been shown to increase both collagen and proteoglycan synthesis while inhibiting matrix degradation and cell proliferation. Insulin-like growth factor 1 (IGF1) is produced by articular chondrocytes and increased collagen and proteoglycan synthesis. It has a role in the development of osteoarthritis. Decreased expression of IGF1 and increased binding proteins decrease the availability of the growth factors, accelerating tissue catabolism in arthritic cartilage.

Question 3624

Topic: 1. General Principles & Basic Science

A 20-year-old man involved in a motor vehicle accident is brought to the emergency department with a C6-7 unilateral facet dislocation. His neurologic examination reveals a focal left-sided C7 nerve root palsy. He is awake and cooperative with questioning and has no other obvious traumatic injuries. What is the most appropriate treatment at this time? Review Topic

. Further imaging studies, including MRI
. An awake closed reduction with Gardner-Wells traction with neurologic examination
. Immobilization in a halo skeletal fixation for definitive treatment
. Closed reduction under general anesthesia
. Immediate open reduction and internal fixation in the surgical suite

Correct Answer & Explanation

. Further imaging studies, including MRI

Explanation

In the patient who is neurologically intact or has an incomplete injury from a cervical facet dislocation, a closed reduction with weighted tong traction is appropriate when the patient is awake, alert, and cooperative. Although there is a risk that a cervical facet dislocation could occur with an underlying cervical disk herniation, Vaccaro and associates have shown that closed reduction can be safely carried out in the awake, responsive patient. Closed reduction can be performed in the emergency department with traction with skull tongs or a halo ring. A slow stepwise application of weight is added until a reduction is achieved. Any worsening of the neurologic status of the patient requires immediate termination of the closed reduction and further diagnostic imaging before proceeding with further treatment.

Question 3625

Topic: 1. General Principles & Basic Science
Type II collagen in nondiseased adult human articular cartilage has a half-life that is generally
. several months.
. 6 months.
. 1 year.
. 10 years.
. more than 25 years.

Correct Answer & Explanation

. more than 25 years.

Explanation

DISCUSSION: Type II collagen in articular cartilage is amazingly stable. This is important to know because matrix homeostasis generally is associated with minimal synthesis and degradation of type II collagen. Passive glycation has a consistent rate and occurs over decades. The relative amount of glycation in cartilage with age has been used as a measure of stability. Also, the rate of racemization of aspartic acid from the L to D form occurs spontaneously at a very slow rate. The relative stability of collagen can be estimated by calculating the percentage of D aspartic acid per dry weight of type II collagen.

Question 3626

Topic: 1. General Principles & Basic Science

When the data are normally distributed, what statistical test is best used to compare means of three or more independent groups?

. Kaplan-Meier analysis
. Analysis of variance
. Chi-square test
. Meta-analysis
. Log rank test

Correct Answer & Explanation

. Kaplan-Meier analysis

Explanation

Analysis of variance (ANOVA) is used to compare means of three or more independent groups with continuous variables that are normally distributed (eg, age, weight, height, etc). Kaplan-Meier analysis is used to analyze survivorship of subjects or products in an outcome study. Chi-square test is used to compare proportions for categorical variables. Meta-analysis is a systematic review method to analyze combined results of several independent studies, usually randomized clinical trials. Log rank is a statistical test to compare survivorship.

Question 3627

Topic: 1. General Principles & Basic Science

A 16-year-old boy who is a competitive basketball player (Figure 43)

. Ligamentous reconstruction
. Meniscal repair
. Meniscectomy39
. Immobilization

Correct Answer & Explanation

. Ligamentous reconstruction

Explanation

Question 3628

Topic: Surgical Anatomy & Approaches
The brachialis muscle is innervated by what two nerves?
. Radial and musculocutaneous
. Lateral and medial brachial cutaneous
. Axillary and medial and lateral pectoral
. Radial and ulnar
. Ulnar and musculocutaneous

Correct Answer & Explanation

. Radial and musculocutaneous

Explanation

The brachialis is innervated by two nerves: medially, the musculocutaneous nerve; laterally, the radial nerve. The muscle is split longitudinally to approach the humerus anteriorly.

Question 3629

Topic: Biomechanics & Biomaterials
A 45-year-old man has severe pain in both feet after his boots become wet while hunting. Examination 3 hours after the onset of symptoms reveals that his feet are cold to touch and the skin appears blanched. Management should consist of
. slow rewarming in cool 77 degrees F (25 degrees C) water.
. rapid rewarming in a footbath at 104.0 degrees F to 107.6 degrees F (40 degrees C to 42 degrees C).
. rewarming in 98.6 degrees F (37 degrees C) water.
. heated blankets at 100.4 degrees F (38 degrees C).
. a heating pad at 104.0 degrees F (40 degrees C).

Correct Answer & Explanation

. rapid rewarming in a footbath at 104.0 degrees F to 107.6 degrees F (40 degrees C to 42 degrees C).

Explanation

The patient has frostbite involving both feet. Rapid rewarming in a protected environment is the initial treatment. A footbath with water at 104.0 degrees F to 107.6 degrees F (40 degrees C to 42 degrees C) is ideal.

Question 3630

Topic: 1. General Principles & Basic Science

The patient does well initially but returns for the 4-month postsurgical evaluation with ongoing stiffness and pain despite going to physical therapy twice weekly and working on motion at home. She is unable to bear weight comfortably. What is the best next step?

. Manipulate the knee under anesthesia
. Aspirate the knee for persistent hematoma to improve motion
. Obtain advanced imaging to evaluate the lesion and fixation
. Prescribe more intensive physical therapy 3 to 5 times a week to achieve motion

Correct Answer & Explanation

. Manipulate the knee under anesthesia

Explanation

DISCUSSIONIn a skeletally immature patient with OCD and minor symptoms, the lesion can be observed and healing obtained with activity limitations if the cartilage is stable (but this cannot be determined radiographically or clinically). Activity restriction and serial follow-up are appropriate if an MRI reveals a stable lesion. MRI is indicated when there is concern that a lesion may be unstable. Surgical treatment depends on MRI findings.Observation is recommended for OCD lesions in growing patients for 6 months because healing has been observed. Early surgical procedures, although they may be needed in the future, are not appropriate for patients with well-controlled symptoms.If symptoms continue for longer than 6 months, arthroscopic drilling is not indicated for unstable OCD. The appropriate treatment is OCD fixation. Debridement is not appropriate with a stable lesion.Evaluation of the fixation and stability of the lesion with advanced imaging after weight bearing and therapy initiation is the most appropriate option. Manipulating the knee without determining whether the stiffness is attributable to subsidence of the fixation or mechanical block is not appropriate. After 4 months, aspiration of a hematoma (if still present) would not yield much benefit. More therapy is not likely to be useful when a patient is attending therapy regularly and working on a home program.

Question 3631

Topic: Infection, Pharmacology & VTE

Bacterial resistance to antibiotics in biofilm is an example of Review Topic

. avoidance.
. decreased susceptibility.
. inactivation.
. mutation.

Correct Answer & Explanation

. avoidance.

Explanation

Three basic mechanisms of antibiotic resistance have been identified: avoidance, decreased susceptibility, and inactivation. Biofilm formation is a classic example of avoidance, whereby the biofilm creates a physical barrier to the antibiotic. Bacteria can decrease their susceptibility to antibiotics by mutating the antibiotic target or generating a mechanism to inactivate the antibiotic. Biofilm formation develops when a sufficient mass of bacteria forms on a surface. The cell-to-cell signaling becomes sufficient to activate transcription of genes needed for biofilm formation in a processknown as quorum sensing. Once the bacteria produce a mature biofilm, they enter a greatly reduced or stationary phase of growth. Lastly, high-shear environments seem to stimulate biofilm production.

Question 3632

Topic: 1. General Principles & Basic Science
Which of the following is considered a physiologic effect of anemia?
. Decreased heart rate
. Decreased coronary artery flow requirement
. Increased cardiac output
. Increased peripheral resistance
. Increased blood viscosity

Correct Answer & Explanation

. Increased cardiac output

Explanation

The expected physiologic effects of anemia include an increased heart rate and increased cardiac output. The coronary blood flow requirement increases. There is a decrease in peripheral resistance and blood viscosity.

Question 3633

Topic: 1. General Principles & Basic Science

The force generated by a muscle is most highly dependent on its

. cross-sectional area.
. fiber type.
. length.
. morphology.
. level of conditioning.

Correct Answer & Explanation

. cross-sectional area.

Explanation

The cross-sectional area of a muscle determines to a great extent the force generated by the muscle. The force of a muscle contraction is controlled by the amount of myofibrils that contract; the greater the amount of contracting myofibrils, the greater the force of contraction. Fiber types have less to do with the force of contraction and more to do with the duration and speed of contraction. Muscle length affects contraction force through the Blix curve. The morphology of a muscle can affect the cross-sectional area by varying the angle of the fibers in relation to the force vector. Conditioning mostly affects duration and fatigability.

Question 3634

Topic: 1. General Principles & Basic Science
  • Which of the following acetabular/femoral head components would be expected to show an optimal combination of linear and volumetric wear?
. mm femoral head in combination with a metal-backed polyethylene component
. mm femoral head in combination with an all-polyethylene acetabular component
. mm femoral head in combination with a metal-backed polyethylene component
. mm femoral head in combination with an all-polyethylene component
. mm femoral head in combination with a metal-backed polyethylene component

Correct Answer & Explanation

. mm femoral head in combination with a metal-backed polyethylene component

Explanation

The size of the femoral head and the calculated mean annual rate of volumetric wear has a significant relationship. Rate of volumetric wear was highest in assoc with 32 mm femoral lowest in assoc with 22 mm heads. The predominant mechanisms of wear of the polyethylene were abrasion and adhesions rather than fatigue-cracking or delamination on the subsurface. Decreased thickness of the polyethylene has an adverse effect on the rate of wear of the metal-backed components. Rate of linear wear is highest in assoc. with 22-mm heads and lowest in relation to 32-mm heads, so the optimal size of a femoral head should be 28 mm where there is minimal linear and volumetric wear.

Question 3635

Topic: Infection, Pharmacology & VTE
The abdominal radiograph obtained from a patient who experiences nausea and abdominal tightness 48 hours following left total knee arthroplasty performed under general anesthesia. She received 24 hours of cefazolin antibiotic prophylaxis and a patient-controlled analgesia narcotic pump for pain management. She has been receiving warfarin for thromboembolic prophylaxis. Her severe abdominal distension and markedly decreased bowel sounds are most likely secondary to the administration of:
. general anesthesia.
. antibiotics.
. warfarin.
. narcotics.

Correct Answer & Explanation

. narcotics.

Explanation

DISCUSSION: The radiograph reveals severe intestinal dilatation, which has occurred as the result of acute colonic pseudo-obstruction and is associated with excessive narcotic administration following total joint arthroplasty. Anesthetic type, antibiotic administration, and warfarin have not been associated with this obstruction. Electrolyte imbalances such as hypokalemia have been associated with postsurgical acute colonic pseudo-obstruction.

Question 3636

Topic: Infection, Pharmacology & VTE

Corticosteroids inhibit the formation of effectors of the inflammatory pathway via inhibition of

. phospholipase A2.
. lipoxygenase.
. cyclooxygenase-1.
. thromboxane A2.
. prostacyclin.

Correct Answer & Explanation

. phospholipase A2.

Explanation

Corticosteroids prevent the formation of the pre-inflammatory mediator arachidonic acid from cell membrane phospholipids by inhibiting phospholipase A2. This inhibition prevents the earliest step in the inflammatory cascade. Arachidonic acid proceeds through the lipoxygenase pathway to produce leukotrienes, responsible for autocrine and paracrine signaling, or through the cyclooxygenase pathway (either COX-1 or COX-2) to produce prostaglandins. Thromboxane A2, present in platelets, activates phospholipase C which causes cellular effects resulting in platelet aggregation. Prostacyclin and thromboxane A2 work as antagonists. Prostacyclin is released from endothelial cells, inhibiting platelet aggregation and causing vasodilation.

Question 3637

Topic: 1. General Principles & Basic Science
What changes in muscle physiology would be expected in an athlete who begins a rigorous aerobic program for an upcoming marathon?
. Hypertrophy of type I muscle fibers
. Reduced fatigue resistance
. Decreased capillary density
. Decreased VO2 max
. Decreased mitochondrial density per muscle cell

Correct Answer & Explanation

. Hypertrophy of type I muscle fibers

Explanation

DISCUSSION: Muscle fibers can be categorized grossly into two types. Type I muscle, also known as slow-twitch muscle, is responsible for aerobic, oxidative muscle metabolism. It has a much lower strength and speed of contraction than fast-twitch type II muscle but is significantly more fatigue resistant. With training for endurance sports, the type I muscle undergoes adaptive changes to the increased stress. Increases in capillary density, oxidative capacity, mitochondrial density, and subsequent fatigue resistance are all observed changes.

Question 3638

Topic: 1. General Principles & Basic Science
When performing a saline load test to evaluate for a traumatic arthrotomy of the knee, a minimum of how much saline should be utilized?
. 30 mL
. 50 mL
. 75 mL
. 100 mL
. 155 mL

Correct Answer & Explanation

. 155 mL

Explanation

DISCUSSION: A saline load test is commonly utilized to evaluate for intraarticular penetration of superficial lacerations (traumatic arthrotomies). In this technique, a large gauge needle is used (18 ga) and saline is injected into the knee with passive ROM provided. Saline egress from the soft tissue injury is a positive test (traumatic arthrotomy present). The study by Nord et al found that the volumes of saline that were needed in order to effectively diagnose 75%, 90%, 95%, and 99% of the knee arthrotomies were 110, 145, 155, and 175 mL, respectively. The other referenced study by Keese et al found that 50 mL of saline successfully identified only 46% of known knee arthrotomies and that 194 mL was needed to reach a 95% identification rate.

Question 3639

Topic: 1. General Principles & Basic Science
Which of the following statements most accurately describes the layers of articular cartilage?
. The superficial zone has condensed proteoglycan and sparse collagen.
. The intermediate zone transition is the thinnest layer and the chondrocytes are oriented tangentially.
. The basal zone (middle, radial, deep) contains flattened chondrocytes.
. Tidemark is found only in joints and not in the growing cartilage cap of an enchondroma.
. Tidemark is more prominent in newborn joints.

Correct Answer & Explanation

. Tidemark is found only in joints and not in the growing cartilage cap of an enchondroma.

Explanation

DISCUSSION: Normal articular cartilage is composed of three zones that are based on the shape of the chondrocytes and the distribution of the type II collagen. The tangential zone has flattened chondrocytes, condensed collagen fibers, and sparse proteoglycan. The intermediate zone is the thickest layer with round chondrocytes oriented in perpendicular or vertical columns paralleling the collagen fibers. The basal layer is deepest with round chondrocytes. The tidemark is deep to the basal layer and separates the true articular cartilage from the deeper cartilage that is a remnant of the cartilage anlage, which participated in endochondral ossification during longitudinal growth in childhood. The tidemark divides the superficial uncalcified cartilage from the deeper calcified cartilage and also is the division between nutritional sources for the chondrocytes. The tidemark is the zone in which chondrocyte renewal took place in childhood. The tidemark is found only in joints and not in the cap of an enchondroma. It is seen most prominently in the adult, nongrowing joint. REFERENCE: Schiller AL: Pathology of osteoarthritis, in Kuettner KE, Goldberg VM (eds): Osteoarthritic Disorders. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1995, pp 95-101.

Question 3640

Topic: 1. General Principles & Basic Science

To be an expert orthopaedic witness in a trial, an orthopaedic surgeon must

. Demonstrate competence in the subject of the case
. Be fellowship trained in the subject of the case
. Be paid on a contingency basis
. Be board certified by the American Board of Orthopaedic Surgery
. Have been involved in the case as a consultant

Correct Answer & Explanation

. Demonstrate competence in the subject of the case

Explanation

An expert witness need not be involved in the case, be certified, or fellowship trained. The only requirement is that the surgeon show competency in the subject matter. There are very nonspecific requirements to be called to the stand as an “expert witness”.

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