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1. General Principles & Basic Science MCQs

Practice Set 222 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 4421

Topic: Infection, Pharmacology & VTE

Figure 40 shows the AP radiograph of a 55-year-old man who reports left knee pain. Which of the following conditions is least likely to produce this radiographic presentation?

Anatomy 2002 Practice Questions: Set 3 (Solved) - Figure 22

. Hemochromatosis
. Alkaptonuria
. Wilson's disease
. Septic arthritis
. Calcium pyrophosphate dihydrate crystal deposition

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate crystal deposition

Explanation

The radiograph reveals densities within the articular cartilage of the knee commonly referred to as chondrocalcinosis. The term chondrocalcinosis refers to the presence of calcium-containing crystals detected as radiodensities in cartilage. Calcium-containing crystals other than calcium pyrophosphate dihydrate may also deposit in articular cartilage and menisci, producing both radiographically detectable densities in cartilage and joint inflammation or degeneration. Hemochromatosis, alkaptonuria (ochronosis), and Wilson's disease are characterized by cellular deposition of iron, calcium, and copper ions, respectively, into various tissues including articular cartilage and can give this appearance. Septic arthritis does not usually cause chondrocalcinosis. Klippel JH (ed): Primer on the Rheumatic Diseases, ed 11. Atlanta, GA, Arthritis Foundation, 1997, pp 226-229 and 328-331.

Question 4422

Topic: Infection, Pharmacology & VTE
A 6-year-old African-American boy with sickle cell disease has had pain and limited use of his right arm for the past 3 days. History reveals that he sustained a humeral fracture approximately 3 years ago. A lateral radiograph is shown in Figure 25. Based on these findings, a presumptive diagnosis of chronic osteomyelitis is made. What are the two most likely organisms?
. Haemophilus influenzae and Staphylococcus aureus
. Kingella kingae and Streptococcus pneumoniae
. Staphylococcus aureus and Salmonella
. Streptococcus pneumoniae and Staphylococcus aureus
. Salmonella and Shigella

Correct Answer & Explanation

. Staphylococcus aureus and Salmonella

Explanation

The risk of Salmonella osteomyelitis is much greater in patients with sickle cell disease than the general population. The exact reason for this increased risk is still unclear, but it appears to be associated with an increased incidence of gastrointestinal microinfarcts and abscesses. Both Staphylococcus aureus and Salmonella have been mentioned as the most prevalent causative organisms.

Question 4423

Topic: 1. General Principles & Basic Science

A 32-year-old woman with systemic lupus erythematosus treated with methotrexate and oral corticosteroids reports right groin pain with ambulation and night pain. Examination reveals pain with internal and external rotation and flexion that is limited to 105 degrees because of discomfort. Laboratory studies show a serum WBC of 9.0/mm3 and an erythrocyte sedimentation rate of 35 mm/h. Figures 5a and 5b show AP and lateral radiographs of the right hip. Further evaluation should include

. examination under fluoroscopy.
. MRI.
. a bone scan.
. arthrography.
. aspiration and arthrography.

Correct Answer & Explanation

. MRI.

Explanation

The radiographs show Ficat and Arlet stage 2 osteonecrosis. The femoral head remains round, and there are sclerotic changes in the superolateral quadrant. Patients with systemic lupus erythematosus are at risk for osteonecrosis because of prednisone use and the underlying metabolic changes associated with the condition (hypofibrinolysis and thrombophilia). MRI is the best diagnostic method for detecting osteonecrosis, with a greater than 98% sensitivity and specificity. For this patient, an MRI can assess the contralateral hip for any involvement and can quantify the extent of the lesion. Mont MA, Jones LC, Sotereanos DG, Amstutz HC, Hungerford DS: Understanding and treating osteonecrosis of the femoral head. Instr Course Lect 2000;49:169-185.

Question 4424

Topic: 1. General Principles & Basic Science

Figure 14 shows a lateral radiograph of a knee joint. The bony structure indicated by the arrow is a sesamoid bone that resides in what tendon?

Anatomy Board Review 2002: High-Yield MCQs (Set 2) - Figure 1

. Biceps femoris
. Lateral gastrocnemius
. Semimembranosus
. Semitendinosus
. Popliteus

Correct Answer & Explanation

. Lateral gastrocnemius

Explanation

The radiograph shows a fabella, a sesamoid bone that is usually found within the tendon of the lateral head of the gastrocnemius. It can be confused with a loose body on radiographs. It occurs in 18% of patients and is often bilateral. Anderson JE (ed): Grant's Atlas of Anatomy, ed 7. Baltimore, MD, Williams & Wilkins, 1978, pp 4-69.

Question 4425

Topic: 1. General Principles & Basic Science

A 4-month-old infant is unable to flex her elbow as a result of an obstetrical brachial plexus palsy. This most likely illustrates a predominate injury to what structure?

. C4
. Upper trunk
. Posterior cord
. Lateral cord
. Musculocutaneous nerve

Correct Answer & Explanation

. Upper trunk

Explanation

Erb's palsy is the most common form of obstetrical plexus palsy resulting in C5, C6, or upper trunk deficits. This causes loss of shoulder abduction and elbow flexion. The biceps muscle and the brachialis muscles are predominately responsible for flexion of the elbow. Each of these muscles is innervated by individual branches of the musculocutaneous nerve which are supplied predominately by axons from the C6 nerve root and the upper trunk of the brachial plexus. Netter F: The Ciba Collection of Medical Illustrations: The Musculoskeletal System, Part 1: Anatomy, Physiology and Metabolic Disorders. West Caldwell, NJ, Ciba-Geigy Corporation, 1987, vol 8, pp 28-29. Wolock B, Millesi H: Brachial plexus-applied anatomy and operative exposure, in Gelberman RH (ed): Operative Nerve Repair and Reconstruction. Philadelphia, PA, JB Lippincott, 1991, pp 1255-1272.

Question 4426

Topic: Surgical Anatomy & Approaches

A 32-year-old man has a closed oblique displaced fracture at the junction of the lower and middle third of the humeral shaft and a complete radial nerve palsy. Closed reduction is performed and is felt to be acceptable. Management of the radial nerve palsy should consist of

. exploration and repair of the radial nerve if clinical findings or electromyographic studies show no improvement at 2 to 3 weeks.
. exploration and repair of the radial nerve if clinical findings or electromyographic studies show no improvement at 14 weeks.
. transfer of the pronator teres to the extensor carpi radialis brevis if clinical findings or electromyographic studies show no improvement at 14 weeks.
. immediate exploration and repair of the radial nerve, along with internal fixation with a plate and screws.
. immediate exploration and repair of the radial nerve, along with internal fixation with an intramedullary nail.

Correct Answer & Explanation

. exploration and repair of the radial nerve if clinical findings or electromyographic studies show no improvement at 14 weeks.

Explanation

In patients who have radial nerve dysfunction associated with a closed humeral fracture, nerve function usually will return to normal without surgical exploration. If clinical findings or electromyographic studies show no improvement at 3 months, surgical exploration and repair can be performed. Tendon transfers are performed if nerve repair is deemed unsuccessful. Pollock FH, Drake D, Bovill EG, et al: Treatment of radial neuropathy associated with fractures of the humerus. J Bone Joint Surg Am 1981;63:239-243.

Question 4427

Topic: Biomechanics & Biomaterials

The acceleration of an object under the influence of a force depends directly on the mass of the object. The angular acceleration of an object under the influence of a moment depends directly on the

Basic Science 2006 Practice Questions: Set 1 (Solved) - Figure 3

. area moment of inertia.
. weight squared.
. length of the lever arm.
. mass moment of inertia.
. initial velocity.

Correct Answer & Explanation

. mass moment of inertia.

Explanation

Similar to the action of a force, a moment tends to angularly accelerate an object in a manner proportional to a quantity related to the mass of the object. The concept of a more massive object requiring a larger force to cause the same straight line acceleration is straightforward. The concept for changing angular velocity is similar but not identical. The proportional constant between the moment and the resulting angular acceleration is the mass moment of inertia, which depends not only on the mass of the object, but also its distribution. The unit of mass moment of inertia is obtained by multiplying the mass of the object by the square of the distance between an equivalent location of the center of rotation of the object and an equivalent location of the center of mass. Orthopaedic surgeons can change both the amount of mass carried by a limb and the way that the mass is distributed. For example, in applying a cast to the leg, the physician can affect the mass of the cast by the choice of casting material and by the size of the cast. As the mass moment of inertia of the limb increases (eg, by applying the cast farther down on the leg or using a heavier casting material), the patient will need to exert larger moments to angularly accelerate the leg during gait. Andriacchi T, Natarajan RN, Hurwitz DE: Musculoskeletal dynamics, locomotion, and clinical applications, in Mow VC, Hayes WC (eds): Basic Orthopaedic Biomechanics, ed 2. New York, NY, Lippincott-Raven, 1997, pp 43-47.

Question 4428

Topic: Biomechanics & Biomaterials

Figure 6 shows an object being held in an outstretched hand. To offset the moment created by the object (ignoring the weight of the forearm), the biceps must generate a force of

Basic Science Board Review 2006: High-Yield MCQs (Set 4) - Figure 1

. 7.5 N.
. 15 N.
. 30 N.
. 75 N.
. 150 N.

Correct Answer & Explanation

. 75 N.

Explanation

Answering this question requires understanding of two important biomechanics concepts. First, because neither the object being held in the hand nor the body is moving and, hence, their accelerations are zero, the problem is one of static equilibrium in which the sum of the moments acting on the body is zero. Second, a moment is the action of a force that causes an object to rotate about any point away from its line of action. The magnitude of the moment is the magnitude of the force multiplied by the perpendicular distance between the line of action and the point (often called the moment arm or lever arm). In this problem, two forces are causing moments about the elbow. The magnitude of the moment caused by the object in the hand is 5 N times 30 cm or 150 N-cm. To maintain equilibrium, the moment caused by the biceps force must also have a magnitude of 150 N-cm. Its moment arm is 2 cm, so the magnitude of the biceps force is 150 N-cm divided by 2 cm, which equals 75 N. In general, functional loads such as the object are always at a mechanical advantage (ie, have a longer moment arm) over the muscle. Therefore, muscles must generate large forces to overcome the moments caused by even small functional loads. An KN, Chao ES, Kaufman KR: Analysis of muscle and joint loads, in Mow VC, Hayes WC (eds): Basic Orthopaedic Biomechanics, ed 2. New York, NY, Lippincott-Raven, 1997, pp 1-14.

Question 4429

Topic: Biomechanics & Biomaterials

The wear resistance of ultra-high molecular weight polyethylene can be improved by exposing the polymer to high-energy radiation (eg, gamma or electron beam), followed by a thermal treatment. What is one detrimental side effect of this process?

. Decreased resistance to oxidative degradation
. Decreased toughness
. Increased density of nonconsolidated particles
. Increased elastic modulus
. High levels of residual free radicals

Correct Answer & Explanation

. Decreased toughness

Explanation

Highly cross-linked polyethylene has gained widespread acceptance for joint arthroplasty components because of reported experimental and early clinical accounts of significant reductions in wear. Cross-linking is increased by imparting additional energy into the polymer (above that conventionally used for sterilization). The thermal treatments after cross-linking stabilize the material against oxidative degradation by quenching free radicals and also reduce the elastic modulus. One disadvantage of the increased cross-linking is a reduction in toughness that makes the polyethylene more susceptible to crack initiation and propagation. The reduced toughness raises concerns for gross component fracture and fracture at stress concentrations that can arise with the locking mechanisms used to secure polyethylene inserts into metallic backings. Nonconsolidated polyethylene particles have been associated with increased subsurface density secondary to oxidative degradation in conventional polyethylene implants. The quenching of free radicals by thermal treatment in highly cross-linked polyethylene should prevent this problem. Collier JP, Currier BH, Kennedy FE, et al: Comparison of cross-linked polyethylene materials for orthopaedic applications. Clin Orthop 2003;414:289-304. Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 203-208.

Question 4430

Topic: 1. General Principles & Basic Science
An orthopaedic surgeon frequently uses hip and knee prostheses from a specific manufacturer. The surgeon becomes acquainted with the manufacturer's representative who provides the support for these prostheses in the hospital. They develop a personal relationship outside of work through a common interest in sailing. Together they become interested in buying a sailboat. The manufacturer's representative suggests a partnership in a boat costing $200,000. The manufacturer's representative would purchase a 90% interest and the surgeon a 10% interest in the boat. There would be no restrictions on use of the boat by the surgeon. What should the orthopaedic surgeon do?
. Accept the offer because it would allow the physician to have a boat and enjoy a hobby of sailing with a minimal financial outlay.
. Accept this offer because it would have nothing to do with the orthopaedic practice and because the physician feels strongly that it would have no influence on practice decisions.
. Reject the offer because it represents an unacceptable conflict of interest.
. Accept the offer but disclose the relationship to patients when using the representative's products.
. Accept the offer but only with a equal interest arrangement in the purchase and use of the boat.

Correct Answer & Explanation

. Reject the offer because it represents an unacceptable conflict of interest.

Explanation

Rejecting this proposal is the only appropriate course of action. Accepting it would, in essence, be receiving a huge gift from industry in the form of a sailboat. Physicians frequently assert that they are not influenced by gifts and relationships with industry representatives, but evidence is to the contrary. Such an arrangement constitutes a tremendous incentive to use the manufacturer's products. The fact that the boat partnership seems completely outside of the orthopaedic business relationship does not excuse it. Conflicts of interest should always be resolved and in the best interest of patient care, and in this case the best course clearly is to avoid the conflict of interest totally. An equal interest in the boat does not eliminate the conflict of interest.

Question 4431

Topic: Surgical Anatomy & Approaches

A 35-year-old man has profound deltoid weakness after sustaining a traumatic anterior shoulder dislocation 6 weeks ago. Electromyographic (EMG) studies confirm an axillary nerve injury. Follow-up examination at 3 months reveals no recovery of function. What is the best course of action?

. Surgical repair of the Bankart lesion
. Exploration of the axillary nerve
. MRI neurography
. Repeat EMG studies
. Continued observation and physical therapy

Correct Answer & Explanation

. Repeat EMG studies

Explanation

Documenting the status of recovery at this time is appropriate; therefore, repeat EMG studies should be conducted to check for early signs of reinnervation. Timing of nerve exploration in this setting is debated, with authors suggesting exploration if there is no sign of recovery at 6 to 9 months. Perlmutter GS: Axillary nerve injury. Clin Orthop 1999;368:28-36. Artico M, Salvati M, D'Andrea V, et al: Isolated lesions of the axillary nerves: Surgical treatment and outcome in twelve cases. Neurosurgery 1991;29:697-700. Vissar CP, Coene LN, Brand R, et al: The incidence of nerve injury in anterior dislocation of the shoulder and its influence on functional recovery: A prospective clinical and EMG study. J Bone Joint Surg Br 1999;81:679-685.

Question 4432

Topic: Biology, Genetics & Bone Healing

Figure 26 shows the MRI scan of a 60-year-old man who has had groin pain for the past 2 months. The patient reports pain with ambulation, and examination reveals an antalgic gait. He denies any history of steroid or alcohol abuse. Plain radiographs are normal. Management should include

Hip 2001 Practice Questions: Set 3 (Solved) - Figure 8

. core decompression.
. a vascularized fibula graft.
. intraosseous steroid injection.
. total hip replacement.
. protected weight bearing.

Correct Answer & Explanation

. protected weight bearing.

Explanation

The patient has transient osteoporosis of the hip. Transient osteoporosis is usually a self-limited condition that is most frequently seen in women in the third trimester of pregnancy and in men in the sixth decade of life. Transient osteoporosis is best treated with protected weight bearing.

Question 4433

Topic: Surgical Anatomy & Approaches

An adult patient has a closed humeral fracture that was treated nonsurgically and a concomitant radial nerve injury. Six weeks after injury, electromyography shows no evidence of recovery. Management should now consist of

. exploration and neurolysis/repair.
. MRI of the arm.
. functional electrical stimulation.
. radial nerve tendon transfers.
. observation.

Correct Answer & Explanation

. observation.

Explanation

In patients with radial nerve injuries with closed humeral fractures, it has been reported that 85% to 95% spontaneously recover. Based on this premise, most surgeons favor expectant management of these injuries. Even if there is no evidence of recovery at 6 weeks, repeat electromyography at 12 weeks is advocated. If there is no clinical or electromyographic signs of recovery at 6 months, exploration is recommended. If the nerve is in continuity at the time of exploration, nerve action potentials are useful in helping determine the need for neurolysis, excision, and grafting, or if excision and repair is the best option. Pollock FH, Drake D, Bovill EG, et al: Treatment of radial neuropathy associated with fractures of the humerus. J Bone Joint Surg Am 1981;63:239-243.

Question 4434

Topic: 1. General Principles & Basic Science

Figure 41 shows the MRI scan of a 39-year-old man who has severe left groin and anterior thigh pain. What is the most likely diagnosis?

Anatomy 2002 Practice Questions: Set 3 (Solved) - Figure 23

. Osteoarthritis
. Rheumatoid arthritis
. Synovial chondromatosis
. Gout
. Osteonecrosis

Correct Answer & Explanation

. Osteonecrosis

Explanation

The MRI scan shows near complete involvement of the femoral head with bone marrow changes and some collapse of the necrotic segment. This is most suggestive of osteonecrosis.

Question 4435

Topic: 1. General Principles & Basic Science

Stiffness relates the amount of load applied to a structure like a long bone or an intramedullary nail to the amount of resulting deformation that occurs in the structure. What is the most important material property affecting the axial and bending stiffness of a structure?

. Elastic modulus
. Ductility
. Ultimate stress
. Yield stress
. Toughness

Correct Answer & Explanation

. Elastic modulus

Explanation

The amount of deformation resulting in response to an applied load depends on the stress distribution that the load creates in the structure and the stress versus strain behavior of the material that makes up the structure. Axial and bending loads create stress distributions that involve normal stresses and normal strains. Although all five responses are indeed material properties, only one, elastic modulus, relates normal stresses to normal strains. In fact, axial and bending stiffness are directly proportional to modulus, so that a nail made from stainless steel will have nearly twice the stiffness of a nail made from titanium alloy (because their respective elastic moduli differ by about a factor of two). Hayes WC, Bouxsein ML: Analysis of muscle and joint loads, in Mow VC, Hayes WC (eds): Basic Orthopaedic Biomechanics, ed 2. New York, NY, Lippincott-Raven, 1997, pp 74-82. Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 159-165.

Question 4436

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?

Basic Science 2008 Practice Questions: Set 1 (Solved) - Figure 8

. 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. Gass M, Dawson-Hughes B: Preventing osteoporosis-related fractures: An overview. Am J Med 2006;119:S3-S11.

Question 4437

Topic: Biomechanics & Biomaterials

Plots of stress versus strain for four orthopaedic biomaterials are shown in Figure 3. Referring to the figure, what is the correct identification of the curves?

Basic Science 2006 Practice Questions: Set 3 (Solved) - Figure 1

. A = cortical bone; B = bone cement; C = cobalt alloy; D = titanium alloy
. A = cortical bone; B = bone cement; C = cobalt alloy; D = stainless steel
. A = bone cement; B = cortical bone; C = titanium alloy; D = stainless steel
. A = bone cement; B = cortical bone; C = cobalt alloy; D = titanium alloy
. A = polyethylene; B = cortical bone; C = stainless steel; D = titanium alloy

Correct Answer & Explanation

. A = bone cement; B = cortical bone; C = cobalt alloy; D = titanium alloy

Explanation

Stress-strain plots allow easy comparison of a number of important mechanical properties, including elastic modulus (the slope of the initial straight line portion of the curve) and yield stress (the stress at the break in the curves for bone, steel, and titanium alloy). Important considerations here are much lower modulus and ultimate stress of bone and cement compared to the two metallic alloys, the fact that titanium is lower modulus but higher strength than stainless steel, and the identification of cement as the only brittle material among the four. Burstein AH, Wright TM: Fundamentals of Orthopaedic Biomechanics. Baltimore, MD, Williams and Wilkins, 1994, pp 97-129.

Question 4438

Topic: 1. General Principles & Basic Science

Which of the following patient factors is associated with recurrent radicular pain following lumbar diskectomy for sciatica?

. Initial symptoms of more than 3 months' duration
. Large annular defects seen intraoperatively
. Large sequestered disk herniations
. Initial treatment with lumbar epidural steroid injections prior to diskectomy
. Preoperative reproduction of sciatica with straight leg raising (SLR)

Correct Answer & Explanation

. Large annular defects seen intraoperatively

Explanation

A large annular defect at the site of a lumbar disk herniation is associated with persistent radicular pain postoperatively. Large sequestered herniations and a positive SLR preoperatively correlate with good outcomes after diskectomy. Neither symptoms of more than 3 months' duration nor preoperative epidural steroid injections correlate with postoperative results after diskectomy. Carragee EJ, Han MY, Suen PW, et al: Clinical outcomes after lumbar discectomy for sciatica: The effects of fragment type and anular competence. J Bone Joint Surg Am 2003;85:102-108.

Question 4439

Topic: Biology, Genetics & Bone Healing

During the evaluation of a patient suspected of having a lumbar disk herniation, T1- and T2-weighted MRI scans reveal a hyperintence lobular, well-defined lesion in the L2 vertebral body. What is the most likely diagnosis?

Spine Surgery 2000 Practice Questions: Set 1 (Solved) - Figure 24

. Metastatic focus
. Bony island
. Intravertebral disk herniation
. Osteoporosis
. Hemangioma

Correct Answer & Explanation

. Hemangioma

Explanation

The findings are characteristic of hemangioma. When the hemangioma is large enough, vertical striations may be visible on plain radiographs. Axial CT scans commonly reveal a speckled appearance. Metastatic lesions are typically hypointense on T1-weighted images because they replace the fatty marrow. Bony islands, like cortical bone, are dark on T1- and T2-weighted images. Intravertebral disk herniation would have characteristics similar to the disk and be in continuity with the disk. Osteoporosis is more diffuse. Ross JS, Masaryk TJ, Modic MT, Carter JR, Mapstone T, Dengel FH: Vertebral hemangiomas: MR imaging. Radiology 1987;165:165-169.

Question 4440

Topic: 1. General Principles & Basic Science

Figures 40a and 40b show the pre- and postoperative radiographs of an 82-year-old woman with bilateral hip pain who has had staged total hip arthroplasties. To minimize potential injury to the sciatic nerve at the time of surgery, the surgeon should

. perform a femoral shortening.
. perform a sciatic neurolysis.
. release the piriformis tendon.
. avoid use of posterior acetabular retractors.
. apply postoperative abduction bracing.

Correct Answer & Explanation

. perform a femoral shortening.

Explanation

To improve hip biomechanics and secure more suitable bone for acetabular fixation, the true acetabulum is often resurfaced in patients who have developmental dysplasia of the hip, thus lowering the hip center and lengthening the leg. Acute lengthening of more than 3 cm will place excessive tension on the sciatic nerve and require a femoral shortening to avoid sciatic nerve injury. The other maneuvers will not relieve sciatic nerve tension because of limb lengthening. Koval KJ (ed): Orthopaedic Knowledge Update 7. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 430-431.

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