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1. General Principles & Basic Science MCQs

Practice Set 197 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 3921

Topic: 1. General Principles & Basic Science

A 22-year-old rugby player is tackled with his knee in a flexed position. He presents with a prominent fibular head and is diagnosed with an anterolateral proximal tibiofibular joint dislocation. Which nerve is most at risk in this specific injury pattern?

. Tibial nerve
. Deep peroneal nerve
. Common peroneal nerve
. Sural nerve
. Saphenous nerve

Correct Answer & Explanation

. Tibial nerve

Explanation

The common peroneal nerve wraps directly around the fibular neck. Proximal tibiofibular joint dislocations, particularly the most common anterolateral type, place direct traction or mechanical compression on the common peroneal nerve, predisposing it to injury.

Question 3922

Topic: Infection, Pharmacology & VTE

A 22-year-old sustains an acute ACL tear and a complete distal avulsion of the MCL from its tibial insertion. MRI reveals the distal end of the MCL is displaced superficial to the pes anserinus tendons. What is the most appropriate management for the MCL injury?

. Brace the knee for 6 weeks, followed by ACL reconstruction
. Acute surgical repair of the MCL, with delayed ACL reconstruction
. Corticosteroid injection into the pes bursa to prevent scarring
. Immediate ACL reconstruction leaving the MCL to heal secondarily
. Excision of the torn MCL to prevent symptomatic painful neuroma

Correct Answer & Explanation

. Brace the knee for 6 weeks, followed by ACL reconstruction

Explanation

A distal tibial avulsion of the MCL displaced superficial to the pes anserinus is termed a 'Stener-like lesion of the knee.' Because the pes tendons physically block anatomic reduction, this injury cannot heal nonoperatively with bracing. Acute surgical repair of the MCL is indicated.

Question 3923

Topic: Biomechanics & Biomaterials

A 50-year-old male requires a total patellectomy due to a highly comminuted, unsalvageable patella fracture. How does a total patellectomy fundamentally alter the biomechanics of the knee joint?

. It increases the moment arm of the extensor mechanism.
. It requires up to 30% greater quadriceps force to achieve full extension.
. It decreases the tibiofemoral joint contact forces.
. It shifts the center of rotation of the knee anteriorly.
. It improves the mechanical advantage of the quadriceps tendon during terminal extension.

Correct Answer & Explanation

. It increases the moment arm of the extensor mechanism.

Explanation

The patella acts as a fulcrum to increase the moment arm of the extensor mechanism. Total patellectomy dramatically decreases this moment arm, mechanically disadvantaging the extensor mechanism. Consequently, it requires 15% to 30% more quadriceps force to achieve full extension, often leading to an extensor lag and earlier fatigue.

Question 3924

Topic: Biology, Genetics & Bone Healing

A 45-year-old female develops severe post-traumatic arthrofibrosis of the knee following open reduction and internal fixation of a bicondylar tibial plateau fracture. At a cellular level, which cytokine is most strongly implicated in the pathogenesis of this excessive intra-articular scar formation?

. Interleukin-1 (IL-1)
. Tumor Necrosis Factor-alpha (TNF-alpha)
. Transforming Growth Factor-beta (TGF-beta)
. Interleukin-6 (IL-6)
. Bone Morphogenetic Protein-2 (BMP-2)

Correct Answer & Explanation

. Transforming Growth Factor-beta (TGF-beta)

Explanation

Transforming growth factor-beta (TGF-beta) is a potent profibrotic cytokine heavily implicated in the development of arthrofibrosis. It stimulates fibroblast proliferation and excessive collagen deposition within the joint capsule.

Question 3925

Topic: Biomechanics & Biomaterials

A 50-year-old female presents with acute medial knee pain and a popping sensation while deep squatting. MRI reveals a medial meniscus posterior root tear. If left untreated, which biomechanical consequence is most likely to occur within the knee joint?

. Decreased tibiofemoral contact pressure
. Loss of hoop stresses simulating a total meniscectomy
. Significantly increased anterior tibial translation
. Medial compartment gapping in full extension
. Accelerated isolated patellofemoral osteoarthritis

Correct Answer & Explanation

. Loss of hoop stresses simulating a total meniscectomy

Explanation

A posterior root tear completely disrupts the meniscal ring, leading to a loss of hoop stresses and lateral meniscal extrusion. This alters joint kinematics to be functionally equivalent to a total meniscectomy, drastically increasing peak articular contact pressures.

Question 3926

Topic: 1. General Principles & Basic Science

A 50-year-old female feels a pop in her posterior knee while squatting. MRI confirms a complete radial tear of the posterior horn of the medial meniscus root. Biomechanically, this injury is most equivalent to which of the following?

. A stable longitudinal tear in the red-red zone
. A total medial meniscectomy
. An isolated posterior cruciate ligament tear
. A bucket-handle tear with preserved root attachments
. A partial meniscectomy of the anterior horn

Correct Answer & Explanation

. A total medial meniscectomy

Explanation

A complete medial meniscus posterior root tear disrupts the hoop stresses of the meniscus, causing it to extrude. Biomechanical studies have shown this results in contact pressures equivalent to a total meniscectomy, leading to rapid articular cartilage degeneration.

Question 3927

Topic: 1. General Principles & Basic Science

A 45-year-old male with medial compartment osteoarthritis and varus malalignment undergoes a medial opening wedge high tibial osteotomy (HTO). If the osteotomy gap is disproportionately opened anteriorly relative to posteriorly, what is the most likely geometric consequence on the knee?

. Decreased posterior tibial slope and patella alta
. Increased posterior tibial slope and patella baja
. No change in tibial slope with patella alta
. Increased posterior tibial slope with patella alta
. Decreased posterior tibial slope and patella baja

Correct Answer & Explanation

. Increased posterior tibial slope and patella baja

Explanation

In an opening wedge HTO, opening the anterior gap more than the posterior gap increases the posterior tibial slope. Additionally, opening wedge osteotomies inherently lower the relative height of the patella, creating patella baja.

Question 3928

Topic: 1. General Principles & Basic Science

Figure A demonstrates the molecular structure of a cell membrane protein important in propagating the action potential of a neuron. Which of the following medications acts by binding to the location marked with an X in the illustration?

. Phentolamine
. Rocuronium
. Bupivacaine
. Midazolam
. Fentanyl

Correct Answer & Explanation

. Bupivacaine

Explanation

Bupivacaine exerts its actions through blockade of the voltage gated sodium channel.Local anesthetics of the amide family (lidocaine, bupivacaine) bind to the intracellular portion of voltage-gated sodium channels to block sodium influx. This prevents depolarization and the initiation or conduction pain. Lidocaine and bupivacaine have a duration of action of 2 and 4 hours, respectively (4 and 8 hours with epinephrine), and maximum doses are 4.5mg/kg and 2.5mg/kg, respectively (7mg/kg and 3mg/kg with epinephrine respectively). Both are metabolized in the liver, and excreted by the kidneys.Phillips et al. review specific analgesics. Agents used to manage chronic pain include tricyclic antidepressants, anticonvulsants, GABA agonists, local anesthetic analogs, and NMDA antagonists. Opiates may trigger tolerance and lack of efficacy may develop. In those with refractory chronic pain, centrally administered analgesics may be considered, including opiates, dilute local anesthetic, NMDA receptor antagonists, clonidine, midazolam, baclofen, or calcium channel blockers. Single agents may be less effective than analgesic combinations.Scholz discussed the function of local anesthetics and sodium channels. There are 3 states to sodium channels: (1) The closed state at potentials below -70mV. In this state, Na+ ions cannot pass from 1 side to another. (2) The open state, initiated by depolarization of the membrane to above -40mV. The channel opens to allow Na+ ions to diffuse through the pore, causing an inward current, depolarizing the membrane further. (3) The inactivated state follows activation during prolonged depolarization. In this state, inactivation is seen in macroscopic currents.Figure A shows the voltage gated sodium channel. Local anesthetics such as lidocaine and bupivacaine act at the binding site marked "X".Incorrect Answers:

Question 3929

Topic: Biology, Genetics & Bone Healing
Calcitonin acts as an antiresorptive agent by
. decreasing osteoblast number.
. decreasing osteoclast activity and number.
. increasing osteoclast activity.
. increasing osteoblast activity.
. increasing osteoblast number.

Correct Answer & Explanation

. decreasing osteoclast activity and number.

Explanation

DISCUSSION: Calcitonin is a hormone that binds to osteoclasts and acts to decrease both osteoclast activity and number. Calcitonin is most effective in reducing vertebral compression fractures in high-turnover osteoporosis. It is also effective in treating regional osteoporosis. Because of its analgesic effect, it is helpful in treating painful acute compression fractures associated with osteoporosis. REFERENCE: Lane JM, Nydick M: Osteoporosis: Current modes of prevention and treatment. J Am Acad Orthop Surg 1999;7:19-31.

Question 3930

Topic: 1. General Principles & Basic Science

Endurance training primarily involving aerobic activities results in which of the following muscular adaptations? Review Topic

. Hypertrophy of individual myofibers
. Increases in the muscle cross-sectional area
. Increase in the number of motor units recruited
. Increase in the capillary density of active muscles
. Changes in the activity of glycolytic enzymes

Correct Answer & Explanation

. Increase in the capillary density of active muscles

Explanation

Endurance training primarily involves aerobic activities and results in different muscular adaptations compared with resistance training. The most important adaptation is a significant increase in the capillary density of active muscles. The respiratory capacity of mitochondria is increased, resulting in greater maximal oxygen consumption; however, there are no significant changes in the activity of glycolytic enzymes. With resistance training, initial gains in strength observed are caused primarily by an increase in the number of motor units recruited to execute a particular movement. After approximately 4 to 6 weeks, individual myofibers begin to exhibit hypertrophy. Other changes that occur with muscular resistance training include an increase in the number of type IIA fibers with a concomitant decrease in type IIB fibers.

Question 3931

Topic: 1. General Principles & Basic Science
Posterior sternoclavicular dislocations are most commonly associated with which of the following complications?
. Chronic instability
. Brachial plexus palsy
. Pneumothorax
. Esophageal compression
. Tracheal compression

Correct Answer & Explanation

. Tracheal compression

Explanation

DISCUSSION: Posterior sternoclavicular dislocations are commonly associated with tracheal compression, which can be a life-threatening condition requiring immediate reduction. The other listed complications are less common. REFERENCES: Brooks AL, Henning GD: Injury to the proximal clavicular epiphysis, abstracted. J Bone Joint Surg Am 1972;54:1347-1348. Beaty JH (ed): Orthopaedic Knowledge Update 6. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 255-260.

Question 3932

Topic: Biomechanics & Biomaterials
Which of the following bearing materials is most resistant to scratching from third-body debris?
. Alumina
. Stainless steel
. Forged cobalt-chromium
. Ion bombarded and forged cobalt-chromium
. Oxidized titanium

Correct Answer & Explanation

. Alumina

Explanation

DISCUSSION: Alumina is the hardest of all the materials listed. Clinical retrieval demonstrates resistance to scratching from third-body debris. REFERENCE: Cooper JR, Dowson D, Fisher J, Jobbins B: Ceramic bearing surfaces in total articular joints: Resistance to third body damage from bone cement particles. J Med Eng Technol 1991;15:63-67.

Question 3933

Topic: Biomechanics & Biomaterials

What is the primary reason for including the ilium in the distal fixation of long instrumentation constructs in adult scoliosis? Review Topic

. Better coronal balance
. Better pelvic balance
. Reduced fretting and corrosion
. Improved curve correction
. Improved fusion success

Correct Answer & Explanation

. Better coronal balance

Explanation

Studies have shown that when compared with fixation to the sacrum alone, the success rate of fusion across the lumbosacral junction increases when both the sacrum and ilium are included in the posterolateral construct. Curve correction, coronal balance, and pelvic balance are all attended to within the thoracolumbar spine and are not directly related to the pelvic fixation. Fretting and corrosion are a byproduct of metal-to-metal connections.

Question 3934

Topic: 1. General Principles & Basic Science
Figure 9 shows the AP radiograph of a 65-year-old man who has knee pain and swelling. What is the most likely diagnosis?
. Gout
. Chondrocalcinosis (pseudogout)
. Hemochromatosis
. Rheumatoid arthritis
. Ochronosis

Correct Answer & Explanation

. Chondrocalcinosis (pseudogout)

Explanation

Discussion: Although all the choices are known causes of joint degeneration (secondary osteoarthritis), only chondrocalcinosis shows distinct linear calcification of the cartilage due to deposition of calcium pyrophosphate crystals. Gout is a recurrent acute arthritis resulting from the deposition of monosodium urate from supersaturated hyperuricemic body fluids. Hemochromatosis is characterized by focal or generalized deposition of iron within body tissues. Rheumatoid arthritis is a nonspecific, usually symmetric inflammation of peripheral joints resulting in destruction of articular and periarticular structures. Ochronosis is a hereditary enzyme deficiency (homogentisic acid oxidase) resulting in deposition of homogentisic acid polymers in articular cartilage.

Question 3935

Topic: Biology, Genetics & Bone Healing

A minimally invasive plate osteosynthesis is seen in Figure 15. The resultant fracture healing can best be attributed to a fixation construct that was

. stiff and stable.
. flexible and stable.
. facilitating direct osteonal healing.
. inhibitory to endochondral ossification.
. stimulatory to intramembranous ossification.

Correct Answer & Explanation

. stiff and stable.

Explanation

Locked plating constructs with long-working lengths provide flexible but stable constructs that promote (not inhibit) endochondral ossification. Because of the longer working length they are not stiff, and these fractures do not heal with intramembranous ossification which occurs in bones like the calvarium. Direct osteonal healing is usually seen with constructs where absolute stability is achieved through interfragmentary compression, unlike in this case.

Question 3936

Topic: 1. General Principles & Basic Science
A patient sustains a severe lower extremity injury. What can be said about his outcome at 2 years if he chooses reconstruction over amputation?
. He has a higher risk of rehospitalization
. He has a higher chance of returning to work
. He will have a higher overall SIP (Sickness Impact Profile) score
. His psychosocial SIP score will improve with time
. He will have a better SIP score if he did not complete high school

Correct Answer & Explanation

. He has a higher risk of rehospitalization

Explanation

DISCUSSION: Severe lower extremity injury patients undergoing reconstruction have a higher rate of rehospitalization at 2 years. This question is based on data published by the LEAP study group, a multi-centered study of severe extremity injuries treated with either amputation or reconstruction. Bosse et al found that at 2 years the SIP score and return to work were not statistically significantly different between amputation and reconstruction groups. Reconstruction patients had a higher risk of rehospitalization. The psychosocial subscale of SIP did not improve with time.

Question 3937

Topic: Biology, Genetics & Bone Healing

Which of the following is not a cause of childhood osteomalacia (rickets)?

. Vitamin D deficiency
. Renal osteodystrophy
. X-linked hypophosphatemia
. Vitamin D malabsorption
. Vitamin K deficiency

Correct Answer & Explanation

. Vitamin D deficiency

Explanation

Rickets is caused by a decrease in calcium and phosphate that affects mineralization at the physes of the long bones. This disease is characterized by brittle bones; physeal widening is seen on radiographs with long-bone bowing, Looser's lines, enlargement of costal cartilages, and dorsal kyphosis. All of the above-mentioned choices are known causes of osteomalacia or rickets except vitamin K deficiency.

Question 3938

Topic: Infection, Pharmacology & VTE
The mother of a 26-month-old boy reports that he has been unwilling to bear weight on his left lower extremity since he awoke this morning. She denies any history of trauma. He has a temperature of 99.4ยฐF (37.4ยฐC), and examination reveals that abduction of the left hip is limited to 30ยฐ. Laboratory studies show a WBC of 11,000/mmยณ and an erythrocyte sedimentation rate of 22 mm/h. A radiograph of the pelvis is shown in Figure 13. Management should consist of
. aspiration of the hip.
. a bone scan.
. an MRI scan.
. bed rest, frequent temperature checks, and reevaluation in 24 to 48 hours.
. hospital admission and placement in traction.

Correct Answer & Explanation

. bed rest, frequent temperature checks, and reevaluation in 24 to 48 hours.

Explanation

The most likely diagnosis is transient synovitis. Initial management should consist of bed rest and serial observation to rule out atypical septic arthritis of the hip. In an unreliable family situation, hospitalization for bed rest and observation may be indicated. Transient synovitis of the hip in children is a diagnosis of exclusion; other possibilities should be explored if the patientโ€™s symptoms do not follow a typical course and resolve in 4 to 21 days.

Question 3939

Topic: Surgical Anatomy & Approaches

When performing hip arthroscopy, the hip should be placed in neutral to slight internal rotation to protect which of the following structures? Review Topic

. Femoral nerve
. Lateral femoral cutaneous nerve
. Ascending lateral femoral circumflex artery
. Ascending medial femoral circumflex artery
. Sciatic nerve

Correct Answer & Explanation

. Femoral nerve

Explanation

The sciatic nerve is at greatest risk for injury during hip arthroscopy with placement of a posterolateral (posterior paratrochanteric portal). It can be within 3 cm of this portal. Advancing the trocar with the hip in neutral to slight internal rotation helps to protect the sciatic nerve from iatrogenic injury. The two structures in closest proximity with placement of arthroscopy portals are the lateral femoral cutaneous nerve (anterior portal) and the ascending branch of the lateral femoral circumflex artery (mid-anterior portal). The femoral nerve and medial femoral circumflex arteries are located medial to these anterior portals. Rotation of the hip has not been associated with increased risk of injury to any of these additional structures.

Question 3940

Topic: Biology, Genetics & Bone Healing
When evaluating articular cartilage, what extracellular matrix component is most closely associated with the deep calcified cartilage zone?
. Collagen type I
. Collagen type II
. Collagen type X
. Proteoglycan aggrecan
. Hyaluronic acid

Correct Answer & Explanation

. Collagen type X

Explanation

Collagen type X is produced only by hypertrophic chondrocytes during enchondral ossification (growth plate, fracture callus, heterotopic ossification) and is associated with calcification of cartilage in the deep zone of articular cartilage. Collagen type I is the predominant collagen in bone, ligament, and tendon. Collagen type II is the predominant collagen in articular cartilage. Proteoglycan aggrecan and hyaluronic acid are components of the extracellular matrix and are involved in the compressive strength characteristics of articular cartilage.

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