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1. General Principles & Basic Science MCQs

Practice Set 213 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 4241

Topic: 1. General Principles & Basic Science

In a patient presenting with a complete flail upper extremity after a motorcycle accident, which of the following electrodiagnostic findings most specifically indicates a pre-ganglionic (avulsion) brachial plexus injury rather than a post-ganglionic lesion?

. Absence of motor unit action potentials (MUAPs) in the biceps
. Preserved sensory nerve action potentials (SNAPs) in an anesthetic dermatome
. Absent somatosensory evoked potentials (SSEPs) at the cortex
. Fibrillation potentials in the paraspinal muscles
. Decreased compound muscle action potentials (CMAPs) in the thenar eminence

Correct Answer & Explanation

. Preserved sensory nerve action potentials (SNAPs) in an anesthetic dermatome

Explanation

In a pre-ganglionic root avulsion, the dorsal root ganglion remains intact and connected to the peripheral nerve. Therefore, SNAPs remain preserved despite central disconnection and clinical anesthesia.

Question 4242

Topic: 1. General Principles & Basic Science

Biomechanical studies evaluating flexor tendon repairs in Zone 2 demonstrate that the initial tensile strength of the repair before biologic healing occurs is most directly proportional to which of the following factors?

. The use of a running, locking epitenon suture
. The caliber and number of core suture strands crossing the repair site
. The length of the tendon purchase (bite size) beyond 10 mm
. The specific configuration of the grasping knots
. The use of non-absorbable versus absorbable suture material

Correct Answer & Explanation

. The caliber and number of core suture strands crossing the repair site

Explanation

The initial tensile strength of a flexor tendon repair is directly proportional to the number of core suture strands crossing the repair site and the thickness (caliber) of the suture material utilized.

Question 4243

Topic: Surgical Anatomy & Approaches

A 22-year-old motorcyclist sustains a traumatic brachial plexus injury. Clinical examination shows complete paralysis of the C5 and C6 myotomes. Sensory examination reveals anesthesia in the C5 and C6 dermatomes, yet Sensory Nerve Action Potentials (SNAPs) for the median and radial nerves are preserved. What is the anatomical location of this nerve injury?

. Postganglionic rupture at the trunk level
. Postganglionic rupture at the cord level
. Preganglionic avulsion at the root level
. Neuroma-in-continuity at the division level
. Peripheral nerve compression at the thoracic outlet

Correct Answer & Explanation

. Preganglionic avulsion at the root level

Explanation

The presence of preserved SNAPs in an anesthetic dermatome is the hallmark of a preganglionic root avulsion. The dorsal root ganglion remains intact and connected to the peripheral nerve, maintaining the distal axon's viability despite central disconnection.

Question 4244

Topic: 1. General Principles & Basic Science

A 28-year-old male sustains a severe traction injury to his right upper extremity. Clinical examination reveals complete flaccidity of the arm, absent sensation, ptosis, miosis, and anhidrosis on the right side of his face. This specific facial triad implies poor prognosis for spontaneous nerve recovery because it indicates injury to which structure?

. Postganglionic C8 nerve root
. Preganglionic T1 nerve root
. Lower trunk of the brachial plexus
. Medial cord of the brachial plexus
. Stellate ganglion compression via hematoma

Correct Answer & Explanation

. Preganglionic T1 nerve root

Explanation

The presence of Horner syndrome (ptosis, miosis, anhidrosis) indicates a preganglionic avulsion of the T1 nerve root. This interrupts the sympathetic chain connection to the stellate ganglion, confirming an irreparable preganglionic lesion.

Question 4245

Topic: Biomechanics & Biomaterials

In the context of scapholunate dissociation, a patient is planned for a capsulodesis and ligamentous reconstruction. Which distinct region of the scapholunate interosseous ligament is thickest, strongest, and most critical to reconstruct to restore normal carpal kinematics?

. Volar (palmar) region
. Proximal membranous region
. Central fibrocartilaginous region
. Dorsal region
. Radioscaphocapitate complex

Correct Answer & Explanation

. Dorsal region

Explanation

The dorsal region of the scapholunate interosseous ligament is the thickest and mechanically most important stabilizer of the scapholunate joint. Reconstruction efforts primarily focus on restoring this dorsal continuity.

Question 4246

Topic: 1. General Principles & Basic Science

A surgeon is harvesting an autologous sural nerve graft for a brachial plexus reconstruction. To predictably locate the sural nerve with minimal dissection, the initial incision should be placed precisely in which anatomical location?

. Posterior to the medial malleolus, adjacent to the great saphenous vein
. Anterior to the medial malleolus, adjacent to the great saphenous vein
. Posterior to the lateral malleolus, adjacent to the small saphenous vein
. Anterior to the lateral malleolus, adjacent to the small saphenous vein
. In the popliteal fossa, between the two heads of the gastrocnemius

Correct Answer & Explanation

. Posterior to the lateral malleolus, adjacent to the small saphenous vein

Explanation

The sural nerve is most reliably found running immediately posterior to the lateral malleolus in close association with the small saphenous vein. This is the standard distal landmark for its harvest.

Question 4247

Topic: Surgical Anatomy & Approaches

A patient with a chronic, isolated, traumatic avulsion of the axillary nerve with complete deltoid atrophy is scheduled for a nerve transfer 5 months post-injury. Which of the following is the most highly successful donor nerve for restoring deltoid function in this setting?

. Medial pectoral nerve
. Thoracodorsal nerve
. Branch of the radial nerve to the triceps
. Spinal accessory nerve
. Intercostal nerves

Correct Answer & Explanation

. Branch of the radial nerve to the triceps

Explanation

The Somsak procedure (or its variations) utilizes a motor branch of the radial nerve to the long or medial head of the triceps transferred directly to the anterior division of the axillary nerve. It is highly successful for isolated axillary nerve injuries due to synergistic action and proximity.

Question 4248

Topic: Surgical Anatomy & Approaches

A 22-year-old male presents with a complete C5-C6 root avulsion following a motorcycle accident. An Oberlin transfer is planned to restore elbow flexion. Which of the following describes the correct neurological transfer performed in this procedure?

. Spinal accessory nerve to the suprascapular nerve
. Medial pectoral nerve to the musculocutaneous nerve
. Ulnar nerve fascicle to the biceps branch of the musculocutaneous nerve
. Intercostal nerves to the musculocutaneous nerve
. Radial nerve branch to the axillary nerve

Correct Answer & Explanation

. Ulnar nerve fascicle to the biceps branch of the musculocutaneous nerve

Explanation

The classic Oberlin transfer involves taking an expendable motor fascicle from the ulnar nerve (usually supplying the FCU) and coapting it directly to the biceps motor branch of the musculocutaneous nerve to restore elbow flexion.

Question 4249

Topic: 1. General Principles & Basic Science

During the incorporation of a free vascularized fibular graft used for a 10 cm radial defect, how does the biological healing process distinctly differ from that of a massive non-vascularized cortical bone autograft?

. It relies exclusively on osteoconduction without osteogenesis
. It undergoes rapid creeping substitution within 6 weeks
. It bypasses the inflammatory phase of bone healing entirely
. It heals via primary bone union at the host-graft interface without creeping substitution
. It requires a robust local periosteal reaction from the recipient bed for survival

Correct Answer & Explanation

. It heals via primary bone union at the host-graft interface without creeping substitution

Explanation

Vascularized bone grafts maintain their intrinsic blood supply, avoiding the necrosis and creeping substitution seen in non-vascularized cortical grafts. They heal to the host bone via primary (callus-forming) bone union at the docking sites.

Question 4250

Topic: 1. General Principles & Basic Science

When performing a nerve repair, the surgeon decides to use a 4-strand core suture technique for a Zone II flexor tendon repair rather than a 2-strand repair. What is the primary biomechanical advantage of the 4-strand repair in this setting?

. It decreases the cross-sectional area of the repair site
. It provides sufficient gap resistance to allow for an early active motion rehabilitation protocol
. It enhances the diffusion of synovial fluid into the tendon core
. It eliminates the need for an epitendinous suture
. It allows the tendon to heal exclusively via intrinsic mechanisms

Correct Answer & Explanation

. It provides sufficient gap resistance to allow for an early active motion rehabilitation protocol

Explanation

A 4-strand (or greater) core suture significantly increases the tensile strength and gap resistance of a flexor tendon repair, safely permitting early active motion protocols which reduce adhesion formation.

Question 4251

Topic: 1. General Principles & Basic Science

Wallerian degeneration begins shortly after a peripheral nerve is completely transected. Which of the following cellular events is most responsible for clearing myelin debris during the first two weeks to prepare the distal stump for regenerating axons?

. Proliferation of fibroblasts
. Phagocytosis by invading macrophages and resident Schwann cells
. Secretion of neurotrophic factors by the axolemma
. Endothelial cell hyperplasia in the vasa nervorum
. Astrocytic scar formation

Correct Answer & Explanation

. Phagocytosis by invading macrophages and resident Schwann cells

Explanation

During Wallerian degeneration, both blood-borne macrophages and resident Schwann cells undergo phagocytosis to clear myelin and axonal debris distal to the injury, creating a permissive environment for nerve regeneration.

Question 4252

Topic: Surgical Anatomy & Approaches

A 32-year-old man presents with a high radial nerve palsy following a humeral shaft fracture. A tendon transfer is planned to restore thumb extension. Which of the following is the most commonly used donor tendon to restore function to the extensor pollicis longus (EPL)?

. Flexor carpi radialis (FCR)
. Palmaris longus (PL)
. Extensor indicis proprius (EIP)
. Flexor digitorum superficialis (FDS) of the ring finger
. Brachioradialis (BR)

Correct Answer & Explanation

. Palmaris longus (PL)

Explanation

To restore thumb extension in radial nerve palsy, the Palmaris Longus (PL) is most commonly transferred to the EPL. (Note: EIP to EPL is typically used for isolated EPL ruptures, such as post-distal radius fractures, but in high radial nerve palsy, EIP is also paralyzed).

Question 4253

Topic: 1. General Principles & Basic Science

Which of the following intrinsic properties of a peripheral nerve graft determines the maximum length it can bridge without succumbing to central ischemic necrosis, barring the use of a vascularized nerve graft?

. The diameter of the nerve graft
. The ratio of sensory to motor fascicles
. The density of nodes of Ranvier
. The age of the donor
. The degree of initial Wallerian degeneration

Correct Answer & Explanation

. The diameter of the nerve graft

Explanation

The diameter of a non-vascularized nerve graft dictates its survival. Large diameter nerve grafts (like whole sciatic or median) undergo central ischemic necrosis because revascularization from the recipient bed cannot penetrate the core fast enough.

Question 4254

Topic: 1. General Principles & Basic Science

(3875) Q4-7658:

. Optimum conditions for nerve healing after direct repair include:
. Gapping at suture repair site
. Early motion of extremity
. Tension-free repair
. lacing sutures through the endoneurium to increase repair strength
. Preservation of all tissue whether devitalized or viable
. Tension-free repair is the optimal technique to improve the potential for nerve recovery. Gapping, failure to splint to prevent tension on the nerve with motion, and failure to excise scarred or devitalized nerve tissue are impairments to successful nerve repairs. Suture repairs through the deep nerve segments can damage the axons. Sutures should be placed through the epineurium or, in a grouped fascicular repair, through the perineurium around the fascicles.

Correct Answer & Explanation

. Tension-free repair

Explanation

TrueFalseMissile wounds can cause a blast stretch injury to peripheral nerves and may recover with observation. Correct Answer: True

Question 4255

Topic: Biology, Genetics & Bone Healing

A 32-year-old man with a recurrent giant cell tumor of the distal radius is treated with denosumab prior to surgical resection. What is the mechanism of action of this medication?

. Inhibits osteoblast differentiation via Wnt pathway
. Binds to RANKL, preventing osteoclast activation
. Directly induces apoptosis in neoplastic stromal cells
. Inhibits VEGF-mediated angiogenesis
. Blocks the mammalian target of rapamycin (mTOR)

Correct Answer & Explanation

. Binds to RANKL, preventing osteoclast activation

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclasts and osteoclast precursors. This inhibits osteoclast-mediated bone destruction, which is driven by the neoplastic stromal cells in giant cell tumors.

Question 4256

Topic: Surgical Anatomy & Approaches

A 60-year-old man presents with chronic sacral pain and bowel/bladder dysfunction. Imaging shows a large, destructive, midline mass in the sacrum. Biopsy reveals physaliferous cells in a myxoid background. What is the most appropriate surgical approach for definitive treatment?

. Intralesional curettage
. Marginal excision to preserve nerve roots
. Wide en bloc resection
. Debulking followed by chemotherapy
. Radiofrequency ablation

Correct Answer & Explanation

. Wide en bloc resection

Explanation

Chordomas are chemoresistant and relatively radioresistant low-grade malignancies characterized by physaliferous cells. Wide en bloc resection with negative margins offers the best chance for local control and long-term survival.

Question 4257

Topic: 1. General Principles & Basic Science

A 50-year-old female presents with a destructive sacral mass causing bowel and bladder dysfunction. Histology demonstrates lobules of cells with abundant vacuolated cytoplasm in a myxoid background. Which immunohistochemical marker is most specific for this diagnosis?

. Cytokeratin
. S-100
. Brachyury
. Vimentin
. CD99

Correct Answer & Explanation

. Brachyury

Explanation

The clinical scenario and presence of physaliferous cells describe a chordoma. Brachyury, a transcription factor involved in notochordal development, is a highly sensitive and specific immunohistochemical marker for chordoma.

Question 4258

Topic: Biology, Genetics & Bone Healing

Denosumab is often utilized in the management of surgically unsalvageable or metastatic Giant Cell Tumor of bone. What is the specific mechanism of action of this medication?

. Directly induces apoptosis of the neoplastic stromal cells
. Binds to RANK receptor on osteoclasts
. Binds to RANK ligand (RANKL) preventing interaction with RANK
. Inhibits vascular endothelial growth factor (VEGF)
. Inhibits matrix metalloproteinases

Correct Answer & Explanation

. Binds to RANK ligand (RANKL) preventing interaction with RANK

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor on osteoclast precursors. This inhibits the recruitment and action of osteoclast-like giant cells, halting the bone destruction characteristic of Giant Cell Tumor.

Question 4259

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a large, lytic, eccentrically located lesion in the distal femur extending to the subchondral bone. Biopsy confirms Giant Cell Tumor (GCT) of bone. She is treated preoperatively with denosumab to downstage the tumor. What is the precise mechanism of action of this medication?

. Inhibits osteoclast ruffled border H+-ATPase
. Binds to the RANK receptor on osteoclasts
. Binds to RANKL, preventing osteoclast activation
. Inhibits vascular endothelial growth factor (VEGF)
. Inhibits CD99 surface antigen expression

Correct Answer & Explanation

. Binds to RANKL, preventing osteoclast activation

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANK Ligand (RANKL). This prevents RANKL from binding to the RANK receptor on osteoclasts and their precursors, thereby halting osteoclastogenesis and bone destruction.

Question 4260

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with severe back pain, anemia, and hypercalcemia. A skeletal survey reveals multiple punched-out lytic lesions in the skull and spine. Which of the following imaging modalities is most likely to yield false-negative results when evaluating his bone lesions?

. Technetium-99m bone scintigraphy
. Whole-body low-dose CT
. Magnetic Resonance Imaging (MRI)
. Positron Emission Tomography (PET)
. Plain radiography

Correct Answer & Explanation

. Technetium-99m bone scintigraphy

Explanation

Technetium-99m bone scintigraphy relies on osteoblastic activity. Because multiple myeloma primarily stimulates osteoclast activity without a coupled osteoblast response, traditional bone scans are frequently negative ("cold") and are not reliable for staging.

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