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1. General Principles & Basic Science MCQs

Practice Set 493 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 9841

Topic: Biology, Genetics & Bone Healing

In severe, lethal Osteogenesis Imperfecta (Type II), the most common molecular defect involves which of the following alterations in collagen synthesis?

. Substitution of a glycine residue by a bulkier amino acid in the collagen triple helix
. Decreased synthesis of structurally normal type I procollagen chains
. Defect in lysyl hydroxylase preventing adequate cross-linking
. A missense mutation in the COL2A1 gene
. Deficiency of tissue-nonspecific alkaline phosphatase

Correct Answer & Explanation

. Substitution of a glycine residue by a bulkier amino acid in the collagen triple helix

Explanation

Lethal OI (Type II) is usually caused by a qualitative defect where a single base substitution replaces glycine (the smallest amino acid) with a bulkier amino acid. This physically prevents the normal coiling of the collagen type I triple helix. Type I OI is typically a quantitative defect (decreased normal collagen).

Question 9842

Topic: Biology, Genetics & Bone Healing

A 10-year-old child with normal intelligence presents with a prominent forehead, delayed eruption of secondary teeth, and the ability to appose both shoulders at the anterior midline. A mutation in which of the following genes is the underlying cause?

. RUNX2 (CBFA1)
. FGFR3
. COL2A1
. COMP
. GNAS1

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

This classic presentation describes Cleidocranial Dysplasia, characterized by hypoplastic or absent clavicles. It is caused by a mutation in the RUNX2 (also known as CBFA1) gene, essential for osteoblast differentiation.

Question 9843

Topic: Biology, Genetics & Bone Healing

A 12-year-old female sustains a subtrochanteric femur fracture. She has a history of anemia, hepatosplenomegaly, and recurrent fractures. Radiographs reveal a uniform 'bone-within-bone' appearance. The underlying pathogenesis involves failure of which cellular mechanism?

. Defective osteoid synthesis by osteoblasts
. Impaired osteoclast ruffled border formation
. Excessive osteoblast proliferation
. Abnormal cartilage template vascularization
. Mutation in type X collagen

Correct Answer & Explanation

. Impaired osteoclast ruffled border formation

Explanation

This patient has Osteopetrosis, characterized by dense but brittle bones. The disease is caused by defective osteoclast function (often TCIRG1 or CLCN7 mutations) leading to an absent or impaired ruffled border and failure of bone resorption.

Question 9844

Topic: Biology, Genetics & Bone Healing
A 4-year-old with osteogenesis imperfecta type III is undergoing treatment with intravenous pamidronate. What is the primary cellular mechanism of action of this pharmacological therapy?
. Stimulates osteoblast activity and collagen synthesis
. Inhibits osteoclast-mediated bone resorption
. Promotes cross-linking of defective type I collagen
. Enhances intestinal calcium absorption
. Replaces the defective COL1A1 gene product

Correct Answer & Explanation

. Inhibits osteoclast-mediated bone resorption

Explanation

Bisphosphonates like pamidronate are analogs of pyrophosphate that bind to hydroxyapatite and are ingested by osteoclasts. They induce osteoclast apoptosis, thereby inhibiting bone resorption and increasing overall bone density.

Question 9845

Topic: Biology, Genetics & Bone Healing

A phenotypic female newborn presents with severe anterior bowing of the tibiae, pretibial skin dimples, and respiratory distress due to tracheomalacia. Karyotype analysis surprisingly reveals a 46,XY chromosomal pattern. A mutation in which gene is responsible for this condition?

. SOX9
. GNAS1
. FGFR3
. CBFA1
. EXT1

Correct Answer & Explanation

. SOX9

Explanation

This presentation describes Campomelic Dysplasia, which features severe bowing of long bones, pretibial dimples, and tracheomalacia. It is caused by a mutation in the SOX9 gene, which frequently leads to sex reversal in 46,XY individuals.

Question 9846

Topic: Biology, Genetics & Bone Healing

In an elderly patient with severe osteoporosis and a displaced intra-articular distal humerus fracture, what is a potential drawback of using conventional non-locking plates for fixation?

. Increased risk of infection
. Higher incidence of heterotopic ossification
. Poor purchase in osteoporotic bone leading to screw pull-out
. Slower healing due to motion at the fracture site
. Difficulty with plate contouring

Correct Answer & Explanation

. Poor purchase in osteoporotic bone leading to screw pull-out

Explanation

In osteoporotic bone, conventional non-locking plates (which rely on screw purchase into the bone for stability) are prone to screw pull-out. The poor bone quality provides inadequate fixation, leading to loss of reduction and implant failure. Locking plates, which provide angular stability, are generally preferred in osteoporotic bone because the screws lock into the plate, creating a fixed-angle construct that does not rely as heavily on bone-screw interface compression. Infection and HO are not direct drawbacks of non-locking plates in osteoporosis. Slower healing could occur due to instability, but the primary mechanism is pull-out. Contouring is a general plating challenge.

Question 9847

Topic: 1. General Principles & Basic Science

A 60-year-old active female undergoes ORIF for a bicondylar distal humerus fracture. To minimize the risk of heterotopic ossification (HO) post-operatively, which prophylaxis is commonly employed?

. Daily vitamin D supplements
. Long-term antibiotic therapy
. Non-steroidal anti-inflammatory drugs (NSAIDs) or radiation therapy
. Early, aggressive passive stretching exercises
. Corticosteroids

Correct Answer & Explanation

. Non-steroidal anti-inflammatory drugs (NSAIDs) or radiation therapy

Explanation

For patients at high risk of heterotopic ossification (HO) after elbow trauma or surgery (e.g., those with complex distal humerus fractures), prophylaxis with non-steroidal anti-inflammatory drugs (NSAIDs), such as indomethacin, or a single dose of perioperative radiation therapy is commonly employed. These interventions help to inhibit the inflammatory cascade and osteoblast differentiation that lead to HO. Early aggressive stretching can actually promote HO. Vitamin D, antibiotics, and corticosteroids are not standard HO prophylaxis.

Question 9848

Topic: Surgical Anatomy & Approaches

During the posterolateral approach to the distal humerus (e.g., Kocher approach), what is the interval primarily utilized?

. Between the brachialis and brachioradialis muscles
. Between the triceps and brachialis muscles
. Between the anconeus and extensor carpi ulnaris (ECU) muscles
. Between the flexor carpi ulnaris and flexor digitorum superficialis
. Between the brachioradialis and extensor carpi radialis longus

Correct Answer & Explanation

. Between the anconeus and extensor carpi ulnaris (ECU) muscles

Explanation

The posterolateral approach to the elbow, often referred to as the Kocher approach, utilizes the interval between the anconeus muscle and the extensor carpi ulnaris (ECU) muscle. This approach provides access to the lateral aspect of the elbow joint and distal humerus, particularly the capitellum, while protecting the radial nerve (which is more anterior and can be identified and protected with care). The other intervals are typically used for different approaches or expose different anatomical regions.

Question 9849

Topic: 1. General Principles & Basic Science
What is the typical sequence of ligamentous disruption in a progressive perilunar instability, as described by Mayfield?
. Lunotriquetral, Radioscaphocapitate, Scapholunate
. Scapholunate, Lunotriquetral, Radioscaphocapitate
. Scapholunate, Capitolunate (dorsal radiocarpal), Lunotriquetral
. Radioscaphocapitate, Scapholunate, Lunotriquetral
. Dorsal radiocarpal, Scapholunate, Volar radiocarpal

Correct Answer & Explanation

. Scapholunate, Capitolunate (dorsal radiocarpal), Lunotriquetral

Explanation

Mayfield's classification describes progressive failure of ligaments from radial to ulnar in a perilunar injury. Stage I: Scapholunate interosseous ligament and volar radioscaphocapitate ligament rupture. Stage II: Dorsal capitolunate ligament rupture. Stage III: Lunotriquetral interosseous ligament ruptures.

Question 9850

Topic: 1. General Principles & Basic Science

What is the approximate range of motion of forearm pronation and supination that must be preserved for most activities of daily living (ADLs)?

. 20 degrees pronation, 20 degrees supination
. 50 degrees pronation, 50 degrees supination
. 70 degrees pronation, 70 degrees supination
. 90 degrees pronation, 90 degrees supination
. Full physiological range (180 degrees combined)

Correct Answer & Explanation

. 50 degrees pronation, 50 degrees supination

Explanation

Approximately 50 degrees of pronation and 50 degrees of supination are generally considered sufficient for most activities of daily living (ADLs). While a full range is desirable, this 100-degree arc of forearm rotation allows for adequate function in many tasks. Loss beyond this threshold often leads to significant functional impairment.

Question 9851

Topic: 1. General Principles & Basic Science

What anatomical structure stabilizes the proximal radio-ulnar joint (PRUJ)?

. Medial collateral ligament
. Lateral ulnar collateral ligament
. Annular ligament
. Oblique cord
. Posterior interosseous nerve

Correct Answer & Explanation

. Annular ligament

Explanation

The annular ligament is a strong fibrous band that encircles the head of the radius, holding it in firm apposition with the radial notch of the ulna. It is the primary stabilizer of the proximal radio-ulnar joint (PRUJ), allowing for pronation and supination while maintaining joint integrity. The collateral ligaments stabilize the humeroulnar and humeroradial joints primarily, while the oblique cord is a secondary stabilizer of the forearm.

Question 9852

Topic: Surgical Anatomy & Approaches

Which muscle group is typically spared in a posterior interosseous nerve (PIN) palsy?

. Wrist extensors (e.g., extensor carpi radialis brevis)
. Finger extensors (e.g., extensor digitorum communis)
. Supinator
. Anconeus
. Extensor carpi radialis longus (ECRL)

Correct Answer & Explanation

. Extensor carpi radialis longus (ECRL)

Explanation

The extensor carpi radialis longus (ECRL) is typically spared in a posterior interosseous nerve (PIN) palsy because it is innervated by the radial nerve proximal to the division into superficial radial nerve and PIN. Therefore, patients with PIN palsy can still extend their wrist radially (ECRL action) but will have weakness or paralysis of finger and thumb extension, as well as ulnar wrist extension (ECU) and often weak supination (supinator). The anconeus is also innervated proximally to the PIN split.

Question 9853

Topic: 1. General Principles & Basic Science

What anatomical feature of the FDP tendon in the small finger sometimes accounts for poorer outcomes compared to other digits following repair?

. Its unique vincula tendinum configuration.
. Its greater reliance on the FDS for synergistic action.
. The consistently smaller diameter of the small finger FDP tendon.
. Its higher risk of associated nerve injury.
. Its independent muscle belly, leading to isolated weakness.

Correct Answer & Explanation

. The consistently smaller diameter of the small finger FDP tendon.

Explanation

The small finger FDP tendon is often found to have a consistently smaller diameter and poorer intrinsic quality compared to the other FDP tendons. This smaller caliber and potentially weaker tendon tissue can make repairs more challenging and contribute to a higher rate of re-rupture or less optimal outcomes. While other factors might play a role, the tendon's intrinsic size and quality are specifically cited in literature as a potential reason for poorer small finger outcomes. The FDP tendons of the medial four fingers share a common muscle belly, so it does not have an independent muscle belly in this context.

Question 9854

Topic: 1. General Principles & Basic Science

Which rehabilitation phase typically begins immediately post-operative and aims to prevent adhesions while protecting the repair in a flexor tendon injury?

. Passive protected motion phase.
. Active resistance exercise phase.
. Unrestricted activity phase.
. Strengthening and conditioning phase.
. Delayed mobilization phase.

Correct Answer & Explanation

. Passive protected motion phase.

Explanation

The immediate post-operative phase for flexor tendon repairs typically involves passive protected motion protocols. The goal is to allow controlled, passive movement of the repaired digit within a protective splint (e.g., dorsal blocking splint) to promote tendon gliding and prevent adhesions without putting excessive stress on the repair. Active resistance and unrestricted activity are introduced much later. Delayed mobilization is less common now due to the risk of significant stiffness.

Question 9855

Topic: 1. General Principles & Basic Science

Which of the following is considered a relative contraindication for primary FDP repair in an acute setting?

. Associated injury to the extensor mechanism.
. Patient occupation requiring fine motor skills.
. Significant contamination of the wound, increasing infection risk.
. Patient request for non-operative management.
. Inability to achieve full passive DIP flexion pre-operatively.

Correct Answer & Explanation

. Significant contamination of the wound, increasing infection risk.

Explanation

Significant wound contamination is a relative contraindication to immediate primary flexor tendon repair. Attempting to repair a tendon in a contaminated field dramatically increases the risk of deep infection, which can be devastating to the outcome. In such cases, thorough debridement, antibiotics, and a delayed primary repair or staged reconstruction might be considered after infection control. Associated extensor injury or patient occupation are not contraindications. Patient request for non-operative management is a patient choice, not a contraindication based on injury characteristics. Inability to achieve full passive DIP flexion pre-operatively is unusual in acute FDP rupture and might suggest other pathology.

Question 9856

Topic: 1. General Principles & Basic Science

What is the typical clinical finding that differentiates a complete FDP rupture from a partial FDP rupture?

. Complete inability to flex the DIP joint versus painful but weak DIP flexion.
. Presence of ecchymosis versus absence of ecchymosis.
. Palpable tendon gap versus no palpable gap.
. Positive modified tabletop test versus negative modified tabletop test.
. Presence of a bony avulsion versus absence of a bony avulsion.

Correct Answer & Explanation

. Complete inability to flex the DIP joint versus painful but weak DIP flexion.

Explanation

A complete FDP rupture results in a complete inability to actively flex the DIP joint of the affected finger. In contrast, a partial FDP rupture would typically present with painful but weak or incomplete active DIP flexion, rather than a total absence of motion. While other findings like ecchymosis or a palpable gap can be present, the key clinical differentiator for degree of rupture lies in the active motion test. The modified tabletop test would be positive (disrupted cascade) in a complete rupture. Bony avulsion classifies the injury type but doesn't differentiate complete vs. partial tear of the tendon substance itself.

Question 9857

Topic: 1. General Principles & Basic Science

What is the average ultimate tensile strength of a 4-strand core suture repair of a flexor tendon, a critical consideration for early motion protocols?

. Approximately 5-10 N.
. Approximately 10-20 N.
. Approximately 20-40 N.
. Approximately 40-60 N.
. Approximately 60-80 N.

Correct Answer & Explanation

. Approximately 40-60 N.

Explanation

The average ultimate tensile strength of a 4-strand core suture repair (e.g., Modified Kessler) is generally reported to be in the range of 40-60 Newtons (N). This level of strength is considered sufficient to withstand the forces generated during early protected motion protocols without re-rupture, allowing for the benefits of tendon gliding while maintaining repair integrity. Repairs with fewer strands (2-strand) are weaker, and 6-strand repairs offer more strength.

Question 9858

Topic: 1. General Principles & Basic Science

Which of the following is an expected long-term complication unique to FDP avulsion injuries involving the small finger?

. Increased risk of intrinsic muscle tightness.
. Higher incidence of lumbrical plus phenomenon.
. Greater propensity for persistent stiffness, even with good repair.
. More challenging aesthetic outcome.
. Risk of common digital nerve neuroma.

Correct Answer & Explanation

. Greater propensity for persistent stiffness, even with good repair.

Explanation

While stiffness can occur in any digit, the small finger FDP avulsion injuries are often associated with a greater propensity for persistent stiffness, less range of motion, and generally poorer functional outcomes compared to other digits, even with technically successful repairs and diligent rehabilitation. This is often attributed to the smaller tendon size, anatomical variations, and potentially higher tension in the small finger unit. Intrinsic tightness, lumbrical plus, and neuromas are not unique to the small finger FDP injury specifically.

Question 9859

Topic: Surgical Anatomy & Approaches

Which of the following describes the anatomical relationship of the FDP tendon relative to the FDS tendon in the finger?

. The FDP tendon lies superficial (more volar) to the FDS tendon.
. The FDP tendon lies deep (more dorsal) to the FDS tendon.
. The FDP and FDS tendons lie side-by-side in the flexor sheath.
. The FDP tendon passes through the split (decussation) of the FDS tendon at the DIP joint.
. The FDP tendon passes through the split (decussation) of the FDS tendon at the PIP joint.

Correct Answer & Explanation

. The FDP tendon passes through the split (decussation) of the FDS tendon at the PIP joint.

Explanation

In the finger, the FDP tendon lies deep (dorsal) to the FDS tendon until the level of the PIP joint. At the PIP joint, the FDS tendon splits (decussates) into two slips, allowing the FDP tendon to pass through this split to insert onto the distal phalanx. This anatomical relationship is critical for understanding flexor tendon mechanics and surgical approaches.

Question 9860

Topic: 1. General Principles & Basic Science

What is the primary function of the annular pulleys (A1-A5) in the flexor tendon sheath?

. To provide blood supply to the flexor tendons.
. To prevent excessive friction between the tendons and bone.
. To maintain the flexor tendons in close proximity to the phalanges, optimizing mechanical advantage.
. To absorb shock during forceful gripping activities.
. To produce synovial fluid for lubrication.

Correct Answer & Explanation

. To maintain the flexor tendons in close proximity to the phalanges, optimizing mechanical advantage.

Explanation

The primary function of the annular pulleys (A1-A5) is to keep the flexor tendons closely apposed to the phalanges. This prevents 'bowstringing' of the tendons, which would otherwise reduce their mechanical advantage and drastically diminish their efficiency in generating joint flexion. The vincula provide blood supply. The synovial sheath produces fluid and reduces friction. Pulleys are structural, not shock absorbers.

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