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1. General Principles & Basic Science MCQs

Practice Set 108 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 2141

Topic: Biomechanics & Biomaterials

What process is most commonly used to eliminate free radicals in highly cross-linked polyethylene components used in total joint arthroplasty?

. Gamma irradiation in air
. Ethylene oxide sterilization
. Melting or annealing the polyethylene
. Addition of polymethylmethacrylate
. Cold forging

Correct Answer & Explanation

. Melting or annealing the polyethylene

Explanation

After cross-linking via irradiation, free radicals are eliminated by either melting or annealing the polyethylene. This critical step prevents long-term oxidation and subsequent abrasive wear in vivo.

Question 2142

Topic: Infection, Pharmacology & VTE

The 33-year-old patient's current symptom of intermittent painful locking is directly caused by the loose body. What is the most appropriate definitive treatment for this patient's current symptoms and to prevent future locking episodes?

. Physical therapy and activity modification
. NSAIDs and observation
. Arthroscopic removal of the loose body
. Open reduction and internal fixation of the loose body
. Corticosteroid injection into the elbow joint

Correct Answer & Explanation

. Arthroscopic removal of the loose body

Explanation

Correct Answer: CExplanation:The patient's primary symptom is intermittent painful locking caused by a loose body. The most appropriate definitive treatment for a symptomatic intra-articular loose body in the elbow isarthroscopic removal of the loose body. This procedure directly addresses the mechanical obstruction causing the locking and pain. Physical therapy and activity modification (A) and NSAIDs and observation (B) are conservative measures that may temporarily alleviate symptoms but will not remove the mechanical block or prevent future locking episodes. Open reduction and internal fixation (D) would be considered if the loose body was a large, viable osteochondral fragment that could be reattached to its bed, but for a free, symptomatic loose body causing locking, simple removal is typically preferred. Corticosteroid injections (E) may reduce inflammation but will not resolve the mechanical issue of a loose body.

Question 2143

Topic: 1. General Principles & Basic Science

The patient's current symptoms of intermittent painful locking are a direct consequence of the loose body. What is the primary mechanism by which an intra-articular loose body causes locking in a joint?

. Inflammation of the synovial lining
. Direct compression of articular cartilage
. Mechanical impingement between joint surfaces
. Increased intra-articular pressure
. Ligamentous laxity

Correct Answer & Explanation

. Mechanical impingement between joint surfaces

Explanation

Correct Answer: CExplanation:The primary mechanism by which an intra-articular loose body causes locking in a joint ismechanical impingement between joint surfaces. A loose body, which is a free-floating fragment of bone or cartilage, can get caught between the articulating surfaces of the joint during movement. This physical obstruction prevents the joint from moving through its full range of motion, leading to a sudden, painful block or 'locking' sensation. While a loose body can cause some inflammation (A) or direct compression (B) if it's large, the characteristic locking symptom is due to its physical interposition. Increased intra-articular pressure (D) is not the direct cause of locking, and ligamentous laxity (E) is unrelated to loose body locking.

Question 2144

Topic: Surgical Anatomy & Approaches

During arthroscopic removal of a loose body in the anterior elbow compartment, the surgeon establishes the anterolateral portal. Which nerve is most at risk during the establishment of this specific portal?

. Ulnar nerve
. Median nerve
. Radial nerve
. Musculocutaneous nerve
. Axillary nerve

Correct Answer & Explanation

. Radial nerve

Explanation

The anterolateral portal places the radial nerve at risk. To minimize risk, the portal should be established just anterior to the radiocapitellar joint and the joint should be distended with fluid prior to portal placement.

Question 2145

Topic: Surgical Anatomy & Approaches

A 45-year-old male undergoes elbow arthroscopy for removal of multiple loose bodies. Which standard arthroscopic portal places the radial nerve at the highest risk of injury?

. Anteromedial
. Anterolateral
. Proximal anteromedial
. Direct lateral
. Posterocentral

Correct Answer & Explanation

. Anterolateral

Explanation

The anterolateral portal places the radial nerve at highest risk, as the nerve lies approximately 3-7 mm from the portal tract. The anteromedial portals place the median nerve and brachial artery at risk.

Question 2146

Topic: Surgical Anatomy & Approaches

A patient with multiple radiocapitellar loose bodies undergoes an anterior capsulotomy and loose body excision via a lateral approach. Postoperatively, they cannot actively extend their fingers at the metacarpophalangeal joints, but wrist extension is preserved with radial deviation. Which nerve was most likely injured?

. Superficial radial nerve
. Posterior interosseous nerve (PIN)
. Anterior interosseous nerve (AIN)
. Ulnar nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Posterior interosseous nerve (PIN)

Explanation

The posterior interosseous nerve (PIN) supplies the extensor digitorum communis but not the extensor carpi radialis longus (ECRL). PIN injury results in an inability to extend the digits at the MCP joints, while wrist extension persists with a radial deviation bias due to the intact ECRL.

Question 2147

Topic: Surgical Anatomy & Approaches

When performing elbow arthroscopy to remove loose bodies, establishing the anteromedial portal places which neurological structure at the greatest superficial risk of iatrogenic injury?

. Ulnar nerve
. Radial nerve
. Posterior interosseous nerve
. Medial antebrachial cutaneous nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Medial antebrachial cutaneous nerve

Explanation

The medial antebrachial cutaneous (MABC) nerve is at the highest superficial risk when establishing the anteromedial portal. The ulnar nerve is also at risk but is typically protected by keeping instruments anterior to the intermuscular septum.

Question 2148

Topic: Biology, Genetics & Bone Healing

A 72-year-old female on long-term bisphosphonate therapy presents with prodromal thigh pain followed by an atraumatic, transverse subtrochanteric fracture. Radiographs show lateral cortical thickening and a medial cortical spike. What is the most appropriate surgical management?

. Short cephalomedullary nail
. Full-length cephalomedullary nail
. Dynamic hip screw
. Lateral locked plating
. Proximal femoral replacement

Correct Answer & Explanation

. Full-length cephalomedullary nail

Explanation

Atypical femur fractures associated with bisphosphonate use are best treated with full-length cephalomedullary nailing to protect the entire femur, as the bone quality is universally poor and concomitant lesions may exist distally.

Question 2149

Topic: Physiology & Rehabilitation

In terms of meniscal innervation, which region is primarily responsible for proprioceptive feedback?

. The inner one-third (white-white zone).
. The central body, along its inferior surface.
. The anterior and posterior horns, particularly the vascularized periphery.
. The entire articular surface equally.
. Only the attachments to the tibial plateau.

Correct Answer & Explanation

. The anterior and posterior horns, particularly the vascularized periphery.

Explanation

Correct Answer: CThe menisci are innervated primarily in their vascularized periphery, particularly the anterior and posterior horns. Mechanoreceptors (Ruffini endings, Pacinian corpuscles, Golgi tendon organ-like endings) and free nerve endings are concentrated in these regions, contributing to proprioception and nociception. The inner two-thirds (white-white zone) are largely aneural and thus lack significant innervation for proprioception.

Question 2150

Topic: 1. General Principles & Basic Science

A discoid meniscus is an anatomical variant most commonly affecting which meniscus?

. Medial meniscus, posterior horn.
. Lateral meniscus, complete type.
. Medial meniscus, anterior horn.
. Lateral meniscus, incomplete type.
. Medial and lateral menisci equally.

Correct Answer & Explanation

. Lateral meniscus, complete type.

Explanation

Correct Answer: BA discoid meniscus is an abnormally shaped, usually thicker and wider, meniscus that is prone to tearing. It most commonly affects the lateral meniscus, with the 'complete' type being the most recognized. It can be asymptomatic or present with snapping, pain, or locking, particularly with activity. While incomplete types exist, the lateral complete discoid meniscus is the classic presentation.

Question 2151

Topic: Biomechanics & Biomaterials

What is the typical water content of a healthy adult meniscus?

. Approximately 30-40% of wet weight.
. Approximately 50-60% of wet weight.
. Approximately 70-80% of wet weight.
. Approximately 90-95% of wet weight.
. Less than 20% of wet weight.

Correct Answer & Explanation

. Approximately 70-80% of wet weight.

Explanation

Correct Answer: CThe meniscus is rich in water, which accounts for approximately 70-80% of its wet weight in healthy adults. This high water content, along with the proteoglycan matrix, contributes to its viscoelastic properties and ability to distribute loads and absorb shock. With age and degeneration, water content can decrease, affecting its biomechanical function.

Question 2152

Topic: Surgical Anatomy & Approaches

A patient demonstrates a positive "lift-off" test and a positive "belly-press" test after a traumatic shoulder injury. These tests isolate the subscapularis muscle. Which of the following nerves supplies the isolated muscle?

. Axillary nerve
. Upper and lower subscapular nerves
. Suprascapular nerve
. Musculocutaneous nerve
. Long thoracic nerve

Correct Answer & Explanation

. Upper and lower subscapular nerves

Explanation

The subscapularis muscle is evaluated via the lift-off, belly-press, and bear-hug tests. It is innervated by the upper and lower subscapular nerves, which are branches of the posterior cord of the brachial plexus.

Question 2153

Topic: 1. General Principles & Basic Science

A 10-year-old boy presents with a painful, snapping knee. MRI demonstrates a discoid lateral meniscus. In the Wrisberg variant of a discoid meniscus, which of the following normal anatomic attachments is absent?

. The transverse intermeniscal ligament
. The ligament of Humphry
. The posterior meniscotibial (coronary) ligaments
. The anterior horn attachment to the tibia
. The medial collateral ligament

Correct Answer & Explanation

. The posterior meniscotibial (coronary) ligaments

Explanation

The Wrisberg variant of the discoid meniscus lacks the normal posterior meniscotibial (coronary) attachments. The posterior horn is exclusively tethered by the meniscofemoral ligament of Wrisberg, leading to hypermobility and the classic "snapping knee" syndrome.

Question 2154

Topic: 1. General Principles & Basic Science

A 19-year-old male presents with acute dyspnea, dysphagia, and a choking sensation after a pile-up in a rugby game. Physical examination reveals an asymmetric depression at the medial aspect of the right clavicle. A CT scan confirms a posterior sternoclavicular joint dislocation. What is the most critical anatomical structure at risk immediately posterior to this injury?

. Brachial plexus
. Subclavian artery
. Innominate vein and artery
. Recurrent laryngeal nerve
. Thoracic duct

Correct Answer & Explanation

. Innominate vein and artery

Explanation

Posterior sternoclavicular dislocations are true orthopedic emergencies due to the risk of compression or laceration to the great vessels (innominate vein/artery, superior vena cava), trachea, and esophagus.

Question 2155

Topic: Infection, Pharmacology & VTE

A 72-year-old diabetic female undergoes a two-stage revision for chronic PJI due to MRSA. The first stage involves implant removal, extensive debridement, and placement of an articulating antibiotic-loaded cement spacer. After 6 weeks of targeted intravenous antibiotics, her ESR is 25 mm/hr (down from 80), CRP is 3 mg/L (down from 55), and repeat knee aspirations are negative for growth on multiple cultures. What is the most critical next step before proceeding to the second stage of reimplantation?

. Obtain a new MRI to rule out osteomyelitis.
. Perform a CT scan to assess bone stock.
. Confirm absence of infection with at least two consecutive negative synovial fluid cultures, ideally off antibiotics for a period.
. Empirically continue intravenous antibiotics for an additional 2 weeks.
. Order serum alpha-defensin to confirm infection eradication.

Correct Answer & Explanation

. Confirm absence of infection with at least two consecutive negative synovial fluid cultures, ideally off antibiotics for a period.

Explanation

Correct Answer: CThe most critical step to confirm infection eradication before proceeding to the second stage of reimplantation is obtaining at least two, preferably three, consecutive negative synovial fluid cultures from the knee, ideally after a period off antibiotics (e.g., 2 weeks) to reduce false negatives. While inflammatory markers (ESR, CRP) can guide treatment, they are not definitive for eradication. Imaging (MRI, CT) may be useful for assessing bone stock or identifying occult infection but does not replace microbiological confirmation. Serum alpha-defensin is a diagnostic marker for PJI, not typically used for confirming eradication post-treatment. Empirically continuing antibiotics without microbiological clearance increases the risk of resistance and does not confirm eradication.

Question 2156

Topic: 1. General Principles & Basic Science

What is the primary mechanism by which antibiotic-loaded bone cement (ALBC) spacers help in eradicating infection during the first stage of a two-stage revision for PJI?

. They provide structural support, allowing early weight-bearing.
. They absorb inflammatory cytokines, reducing systemic inflammation.
. They create a high local concentration of antibiotics at the infection site.
. They mechanically remove bacterial biofilm from the surrounding bone.
. They stimulate local immune responses against bacteria.

Correct Answer & Explanation

. They create a high local concentration of antibiotics at the infection site.

Explanation

Correct Answer: CThe primary mechanism by which antibiotic-loaded bone cement (ALBC) spacers aid in infection eradication is by creating a very high local concentration of antibiotics at the infection site. This local delivery allows for concentrations far exceeding what can be achieved systemically, which is crucial for penetrating biofilms and effectively killing bacteria. While some structural support is offered, and they maintain the joint space, their main therapeutic benefit is antibiotic elution. They do not directly absorb cytokines, mechanically remove biofilm (though debridement does), or primarily stimulate local immune responses in this context.

Question 2157

Topic: Infection, Pharmacology & VTE

The examiner asks about removing the acetabular component. The candidate states the safest way is to disrupt the PE cup from the cement using curved gouges. After removal of the cup, the cement is removed piecemeal. What is the primary reason for this specific initial approach to acetabular component removal?

. A. To allow for easier visualization of anchoring holes for burring
. B. To prevent inadvertent damage to the bone of the acetabulum bed
. C. To facilitate the use of a threaded extractor through a drill hole
. D. To reduce operating time and blood loss
. E. To ensure complete removal of all polyethylene debris

Correct Answer & Explanation

. B. To prevent inadvertent damage to the bone of the acetabulum bed

Explanation

Correct Answer: BExplanation:The case describes the acetabular component removal: 'The safest way is to disrupt the PE cup from the cement using curved gouges. This prevents inadvertent damage to the bone of the acetabulum bed. After removal of the cup the cement is removed piecemeal.'A. To allow for easier visualization of anchoring holes for burring:While visualization is important, the primary reason stated for this initial step is bone protection, not specifically visualization for burring. Burring comes later for debulking cement.B. To prevent inadvertent damage to the bone of the acetabulum bed:This is the explicit reason given in the case for disrupting the PE cup from the cement first with curved gouges. Protecting the host bone is paramount in revision surgery.C. To facilitate the use of a threaded extractor through a drill hole:A threaded extractor is mentioned as analternativemethod ('Sometimes a threaded extractor through a drill hole in the PE can be used'), not the primary reason for the initial gouge technique.D. To reduce operating time and blood loss:While efficient removal can contribute to this, the primary stated reason for this specific technique is safety and bone preservation, not necessarily a reduction in time or blood loss.E. To ensure complete removal of all polyethylene debris:While removing the PE cup is part of the process, the stated reason forthis specific initial techniqueis bone protection, not debris removal.

Question 2158

Topic: Infection, Pharmacology & VTE

Which of the following is the most critical factor determining the success of a debridement, antibiotics, and implant retention (DAIR) procedure for an acute periprosthetic knee infection?

. Type of bearing surface used
. Age of the patient
. Duration of symptoms prior to intervention
. Preoperative erythrocyte sedimentation rate
. Use of a constrained liner

Correct Answer & Explanation

. Duration of symptoms prior to intervention

Explanation

The duration of symptoms is the most critical determinant of DAIR success, with significantly higher failure rates if symptoms have been present for more than 3 to 4 weeks. Early intervention is paramount before a mature biofilm can fully establish on the implant surfaces.

Question 2159

Topic: Surgical Anatomy & Approaches

During a total hip arthroplasty via the direct anterior approach, the surgeon utilizes the internervous plane between the tensor fasciae latae (TFL) and the sartorius. Which nerves supply these two muscles, respectively?

. Femoral nerve and obturator nerve
. Superior gluteal nerve and femoral nerve
. Inferior gluteal nerve and superior gluteal nerve
. Sciatic nerve and femoral nerve
. Femoral nerve and superior gluteal nerve

Correct Answer & Explanation

. Superior gluteal nerve and femoral nerve

Explanation

The direct anterior approach (Smith-Petersen) exploits the internervous plane between the TFL, innervated by the superior gluteal nerve, and the sartorius, innervated by the femoral nerve. Using this true internervous plane helps minimize postoperative muscle denervation.

Question 2160

Topic: Infection, Pharmacology & VTE

Which of the following describes the primary mechanism by which adding Rifampin enhances the efficacy of antibiotic regimens in the treatment of staphylococcal periprosthetic joint infections?

. It acts synergistically by inhibiting bacterial cell wall synthesis alongside beta-lactams.
. It irreversibly binds to the 50S ribosomal subunit to halt protein synthesis.
. It penetrates bacterial biofilms and kills stationary-phase organisms on the implant surface.
. It alters the local pH of the synovial fluid, creating a hostile environment for staphylococci.
. It prevents the systemic dissemination of methicillin-resistant strains by blocking exotoxin release.

Correct Answer & Explanation

. It penetrates bacterial biofilms and kills stationary-phase organisms on the implant surface.

Explanation

Rifampin is uniquely highly effective against staphylococcal species residing within biofilms on orthopedic implants. It penetrates the biofilm matrix and kills slow-growing, stationary-phase bacteria by inhibiting DNA-dependent RNA polymerase.

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