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1. General Principles & Basic Science MCQs

Practice Set 567 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 11321

Topic: Surgical Anatomy & Approaches

A surgeon is performing a primary THA using a direct anterior (Smith-Petersen) approach. Which of the following neurologic structures is at highest risk during the superficial dissection, and what is its expected sensory distribution if injured?

. Femoral nerve; Anterior thigh sensation
. Lateral femoral cutaneous nerve; Lateral thigh sensation
. Superior gluteal nerve; Gluteal region sensation
. Sciatic nerve; Posterior thigh sensation
. Obturator nerve; Medial thigh sensation

Correct Answer & Explanation

. Femoral nerve; Anterior thigh sensation

Explanation

The direct anterior approach utilizes the internervous plane between the sartorius (femoral n.) and tensor fasciae latae (superior gluteal n.). The lateral femoral cutaneous nerve (LFCN) is highly vulnerable during the superficial dissection as it courses over or near the sartorius muscle just distal to the ASIS. Injury results in lateral/anterolateral thigh numbness (meralgia paresthetica).

Question 11322

Topic: Biology, Genetics & Bone Healing

What is the primary cellular cascade responsible for aseptic loosening and periprosthetic osteolysis in a total hip arthroplasty?

. Direct toxicity of cobalt and chromium ions leading to osteoblast apoptosis
. Macrophage phagocytosis of particulate wear debris leading to the release of TNF-alpha and IL-1, and subsequent osteoclast activation
. Neutrophil-mediated respiratory burst causing local tissue necrosis around the implant
. T-cell mediated delayed type IV hypersensitivity reaction to nickel
. Osteoclast activation driven exclusively by mechanically induced sheer stress on the bone-cement interface

Correct Answer & Explanation

. Direct toxicity of cobalt and chromium ions leading to osteoblast apoptosis

Explanation

Periprosthetic osteolysis is primarily a macrophage-mediated biologic response to particulate wear debris (most commonly polyethylene). Macrophages phagocytose these particles but cannot digest them, leading to activation and the release of pro-inflammatory cytokines such as TNF-alpha, IL-1, IL-6, and PGE2. These cytokines increase the expression of RANKL, which strongly activates osteoclasts, leading to bone resorption and eventual implant loosening.

Question 11323

Topic: 1. General Principles & Basic Science

Intravenous Tranexamic Acid (TXA) is routinely utilized in total joint arthroplasty to reduce perioperative blood loss. Which of the following accurately describes its pharmacological mechanism of action?

. Direct inhibition of cyclooxygenase-1 in platelets
. Direct activation of thrombin via the intrinsic cascade
. Reversible competitive blockade of lysine binding sites on plasminogen
. Inhibition of Vitamin K epoxide reductase
. Direct antagonism of the ADP receptor on platelets

Correct Answer & Explanation

. Direct inhibition of cyclooxygenase-1 in platelets

Explanation

Tranexamic acid is an antifibrinolytic agent. It works by reversibly and competitively binding to the lysine receptor sites on plasminogen. This prevents plasminogen from binding to fibrin and subsequently being activated into plasmin, thereby inhibiting the degradation of fibrin clots (fibrinolysis).

Question 11324

Topic: 1. General Principles & Basic Science

A 45-year-old female is scheduled for a TKA. She reports a history of severe localized blistering and eczematous rash whenever she wears inexpensive jewelry or metal watch bands. Which of the following pre-operative steps and implant choices represents the most appropriate evidence-based management?

. Utilize an oxidized zirconium or fully titanium-based femoral component without needing to delay for skin patch testing
. Order a serum chromium level and use standard CoCr implants if levels are normal
. Proceed with standard Cobalt-Chromium implants as cutaneous sensitivity does not correlate with deep implant allergy
. Administer pre-operative systemic corticosteroids and use standard Cobalt-Chromium implants
. Delay surgery for 6 months to allow natural desensitization before placing standard implants

Correct Answer & Explanation

. Utilize an oxidized zirconium or fully titanium-based femoral component without needing to delay for skin patch testing

Explanation

Patients with a strong clinical history of severe metal hypersensitivity (most commonly Nickel or Cobalt) are at risk for complications if standard Cobalt-Chromium (CoCr) implants are used. While routine patch testing or Lymphocyte Transformation Testing (LTT) is debated and often unreliable, the standard of care for a patient with a compelling history of metal allergy is to bypass testing and utilize hypoallergenic implants, such as oxidized zirconium (Oxinium) or Titanium alloy components.

Question 11325

Topic: Biomechanics & Biomaterials
A 55-year-old active male is undergoing total hip arthroplasty. The surgeon chooses a highly cross-linked polyethylene (HXLPE) liner. Which of the following is an expected trade-off compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE)?
. Increased adhesive wear
. Decreased fatigue resistance
. Increased abrasive wear
. Increased oxidation potential after remelting
. Decreased volumetric wear linearly proportional to cup diameter

Correct Answer & Explanation

. Decreased fatigue resistance

Explanation

Cross-linking of polyethylene significantly reduces adhesive and abrasive wear, decreasing the volumetric wear rate. However, the irradiation process decreases the mechanical properties of the material, specifically reducing its fracture toughness, yield strength, ultimate tensile strength, and fatigue crack propagation resistance.

Question 11326

Topic: Surgical Anatomy & Approaches

A direct anterior approach to the hip is chosen for a primary total hip arthroplasty. The superficial surgical dissection utilizes an internervous plane between muscles supplied by which two nerves?

. Superior gluteal nerve and inferior gluteal nerve
. Femoral nerve and superior gluteal nerve
. Femoral nerve and obturator nerve
. Sciatic nerve and superior gluteal nerve
. Femoral nerve and sciatic nerve

Correct Answer & Explanation

. Superior gluteal nerve and inferior gluteal nerve

Explanation

The direct anterior approach (Smith-Petersen) utilizes the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve) during the superficial dissection.

Question 11327

Topic: Biology, Genetics & Bone Healing

A patient presents with aseptic loosening and extensive periprosthetic osteolysis 15 years after a cementless total hip arthroplasty. What is the primary biological mediator responsible for osteoclast activation in this process?

. Interleukin-10 (IL-10)
. Transforming growth factor beta (TGF-beta)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Osteoprotegerin (OPG)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Interleukin-10 (IL-10)

Explanation

Particle wear debris is phagocytosed by macrophages, which release pro-inflammatory cytokines. These cytokines stimulate the expression of RANKL by osteoblasts and fibroblasts. RANKL binds to the RANK receptor on osteoclast precursors, leading to osteoclastogenesis and subsequent osteolysis.

Question 11328

Topic: Infection, Pharmacology & VTE

During a total knee arthroplasty for a severe varus deformity, the medial compartment remains tight in both flexion and extension after initial bone resections. Which of the following is the most appropriate sequence of soft tissue release?

. Deep medial collateral ligament (MCL), posterior medial corner, semimembranosus, superficial MCL
. Superficial MCL, pes anserinus, deep MCL, posterior oblique ligament
. Deep MCL, superficial MCL (anterior aspect), pes anserinus, posterior medial corner
. Deep MCL, posteromedial capsule, semimembranosus, superficial MCL
. Iliotibial band, popliteus, lateral collateral ligament

Correct Answer & Explanation

. Deep medial collateral ligament (MCL), posterior medial corner, semimembranosus, superficial MCL

Explanation

For a tight medial compartment (varus knee) in both flexion and extension, standard releases proceed sequentially: 1. Osteophyte removal; 2. Deep MCL release; 3. Posteromedial capsule and semimembranosus (to address extension tightness); 4. Superficial MCL subperiosteal stripping; 5. Pes anserinus.

Question 11329

Topic: Biomechanics & Biomaterials

During a cemented total hip arthroplasty, which of the following techniques is most important to maximize the fatigue strength of the polymethylmethacrylate (PMMA) bone cement?

. Hand-mixing the cement in an open bowl
. Adding aqueous antibiotics to the cement powder
. Vacuum mixing to reduce porosity
. Delaying insertion until the cement is in the doughy phase
. Minimizing pressurization during insertion

Correct Answer & Explanation

. Hand-mixing the cement in an open bowl

Explanation

Vacuum mixing significantly reduces the porosity of PMMA bone cement by eliminating air bubbles trapped during mixing. Reduced porosity decreases stress risers within the cement mantle, thereby maximizing its intrinsic fatigue strength.

Question 11330

Topic: Biomechanics & Biomaterials

A 62-year-old male with a primary metal-on-polyethylene THA presents with a 6-month history of worsening hip pain. Blood tests reveal elevated serum cobalt and chromium levels. Radiographs demonstrate a well-fixed modular titanium stem and acetabular cup. What is the most likely source of the metal ion elevation in this specific clinical scenario?

. Impingement of the femoral neck on the metallic acetabular rim
. Mechanically assisted crevice corrosion at the head-neck junction
. Third-body wear of the polyethylene transferring to the trunnion
. Corrosion at the interface of a modular distal femoral sleeve
. Galvanic corrosion between the titanium stem and cortical bone

Correct Answer & Explanation

. Impingement of the femoral neck on the metallic acetabular rim

Explanation

In a metal-on-polyethylene bearing with elevated metal ions, the most common source of cobalt and chromium is mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck taper junction. This is increasingly recognized with large diameter metal heads on titanium stems.

Question 11331

Topic: Surgical Anatomy & Approaches

During a direct anterior approach for a total hip arthroplasty, the surgeon develops the internervous plane superficially between the tensor fasciae latae and the sartorius. Which nerve is anatomically at greatest risk of iatrogenic injury during this superficial dissection?

. Superior gluteal nerve
. Femoral nerve
. Lateral femoral cutaneous nerve
. Sciatic nerve
. Obturator nerve

Correct Answer & Explanation

. Superior gluteal nerve

Explanation

The direct anterior (Smith-Petersen) approach uses the superficial interval between the tensor fasciae latae (superior gluteal n.) and sartorius (femoral n.). The lateral femoral cutaneous nerve (LFCN) courses over the sartorius and can cross the surgical interval, putting it at high risk for stretch or transection during the superficial approach.

Question 11332

Topic: Biomechanics & Biomaterials

Early formulations of zirconia ceramic femoral heads in total hip arthroplasty experienced an unacceptably high rate of catastrophic failure in vivo. This mechanical failure was fundamentally attributed to which of the following material properties?

. Galvanic corrosion at the interface between the ceramic head and the titanium trunnion
. Phase transformation from the stable tetragonal phase to the weaker monoclinic phase in an aqueous environment
. High levels of continuous alpha radiation emitting from the zirconia matrix
. Severe impingement leading to focal stripe wear and eventual shattering
. Rapid third-body wear initiated by hydroxyapatite shedding from the acetabular cup

Correct Answer & Explanation

. Galvanic corrosion at the interface between the ceramic head and the titanium trunnion

Explanation

Yttria-stabilized zirconia was introduced for its high fracture toughness. However, in the aqueous, warm environment of the human body, the material undergoes a slow phase transformation from the strong tetragonal phase to the weaker monoclinic phase. This transformation is accompanied by a volume expansion that creates microcracks, ultimately leading to catastrophic shattering of the femoral head.

Question 11333

Topic: Biomechanics & Biomaterials

In the manufacturing of highly cross-linked polyethylene (HXLPE) for total hip arthroplasty, the polymer is often subjected to a thermal treatment of remelting (heating above its melting point of 135°C). What is the primary advantage of remelting compared to annealing (heating below the melting point)?

. It completely eliminates free radicals, maximizing oxidation resistance.
. It increases the ultimate tensile strength of the polyethylene.
. It enhances the fatigue crack propagation resistance.
. It promotes further cross-linking to decrease wear rates.
. It increases the crystallinity of the polyethylene structure.

Correct Answer & Explanation

. It completely eliminates free radicals, maximizing oxidation resistance.

Explanation

Remelting highly cross-linked polyethylene above its melting point allows polymer chains enough mobility to recombine and completely eliminate free radicals, which maximizes long-term oxidation resistance. However, it does cause a slight reduction in mechanical properties (like fatigue strength and crystallinity) compared to annealing. Annealing preserves more mechanical strength but leaves residual free radicals.

Question 11334

Topic: Surgical Anatomy & Approaches

The direct anterior (Smith-Petersen) approach to the hip has gained popularity for total hip arthroplasty. During the superficial dissection, the internervous plane is developed between muscles innervated by which of the following pairs of nerves?

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

Correct Answer & Explanation

. Superior gluteal nerve and inferior gluteal nerve

Explanation

The superficial internervous plane in the direct anterior approach to the hip is between the tensor fasciae latae (innervated by the superior gluteal nerve) laterally and the sartorius (innervated by the femoral nerve) medially.

Question 11335

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is frequently used for component fixation in arthroplasty. What is the primary mechanism by which PMMA secures a prosthesis to the host bone?

. Covalent chemical bonding to the hydroxyapatite of the bone.
. Covalent chemical bonding to the metallic surface of the prosthesis.
. Osteoinductive stimulation of local bone ingrowth.
. Mechanical interlock by acting as a grout within the interstices of cancellous bone.
. Thermal necrosis of the bone bed resulting in a fibrous ankylosis.

Correct Answer & Explanation

. Covalent chemical bonding to the hydroxyapatite of the bone.

Explanation

PMMA bone cement acts strictly as a grout, not an adhesive. It does not chemically bond to bone or the implant. Its primary mechanism of fixation relies on mechanical interdigitation as the liquid cement flows into the trabecular interstices of the prepared cancellous bone bed and subsequently cures and hardens into a solid mantle.

Question 11336

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum gap strain tolerated for lamellar bone formation?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Up to 50%
. Up to 100%

Correct Answer & Explanation

. Less than 2%

Explanation

According to Perren's strain theory, lamellar bone can only form when the interfragmentary strain is less than 2%. Woven bone forms at strains between 2% and 10%, while granulation tissue can tolerate up to 100% strain without rupturing.

Question 11337

Topic: Infection, Pharmacology & VTE
A 4-year-old child presents with a limp, fever of 39.0°C, and inability to bear weight. Laboratory tests show a WBC of 14,000/mm³ and an ESR of 55 mm/hr. According to the Kocher criteria, what is the probability that this child has septic arthritis of the hip?
. Less than 10%
. Approximately 40%
. Approximately 70%
. Greater than 90%
. 100%

Correct Answer & Explanation

. Greater than 90%

Explanation

The Kocher criteria to differentiate septic arthritis from transient synovitis include: non-weight-bearing on the affected side, temperature > 38.5°C, ESR > 40 mm/hr, and WBC > 12,000/mm³. Having all 4 predictors yields a 99% probability (greater than 90%) of septic arthritis.

Question 11338

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft substitutes or biological agents possesses strictly osteoinductive properties without being osteoconductive or osteogenic?

. Demineralized bone matrix (DBM)
. Cancellous allograft
. Bone morphogenetic protein-2 (BMP-2)
. Calcium phosphate cement
. Autologous iliac crest bone graft

Correct Answer & Explanation

. Demineralized bone matrix (DBM)

Explanation

BMP-2 is a purely osteoinductive agent (it induces differentiation of mesenchymal stem cells into osteoblasts). Demineralized bone matrix (DBM) is both osteoinductive and osteoconductive. Cancellous allograft and calcium phosphate are solely osteoconductive. Autograft provides all three: osteoinduction, osteoconduction, and osteogenesis.

Question 11339

Topic: Biomechanics & Biomaterials

Which of the following orthopedic biomaterials has a modulus of elasticity (Young's modulus) that most closely matches that of normal human cortical bone?

. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Polymethylmethacrylate (PMMA)
. Alumina ceramic

Correct Answer & Explanation

. Cobalt-chromium alloy

Explanation

Titanium alloy has a modulus of elasticity (approx. 110 GPa) that is closer to that of cortical bone (approx. 15-20 GPa) compared to stainless steel (200 GPa) or cobalt-chromium (220 GPa). This closer match helps reduce stress shielding around implants.

Question 11340

Topic: 1. General Principles & Basic Science

The vascular supply to the menisci of the adult knee originates primarily from a perimeniscal capillary plexus. Which of the following arteries provide the major contribution to this plexus?

. Middle genicular artery alone
. Superior and inferior genicular arteries
. Sural arteries
. Descending genicular artery
. Anterior tibial recurrent artery

Correct Answer & Explanation

. Middle genicular artery alone

Explanation

The peripheral 10-30% of the menisci is vascularized by a capillary plexus originating from the medial and lateral superior and inferior genicular arteries. The middle genicular artery primarily supplies the cruciate ligaments and posterior horns, but the main peripheral supply is from the superior and inferior genicular vessels.

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