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1. General Principles & Basic Science MCQs

Practice Set 348 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 6941

Topic: Surgical Anatomy & Approaches

During a direct anterior approach (Smith-Petersen) to the hip, an internervous plane is utilized. The superficial interval is developed between which of the following two muscles?

. Rectus femoris and Gluteus medius
. Sartorius and Tensor fasciae latae
. Tensor fasciae latae and Gluteus medius
. Pectineus and Adductor longus
. Sartorius and Rectus femoris

Correct Answer & Explanation

. Rectus femoris and Gluteus medius

Explanation

The direct anterior approach exploits a true internervous plane. Superficial dissection is between the sartorius (femoral nerve) and tensor fasciae latae (superior gluteal nerve).

Question 6942

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is widely utilized to reduce perioperative blood loss in joint arthroplasty. What is its precise mechanism of action?

. Promotes the activation of factor X to Xa
. Inhibits cyclooxygenase enzymes
. Competitively inhibits the activation of plasminogen to plasmin
. Directly stimulates platelet aggregation and plug formation
. Cleaves fibrinogen into fibrin monomers

Correct Answer & Explanation

. Promotes the activation of factor X to Xa

Explanation

TXA is a synthetic analog of the amino acid lysine. It reversibly and competitively inhibits the activation of plasminogen to plasmin, thereby preventing the degradation of fibrin clots (antifibrinolytic effect).

Question 6943

Topic: Biomechanics & Biomaterials

Trunnionosis has emerged as a significant mode of failure in modern total hip arthroplasty, particularly involving modular head-neck junctions. This process is most accurately described by which of the following mechanisms?

. Galvanic corrosion exclusively due to dissimilar metals
. Abrasive wear from third-body bone cement particles
. Mechanically assisted crevice corrosion
. Polyethylene delamination
. Adhesive wear from edge loading

Correct Answer & Explanation

. Galvanic corrosion exclusively due to dissimilar metals

Explanation

Trunnionosis refers to the wear and corrosion at the modular head-neck taper interface. It is primarily driven by mechanically assisted crevice corrosion (MACC), which is a combination of fretting wear and subsequent electrochemical corrosion.

Question 6944

Topic: Physiology & Rehabilitation

A patient with advanced unilateral hip osteoarthritis is instructed to use a cane. To maximally reduce the joint reaction force on the affected hip, the cane should be held in the contralateral hand. What is the primary biomechanical reason for this reduction?

. It shifts the center of gravity laterally over the affected hip
. It provides a force that assists the abductor muscles, decreasing the required abductor force
. It increases the lever arm of the body weight
. It transfers the body weight entirely to the ipsilateral upper extremity
. It limits hip flexion during the stance phase of gait

Correct Answer & Explanation

. It shifts the center of gravity laterally over the affected hip

Explanation

Holding a cane in the contralateral hand provides an upward force at a long lever arm from the affected hip. This counter-torque dramatically reduces the amount of force the ipsilateral abductor muscles must generate, thereby decreasing the total joint reaction force.

Question 6945

Topic: Surgical Anatomy & Approaches

During an anterior (Smith-Petersen) approach to the hip for a periacetabular osteotomy, the surgeon develops the superficial internervous plane. Which of the following represents the correct muscles and their respective innervations for this interval?

. Sartorius (Femoral nerve) and Tensor Fasciae Latae (Superior gluteal nerve)
. Rectus Femoris (Femoral nerve) and Gluteus Medius (Superior gluteal nerve)
. Pectineus (Femoral/Obturator nerve) and Iliopsoas (Lumbar plexus/Femoral nerve)
. Tensor Fasciae Latae (Superior gluteal nerve) and Gluteus Medius (Superior gluteal nerve)
. Gluteus Maximus (Inferior gluteal nerve) and Gluteus Medius (Superior gluteal nerve)

Correct Answer & Explanation

. Sartorius (Femoral nerve) and Tensor Fasciae Latae (Superior gluteal nerve)

Explanation

The superficial interval of the Smith-Petersen approach utilizes the true internervous plane between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve).

Question 6946

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for an anterior column acetabular fracture, significant arterial bleeding is encountered near the superior pubic ramus. This bleeding is most likely from the 'corona mortis', which is an anastomosis between the obturator vessels and which of the following?

. Internal iliac vessels
. Superior gluteal vessels
. External iliac or inferior epigastric vessels
. Medial femoral circumflex vessels
. Pudendal vessels

Correct Answer & Explanation

. Internal iliac vessels

Explanation

The corona mortis is a vascular anastomosis between the obturator and the external iliac or inferior epigastric systems. It crosses the superior pubic ramus and is highly susceptible to injury during the ilioinguinal approach to the pelvis.

Question 6947

Topic: Surgical Anatomy & Approaches

The direct anterior approach (DAA) to the hip is an internervous plane. Which of the following best describes the superficial neural interval used in this approach?

. Between the femoral nerve and the obturator nerve
. Between the superior gluteal nerve and the inferior gluteal nerve
. Between the femoral nerve and the superior gluteal nerve
. Between the superior gluteal nerve and the sciatic nerve
. Between the obturator nerve and the sciatic nerve

Correct Answer & Explanation

. Between the femoral nerve and the obturator nerve

Explanation

The direct anterior approach exploits the superficial interval between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep interval is between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 6948

Topic: Surgical Anatomy & Approaches

Which of the following ligaments of the hip joint is the strongest and serves as the primary static restraint to hip extension?

. Ischiofemoral ligament
. Pubofemoral ligament
. Ligamentum teres
. Iliofemoral ligament
. Transverse acetabular ligament

Correct Answer & Explanation

. Ischiofemoral ligament

Explanation

The iliofemoral ligament (Y ligament of Bigelow) is the strongest ligament in the body and is the primary restraint to hip extension and external rotation. It spans from the AIIS to the intertrochanteric line.

Question 6949

Topic: Physiology & Rehabilitation

When advising a patient with severe left hip osteoarthritis on the use of a single-point cane, you instruct them to hold the cane in their right hand. What is the primary biomechanical rationale for this instruction?

. It shifts the center of gravity laterally over the affected hip.
. It eliminates the need for gluteus medius contraction on the affected side.
. It provides a counter-moment that decreases the required force of the left abductor muscles, reducing the joint reaction force.
. It increases the lever arm of the body weight, effectively unloading the medial compartment of the knee.
. It restricts hip external rotation during the stance phase of gait.

Correct Answer & Explanation

. It shifts the center of gravity laterally over the affected hip.

Explanation

Using a cane in the contralateral hand provides a long lever arm that assists the ipsilateral hip abductors in maintaining a level pelvis. This significantly reduces the force the abductor muscles must generate, thereby profoundly decreasing the compressive joint reaction force across the hip.

Question 6950

Topic: Surgical Anatomy & Approaches

A 25-year-old male sustains a posterior wall acetabular fracture with a posterior hip dislocation. Post-reduction, he undergoes open reduction and internal fixation via a Kocher-Langenbeck approach. Postoperatively, he is noted to have an inability to extend his great toe and decreased sensation in the first dorsal web space. Which specific neural element was most likely injured?

. Tibial division of the sciatic nerve
. Femoral nerve
. Common peroneal division of the sciatic nerve
. Superior gluteal nerve
. Obturator nerve

Correct Answer & Explanation

. Tibial division of the sciatic nerve

Explanation

The common peroneal division of the sciatic nerve is anatomically more lateral and its fibers are more superficial/tethered, making it highly susceptible to injury from retractor placement or trauma during posterior hip dislocations and the Kocher-Langenbeck approach.

Question 6951

Topic: Biomechanics & Biomaterials

In modern cementing techniques for total hip arthroplasty (third-generation cementing), vacuum mixing of the polymethylmethacrylate (PMMA) bone cement is standard practice. What is the primary biomechanical benefit of vacuum mixing?

. It accelerates the polymerization time to allow faster stem insertion.
. It decreases the porosity of the cement, thereby increasing its fatigue strength.
. It prevents the exothermic reaction of PMMA from causing thermal necrosis of bone.
. It increases the viscosity of the cement to prevent distal migration past the restrictor.
. It chemically bonds the cement to the titanium femoral stem.

Correct Answer & Explanation

. It accelerates the polymerization time to allow faster stem insertion.

Explanation

Vacuum mixing removes air bubbles from the PMMA during the mixing process, which significantly reduces the cement's macroporosity. This reduction in porosity eliminates stress risers, markedly increasing the fatigue life and tensile strength of the cement mantle.

Question 6952

Topic: Surgical Anatomy & Approaches

Anatomical variation of the sciatic nerve as it exits the greater sciatic foramen is well documented. In approximately 10-15% of the population, a variant exists that can predispose to iatrogenic injury or piriformis syndrome. What is the most common anatomical variant of the sciatic nerve?

. The entire sciatic nerve exits superior to the piriformis muscle.
. The tibial division pierces the piriformis, while the common peroneal division exits inferiorly.
. The common peroneal division pierces the piriformis muscle, while the tibial division exits inferiorly.
. The entire sciatic nerve pierces the substance of the piriformis muscle.
. The sciatic nerve exits anterior to the obturator internus.

Correct Answer & Explanation

. The entire sciatic nerve exits superior to the piriformis muscle.

Explanation

The most common anatomical variation (present in roughly 10-15% of people) is the common peroneal division of the sciatic nerve piercing through the piriformis muscle, while the tibial division passes underneath it.

Question 6953

Topic: Surgical Anatomy & Approaches

During a direct anterior (Smith-Petersen) approach to the hip for total hip arthroplasty, the surgeon utilizes both superficial and deep internervous planes. Which of the following accurately describes the deep internervous plane for this approach?

. Sartorius and tensor fasciae latae
. Rectus femoris and gluteus medius
. Gluteus maximus and gluteus medius
. Tensor fasciae latae and rectus femoris
. Iliopsoas and pectineus

Correct Answer & Explanation

. Sartorius and tensor fasciae latae

Explanation

The direct anterior approach exploits the superficial internervous plane between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The deep plane lies between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

Question 6954

Topic: Surgical Anatomy & Approaches

An orthopedic surgeon is performing an anterior intrapelvic (modified Stoppa) approach for an acetabular fracture. The surgeon must identify and ligate the 'corona mortis' to prevent massive hemorrhage. This vascular structure is most commonly an anastomosis between which of the following systems?

. External iliac and obturator systems
. Internal pudendal and inferior gluteal systems
. Superior gluteal and inferior epigastric systems
. Internal iliac and medial femoral circumflex systems
. Lateral sacral and superior vesical systems

Correct Answer & Explanation

. External iliac and obturator systems

Explanation

The corona mortis is a critical vascular anastomosis connecting the external iliac (or deep inferior epigastric) system and the internal iliac (obturator) system. It courses over the posterior aspect of the superior pubic ramus and is highly vulnerable during intrapelvic approaches.

Question 6955

Topic: Infection, Pharmacology & VTE

A surgeon is planning a posteromedial approach to address a displaced posteromedial shear fragment in a bicondylar tibial plateau fracture. Which surgical interval is typically utilized for this approach?

. Between the medial head of the gastrocnemius and the pes anserinus
. Between the lateral head of the gastrocnemius and the soleus
. Between the tibialis anterior and extensor hallucis longus
. Between the semimembranosus and semitendinosus
. Between the peroneus longus and brevis

Correct Answer & Explanation

. Between the medial head of the gastrocnemius and the pes anserinus

Explanation

The standard posteromedial approach to the proximal tibia exploits the interval between the pes anserinus anteriorly and the medial head of the gastrocnemius posteriorly. This safely exposes the posteromedial cortex for anti-glide plating.

Question 6956

Topic: Surgical Anatomy & Approaches

In the setting of a complex posterior pilon fracture, a posterolateral surgical approach is planned. Which of the following anatomic intervals is typically utilized to access the posterolateral fragment (Volkmann's fragment)?

. Between the flexor hallucis longus (FHL) and the peroneal tendons
. Between the Achilles tendon and the FHL
. Between the tibialis posterior and the flexor digitorum longus (FDL)
. Between the tibialis anterior and extensor hallucis longus
. Between the medial malleolus and tibialis posterior

Correct Answer & Explanation

. Between the flexor hallucis longus (FHL) and the peroneal tendons

Explanation

The posterolateral approach to the distal tibia utilizes the interval between the flexor hallucis longus (FHL) medially and the peroneal tendons laterally to safely access the posterolateral Volkmann fragment.

Question 6957

Topic: Surgical Anatomy & Approaches

A 24-year-old unrestrained driver is involved in a motor vehicle collision. He presents with his right lower extremity positioned in flexion, adduction, and internal rotation.

Which of the following structures is at greatest risk of injury?

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

Correct Answer & Explanation

. Femoral nerve

Explanation

The clinical posture described is classic for a posterior hip dislocation. This injury places the sciatic nerve, specifically the common peroneal division, at greatest risk due to stretching or direct compression by the displaced femoral head.

Question 6958

Topic: Biology, Genetics & Bone Healing

A 55-year-old woman presents with severe thigh pain and a low-energy, transverse diaphyseal femur fracture with focal lateral cortical thickening. She has been taking alendronate for 8 years. Which of the following statements regarding her management is most accurate?

. Use of a cephalomedullary nail is absolutely contraindicated
. She should be immediately switched from alendronate to zoledronic acid
. Teriparatide is an anabolic agent that may be beneficial to enhance fracture healing
. Reamed intramedullary nailing has a substantially higher nonunion rate than plate fixation
. Initiation of denosumab is the first-line medical intervention

Correct Answer & Explanation

. Use of a cephalomedullary nail is absolutely contraindicated

Explanation

This patient has an atypical femur fracture (AFF) associated with long-term bisphosphonate use. Teriparatide (recombinant PTH) is an anabolic agent that stimulates bone formation and has been shown to aid in the healing of these challenging fractures.

Question 6959

Topic: Biology, Genetics & Bone Healing

A 68-year-old woman on long-term alendronate therapy presents with a low-energy, transverse subtrochanteric femur fracture. Radiographs show lateral cortical thickening and a medial spike. What is the most crucial next step in the workup prior to surgical intervention?

. DEXA scan
. Serum calcium and vitamin D levels
. Radiographs of the contralateral femur
. MRI of the affected femur
. Bone scintigraphy

Correct Answer & Explanation

. DEXA scan

Explanation

Bisphosphonate-associated atypical femur fractures are frequently bilateral. It is critical to obtain radiographs of the contralateral femur to evaluate for a prodromal or complete atypical fracture, which may require prophylactic fixation.

Question 6960

Topic: Surgical Anatomy & Approaches

A 30-year-old male sustains a closed midshaft humerus fracture and presents with an immediate, complete radial nerve palsy. The fracture is acceptably reduced and placed in a coaptation splint. If there is no clinical sign of nerve recovery, at what post-injury timeframe is an EMG/NCS most indicated to evaluate for subclinical reinnervation?

. Immediately
. 3 to 4 weeks
. 6 to 12 weeks
. 6 months
. 1 year

Correct Answer & Explanation

. Immediately

Explanation

Primary radial nerve palsies associated with closed humerus fractures are usually managed observationally, as the majority are neurapraxias. If no clinical signs of recovery are present by 6 to 12 weeks, an EMG/NCS should be obtained to assess for denervation and subclinical reinnervation.

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