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1. General Principles & Basic Science MCQs

Practice Set 83 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 1641

Topic: 1. General Principles & Basic Science

A 60-year-old female undergoes a primary total hip replacement. Post-operatively, she develops a significant leg length discrepancy (LLD) of 2.5 cm, with the operative leg being longer. She experiences persistent low back pain and a feeling of instability, despite using a shoe lift on the contralateral side. Which of the following mechanisms best explains how excessive leg lengthening can contribute to instability or related complications?

. Reduced abductor tension leading to Trendelenburg gait.
. Increased jump distance, paradoxically leading to impingement.
. Nerve stretch injury (e.g., sciatic or femoral nerve) or prosthetic impingement.
. Accelerated polyethylene wear due to altered kinematics.
. Increased risk of periprosthetic infection.

Correct Answer & Explanation

. Nerve stretch injury (e.g., sciatic or femoral nerve) or prosthetic impingement.

Explanation

Correct Answer: CThe teaching case, under 'Complications & Management' and 'Leg Length Discrepancy (LLD),' states: 'Excessive lengthening can cause nerve stretch, while shortening reduces abductor tension, both increasing dislocation risk.' A 2.5 cm lengthening is significant. Excessive lengthening can stretch nerves (e.g., sciatic nerve, leading to foot drop, or femoral nerve) or cause prosthetic impingement (e.g., the femoral neck/stem impinging on the acetabular rim or capsule due to the altered biomechanics), which can lead to pain and instability. The patient's symptoms of low back pain and instability are consistent with these issues.A. Reduced abductor tension leading to Trendelenburg gait:This is associated withleg shortening, not lengthening. Excessive lengthening would typically increase abductor tension, potentially leading to pain but not reduced tension.B. Increased jump distance, paradoxically leading to impingement:While increased jump distance generally improves stability, excessive lengthening can alter the hip's biomechanics in a way that promotes impingement, which then acts as a lever-out mechanism for dislocation. The primary issue is the impingement or nerve stretch, not a paradoxical effect of jump distance itself.D. Accelerated polyethylene wear due to altered kinematics:While altered kinematics can affect wear, nerve stretch or impingement are more direct and immediate complications of excessive lengthening leading to instability or pain.E. Increased risk of periprosthetic infection:There is no direct causal link between leg length discrepancy and increased risk of periprosthetic infection.

Question 1642

Topic: Surgical Anatomy & Approaches

During a direct anterior approach for a total hip arthroplasty, the ascending branch of the lateral femoral circumflex artery is encountered. In which internervous plane does this surgical approach initially proceed?

. Gluteus medius and tensor fasciae latae
. Tensor fasciae latae and sartorius
. Sartorius and rectus femoris
. Rectus femoris and vastus lateralis
. Gluteus maximus and gluteus medius

Correct Answer & Explanation

. Tensor fasciae latae and sartorius

Explanation

The direct anterior approach utilizes the superficial internervous plane between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve). The ascending branch of the lateral femoral circumflex artery is ligated in this interval.

Question 1643

Topic: Biomechanics & Biomaterials
Compared to standard ultra-high-molecular-weight polyethylene (UHMWPE), highly cross-linked polyethylene used in THA offers which of the following mechanical trade-offs?
. Increased wear resistance and increased ductility
. Decreased wear resistance and increased fatigue strength
. Increased wear resistance and decreased fatigue crack propagation resistance
. Decreased wear resistance and decreased oxidation potential
. Increased oxidation potential and increased yield strength

Correct Answer & Explanation

. Increased wear resistance and decreased fatigue crack propagation resistance

Explanation

High-dose irradiation cross-links the polyethylene, significantly reducing adhesive and abrasive wear. However, this process decreases mechanical properties such as ductility, toughness, and fatigue crack propagation resistance.

Question 1644

Topic: Surgical Anatomy & Approaches

During the inferior capsular release for a total shoulder arthroplasty, the axillary nerve is at greatest risk. What is its typical anatomic relationship to the inferior glenohumeral capsule?

. It lies directly on the superior capsule
. It passes 10-15 mm inferior to the most inferior aspect of the capsule
. It penetrates the inferior capsule directly to enter the joint
. It passes anterior to the subscapularis and superior to the coracoid
. It runs 30-40 mm medial to the glenoid rim

Correct Answer & Explanation

. It passes 10-15 mm inferior to the most inferior aspect of the capsule

Explanation

The axillary nerve passes through the quadrangular space and typically lies approximately 10 to 15 mm inferior to the inferior glenohumeral capsule. Dissection must remain directly on the capsule to avoid nerve injury.

Question 1645

Topic: Surgical Anatomy & Approaches

The axillary nerve is a critical structure at risk during shoulder arthroplasty. During the inferior capsular release, what is the approximate average distance from the inferior margin of the glenoid rim to the axillary nerve?

. 2 - 5 mm
. 10 - 15 mm
. 25 - 30 mm
. 35 - 40 mm
. Greater than 50 mm

Correct Answer & Explanation

. 10 - 15 mm

Explanation

Anatomical studies show that the axillary nerve runs immediately inferior to the glenohumeral capsule. The average distance from the inferior bony rim of the glenoid to the axillary nerve is approximately 10 to 15 mm, making careful retractor placement essential to avoid neuropraxia or transection.

Question 1646

Topic: Surgical Anatomy & Approaches

A 70-year-old male undergoes a primary total hip arthroplasty via the direct anterior approach. Postoperatively, he has profound numbness over the anterolateral thigh but normal quadriceps strength. Which inter-nervous plane was utilized, and what nerve is likely affected?

. Gluteus medius and TFL; Superior gluteal nerve
. Sartorius and TFL; Lateral femoral cutaneous nerve
. Rectus femoris and Sartorius; Femoral nerve
. Gluteus maximus and Gluteus medius; Sciatic nerve
. Iliopsoas and Pectineus; Obturator nerve

Correct Answer & Explanation

. Sartorius and TFL; Lateral femoral cutaneous nerve

Explanation

The direct anterior approach (Smith-Petersen) utilizes the internervous plane between the Sartorius (femoral nerve) and TFL (superior gluteal nerve). The lateral femoral cutaneous nerve crosses this interval superficially and is highly susceptible to traction or transection.

Question 1647

Topic: Surgical Anatomy & Approaches

When placing the glenosphere baseplate during a reverse total shoulder arthroplasty, peripheral locking screws are utilized for fixation. Aiming the anterior screw excessively far anteriorly risks injury to which neurovascular structure?

. Suprascapular nerve
. Axillary nerve
. Musculocutaneous nerve
. Cephalic vein
. Thoracoacromial artery

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

The anterior screw in a baseplate is directed towards the coracoid process. If placed excessively long or strayed anteriorly past the coracoid base, it can injure the musculocutaneous nerve, which enters the conjoined tendon just inferior to the coracoid.

Question 1648

Topic: Surgical Anatomy & Approaches

During a primary total hip arthroplasty utilizing the direct anterior approach, the surgeon develops the superficial internervous plane. To minimize the risk of denervation, the surgeon must remember that this interval is bordered by muscles supplied by which two nerves?

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

Correct Answer & Explanation

. Superior gluteal nerve and femoral nerve

Explanation

The direct anterior approach utilizes the internervous plane between the tensor fasciae latae (supplied by the superior gluteal nerve) and the sartorius (supplied by the femoral nerve). This true internervous and intermuscular plane helps preserve abductor function.

Question 1649

Topic: Surgical Anatomy & Approaches

A 65-year-old female undergoes a complex primary total hip arthroplasty requiring 4 cm of leg lengthening. Postoperatively, she exhibits a foot drop and numbness in the first dorsal web space, but retains normal plantar flexion. Which nerve division is most likely injured, and what anatomic feature makes it particularly susceptible?

. Tibial division of the sciatic nerve; courses anterior to the piriformis
. Peroneal division of the sciatic nerve; courses posterior to the short external rotators
. Peroneal division of the sciatic nerve; fibers are strictly tethered at the sciatic notch and fibular head
. Femoral nerve; courses lateral to the psoas major
. Obturator nerve; courses through the obturator foramen

Correct Answer & Explanation

. Peroneal division of the sciatic nerve; courses posterior to the short external rotators

Explanation

The peroneal division of the sciatic nerve is the most commonly injured nerve during THA leg lengthening, presenting as a foot drop. It is more susceptible to stretch injuries than the tibial division because its fibers are securely tethered at the sciatic notch and the fibular neck.

Question 1650

Topic: Surgical Anatomy & Approaches

A 32-year-old male undergoes an ilioinguinal approach for a displaced anterior column acetabular fracture. Postoperatively, he complains of numbness and a burning sensation over the anterolateral aspect of his ipsilateral thigh. Which nerve was most likely injured or irritated during the procedure?

. Iliohypogastric nerve
. Ilioinguinal nerve
. Lateral femoral cutaneous nerve
. Femoral nerve
. Obturator nerve

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

Correct Answer: CThe lateral femoral cutaneous nerve (LFCN) is the most commonly injured nerve during the ilioinguinal approach, with sensory deficits reported in up to 80% of cases and persistent symptoms in 5-10%. It emerges from beneath the inguinal ligament, lateral to the sartorius, and its course is highly variable, making it susceptible to traction, compression, or direct injury during dissection and retraction, particularly in the lateral window. Symptoms typically involve numbness, tingling, or burning pain (meralgia paresthetica) over the anterolateral thigh. The iliohypogastric and ilioinguinal nerves are typically retracted superiorly with the external oblique aponeurosis and spermatic cord, respectively, and while they can be injured, their sensory distribution is more medial and inferior (groin, scrotum/labia, medial thigh). The femoral nerve and obturator nerve are deeper structures, and their injury would typically result in motor deficits (quadriceps weakness for femoral nerve, adductor weakness for obturator nerve) in addition to sensory changes, and are much rarer but more severe complications.

Question 1651

Topic: Surgical Anatomy & Approaches

The image below depicts the lateral window of the ilioinguinal approach. Which of the following structures are typically detached from the ASIS and retracted laterally to develop this window?

. Rectus abdominis and pyramidalis muscles
. Femoral neurovascular bundle
. Sartorius and tensor fascia lata muscles
. Spermatic cord and ilioinguinal nerve
. Iliacus and psoas muscles

Correct Answer & Explanation

. Sartorius and tensor fascia lata muscles

Explanation

Correct Answer: CThe lateral window of the ilioinguinal approach is developed by detaching the origins of the sartorius and tensor fascia lata (TFL) muscles from the anterior superior iliac spine (ASIS) and retracting them laterally. This maneuver exposes the lateral aspect of the iliac wing. Subsequently, subperiosteal dissection elevates the iliacus muscle, which, along with the psoas muscle, is retracted medially to expose the inner table of the ilium. The rectus abdominis and pyramidalis muscles are detached and reflected superiorly in the medial window. The femoral neurovascular bundle is retracted medially in the middle window. The spermatic cord and ilioinguinal nerve are mobilized and retracted inferiorly/superiorly during the initial exposure of the inguinal canal and development of the medial window, respectively.

Question 1652

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for a complex acetabular fracture, a surgeon encounters significant difficulty retracting the femoral neurovascular bundle in the middle window. Despite careful technique, the patient develops a new, profound ipsilateral lower extremity weakness and an absent femoral pulse post-operatively. Which of the following is the most appropriate immediate management step?

. Initiate high-dose corticosteroids to reduce nerve swelling.
. Order an immediate CT angiogram of the pelvis and lower extremity.
. Begin aggressive physical therapy to encourage nerve recovery.
. Administer broad-spectrum antibiotics to prevent infection.
. Perform immediate surgical exploration and vascular repair.

Correct Answer & Explanation

. Perform immediate surgical exploration and vascular repair.

Explanation

Correct Answer: EThe clinical presentation of profound lower extremity weakness (suggesting femoral nerve injury) and an absent femoral pulse (indicating femoral artery occlusion) constitutes a surgical emergency. This is a rare but devastating complication of the ilioinguinal approach, typically due to direct injury, prolonged compression, or thrombosis of the femoral neurovascular bundle. Immediate surgical exploration and repair by a vascular surgeon are paramount to restore blood flow and potentially salvage nerve function. Delay in revascularization can lead to limb ischemia, muscle necrosis, and permanent neurological deficits. While a CT angiogram might be useful for detailed mapping, the urgency of the situation dictates immediate surgical intervention based on clinical findings. Corticosteroids, physical therapy, and antibiotics are not primary treatments for acute vascular occlusion or severe nerve injury in this context.

Question 1653

Topic: Surgical Anatomy & Approaches

The image below illustrates the medial window of the ilioinguinal approach. During the development of this window, which anatomical variant must be anticipated and carefully managed to prevent significant hemorrhage?

. Aberrant course of the lateral femoral cutaneous nerve
. High bifurcation of the femoral artery
. The 'corona mortis' anastomosis
. Accessory obturator nerve branch
. Deep circumflex iliac artery

Correct Answer & Explanation

. The 'corona mortis' anastomosis

Explanation

Correct Answer: CDuring the development of the medial window, meticulous dissection is performed along the superior pubic ramus, deep to the pubic tubercle. In this region, the 'corona mortis' (crown of death) is an anatomical variant involving an anastomosis between the obturator and external iliac/inferior epigastric vessels. This vascular connection crosses the superior pubic ramus in 10-30% of cases and can cause significant, life-threatening bleeding if inadvertently injured. Therefore, careful identification and either ligation and division or protection of these vessels are critical. The lateral femoral cutaneous nerve is relevant to the lateral aspect of the incision, not the medial window. A high bifurcation of the femoral artery or an accessory obturator nerve branch are not specific to this region or associated with the same risk of massive hemorrhage. The deep circumflex iliac artery is typically encountered more laterally along the iliac crest.

Question 1654

Topic: Surgical Anatomy & Approaches

The image below demonstrates the middle window of the ilioinguinal approach. Which of the following structures, located deep to the external iliac vein in this region, requires meticulous protection to prevent iatrogenic injury during dissection and retraction?

. Ilioinguinal nerve
. Lateral femoral cutaneous nerve
. Femoral nerve
. Obturator nerve and vessels
. Superior gluteal nerve

Correct Answer & Explanation

. Obturator nerve and vessels

Explanation

Correct Answer: DThe middle window of the ilioinguinal approach involves the careful medial retraction of the femoral neurovascular bundle (femoral artery, vein, and nerve) along with the iliopsoas muscle. Deep to the external iliac vein, the obturator nerve and vessels cross the medial aspect of this window. Injury to these structures is rare but can lead to adductor weakness (obturator nerve) or significant hemorrhage (obturator vessels). Therefore, meticulous dissection and careful retraction are essential to protect the obturator nerve and vessels in this critical area. The ilioinguinal and lateral femoral cutaneous nerves are more superficial and lateral, respectively. The femoral nerve is part of the bundle being retracted. The superior gluteal nerve is located more posteriorly, exiting the pelvis through the greater sciatic notch, and is not directly exposed or at risk in the ilioinguinal approach.

Question 1655

Topic: 1. General Principles & Basic Science

A 55-year-old male with a history of traumatic brain injury and a complex acetabular fracture is undergoing surgical fixation via the ilioinguinal approach. Given his risk factors, the surgical team plans for prophylaxis against heterotopic ossification (HO). Which of the following is a recommended prophylactic regimen for HO in this setting?

. Daily low-molecular-weight heparin for 6 weeks.
. Indomethacin 25 mg three times daily for 6 weeks.
. Immediate post-operative continuous passive motion (CPM) for 24 hours.
. High-dose systemic corticosteroids for 7 days.
. Surgical excision of any developing HO at 3 weeks post-op.

Correct Answer & Explanation

. Indomethacin 25 mg three times daily for 6 weeks.

Explanation

Correct Answer: BHeterotopic ossification (HO) is a common complication after acetabular fracture surgery, with radiographic incidence ranging from 15-50%. Patients with traumatic brain injury are at a significantly increased risk. The recommended prophylactic regimens for HO include either non-steroidal anti-inflammatory drugs (NSAIDs) like Indomethacin (typically 25 mg three times daily for 6 weeks) or a single dose of radiation therapy (700-800 cGy) administered within 72 hours post-operatively. Low-molecular-weight heparin is for DVT prophylaxis. Continuous passive motion (CPM) has variable evidence for HO prevention and is not a primary prophylactic measure. High-dose systemic corticosteroids are not a standard HO prophylaxis. Surgical excision of HO is a treatment for symptomatic, mature HO, typically performed more than a year post-op, not a prophylactic measure at 3 weeks.

Question 1656

Topic: Surgical Anatomy & Approaches

A 45-year-old male sustains a posterior wall acetabular fracture with a posterior hip dislocation. Closed reduction is performed in the emergency department. Which of the following findings is the most definitive indication for operative fixation of the posterior wall fragment?

. Fragment size comprising 15% of the posterior articular surface
. Displacement of the fragment by 1 mm
. Dynamic instability of the hip joint in flexion and internal rotation under anesthesia
. Concomitant partial sciatic nerve palsy present before reduction
. Presence of marginal impaction on CT scan

Correct Answer & Explanation

. Dynamic instability of the hip joint in flexion and internal rotation under anesthesia

Explanation

Dynamic stress fluoroscopy under anesthesia is the most definitive method to assess hip stability. Hip instability is an absolute indication for operative fixation, even if the fragment size is considered borderline.

Question 1657

Topic: Surgical Anatomy & Approaches

A trauma surgeon is performing an ilioinguinal approach for a complex anterior column acetabular fracture. The middle window is developed to access the pelvic brim. What structure defines the medial boundary of this middle window?

. Iliopectineal fascia
. External iliac vessels
. Symphysis pubis
. Spermatic cord
. Rectus abdominis muscle

Correct Answer & Explanation

. Iliopectineal fascia

Explanation

The middle window of the ilioinguinal approach is bounded laterally by the iliopectineal fascia and medially by the external iliac vessels. It allows direct access to the pelvic brim and quadrilateral plate.

Question 1658

Topic: Surgical Anatomy & Approaches

During the distal portion of a volar (Henry) approach to the radius for fracture fixation, the surgeon develops an internervous plane. Which two structures define this distal interval?

. Flexor carpi radialis and palmaris longus
. Brachioradialis and flexor carpi radialis
. Flexor carpi ulnaris and flexor digitorum superficialis
. Pronator teres and flexor carpi radialis
. Extensor carpi radialis longus and brevis

Correct Answer & Explanation

. Brachioradialis and flexor carpi radialis

Explanation

The distal interval of the Henry approach is between the brachioradialis (innervated by the radial nerve) and the flexor carpi radialis (innervated by the median nerve). This true internervous plane provides safe access to the volar distal radius.

Question 1659

Topic: Surgical Anatomy & Approaches

During a Kocher-Langenbeck approach for a posterior wall acetabular fracture, the surgeon must carefully protect the sciatic nerve. Which of the following patient positioning maneuvers most effectively decreases tension on the sciatic nerve during this approach?

. Hip flexion and knee extension
. Hip extension and knee flexion
. Hip flexion and knee flexion
. Hip extension and knee extension
. Hip abduction and knee extension

Correct Answer & Explanation

. Hip extension and knee flexion

Explanation

To minimize tension on the sciatic nerve during the Kocher-Langenbeck approach, the hip should be extended and the knee flexed. The peroneal division of the sciatic nerve is particularly vulnerable to stretch injury during retraction.

Question 1660

Topic: Biology, Genetics & Bone Healing

A 72-year-old female taking alendronate for 8 years presents with progressive thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region. What is the most appropriate management?

. Immediate discontinuation of alendronate and physical therapy
. Prophylactic cephalomedullary nailing of the affected femur
. Core decompression of the femoral head
. Prescription of a different bisphosphonate
. Teriparatide therapy alone without surgical intervention

Correct Answer & Explanation

. Prophylactic cephalomedullary nailing of the affected femur

Explanation

This patient has an impending atypical femoral fracture due to long-term bisphosphonate use. Because she has prodromal pain and a visible cortical radiolucency, prophylactic intramedullary nailing is indicated to prevent completion of the fracture.

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