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1. General Principles & Basic Science MCQs

Practice Set 92 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 1821

Topic: Biomechanics & Biomaterials

Cortical screws typically have a smaller pitch compared to cancellous screws. What does the term "pitch" refer to in screw biomechanics?

. The angle of the screw thread relative to the core
. The distance between adjacent screw threads
. The difference between the outer diameter and core diameter
. The length of the non-threaded shaft
. The ratio of bone volume to metal volume between threads

Correct Answer & Explanation

. The distance between adjacent screw threads

Explanation

Screw pitch is defined as the linear distance traveled by the screw with one full 360-degree turn, which corresponds to the distance between adjacent threads. Cancellous screws have a larger pitch to capture more bone per turn in less dense trabecular bone.

Question 1822

Topic: Biomechanics & Biomaterials

Which of the following accurately describes the typical failure mechanism of a locked plating construct under excessive axial load compared to a non-locked construct?

. Screws fail sequentially starting from the fracture site
. The plate undergoes friction-induced loosening
. Screws pull out sequentially from the far cortex
. The construct typically fails as a single unit via simultaneous screw pullout or plate breakage
. Failure occurs primarily through galvanic corrosion at the screw head

Correct Answer & Explanation

. The construct typically fails as a single unit via simultaneous screw pullout or plate breakage

Explanation

Because a locked plate acts as a single fixed-angle beam, the screws do not fail sequentially. Under excessive load, the entire construct typically fails simultaneously, often through catastrophic en masse screw pullout or plate breakage.

Question 1823

Topic: Biomechanics & Biomaterials

Cortical bone exhibits different mechanical properties depending on the direction of the applied load. It is strongest in compression and weakest in shear. What is the biomechanical term for this property?

. Viscoelasticity
. Isotropy
. Anisotropy
. Hysteresis
. Plasticity

Correct Answer & Explanation

. Anisotropy

Explanation

Anisotropy refers to a material having different mechanical properties when loaded in different directions. Cortical bone is highly anisotropic, being strongest under longitudinal compression and weakest under transverse shear forces.

Question 1824

Topic: 1. General Principles & Basic Science

A surgeon is evaluating screw options for osteoporotic bone fixation. According to the biomechanical equation for screw pull-out strength, which of the following modifications will most significantly increase the holding power of a cortical screw?

. Increasing the inner root diameter
. Increasing the outer thread diameter
. Decreasing the thread pitch
. Increasing the length of the screw by 2 mm
. Decreasing the length of thread engagement

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

Screw pullout strength is most significantly determined by the outer thread diameter. Pullout strength is directly proportional to the outer diameter, thread engagement length, and shear strength of the bone, and inversely proportional to thread pitch.

Question 1825

Topic: Biomechanics & Biomaterials

A surgeon decides to use a titanium intramedullary nail instead of a stainless steel nail for a tibial shaft fracture. Which of the following accurately describes a key biomechanical difference between titanium alloy (Ti-6Al-4V) and 316L stainless steel?

. Titanium has a higher modulus of elasticity than stainless steel
. Titanium is substantially more rigid than stainless steel of the same dimensions
. Titanium has a modulus of elasticity closer to that of cortical bone
. Stainless steel exhibits greater notch sensitivity than titanium
. Titanium relies exclusively on its carbon content for fatigue resistance

Correct Answer & Explanation

. Titanium has a modulus of elasticity closer to that of cortical bone

Explanation

Titanium alloy has a lower modulus of elasticity than stainless steel, making it less rigid and closer to the modulus of elasticity of cortical bone. This property significantly reduces stress shielding at the fracture site compared to stiffer stainless steel implants.

Question 1826

Topic: Surgical Anatomy & Approaches

A 14-year-old obese male presents with progressive unilateral left genu varum. Radiographs confirm adolescent Blount disease with a Medial Proximal Tibial Angle (MPTA) of 78 degrees and a Mechanical Axis Deviation (MAD) of 25 mm medial to the center of the knee. His skeletal age is 13 years, with open physes. Lateral hemiepiphysiodesis of the proximal tibia is planned. During the surgical approach to the lateral proximal tibia, which neurovascular structure is at highest risk of injury and requires meticulous attention, particularly with deep or misguided retraction?

. Popliteal artery
. Saphenous nerve
. Common peroneal nerve
. Anterior tibial artery
. Posterior tibial nerve

Correct Answer & Explanation

. Common peroneal nerve

Explanation

Correct Answer: CThe common peroneal nerve (C) courses superficially around the fibular neck, approximately 3-5 cm distal to the proximal tibial physis. During a lateral approach to the proximal tibia for hemiepiphysiodesis, aggressive or misguided deep retractors, especially those placed distally or posteriorly, can put this nerve at significant risk of stretch or direct injury, leading to a foot drop. The popliteal artery (A) and posterior tibial nerve (E) are located more posteriorly in the popliteal fossa and are less directly at risk with a lateral approach to the tibia, though deep posterior instrumentation could theoretically endanger them. The saphenous nerve (B) is a cutaneous nerve located more medially in the thigh and leg. The anterior tibial artery (D) passes through the interosseous membrane anteriorly and is generally not at direct risk during a lateral approach to the proximal tibia unless dissection is carried too deep and anteriorly.

Question 1827

Topic: 1. General Principles & Basic Science

A 9-year-old male with progressive right tibia vara (MPTA 75 degrees) undergoes lateral hemiepiphysiodesis. Post-operatively, he is allowed weight-bearing as tolerated. Which of the following statements accurately describes the typical post-operative rehabilitation protocol and monitoring for this patient?

. Non-weight-bearing for 6 weeks, followed by gradual progression to full weight-bearing.
. Strict immobilization in a cast for 3 months to ensure bone healing around the plate.
. Regular clinical and radiographic follow-up every 3-6 months until slight overcorrection into valgus is achieved.
. Hardware removal is typically performed at 12 months post-surgery, regardless of alignment.
. Intensive physical therapy focusing on aggressive strengthening and high-impact activities immediately post-op.

Correct Answer & Explanation

. Regular clinical and radiographic follow-up every 3-6 months until slight overcorrection into valgus is achieved.

Explanation

Correct Answer: CPost-operative rehabilitation for hemiepiphysiodesis is generally straightforward. Patients are typically allowed weight-bearing as tolerated (WBAT) immediately or shortly after surgery, making options A and B incorrect. The most critical aspect of post-operative management is regular clinical and radiographic follow-up (C) every 3-6 months. These visits are essential to monitor the progression of correction and determine the precise timing for hardware removal, which occurs when a slight overcorrection into valgus (e.g., 5-7 degrees mechanical valgus) is achieved. Hardware removal is not based on a fixed time frame (D) but on radiographic alignment. Intensive physical therapy with aggressive strengthening and high-impact activities (E) is generally avoided in the immediate post-operative period to allow for soft tissue healing, though gentle ROM and strengthening are encouraged.

Question 1828

Topic: Infection, Pharmacology & VTE

A 48-year-old male undergoes open repair of an acute Achilles tendon rupture. Post-operatively, he develops a wound dehiscence with signs of superficial infection. Despite oral antibiotics and local wound care, the wound continues to show poor healing. Which of the following complications is he at highest risk for, and what is a common salvage strategy for significant wound issues in this region?

. Sural nerve neuroma; requiring immediate surgical exploration and neurolysis.
. Deep vein thrombosis; managed with increased pharmacological prophylaxis.
. Rerupture; requiring revision surgery with FHL transfer.
. Tendon lengthening; managed with aggressive physical therapy and eccentric strengthening.
. Significant wound necrosis; potentially requiring plastic surgery consultation for local flaps or skin grafts.

Correct Answer & Explanation

. Significant wound necrosis; potentially requiring plastic surgery consultation for local flaps or skin grafts.

Explanation

Correct Answer: EThe case lists 'Wound Healing Complications' as a specific surgical complication, with an incidence of 5-20% for open repairs. It states, 'The skin over the Achilles is thin with poor vascularity, especially in the watershed area.' For 'significant necrosis or deep infection,' the management includes 'Debridement, wound VAC, and potentially plastic surgery consultation (local flaps, skin grafts).' This scenario directly aligns with the patient's ongoing poor wound healing despite initial measures.Incorrect Options:A:Sural nerve neuroma is a complication of nerve injury, not directly of wound dehiscence and infection, although a deep infection could theoretically involve the nerve. The primary concern with wound dehiscence is tissue viability.B:DVT is a general complication, but not the highest risk directly stemming from a persistent wound dehiscence and superficial infection. While DVT prophylaxis is important, it's not the primary salvage strategy for a wound issue.C:Rerupture is a risk, but it's a mechanical failure of the repair, not a direct consequence of a superficial wound infection and dehiscence. While a severe wound complication could compromise the repair, the immediate and highest risk from a persistent wound issue is further tissue breakdown.D:Tendon lengthening is a complication of a lax repair, not typically a direct result of a superficial wound infection.

Question 1829

Topic: 1. General Principles & Basic Science

Adolescent Blount disease typically presents with a complex triplanar deformity that must be carefully evaluated prior to surgical correction. Which of the following best describes the classical deformity of the proximal tibia in this condition?

. Varus, external tibial torsion, and recurvatum
. Varus, internal tibial torsion, and recurvatum
. Varus, internal tibial torsion, and procurvatum
. Valgus, internal tibial torsion, and procurvatum
. Valgus, external tibial torsion, and recurvatum

Correct Answer & Explanation

. Varus, internal tibial torsion, and procurvatum

Explanation

The classical triplanar deformity of the proximal tibia in adolescent Blount disease includes varus, internal tibial torsion, and procurvatum. Surgical correction, often utilizing a Taylor Spatial Frame or multiplanar osteotomy, must address all three components simultaneously.

Question 1830

Topic: Physiology & Rehabilitation

An 18-month-old male presents with bilateral genu varum. The parents are concerned about his bowed legs since he began walking at 10 months. Which of the following radiographic parameters is the strongest predictor that his deformity will progress to infantile Blount disease rather than resolve as physiologic bowing?

. Metaphyseal-diaphyseal angle greater than 16 degrees
. Tibiofemoral angle of 10 degrees varus
. Metaphyseal-diaphyseal angle less than 11 degrees
. Symmetrical bowing involving both the femur and the tibia
. Lateral thrust noted during the stance phase of gait

Correct Answer & Explanation

. Metaphyseal-diaphyseal angle greater than 16 degrees

Explanation

The metaphyseal-diaphyseal angle (Drennan's angle) is crucial for differentiating physiologic bowing from infantile Blount disease. An angle greater than 16 degrees has a high predictive value (up to 95%) for progression to Blount disease, whereas an angle less than 11 degrees typically indicates resolving physiologic bowing.

Question 1831

Topic: 1. General Principles & Basic Science

In comparing infantile and adolescent Blount disease, which of the following statements regarding laterality is most accurate?

. Infantile is typically unilateral; adolescent is typically bilateral.
. Both are almost exclusively bilateral.
. Infantile is typically bilateral; adolescent is typically unilateral.
. Both are almost exclusively unilateral.
. Laterality has no typical pattern in either type.

Correct Answer & Explanation

. Infantile is typically bilateral; adolescent is typically unilateral.

Explanation

Infantile Blount disease presents bilaterally in approximately 80% of cases. In contrast, adolescent Blount disease is typically unilateral, or strongly asymmetric, reflecting different underlying mechanical stresses and weight-bearing patterns.

Question 1832

Topic: Surgical Anatomy & Approaches

During percutaneous iliosacral screw placement for a residual SI joint diastasis in a 30-year-old male, the surgeon notes a sudden increase in resistance during K-wire insertion into the S1 body, followed by a brief twitching of the patient's great toe. Which of the following neurological structures is most likely at risk of iatrogenic injury in this scenario?

. Femoral nerve
. Obturator nerve
. Lumbosacral plexus (S1 nerve root)
. Superior gluteal nerve
. Pudendal nerve

Correct Answer & Explanation

. Lumbosacral plexus (S1 nerve root)

Explanation

Correct Answer: CThe case content, under 'Complications & Management' and 'Neurological Injury,' explicitly warns about nerve injuries during iliosacral screw placement: 'For lumbosacral plexus/sciatic nerve (often with SI screw malposition or direct trauma).' The S1 nerve root is particularly vulnerable during S1 iliosacral screw placement, as it exits the S1 foramen. A 'twitching of the great toe' is a classic sign of S1 nerve root irritation or impingement, as the S1 nerve root contributes to plantarflexion and sensation in the foot, including the great toe.Option A (Femoral nerve)andOption B (Obturator nerve)are typically at risk with anterior approaches or acetabular fixation, not directly with posterior iliosacral screw placement into S1.Option D (Superior gluteal nerve)is at risk during open posterior approaches, particularly with extensive dissection around the greater sciatic notch, but less directly from a percutaneous S1 iliosacral screw trajectory unless the screw is significantly malpositioned laterally and superiorly.Option E (Pudendal nerve)is located more inferiorly and medially in the pelvis and is not typically at direct risk during S1 iliosacral screw placement.

Question 1833

Topic: Surgical Anatomy & Approaches
A 40-year-old male with a Young-Burgess APC III pelvic fracture is undergoing definitive fixation. The surgeon plans to perform percutaneous iliosacral screw fixation for the posterior ring instability. Which of the following nerve roots is at the highest risk of iatrogenic injury during S1 iliosacral screw placement if the trajectory is too anterior or caudal?
. Femoral nerve.
. Obturator nerve.
. L5 nerve root.
. Sciatic nerve.
. Pudendal nerve.

Correct Answer & Explanation

. L5 nerve root.

Explanation

During percutaneous S1 iliosacral screw placement, the L5 nerve root is at the highest risk of iatrogenic injury. The L5 nerve root exits the sacrum through the L5-S1 foramen, which is located immediately anterior and slightly caudal to the typical entry point and trajectory for an S1 iliosacral screw. If the screw trajectory is too anterior, too caudal, or penetrates the anterior cortex of the sacrum, it can directly impinge upon or injure the L5 nerve root.

Question 1834

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (Stoppa) approach for acetabular/pelvic ring fixation, profuse bleeding occurs just posterior to the superior pubic ramus near the symphysis. This hemorrhage is most likely originating from an anastomosis between the external iliac system and which internal iliac branch?

. Superior gluteal artery
. Internal pudendal artery
. Inferior gluteal artery
. Obturator artery
. Middle sacral artery

Correct Answer & Explanation

. Obturator artery

Explanation

The corona mortis is a critical vascular anastomosis connecting the external iliac system (usually inferior epigastric) to the internal iliac system (usually the obturator artery or vein). It courses over the superior pubic ramus and is highly vulnerable during anterior pelvic approaches.

Question 1835

Topic: 1. General Principles & Basic Science

When utilizing intraoperative fluoroscopy for the placement of an S1 iliosacral screw, the surgeon uses the inlet view to monitor the screw's trajectory. The anterior margin of the 'safe zone' on this specific view represents which anatomic structure?

. The anterior cortex of the sacral ala
. The sacral promontory
. The anterior cortex of the S1 vertebral body
. The S1 neural foramen
. The iliac cortical density

Correct Answer & Explanation

. The anterior cortex of the S1 vertebral body

Explanation

On the pelvic inlet view, the anterior boundary of the safe zone is defined by the anterior cortex of the S1 sacral body. Violating this boundary anteriorly risks devastating injury to the internal iliac vessels and the L5 nerve root.

Question 1836

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach for anterior pelvic ring fixation, significant brisk arterial bleeding is encountered posterior to the superior pubic ramus near the symphysis. This hemorrhage is most likely originating from an anastomosis between which of the following vessels?

. Internal pudendal and superior gluteal arteries
. External iliac and obturator systems
. Internal iliac and inferior epigastric arteries
. Superior and inferior gluteal arteries
. Femoral and circumflex iliac arteries

Correct Answer & Explanation

. External iliac and obturator systems

Explanation

The corona mortis ('crown of death') is a common vascular anastomosis connecting the external iliac system (usually the inferior epigastric artery/vein) with the internal iliac system (obturator artery/vein). It is located on the posterior aspect of the superior pubic ramus and is highly susceptible to iatrogenic injury.

Question 1837

Topic: 1. General Principles & Basic Science

Which of the following is a classic radiographic characteristic of a dysmorphic sacrum, which increases the risk of neurologic injury during percutaneous placement of an S1 iliosacral screw?

. Circular S1 neural foramina
. Collinear alignment of the anterior S1 and S2 bodies
. Upper sacral segment positioned above the iliac crests
. Sacral ala slope coplanar with the pelvic brim
. Wide anterior-posterior depth of the S1 body

Correct Answer & Explanation

. Upper sacral segment positioned above the iliac crests

Explanation

Dysmorphic sacrums feature an upper sacral segment located above the iliac crests, non-circular (teardrop) upper sacral foramina, a residual S1-S2 disc space, and an acute alar slope. These morphological variants severely restrict the safe zone for S1 iliosacral screws.

Question 1838

Topic: Surgical Anatomy & Approaches

A 24-year-old male is treated with an anterior subcutaneous pelvic internal fixator (INFIX) for an APC-II pelvic injury. Post-operatively, he complains of burning pain and numbness over the anterolateral aspect of his thigh. Injury to which of the following nerves is the most likely cause?

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

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

The most common nerve complication associated with the INFIX procedure is irritation or injury to the lateral femoral cutaneous nerve (LFCN) due to the subcutaneous placement of the connecting rod and supra-acetabular screws.

Question 1839

Topic: Infection, Pharmacology & VTE

An 18-year-old female sustains an unstable pelvic fracture. She is successfully stabilized in the ICU. The surgical team plans for internal fixation on hospital day 3. According to major orthopedic trauma guidelines, what is the optimal strategy for deep vein thrombosis (DVT) prophylaxis in this patient?

. Mechanical prophylaxis only for 4 weeks post-injury
. Low molecular weight heparin starting immediately upon admission
. Chemical prophylaxis (LMWH) starting 24-48 hours after injury, continuing post-operatively
. Aspirin 81 mg daily for 2 weeks
. Placement of an IVC filter within 24 hours

Correct Answer & Explanation

. Chemical prophylaxis (LMWH) starting 24-48 hours after injury, continuing post-operatively

Explanation

Patients with pelvic ring injuries are at a very high risk for DVT/PE. Current guidelines recommend initiating chemical prophylaxis (typically LMWH) within 24 to 48 hours of injury, provided bleeding is controlled, and continuing it throughout the perioperative period.

Question 1840

Topic: Surgical Anatomy & Approaches

During the anterior intrapelvic (Stoppa) approach for a pelvic ring injury, massive hemorrhage occurs from a vessel located superior to the superior pubic ramus. This vessel is an anastomosis between which two vascular systems?

. Internal pudendal and external iliac
. Obturator and external iliac
. Obturator and internal iliac
. Inferior epigastric and internal pudendal
. Superior gluteal and internal pudendal

Correct Answer & Explanation

. Obturator and external iliac

Explanation

The corona mortis is a vascular anastomosis between the obturator and external iliac systems (or inferior epigastric vessels) located over the superior pubic ramus. It is at high risk of iatrogenic injury during anterior intrapelvic approaches.

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