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1. General Principles & Basic Science MCQs

Practice Set 209 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 4161

Topic: 1. General Principles & Basic Science

A 45-year-old male sustains a high-energy Moore Type I (coronal split) fracture of the medial tibial plateau. A posteromedial surgical approach is chosen for buttress plating. Which of the following describes the correct anatomic interval for this surgical approach?

. Between the lateral head of the gastrocnemius and the biceps femoris
. Between the medial head of the gastrocnemius and the pes anserinus
. Between the tibialis posterior and the flexor digitorum longus
. Between the sartorius and the gracilis
. Between the medial head of the gastrocnemius and the soleus

Correct Answer & Explanation

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

Explanation

The posteromedial approach to the tibial plateau utilizes the interval between the medial head of the gastrocnemius (retracted posteriorly/laterally) and the pes anserinus (retracted anteriorly/medially). This allows direct visualization and buttress plating of posteromedial shear fragments.

Question 4162

Topic: Surgical Anatomy & Approaches
A 32-year-old male sustains an APC-III pelvic ring injury. Despite external pelvic binding and aggressive fluid resuscitation, he remains hypotensive. Pre-peritoneal pelvic packing is initiated. During the approach, the surgeon must be cautious of the "corona mortis." This vascular structure represents an anastomosis between which two vascular systems?
. External iliac and obturator systems
. Internal iliac and superior gluteal systems
. Internal pudendal and obturator systems
. Femoral and inferior gluteal systems
. Deep circumflex iliac and internal pudendal systems

Correct Answer & Explanation

. External iliac and obturator systems

Explanation

The corona mortis is a vascular anastomosis between the external iliac (or deep inferior epigastric) vessels and the obturator vessels. It crosses the superior pubic ramus and is highly susceptible to injury in pelvic ring disruptions and anterior surgical approaches.

Question 4163

Topic: Biomechanics & Biomaterials

To optimize gait biomechanics and minimize adjacent joint arthritis, what is the ideal position for a tibiotalar arthrodesis?

. Neutral dorsiflexion, 0 to 5 degrees of valgus, and 5 to 10 degrees of external rotation
. 5 degrees of plantarflexion, neutral coronal alignment, and neutral rotation
. 5 degrees of dorsiflexion, 5 degrees of varus, and neutral rotation
. Neutral dorsiflexion, 5 degrees of varus, and 15 degrees of external rotation
. 5 degrees of plantarflexion, 5 degrees of valgus, and 15 degrees of external rotation

Correct Answer & Explanation

. Neutral dorsiflexion, 0 to 5 degrees of valgus, and 5 to 10 degrees of external rotation

Explanation

The optimal position for ankle arthrodesis is neutral dorsiflexion, slight valgus (0-5 degrees), and slight external rotation (5-10 degrees) matching the contralateral limb. Plantarflexion or varus malalignment significantly impairs gait and accelerates adjacent joint arthritis.

Question 4164

Topic: Surgical Anatomy & Approaches

During the intrapelvic Stoppa approach for an acetabular fracture, the surgeon must be acutely aware of a major vascular anastomosis that frequently crosses over the superior pubic ramus at an average distance of 4 to 6 cm from the pubic symphysis. This structure, often termed the 'Corona Mortis', typically connects which two vascular systems?

. The external iliac and internal pudendal systems
. The obturator and external iliac (or inferior epigastric) systems
. The internal iliac and deep circumflex iliac systems
. The superior gluteal and inferior gluteal systems
. The superficial femoral and medial circumflex femoral systems

Correct Answer & Explanation

. The obturator and external iliac (or inferior epigastric) systems

Explanation

The Corona Mortis is an anastomotic arterial or venous connection between the obturator vessels (branching from the internal iliac system) and the external iliac or inferior epigastric vessels. It crosses the superior pubic ramus and is highly susceptible to iatrogenic injury during anterior intrapelvic approaches (e.g., Stoppa, ilioinguinal), which can result in life-threatening hemorrhage.

Question 4165

Topic: Biology, Genetics & Bone Healing

A 65-year-old female on long-term alendronate therapy presents with progressively worsening prodromal thigh pain. Radiographs demonstrate lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the femur. What is the most appropriate prophylactic management?

. Switching to denosumab and protected weight bearing
. Discontinuation of bisphosphonates and weekly radiographic observation
. Prophylactic cephalomedullary nailing
. Open reduction and dynamic compression plating
. Application of a cortical strut allograft with cerclage wires

Correct Answer & Explanation

. Prophylactic cephalomedullary nailing

Explanation

This patient presents with a symptomatic impending atypical femoral fracture secondary to long-term bisphosphonate use. Prophylactic intramedullary nailing is indicated to relieve pain and prevent completion of the fracture, which is known for a high rate of delayed union or nonunion.

Question 4166

Topic: Surgical Anatomy & Approaches

A 29-year-old male presents with a posterior hip dislocation following a dashboard injury in a motor vehicle collision. Following closed reduction, he exhibits a complete foot drop but normal plantar flexion. Which specific neural structure is most commonly injured in this scenario?

. Tibial division of the sciatic nerve
. Common peroneal division of the sciatic nerve
. Deep peroneal nerve strictly at the fibular head
. Femoral nerve
. Obturator nerve

Correct Answer & Explanation

. Common peroneal division of the sciatic nerve

Explanation

The common peroneal division of the sciatic nerve is most vulnerable during a posterior hip dislocation. Its lateral location and tighter tethering at the sciatic notch make it more susceptible to stretch or compression from the posteriorly displaced femoral head.

Question 4167

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach for an anterior column acetabular fracture, significant hemorrhage occurs while dissecting over the posterior aspect of the superior pubic ramus. This bleeding is most likely originating from an anastomosis between which two vascular systems?

. Internal pudendal and obturator
. External iliac and internal iliac
. Inferior epigastric and obturator
. Superior gluteal and internal pudendal
. Femoral and inferior epigastric

Correct Answer & Explanation

. Inferior epigastric and obturator

Explanation

The corona mortis is a potentially life-threatening vascular anastomosis between the obturator (internal iliac system) and inferior epigastric (external iliac system) vessels. It is consistently located on the posterior aspect of the superior pubic ramus, averaging 4-6 cm from the symphysis pubis.

Question 4168

Topic: 1. General Principles & Basic Science

In planning an osteotomy for a uniplanar angular deformity of the tibia, placing the hinge of the osteotomy directly on the convex cortex at the center of rotation of angulation (CORA) will result in which of the following?

. Opening wedge correction without translation
. Closing wedge correction without translation
. Opening wedge correction with translation
. Closing wedge correction with translation
. Neutral wedge correction with translation

Correct Answer & Explanation

. Opening wedge correction without translation

Explanation

According to Paley's rules of osteotomy, if the osteotomy and the hinge are both placed at the CORA on the convex side of the deformity, an opening wedge correction without translation will result. If the hinge is placed at the CORA on the concave side, a closing wedge correction without translation results.

Question 4169

Topic: Biology, Genetics & Bone Healing

A 14-year-old boy is undergoing tibial lengthening via distraction osteogenesis. Four weeks into the distraction phase, radiographs show poor regenerate bone formation (the gap is radiolucent, without premature consolidation). Which of the following modifications to the distraction protocol is the most appropriate next step?

. Increase the distraction rate to 1.5 mm/day
. Perform open bone grafting of the distraction gap
. Stop distraction and compress the gap temporarily (accordion technique)
. Switch to acute docking and immediate internal fixation
. Administer bisphosphonates to stimulate bone formation

Correct Answer & Explanation

. Stop distraction and compress the gap temporarily (accordion technique)

Explanation

Poor regenerate bone formation (hypotrophic regenerate) during distraction osteogenesis can be addressed by the 'accordion technique,' which involves temporarily stopping distraction and compressing the site (typically 1 mm/day for several days) followed by resuming distraction. This cyclical compression and distraction mechanically stimulates osteogenesis. Increasing the rate would worsen the gap.

Question 4170

Topic: Biology, Genetics & Bone Healing

A 5-year-old child presents with severe bilateral genu varum, short stature, and waddling gait. Laboratory tests reveal low serum phosphate, normal serum calcium, normal parathyroid hormone, and elevated alkaline phosphatase. Genetic testing confirms an X-linked dominant mutation in the PHEX gene. Which of the following medications is currently considered disease-modifying and targets the underlying pathophysiology of this condition?

. High-dose oral Vitamin D3 (Cholecalciferol)
. Burosumab
. Denosumab
. Recombinant human growth hormone
. Pamidronate

Correct Answer & Explanation

. Burosumab

Explanation

The child has X-linked hypophosphatemic rickets (XLH), caused by a PHEX mutation leading to excess FGF23 production. High FGF23 causes renal phosphate wasting and impairs calcitriol synthesis. Burosumab is a monoclonal antibody that binds and inhibits FGF23, directly addressing the pathophysiology of XLH and improving phosphate homeostasis, rickets severity, and lower limb deformity.

Question 4171

Topic: 1. General Principles & Basic Science

During surgical repair of a lacerated flexor digitorum profundus (FDP) tendon in Zone II, a surgeon performs a multi-strand core suture and an epitendinous repair. What is the primary biomechanical advantage of adding a running epitendinous suture to the core suture?

. It decreases the gliding resistance of the tendon and increases gap formation strength.
. It relies on the extrinsic healing capacity by recruiting blood supply from the vincula.
. It primarily prevents adhesion formation to the flexor sheath without affecting strength.
. It replaces the need for a 4-strand core suture by providing equivalent tensile strength.
. It promotes rapid degradation of the fibrin clot, shortening the inflammatory phase.

Correct Answer & Explanation

. It decreases the gliding resistance of the tendon and increases gap formation strength.

Explanation

The addition of a peripheral epitendinous suture to a core tendon repair provides two major biomechanical benefits: it significantly increases the overall tensile strength of the repair (increasing load to gap formation by 10-50%), and it smooths the repair site by tucking in frayed edges, thereby decreasing gliding resistance and work of flexion within the flexor sheath.

Question 4172

Topic: 1. General Principles & Basic Science

In the context of lower extremity deformity correction utilizing Paley's osteotomy rules, what is the resultant effect on the mechanical axis if both the osteotomy and the axis of correction of angulation (ACA) are performed at a level distinct from the center of rotation of angulation (CORA)?

. The proximal and distal mechanical axes become perfectly collinear
. The mechanical axes will intersect at the new ACA creating a single angulation
. A secondary translation deformity is created with parallel axes
. Pure shortening occurs along the anatomical axis
. Pure lengthening occurs along the mechanical axis

Correct Answer & Explanation

. A secondary translation deformity is created with parallel axes

Explanation

According to Paley's Rule 3, if the osteotomy and the ACA are placed at a level different from the CORA, the mechanical axes of the proximal and distal segments will end up parallel to each other, resulting in a secondary translation deformity. Rule 1 (osteotomy and ACA at CORA) yields pure angulation and collinear axes. Rule 2 (ACA at CORA, osteotomy at a different level) yields angulation and translation at the osteotomy site, but collinear mechanical axes.

Question 4173

Topic: 1. General Principles & Basic Science

A 2-year-old obese boy presents with bilateral genu varum. Radiographs demonstrate medial metaphyseal beaking of the proximal tibia. Measurement of the metaphyseal-diaphyseal angle of Drennan is performed. Which of the following values is most highly predictive of progression to infantile Blount disease rather than physiologic bowing?

. Less than 9 degrees
. 10 to 15 degrees
. Greater than 16 degrees
. Negative 5 degrees
. Greater than 30 degrees (femoral-tibial angle)

Correct Answer & Explanation

. Greater than 16 degrees

Explanation

The metaphyseal-diaphyseal angle (Drennan's angle) is measured between a line drawn through the transverse plane of the proximal tibial metaphysis and a line perpendicular to the anatomical axis of the tibial diaphysis. An angle greater than 16 degrees is highly predictive (95% probability) of progression to infantile Blount disease, whereas an angle less than 10 degrees typically indicates physiologic bowing that will resolve spontaneously.

Question 4174

Topic: 1. General Principles & Basic Science
A 2-year-old boy presents with an anterolateral bow of the tibia and a radiolucent area in the diaphysis. Examination reveals 6 café-au-lait macules measuring >5 mm. He is diagnosed with congenital pseudarthrosis of the tibia (CPT). Histological analysis of the tissue resected from the pseudarthrosis site during surgery is most likely to reveal which of the following?
. Hypervascular woven bone with abundant giant cells
. A highly cellular hamartoma of dense fibrous tissue
. Malignant spindle cells arranged in a herringbone pattern
. Normal hyaline cartilage without a provisional zone of calcification
. Avascular necrosis with empty lacunae and creeping substitution

Correct Answer & Explanation

. A highly cellular hamartoma of dense fibrous tissue

Explanation

Congenital pseudarthrosis of the tibia (CPT) is strongly associated with Neurofibromatosis type 1 (NF1). The pathology at the pseudarthrosis site typically demonstrates a thick, constricting band of highly cellular, dense fibrous tissue (a hamartoma) that replaces the normal periosteum and prevents normal bone formation and healing, leading to persistent nonunion.

Question 4175

Topic: 1. General Principles & Basic Science

According to Paley's rules of osteotomy, if the osteotomy and the hinge are placed on the transverse bisector line but at a distance from the center of rotation of angulation (CORA), what is the resultant effect on the bone segments?

. Pure angulation without translation
. Angulation with translation resulting in colinear mechanical axes
. Angulation with translation resulting in parallel but non-colinear mechanical axes
. Pure translation without angulation
. Lengthening without translation

Correct Answer & Explanation

. Angulation with translation resulting in colinear mechanical axes

Explanation

Paley's Rule 2 states that placing the hinge on the bisector line but away from the CORA results in both angular correction and translation, producing colinear mechanical axes. Rule 1 yields pure angulation, while Rule 3 results in non-colinear axes.

Question 4176

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy with X-linked hypophosphatemic (XLH) rickets presents with severe genu varum. Prior to surgical deformity correction, medical optimization should ideally include which of the following targeted therapies?

. High-dose oral calcium supplementation
. Intravenous bisphosphonates
. Burosumab
. Teriparatide (recombinant PTH)
. Cinacalcet

Correct Answer & Explanation

. Burosumab

Explanation

XLH is characterized by excess FGF23, which leads to renal phosphate wasting and impaired bone mineralization. Burosumab, an anti-FGF23 monoclonal antibody, normalizes phosphate homeostasis and optimizes bone quality before osteotomy.

Question 4177

Topic: 1. General Principles & Basic Science

When performing an osteotomy for angular deformity, if the osteotomy and the hinge are both placed away from the Center of Rotation of Angulation (CORA) but parallel to the transverse bisector line, which of the following is true regarding the resulting mechanical axis?

. Pure angulation without translation
. Complete correction of angulation with an iatrogenic translation
. Pure translation without correction of angulation
. Neither angulation nor translation is corrected
. Shortening of the limb segment with rotational deformity

Correct Answer & Explanation

. Complete correction of angulation with an iatrogenic translation

Explanation

According to Paley's rules of deformity correction (Rule 2), if the osteotomy axis (hinge) is away from the CORA, angular correction is accompanied by a translation of the axis. This can be used intentionally to correct pre-existing translation.

Question 4178

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis using the Ilizarov method, what is the optimal biological environment for regenerate bone formation?

. Immediate distraction post-osteotomy at 2 mm per day
. A 7-10 day latency period followed by distraction at 1 mm per day in divided doses
. Corticotomy with extensive periosteal stripping followed by distraction at 0.5 mm per day
. Immediate distraction followed by a 14-day latency period
. A 21-day latency period followed by distraction at 1.5 mm per day

Correct Answer & Explanation

. A 7-10 day latency period followed by distraction at 1 mm per day in divided doses

Explanation

Optimal regenerate formation in distraction osteogenesis requires a low-energy corticotomy preserving the periosteum, a 7-10 day latency period to allow soft callus formation, and a distraction rate of roughly 1 mm per day in small, divided increments.

Question 4179

Topic: Biology, Genetics & Bone Healing

A 68-year-old female on long-term alendronate for osteoporosis presents with dull aching thigh pain. Radiographs demonstrate lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the right femur. If prophylactic surgical fixation is chosen, which of the following is true regarding her management?

. Bisphosphonates should be continued to augment fracture healing
. Teriparatide is absolutely contraindicated in this scenario
. Cephalomedullary nailing is the preferred construct over plate fixation
. Prophylactic fixation is only indicated if the fracture line crosses the medial cortex
. The contralateral femur rarely requires radiographic evaluation

Correct Answer & Explanation

. Cephalomedullary nailing is the preferred construct over plate fixation

Explanation

Atypical femur fractures are highly associated with prolonged bisphosphonate use. Because the bone biology is altered, plate fixation has a high failure rate. Intramedullary (cephalomedullary) nailing is the preferred construct for prophylactic or definitive fixation. Bisphosphonates must be discontinued, the contralateral femur must be imaged (due to high bilateral incidence), and anabolic agents like teriparatide may actually be considered off-label to aid healing.

Question 4180

Topic: 1. General Principles & Basic Science

A 25-year-old soccer player complains of a snapping sensation behind his lateral malleolus during push-off. Examination reveals subluxation of the peroneal tendons with resisted dorsiflexion and eversion. Which of the following structures is the primary restraint to this subluxation?

. Inferior peroneal retinaculum
. Superior peroneal retinaculum
. Calcaneofibular ligament
. Posterior talofibular ligament
. Peroneus quartus muscle

Correct Answer & Explanation

. Superior peroneal retinaculum

Explanation

The superior peroneal retinaculum (SPR) is the primary restraint to peroneal tendon subluxation. It originates from the posterolateral ridge of the fibula and inserts onto the lateral calcaneal wall. Injury to the SPR, often through forced dorsiflexion and inversion causing an avulsion from the fibula, results in peroneal tendon instability.

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