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1. General Principles & Basic Science MCQs

Practice Set 763 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 15241

Topic: Physiology & Rehabilitation

Normal human walking gait is traditionally divided into stance and swing phases. In a healthy adult walking at a self-selected pace, the stance phase comprises approximately what percentage of the entire gait cycle?

. 30%
. 40%
. 50%
. 60%
. 80%

Correct Answer & Explanation

. 60%

Explanation

During a normal gait cycle, the stance phase (foot in contact with the ground) constitutes approximately 60% of the cycle, while the swing phase accounts for the remaining 40%.

Question 15242

Topic: 1. General Principles & Basic Science

According to the principles of deformity correction, what is the expected outcome if the osteotomy is made at a level different from the Center of Rotation of Angulation (CORA), but the hinge is placed exactly at the CORA?

. Pure angulation without translation
. Pure translation without angulation
. Angulation with translation of the bone ends
. Lengthening without angulation
. Shortening without translation

Correct Answer & Explanation

. Angulation with translation of the bone ends

Explanation

This describes Osteotomy Rule 2. When the hinge is at the CORA but the osteotomy is at a different level, the bone ends will angulate and undergo translation at the osteotomy site to achieve collinear realignment of the axes.

Question 15243

Topic: 1. General Principles & Basic Science

In deformity planning, if an osteotomy and the hinge are both placed exactly at the Center of Rotation of Angulation (CORA), which of the following best describes the correction (Osteotomy Rule 1)?

. Angulation with intentional shortening
. Pure translation with no angulation
. Angulation with collinear realignment of the mechanical axes without translation
. Angulation accompanied by obligatory translation
. Rotational correction only

Correct Answer & Explanation

. Angulation with collinear realignment of the mechanical axes without translation

Explanation

Osteotomy Rule 1 states that if both the osteotomy and the hinge (axis of correction) are located at the CORA, the mechanical axes will realign perfectly with pure angulation and no displacement (translation) of the bone ends.

Question 15244

Topic: Physiology & Rehabilitation

During gait analysis, a patient exhibits a significant "pelvic drop" on the swing side. Weakness in which of the following muscles during the stance phase of the contralateral leg is most likely responsible?

. Gluteus maximus
. Gluteus medius
. Iliopsoas
. Adductor magnus
. Quadriceps femoris

Correct Answer & Explanation

. Gluteus medius

Explanation

This describes a Trendelenburg gait. The gluteus medius and minimus (hip abductors) on the stance leg must contract to stabilize the pelvis and prevent it from dropping on the contralateral (swing) side.

Question 15245

Topic: 1. General Principles & Basic Science

When performing an opening wedge high tibial osteotomy (HTO) for medial compartment osteoarthritis with a varus deformity, what is a common unintended consequence on the sagittal profile of the tibia?

. Decreased posterior tibial slope
. Increased posterior tibial slope
. Anterior translation of the tibial tubercle
. Patella alta
. Fixed knee extension contracture

Correct Answer & Explanation

. Increased posterior tibial slope

Explanation

Opening wedge HTOs tend to increase the posterior tibial slope if the gap is opened equally anteriorly and posteriorly, because the proximal tibia is triangular (narrower anteriorly). To maintain the native slope, the gap must be larger posteromedially than anteromedially.

Question 15246

Topic: Physiology & Rehabilitation

Which phase of the normal gait cycle requires the maximum amount of hip extension?

. Initial contact
. Loading response
. Mid-stance
. Terminal stance
. Initial swing

Correct Answer & Explanation

. Terminal stance

Explanation

Maximum hip extension (approximately 10 to 20 degrees) occurs at the end of terminal stance, just before initial contact of the contralateral limb (pre-swing). This facilitates forward progression of the body.

Question 15247

Topic: 1. General Principles & Basic Science

You are assessing a patient's long-leg alignment radiograph. The Joint Line Convergence Angle (JLCA) is measured at 8 degrees (normal is 0-2 degrees) in a varus knee. What does this abnormally increased JLCA suggest?

. The deformity is entirely metaphyseal.
. There is a fixed structural deformity of the femoral diaphysis.
. There is intra-articular deformity or ligamentous laxity contributing to the varus.
. The patient has an ipsilateral limb length discrepancy.
. The mechanical axis of the tibia is normal.

Correct Answer & Explanation

. There is intra-articular deformity or ligamentous laxity contributing to the varus.

Explanation

An abnormally large JLCA indicates that the knee joint lines are not parallel. This points to an intra-articular source of deformity, such as asymmetric cartilage loss, subchondral bone collapse, or lateral collateral ligament laxity.

Question 15248

Topic: Physiology & Rehabilitation

A patient presents with a 'stiff-knee gait' following a severe traumatic brain injury. During the swing phase, the knee fails to flex adequately. Overactivity of which muscle is the primary culprit and can be evaluated using dynamic electromyography (EMG)?

. Biceps femoris
. Rectus femoris
. Vastus medialis
. Gastrocnemius
. Iliopsoas

Correct Answer & Explanation

. Rectus femoris

Explanation

Stiff-knee gait is typically caused by overactivity or spasticity of the rectus femoris during the swing phase, which actively prevents normal knee flexion. This is often treated with a rectus femoris transfer or release.

Question 15249

Topic: Physiology & Rehabilitation

During normal human gait, maximum knee flexion during the swing phase reaches approximately what angle to allow for adequate foot clearance?

. 30 degrees
. 45 degrees
. 60 degrees
. 90 degrees
. 110 degrees

Correct Answer & Explanation

. 60 degrees

Explanation

During the initial and mid-swing phases of the normal gait cycle, the knee flexes to a maximum of approximately 60 degrees. This flexion, combined with ankle dorsiflexion and hip flexion, is critical for adequate foot clearance.

Question 15250

Topic: 1. General Principles & Basic Science

A 55-year-old patient with end-stage renal disease presents with diffuse bone pain. Laboratory studies reveal significantly elevated parathyroid hormone (PTH) levels. Which of the following best explains the primary mechanism for the elevated PTH in this patient?

. Decreased hepatic clearance of PTH
. Impaired renal degradation and clearance of PTH
. Autonomous hypersecretion from a parathyroid adenoma
. Ectopic PTH production from a malignancy
. Decreased intestinal absorption of PTH

Correct Answer & Explanation

. Impaired renal degradation and clearance of PTH

Explanation

Correct Answer: Impaired renal degradation and clearance of PTHThe kidney is the primary organ responsible for the metabolic clearance and degradation of parathyroid hormone (PTH). In patients with chronic kidney disease (CKD) or end-stage renal disease, impaired renal function leads to decreased clearance of PTH, contributing to secondary hyperparathyroidism. Additionally, failing kidneys cannot adequately convert 25-hydroxyvitamin D to its active form (1,25-dihydroxyvitamin D), leading to hypocalcemia, which further stimulates PTH secretion.

Question 15251

Topic: Biology, Genetics & Bone Healing

During the reparative phase of secondary fracture healing in a diaphyseal tibia fracture treated with a cast, a soft callus forms. Which of the following biological processes is primarily responsible for the initial stabilization of the fracture site during this specific phase?

. Direct osteoblastic bone formation without a cartilage intermediate
. Proliferation of chondrocytes and production of a cartilaginous matrix
. Osteoclastic resorption of necrotic bone ends
. Formation of a hematoma and release of inflammatory cytokines
. Remodeling of woven bone into lamellar bone

Correct Answer & Explanation

. Proliferation of chondrocytes and production of a cartilaginous matrix

Explanation

Correct Answer: Proliferation of chondrocytes and production of a cartilaginous matrixSecondary fracture healing occurs in stages: hematoma formation (inflammation), soft callus formation (reparative), hard callus formation, and remodeling. The soft callus phase is characterized by endochondral ossification, where mesenchymal stem cells differentiate into chondrocytes that produce a cartilaginous matrix. This cartilage bridges the fracture gap and provides initial semi-rigid stabilization before being replaced by woven bone (hard callus).

Question 15252

Topic: Surgical Anatomy & Approaches

The primary blood supply to the adult femoral head is derived from the medial circumflex femoral artery (MCFA). Which specific branch of the MCFA provides the majority of this perfusion, and what is its anatomical relationship to the hip joint?

. Anterior retinacular artery, coursing anterior to the iliofemoral ligament
. Lateral epiphyseal artery, coursing posterosuperiorly along the femoral neck
. Inferior metaphyseal artery, entering through the ligamentum teres
. Medial epiphyseal artery, piercing the anterior capsule
. Ascending branch of the lateral circumflex artery, running within the pubofemoral ligament

Correct Answer & Explanation

. Lateral epiphyseal artery, coursing posterosuperiorly along the femoral neck

Explanation

Correct Answer: BThe lateral epiphyseal artery, a terminal branch of the medial circumflex femoral artery (MCFA), provides the majority of the blood supply to the adult femoral head. It courses posterosuperiorly along the femoral neck within the retinacular folds before penetrating the head. Disruption of this specific vascular pathway is the primary cause of avascular necrosis following displaced femoral neck fractures.

Question 15253

Topic: Biology, Genetics & Bone Healing
During the reparative phase of secondary fracture healing, a soft callus forms to stabilize the fracture site. Which of the following best describes the predominant collagen type synthesized during this specific stage, and the primary cell type responsible?
. Type I collagen synthesized by osteoblasts
. Type II collagen synthesized by chondrocytes
. Type III collagen synthesized by fibroblasts
. Type IV collagen synthesized by endothelial cells
. Type X collagen synthesized by hypertrophic chondrocytes

Correct Answer & Explanation

. Type II collagen synthesized by chondrocytes

Explanation

The soft callus phase of secondary fracture healing is characterized by the formation of cartilaginous tissue. Chondrocytes proliferate in the hypoxic environment of the fracture gap and synthesize a matrix predominantly composed of Type II collagen. This soft callus is later replaced by woven bone (Type I collagen) during the hard callus phase via endochondral ossification.

Question 15254

Topic: Biology, Genetics & Bone Healing

During the reparative phase of secondary fracture healing, a soft callus forms to bridge the fracture gap. Which of the following biological conditions most strongly favors the differentiation of mesenchymal stem cells into chondrocytes rather than osteoblasts during this phase?

. High oxygen tension and high mechanical stability
. Low oxygen tension and moderate mechanical strain
. High oxygen tension and low mechanical strain
. Complete absence of mechanical strain
. High pH and elevated calcium concentration

Correct Answer & Explanation

. Low oxygen tension and moderate mechanical strain

Explanation

Correct Answer: BSecondary fracture healing involves soft callus formation via endochondral ossification. The fracture hematoma and early reparative tissue are relatively avascular, resulting in a hypoxic environment (low oxygen tension). This hypoxia, combined with moderate mechanical strain (interfragmentary motion), drives mesenchymal stem cells to differentiate into chondrocytes to form the cartilaginous soft callus. High oxygen tension and rigid stability would instead favor direct (primary) bone healing or intramembranous ossification.

Question 15255

Topic: Infection, Pharmacology & VTE

Acute hematogenous osteomyelitis in children most commonly localizes to the metaphysis of long bones. Which of the following anatomical features of the pediatric metaphysis is the primary reason for this specific localization?

. High concentration of phagocytic cells in the metaphyseal marrow
. Presence of sluggish, turbulent blood flow in terminal venous sinusoids
. Direct arterial anastomoses between the metaphysis and epiphysis
. Lack of a periosteal layer covering the metaphyseal cortex
. High oxygen tension favoring aerobic bacterial proliferation

Correct Answer & Explanation

. Presence of sluggish, turbulent blood flow in terminal venous sinusoids

Explanation

Correct Answer: BIn children, the metaphysis is the most common site for acute hematogenous osteomyelitis. The nutrient artery branches into small arterioles that form sharp, hairpin loops at the physeal border before emptying into large venous sinusoids. This anatomical arrangement causes sluggish, turbulent blood flow, which allows blood-borne bacteria to settle and proliferate in an area with relatively low local phagocytic activity.

Question 15256

Topic: Biology, Genetics & Bone Healing

The kidney is the primary organ responsible for the clearance of parathyroid hormone (PTH). In a patient with end-stage renal disease, impaired clearance and altered vitamin D metabolism most commonly lead to which of the following secondary bone pathologies?

. Osteopetrosis
. Osteomalacia
. Secondary hyperparathyroidism
. Paget's disease
. Primary hyperparathyroidism

Correct Answer & Explanation

. Secondary hyperparathyroidism

Explanation

Correct Answer: Secondary hyperparathyroidismImpaired renal function leads to decreased phosphate excretion and decreased 1-alpha-hydroxylase activity (lowering active Vitamin D). This causes hypocalcemia, which stimulates the parathyroid glands to overproduce PTH, leading to secondary hyperparathyroidism and renal osteodystrophy.

Question 15257

Topic: Biology, Genetics & Bone Healing
During the reparative phase of secondary fracture healing, a soft callus is formed. Which of the following collagen types is predominantly synthesized during this specific stage of callus formation?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

The soft callus phase of fracture healing is characterized by the formation of cartilaginous tissue by chondrocytes. The predominant collagen in this cartilaginous soft callus is Type II collagen. As the soft callus undergoes endochondral ossification to become a hard callus, Type I collagen becomes predominant.

Question 15258

Topic: Biology, Genetics & Bone Healing

Paget's disease of bone is characterized by disorganized bone remodeling and a 'mosaic' pattern on histology. Which of the following represents the primary cellular abnormality that initiates the pathogenesis of this disease?

. Decreased osteoblast apoptosis
. Hyperactive, multinucleated osteoclasts
. Defective mineralization by osteocytes
. Overproduction of Type I collagen by fibroblasts
. Malignant transformation of mesenchymal stem cells

Correct Answer & Explanation

. Hyperactive, multinucleated osteoclasts

Explanation

Correct Answer: Hyperactive, multinucleated osteoclastsThe initial phase of Paget's disease is characterized by a marked increase in osteoclastic bone resorption. The osteoclasts in Paget's disease are abnormal, being larger and containing many more nuclei than normal osteoclasts. This intense resorption is followed by a disorganized, chaotic osteoblastic response, leading to the characteristic 'mosaic' woven bone.

Question 15259

Topic: Surgical Anatomy & Approaches

A 25-year-old male sustains a posterior hip dislocation in a motor vehicle collision. He subsequently demonstrates a foot drop. Which specific neural structure is most likely injured?

. Femoral nerve
. Obturator nerve
. Tibial division of the sciatic nerve
. Peroneal division of the sciatic nerve
. Superior gluteal nerve

Correct Answer & Explanation

. Peroneal division of the sciatic nerve

Explanation

Correct Answer: Peroneal division of the sciatic nervePosterior hip dislocations are frequently associated with sciatic nerve injuries (up to 10-20% of cases). The peroneal (fibular) division of the sciatic nerve is much more commonly injured than the tibial division because it is tethered at the sciatic notch and positioned more laterally and superficially, making it vulnerable to stretch or direct compression by the displaced femoral head.

Question 15260

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during fracture healing. Which of the following intracellular signaling pathways is primarily activated by BMPs?

. Wnt/beta-catenin pathway
. JAK/STAT pathway
. SMAD pathway
. MAPK/ERK pathway
. Notch signaling pathway

Correct Answer & Explanation

. SMAD pathway

Explanation

BMPs are members of the TGF-beta superfamily that promote osteoblast differentiation. They exert their osteoinductive effects primarily by binding to serine/threonine kinase receptors that directly activate the intracellular SMAD signaling cascade.

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