Menu

1. General Principles & Basic Science MCQs

Practice Set 217 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 4321

Topic: 1. General Principles & Basic Science
During the early pathogenesis of osteoarthritis, the degradation of the extracellular matrix is a critical event. Which of the following enzymes is considered the primary aggrecanase responsible for the initial cleavage of the aggrecan core protein?
. MMP-1
. MMP-13
. Cathepsin K
. ADAMTS-4
. Caspase-3

Correct Answer & Explanation

. ADAMTS-4

Explanation

ADAMTS-4 and ADAMTS-5 (A Disintegrin and Metalloproteinase with Thrombospondin motifs) are the primary aggrecanases responsible for the early degradation of aggrecan in osteoarthritis. MMP-13 (Matrix Metalloproteinase 13) is the primary collagenase responsible for the degradation of Type II collagen, a process that typically follows aggrecan loss.

Question 4322

Topic: 1. General Principles & Basic Science

Under low-speed, high-load conditions such as prolonged static standing, which of the following molecular components is primarily responsible for the boundary lubrication of articular cartilage?

. Aggrecan
. Hyaluronic acid
. Type II collagen
. Lubricin (PRG4)
. Chondroitin sulfate

Correct Answer & Explanation

. Lubricin (PRG4)

Explanation

Joint lubrication is complex. Boundary lubrication dominates during high contact pressures and low sliding speeds (e.g., standing). This mechanism relies on surface-active molecules bound to the articular surface to prevent direct cartilage-on-cartilage wear. Lubricin (proteoglycan 4 or PRG4) is the primary glycoprotein responsible for boundary lubrication. Fluid-film lubrication dominates at high sliding speeds.

Question 4323

Topic: Physiology & Rehabilitation

During the 'screw-home' mechanism of the knee, which muscle is uniquely responsible for 'unlocking' the knee from terminal extension to initiate flexion by internally rotating the tibia relative to the femur?

. Semimembranosus
. Biceps femoris
. Popliteus
. Plantaris
. Gastrocnemius

Correct Answer & Explanation

. Popliteus

Explanation

The popliteus muscle acts to unlock the fully extended knee joint. In an open kinetic chain, it internally rotates the tibia relative to the femur. In a closed kinetic chain, it externally rotates the femur relative to the fixed tibia. It is innervated by the tibial nerve.

Question 4324

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage contains the highest concentration of proteoglycans, the lowest water content, and chondrocytes that are arranged in columnar networks perpendicular to the joint surface?

. Superficial zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans, lowest water content, and chondrocytes arranged in vertical columns perpendicular to the joint surface. The collagen fibers are also oriented perpendicular to the articular surface to resist compressive forces.

Question 4325

Topic: 1. General Principles & Basic Science

Lubricin (PRG4) is a highly glycosylated protein that provides boundary lubrication in synovial joints. Which zone of articular cartilage is primarily responsible for the synthesis of lubricin?

. Superficial zone
. Transitional zone
. Deep zone
. Calcified zone
. Synovial intima

Correct Answer & Explanation

. Superficial zone

Explanation

Lubricin (PRG4) is synthesized primarily by the chondrocytes in the superficial zone of articular cartilage (as well as by synovial fibroblasts in the synovium). It plays a crucial role in boundary lubrication, reducing friction at the articular surface.

Question 4326

Topic: Biology, Genetics & Bone Healing

A 55-year-old male presents with chronic sacral pain and mild bowel/bladder dysfunction. Imaging reveals a large, midline, destructive lytic lesion in the sacrum. Biopsy demonstrates physaliferous cells with large cytoplasmic vacuoles. Which of the following is the most appropriate definitive management?

. Intralesional curettage and bone grafting
. Radiation therapy followed by chemotherapy
. En bloc wide surgical resection
. Radiofrequency ablation
. Denosumab therapy

Correct Answer & Explanation

. En bloc wide surgical resection

Explanation

The clinical picture and histologic finding of physaliferous cells confirm a chordoma. Chordomas are locally aggressive and largely resistant to conventional chemotherapy and radiation. The standard of care for definitive management is en bloc wide surgical excision with negative margins to prevent recurrence.

Question 4327

Topic: 1. General Principles & Basic Science

A 45-year-old active male presents with medial compartment osteoarthritis and varus malalignment. He is planned for a medial opening-wedge high tibial osteotomy (HTO). To maintain the native posterior tibial slope during the procedure, how should the anterior osteotomy gap compare to the posterior gap?

. The anterior gap should be equal to the posterior gap
. The anterior gap should be roughly half the size of the posterior gap
. The anterior gap should be roughly twice the size of the posterior gap
. The posterior gap should be completely closed
. The anterior gap should be three times the posterior gap

Correct Answer & Explanation

. The anterior gap should be roughly half the size of the posterior gap

Explanation

In an opening-wedge HTO, the triangular cross-sectional shape of the proximal tibia dictates that to maintain the normal posterior slope, the anterior opening gap must be approximately half the size of the posterior gap. Opening the anterior and posterior gaps equally will inadvertently increase the posterior tibial slope.

Question 4328

Topic: 1. General Principles & Basic Science

Duplication of the tidemark is a hallmark histological finding in early osteoarthritis. In normal articular cartilage microanatomy, the tidemark separates the deep (uncalcified) zone from which of the following layers?

. Calcified cartilage zone
. Superficial tangential zone
. Subchondral bone plate
. Middle transitional zone
. Synovial lining

Correct Answer & Explanation

. Calcified cartilage zone

Explanation

The tidemark is a distinct histological line that separates the deep zone of uncalcified articular cartilage from the calcified cartilage zone. Its duplication signifies the advancement of calcification into the uncalcified cartilage, typical of osteoarthritis.

Question 4329

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which structural molecule is primarily responsible for generating the internal swelling pressure that resists compressive loads via the Donnan osmotic effect?

. Type II collagen
. Hyaluronic acid backbone
. Aggrecan
. Type IX collagen
. Decorin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan, a large proteoglycan, contains numerous glycosaminoglycans (chondroitin and keratan sulfate) with highly negative charge densities. This attracts cations and water, creating a swelling pressure that allows cartilage to resist compression.

Question 4330

Topic: 1. General Principles & Basic Science

Under conditions of high loading and low speed in a synovial joint, boundary lubrication is the dominant mechanism protecting the cartilage surfaces. Which specific glycoprotein is primarily responsible for boundary lubrication?

. Hyaluronic acid
. Lubricin (PRG4)
. Type II collagen
. Aggrecan
. Chondroitin sulfate

Correct Answer & Explanation

. Lubricin (PRG4)

Explanation

Lubricin (proteoglycan 4 or PRG4) is synthesized by superficial zone chondrocytes and synoviocytes. It is the primary molecule responsible for boundary lubrication, which reduces friction under high-load and low-speed conditions.

Question 4331

Topic: 1. General Principles & Basic Science

A 55-year-old female experiences a sudden "pop" in the back of her knee while squatting. MRI reveals a complete radial tear adjacent to the posterior root attachment of the medial meniscus. Biomechanically, this injury is most equivalent to which of the following?

. Loss of 25% of the total meniscal volume
. An intact meniscus under normal physiologic load
. Total medial meniscectomy
. A peripheral longitudinal tear in the red-red zone
. A stable flap tear of the anterior horn

Correct Answer & Explanation

. Total medial meniscectomy

Explanation

A posterior root tear completely disrupts the circumferential hoop stresses of the meniscus. Biomechanical studies have shown that this renders the meniscus entirely non-functional, resulting in contact pressures equivalent to a total meniscectomy.

Question 4332

Topic: Biology, Genetics & Bone Healing
The pathogenesis of osteoarthritis is heavily mediated by an imbalance between anabolic and catabolic factors in the joint environment. Which of the following cytokine pairs are considered the primary catabolic drivers of cartilage degradation?
. IL-4 and IL-10
. TGF-beta and IGF-1
. IL-1beta and TNF-alpha
. BMP-2 and BMP-7
. PDGF and VEGF

Correct Answer & Explanation

. IL-1beta and TNF-alpha

Explanation

Interleukin-1 beta (IL-1β) and Tumor Necrosis Factor-alpha (TNF-α) are the principal pro-inflammatory, catabolic cytokines in osteoarthritis. They upregulate matrix metalloproteinases (MMPs) and aggressively promote the breakdown of the extracellular matrix.

Question 4333

Topic: 1. General Principles & Basic Science

The superficial zone of articular cartilage is uniquely adapted to resist shear stress. Which of the following best describes the histologic and biochemical composition characteristic of this specific zone?

. Highest proteoglycan content with random collagen orientation
. Collagen fibers oriented parallel to the articular surface with the highest water content
. Chondrocytes arranged in columns with thick collagen fibrils
. Primary resistance to compressive forces via high glycosaminoglycan concentration
. Presence of the tidemark dividing it from the underlying calcified cartilage

Correct Answer & Explanation

. Collagen fibers oriented parallel to the articular surface with the highest water content

Explanation

The superficial zone contains collagen fibers parallel to the joint surface, providing significant shear resistance. It also has the highest water content and the lowest proteoglycan concentration of all cartilage zones.

Question 4334

Topic: 1. General Principles & Basic Science

A 55-year-old female sustains a complete radial tear of the medial meniscus posterior root. Biomechanically, the loss of hoop stress in this specific injury creates tibiofemoral contact pressures equivalent to which of the following?

. A 25% partial meniscectomy
. A 50% partial meniscectomy
. A total meniscectomy
. Loss of the anterior horn only
. Disruption of the meniscofemoral ligaments

Correct Answer & Explanation

. A total meniscectomy

Explanation

Complete posterior root tears of the medial meniscus disrupt circumferential hoop stresses, rendering the meniscus completely biomechanically incompetent. This results in elevated peak contact pressures and decreased contact areas equivalent to a total meniscectomy.

Question 4335

Topic: Biology, Genetics & Bone Healing

The compressive resilience of articular cartilage is primarily provided by aggrecan. Aggrecan monomers achieve this massive structural and biomechanical property through non-covalent binding with which of the following substances?

. Collagen type II
. Hyaluronic acid
. Fibronectin
. Decorin
. Chondroitin sulfate

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Aggrecan monomers use link proteins to non-covalently bind to long hyaluronic acid backbones, forming massive proteoglycan aggregates. The highly negatively charged glycosaminoglycan side chains of these aggregates attract water, providing compressive stiffness via swelling pressure.

Question 4336

Topic: 1. General Principles & Basic Science

Boundary lubrication is essential for minimizing friction at the immediate surface of articulating joint cartilage. Which specific molecule is primarily responsible for this boundary lubrication mechanism?

. Aggrecan
. Hyaluronic acid
. Lubricin (PRG4)
. Type II collagen
. Decorin

Correct Answer & Explanation

. Lubricin (PRG4)

Explanation

Lubricin (Proteoglycan 4 or PRG4) is a highly glycosylated protein secreted by superficial zone chondrocytes and synoviocytes. It specifically coats the articular surface to provide boundary lubrication, drastically reducing friction between opposing cartilage layers under load.

Question 4337

Topic: 1. General Principles & Basic Science

A 45-year-old male with end-stage renal disease suffers a spontaneous patellar tendon rupture. During surgical repair, the surgeon decides to augment the repair with heavy non-absorbable suture passed through the tibial tubercle and the patella. What is the primary purpose of this augmentation?

. To promote robust neovascularization of the avascular tendon substance
. To offload tension on the primary repair to allow early, protected range of motion
. To prevent the development of post-operative patella baja
. To directly stimulate collagen type I deposition at the rupture site
. To permanently increase the ultimate load to failure of the native tendon tissue

Correct Answer & Explanation

. To offload tension on the primary repair to allow early, protected range of motion

Explanation

Augmentation of a patellar tendon repair with heavy suture or wire protects the primary repair site by mechanically offloading tension. This facilitates early, protected range of motion, which is crucial for preventing arthrofibrosis and restoring functional kinematics.

Question 4338

Topic: 1. General Principles & Basic Science
The above surgery was performed with recombinant human bone morphogenetic protein-2 (rhBMP-2). She reports immediate relief of her leg pain and is discharged home on postoperative day 2. The patient reports new-onset radicular pain and weakness in her leg 1 year later. Figures 22a and 22b are her postoperative CT myelogram images. What is the most likely cause of her pain?
. Excessive retraction of the traversing nerve root
. Bony overgrowth from the use of BMP protein in the disk space
. Osteomyelitis with compression of the nerve roots
. Inadequate decompression after surgery

Correct Answer & Explanation

. Bony overgrowth from the use of BMP protein in the disk space

Explanation

DISCUSSION: Transient thigh pain after lateral, transpsoas interbody fusion is common and generally lasts for less than 3 months. Transpsoas interbody fusion with slip reduction can result in indirect spinal decompression and often obviates the need for a laminectomy for most patients. Complications with this approach are comparable to those experienced with open surgery, but the hospital stay is generally shorter. Use of BMP in interbody devices has also become common. The images above show heterotopic bone growth into the spinal canal causing nerve compression. This complication is more commonly encountered after posterior lumbar interbody fusions.

Question 4339

Topic: Surgical Anatomy & Approaches
What nerve is at greatest risk when developing the superficial plane between the tensor fascia lata and sartorius during the anterior (Smith-Peterson) approach to the hip?
. Lateral femoral cutaneous
. Superior gluteal
. Inferior gluteal
. Obturator
. Femoral

Correct Answer & Explanation

. Lateral femoral cutaneous

Explanation

DISCUSSION: The lateral femoral cutaneous nerve pierces the fascia between the tensor fascia lata and the sartorius approximately 2.5 cm distal to the anterosuperior iliac spine and is at risk when the interval is defined. The superior gluteal and femoral nerves define the internervous plane between the tensor fascia lata and the sartorius and are not at risk for injury.

Question 4340

Topic: Surgical Anatomy & Approaches

During an ilioinguinal or Stoppa approach for open reduction and internal fixation of an acetabular fracture, the surgeon must identify the 'corona mortis' to prevent catastrophic hemorrhage. This structure is classically defined as a vascular anastomosis between which two systems?

. External iliac (or inferior epigastric) and obturator
. Internal iliac and superior gluteal
. External pudendal and internal pudendal
. Inferior epigastric and femoral
. Obturator and internal pudendal

Correct Answer & Explanation

. External iliac (or inferior epigastric) and obturator

Explanation

The corona mortis (crown of death) is a highly variable but frequent vascular anastomosis between the external iliac system (or its branch, the inferior epigastric artery/vein) and the obturator system. It typically crosses over the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis and is at significant risk of iatrogenic injury during anterior pelvic approaches.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page