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1. General Principles & Basic Science MCQs

Practice Set 338 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 6741

Topic: 1. General Principles & Basic Science

The pes anserinus is composed of the tendons of the sartorius, gracilis, and semitendinosus muscles. Which of the following accurately lists their respective motor nerve supplies in that order?

. Femoral, obturator, tibial
. Tibial, obturator, femoral
. Sciatic, femoral, obturator
. Obturator, tibial, femoral
. Femoral, tibial, obturator

Correct Answer & Explanation

. Femoral, obturator, tibial

Explanation

The sartorius is innervated by the femoral nerve, the gracilis by the obturator nerve, and the semitendinosus by the tibial division of the sciatic nerve. These three muscles represent three distinct fascial compartments of the thigh converging on the proximal medial tibia.

Question 6742

Topic: 1. General Principles & Basic Science

Which of the following statements best describes the biomechanical and structural difference between woven bone and lamellar bone?

. Woven bone has a highly organized collagen structure making it stronger in tension.
. Lamellar bone is formed exclusively during the initial inflammatory stages of fracture healing.
. Woven bone is mechanically isotropic and weaker due to randomly oriented collagen.
. Lamellar bone has significantly higher cellularity and turns over faster than woven bone.
. Woven bone gradually remodels into hyaline cartilage over time under mechanical load.

Correct Answer & Explanation

. Woven bone has a highly organized collagen structure making it stronger in tension.

Explanation

Woven bone is immature, formed rapidly, and characterized by randomly oriented collagen fibers, making it mechanically isotropic and weak. Lamellar bone is mature, highly organized into parallel sheets, and anisotropic, providing greater mechanical strength.

Question 6743

Topic: 1. General Principles & Basic Science

In the microstructure of articular cartilage, what is the primary biomechanical function of the superficial (tangential) zone?

. Resist high compressive loads
. Anchor the cartilage firmly to the underlying subchondral bone
. Resist shearing forces and provide tensile strength
. Produce the majority of the tissue's proteoglycan content
. Facilitate endochondral ossification during skeletal growth

Correct Answer & Explanation

. Resist high compressive loads

Explanation

The superficial zone of articular cartilage contains densely packed collagen fibers oriented parallel to the articular surface. This specialized arrangement acts as a protective skin that primarily resists shear forces and provides tensile strength to the joint surface.

Question 6744

Topic: 1. General Principles & Basic Science

Low-intensity pulsed ultrasound (LIPUS) accelerates fracture healing primarily through which of the following hypothesized mechanisms at the cellular level?

. Increasing local tissue temperature to promote vasodilation and nutrient delivery.
. Direct conversion of ultrasound waves into piezoelectric currents across the fracture gap.
. Promoting acoustic streaming and micro-mechanical strain, which upregulates integrins and COX-2.
. Destroying active osteoclasts locally to shift the balance toward bone formation.
. Inhibiting the inflammatory phase to allow immediate transition to hard callus formation.

Correct Answer & Explanation

. Increasing local tissue temperature to promote vasodilation and nutrient delivery.

Explanation

LIPUS applies micro-mechanical stress to bone cells via acoustic streaming. This mechanical stimulation is transduced by cell surface integrins, upregulating COX-2 expression and prostaglandin E2 production, which accelerates callus formation and maturation.

Question 6745

Topic: Biology, Genetics & Bone Healing

A 35-year-old man undergoes open reduction and internal fixation of a transverse radial shaft fracture. A dynamic compression plate is applied to achieve absolute stability. Which of the following best describes the primary mechanism of bone healing expected in this scenario?

. Endochondral ossification
. Intramembranous ossification
. Haversian remodeling with cutting cones
. Fibrocartilage callus formation
. Osteoinduction via BMP release

Correct Answer & Explanation

. Endochondral ossification

Explanation

Under conditions of absolute stability and anatomic reduction, primary bone healing occurs without callus formation. This is driven by osteoclastic cutting cones crossing the fracture site, followed by osteoblasts laying down new lamellar bone via Haversian remodeling.

Question 6746

Topic: 1. General Principles & Basic Science

In the design of orthopedic screws for use in osteoporotic cancellous bone, maximizing pullout strength is critical. Which of the following geometric modifications to a standard screw design will most effectively increase its pullout strength?

. Decreasing the outer (major) diameter
. Increasing the inner (minor) diameter
. Decreasing the thread pitch
. Decreasing the length of thread engagement
. Increasing the core diameter

Correct Answer & Explanation

. Decreasing the outer (major) diameter

Explanation

Screw pullout strength is positively correlated with the outer (major) diameter and length of engagement, and negatively correlated with the inner (minor) diameter. Decreasing the thread pitch (resulting in more threads per inch) increases the sheer area of bone engaged, thereby increasing pullout strength.

Question 6747

Topic: 1. General Principles & Basic Science

Articular cartilage is composed of multiple distinct zones that provide specific biomechanical properties. Which of the following zones is primarily responsible for resisting shear stress during joint motion?

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

Correct Answer & Explanation

. Superficial zone

Explanation

The superficial zone of articular cartilage features densely packed collagen fibers oriented parallel to the articular surface. This specific orientation allows the superficial zone to effectively resist shear forces and provide a low-friction gliding surface.

Question 6748

Topic: Surgical Anatomy & Approaches

A surgeon utilizes the standard deltopectoral approach for a total shoulder arthroplasty. To safely access the anterior shoulder joint, the internervous plane developed relies on the innervation of the deltoid and pectoralis major muscles. Which of the following represents the correct internervous plane?

. Axillary nerve and suprascapular nerve
. Axillary nerve and medial/lateral pectoral nerves
. Musculocutaneous nerve and axillary nerve
. Spinal accessory nerve and medial pectoral nerve
. Thoracodorsal nerve and axillary nerve

Correct Answer & Explanation

. Axillary nerve and suprascapular nerve

Explanation

The deltopectoral approach exploits the internervous plane between the deltoid (innervated by the axillary nerve) and the pectoralis major (innervated by the medial and lateral pectoral nerves). This allows safe access to the anterior shoulder without denervating either muscle.

Question 6749

Topic: Biomechanics & Biomaterials

The stiffness of an orthopedic implant is determined by its material properties, specifically the Young modulus. Among the following common implant materials, which possesses a Young modulus most similar to that of cortical bone?

. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Polymethylmethacrylate (PMMA)
. Ultra-high-molecular-weight polyethylene (UHMWPE)

Correct Answer & Explanation

. Cobalt-chromium alloy

Explanation

Cortical bone has a Young modulus of approximately 15-20 GPa. Titanium alloy (~110 GPa) is closer to cortical bone than stainless steel (~200 GPa) or cobalt-chromium (~220 GPa), resulting in less stress shielding when implanted.

Question 6750

Topic: Biomechanics & Biomaterials

A viscoelastic material, such as a ligament, exhibits time-dependent mechanical behavior. If a constant static tensile load is continuously applied to a ligament over time, the gradual increase in its length is referred to as:

. Stress relaxation
. Hysteresis
. Creep
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation (increase in length) of a viscoelastic material when subjected to a constant load over time. Conversely, stress relaxation is the decrease in stress over time when the material is held at a constant length.

Question 6751

Topic: Biomechanics & Biomaterials

When selecting an orthopedic implant to minimize stress shielding of the underlying bone, which of the following materials is most appropriate due to its modulus of elasticity being closest to that of human cortical bone?

. Stainless steel
. Titanium alloy
. Cobalt-chromium alloy
. Polymethylmethacrylate (PMMA)
. Ultra-high-molecular-weight polyethylene (UHMWPE)

Correct Answer & Explanation

. Stainless steel

Explanation

Titanium alloy has a modulus of elasticity (approx 100 GPa) that is much closer to cortical bone (15-20 GPa) than stainless steel (200 GPa) or cobalt-chrome (220 GPa). This closer match reduces the phenomenon of stress shielding, potentially minimizing bone resorption around the implant.

Question 6752

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis using the Ilizarov technique, if mechanical stability is maintained and the distraction rate is optimal (1 mm/day), new bone formation in the distraction gap predominantly occurs via which process?

. Endochondral ossification
. Intramembranous ossification
. Creeping substitution
. Chondrogenesis
. Appositional growth

Correct Answer & Explanation

. Endochondral ossification

Explanation

Distraction osteogenesis primarily occurs via intramembranous ossification under mechanically stable conditions with adequate blood supply. Mesenchymal cells differentiate directly into osteoblasts to form bone without an intermediate cartilaginous phase.

Question 6753

Topic: Surgical Anatomy & Approaches

The anterior (Smith-Petersen) surgical approach to the hip is favored in certain procedures because it utilizes a true internervous plane. This plane is located between muscles innervated by which of the following nerve pairs?

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

Correct Answer & Explanation

. Femoral nerve and obturator nerve

Explanation

The anterior approach utilizes the internervous plane between the tensor fasciae latae (innervated by the superior gluteal nerve) and the sartorius (innervated by the femoral nerve). This preserves the motor supply to both muscles.

Question 6754

Topic: 1. General Principles & Basic Science

A surgeon decides to upsize a solid intramedullary tibial nail from 8 mm to 10 mm in diameter. Based on biomechanical principles, changing the radius by a factor of 1.25 will increase the nail's bending stiffness by a factor of approximately:

. 1.25
. 1.56
. 1.95
. 2.44
. 3.12

Correct Answer & Explanation

. 1.25

Explanation

The bending stiffness of a solid cylinder is proportional to the area moment of inertia, which relates to the radius to the 4th power (r^4). Thus, increasing the radius by a factor of 1.25 increases stiffness by 1.25^4, which is approximately 2.44.

Question 6755

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMP-2 and BMP-7) are frequently used in complex fusions and nonunion surgery. They promote bone healing primarily through which of the following mechanisms?

. Chemotaxis of circulating macrophages
. Osteoconduction along a structural scaffold
. Osteoinduction via differentiation of mesenchymal stem cells
. Inhibition of osteoclast-mediated bone resorption
. Promotion of initial angiogenesis independently of osteoblasts

Correct Answer & Explanation

. Chemotaxis of circulating macrophages

Explanation

BMPs are members of the TGF-beta superfamily and act as potent osteoinductive agents. They bind to cell surface receptors to stimulate the differentiation of multipotent mesenchymal stem cells into bone-forming osteoblasts.

Question 6756

Topic: Biomechanics & Biomaterials

Which of the following viscoelastic properties describes the progressive deformation of a ligament or tendon when it is subjected to a constant tensile load over an extended period of time?

. Stress relaxation
. Hysteresis
. Creep
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive, time-dependent deformation of a viscoelastic material under a constant load. In contrast, stress relaxation is the decrease in stress within a material when held at a constant length.

Question 6757

Topic: 1. General Principles & Basic Science

When utilizing a massive cortical bone allograft for structural support after tumor resection, which of the following best describes its incorporation characteristics compared to a cancellous bone autograft?

. Slower rate of revascularization and incomplete central remodeling
. Faster rate of osteoconduction due to preserved haversian systems
. Greater initial osteogenic potential from retained vital cells
. Complete replacement by host bone within 6 months
. Incorporation primarily via endochondral ossification

Correct Answer & Explanation

. Slower rate of revascularization and incomplete central remodeling

Explanation

Cortical allografts incorporate very slowly via creeping substitution and osteoconduction. Their core often remains necrotic and unremodeled for years, in contrast to the rapid revascularization and complete remodeling seen in cancellous autografts.

Question 6758

Topic: 1. General Principles & Basic Science

To maximize the pullout strength of a cortical screw placed into the diaphyseal shaft, which of the following alterations in screw design or application is most effective?

. Increasing the inner (core) diameter of the screw
. Increasing the outer thread diameter of the screw
. Increasing the thread pitch (fewer threads per unit length)
. Decreasing the depth of insertion
. Utilizing an oversized drill bit for the pilot hole

Correct Answer & Explanation

. Increasing the inner (core) diameter of the screw

Explanation

Screw pullout strength is directly proportional to the outer thread diameter, the length of thread engagement in the bone, and the bone's shear strength. Increasing the core diameter or the pitch typically decreases the volume of bone caught between threads.

Question 6759

Topic: Biology, Genetics & Bone Healing

Primary (strain-free) bone healing across a fracture requires highly specific mechanical conditions. Which of the following is absolutely required for primary bone healing to occur?

. Intramedullary nailing to permit micromotion
. Endochondral ossification with a cartilage intermediate
. Absolute stability with an interfragmentary gap less than 0.1 mm
. Controlled interfragmentary micromotion up to 2 mm
. Robust periosteal callus formation

Correct Answer & Explanation

. Intramedullary nailing to permit micromotion

Explanation

Primary bone healing occurs via cutting cones and Haversian remodeling without intermediate callus formation. It strictly requires absolute mechanical stability and near-anatomic reduction (gaps < 0.1 mm).

Question 6760

Topic: Physiology & Rehabilitation

Biomechanical analysis of normal human gait reveals significant joint reaction forces. During the single-limb stance phase, the hip joint reaction force is approximately what multiple of total body weight?

. 1 time body weight
. 2.5 to 3 times body weight
. 5 to 6 times body weight
. 8 to 10 times body weight
. 0.5 times body weight

Correct Answer & Explanation

. 1 time body weight

Explanation

During the single-limb stance phase of normal gait, the hip joint reaction force reaches approximately 2.5 to 3 times body weight. This force is a vector sum of the body weight and the large counteracting force generated by the abductor musculature.

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