Orthopedic Basic Review | Dr Hutaif Basic Science Revie -...

To minimize stress shielding after total hip arthroplasty, a femoral stem material with a Young's modulus closest to that of cortical bone is desired. Which of the following orthopedic materials possesses the lowest Young's modulus?

Osteoclast differentiation and activation are directly stimulated by the binding of RANK ligand (RANKL) to RANK. Which of the following cell types is the primary source of RANKL in the bone microenvironment?

In normal articular cartilage, the highest concentration of proteoglycans and the lowest concentration of water are found in which of the following zones?

Which of the following bone morphogenetic proteins (BMPs) is NOT osteoinductive in humans and instead acts as an inhibitor of bone formation?

A ligament graft is tensioned and secured during an anterior cruciate ligament (ACL) reconstruction. Over time, the tension in the graft decreases despite the graft remaining at a constant length. This biomechanical phenomenon is known as:

According to Perren's strain theory, what is the maximum tissue strain that allows for the formation of lamellar bone during fracture healing?

Sclerostin is a key negative regulator of bone formation that is primarily secreted by osteocytes. Which signaling pathway does sclerostin directly inhibit?

Which of the following characteristics best describes Type I skeletal muscle fibers?

In aseptic loosening of a total hip arthroplasty, osteolysis is primarily driven by the biological response to particulate wear debris. Which of the following cell types is the primary effector that phagocytoses the polyethylene debris and initiates the inflammatory cascade?

During collagen synthesis, the hydroxylation of proline and lysine residues is a critical intracellular step that provides structural stability to the collagen triple helix. Which of the following is required as an essential cofactor for this process?

The large aggregating proteoglycan found predominantly in articular cartilage is aggrecan. Which of the following glycosaminoglycans (GAGs) are the primary components of aggrecan?

Polymethylmethacrylate (PMMA) bone cement is often loaded with antibiotics for the treatment or prophylaxis of infection. To be effective and not compromise the cement's mechanical properties, the ideal antibiotic should possess which of the following characteristics?

Osteogenesis imperfecta (OI) type I is the most common form of the disease. It is primarily characterized by which of the following genetic defects?

A 45-year-old male presents with an acute, swollen, and painful knee. Synovial fluid analysis reveals a white blood cell count of 65,000 cells/mm³ with 90% polymorphonuclear leukocytes. Under polarized light microscopy, negatively birefringent needle-shaped crystals are observed. What is the composition of these crystals?

Galvanic corrosion is a concern when mixing different metals in orthopedic implants. If a stainless steel screw is placed through a titanium alloy plate, which metal acts as the anode and is subject to accelerated corrosion?

Which of the following cells is considered the primary mechanosensor in bone, responsible for translating mechanical strain into biochemical signals to regulate bone remodeling?

Creeping substitution is the process by which cortical bone grafts are incorporated. What is the correct sequence of events in creeping substitution of a cortical bone graft?

According to the Sunderland classification of nerve injuries, a third-degree nerve injury involves disruption of which of the following structures?

Rivaroxaban is an oral anticoagulant frequently used for DVT prophylaxis following total joint arthroplasty. What is its mechanism of action?

Highly cross-linked polyethylene (HXLPE) was developed to reduce wear rates in total hip arthroplasty. What is the primary trade-off or mechanical disadvantage of increasing the cross-linking of ultra-high molecular weight polyethylene (UHMWPE)?

According to Perren's strain theory, fracture healing pathways are dictated by the mechanical strain environment at the fracture gap. What is the maximum interfragmentary strain tolerance of normal lamellar bone before mechanical failure occurs?

In total joint arthroplasty, particulate debris can lead to osteolysis and implant loosening. Wear that occurs between two primary bearing surfaces intended for motion (e.g., the femoral head and the polyethylene liner) is classified as which of the following?

During an anterior cruciate ligament reconstruction, the graft is tensioned to a specific length and fixed. Over the next several hours, the tension required to maintain this constant length gradually decreases. This viscoelastic property is best described by which of the following terms?

Osteoclasts utilize a highly specialized mechanism to dissolve inorganic hydroxyapatite and degrade the organic bone matrix. Which of the following enzymes is primarily secreted by osteoclasts into the sealed zone to degrade type I collagen in an acidic environment?

A 10-year-old child presents with diffuse joint pain, bleeding gums, and petechiae. Radiographs show a prominent white line of Frankel at the metaphyses. The underlying defect is a failure of which step in collagen synthesis?

The synovial membrane plays a critical role in joint homeostasis and nutrition. Which of the following cell types in the synovial lining is primarily responsible for the production of hyaluronic acid?

Titanium alloys (e.g., Ti-6Al-4V) are widely used in orthopedics due to their excellent biocompatibility and modulus of elasticity that is closer to cortical bone than stainless steel. Which of the following is a primary biomechanical disadvantage of using titanium alloys for internal fixation plates?

The process of highly cross-linking ultra-high-molecular-weight polyethylene (UHMWPE) using gamma or electron beam irradiation significantly alters its material properties. Which of the following best describes the effect of increasing the cross-linking in UHMWPE?

During the surgical planning for a diaphyseal femur fracture, the surgeon selects a solid intramedullary nail. The torsional stiffness of a solid intramedullary nail is proportional to its radius raised to what power?

Normal articular cartilage utilizes multiple lubrication mechanisms depending on the load and joint velocity. Under high-load, low-velocity conditions, which of the following molecules acts as the primary agent responsible for boundary lubrication?

A marathon runner sustains a minor muscle tear in the gastrocnemius. The primary skeletal muscle fibers utilized by this athlete during endurance running are characterized by which of the following physiological profiles?

In pediatric orthopedics, guided growth procedures for angular deformities exploit a fundamental physiological principle regarding the physis. The principle that increasing mechanical compression across a growth plate slows longitudinal growth, whereas increasing tension accelerates it, is known as:

Which of the following pharmacological agents used in the treatment of severe osteoporosis acts primarily as an anabolic agent through the direct inhibition of the Wnt signaling antagonist, sclerostin?

Primary (direct) bone healing circumvents the formation of a provisional cartilaginous callus.

Which of the following mechanical conditions is an absolute requirement for contact healing to occur across a fracture site?

During plate fixation of a fracture, a surgeon must maximize the pullout strength of the cortical screws placed into osteoporotic bone. The pullout strength of a bone screw is most significantly increased by an increase in which of the following screw parameters?

At a direct ligament or tendon insertion site (enthesis) into bone, the tissue transitions through four distinct histological zones. The transition from unmineralized fibrocartilage to mineralized fibrocartilage is demarcated by which of the following structures?

Galvanic corrosion can occur when two dissimilar metals are placed in physical contact within the electrolytic environment of the human body. If a 316L stainless steel screw is placed into a Ti-6Al-4V titanium plate, which of the following reactions is most likely to occur?

A surgeon applies a locking compression plate (LCP) to bridge a comminuted diaphyseal fracture. Which of the following biomechanical principles best describes how a purely locked plate construct achieves stability?

Bone morphogenetic proteins (BMPs) are potent osteoinductive factors utilized in orthopedic surgery to stimulate bone formation. The intracellular signaling cascade triggered by BMP binding to its cell-surface serine/threonine kinase receptor is primarily mediated by which of the following molecules?

Osteoinductive bone grafts such as demineralized bone matrix (DBM) rely on Bone Morphogenetic Proteins (BMPs) to stimulate bone formation. BMP-2 initiates intracellular signaling by directly binding to which of the following types of receptors on osteoprogenitor cells?

A surgeon is repairing a highly comminuted midshaft humerus fracture in an osteoporotic patient and wishes to maximize the pullout strength of the cortical screws. Which of the following screw modifications will most significantly increase screw pullout strength in this osteoporotic bone?

Highly cross-linked polyethylene (HXLPE) is manufactured to decrease wear rates in total hip arthroplasty components. While the irradiation process successfully increases wear resistance, which of the following material properties is most significantly DECREASED as a direct result?

Articular cartilage relies on specific mechanisms for lubrication depending on the applied load and sliding speed. Under high-load, low-speed conditions, boundary lubrication is primarily mediated by which of the following molecules synthesized by superficial zone chondrocytes?

According to Perren's strain theory, the mechanical environment at a fracture site dictates the mode of biological healing. What is the maximum interfragmentary strain threshold that allows for primary bone healing (direct lamellar bone formation) without an intermediate fibrocartilage callus?

A patient sustains a closed midshaft humerus fracture and immediately develops a complete radial nerve palsy. The surgeon elects for nonoperative management and orders an electromyogram (EMG). At what minimum time point after the injury will fibrillation potentials characteristic of axonal denervation first be reliably detected?

A 25-year-old male presents with a deep, slow-growing soft tissue mass in the posterior thigh. Core needle biopsy reveals a biphasic tumor consisting of both epithelial and spindle cell components. Which of the following chromosomal translocations is highly specific and diagnostic for this malignancy?

Continuous systemic administration of parathyroid hormone (PTH) leads to net bone resorption, a process requiring osteoclast activation. However, osteoclasts lack receptors for PTH. The catabolic effect of PTH is mediated primarily through its direct binding to receptors on which of the following cell types?

During the remodeling phase of tendon healing, the biomechanical strength of the tendon gradually increases as the provisional matrix is replaced with a more organized, definitive matrix. Which of the following represents the correct sequence of collagen transition during this process?

A surgeon plans to use a titanium locking plate with 316L stainless steel screws to fix a complex periarticular fracture. This combination is generally avoided due to the risk of galvanic corrosion. In this mixed-metal construct, which of the following accurately describes the electrochemical reaction?

Following a total knee arthroplasty, a patient is prescribed oral rivaroxaban for venous thromboembolism (VTE) prophylaxis. This medication exerts its anticoagulant effect by directly and reversibly inhibiting which of the following factors in the coagulation cascade?

Understanding joint reaction forces is critical for orthopedic implant design. During a normal gait cycle, the peak joint reaction force across the hip occurs during which phase, and is approximately what multiple of body weight?

A surgeon reams the femoral medullary canal to insert a larger diameter solid intramedullary nail. If the radius of the selected solid titanium nail is increased by a factor of 2, the theoretical torsional rigidity (polar moment of inertia) of the nail increases by a factor of:

A patient presents with a painful total knee arthroplasty, overlying eczematous dermatitis, and aseptic loosening 1 year postoperatively. Patch testing reveals a severe systemic nickel allergy. This implant complication is mediated by which of the following immunologic mechanisms?

When preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for an articulating spacer in a two-stage revision for periprosthetic joint infection, which of the following antibiotic properties is most critical for ensuring its effective local elution?

During post-operative rehabilitation following an Achilles tendon repair, the physical therapist applies different types of muscle contractions to safely load the musculotendinous unit. Which of the following types of muscle contraction physiologically generates the highest maximal force?

A 16-year-old boy presents with severe localized knee pain and a destructive, sunburst-pattern bone lesion in the distal femoral metaphysis. Biopsy reveals highly pleomorphic spindle cells. The definitive histologic criterion for diagnosing this lesion as conventional osteosarcoma rather than a high-grade undifferentiated pleomorphic sarcoma is the presence of:

A 4-year-old child presents with frequent extremity fractures from minimal trauma, clinically visible blue sclerae, and dentinogenesis imperfecta. Radiographs reveal generalized osteopenia and multiple healed long bone fractures. This condition is most commonly caused by a genetic mutation affecting the synthesis of which structural protein?

During an interscalene nerve block for a rotator cuff repair, the patient inadvertently receives an intravascular injection of bupivacaine and subsequently develops seizures and ventricular arrhythmias. The toxic mechanism of this drug is primarily due to the blockade of which of the following cellular ion channels?

During in vitro tensile testing of an intact anterior cruciate ligament (ACL), the initial portion of the stress-strain curve is non-linear and exhibits high compliance, a region known as the "toe region". This biomechanical behavior is primarily due to which of the following microstructural phenomena?

Sclerostin regulates bone mass by inhibiting osteoblastogenesis and bone formation. This molecule exerts its primary effect by blocking which of the following intracellular signaling pathways?

According to the principles of orthopedic screw biomechanics, which of the following variables has the most significant mathematical influence on the pull-out strength of a cortical screw?

A surgeon plans to use a 316L stainless steel plate for a femur fracture but only has titanium screws available. Which type of corrosion is most likely to occur at the screw-plate interface?

Boundary lubrication is crucial for minimizing friction in articular cartilage, particularly under conditions of low loads and low speeds. Which of the following molecules is primarily responsible for boundary lubrication at the articular surface?

In Paget disease of bone, the primary cellular abnormality is excessive osteoclastic resorption followed by disorganized osteoblastic bone formation. This hyperactive osteoclast state is most frequently associated with a mutation in which of the following?

A skeletal traction pin is placed in the proximal tibia, and a constant 15-pound weight is applied over several days. The progressive, time-dependent increase in deformation of the bone and soft tissues under this constant load is defined as:

In a randomized controlled trial comparing two fracture fixation devices, the authors report no statistically significant difference in nonunion rates (p = 0.15). However, a true difference in efficacy exists between the devices in the general population. This study result is an example of:

Demineralized bone matrix (DBM) is frequently used in orthopedic surgery to augment fracture healing. Which of the following best describes the primary biological mechanism by which DBM promotes bone formation?

Skeletal muscle fibers are broadly classified into slow-twitch (Type I) and fast-twitch (Type II) fibers based on their metabolic and contractile properties. Which of the following profiles best characterizes Type I muscle fibers?

Osteogenesis imperfecta (OI) type I is the most common and mildest form of the disease. It is primarily characterized by a genetic defect resulting in which of the following structural abnormalities?

During the pathogenesis of periprosthetic joint infection, bacteria form a biofilm on the implant surface. The irreversible adherence of bacteria and subsequent biofilm maturation is primarily mediated by the production of:

Following peripheral nerve transection, Wallerian degeneration occurs distal to the injury site. Which cell type is predominantly responsible for phagocytosing and clearing myelin debris during the first 1 to 2 weeks of this process?

A 4-year-old boy presents with severe bilateral genu varum. Laboratory evaluation reveals low serum phosphate, normal serum calcium, and elevated alkaline phosphatase. Parathyroid hormone (PTH) levels are normal. Which of the following is the most likely diagnosis?

In total joint arthroplasty, aseptic loosening is frequently driven by a macrophage-mediated biological response to ultra-high-molecular-weight polyethylene (UHMWPE) wear debris. Which particle size is most biologically active in inducing this osteolytic response?

During the single-leg stance phase of the normal gait cycle, the hip abductor muscles must generate significant force to maintain a level pelvis. This abductor force is approximately equivalent to:

In articular cartilage, proteoglycans are vital for providing compressive stiffness. Aggrecan monomers attach to a central backbone to form massive proteoglycan aggregates. Which molecule forms this central backbone?

According to Perren's strain theory, the mechanical environment dictates the type of bone healing. Absolute stability, requiring interfragmentary strain to be less than 2%, exclusively permits which type of healing?

A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total knee arthroplasty. This medication exerts its anticoagulant effect primarily by directly inhibiting:

Titanium alloys (e.g., Ti-6Al-4V) are frequently used in orthopedics due to their excellent biocompatibility and favorable modulus of elasticity. Which of the following is a primary mechanical disadvantage of titanium alloys compared to stainless steel or cobalt-chromium?

During the post-operative rehabilitation of an acutely lacerated and repaired zone II flexor tendon, the tensile strength of the repair generally reaches its weakest point at what time frame?

Achondroplasia is the most common form of short-limbed dwarfism. The underlying genetic mutation involves a gain-of-function in the fibroblast growth factor receptor 3 (FGFR3). Which specific zone of the physis is primarily inhibited by this mutation?

A researcher is evaluating the mechanical properties of a newly designed intramedullary nail.

Which parameter on the stress-strain curve represents the material's stiffness (Young's modulus)?

Tranexamic acid (TXA) is frequently used in orthopedic surgery to reduce perioperative blood loss. Which of the following describes the primary mechanism of action of TXA?

Nitrogen-containing bisphosphonates, such as alendronate, are widely used to treat osteoporosis and prevent skeletal-related events in metastatic bone disease. What is their primary molecular mechanism of action?

An orthopedic resident applies a dynamic flexion splint to a patient with knee stiffness. Over time, the force required to maintain the knee at a constant angle of deformation gradually decreases. This viscoelastic phenomenon is known as:

A surgeon uses a 316L stainless steel screw to secure a Ti-6Al-4V titanium alloy plate. Several months later, rapid localized corrosion is noted at the screw-plate interface. Which type of corrosion is most directly caused by using these two dissimilar metals?

In the pathogenesis of osteoarthritis, the degradation of the articular cartilage extracellular matrix is driven by specific enzymes. Which of the following matrix metalloproteinases (MMPs) is primarily responsible for the cleavage of type II collagen?

Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is routinely used in total hip arthroplasty. Compared to conventional UHMWPE, the highly cross-linked variant provides which of the following biomechanical trade-offs?

A 12-year-old girl presents with a "shepherd's crook" deformity of the proximal femur.

Radiographs show a classic ground-glass appearance. The underlying condition is driven by a genetic mutation that results in the constitutive activation of which of the following?

Following a peripheral nerve transection, Wallerian degeneration occurs distal to the injury site. Which cell type is primarily responsible for orchestrating the clearance of myelin debris to allow for subsequent nerve regeneration?

During a prolonged endurance event, such as a marathon, an athlete relies heavily on specific skeletal muscle fibers. Which of the following accurately describes the primary muscle fiber type recruited and its dominant metabolic pathway?

Bone morphogenetic protein-2 (BMP-2) is utilized clinically to enhance spinal fusion and fracture healing. Upon binding to its cell surface receptor, which of the following intracellular molecules translocates to the nucleus to regulate target gene transcription?

A patient undergoes surgical repair of an acute Achilles tendon rupture.

During the early proliferative phase of tendon healing, the newly synthesized extracellular matrix is predominantly composed of which type of collagen?

A 6-year-old child presents with gingival bleeding, petechiae, and metaphyseal radiolucencies on radiographs. The child is diagnosed with scurvy due to severe Vitamin C deficiency. The defective biochemical process in collagen synthesis primarily occurs in which cellular compartment?

An orthopedic surgeon is selecting a bone graft substitute for filling a metaphyseal defect. Which of the following synthetic graft materials possesses the highest compressive strength but has the slowest rate of in vivo resorption?

A patient presents with a painful total hip arthroplasty 5 years post-operation. Aspiration yields sterile, thick, metal-stained fluid. The biological process occurring at the modular head-neck taper (trunnionosis) is primarily driven by a combination of which two forms of corrosion?

Osteocytes act as mechanosensors in bone, coordinating remodeling responses to mechanical loads.

Which type of cell junction allows for the direct intercellular exchange of signaling molecules, such as calcium and prostaglandins, between the dendritic processes of adjacent osteocytes?

An orthopedic manufacturer creates two solid circular intramedullary nails. If the radius of the second nail is increased by 10% compared to the first, approximately how much does its bending rigidity increase?

Osteogenesis imperfecta is a genetic disorder of connective tissue characterized by bone fragility and recurrent fractures. The majority of cases involve a mutation in the COL1A1 or COL1A2 genes. This mutation most commonly results in the substitution of which critical amino acid in the collagen triple helix?

Secondary fracture healing relies on the formation of a soft and hard callus. Which specific local mechanical and physiological environment most strongly favors endochondral ossification (cartilage intermediate) over intramembranous ossification during this process?