Which of the following is a recognized predictor of mortality after hip fracture?

American Society of Anesthesiologist (ASA) classification

A healthy 2-year-old boy falls from a swing and sustains a displaced midshaft femoral fracture with 1 cm of shortening. What is the most appropriate treatment?

Closed reduction and spica casting

03 A 28-year-old man underwent surgical fixation for an intra-articular distal humeral fracture 8 weeks ago now reports progressively restricted elbow motion. Radiographs at the time of union are shown in Figures 13a and 13b. Management should now co

Immediate elbow release and ectopic bone excision.back answerQuestion 59.03

In a fracture such as the one shown in Figure 16 (Salter-Harris type I fracture of the distal femur), which of the following best describes the location of the fracture?

The fracture generally propagates through multiple layers of the physis.

A 2-year-old child is being evaluated for limb-length and girth discrepancy. As a newborn, the patient was large for gestational age and had hypoglycemia. Current examination shows enlargement of the entire right side of the body, including the right

renal and abdominal ultrasonography.

A 12-year-old girl has back pain after falling 20 feet and landing in the sitting position. She has no fractures or other injuries, and her neurologic examination is normal. A lateral radiograph, transverse CT scan, and reformatted sagittal CT scan a

Posterior fusion with instrumentation, with sagittal plane correction

Dr. Hutaif General Orthopedics Review: Practice MCQs

Question 1

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Following the binding of BMP-2 to its cell surface receptor, which of the following intracellular signaling molecules is directly phosphorylated to propagate the osteogenic signal to the nucleus?

Explanation

BMPs act through serine/threonine kinase cell surface receptors. Upon binding, the receptor phosphorylates receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These then form a complex with the common-mediator Smad (Smad 4) and translocate to the nucleus to regulate target gene transcription. Beta-catenin is primarily involved in the Wnt signaling pathway, while JAK/STAT is utilized by cytokine receptors.

Question 2

A 24-year-old male presents with a slow-growing, deep-seated soft tissue mass in his thigh. Core needle biopsy demonstrates a biphasic pattern of epithelial and spindle cells. Molecular analysis is most likely to reveal which of the following chromosomal translocations?

Explanation

The clinical and histologic description (biphasic epithelial and spindle cells in a young adult soft tissue mass) is classic for Synovial Sarcoma. The pathognomonic chromosomal translocation is t(X;18)(p11;q11), resulting in the SYT-SSX fusion gene. The t(11;22) mutation is seen in Ewing sarcoma, t(12;16) in myxoid liposarcoma, and t(2;13) in alveolar rhabdomyosarcoma.

Question 3

An 68-year-old man presents with progressive bowing of his tibiae and increasing head size. Radiographs demonstrate cortical thickening, trabecular coarsening, and mixed lytic-sclerotic lesions. Which of the following best describes the initial cellular event in the pathogenesis of this condition?

Explanation

Paget's disease of bone (osteitis deformans) begins with a markedly active osteoclastic (lytic) phase, characterized by massive, multinucleated osteoclasts containing viral-like inclusion bodies suspected to be paramyxovirus (such as RSV or measles). This intense resorption triggers a subsequent mixed osteoblastic/osteoclastic phase, and finally a dense but mechanically weak sclerotic phase. Monoclonal plasma cell proliferation describes Multiple Myeloma.

Question 4

In orthopedic biomaterials, Young's modulus is a measure of a material's intrinsic stiffness. Which of the following lists represents the correct sequence of materials from highest to lowest Young's modulus (greatest to least stiffness)?

Explanation

Young's modulus (elastic modulus) defines material stiffness in the linear elastic region. The correct order from stiffest to least stiff is: Ceramic (Alumina, ~380 GPa) > Cobalt-Chromium (~210 GPa) > Stainless Steel (~200 GPa) > Titanium alloy (~110 GPa) > Cortical bone (~15-20 GPa) > PMMA (~3 GPa) > Cancellous bone (0.1-2 GPa).

Question 5

A surgeon is utilizing a locked plating construct for a comminuted diaphyseal femur fracture to promote secondary bone healing. To purposefully decrease the stiffness of the construct and increase interfragmentary strain at the fracture site, which of the following technical modifications is most appropriate?

Explanation

Increasing the working length of a locked plate (the distance between the innermost screws on either side of the fracture) acts to decrease the construct stiffness. This allows for greater micromotion (interfragmentary strain) at the fracture site, which is optimal for secondary bone healing via callus formation. Placing screws closer to the fracture or using stainless steel makes the construct stiffer.

Question 6

In evaluating normal articular cartilage, the distinct zones vary significantly in composition. Which of the following best characterizes the deep (radial) zone of normal articular cartilage?

Explanation

Articular cartilage consists of four zones: superficial, middle (transitional), deep (radial), and calcified. The deep zone possesses the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers oriented perpendicular to the joint surface to effectively resist compressive forces. The superficial zone has the highest water content, lowest proteoglycan content, and parallel collagen fibers to resist shear.

Question 7

A 10-year-old boy presents with progressive lower extremity varus bowing. Laboratory testing reveals low serum calcium, low serum phosphate, markedly elevated alkaline phosphatase, and elevated parathyroid hormone (PTH) levels. Which of the following is the primary physiological mechanism leading to this specific set of laboratory abnormalities?

Explanation

These laboratory findings are diagnostic for nutritional rickets (Vitamin D deficiency). The lack of Vitamin D reduces intestinal calcium absorption, triggering hypocalcemia and secondary hyperparathyroidism (elevated PTH). The high PTH initially corrects calcium levels via bone resorption but causes severe phosphaturia, leading to hypophosphatemia. PHEX mutation (X-linked hypophosphatemia) typically presents with normal serum calcium and normal PTH levels.

Question 8

In Legg-Calve-Perthes disease, the lateral pillar classification is highly prognostic of long-term head shape outcomes. According to Herring's lateral pillar classification, a Type B hip is characterized radiographically by which of the following?

Explanation

Herring's lateral pillar classification assesses the height of the lateral portion of the capital femoral epiphysis on an AP pelvis radiograph during the fragmentation phase. Type A involves no lateral pillar involvement. Type B involves >50% maintenance of lateral pillar height. Type C involves <50% maintenance of lateral pillar height. Type B/C border cases have a specific prognostic significance.

Question 9

During a volar approach to the forearm (Henry approach), the internervous plane in the proximal third of the forearm is developed between which of the following muscles?

Explanation

The proximal Henry approach to the radius utilizes the internervous plane between the Brachioradialis (innervated by the Radial nerve) and the Pronator Teres (innervated by the Median nerve). Distally, the plane shifts to run between the Brachioradialis and the Flexor Carpi Radialis (Median nerve).

Question 10

Staphylococcus aureus is a predominant pathogen in periprosthetic joint infections. Its ability to form a robust biofilm is a key virulence factor. Which of the following molecules mediates the initial phase of biofilm formation, allowing S. aureus to adhere directly to host extracellular matrix proteins on the implant surface?

Explanation

Biofilm formation involves initial attachment, accumulation/maturation, and dispersal. The initial attachment to biomaterials is mediated by MSCRAMMs, which bind to host proteins (like fibronectin and fibrinogen) that immediately coat the implant upon insertion. Polysaccharide intercellular adhesin (PIA) is crucial for the subsequent accumulation phase. Autoinducers regulate quorum sensing during the dispersal phase.

Question 11

A 15-year-old boy complains of localized knee pain that is worse at night and dramatically relieved by ibuprofen. Radiographs show a 1.5 cm radiolucent nidus surrounded by dense reactive sclerosis in the proximal tibial diaphysis. This tumor produces pain primarily through the localized secretion of which of the following mediators?

Explanation

The clinical presentation is classic for an Osteoid Osteoma. The nidus contains osteoblasts that secrete high levels of Prostaglandin E2 (PGE2) via cyclooxygenase-2 (COX-2) overexpression. The high concentration of PGE2 causes the severe, characteristic night pain, which explains the dramatic and diagnostic relief provided by NSAIDs (which inhibit COX enzymes and PGE2 production).

Question 12

In the systemic response to major orthopedic trauma, the 'second hit' phenomenon refers to an exaggerated systemic inflammatory response following early total care surgical intervention. Which of the following cytokines is most widely recognized as the primary marker for the magnitude of this initial systemic inflammatory response?

Explanation

Interleukin-6 (IL-6) is established as the best clinical marker for the magnitude of the systemic inflammatory response syndrome (SIRS) following major trauma and surgery. IL-6 levels correlate directly with the severity of tissue injury, blood loss, risk of multi-organ failure (MOF), and overall mortality. IL-10 is primarily an anti-inflammatory cytokine that attempts to regulate this response.

Question 13

Osteolysis following total hip arthroplasty is primarily driven by a macrophage-induced foreign body reaction to particulate wear debris. Following phagocytosis of ultra-high molecular weight polyethylene (UHMWPE) particles, macrophages secrete cytokines that stimulate osteolysis via which of the following direct mechanisms?

Explanation

Polyethylene wear particles are phagocytosed by local macrophages, which subsequently release pro-inflammatory cytokines such as TNF-alpha, IL-1, and IL-6. These cytokines stimulate local osteoblasts and fibroblasts to upregulate the expression of RANKL. RANKL then binds to RANK on osteoclast precursors, leading to aggressive osteoclast differentiation and massive localized bone resorption (osteolysis).

Question 14

A 72-year-old female with severe postmenopausal osteoporosis is started on Romosozumab. This monoclonal antibody increases bone mass primarily by targeting and inhibiting which of the following proteins?

Explanation

Romosozumab is a monoclonal antibody that specifically binds to and inhibits sclerostin. Sclerostin is a glycoprotein secreted by mature osteocytes that normally inhibits the Wnt/beta-catenin signaling pathway, thereby reducing bone formation. By inhibiting sclerostin, Romosozumab exerts a unique dual effect: profoundly stimulating bone formation (osteoanabolic) while mildly decreasing bone resorption.

Question 15

Tranexamic acid (TXA) is widely used in orthopedic surgery to safely reduce perioperative blood loss. Which of the following best describes its pharmacological mechanism of action?

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It functions as an antifibrinolytic by reversibly and competitively binding to the lysine-binding sites on plasminogen. This prevents plasminogen from converting into active plasmin, thereby inhibiting the degradation of fibrin clots (fibrinolysis) and significantly reducing surgical bleeding.

Question 16

Following a closed humerus fracture, a patient develops a radial nerve palsy. Electromyography at 4 weeks shows active fibrillation potentials, and the nerve injury is determined to be a Sunderland Grade III. Which of the following neural connective tissue structures remains intact in this specific grade of injury?

Explanation

In the Sunderland classification of nerve injury: Grade I = Neuropraxia (local myelin damage, no axon disruption). Grade II = Axonotmesis (axon disrupted, endoneurium intact). Grade III = Axon and endoneurium disrupted, perineurium intact. Grade IV = Axon, endoneurium, and perineurium disrupted, epineurium intact. Grade V = Neurotmesis (complete transection, epineurium disrupted). Thus, in Grade III, the perineurium remains intact.

Question 17

A 45-year-old male is undergoing a posterolateral lumbar fusion at L4-L5. During the exposure, the surgeon identifies the mamillo-accessory ligament. Which of the following neural structures passes beneath this ligament and is at risk of iatrogenic injury during local dissection?

Explanation

The medial branch of the dorsal primary ramus provides vital innervation to the facet joints and the deep multifidus muscles. At the lumbar spine level, this nerve travels through an osseo-fibrous tunnel formed by the mamillo-accessory ligament (running between the mamillary process and the accessory process). Knowledge of this anatomy is critical for surgical exposure and radiofrequency ablation procedures.

Question 18

Galvanic corrosion is a significant concern when dissimilar metals are implanted in the same physiological environment. If a stainless steel screw is placed through a titanium plate in an orthopedic construct, which of the following best describes the resulting electrochemical process?

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolyte solution (in vivo fluids). The less noble metal (lower on the galvanic series) becomes the anode and undergoes oxidation (corrosion), while the more noble metal becomes the protected cathode. Because titanium is more noble (more cathodic) than stainless steel, the stainless steel screw acts as the anode and will corrode.

Question 19

Achondroplasia is the most common form of short-limb dwarfism. The underlying pathophysiology involves a specific genetic mutation that leads to which of the following cellular effects at the physeal growth plate?

Explanation

Achondroplasia is caused by a dominantly inherited, gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. Normally, FGFR3 signaling negatively regulates chondrocyte proliferation and hypertrophy in the growth plate. The gain-of-function mutation leads to constitutive activation of the receptor, causing profound, continuous inhibition of normal physeal growth and resulting in short-limb dwarfism.

Question 20

A 13-year-old obese boy presents with an acute-on-chronic slipped capital femoral epiphysis (SCFE). He is unable to bear weight. The biomechanical failure through the proximal femoral physis in a SCFE primarily occurs within which specific histologic zone of the growth plate?

Explanation

A Slipped Capital Femoral Epiphysis (SCFE) is characterized by a biomechanical failure (shear) primarily through the zone of hypertrophy of the physis. The hypertrophic zone in these patients is abnormally widened due to complex endocrine and mechanical factors, creating a structurally weak plane. In contrast, typical Salter-Harris fractures classically fail through the zone of provisional calcification or the junction of the hypertrophic/calcification zones.

Question 21

A 13-year-old obese male presents with right groin pain and a limp for 3 weeks. On physical examination, as his right hip is passively flexed, it falls into obligatory external rotation. He is unable to bear weight on the right leg, even with the use of crutches. Which of the following is the most accurate statement regarding his condition?

Explanation

The patient's presentation of obligatory external rotation with hip flexion is classic for Slipped Capital Femoral Epiphysis (SCFE). The inability to bear weight, even with crutches, defines an unstable SCFE according to Loder's classification. Unstable SCFE carries a significantly higher risk of avascular necrosis (AVN), historically ranging from 20% to 50%, compared to nearly 0% in stable SCFE.

Question 22

A 24-year-old male is admitted after a motorcycle collision resulting in a closed tibial shaft fracture. He complains of severe, progressively worsening pain. Which of the following pressure measurements is generally considered the threshold for performing a four-compartment fasciotomy?

Explanation

The delta pressure, defined as the diastolic blood pressure minus the absolute compartment pressure, is the most reliable indicator for acute compartment syndrome. A delta pressure of less than 30 mmHg is the widely accepted threshold that indicates the need for emergent fasciotomy. Relying solely on absolute pressure can lead to unnecessary fasciotomies or missed diagnoses in hypotensive patients.

Question 23

A 15-year-old male presents with severe knee pain and a palpable distal femoral mass. Biopsy confirms classic high-grade intramedullary osteosarcoma. Which of the following genetic mutations or conditions is most strongly associated with the development of this tumor?

Explanation

Osteosarcoma is strongly associated with mutations in tumor suppressor genes, particularly the retinoblastoma gene (RB1) and the TP53 gene. TP53 mutations are the hallmark of Li-Fraumeni syndrome, which greatly increases the risk of osteosarcoma and other malignancies. t(11;22) is associated with Ewing sarcoma, t(X;18) with synovial sarcoma, NF1 with malignant peripheral nerve sheath tumors, and GNAS with fibrous dysplasia.

Question 24

A 35-year-old manual laborer presents to the emergency department with a swollen, painful index finger 3 days after sustaining a puncture wound. Which of the following is NOT one of Kanavel's cardinal signs for acute suppurative flexor tenosynovitis?

Explanation

Kanavel's four cardinal signs of flexor tenosynovitis are: 1) fusiform (sausage-like) swelling of the digit, 2) flexed resting posture, 3) tenderness along the flexor tendon sheath, and 4) severe pain with passive extension. Pain with active flexion is not considered one of the four classic Kanavel signs, though the patient may have generalized pain with any movement.

Question 25

In total hip arthroplasty, utilizing a larger diameter femoral head (e.g., 36 mm vs. 28 mm) utilizing conventional non-highly cross-linked polyethylene has which of the following effects on wear mechanics?

Explanation

For conventional (non-highly cross-linked) polyethylene, increasing the size of the femoral head decreases the linear wear (due to increased surface area distributing the load), but it increases the volumetric wear (because the sliding distance per step is greater). This principle is described by Archard's Law. Highly cross-linked polyethylene drastically reduces wear, allowing larger heads to be used to decrease dislocation risk without significant osteolysis from volumetric wear.

Question 26

Primary (direct) bone healing, characterized by cutting cones crossing the fracture site, requires an environment with which of the following biomechanical characteristics?

Explanation

Primary (direct) bone healing relies on Haversian remodeling with cutting cones. This mechanism requires absolute stability and an extremely low strain environment (<2%). If strain is higher, primary bone healing cannot occur, and the fracture will either undergo secondary healing with callus formation (if strain is between 2-10% and relative stability is provided) or go on to nonunion (if strain >10%).

Question 27

A 45-year-old pedestrian is struck by a vehicle and sustains a pelvic ring injury. Imaging shows a 3 cm diastasis of the pubic symphysis. The anterior sacroiliac ligaments are disrupted, but the posterior sacroiliac ligaments are intact. According to the Young and Burgess classification, this injury is classified as:

Explanation

An Anteroposterior Compression (APC) type II injury involves a symphyseal diastasis > 2.5 cm with rupture of the anterior sacroiliac (SI), sacrotuberous, and sacrospinous ligaments. Crucially, the posterior SI ligaments remain intact, providing vertical stability but resulting in rotational instability (an "open book" pelvis). APC I is diastasis < 2.5 cm. APC III involves complete disruption of both anterior and posterior SI ligaments, causing complete rotational and vertical instability.

Question 28

A 32-year-old recreational basketball player feels a "pop" in the back of his heel and is diagnosed with an acute Achilles tendon rupture. The typical "watershed" area where most Achilles tendon ruptures occur is located approximately how far proximal to its insertion on the calcaneus?

Explanation

The "watershed" area of the Achilles tendon, which is relatively hypovascular and most prone to rupture, is located approximately 2 to 6 cm proximal to its insertion on the calcaneal tuberosity. Its blood supply in this region is primarily dependent on the paratenon rather than robust intrinsic intramedullary or osseous vessels.

Question 29

A 50-year-old male presents with severe lower back pain radiating down both legs. Which of the following clinical findings is considered the most sensitive for the diagnosis of cauda equina syndrome?

Explanation

Urinary retention is the most sensitive symptom (sensitivity of ~90%) for the diagnosis of cauda equina syndrome. If a patient does not have urinary retention (which leads to overflow incontinence), the diagnosis of complete cauda equina syndrome is highly unlikely. A post-void residual > 100-200 mL is often used as a clinical threshold to assess for this finding.

Question 30

During anterior cruciate ligament (ACL) reconstruction, understanding the function of the two primary bundles is critical. The posterolateral (PL) bundle of the ACL is primarily responsible for which of the following biomechanical functions?

Explanation

The ACL is composed of the anteromedial (AM) and posterolateral (PL) bundles. The AM bundle is tight in flexion and is the primary restraint to anterior tibial translation at 90 degrees of knee flexion. The PL bundle is tight in extension and is the primary restraint to rotatory loads (and anterior translation) when the knee is near full extension.

Question 31

A 6-month-old infant is brought to the emergency department for irritability. Radiographs demonstrate a 'bucket-handle' fracture of the distal femur. Which of the following statements regarding this type of fracture is most accurate?

Explanation

The 'bucket-handle' or 'corner' fracture is a classic metaphyseal lesion (CML) resulting from planar microfractures through the immature primary spongiosa. It is typically caused by pulling, twisting, or shaking of the infant's limb. These fractures are considered pathognomonic (highly specific) for non-accidental trauma (child abuse) in infants.

Question 32

In the context of flexor tendon injuries of the hand, Zone II (historically known as 'no man's land') is anatomically bounded by which of the following structures?

Explanation

Flexor tendon Zone II begins at the proximal edge of the A1 pulley (often correlating superficially with the distal palmar crease) and ends at the insertion of the flexor digitorum superficialis (FDS) at the middle phalanx. This zone contains both the FDS and FDP tendons tightly enclosed within the fibro-osseous sheath, making repairs historically challenging due to adhesions (hence 'no man's land').

Question 33

A 28-year-old farmer sustains a low-velocity gunshot wound to the thigh while hunting. The bullet did not hit the femur, but the entry wound is heavily contaminated with soil. According to orthopaedic principles for gunshot wounds, what is the most appropriate antibiotic prophylaxis?

Explanation

For gunshot wounds heavily contaminated with soil, particularly in farm environments, there is a high risk of Clostridium infection. The standard antibiotic protocol for heavily contaminated or farm-related open fractures/GSWs is a first-generation cephalosporin (Cefazolin) plus an aminoglycoside (Gentamicin) for gram-negative coverage, with the mandatory addition of high-dose Penicillin to cover Clostridium species.

Question 34

A patient with acute spinal cord injury presents with flaccid paralysis, absent reflexes, and no autonomic tone below the level of the injury. The definitive clinical indicator that the patient has emerged from the phase of 'spinal shock' is the return of which of the following?

Explanation

Spinal shock is a temporary physiological state characterized by flaccidity and loss of reflexes below the level of a spinal cord injury. The hallmark of the end of spinal shock is the return of the bulbocavernosus reflex. Until this reflex returns, a true assessment of the completeness of the spinal cord injury cannot be fully determined.

Question 35

A 12-year-old girl presents with pain in her mid-thigh. Radiographs show a permeative, lytic lesion in the diaphyseal region of the femur with a prominent 'onion-skin' periosteal reaction. Histology reveals small, round, blue cells. Which specific fusion gene product is most likely driving this malignancy?

Explanation

The clinical presentation, radiographic appearance (diaphyseal, onion-skin), and histology (small round blue cells) are classic for Ewing Sarcoma. The vast majority (>85%) of Ewing sarcomas are characterized by a t(11;22)(q24;q12) chromosomal translocation, which results in the EWS-FLI1 fusion protein. SYT-SSX is seen in synovial sarcoma, PAX3-FOXO1 in alveolar rhabdomyosarcoma.

Question 36

A 'floating shoulder' injury typically refers to a dual disruption of the superior shoulder suspensory complex (SSSC). This is most classically represented by ipsilateral fractures of which two structures?

Explanation

A 'floating shoulder' classically refers to double disruptions of the Superior Shoulder Suspensory Complex (SSSC). The most common combination is an ipsilateral fracture of the clavicle and the scapular neck. This potentially renders the glenohumeral articulation unstable with respect to the axial skeleton, though conservative management is increasingly supported for minimally displaced variants.

Question 37

Bone Morphogenetic Proteins (BMPs) are utilized in orthopaedic surgery to stimulate bone healing. BMPs primarily exert their osteoinductive effects by binding to serine-threonine kinase receptors on the cell surface, which then directly phosphorylate and activate which of the following intracellular signaling pathways?

Explanation

BMPs are members of the TGF-beta superfamily. They bind to type I and type II serine/threonine kinase receptors. Upon activation, these receptors phosphorylate intracellular receptor-regulated Smad proteins, specifically Smad 1, Smad 5, and Smad 8. These then form a complex with the co-Smad (Smad 4) and translocate to the nucleus to initiate transcription of osteogenic genes.

Question 38

In a severe midfoot trauma, a patient sustains a Lisfranc injury. Anatomically, the Lisfranc ligament is an interosseous ligament that connects which two osseous structures?

Explanation

The Lisfranc ligament is an oblique, strong plantar interosseous ligament that originates on the lateral aspect of the medial cuneiform and inserts on the medial aspect of the base of the second metatarsal. It is a critical stabilizer of the midfoot because there is no transverse intermetatarsal ligament between the bases of the first and second metatarsals.

Question 39

A 28-year-old professional volleyball player presents with insidious onset of shoulder weakness. Examination reveals isolated weakness in external rotation with the arm at the side, but full strength in shoulder abduction. Atrophy is noted over the posterior scapula below the spine. Entrapment of the suprascapular nerve at which of the following anatomical locations best explains this specific deficit?

Explanation

The suprascapular nerve innervates both the supraspinatus (abduction) and infraspinatus (external rotation). If the nerve is entrapped at the suprascapular notch, both muscles are affected. If it is entrapped more distally at the spinoglenoid notch (commonly by a paralabral cyst in overhead athletes), it causes isolated denervation and weakness of the infraspinatus, sparing the supraspinatus.

Question 40

According to the Musculoskeletal Infection Society (MSIS) criteria, an elevated level of Alpha-defensin in synovial fluid is utilized as a diagnostic marker for periprosthetic joint infection (PJI). Alpha-defensin is primarily secreted by which of the following cell types in response to pathogens?

Explanation

Alpha-defensin is a highly specific antimicrobial peptide that is released by activated neutrophils in response to the presence of pathogens. The synovial fluid alpha-defensin test has been validated as a highly sensitive and specific minor criterion (or standalone test in recent algorithms) for diagnosing periprosthetic joint infection (PJI).

Question 41

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

Explanation

TXA is a synthetic analog of the amino acid lysine. It reversibly and competitively binds to the lysine-binding sites on plasminogen, preventing its conversion to plasmin and thereby inhibiting fibrinolysis.

Question 42

A 6-year-old child presents with frequent fractures, blue sclerae, and conductive hearing loss. Genetic analysis reveals a mutation in the COL1A1 gene. At the molecular level, this condition is most commonly characterized by which of the following?

Explanation

Osteogenesis imperfecta is primarily caused by autosomal dominant mutations in COL1A1 or COL1A2. The most common molecular defect is the substitution of a bulky amino acid for glycine, which disrupts the tight coiling of the collagen triple helix.

Question 43

A 30-year-old male presents with recurrent fractures and a radiograph showing generalized osteosclerosis with a rugger jersey spine appearance. A defect in the osteoclast ruffled border is suspected. A mutation in which of the following is the most likely cause?

Explanation

Osteopetrosis is caused by defective osteoclastic bone resorption. A common mutation involves carbonic anhydrase II, which is essential for generating the acidic environment required at the ruffled border to dissolve bone mineral.

Question 44

A 14-year-old boy presents with a destructive diaphyseal lesion of the femur and an associated large soft-tissue mass. Biopsy reveals sheets of small round blue cells. Cytogenetic testing of this tumor is most likely to demonstrate a translocation resulting in which of the following fusion proteins?

Explanation

Ewing sarcoma is classically characterized by the t(11;22) translocation. This chromosomal rearrangement fuses the EWSR1 gene with the FLI1 gene, creating the EWS-FLI1 fusion protein which acts as an oncogenic transcription factor.

Question 45

Articular cartilage is highly specialized to withstand complex mechanical environments. Which zone of articular cartilage is primarily responsible for resisting shear stress and contains collagen fibers oriented parallel to the joint surface?

Explanation

The superficial zone comprises 10-20% of articular cartilage thickness and contains densely packed collagen fibrils aligned parallel to the articular surface. This orientation provides the cartilage with its primary resistance to shear stress.

Question 46

A 65-year-old female with a modular unipolar hemiarthroplasty presents with new-onset groin pain and a large sterile effusion 5 years postoperatively. Revision surgery reveals black debris and corrosion at the head-neck junction. Which of the following best describes the underlying tribological mechanism?

Explanation

Mechanically assisted crevice corrosion (MACC), or fretting corrosion, occurs at modular junctions like the head-neck taper in hip arthroplasty. Cyclic loading continuously disrupts the protective oxide layer, accelerating local corrosive processes.

Question 47

A synovial fluid aspirate is obtained to evaluate a painful total knee arthroplasty. The alpha-defensin immunoassay returns positive. In the context of periprosthetic joint infection, which of the following cells is the primary source of alpha-defensin?

Explanation

Alpha-defensin is an antimicrobial peptide released predominantly by activated neutrophils in response to infection. It is a highly sensitive and specific biomarker for diagnosing periprosthetic joint infections.

Question 48

A newborn is evaluated for short-limbed dwarfism, frontal bossing, and midface hypoplasia. Radiographs show rhizomelic shortening of the long bones. This condition is caused by a gain-of-function mutation in FGFR3, which leads to which of the following abnormalities at the physis?

Explanation

Achondroplasia is due to a gain-of-function mutation in FGFR3, which constitutively suppresses chondrocyte proliferation. This leads to early closure of the physis and a narrowed zone of proliferative chondrocytes.

Question 49

Which of the following best describes the viscoelastic property of cortical bone when subjected to a rapid rate of loading?

Explanation

Bone is viscoelastic, meaning its mechanical properties depend on the loading rate. At higher rates of loading, bone becomes stiffer, sustains higher loads, and absorbs more energy before failing.

Question 50

A 14-year-old boy presents with a painful, enlarging mass on his proximal humerus. Biopsy reveals uniform small blue cells. Molecular analysis demonstrates an EWS-FLI1 fusion protein. Which chromosomal translocation is pathognomonic for this tumor?

Explanation

Ewing sarcoma is characterized by the t(11;22) translocation, resulting in the EWS-FLI1 fusion gene. t(X;18) is seen in synovial sarcoma, and t(12;16) in myxoid liposarcoma.

Question 51

A 65-year-old patient undergoing total hip arthroplasty is prescribed rivaroxaban for venous thromboembolism prophylaxis. What is the specific mechanism of action of this medication?

Explanation

Rivaroxaban is an oral anticoagulant that works as a direct Factor Xa inhibitor. It interrupts both the intrinsic and extrinsic pathways of the blood coagulation cascade.

Question 52

According to Perren's strain theory, what interfragmentary strain environment is required to allow for primary (direct) bone healing without callus formation?

Explanation

Primary bone healing occurs only under conditions of absolute stability, defined by an interfragmentary strain of less than 2%. Strains between 2% and 10% result in secondary bone healing via endochondral ossification.

Question 53

Articular cartilage is composed of multiple zones with varying biochemical compositions. Which zone contains the highest concentration of water and the lowest concentration of proteoglycans?

Explanation

The superficial zone of articular cartilage has the highest water content and the lowest proteoglycan concentration. Collagen fibers here are oriented parallel to the joint surface to resist shear forces.

Question 54

A 10-year-old child presents with cavovarus feet, clumsy gait, and distal muscle weakness. Neurologic examination reveals decreased deep tendon reflexes. What is the most common genetic mutation associated with this condition?

Explanation

The patient has Charcot-Marie-Tooth (CMT) disease. CMT type 1A is the most common variant and is caused by a duplication of the PMP22 gene on chromosome 17.

Question 55

A 68-year-old female presents with anterior knee pain and a painful 'clunk' when extending her knee from a flexed position, one year after a total knee arthroplasty (TKA). This complication is most classically associated with which TKA design?

Explanation

Patellar clunk syndrome is caused by a fibrous nodule forming at the superior pole of the patella that catches in the intercondylar notch of the femoral component. It is classically associated with posterior-stabilized TKA designs.

Question 56

During repair of a flexor tendon laceration in Zone II of the hand, preserving the intrinsic blood supply to the tendon is critical. Blood is supplied to the flexor tendons within the digital sheath primarily through which of the following structures?

Explanation

Within the fibro-osseous sheath (Zone II), flexor tendons receive their intrinsic blood supply primarily via the vincula longa and brevia. Synovial diffusion also contributes to nutrition but is not the primary vascular structure.

Question 57

A 45-year-old woman with a history of malabsorption syndrome presents with bone pain and a fragility fracture. Labs show low 25-hydroxyvitamin D. Which of the following laboratory profiles is most consistent with severe nutritional osteomalacia?

Explanation

Vitamin D deficiency leads to decreased intestinal absorption of calcium and phosphate. This triggers secondary hyperparathyroidism, which normalizes calcium slightly but causes further renal phosphate wasting, resulting in low Ca, low PO4, and high PTH.

Question 58

A 60-year-old man presents with back pain, anemia, and hypercalcemia. Radiographs show multiple punched-out lytic lesions in his skull and spine. In this condition, which cytokine is predominantly secreted by neoplastic plasma cells to activate osteoclasts?

Explanation

In multiple myeloma, neoplastic plasma cells secrete high levels of IL-6 and osteoclast activating factor (OAF). This upregulates RANKL, leading to profound osteoclast activation and lytic bone lesions.

Question 59

An infant is being treated for developmental dysplasia of the hip (DDH) with a Pavlik harness. While examining the child, you notice the harness is adjusted in extreme hyperflexion. This positioning places the infant at highest risk for which complication?

Explanation

Extreme hyperflexion in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to femoral nerve palsy. Excessive abduction is the primary risk factor for avascular necrosis.

Question 60

A 35-year-old male sustains a Gustilo-Anderson Type IIIB open tibia fracture with an extensive soft tissue defect over the distal third of the tibia. Following debridement, which of the following is the most appropriate flap option for coverage?

Explanation

Soft tissue defects of the distal third of the tibia typically require free tissue transfer, such as a latissimus dorsi or anterolateral thigh free flap. Gastrocnemius flaps are used for the proximal third, and soleus flaps for the middle third.

Question 61

A 22-year-old male is brought to the trauma bay after a high-speed motorcycle collision. He is hypotensive with a blood pressure of 80/50 mmHg and has a heart rate of 50 bpm. He is flaccid and areflexic below the C6 level. Which of the following is the primary mechanism for his hemodynamic instability?

Explanation

The patient is experiencing neurogenic shock, characterized by hypotension and bradycardia due to the loss of sympathetic tone. This allows unopposed vagal parasympathetic tone to slow the heart rate and dilate peripheral vessels.

Question 62

In the manufacturing of highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) for total joint arthroplasty, which process is utilized to eliminate free radicals and prevent long-term oxidative degradation?

Explanation

Irradiation is used to create cross-links that improve wear resistance. However, it generates free radicals. Remelting or annealing the polyethylene is necessary to extinguish these free radicals and prevent oxidative degradation.

Question 63

A 13-year-old obese boy presents with severe, sudden hip pain and inability to bear weight after a minor fall, superimposed on months of mild groin pain. In an unstable slipped capital femoral epiphysis (SCFE), which vessel is at greatest risk of injury leading to osteonecrosis?

Explanation

The medial femoral circumflex artery, specifically its posterosuperior retinacular branches, provides the primary blood supply to the femoral head. It is at the highest risk of disruption in an unstable SCFE.

Question 64

During the lifecycle of a bacterial biofilm on an infected orthopedic implant, which phase represents the systemic shedding of bacteria to colonize new sites?

Explanation

The final stage of biofilm development is planktonic dispersion (or detachment). Bacteria revert to their free-floating planktonic state, escaping the biofilm to spread hematogenously and colonize distant sites.

Question 65

A 19-year-old male presents with night pain in his proximal femur that is dramatically relieved by ibuprofen. Radiographs show a 1 cm radiolucent nidus surrounded by reactive sclerosis. The intense pain associated with this lesion is primarily mediated by local production of:

Explanation

Osteoid osteomas secrete extremely high levels of prostaglandins, particularly PGE2, due to high expression of cyclooxygenase-2 (COX-2) by the lesional osteoblasts. This is why NSAIDs provide dramatic pain relief.

Question 66

A newborn suffers a brachial plexus injury during a difficult macrosomic delivery, affecting the C5 and C6 nerve roots. Which of the following best describes the classic upper extremity posture associated with this injury?

Explanation

Erb's palsy (C5-C6 injury) leads to weakness of the shoulder abductors, external rotators, elbow flexors, and forearm supinators. This results in the classic 'waiter's tip' posture: adducted, internally rotated shoulder, extended elbow, and pronated forearm.

Question 67

A 40-year-old male sustains a severe anteroposterior compression (APC III) pelvic ring injury. In the setting of massive retroperitoneal hemorrhage associated with pelvic fractures, the primary anatomic source of bleeding is most commonly:

Explanation

While arterial bleeding (e.g., superior gluteal or internal iliac) can be life-threatening and require embolization, 80-90% of pelvic hemorrhage is venous in origin, arising from the presacral venous plexus and exposed cancellous bone.

Question 68

A 70-year-old woman with severe osteoporosis and a recent vertebral compression fracture is started on teriparatide. What is the mechanism of action of this medication?

Explanation

Teriparatide is a recombinant fragment of human parathyroid hormone (PTH 1-34). When administered intermittently, it possesses strong anabolic effects, stimulating osteoblast activity and bone formation.

Question 69

A 4-year-old boy presents with rhizomelic short stature, frontal bossing, and midface hypoplasia. Radiographs show narrowing of the interpedicular distances in the lumbar spine. What is the precise cellular mechanism of the genetic mutation responsible for this condition?

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This mutation aberrantly activates signaling pathways that inhibit chondrocyte proliferation in the proliferative zone of the physis.

Question 70

According to Perren's strain theory of fracture healing, different tissues tolerate varying levels of mechanical strain before failure. What is the maximum approximate strain tolerance of granulation tissue?

Explanation

Granulation tissue can tolerate up to 100% strain, allowing it to bridge highly mobile fracture gaps initially. As the tissue stiffens into cartilage (10% strain) and then bone (2% strain), the interfragmentary strain must decrease accordingly.

Question 71

During the remodeling phase of tendon healing, the biomechanical strength of the repair tissue progressively increases. This increase in tensile strength is primarily due to the substitution of which collagen type for another?

Explanation

During early tendon healing, fibroblasts predominantly synthesize disorganized Type III collagen. During the remodeling phase, this is gradually replaced by highly organized, stronger Type I collagen.

Question 72

A 65-year-old osteoporotic woman is prescribed alendronate. By which of the following intracellular mechanisms does this nitrogen-containing bisphosphonate inhibit osteoclast-mediated bone resorption?

Explanation

Nitrogen-containing bisphosphonates like alendronate inhibit farnesyl pyrophosphate synthase. This disrupts the mevalonate pathway, preventing prenylation of small GTPases essential for osteoclast ruffled border formation and survival.

Question 73

A 30-year-old female presents with knee pain. Radiographs show an eccentric, lytic epiphyseal lesion in the distal femur. Biopsy reveals multinucleated giant cells interspersed among mononuclear cells. Which cell population in this lesion harbors the primary neoplastic defect and what factor do they secrete?

Explanation

In Giant Cell Tumor of bone, the spindle-shaped mononuclear stromal cells are the true neoplastic cells. They secrete high levels of RANKL, which recruits and activates the reactive multinucleated osteoclast-like giant cells.

Question 74

A 14-year-old boy presents with a diaphyseal femur lesion with an "onion-skin" periosteal reaction. Molecular analysis confirms a t(11;22)(q24;q12) translocation. The resulting EWS-FLI1 fusion protein primarily functions as which of the following?

Explanation

Ewing sarcoma is characterized by the t(11;22) translocation creating the EWS-FLI1 fusion gene. This fusion protein acts as an aberrant transcription factor that dysregulates target genes leading to tumorigenesis.

Question 75

Articular cartilage relies on its distinct zonal architecture for unique biomechanical properties. Which of the following best describes the structural composition of the superficial (tangential) zone?

Explanation

The superficial zone of articular cartilage has the highest water content and lowest proteoglycan concentration. Its densely packed Type II collagen fibers run parallel to the joint surface to resist shear forces.

Question 76

A 6-year-old girl is evaluated for recurrent fractures following minor trauma. Examination reveals blue sclerae and mild dentinogenesis imperfecta. Genetic testing is most likely to show a mutation resulting in the substitution of which amino acid in the collagen triple helix?

Explanation

Osteogenesis imperfecta is most commonly caused by mutations in COL1A1 or COL1A2. This typically results in the substitution of bulkier amino acids for glycine, the smallest amino acid, disrupting the tight packing of the collagen triple helix.

Question 77

A 22-year-old patient presents with a subtrochanteric fracture after a minor fall. Radiographs demonstrate uniformly dense bones with an "Erlenmeyer flask" deformity of the distal femurs. A defect in which of the following is most likely responsible for this condition?

Explanation

Osteopetrosis is caused by defective osteoclastic bone resorption. Common mutations involve TCIRG1 (a proton pump subunit) or Carbonic Anhydrase II, preventing the osteoclast from creating the acidic microenvironment needed to dissolve hydroxyapatite.

Question 78

Teriparatide is utilized in the management of severe osteoporosis. What is the fundamental mechanism by which intermittent, rather than continuous, administration of this parathyroid hormone analog results in an anabolic effect on bone?

Explanation

Intermittent PTH exposure is highly anabolic because it stimulates osteoblast differentiation, inhibits osteoblast apoptosis, and promotes Wnt signaling. Conversely, continuous PTH exposure favors osteoclastogenesis via increased RANKL expression.

Question 79

An elite marathon runner undergoes a muscle biopsy for a research study. Compared to a sprinter, the runner's predominant muscle fiber type is expected to demonstrate which of the following characteristics?

Explanation

Endurance athletes have predominantly Type I (slow-twitch) muscle fibers. These fibers are characterized by high mitochondrial density, high myoglobin, high capillary density, and rely on oxidative phosphorylation, making them highly fatigue-resistant.

Question 80

A surgeon plans to use a structural cortical bone allograft to reconstruct an intercalary defect. At approximately 6 months postoperatively, what is the primary reason the allograft experiences a significant transient reduction in biomechanical strength?

Explanation

Cortical bone grafts incorporate via creeping substitution, initially beginning with osteoclastic resorption along Haversian canals. This creates significant porosity and a temporary nadir in mechanical strength around 6 months before new osteoblastic bone formation restores it.

Question 81

A 68-year-old man presents with back pain, anemia, and hypercalcemia. Skeletal survey reveals multiple "punched-out" lytic lesions. The extensive bone destruction in this condition is primarily mediated by myeloma cells secreting which of the following factors?

Explanation

Multiple myeloma causes lytic lesions via an uncoupling of bone remodeling. Myeloma cells secrete MIP-1alpha (stimulating osteoclasts) and DKK1 (inhibiting osteoblasts by antagonizing Wnt signaling).

Question 82

A 5-year-old boy is diagnosed with X-linked hypophosphatemic rickets. Which of the following pathophysiologic sequences best explains his condition?

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX mutation leading to elevated FGF23 levels. High FGF23 causes profound renal phosphate wasting and inappropriately downregulates 1-alpha-hydroxylase, preventing calcitriol synthesis.

Question 83

The lubricating properties of normal synovial fluid are crucial for protecting articular cartilage. While lubricin primarily handles boundary lubrication, which of the following molecules is predominantly responsible for the fluid-film lubrication and high viscosity of synovial fluid?

Explanation

Hyaluronic acid (hyaluronan) is a non-sulfated glycosaminoglycan synthesized by Type B synoviocytes. It is the primary molecule responsible for the high viscosity and fluid-film elastohydrodynamic lubrication of synovial fluid.

Question 84

A patient with profound dietary restrictions presents with perifollicular hemorrhages, gingival bleeding, and poor wound healing. The underlying vitamin deficiency directly impairs which of the following steps in collagen synthesis?

Explanation

Scurvy is caused by Vitamin C deficiency. Vitamin C acts as a necessary cofactor for prolyl hydroxylase and lysyl hydroxylase, which are essential for stabilizing the collagen triple helix.

Question 85

A patient suffers a closed distal humerus fracture resulting in a radial nerve palsy. Electromyography reveals fibrillation potentials but nerve conduction studies suggest continuity of the endoneurial tubes. According to Sunderland's classification, what grade of nerve injury has occurred?

Explanation

Sunderland second-degree injury (axonotmesis) involves disruption of the axon with Wallerian degeneration, but the endoneurial sheath remains intact. This allows for excellent potential for spontaneous, directed axonal regeneration.

Question 86

During a regional nerve block, a patient inadvertently receives an intravascular injection of bupivacaine, leading to cardiovascular collapse. Intravenous lipid emulsion therapy is initiated. What is the primary mechanism of action of the local anesthetic responsible for this toxicity?

Explanation

Local anesthetics like bupivacaine work by crossing the neuronal cell membrane and binding to the intracellular portion of voltage-gated sodium channels, preventing depolarization. Toxicity affects cardiac sodium channels similarly.

Question 87

During revision hip arthroplasty, a surgeon considers placing a stainless steel cable around a titanium femoral stem. What is the primary concern regarding mixed-metal combinations in this orthopaedic setting?

Explanation

Mixing dissimilar metals in an electrolytic environment (the human body) causes galvanic corrosion. The less noble metal (stainless steel) becomes the anode and undergoes accelerated dissolution, while titanium acts as the cathode.

Question 88

A 45-year-old male presents with a large, deep intramuscular mass in his thigh. Biopsy shows a prominent myxoid stroma, lipoblasts, and a delicate "chicken-wire" capillary network. The diagnosis is confirmed by identifying the t(12;16)(q13;p11) translocation. This sarcoma is clinically notable for which of the following?

Explanation

Myxoid liposarcoma is characterized by the t(12;16) FUS-DDIT3 translocation. It is uniquely highly sensitive to radiation therapy and has a distinct predilection for metastasizing to extrapulmonary sites, particularly the spine/bones.

Updated Orthopedic Review | Dr Hutaif General Orthopedi -...

Orthopedic Review | Dr Hutaif General Orthopedics Revie -...

Key Takeaway

Orthopedic Review | Dr Hutaif General Orthopedics Revie -...

Chapter Index