Figure 17 shows the radiograph of an 82-year-old right-hand dominant woman who fell while weeding her garden. She has severe right shoulder pain. She is neurovascularly intact. What is the most appropriate treatment? Review Topic

Surgical replacement with hemiarthroplasty or reverse total shoulder arthroplasty

A 38-year-old man has winging of the ipsilateral scapula after undergoing a transaxillary resection of the first rib 3 weeks ago. What is the most likely cause of this finding?

Injury to the long thoracic nerve

Nonsurgical management of pectoralis major tears is likely to result in weakness of glenohumeral

adduction and internal rotation.

Turf toe typically involves injury to which of the following structures of the great toe?

Capsule of the first metatarsophalangeal joint

Regarding bone erosion in rheumatoid arthritis, which of the following statements is true?

The presence of serum anti-citrullinated protein antibodies is predictive of the extent of synovitis but not bone erosion

Free Orthopedics MCQ Review | Dr Hutaif General Orthopedics

Question 1

A 65-year-old female is started on denosumab for the treatment of osteoporosis. Which of the following best describes the molecular mechanism of this medication in altering bone biology?

Explanation

Denosumab is a fully human monoclonal antibody (IgG2) that specifically binds to the receptor activator of nuclear factor kappa-B ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on the surface of osteoclasts and their precursors. This effectively inhibits osteoclast survival, formation, and function, leading to decreased bone resorption.

Question 2

In normal hyaline articular cartilage, which zone is characterized by the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibers oriented parallel to the joint surface?

Explanation

Articular cartilage is structurally divided into zones. The superficial (tangential) zone contains the highest water content (approximately 80%), the lowest proteoglycan concentration, and Type II collagen fibers aligned parallel to the joint surface to resist shear forces. In contrast, the deep zone has the lowest water content, highest proteoglycan concentration, and vertically oriented collagen fibers to resist compression.

Question 3

Which of the following modifications to ultra-high-molecular-weight polyethylene (UHMWPE) most effectively reduces adhesive and abrasive wear when used in total joint arthroplasty?

Explanation

Highly cross-linking UHMWPE, typically achieved through gamma or electron beam irradiation followed by thermal treatment (remelting or annealing to eliminate free radicals), significantly improves its wear resistance. This process drastically decreases both adhesive and abrasive wear. However, highly cross-linking the material can slightly reduce its mechanical properties, such as fatigue strength and ductility.

Question 4

On a standard stress-strain curve for a typical ductile metal used in orthopedic implants, which of the following best defines the yield point?

Explanation

The yield point on a stress-strain curve marks the limit of elastic behavior and the beginning of plastic behavior. Prior to the yield point, deformation is completely reversible (elastic phase); once the load is removed, the material returns to its original shape. Beyond the yield point, the material undergoes permanent (plastic) deformation.

Question 5

Secondary fracture healing proceeds via endochondral ossification. During the cartilaginous callus phase of this process, which specific cell type is primarily responsible for the production of Type X collagen?

Explanation

During endochondral ossification in secondary fracture healing, the cartilaginous callus undergoes a maturation process. Hypertrophic chondrocytes are the primary cells responsible for secreting Type X collagen. This specialized collagen alters the extracellular matrix, making it permissive to calcification, which is a critical prerequisite for subsequent vascular invasion and replacement by osteoblasts.

Question 6

A pediatric patient is diagnosed with achondroplasia, the most common form of short-limb dwarfism. This condition is classically caused by a specific mutation in which of the following genes?

Explanation

Achondroplasia is an autosomal dominant disorder caused by a gain-of-function mutation in the FGFR3 gene. This mutation results in an exaggerated inhibitory effect on chondrocyte proliferation in the proliferative zone of the physis, leading to diminished longitudinal bone growth.

Question 7

A 72-year-old patient develops a late chronic periprosthetic joint infection caused by Staphylococcus epidermidis. The pathogenesis heavily relies on the formation of a robust biofilm. What is the primary constituent of the extracellular polymeric substance (glycocalyx) produced by these bacteria?

Explanation

Biofilm formation is a hallmark of orthopedic hardware infections. The biofilm is composed of a self-produced extracellular polymeric substance (EPS), often called the glycocalyx. The major structural components of this protective EPS matrix are complex exopolysaccharides, which shield the bacterial colony from both the host immune system and systemic antibiotics.

Question 8

An orthopedic researcher conducts a randomized controlled trial comparing two types of cast materials for distal radius fractures. The study fails to find a statistically significant difference, although a true clinical difference exists in reality. Which of the following would have most effectively decreased the probability of committing this Type II error?

Explanation

A Type II error (beta) occurs when a study fails to reject a false null hypothesis (a false negative). The probability of avoiding a Type II error is known as statistical power (Power = 1 - beta). Increasing the sample size is the most direct and practical method to increase a study's statistical power, thereby decreasing the risk of a Type II error.

Question 9

Demineralized bone matrix (DBM) is commonly utilized in spinal fusion surgery. Based on its structural and biological profile, which of the following bone grafting properties does DBM inherently possess?

Explanation

Demineralized bone matrix (DBM) is produced by acid-extracting minerals from allograft bone. This process exposes osteoinductive growth factors, primarily Bone Morphogenetic Proteins (BMPs). The remaining type I collagen network serves as an osteoconductive scaffold. Because DBM is devoid of live cells, it lacks osteogenic properties.

Question 10

A 68-year-old man presents with increasing hat size, unilateral hearing loss, and bowing of his tibiae. Radiographs show pronounced cortical thickening and coarse trabeculae. What is the primary initial cellular abnormality in the pathophysiology of this patient's disease?

Explanation

The clinical presentation is classic for Paget's disease of bone. The initial and primary cellular defect is an abnormality in osteoclasts, which become increased in number, abnormally large, and hyperactive, containing numerous nuclei. This intense resorptive phase triggers a subsequent, disorganized, and chaotic osteoblastic response, leading to structurally weak, woven bone.

Question 11

In the physiological cascade that leads to acute compartment syndrome following a severe closed tibial fracture, which of the following microvascular events occurs first, setting off the cycle of ischemia?

Explanation

The pathophysiology of acute compartment syndrome initiates with rising tissue pressure within an unyielding fascial space. Because the venous system operates at a much lower pressure than the arterial system, the thin-walled veins collapse first. This venous outflow obstruction leads to congestion, further increasing intracompartmental pressure, ultimately halting capillary perfusion and, much later, compromising arterial inflow.

Question 12

According to Sunderland's classification of peripheral nerve injuries, a third-degree nerve injury involves complete disruption of the axon and which other histological structure?

Explanation

In Sunderland's classification: 1st degree is a localized conduction block (neuropraxia/myelin injury). 2nd degree is loss of axonal continuity with intact endoneurium (axonotmesis). 3rd degree involves loss of the axon and endoneurium, while the perineurium remains intact. 4th degree disrupts the axon, endoneurium, and perineurium. 5th degree is a complete nerve transection (epineurium disrupted).

Question 13

During a knee arthroplasty utilizing a pneumatic tourniquet for 90 minutes, which of the following systemic physiological changes is most likely to occur immediately upon deflation of the tourniquet?

Explanation

Upon tourniquet deflation, the sudden release of ischemic, acidotic, and hypercapnic blood back into systemic circulation causes marked vasodilation. This typically results in an immediate, transient decrease in systemic blood pressure. Additionally, the washout of metabolites causes a transient increase in end-tidal CO2, a decrease in core body temperature, and a decrease in arterial pH (acidosis).

Question 14

An orthopedic surgeon is revising a failed internal fixation and considers placing a titanium screw through a 316L stainless steel plate. Which of the following electrochemical principles explains why this specific mixing of metals should generally be avoided?

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as stainless steel and titanium) are placed in direct physical contact within a conductive electrolyte environment (such as bodily fluids). The difference in their anodic index creates a small electrical current, leading to accelerated corrosion of the less noble metal (in this case, the stainless steel).

Question 15

During the normal human gait cycle, which muscle group undergoes a critical eccentric contraction during the initial contact to the loading response phase to control joint motion and absorb shock?

Explanation

From initial contact (heel strike) to the loading response, the knee flexes slightly to absorb the shock of body weight. The quadriceps muscle group contracts eccentrically during this brief period to control the rate and extent of knee flexion, thereby stabilizing the limb as weight is accepted.

Question 16

A 16-year-old male is diagnosed with high-grade conventional osteosarcoma. A mutation in the TP53 gene is identified in the tumor tissue. A germline mutation in this specific gene is classically associated with which of the following inherited cancer predisposition syndromes?

Explanation

Li-Fraumeni syndrome is a rare, autosomal dominant disorder caused by germline mutations in the TP53 tumor suppressor gene. Individuals with this syndrome have a profoundly increased lifetime risk of developing multiple primary cancers, predominantly osteosarcomas, soft tissue sarcomas, early-onset breast cancers, and brain tumors.

Question 17

During the normal biological healing process of a completely lacerated and surgically repaired flexor tendon, at what time post-operatively does the repair tissue predictably reach its weakest point, making it most susceptible to iatrogenic rupture?

Explanation

Tendon healing proceeds through inflammatory, proliferative, and remodeling phases. During the transition from the inflammatory phase to the early fibroblastic phase (approximately 7 to 14 days post-operatively), endogenous collagen is degraded by matrix metalloproteinases faster than new collagen is synthesized. This results in significant softening, and the repaired tendon is at its weakest.

Question 18

The remarkable compressive stiffness and load-bearing capacity of normal articular cartilage are primarily provided by the interaction between interstitial fluid and which of the following structural macromolecules?

Explanation

Aggrecan is the most abundant large proteoglycan in articular cartilage. It contains a core protein densely packed with chondroitin sulfate and keratan sulfate glycosaminoglycan (GAG) chains. The high concentration of negatively charged GAGs attracts cations and water via the Donnan osmotic effect. This creates a massive swelling pressure that resists compression, providing cartilage with its stiffness.

Question 19

To minimize occupational radiation exposure during orthopedic procedures utilizing a C-arm fluoroscope, which of the following intraoperative configurations exposes the operating surgeon's hands to the highest dose of scatter radiation?

Explanation

In fluoroscopy, the majority of the radiation exposure to the surgical team is scatter radiation reflecting back from the patient. Because the beam is most intense as it exits the X-ray tube and strikes the patient, positioning the X-ray tube above the patient directs the highest intensity of scatter outward toward the upper bodies and hands of the operating personnel. The preferred, safer setup is the X-ray tube below the table.

Question 20

A 68-year-old male is scheduled for a total hip arthroplasty. His cardiologist has instructed him to hold his daily Rivaroxaban, which he takes for non-valvular atrial fibrillation. What is the specific pharmacological mechanism of action of this medication?

Explanation

Rivaroxaban is an oral anticoagulant that functions as a highly selective direct Factor Xa inhibitor. By directly inhibiting Factor Xa, it interrupts both the intrinsic and extrinsic pathways of the blood coagulation cascade, preventing thrombin generation and thrombus formation. Unlike fondaparinux, it does not require antithrombin III to exert its effect.

Question 21

A 12-year-old boy presents with left knee pain and a limp. Radiographs confirm a slipped capital femoral epiphysis (SCFE). Which of the following is the most widely accepted absolute indication for prophylactic in situ pinning of the contralateral, asymptomatic hip?

Explanation

Prophylactic pinning of the contralateral hip in SCFE is highly recommended in patients with an underlying endocrine or metabolic disorder (e.g., hypothyroidism, renal osteodystrophy) due to the extremely high risk (up to 100%) of bilateral involvement. Other indications include prophylactic treatment in patients under 10 years of age or those who cannot be reliably followed.

Question 22

A 15-year-old boy presents with a painful mass in the distal femur. Biopsy reveals malignant spindle cells producing an immature osteoid matrix. Which of the following genetic pathways is most commonly mutated in this primary bone sarcoma?

Explanation

The biopsy describes osteosarcoma. Alterations in the Rb and TP53 tumor suppressor pathways are the most common genetic mutations associated with conventional osteosarcoma. The t(11;22) translocation is characteristic of Ewing sarcoma; t(X;18) is seen in synovial sarcoma; GNAS1 in fibrous dysplasia; and EXT1/EXT2 in multiple hereditary exostoses.

Question 23

During a primary total knee arthroplasty, trial components are placed. The surgeon notes that the knee is excessively tight in both full extension and 90 degrees of flexion. The patella tracks centrally but requires significant force to evert. What is the most appropriate next step in balancing this knee?

Explanation

A knee that is tight in both flexion and extension indicates a symmetrically tight flexion and extension gap. The most appropriate correction is to increase both gaps equally. This is achieved by either resecting more proximal tibia or utilizing a thinner tibial polyethylene insert. Modifying the femur only affects one gap (distal femur affects extension; posterior femur affects flexion).

Question 24

A 24-year-old football player undergoes clinical evaluation following a knee injury. The dial test demonstrates 20 degrees of increased external rotation on the injured side at 30 degrees of flexion, but symmetric external rotation at 90 degrees of flexion compared to the uninjured knee. Which structural injury does this pattern indicate?

Explanation

The dial test is used to evaluate the posterolateral corner (PLC) and posterior cruciate ligament (PCL). Increased external rotation (>10 degrees compared to the normal side) at 30 degrees of flexion but symmetric rotation at 90 degrees indicates an isolated PLC injury. If the external rotation is increased at both 30 and 90 degrees, it suggests a combined PCL and PLC injury.

Question 25

In the repair of a zone II flexor tendon laceration using a multistrand core suture, what is the primary biomechanical advantage of adding a continuous epitendinous suture?

Explanation

Adding an epitendinous suture to a core flexor tendon repair significantly improves the construct. It smooths the repair site, decreasing gliding resistance (work of flexion), and provides a biomechanical advantage by increasing the tensile strength of the repair by 10% to 50%, reducing the risk of gap formation during early active motion protocols.

Question 26

A 60-year-old patient with progressive cervical myelopathy is diagnosed with Ossification of the Posterior Longitudinal Ligament (OPLL). Lateral radiographs demonstrate a negative K-line. Which surgical approach is most appropriate to adequately decompress the spinal cord in this specific scenario?

Explanation

The K-line connects the mid-anteroposterior diameter of the spinal canal at C2 and C7 on a neutral lateral radiograph. A 'negative K-line' means the OPLL mass extends posterior to this line, usually associated with cervical kyphosis. In K-line negative patients, posterior-only decompression (like laminoplasty or laminectomy) fails to allow the spinal cord to drift backward away from the OPLL, leading to poor neurological recovery. Anterior decompression (ACDF or corpectomy) and fusion is the indicated approach.

Question 27

A 35-year-old man arrives in the trauma bay following a motorcycle crash. His blood pressure is 80/40 mmHg. A pelvic radiograph reveals an APC-III pelvic ring injury. A pelvic binder is applied, and he receives massive transfusion protocol, but remains hemodynamically unstable. FAST exam is negative. What is the most common anatomic source of the hemorrhage?

Explanation

In the majority (approximately 80-90%) of hemodynamically unstable pelvic fractures, the source of bleeding is venous (presacral and prevesical venous plexuses) or from the exposed cancellous bone at fracture sites. While arterial bleeding (e.g., superior gluteal, internal pudendal) can be life-threatening and require embolization, it accounts for a smaller percentage (10-20%) of massive pelvic hemorrhage.

Question 28

According to Perren’s strain theory of bone healing, what is the maximum amount of strain that lamellar bone can tolerate before failing?

Explanation

Perren's strain theory dictates that different tissues tolerate different amounts of strain before failing. Lamellar bone can tolerate only up to 2% strain. Woven bone can tolerate up to 10% strain, and granulation tissue can tolerate up to 100% strain. Absolute stability (strain < 2%) is required for primary bone healing (direct Haversian remodeling).

Question 29

A 58-year-old male with poorly controlled diabetes mellitus presents with a swollen, erythematous, and warm right foot without open ulcerations. Radiographs show periarticular osteopenia, early bone fragmentation, and subluxation of the tarsometatarsal joints. According to the Eichenholtz classification of Charcot arthropathy, what is the most appropriate initial management?

Explanation

The patient is in Eichenholtz Stage I (Developmental/Fragmentation) of Charcot arthropathy, characterized by erythema, swelling, warmth, and radiographic evidence of osteopenia, fragmentation, and subluxation. The gold standard treatment in the acute (Stage I) phase is immobilization in a total contact cast (TCC) and strict non-weight-bearing to prevent further deformity until the acute inflammatory phase resolves and the foot enters Stage II (Coalescence).

Question 30

A 62-year-old woman presents with an audible 'squeaking' sound coming from her total hip arthroplasty during ambulation. Review of the operative report indicates she has a ceramic-on-ceramic bearing. Which of the following component malpositions is most strongly associated with this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic THA is a recognized complication. It is most strongly associated with edge loading of the ceramic bearings. Edge loading typically occurs due to acetabular component malposition, specifically excessive cup inclination (steep cup) and excessive anteversion, or due to impingement leading to microseparation.

Question 31

A 5-year-old girl sustains a displaced Gartland Type III supracondylar humerus fracture. On initial presentation, she has a pulseless but pink, well-perfused hand. She is taken to the operating room for closed reduction and percutaneous pinning. Post-operatively, her hand remains pulseless but pink and warm. What is the most appropriate next step in management?

Explanation

In pediatric supracondylar humerus fractures, the 'pulseless, pink' hand implies absent radial pulse but intact collateral capillary perfusion. Current AAOS guidelines and pediatric orthopaedic consensus recommend that if the hand remains pulseless but pink and well-perfused after anatomic closed reduction and percutaneous pinning (CRPP), the most appropriate management is close observation. Vascular exploration is primarily indicated for a 'pulseless, white' (ischemic) hand that does not improve after reduction.

Question 32

A 26-year-old carpenter presents with progressive dorsal wrist pain and decreased grip strength. Radiographs reveal sclerosis and early collapse of the lunate, with an ulnar variance of negative 3 mm. There is no evidence of radiocarpal osteoarthritis. Which of the following surgical interventions is most appropriate?

Explanation

The clinical and radiographic findings describe Kienböck's disease (avascular necrosis of the lunate) with negative ulnar variance and no osteoarthritis (Lichtman Stage II or IIIA). The primary goal of surgery in this stage is to unload the lunate. Joint-leveling procedures, particularly a radial shortening osteotomy, are the treatment of choice for symptomatic patients with negative ulnar variance to redistribute loads away from the radiolunate joint.

Question 33

A 72-year-old man complains of bilateral buttock and posterior thigh pain that worsens with walking. You suspect neurogenic claudication secondary to lumbar spinal stenosis. Which of the following historical features is most specific in differentiating neurogenic claudication from vascular claudication?

Explanation

The 'shopping cart sign' (relief of symptoms with lumbar flexion) is highly characteristic of neurogenic claudication due to lumbar spinal stenosis. Lumbar flexion increases the cross-sectional area of the spinal canal and neural foramina, relieving pressure on the nerve roots. In contrast, vascular claudication is worsened by the increased metabolic demand of walking (especially uphill) and is relieved simply by stopping and resting, regardless of posture.

Question 34

A 25-year-old male is admitted following intramedullary nailing of a closed tibial shaft fracture. Twelve hours post-operatively, he develops severe leg pain out of proportion to the injury, refractory to opioids. Which of the following compartment pressure measurements is universally accepted as an absolute indication for emergency fasciotomy?

Explanation

Compartment syndrome is a clinical diagnosis, but when pressure monitoring is used, the 'delta pressure' (ΔP) is the most reliable threshold. ΔP is calculated as Diastolic Blood Pressure minus absolute Compartment Pressure. A ΔP of less than 30 mmHg (meaning the compartment pressure is approaching the diastolic pressure) is an absolute indication for emergent four-compartment fasciotomy. Absolute pressures alone can be misleading, especially in hypotensive patients.

Question 35

A 19-year-old collegiate wrestler undergoes MR arthrography after multiple anterior shoulder dislocations. The report describes an ALPSA lesion. How does an ALPSA lesion anatomically differ from a classic Bankart lesion?

Explanation

ALPSA stands for Anterior Labroligamentous Periosteal Sleeve Avulsion. Unlike a classic Bankart lesion, where the anterior labrum and periosteum are completely torn from the glenoid rim, an ALPSA lesion involves medial displacement and inferior rotation of the labroligamentous complex along the scapular neck, but the anterior periosteum remains intact (stripped but not torn). It has a higher recurrence rate if not properly mobilized during surgical repair.

Question 36

A 55-year-old female with metastatic breast cancer presents with hip pain. Radiographs reveal a 4 cm lytic lesion in the peritrochanteric region of the right femur, occupying approximately 50% of the cortical diameter. She describes her pain as moderate with weight-bearing. According to Mirels' criteria, what is her score and recommended management?

Explanation

Mirels' criteria evaluate the risk of pathologic fracture based on four factors (1 to 3 points each): Site (Upper limb=1, Lower limb=2, Peritrochanteric=3); Pain (Mild=1, Moderate=2, Severe=3); Lesion type (Blastic=1, Mixed=2, Lytic=3); Size (<1/3 cortex=1, 1/3-2/3 cortex=2, >2/3 cortex=3). This patient's score: Peritrochanteric (3) + Moderate pain (2) + Lytic (3) + Size 50% (2) = 10. A score ≥ 9 indicates a high risk of impending fracture, and prophylactic internal fixation is highly recommended.

Question 37

When designing a cortical bone screw to maximize pullout strength in diaphyseal bone, which of the following geometric modifications will have the greatest direct effect?

Explanation

Screw pullout strength is directly proportional to the outer diameter of the thread, the length of thread engagement, and the shear strength of the surrounding material, and inversely proportional to the thread pitch. Therefore, increasing the outer thread diameter provides the most significant structural increase in pullout strength among the given options. Increasing the core diameter increases the screw's bending or fatigue strength but does not primarily dictate pullout strength.

Question 38

A 22-year-old athlete sustains an axial load to a plantarflexed foot. Weight-bearing radiographs reveal a 3 mm diastasis between the base of the first and second metatarsals. An avulsion fracture (Fleck sign) is noted. The primary ligament injured in this classic Lisfranc injury connects which two osseous structures?

Explanation

The Lisfranc ligament is a strong interosseous ligament that connects the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal. It is critical for the stability of the midfoot arch. Disruption leads to diastasis between the first and second rays. The 'Fleck sign' represents a bony avulsion of this ligament from the base of the second metatarsal.

Question 39

A 28-year-old male sustains a vertically oriented (Pauwels Type III, 70-degree angle) femoral neck fracture. To minimize the high risk of shear failure and nonunion, which of the following internal fixation constructs provides the greatest biomechanical stability for this specific fracture pattern?

Explanation

Pauwels Type III femoral neck fractures have a high vertical shear angle (>50 degrees), placing them at extremely high risk for varus collapse and nonunion. Biomechanical studies have consistently shown that a fixed-angle device, such as a sliding hip screw (SHS), provides superior resistance to vertical shear forces compared to three parallel cannulated screws. The addition of a derotational screw above the SHS lag screw controls rotational instability.

Question 40

A 65-year-old male presents with acute onset of extreme left knee pain, swelling, and fevers over the last 3 days. He underwent an uncomplicated total knee arthroplasty of the left knee 4 years ago. Joint aspiration yields synovial fluid with a WBC count of 75,000 cells/µL and 92% neutrophils. The implant is radiographically well-fixed. What is the most appropriate surgical management?

Explanation

This patient has an acute hematogenous periprosthetic joint infection (PJI), defined as acute onset of symptoms (usually < 3 weeks) in a previously asymptomatic, well-functioning, and well-fixed joint. The standard of care for acute hematogenous PJI is DAIR (Debridement, Antibiotics, and Implant Retention), which includes exchanging the modular polyethylene liner to thoroughly lavage the posterior joint space and reduce the biofilm burden.

Question 41

A 10-year-old boy presents with bilateral slipped capital femoral epiphyses (SCFE). His weight is in the 40th percentile. Which of the following endocrine disorders is most commonly associated with this presentation?

Explanation

Hypothyroidism is the most common endocrine disorder associated with SCFE, particularly in patients presenting outside the typical age range (under 10 or over 16) or with atypical body habitus (e.g., non-obese). Endocrine workup is highly recommended for SCFE in these patient demographics or when bilateral involvement is present at initial presentation.

Question 42

A 15-year-old boy is diagnosed with conventional osteosarcoma of the distal femur. A detailed family history reveals that his mother died of breast cancer at age 35, and his sister was treated for childhood leukemia. A germline mutation in which of the following genes is most likely responsible for this familial cancer syndrome?

Explanation

The clinical picture describes Li-Fraumeni syndrome, an autosomal dominant disorder characterized by a high incidence of childhood and early adult tumors, including osteosarcoma, breast cancer, leukemia, and soft tissue sarcomas. It is caused by a germline mutation in the TP53 tumor suppressor gene. RB1 mutations are associated with hereditary retinoblastoma, which also increases osteosarcoma risk, but does not fit the multi-tumor profile seen here.

Question 43

In total hip arthroplasty, highly cross-linked polyethylene (HXLPE) has significantly reduced the rate of osteolysis compared to conventional ultra-high molecular weight polyethylene (UHMWPE). What is the primary mechanism by which vitamin E is utilized during the manufacturing of modern HXLPE?

Explanation

Highly cross-linked polyethylene is manufactured using radiation to create cross-links that improve wear resistance, but this process generates free radicals. If left untreated, these free radicals react with oxygen, leading to oxidation and subsequent degradation of the polymer. Vitamin E (alpha-tocopherol) is an antioxidant added to HXLPE to quench these free radicals, thereby preventing oxidation without the need for post-irradiation remelting, which can decrease mechanical strength.

Question 44

During an exploration of a Zone II flexor tendon injury, the anatomical relationship of the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) is evaluated. At what anatomical level does the FDS tendon bifurcate to allow the FDP tendon to pass superficially?

Explanation

The FDS tendon bifurcates at the level of the A1 pulley, allowing the FDP to pass superficially. The two slips of the FDS then reunite dorsal to the FDP tendon at Camper's chiasm, which is located at the level of the A2 pulley, before finally inserting on the middle phalanx.

Question 45

A 65-year-old man with lumbar spinal stenosis experiences relief of neurogenic claudication symptoms when leaning forward on a shopping cart. What is the primary biomechanical reason for this improvement in symptoms?

Explanation

In lumbar spinal stenosis, spinal extension leads to buckling of the hypertrophied ligamentum flavum into the spinal canal, decreasing the cross-sectional area and exacerbating neurogenic claudication. Flexion stretches the ligamentum flavum ('unbuckling' it) and increases the canal's cross-sectional area, providing symptomatic relief (the 'shopping cart' sign).

Question 46

In a patient with an anteroposterior compression (APC) type II pelvic ring injury, which of the following ligaments remains primarily intact, preventing vertical instability?

Explanation

In the Young-Burgess classification, an APC II injury involves disruption of the symphysis pubis, as well as the anterior sacroiliac, sacrospinous, and sacrotuberous ligaments, causing rotational instability ('open book'). However, the strong posterior sacroiliac ligaments remain intact, providing vertical stability to the hemipelvis. An APC III injury involves disruption of the posterior sacroiliac ligaments as well, leading to both rotational and vertical instability.

Question 47

A 55-year-old diabetic patient presents with a red, hot, swollen foot. Radiographs show periarticular osteopenia, debris, and fragmentation of the midfoot without frank dislocation. According to the Eichenholtz classification, what is the most appropriate initial management?

Explanation

The patient is in Eichenholtz Stage I (Development/Fragmentation) of Charcot arthropathy, characterized by a red, hot, swollen foot, joint laxity, subluxation, and radiographic fragmentation. The standard of care for acute Stage I Charcot is immobilization and offloading, typically using a total contact cast (TCC), until the foot progresses through Stage II (Coalescence) to Stage III (Consolidation).

Question 48

A 22-year-old football player undergoes arthroscopy for recurrent anterior shoulder instability. The surgeon identifies an anterior capsulolabral injury where the labrum is stripped from the glenoid, but the underlying periosteum remains intact, allowing the labrum to displace medially and inferiorly. What is the specific term for this lesion?

Explanation

An ALPSA (Anterior Labroligamentous Periosteal Sleeve Avulsion) lesion occurs when the anterior labrum is avulsed from the glenoid, but the anterior scapular periosteum remains intact, allowing the labrum to heal in a medially and inferiorly displaced position. A Perthes lesion also features an intact periosteum, but the labrum is not medially displaced. A classic Bankart involves complete disruption of the periosteum.

Question 49

During a direct anterior approach for a total hip arthroplasty, the surgeon develops the superficial internervous plane between the sartorius and the tensor fasciae latae (TFL). What are the respective motor innervations of these two muscles?

Explanation

The direct anterior approach (Smith-Petersen) to the hip utilizes a true internervous plane. Superficial to the fascia, the plane is between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (TFL, innervated by the superior gluteal nerve). Deep to the fascia, the plane is between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 50

According to Perren's strain theory of bone healing, the mechanical environment dictates the type of tissue that forms in a fracture gap. At a strain level of approximately 5%, which of the following tissues is expected to primarily form?

Explanation

Perren's strain theory states that tissues cannot form if the strain exceeds their tolerance limit. Granulation tissue can tolerate high strain (up to 100%). Fibrocartilage tolerates intermediate strain (up to 10%). Woven bone tolerates low strain (up to 2%). Thus, at a strain of 5%, fibrocartilage (cartilaginous callus) will form because the strain is too high for bone formation but within the tolerance of cartilage.

Question 51

A 30-year-old man sustains a closed tibial shaft fracture. Two hours later, he develops severe pain out of proportion to the injury. Which of the following objective measurements is the most accepted threshold to perform an emergent fasciotomy for acute compartment syndrome?

Explanation

The Delta P (Diastolic blood pressure minus compartment pressure) is the most reliable objective indicator for compartment syndrome. A Delta P of less than 30 mm Hg is an absolute indication for emergent fasciotomy. Absolute pressure readings can be misleading, as tissue perfusion depends on the pressure gradient, especially in hypotensive patients.

Question 52

A 2-year-old child presents with bilateral genu varum. Standing radiographs reveal a metaphyseal-diaphyseal angle (Drennan angle) of 20 degrees. Based on this finding, what is the most appropriate management?

Explanation

The patient has infantile Blount's disease. The metaphyseal-diaphyseal (Drennan) angle helps differentiate physiological bowing (<11 degrees) from infantile Blount's. An angle > 16 degrees suggests a very high likelihood of progression to Blount's disease. For a child under 3 years old with early Langenskiöld stages (I-II) and a high Drennan angle, bracing (KAFO) is the initial treatment of choice. Surgery is indicated if bracing fails or if the child is > 3-4 years old.

Question 53

A 35-year-old woman is diagnosed with a large, unresectable Giant Cell Tumor of the sacrum. Her oncologist prescribes Denosumab. What is the specific mechanism of action of this medication in the treatment of Giant Cell Tumor of bone?

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). In Giant Cell Tumor of bone, the neoplastic mononuclear cells express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) that cause the massive bone destruction. By inhibiting RANKL, Denosumab prevents the formation and function of these giant cells, leading to tumor consolidation and ossification.

Question 54

During the physical examination of a patient with severe cubital tunnel syndrome, the examiner observes that the patient's small finger rests in a persistently abducted position. This finding (Wartenberg's sign) is caused by the unopposed action of which muscle?

Explanation

Wartenberg's sign is the persistent abduction of the small finger seen in severe ulnar neuropathy. It occurs because the ulnar-innervated third palmar interosseous muscle (which normally adducts the small finger) is weak, leaving the radial-innervated extensor digiti minimi (and the extensor digitorum communis to the small finger) unopposed. These extensors have a naturally abducted line of pull.

Question 55

In the application of orthopedic implants, mixing a titanium screw with a stainless steel plate is generally avoided to prevent galvanic corrosion. In this specific bimetallic coupling, which of the following accurately describes the electrochemical roles of the two metals?

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic solution (like body fluid). The more noble (less reactive) metal acts as the cathode, while the less noble (more reactive) metal acts as the anode and undergoes accelerated corrosion. Titanium is more noble than stainless steel; therefore, in a titanium-stainless steel coupling, the stainless steel acts as the anode and preferentially corrodes.

Question 56

During a posterior-stabilized total knee arthroplasty, the knee is well-balanced and stable in full extension, but the flexion gap is unacceptably tight. Which of the following surgical steps is the most appropriate to increase the flexion gap without altering the extension gap?

Explanation

A tight flexion gap with a balanced extension gap can be corrected by downsizing the femoral component. When using a posterior referencing system, downsizing the femur removes more posterior condylar bone, effectively increasing the flexion gap without affecting the distal femoral cut (which controls the extension gap). Increasing the posterior tibial slope also selectively increases the flexion gap, but 'decreasing' it would tighten it. A thinner PE insert would undesirably loosen the extension gap.

Question 57

The Lisfranc ligament is a critical stabilizing structure of the midfoot. Which of the following best describes its exact anatomical attachments?

Explanation

The Lisfranc ligament is a strong interosseous ligament that runs from the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal, specifically located on the plantar aspect. There is no direct ligamentous connection between the base of the first and second metatarsals, making the Lisfranc ligament crucial for stabilizing the second metatarsal in its keystone position.

Question 58

A 4-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). At the follow-up visit, the parents report that the child has stopped kicking the leg on the affected side. On examination, the infant lacks active knee extension on that side. This complication is most likely due to which of the following improper harness settings?

Explanation

The infant has developed a femoral nerve palsy, which presents as a loss of active knee extension (decreased kicking). In the setting of Pavlik harness treatment, this is almost exclusively caused by excessive flexion of the hip (hyperflexion), which compresses the femoral nerve against the inguinal ligament. The treatment is to loosen the anterior straps or temporarily remove the harness until nerve function returns. Excessive abduction, conversely, leads to avascular necrosis of the femoral head.

Question 59

During an anterior cruciate ligament (ACL) reconstruction, the surgeon positions the femoral tunnel too anteriorly (shallow) within the intercondylar notch. What is the expected biomechanical consequence of this malpositioned tunnel during knee range of motion?

Explanation

In ACL reconstruction, placing the femoral tunnel too anteriorly (i.e., too shallow or high in the notch when viewed arthroscopically) increases the distance between the tibial and femoral attachment sites as the knee flexes. This results in a graft that is loose in extension and tightens excessively in flexion, potentially leading to a loss of knee flexion or graft stretching/failure. Placing the femoral tunnel too posterior (deep) results in the opposite: tight in extension and loose in flexion.

Question 60

A 12-year-old girl with adolescent idiopathic scoliosis (AIS) presents with a right thoracic curve. Which of the following factors is the most reliable predictor of future curve progression in this patient?

Explanation

The two most important overall predictors of curve progression in adolescent idiopathic scoliosis (AIS) are the magnitude of the curve at the time of diagnosis and the growth potential of the patient (indicated by age, menarchal status, and Risser sign). A larger curve magnitude at initial presentation correlates directly with a higher risk of relentless progression.

Question 61

During the insertion of a cortical screw for fracture fixation, the surgeon wishes to maximize the pullout strength of the construct. According to biomechanical principles, increasing which of the following screw parameters will have the greatest effect on maximizing pullout strength?

Explanation

The outer thread diameter is the most important factor in determining the pullout strength of a screw. Pullout strength is directly proportional to the outer diameter, thread engagement length, and the shear strength of the bone.

Question 62

A diaphyseal radius fracture is treated with open reduction and internal fixation using a dynamic compression plate, achieving absolute mechanical stability. Which of the following best describes the predominant mechanism of bone healing expected in this scenario?

Explanation

Primary bone healing occurs when there is absolute stability and no gap at the fracture site, proceeding without callus formation. It relies on direct remodeling by osteoclastic cutting cones followed by osteoblast-mediated bone deposition.

Question 63

A surgeon is considering mixing different metallic implants in a single surgical site. To prevent severe galvanic corrosion, which of the following combinations of metals should be strictly avoided due to their significant differences in anodic/cathodic potential?

Explanation

Mixing stainless steel and cobalt-chromium in the same electrolyte environment can result in severe galvanic corrosion, particularly degrading the stainless steel. Titanium and cobalt-chromium can occasionally be used together with less risk, but stainless steel mixed with other alloys should be avoided.

Question 64

A pediatric patient presents with bone pain, petechiae, and characteristic radiographic findings of "pelvic bone" and "Wimberger ring" signs. The underlying metabolic defect in this patient's condition directly impairs which of the following cellular processes?

Explanation

The patient has scurvy (Vitamin C deficiency). Vitamin C is an essential cofactor for prolyl and lysyl hydroxylases, and its absence prevents proper hydroxylation and subsequent cross-linking of collagen fibers.

Question 65

Tranexamic acid (TXA) is routinely utilized in total joint arthroplasty to reduce perioperative blood loss. Which of the following best describes its specific mechanism of action?

Explanation

TXA is a synthetic analog of the amino acid lysine. It reversibly and competitively binds to the lysine receptor sites on plasminogen, preventing its activation into the fibrinolytic enzyme plasmin.

Question 66

Nitrogen-containing bisphosphonates are a primary pharmacological treatment for osteoclast-mediated bone loss. They achieve their effect primarily by inhibiting which of the following?

Explanation

Nitrogen-containing bisphosphonates (like alendronate and zoledronate) inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents protein prenylation, ultimately leading to osteoclast apoptosis.

Question 67

When a tensile force is applied to a normal ligament, the initial "toe region" observed on its stress-strain curve represents which of the following biomechanical phenomena?

Explanation

The toe region of a ligament or tendon stress-strain curve occurs at low strains. It corresponds to the physical uncrimping (straightening) of the naturally wavy collagen fibrils before they begin to bear significant tensile load.

Question 68

A 14-year-old boy presents with a destructive, permeative diaphyseal lesion of the femur with an associated soft tissue mass. Biopsy reveals sheets of uniform, small round blue cells. Cytogenetic analysis of this tumor is most likely to reveal which of the following translocations?

Explanation

Ewing sarcoma classically presents as a diaphyseal lesion with small round blue cells. The hallmark genetic mutation is the t(11;22) translocation, which produces the EWS-FLI1 fusion protein.

Question 69

Osteoarthritis is characterized by progressive degeneration of articular cartilage. Which of the following represents the earliest detectable biochemical change in the pathogenesis of osteoarthritis?

Explanation

The earliest biochemical change in osteoarthritic cartilage is an increase in water content due to the disruption of the collagen network. This is subsequently followed by a progressive decrease in proteoglycan concentration.

Question 70

To minimize the complication of stress shielding following cementless total hip arthroplasty, engineers seek biomaterials with mechanical properties similar to host bone. Which of the following implant materials possesses a Young's modulus of elasticity most closely matching that of human cortical bone?

Explanation

Titanium alloy has a Young's modulus (stiffness) closer to that of cortical bone compared to cobalt-chromium or stainless steel. This relative flexibility helps reduce stress shielding around the implant.

Question 71

During intraoperative fluoroscopy, the orthopedic surgeon is exposed to radiation primarily through scatter. Which of the following C-arm configurations most effectively minimizes radiation exposure to the surgeon's eyes and thyroid?

Explanation

Placing the X-ray tube (source) under the operating table and the image intensifier above the patient significantly reduces the amount of scatter radiation directed toward the surgeon's upper body and head.

Question 72

A surgeon uses commercially prepared Demineralized Bone Matrix (DBM) to augment a posterolateral spinal fusion. Based on its biologic properties, DBM functions primarily through which of the following mechanisms?

Explanation

Demineralized bone matrix (DBM) contains a collagen scaffold (osteoconductive) and retains growth factors like BMPs (osteoinductive). Because it is processed and lacks living viable cells, it is not osteogenic.

Question 73

Following a closed humerus fracture, a patient develops a radial nerve palsy. According to the Sunderland classification of nerve injury, a Grade II injury (axonotmesis) is best defined by which of the following?

Explanation

Sunderland Grade II (axonotmesis) involves disruption of the axon and myelin sheath, but the connective tissue framework (endoneurium, perineurium, epineurium) remains intact. This provides a clear tube for axonal regeneration, offering a good prognosis for recovery.

Question 74

Postural muscles, such as the soleus, are uniquely adapted to resist fatigue during prolonged standing. Which of the following profiles best describes the predominant muscle fiber type found in the soleus?

Explanation

The soleus is primarily composed of Type I muscle fibers. Type I fibers are slow-twitch, highly oxidative (aerobic), rich in myoglobin and mitochondria, and highly resistant to fatigue.

Question 75

A randomized controlled trial concludes that there is no difference in functional outcomes between two surgical techniques for rotator cuff repair. The authors report that the study was appropriately powered at 0.80. Statistical power is best defined as the probability of which of the following?

Explanation

Statistical power (1 - Beta) is the probability of correctly rejecting the null hypothesis when a true difference actually exists (when the null hypothesis is false). A power of 0.80 means there is an 80% chance of detecting a significant difference if one truly exists.

Question 76

In the pathogenesis of periprosthetic joint infection (PJI), bacteria such as Staphylococcus epidermidis form robust biofilms. During biofilm maturation, "quorum sensing" plays a critical role. Quorum sensing refers to which of the following processes?

Explanation

Quorum sensing is a chemical communication system utilized by bacteria to detect population density. Once a critical threshold is reached, it triggers the synchronized expression of virulence factors and genes necessary for biofilm maturation.

Question 77

Osteoclasts dissolve the inorganic mineral matrix of bone by creating a localized acidic environment within the Howship lacuna. This active acidification process is primarily mediated by which of the following transporters at the ruffled border?

Explanation

The ruffled border of the osteoclast contains a vacuolar-type H+-ATPase pump that actively transports protons into the resorption pit, lowering the pH to dissolve hydroxyapatite. Carbonic anhydrase II generates the intracellular protons but is not the pump itself.

Question 78

A 30-year-old patient presents with a lytic lesion in the distal femur epiphysis. The lesion is treated with curettage and cementing. Which of the following best describes the classical histological appearance of a Giant Cell Tumor of bone?

Explanation

Giant Cell Tumor of bone is characterized histologically by numerous osteoclast-like multinucleated giant cells scattered evenly throughout a background of plump, neoplastic mononuclear stromal cells. The mononuclear cells express RANKL, driving the formation of the giant cells.

Question 79

Polymethylmethacrylate (PMMA) bone cement is frequently used for implant fixation in joint arthroplasty. Which of the following statements regarding the physical and mechanical properties of PMMA is most accurate?

Explanation

PMMA bone cement acts strictly as a grout, filling voids to create a mechanical interlock between the implant and bone; it has no chemical adhesive properties. It polymerizes via a strongly exothermic reaction and is much stronger in compression than in tension.

Question 80

Bone morphogenetic proteins (BMPs), particularly BMP-2 and BMP-7, are potent stimulators of bone formation. The intracellular signaling cascade initiated by BMP binding to its cell-surface receptor primarily involves the phosphorylation and activation of which of the following?

Explanation

BMPs exert their osteogenic effects by binding to serine/threonine kinase receptors on the cell membrane. This binding directly phosphorylates and activates the intracellular signaling molecules Smad 1, 5, and 8, which then translocate to the nucleus to regulate gene transcription.

Question 81

A 25-year-old male presents with multiple fractures and a history of cranial nerve palsies. Radiographs show a dense, "bone-in-bone" appearance. A defect in which of the following mechanisms is most likely responsible?

Explanation

Osteopetrosis is caused by defective osteoclast function, often due to a deficiency in carbonic anhydrase II. This enzyme is required to generate the hydrogen ions needed to acidify the ruffled border and resorb bone.

Question 82

Which of the following combinations of orthopedic implants poses the highest risk for severe galvanic corrosion if placed in direct physical contact within the body?

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic environment. Stainless steel and titanium have a large difference in their anodic index, leading to significant galvanic corrosion and should not be mixed.

Question 83

A 14-year-old boy presents with an aggressive permeative diaphyseal lesion in his femur with a laminated periosteal reaction. Biopsy reveals sheets of uniform small round blue cells. Which of the following chromosomal translocations is most characteristic of this diagnosis?

Explanation

Ewing sarcoma is classically characterized by the t(11;22) chromosomal translocation, resulting in the EWS-FLI1 fusion protein. It typically presents as a permeative diaphyseal bone lesion in children and young adults.

Question 84

In the management of prosthetic joint infections via debridement and implant retention (DAIR), which of the following antibiotics is essential due to its unique ability to penetrate the glycocalyx biofilm produced by Staphylococcus species?

Explanation

Rifampin is highly lipophilic and has excellent penetration into the glycocalyx biofilm of staphylococcal species. It is a critical adjunctive oral agent used in implant retention protocols after surgical debridement.

Question 85

A 22-year-old male with closed bilateral femur fractures develops hypoxia, confusion, and a petechial rash over his axilla 36 hours after injury. Which of the following is the most critical initial step in the management of this syndrome?

Explanation

Fat embolism syndrome is a clinical diagnosis based on Gurd's criteria, presenting with hypoxemia, neurologic compromise, and petechial rash. The primary treatment is entirely supportive, focusing aggressively on respiratory support and adequate oxygenation.

Question 86

During secondary fracture healing, the process of endochondral ossification requires which of the following critical steps to transition from a soft callus to a hard woven bone callus?

Explanation

Endochondral ossification requires a cartilage intermediate. Hypertrophic chondrocytes within the soft callus undergo apoptosis and release VEGF, which prompts vascular invasion and allows osteoprogenitor cells to enter and form the hard callus.

Question 87

During a direct lateral (deltoid-splitting) approach to the proximal humerus, the distal extent of the deltoid split must be carefully limited to no more than 5 cm distal to the acromion to prevent injury to which of the following structures?

Explanation

The axillary nerve courses circumferentially around the proximal humerus deep to the deltoid muscle, typically 5 to 7 cm distal to the lateral edge of the acromion. Extending a deltoid split beyond this safe zone risks permanent denervation of the anterior deltoid.

Question 88

An 80-year-old man presents with increasing hat size and unilateral hearing loss. Laboratory studies demonstrate markedly elevated serum alkaline phosphatase, with normal calcium and phosphorus. Which of the following describes the primary cellular defect in this condition?

Explanation

Paget's disease of bone is primarily driven by abnormal, enlarged, and highly multinucleated osteoclasts. This leads to a profound increase in bone resorption, followed by a chaotic, compensatory overactivity of osteoblasts producing weak woven bone.

Question 89

A child with short-limbed dwarfism, frontal bossing, and midface hypoplasia is diagnosed with the most common form of skeletal dysplasia. This condition involves a mutation in a gene that primarily affects which zone of the physis?

Explanation

Achondroplasia is caused by an activating mutation in the FGFR3 gene. This mutation specifically inhibits chondrocyte proliferation, thereby disrupting the proliferative zone of the physis and impairing endochondral ossification.

Question 90

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

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively and reversibly inhibits the activation of plasminogen to plasmin, thereby preventing the degradation of fibrin clots (fibrinolysis).

Question 91

A 16-year-old male receives neoadjuvant chemotherapy for a conventional high-grade osteosarcoma of the distal femur. Which of the following factors obtained from the definitive surgical resection specimen is the most important prognostic indicator for overall survival?

Explanation

In conventional high-grade osteosarcoma, the histologic response to neoadjuvant chemotherapy is the single most important prognostic indicator. Greater than 90% tumor necrosis in the resected specimen correlates with significantly improved long-term survival.

Question 92

A 55-year-old diabetic patient presents with rapid onset of severe leg pain out of proportion to examination findings, swelling, and early bullae formation. Non-contrasted imaging shows gas in the soft tissues. What is the most critical intervention?

Explanation

Necrotizing fasciitis is a rapid-onset, life-threatening surgical emergency. While antibiotics are necessary, the cornerstone of definitive treatment is immediate, radical surgical debridement of all nonviable fascia and soft tissue.

Question 93

In the development of acute compartment syndrome, which of the following pathophysiologic events is the initial step that triggers the cascade leading to muscle and nerve ischemia?

Explanation

The pathophysiology of compartment syndrome begins when intracompartmental interstitial pressure rises above venous capillary pressure. This causes venous outflow obstruction, creating a vicious cycle of increasing pressure that ultimately compromises arteriolar microcirculation.

Question 94

Which of the following mechanisms of joint lubrication is most critical in protecting articular hyaline cartilage under conditions of high physiological load and very low speeds (e.g., prolonged standing)?

Explanation

Boundary lubrication occurs under high loads and low speeds where joint surfaces are nearly in direct physical contact. It relies on a monomolecular layer of surface-active glycoproteins, primarily lubricin (PRG4), binding directly to the articular surface.

Question 95

A 50-year-old patient with end-stage renal disease exhibits classic signs of renal osteodystrophy. Laboratory results show hyperphosphatemia, hypocalcemia, and elevated parathyroid hormone (PTH). This secondary hyperparathyroidism is primarily triggered by the kidneys' inability to perform which function?

Explanation

In chronic kidney disease, the failing kidneys lose 1-alpha-hydroxylase activity, halting the conversion of 25(OH)D into active 1,25(OH)2D (calcitriol). The resulting lack of gastrointestinal calcium absorption causes hypocalcemia, which continuously stimulates PTH release.

Question 96

During the remodeling phase of ligament healing, the tensile strength of the repair tissue gradually increases over months. Which of the following biochemical changes is primarily responsible for this improvement?

Explanation

The initial proliferative phase of ligament healing produces a weak, disorganized matrix composed largely of Type III collagen. During remodeling, this is slowly replaced by longitudinally oriented, highly cross-linked Type I collagen, restoring tensile strength.

Question 97

A 35-year-old male is brought to the trauma bay after a high-speed collision. He has flaccid paralysis and absent reflexes below C6. He is currently hypotensive (BP 80/40) and bradycardic (HR 45). Which of the following findings confirms neurogenic shock rather than isolated spinal shock?

Explanation

Neurogenic shock is a true hemodynamic disturbance caused by the loss of descending sympathetic tone, leading to unchecked vagal activity (bradycardia) and loss of vascular resistance (hypotension). Spinal shock refers solely to the temporary loss of somatic and autonomic reflexes below the level of injury.

Question 98

A 65-year-old man with multiple myeloma presents with a solitary "punched-out" lytic lesion in his L4 vertebral body. The extensive focal osteolysis seen in this disease process is primarily mediated by myeloma cells secreting which of the following?

Explanation

Myeloma cells induce uncoupled bone turnover by secreting osteoclast-activating factors such as RANKL, MIP-1 alpha, and IL-6. This directly stimulates aggressive local osteoclastic bone resorption while simultaneously suppressing osteoblast activity.

Self Assessment Examination Adult S Review | Dr Hutaif - ...

Free Orthopedics Review | Dr Hutaif General Orthopedics -...

Key Takeaway

Free Orthopedics Review | Dr Hutaif General Orthopedics -...

Chapter Index