What is the most likely reason open fractures tend to heal more slowly than closed fractures?

Loss of osteoinductive potential from the hematoma that is lost around the fracture

A patient who underwent an L5-S1 hemilaminotomy and partial diskectomy for radiculopathy 3 weeks ago now reports increasing leg and back pain with radicular signs. An axial T2-weighted MRI scan is shown in Figure 97a, an axial T1-weighted MRI scan is

Revision laminotomy and diskectomy

After making a tackle, a football player is found prone and unconscious without spontaneous respirations. Initial management should consist of

head and neck stabilization, log roll to a supine position, face mask removal, and initiation of assisted breathing.

In patients with displaced radial neck fractures treated with open reduction and internal fixation with a plate and screws, the plate must be limited to what surface of the radius to avoid impingement on the proximal ulna?

Within a 90-degree arc or safe zone

A 52-year-old woman with a 2-year history of a flexible (stage II) adult-acquired flatfoot deformity has failed to respond to nonsurgical management consisting of immobilization, custom orthotics, nonsteroidal anti-inflammatory drugs, and physical th

Tendon transfer, lateral column lengthening, medial column arthrodesis, and heel cord lengthening

A 61-year-old woman with a long-standing history of rheumatoid arthritis reports progressive elbow pain for the past 12 months. She denies any recent trauma to the elbow; however, she notes increasing pain and decreased joint motion that are now comp

Semiconstrained total elbow arthroplasty

Orthopedics Hyperguide Review: General Ortho MCQs

Question 1

An 11-year-old boy presents with progressive diaphyseal thigh pain. Radiographs reveal a permeative destructive lesion with an 'onion-skin' periosteal reaction. Biopsy shows small blue round cells. Which of the following chromosomal translocations is most characteristic of this pathology?

Explanation

Ewing sarcoma is characterized by the t(11;22) translocation in approximately 85% of cases, resulting in the EWS-FLI1 fusion protein. t(X;18) is associated with Synovial sarcoma. t(9;22) can be seen in the Philadelphia chromosome (CML) and some mesenchymal chondrosarcomas. t(2;13) is characteristic of Alveolar rhabdomyosarcoma. t(12;16) is found in Myxoid liposarcoma.

Question 2

In articular cartilage, which collagen type primarily provides the tensile strength, and what is the primary proteoglycan responsible for compressive strength?

Explanation

Articular cartilage is primarily composed of water. Its solid matrix consists mainly of Type II collagen, which is distributed to resist shear and provide tensile strength, and proteoglycans. Aggrecan is the primary proteoglycan; it binds to hyaluronic acid and traps water, providing compressive strength through osmotic swelling pressure.

Question 3

A 13-year-old obese male presents with knee pain and a limp. Examination shows obligatory external rotation of the hip during passive flexion. He is diagnosed with a stable Slipped Capital Femoral Epiphysis (SCFE). What is the primary blood supply at risk during in situ pinning of this condition?

Explanation

The medial femoral circumflex artery (MFCA) provides the primary blood supply to the femoral head in adolescents and adults. Its deep branch gives rise to the lateral epiphyseal (retinacular) vessels, which are critically vulnerable during both the natural progression of SCFE and its surgical fixation, risking avascular necrosis (AVN).

Question 4

A 28-year-old male sustains a closed tibial shaft fracture. Two hours post-injury, he develops severe leg pain out of proportion to the injury. Which of the following parameters is the most reliable threshold for diagnosing acute compartment syndrome and indicating a fasciotomy?

Explanation

The differential pressure (Delta P) between diastolic blood pressure and compartment pressure is the most reliable objective indicator for acute compartment syndrome. A Delta P of less than 30 mmHg correlates with significant muscle ischemia and is the standard threshold indicating the need for emergent fasciotomy.

Question 5

During anterior cruciate ligament (ACL) reconstruction using a hamstring autograft, graft healing within the osseous tunnel primarily occurs via which of the following mechanisms?

Explanation

Soft tissue grafts (such as hamstring or quadriceps tendons) heal in bone tunnels via indirect insertion, which is characterized by the formation of Sharpey-like penetrating collagen fibers extending from the surrounding bone into the graft. This typically takes 8-12 weeks and differs from the direct bone-to-bone healing seen with bone-patellar tendon-bone (BPTB) grafts.

Question 6

In total hip arthroplasty, which of the following combinations of bearing surfaces exhibits the lowest volumetric wear rate in vitro?

Explanation

Ceramic-on-ceramic bearing surfaces are exceptionally hard, scratch-resistant, and hydrophilic, leading to the lowest volumetric wear rates in vitro (often <0.1 mm^3/million cycles). This is vastly superior to metal-on-polyethylene and even highly cross-linked polyethylene pairings.

Question 7

A 65-year-old male with long-standing rheumatoid arthritis presents with progressive clumsiness in his hands and a wide-based gait. Cervical flexion and extension radiographs show an anterior atlantodens interval (ADI) of 8 mm. What is the most critical radiographic measurement to evaluate the risk of neurologic progression?

Explanation

In the setting of atlantoaxial subluxation, the posterior atlantodens interval (PADI)—also known as the space available for the cord (SAC)—is the most critical and reliable predictor of neurologic deficit. A PADI of <14 mm is highly correlated with the development of myelopathy and is an absolute indication for surgery.

Question 8

The Lisfranc ligament is a critical stabilizing structure of the midfoot. Between which two osseous structures does the primary band of the Lisfranc ligament course?

Explanation

The Lisfranc ligament is a stout interosseous ligament that connects the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal. Notably, there is no direct ligamentous connection between the bases of the first and second metatarsals, making this interval inherently vulnerable to injury.

Question 9

A 24-year-old man falls on an outstretched hand and sustains a fracture of the scaphoid proximal pole. He is treated with cast immobilization. Why is this specific fracture pattern at a high risk for avascular necrosis and nonunion?

Explanation

The scaphoid receives its primary blood supply from the dorsal carpal branch of the radial artery. The vessels enter the bone distally (at the dorsal ridge near the waist) and flow in a retrograde fashion to supply the proximal pole. Fractures at the proximal pole effectively sever this retrograde flow, leading to very high rates of avascular necrosis and nonunion.

Question 10

According to the Musculoskeletal Infection Society (MSIS) criteria, which of the following is considered a definitive major criterion for diagnosing a periprosthetic joint infection (PJI)?

Explanation

The MSIS major criteria for definitive PJI are: 1) A sinus tract communicating with the prosthesis, OR 2) A pathogen isolated by culture from at least two separate tissue or fluid samples obtained from the affected joint. Elevated inflammatory markers, elevated synovial WBCs, and a single positive culture are all considered minor criteria.

Question 11

A patient with a history of multiple low-energy fractures and a 'rugger-jersey' spine appearance on plain radiographs is diagnosed with a metabolic bone disorder. This condition is primarily characterized by a defect in which of the following cellular mechanisms?

Explanation

The patient has Osteopetrosis (Albers-Schönberg disease), characterized by dense, brittle bones and a 'rugger-jersey' spine. It is caused by impaired osteoclast function. Mutations affecting the proton pump (TCIRG1), chloride channel (CLCN7), or carbonic anhydrase II impair the formation of the acidic microenvironment needed at the osteoclast ruffled border for bone resorption.

Question 12

A 35-year-old male sustains a closed mid-shaft humerus fracture and is noted to have a radial nerve palsy on initial presentation. He is managed non-operatively in a functional brace. At 12 weeks, there is no clinical or electromyographic (EMG) evidence of nerve recovery. What is the most appropriate next step in management?

Explanation

Radial nerve palsy associated with a closed humeral shaft fracture is initially managed expectantly, as up to 90% recover spontaneously. However, if there is no clinical or EMG evidence of reinnervation by 12 weeks (3 months), surgical exploration of the radial nerve is indicated to evaluate for entrapment, severe laceration, or neuroma formation.

Question 13

Biomechanically, how does a locked plating system primarily provide stability to a fracture compared to a conventional compression plating system?

Explanation

Locked plating systems function as single-beam, fixed-angle constructs. The screw heads thread directly into the plate, locking them together. This relies on the threaded screw-plate interface for stability rather than relying on friction generated by compressing the plate against the bone surface, which is the mechanism of conventional non-locked plates.

Question 14

Low molecular weight heparin (LMWH) is frequently used for venous thromboembolism (VTE) prophylaxis following total joint arthroplasty. What is the primary molecular target through which LMWH exerts its anticoagulant effect?

Explanation

LMWH binds to antithrombin, inducing a conformational change that dramatically accelerates its ability to inactivate coagulation factors, primarily Factor Xa. Unlike unfractionated heparin, LMWH chains are too short to efficiently bridge antithrombin to thrombin (Factor IIa), giving it a much higher anti-Xa to anti-IIa activity ratio.

Question 15

Which bone morphogenetic protein (BMP) is an FDA-approved osteoinductive agent commonly used in anterior lumbar interbody fusion (ALIF), and which cell surface receptor type does it primarily bind to?

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for ALIF procedures (delivered via an absorbable collagen sponge). BMPs are part of the TGF-beta superfamily and exert their cellular effects by binding to transmembrane serine/threonine kinase receptors (Types I and II), which subsequently phosphorylate intracellular Smad proteins to alter gene transcription.

Question 16

A 42-year-old male sustains a Gustilo-Anderson IIIB open fracture of the middle third of the tibia. After serial debridements and external fixation, a 6 cm soft tissue defect with exposed bone remains. Which of the following is the most appropriate local muscle flap for coverage of this specific defect?

Explanation

The lower extremity is historically divided into thirds for flap coverage. Proximal third defects are covered by the gastrocnemius flaps. Middle third defects of the tibia are classically covered by a proximally based soleus muscle flap. Distal third defects lack adequate local muscle bulk and typically require a free tissue transfer or a reverse sural artery flap.

Question 17

In an anteroposterior compression type II (APC-II) pelvic ring injury, which of the following sets of ligaments are characteristically ruptured?

Explanation

An APC-II injury (an 'open book' pelvis) involves the rupture of the anterior symphyseal ligaments, the pelvic floor ligaments (sacrospinous and sacrotuberous), and the anterior sacroiliac ligaments. Crucially, the strong posterior sacroiliac ligaments remain intact, providing vertical stability but allowing significant rotational instability.

Question 18

A 4-month-old female is diagnosed with Developmental Dysplasia of the Hip (DDH). During an ultrasound evaluation, the alpha angle is measured. In the Graf classification, what does the alpha angle represent, and what is the normal value in a mature infant hip?

Explanation

In Graf's ultrasound classification for DDH, the alpha angle measures the osseous (bony) roof of the acetabulum (the concavity of the iliac bone). A normal alpha angle (representing a Type I hip) is 60 degrees or greater. The beta angle measures the cartilaginous roof.

Question 19

During the endochondral ossification phase of secondary fracture healing, which factor secreted by hypertrophic chondrocytes is most responsible for triggering vascular invasion into the cartilaginous callus?

Explanation

During endochondral ossification, hypertrophic chondrocytes secrete Vascular Endothelial Growth Factor (VEGF), which is essential for angiogenesis. The invasion of blood vessels brings osteoprogenitor cells and osteoclasts into the cartilaginous callus, triggering chondrocyte apoptosis and the replacement of cartilage with woven bone.

Question 20

A 22-year-old overhead athlete presents with chronic anterior shoulder instability. MRI reveals a Bankart lesion and a significant engaging Hill-Sachs defect. The surgeon performs an arthroscopic Bankart repair with a Remplissage procedure. Which structure is tenodesed into the Hill-Sachs defect during a Remplissage?

Explanation

The Remplissage procedure (French for 'to fill') involves a capsulotenodesis where the posterior joint capsule and the infraspinatus tendon are secured into the Hill-Sachs defect on the posterolateral humeral head. This renders the bony defect extra-articular, preventing it from engaging the anterior glenoid rim during abduction and external rotation.

Question 21

Viscoelastic materials exhibit time-dependent deformation. A surgeon applies a dynamic splint to a contracted joint, keeping the force constant while the tissue slowly lengthens. What viscoelastic property does this demonstrate?

Explanation

Creep is the progressive deformation of a material under a constant load over time. Stress relaxation, in contrast, is the decrease in stress over time when the material is held at a constant strain (deformation).

Question 22

In normal adult articular cartilage, which zone is characterized by the highest concentration of proteoglycans and the lowest concentration of water?

Explanation

The deep (radial) zone of articular cartilage has the highest proteoglycan content and the lowest water concentration. The superficial zone has the highest water and lowest proteoglycan concentration, with collagen fibers oriented parallel to the joint surface to resist shear forces.

Question 23

Mixing dissimilar metals in an orthopedic implant construct, such as utilizing a stainless steel screw through a titanium plate, primarily increases the risk of which type of corrosion?

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within an electrolytic medium (like body fluid), leading to accelerated corrosion of the less noble metal.

Question 24

A patient sustains a closed midshaft humerus fracture and presents with an immediate wrist drop. Electromyography (EMG) performed at 4 weeks shows fibrillation potentials but no voluntary motor unit action potentials. What is the most likely peripheral nerve injury grade according to the Seddon classification?

Explanation

Axonotmesis involves disruption of the axon and myelin sheath but preservation of the connective tissue framework (epineurium, perineurium, and endoneurium). EMG at 4 weeks showing denervation changes (fibrillations) without voluntary potentials confirms axonal disruption. Recovery is expected at approximately 1mm/day. Neurapraxia would typically not show fibrillations.

Question 25

Tranexamic acid (TXA) is frequently used in major orthopedic surgeries to reduce blood loss. What is its exact 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 to plasmin, thereby inhibiting fibrinolysis.

Question 26

Which of the following is considered the most reliable and significant prognostic factor for long-term survival in patients with high-grade conventional osteosarcoma?

Explanation

The percentage of tumor necrosis following neoadjuvant chemotherapy (specifically >90% necrosis representing a 'good responder') is one of the most reliable and significant prognostic indicators for long-term survival in high-grade osteosarcoma.

Question 27

A 24-year-old male is admitted with bilateral closed femur fractures. On hospital day 2, he develops confusion, a petechial rash on his axilla, and significant hypoxia. Which of the following is the most appropriate initial management for his condition?

Explanation

The patient is presenting with the classic triad of Fat Embolism Syndrome (FES): hypoxemia, neurologic abnormalities, and a petechial rash. The mainstay of treatment is supportive care, ensuring adequate oxygenation and ventilation, and maintaining hemodynamics. Heparin, dextran, and corticosteroids are not indicated as primary treatment for established FES.

Question 28

Low-molecular-weight heparin (LMWH) is commonly prescribed for deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty. LMWH exerts its primary anticoagulant effect by binding to antithrombin III, which predominantly inactivates which of the following?

Explanation

LMWH binds to antithrombin III and primarily accelerates the inactivation of Factor Xa. Due to its shorter chain length compared to unfractionated heparin, it has much less inhibitory effect on Factor IIa (thrombin).

Question 29

Which of the following fracture patterns in a 6-month-old child has the highest specificity for non-accidental trauma (child abuse)?

Explanation

Posterior rib fractures are highly specific for non-accidental trauma in infants, usually resulting from squeezing the child's chest. Metaphyseal corner fractures and scapular fractures are also highly specific. Clavicle and linear skull fractures are common in accidental trauma, and a spiral tibial fracture is common in walking toddlers (though suspicious in a 6-month-old, posterior rib fractures carry higher inherent specificity).

Question 30

A 65-year-old patient presents with an acutely swollen and painful prosthetic knee 4 years after index arthroplasty. Aspiration yields cloudy fluid. Which of the following synovial fluid analysis results most strongly suggests chronic prosthetic joint infection (PJI)?

Explanation

In chronic prosthetic joint infections (more than 4-6 weeks out), the threshold for diagnosing PJI is generally lower than native joints (often >3,000 cells/mcL and >80% PMNs depending on criteria). A WBC of 25,000 with 85% PMNs is highly suggestive of PJI. Native septic arthritis typically requires a WBC > 50,000.

Question 31

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Which of the following is a key intracellular signaling molecule directly activated by BMP receptors?

Explanation

BMPs bind to serine/threonine kinase cell surface receptors, which phosphorylate intracellular Smad proteins (specifically R-Smads 1, 5, and 8). These then form a complex with Smad4, translocate to the nucleus, and regulate the transcription of osteogenic genes such as Runx2.

Question 32

In the classical phases of wound healing, which cell type becomes the predominant cell in the wound bed 48 to 72 hours post-injury?

Explanation

Neutrophils are the first inflammatory cells to arrive (within 24 hours). Macrophages migrate into the wound after 48-72 hours, becoming the predominant cell type and orchestrating the transition to the proliferative phase by releasing cytokines (e.g., TGF-beta, PDGF). Fibroblasts predominate later (days 3-5).

Question 33

A patient suffers a penetrating trauma to the spinal cord resulting in Brown-Séquard syndrome. Clinical examination below the level of the lesion will typically demonstrate:

Explanation

Brown-Séquard syndrome (hemisection of the spinal cord) causes ipsilateral loss of motor function (corticospinal tract) and proprioception/vibration (dorsal columns), and contralateral loss of pain and temperature sensation (spinothalamic tract, which decussates 1-2 levels above entry).

Question 34

In the pathogenesis of Rheumatoid Arthritis, the interaction between RANKL and RANK leads to characteristic periarticular bone erosions. Which cell type is the primary source of RANKL in the inflamed rheumatoid synovium?

Explanation

In Rheumatoid Arthritis, the inflamed synovium (pannus) is rich in synovial fibroblasts and activated T-lymphocytes, both of which secrete copious amounts of RANKL. This drives massive local osteoclastogenesis and the characteristic marginal bone erosions.

Question 35

Achondroplasia is the most common form of short-limb dwarfism. The underlying genetic mutation primarily affects which process of bone formation?

Explanation

Achondroplasia is caused by an activating mutation in FGFR3, which inhibits chondrocyte proliferation in the proliferative zone of the physis, thereby stunting endochondral ossification. Intramembranous ossification is relatively unaffected, leading to a normal-sized or enlarged calvaria.

Question 36

A 14-year-old boy presents with severe, progressive right groin pain that is distinctly worse at night and dramatically relieved by NSAIDs. Imaging shows a 1cm radiolucent nidus surrounded by reactive sclerosis in the femoral neck. If this untreated lesion is located within the hip joint capsule, which of the following complications is most likely?

Explanation

An intra-articular osteoid osteoma (such as in the femoral neck/hip) can cause an intense inflammatory synovitis mediated by high levels of prostaglandins produced by the nidus. Over time, this leads to cartilage degradation and early-onset secondary osteoarthritis.

Question 37

Which of the following best describes the physiological effect of continuous high-dose administration of Parathyroid Hormone (PTH) on bone remodeling?

Explanation

Continuous high-dose PTH leads to a net increase in bone resorption. PTH receptors are located on osteoblasts (not osteoclasts). The osteoblasts respond to continuous PTH by upregulating RANKL and downregulating OPG, which in turn activates osteoclasts. Intermittent low-dose PTH (e.g., teriparatide), conversely, favors bone formation.

Question 38

According to the Gustilo-Anderson classification, an open tibial shaft fracture with a 12 cm laceration, severe muscle crushing, periosteal stripping, but adequate soft-tissue coverage (bone can be covered without requiring a local or free flap) is classified as:

Explanation

Gustilo-Anderson Type IIIA is a high-energy injury with extensive soft tissue laceration (>10 cm) or adequate soft tissue coverage of the fractured bone despite extensive periosteal stripping. Type IIIB requires a local or free flap for coverage. Type IIIC involves an arterial injury requiring repair.

Question 39

The 'Dial test' is utilized to evaluate posterolateral corner (PLC) instability of the knee. Increased external rotation of the tibia at 30 degrees of flexion, but normal external rotation at 90 degrees of flexion, indicates an isolated injury to which of the following structures?

Explanation

A positive Dial test (>10 degrees of asymmetry in external rotation compared to the contralateral knee) at 30 degrees of flexion with a normal test at 90 degrees indicates an isolated injury to the posterolateral corner (PLC). If the test is positive at both 30 degrees and 90 degrees, it suggests a combined injury to the PLC and the PCL.

Question 40

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates. However, what is a primary mechanical trade-off or disadvantage of increasing the degree of cross-linking in polyethylene?

Explanation

Highly cross-linking polyethylene decreases wear but negatively impacts its mechanical properties, including decreased ultimate tensile strength, fatigue strength, and fracture toughness. This can theoretically increase the risk of component fracture, particularly in thin liners or constrained designs.

Question 41

Increasing the radiation dose to highly cross-link ultra-high molecular weight polyethylene (UHMWPE) in total joint arthroplasty primarily improves wear resistance at the expense of which of the following mechanical properties?

Explanation

Highly cross-linking UHMWPE significantly reduces abrasive wear but diminishes its mechanical properties, particularly fatigue crack propagation resistance and fracture toughness. This increases the risk of component fracture, especially in thin liners.

Question 42

A 24-year-old male presents with a deep, slow-growing soft tissue mass in his thigh. Biopsy reveals a biphasic spindle cell neoplasm. Which of the following chromosomal translocations is most strongly associated with this diagnosis?

Explanation

The patient has a synovial sarcoma, which is classically associated with the t(X;18) translocation involving the SYT and SSX genes. Ewing sarcoma is associated with t(11;22), and myxoid liposarcoma with t(12;16).

Question 43

A 6-week-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During follow-up, the infant shows absent active knee extension. What is the most likely cause?

Explanation

Femoral nerve palsy is a known complication of the Pavlik harness caused by hyperflexion of the hips. Management involves loosening the anterior straps or temporarily discontinuing the harness until function returns.

Question 44

A 45-year-old male presents 8 months after a midshaft humerus fracture treated with casting. Radiographs show a distinct "elephant shoe" appearance at the fracture site with no bridging callus. What is the most appropriate definitive management?

Explanation

The "elephant shoe" appearance indicates a hypertrophic nonunion, which has excellent biological healing potential but lacks adequate mechanical stability. The treatment of choice is rigid internal fixation to provide stability, typically without the need for bone grafting.

Question 45

A child presents with recurrent fractures, anemia, and cranial nerve palsies. Radiographs reveal generalized osteosclerosis with a "bone-within-bone" appearance. The primary cellular defect in this condition involves a failure of which mechanism?

Explanation

This presentation is characteristic of osteopetrosis, a disease of osteoclast dysfunction. The most common underlying defect is a mutation in carbonic anhydrase II, which prevents osteoclasts from creating the acidic environment necessary for bone resorption.

Question 46

In orthopedic screw design, which of the following geometric alterations will most significantly increase the pullout strength of a cortical screw in bone?

Explanation

The pullout strength of a screw is most directly proportional to the outer (thread) diameter of the screw. Decreasing the pitch or increasing the thread depth also improves pullout strength.

Question 47

A 30-year-old female presents with a lytic, eccentrically located lesion in the distal femur epiphysis. Biopsy confirms Giant Cell Tumor (GCT) of bone. Denosumab is considered for neoadjuvant therapy. What is the specific target of this medication?

Explanation

Denosumab is a monoclonal antibody that binds to and inhibits RANK Ligand (RANKL), which is secreted by the neoplastic stromal cells in a GCT. This prevents RANKL from activating the RANK receptor on normal osteoclast precursors, stopping bone destruction.

Question 48

When evaluating the ultrastructure of normal articular cartilage, which zone is characterized by having the highest water content, lowest proteoglycan content, and collagen fibers oriented parallel to the joint surface?

Explanation

The superficial zone provides the gliding surface of the joint and resists shear forces. It has the highest water content, the lowest proteoglycan concentration, and type II collagen aligned parallel to the articular surface.

Question 49

A 65-year-old patient presents with aseptic loosening of a total hip arthroplasty 15 years after the index surgery. Radiographs show extensive periprosthetic radiolucencies. The biological cascade leading to this osteolysis is primarily initiated by which of the following?

Explanation

Aseptic loosening in total joint arthroplasty is primarily driven by macrophage phagocytosis of sub-micron polyethylene wear debris. This activates macrophages to release inflammatory cytokines (IL-1, IL-6, TNF-alpha), which subsequently stimulate osteoclastic bone resorption.

Question 50

In the evaluation of Legg-Calvé-Perthes disease, the Herring Lateral Pillar Classification is widely used to determine prognosis. This classification is based on the radiolucency and height of which specific anatomic region on an AP pelvis radiograph?

Explanation

The Herring classification assesses the height of the lateral third of the capital femoral epiphysis during the fragmentation stage. A lateral pillar maintaining >50% of its original height (Group B) generally has a better prognosis than one with <50% height (Group C).

Question 51

A patient sustains a severe stretch injury to the brachial plexus. EMG suggests a Sunderland third-degree peripheral nerve injury. Histologically, this grade of injury is defined by disruption of the axon and which of the following structures?

Explanation

A Sunderland third-degree injury involves disruption of the axon and the endoneurium, but the perineurium and epineurium remain intact. Because the endoneurial tubes are disrupted, scarring can occur, making spontaneous recovery unpredictable and often incomplete.

Question 52

A 55-year-old female immigrant presents with diffuse bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low serum phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH). What is the most likely diagnosis?

Explanation

This laboratory profile (low Ca, low PO4, high ALP, and secondary hyperparathyroidism) is the hallmark of osteomalacia, typically caused by severe Vitamin D deficiency. Paget's and osteoporosis generally feature normal calcium and phosphorus levels.

Question 53

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

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It reversibly binds to the lysine-binding sites on plasminogen, competitively inhibiting its activation to plasmin, thereby preventing the degradation of fibrin clots.

Question 54

During an extended orthopedic procedure requiring prolonged tourniquet use, ischemic injury to skeletal muscle occurs. Which type of muscle fibers are most susceptible to this ischemic damage, and what is their primary metabolic pathway?

Explanation

Type I (slow-twitch) muscle fibers rely heavily on oxidative metabolism and have high mitochondrial content. Consequently, they are much more susceptible to ischemic injury during prolonged tourniquet ischemia compared to Type II (fast-twitch, glycolytic) fibers.

Question 55

Which of the following biomechanical environments is an absolute requirement for primary (strain-free) bone healing to occur?

Explanation

Primary bone healing requires absolute stability with less than 2% strain and direct apposition of fracture fragments. This allows cutting cones to directly cross the fracture site without the formation of an intermediate cartilaginous callus.

Question 56

In the stress-strain curve of a given orthopaedic implant material, what term describes the specific point where plastic deformation begins and the material will no longer return to its original shape upon load removal?

Explanation

The yield point marks the transition from the elastic region to the plastic region on a stress-strain curve. Beyond this point, the material sustains permanent, irreversible deformation.

Question 57

A 16-year-old boy presents with knee pain. Radiographs reveal a "sunburst" periosteal reaction in the distal femur. Biopsy confirms malignant spindle cells producing unmineralized osteoid. What is the most significant prognostic factor for overall survival in this patient?

Explanation

In high-grade osteosarcoma, the degree of tumor necrosis following neoadjuvant chemotherapy (measured by the Huvos grading system) is the single most important prognostic indicator for long-term survival. Greater than 90% necrosis is considered a good response.

Question 58

A 4-month-old female is diagnosed with developmental dysplasia of the hip (DDH) and placed in a Pavlik harness. Which of the following limb positions is most highly associated with an iatrogenic femoral nerve palsy?

Explanation

Hyperflexion of the hip in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to transient femoral nerve palsy. Excessive abduction, conversely, places the vascular supply to the femoral head at risk, leading to avascular necrosis.

Question 59

A 28-year-old male sustains a displaced Hawkins Type III fracture of the talar neck. Which artery provides the primary blood supply to the body of the talus, placing it at high risk for avascular necrosis?

Explanation

The artery of the tarsal canal, a branch of the posterior tibial artery, provides the dominant blood supply to the talar body. Disruption of this supply in talar neck fractures significantly increases the risk of avascular necrosis.

Question 60

A 55-year-old female with a history of malabsorption presents with diffuse bone pain. Radiographs show bilateral Looser zones in the femoral necks. Labs reveal low calcium, low phosphate, and elevated alkaline phosphatase. Which histologic finding is diagnostic of this metabolic bone disease?

Explanation

The patient has osteomalacia (adult rickets) caused by vitamin D deficiency or malabsorption. Histologically, it is characterized by defective mineralization of newly formed bone matrix, resulting in thick, unmineralized osteoid seams.

Question 61

A 6-year-old boy presents with high fever and refusal to bear weight on his right leg. MRI confirms acute hematogenous osteomyelitis of the proximal tibia. What is the primary anatomical location for the initial bacterial seeding in this age group?

Explanation

In children, acute hematogenous osteomyelitis most commonly begins in the metaphysis of long bones. Sluggish blood flow in the venous sinusoids adjacent to the physis provides an ideal environment for bacterial deposition and proliferation.

Question 62

A 30-year-old male with a closed, highly comminuted tibial shaft fracture develops severe pain out of proportion to the injury. Which of the following Delta pressure measurements (diastolic blood pressure minus compartment pressure) is considered an absolute indication for emergent fasciotomy?

Explanation

A Delta pressure (diastolic blood pressure minus compartment pressure) of less than 30 mmHg indicates inadequate tissue perfusion and is the standard threshold indicating the need for an emergent fasciotomy to treat compartment syndrome.

Question 63

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

Explanation

The deep (radial) zone of articular cartilage is responsible for resisting compressive forces. It contains the highest proteoglycan content, the lowest water content, and has type II collagen fibers arranged vertically (perpendicular to the joint surface).

Question 64

A 25-year-old male presents with a slow-growing, deep soft-tissue mass near his knee. Biopsy reveals a biphasic pattern consisting of both epithelial and spindle cells. Which chromosomal translocation is specific to this soft-tissue sarcoma?

Explanation

Synovial sarcoma is classically associated with the t(X;18)(p11;q11) chromosomal translocation, which fuses the SYT gene on chromosome 18 with the SSX1 or SSX2 gene on the X chromosome. A biphasic histologic pattern is a classic feature.

Question 65

When comparing Titanium alloy (Ti-6Al-4V) to Stainless Steel (316L) for use in orthopedic fracture fixation plates, Titanium is characterized by which of the following mechanical properties?

Explanation

Titanium alloy has a lower modulus of elasticity compared to stainless steel or cobalt-chrome, making it mechanically closer to the elasticity of cortical bone. This property decreases stress shielding and promotes a more physiologic load transfer.

Question 66

The scaphoid receives its primary intraosseous blood supply from branches of the radial artery. At which precise anatomical location do the predominant nutrient vessels enter the scaphoid?

Explanation

The primary blood supply to the scaphoid enters through the dorsal ridge near the waist and flows in a retrograde fashion to the proximal pole. This retrograde blood flow is why proximal pole fractures have a high rate of avascular necrosis.

Question 67

A patient with a severe ulnar nerve injury at the elbow demonstrates noticeably less severe clawing of the ring and small fingers compared to a patient with an ulnar nerve injury at the wrist. What anatomical mechanism explains this presentation (the Ulnar Paradox)?

Explanation

The Ulnar Paradox refers to the phenomenon where a high ulnar nerve injury produces less severe clawing because it denervates the ulnar half of the flexor digitorum profundus (FDP). Without active FDP contraction, the distal interphalangeal joints do not actively flex, reducing the visible claw deformity.

Question 68

A 6-year-old boy presents with a painless limp and restricted hip internal rotation. Radiographs reveal fragmentation of the proximal femoral epiphysis. According to the Herring Lateral Pillar Classification for Legg-Calvé-Perthes disease, which of the following defines a Group B classification?

Explanation

The Herring Lateral Pillar classification predicts the outcome of Legg-Calvé-Perthes disease. Group B indicates that >50% of the lateral pillar height is maintained, while Group C involves >50% collapse of the lateral pillar.

Question 69

During the remodeling and maturation phase of tendon healing, the cellularity of the tissue decreases and the extracellular matrix becomes highly organized. Which type of collagen primarily replaces Type III collagen during this phase?

Explanation

In the early phases of tendon and ligament healing, the initial scar tissue is predominantly composed of Type III collagen. During the remodeling phase, this is gradually replaced by stronger, more organized Type I collagen.

Question 70

An anteroposterior compression (APC) Type III pelvic ring injury involves complete disruption of the pubic symphysis and both the anterior and posterior sacroiliac ligaments. What is statistically the most common anatomical source of life-threatening hemorrhage in such injuries?

Explanation

While arterial bleeding (e.g., superior gluteal or internal pudendal) can be fatal and requires embolization, the majority (approximately 80%) of massive retroperitoneal bleeding in pelvic ring disruptions originates from the presacral venous plexus and bleeding cancellous bone surfaces.

Question 71

Bupivacaine is commonly used in orthopaedic regional nerve blocks but carries a known risk of severe cardiotoxicity if injected intravascularly. What is the primary molecular mechanism by which local anesthetics like bupivacaine exert their effect?

Explanation

Local anesthetics work by crossing the nerve cell membrane and binding to the intracellular portion of voltage-gated sodium channels. This blockade prevents sodium influx, thereby halting action potential propagation.

Question 72

Alendronate is prescribed to a patient for the treatment of postmenopausal osteoporosis. What is the primary cellular mechanism of action for this nitrogen-containing bisphosphonate?

Explanation

Nitrogen-containing bisphosphonates (like alendronate and zoledronic acid) act by inhibiting farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents prenylation of small GTPase proteins in osteoclasts, leading to osteoclast apoptosis.

Question 73

A 25-year-old motorcyclist sustains a traction injury to his right brachial plexus. Clinical examination shows a flail right arm, Horner syndrome (ptosis, miosis, anhidrosis), and paralysis of the rhomboids and serratus anterior. These findings strongly suggest an injury at which specific anatomical level?

Explanation

Horner syndrome (indicating T1 sympathetic ganglion involvement) and paralysis of muscles innervated by root-level branches (dorsal scapular and long thoracic nerves) indicate a severe pre-ganglionic root avulsion injury. This level of injury is typically not amenable to direct nerve repair.

Question 74

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, expansile lesion in the distal femoral epiphysis extending to the subchondral bone. Histology shows multinucleated giant cells in a background of mononuclear stromal cells. What targeted medical therapy has shown high efficacy for unresectable cases of this tumor?

Explanation

The patient has a Giant Cell Tumor (GCT) of bone. The neoplastic mononuclear stromal cells overexpress RANKL, which recruits osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is an effective targeted therapy to halt bone destruction.

Question 75

A 14-year-old male sustains a subtrochanteric femur fracture. Radiographs show diffusely dense, 'chalk-like' bones with loss of the medullary canal. He has a history of multiple cranial nerve palsies. A defect in which of the following mechanisms is most likely responsible?

Explanation

Osteopetrosis is caused by defective osteoclast function, commonly due to a mutation in carbonic anhydrase II or TCIRG1. This leads to dense but brittle bones and narrowed neural foramina causing cranial nerve palsies.

Question 76

A 72-year-old man with a long-standing history of increasing hat size and bilateral bowing of his tibiae presents with a newly painful swelling over his proximal humerus. Radiographs show a destructive, permeative lesion with cortical breakthrough. Which of the following is the most likely diagnosis?

Explanation

The patient has Paget's disease of bone, characterized by increasing hat size and long bone bowing. A sudden onset of pain and a destructive bone lesion in this demographic strongly suggests secondary osteosarcoma, which has a poor prognosis.

Question 77

When treating a newborn with idiopathic congenital talipes equinovarus using the Ponseti method, what is the correct sequence of deformity correction?

Explanation

The Ponseti method follows the CAVE sequence: Cavus, Adductus, Varus, and finally Equinus. The cavus is corrected first by elevating the first ray to align the forefoot with the hindfoot.

Question 78

In biomechanics, which of the following terms describes the phenomenon where a viscoelastic material experiences a decrease in stress over time when held at a constant strain?

Explanation

Stress relaxation is the decrease in stress over time when a material is held at a constant strain. Creep is the progressive deformation (strain) over time under a constant load (stress).

Question 79

Which of the following manufacturing processes most effectively reduces adhesive and abrasive wear in ultra-high-molecular-weight polyethylene (UHMWPE) for total hip arthroplasty?

Explanation

Highly cross-linked polyethylene is created using gamma or electron beam irradiation to create free radicals that form cross-links. Subsequent melting or annealing quenches these free radicals, preventing long-term oxidative degradation.

Question 80

A 35-year-old female falls from a height and sustains a sacral fracture. According to the Denis classification, which zone of injury carries the highest risk of neurological deficit?

Explanation

Denis Zone 3 involves the central sacral canal and carries the highest risk of neurological injury (up to 57%), commonly affecting bowel, bladder, and sexual function.

Question 81

A 28-year-old male sustains a high-energy Schatzker VI tibial plateau fracture. Which of the following parameters is an absolute indication for emergency four-compartment leg fasciotomy?

Explanation

A Delta pressure (Diastolic blood pressure minus compartment pressure) of less than 30 mmHg is an absolute indication for fasciotomy. Loss of pulses is a late and unreliable sign of compartment syndrome.

Question 82

During the repair of a Zone II flexor digitorum profundus (FDP) laceration, the surgeon decides on a core suture technique. Which of the following factors is most directly proportional to the tensile strength of the repair?

Explanation

The tensile strength of a flexor tendon repair is directly proportional to the number of core strands crossing the repair site. A 4-strand or 6-strand repair provides significantly more strength than a 2-strand repair, allowing for early active mobilization.

Question 83

After an anterior cruciate ligament (ACL) reconstruction using an autograft, during which post-operative time frame is the graft biomechanically at its weakest point?

Explanation

The ACL autograft goes through a process of 'ligamentization' involving necrosis, revascularization, and remodeling. It is biomechanically weakest during the revascularization phase, typically between 6 to 12 weeks post-operatively.

Question 84

In prosthetic joint infections caused by Staphylococcus epidermidis, which of the following is primarily responsible for facilitating the initial adherence to the implant and subsequent biofilm formation?

Explanation

Polysaccharide intercellular adhesin (PIA) is crucial for the cell-to-cell adhesion and biofilm formation of Staphylococcus epidermidis on foreign bodies. This biofilm protects the bacteria from host immune responses and antibiotics.

Question 85

A 25-year-old male sustains a closed Holstein-Lewis humerus fracture and presents with a secondary radial nerve palsy after closed reduction. If the nerve is undergoing Wallerian degeneration and subsequent regeneration, which muscle will be the first to show clinical signs of reinnervation?

Explanation

The brachioradialis is the first muscle innervated by the radial nerve distal to the spiral groove. Therefore, it is the first muscle to exhibit signs of clinical recovery during nerve regeneration.

Question 86

In a hemodynamically unstable patient with an anterior-posterior compression (APC) type III pelvic ring injury, what is the most appropriate anatomical landmark for the correct placement of a circumferential pelvic binder?

Explanation

A pelvic binder should be centered over the greater trochanters to effectively close the pelvic volume and reduce pubic symphysis diastasis. Placement higher over the iliac crests is less effective and can paradoxically open the pelvis in some fracture patterns.

Question 87

A 3-month-old female is being treated with a Pavlik harness for Developmental Dysplasia of the Hip (DDH). At her follow-up, she exhibits an inability to actively extend her knee. This complication is most likely due to which improper positioning in the harness?

Explanation

Excessive hip flexion in a Pavlik harness can cause femoral nerve compression against the inguinal ligament, leading to transient femoral nerve palsy (manifesting as an inability to extend the knee). Excessive abduction is associated with avascular necrosis of the femoral head.

Question 88

During minimally invasive repair of an Achilles tendon rupture, the sural nerve is at risk of iatrogenic entrapment. Where is the sural nerve most intimately related to the lateral border of the Achilles tendon, increasing this risk?

Explanation

The sural nerve crosses the lateral border of the Achilles tendon approximately 10 cm proximal to its insertion on the calcaneus. Proximal lateral suture placement during minimally invasive repair poses the highest risk of nerve entrapment.

Question 89

A 22-year-old male sustains a proximal pole scaphoid fracture. Which vascular anatomical feature explains the high rate of nonunion and avascular necrosis associated with this specific fracture pattern?

Explanation

The scaphoid receives its primary blood supply from branches of the radial artery that enter at the distal pole and dorsal ridge, flowing in a retrograde direction. Proximal pole fractures disrupt this supply, leading to high rates of AVN and nonunion.

Question 90

Which of the following bone graft materials possesses osteoconductive, osteoinductive, and osteogenic properties?

Explanation

Autograft (like iliac crest) is the only graft material that possesses all three properties: osteoconduction (scaffold), osteoinduction (growth factors like BMPs), and osteogenesis (live osteoblasts and progenitor cells).

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