What is the function of the rotator cuff during throwing?

Limits superior migration and anterior and posterior translation

A 4-year-old boy with arthrogryposis has little active motion of his knees or elbows. Both elbows are in full extension with good triceps strength, but he is unable to bring his hand to his face or feed himself. Management should consist of

posterior soft-tissue elbow release and anterior triceps transfer.

Figure 1 shows the radiograph obtained from a 67-year-old man recently diagnosed with osteoarthritis, 8 years after receiving a left metal-on-metal total hip arthroplasty (THA). The acetabular component has a modular cobalt alloy acetabular liner. Th

Conversion of the THA to a ceramic femoral head with an inner titanium sleeve and polyethylene bearing

Orthopedics Hyperguide Review | Dr Hutaif General Ortho

Question 1

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

Explanation

Tranexamic acid (TXA) is an antifibrinolytic agent. It works by competitively and reversibly binding to the lysine receptor sites on plasminogen. This prevents plasminogen from binding to fibrin, thereby preventing its activation to plasmin and inhibiting the degradation of fibrin clots.

Question 2

A 28-year-old overhead athlete presents with posterior shoulder pain and isolated weakness in external rotation. An MRI shows a paralabral cyst. Where is the cyst most likely located to produce these specific clinical findings?

Explanation

Isolated external rotation weakness indicates isolated infraspinatus denervation. The suprascapular nerve innervates the supraspinatus and then passes through the spinoglenoid notch to innervate the infraspinatus. Compression at the spinoglenoid notch affects only the infraspinatus, whereas compression at the suprascapular notch affects both the supraspinatus and infraspinatus.

Question 3

Recent advances in osteoporosis treatment include the use of romosozumab. Which of the following best describes the molecular target of this monoclonal antibody?

Explanation

Romosozumab is a humanized monoclonal antibody that targets and binds to sclerostin. Sclerostin, produced by osteocytes, normally inhibits the Wnt/beta-catenin pathway, which is crucial for osteoblast-mediated bone formation. By blocking sclerostin, romosozumab exerts a dual effect: increasing bone formation and decreasing bone resorption.

Question 4

When evaluating the ultrastructure of normal adult articular cartilage, which of the following accurately describes the deep (radial) zone?

Explanation

In the deep (radial) zone of articular cartilage, chondrocytes are arranged in vertical columns. The Type II collagen fibers are oriented perpendicular to the joint surface to resist compressive forces, and this zone contains the highest concentration of proteoglycans (and lowest water content) of the uncalcified zones.

Question 5

A 35-year-old female undergoes curettage and cementing of a giant cell tumor (GCT) of the distal femur. Six months later, she presents with local recurrence. The multidisciplinary tumor board recommends medical therapy before revision surgery. Which mechanism of action represents the first-line biologic agent for this condition?

Explanation

Giant cell tumor of bone (GCTB) features neoplastic mononuclear stromal cells that express high levels of RANKL, driving the formation of destructive osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is an effective medical treatment for recurrent, unresectable, or metastatic GCTB.

Question 6

A 22-year-old male is involved in a high-speed motor vehicle collision while wearing a lap belt. Radiographs show a fracture line passing horizontally through the spinous process, pedicles, and vertebral body of L2. What is the most commonly associated intra-abdominal injury?

Explanation

The patient has a Chance fracture, which is a flexion-distraction injury of the spine typically occurring in the thoracolumbar junction (often from lap belt use). These fractures are highly associated with intra-abdominal hollow viscus injuries (e.g., bowel perforations or mesenteric tears), which occur in up to 50% of cases.

Question 7

During a physical examination of a knee, a posterior drawer test is performed. The posterior cruciate ligament (PCL) is the primary restraint to posterior tibial translation. Which bundle of the PCL is the tightest in 90 degrees of knee flexion?

Explanation

The PCL consists of two main functional bundles: the anterolateral (AL) and posteromedial (PM) bundles. The AL bundle is the larger of the two and is tightest in knee flexion (which is why the posterior drawer is tested at 90 degrees). The PM bundle is tightest in knee extension.

Question 8

A 34-year-old male sustained a midshaft humerus fracture resulting in an irreversible radial nerve palsy. Tendon transfers are planned to restore function. Which of the following is the most appropriate donor to restore active wrist extension?

Explanation

In the standard transfer for radial nerve palsy to restore wrist extension, the Pronator Teres (PT) is transferred to the Extensor Carpi Radialis Brevis (ECRB). ECRB is chosen over ECRL because its insertion at the base of the 3rd metacarpal produces central wrist extension, whereas ECRL produces radial deviation.

Question 9

Trunnionosis in total hip arthroplasty (THA) leads to adverse local tissue reactions (ALTR) due to mechanically assisted crevice corrosion. Which combination of THA components presents the highest risk for severe trunnionosis?

Explanation

Trunnionosis is the wear and corrosion at the head-neck junction. Risk factors include larger head size (which increases the lever arm and frictional torque at the trunnion), and mixed-metal combinations (galvanic corrosion). A large cobalt-chromium (CoCr) head on a titanium (Ti) stem carries the highest risk for significant trunnionosis.

Question 10

The Lisfranc ligament is crucial for the stability of the midfoot. Which of the following anatomically describes the attachments of this interosseous ligament?

Explanation

The primary Lisfranc ligament is an interosseous ligament that runs from the lateral aspect of the medial cuneiform to the medial base of the second metatarsal. There is no direct ligamentous connection between the base of the first and second metatarsals, making this area vulnerable to injury.

Question 11

The lateral pillar classification (Herring) is widely used to determine the prognosis in Legg-Calvé-Perthes disease. This classification is based on the radiolucency and height of which anatomical structure on the AP pelvis radiograph?

Explanation

The Herring Lateral Pillar classification divides the capital femoral epiphysis into three pillars (medial, central, and lateral). The classification depends on the degree of height loss in the lateral third of the capital femoral epiphysis, as it is the most critical weight-bearing portion. Greater height loss (Groups B and C) correlates with a worse prognosis.

Question 12

A 26-year-old male sustains a high-energy Pauwels Type III femoral neck fracture. Based on biomechanical principles, which fixation construct provides the greatest stability against the high shear forces seen in this fracture pattern?

Explanation

Pauwels Type III fractures are vertical fractures (>50 degrees) subjected to extreme shear forces rather than compressive forces. Standard multiple cancellous screws have high failure rates in this pattern due to a lack of shear stability. A fixed-angle construct, such as a sliding hip screw (dynamic hip screw), provides superior biomechanical resistance to vertical shear.

Question 13

Adolescent Blount disease is an acquired disorder of the proximal tibial physis resulting in a progressive varus deformity. According to the Heuter-Volkmann principle, what is the primary pathophysiological driver of this condition?

Explanation

The Heuter-Volkmann principle states that increased compressive forces inhibit physeal growth, while tension stimulates it. In Blount disease (especially in obese patients), excessive weight places extreme compressive loads on the medial proximal tibial physis, inhibiting its growth and resulting in progressive tibia vara.

Question 14

Degenerative spondylolisthesis most commonly occurs at the L4-L5 level. Which anatomic feature of the L4-L5 segment heavily predisposes it to this condition compared to other lumbar levels?

Explanation

Degenerative spondylolisthesis is most common at L4-L5. A major predisposing factor is the presence of sagittally oriented facet joints at this level. Coronal orientation resists forward translation better; sagittal orientation provides less mechanical resistance to anterior sheer, leading to translation as the disc and ligaments degenerate. L5-S1 facets are more coronal, making degenerative slip less common there.

Question 15

In flexor tendon injuries of the hand, Zone II is historically referred to as 'no man's land'. What are the proximal and distal anatomic boundaries of Zone II?

Explanation

Flexor tendon Zone II begins proximally at the proximal edge of the A1 pulley (approximately at the distal palmar crease) and ends distally at the insertion of the flexor digitorum superficialis (FDS) tendon in the middle phalanx. It is called 'no man's land' due to the tight fibro-osseous sheath housing both FDP and FDS, making surgical outcomes challenging.

Question 16

The Mirels criteria are used to assess the risk of a pathological fracture in a long bone affected by a metastatic lesion. Which of the following is NOT one of the four parameters evaluated in the Mirels scoring system?

Explanation

The Mirels scoring system uses four parameters to predict pathological fracture risk: Site (upper limb, lower limb, peritrochanteric), Pain (mild, moderate, functional), Lesion nature (blastic, mixed, lytic), and Size (<1/3, 1/3-2/3, >2/3 of cortical diameter). Primary tumor histology is not one of the criteria scored.

Question 17

A 55-year-old overweight female presents with progressive flattening of her left medial longitudinal arch and pain behind the medial malleolus. She is unable to perform a single-leg heel rise on the left. Her hindfoot is in valgus but is flexible and corrects when she stands on her toes on both feet. What is the most appropriate surgical management for this stage of posterior tibial tendon dysfunction (PTTD)?

Explanation

The patient has Stage II PTTD (flatfoot deformity that is flexible, indicated by hindfoot correction on toe rise, but inability to perform a single heel rise due to incompetent PTT). The gold standard surgical treatment for Stage II includes a joint-sparing procedure: FDL transfer (to replace the PTT) combined with a medializing calcaneal osteotomy (to correct the valgus and restore biomechanical axes).

Question 18

A Schatzker Type IV tibial plateau fracture involves the medial tibial plateau. What is the classic mechanism of injury, and what associated soft tissue injury must be highly suspected?

Explanation

A Schatzker IV fracture (medial plateau) usually results from a high-energy varus force with axial loading. Because the medial bone is stronger, a fracture here implies high energy and often represents a fracture-dislocation or subluxation of the knee. Therefore, there is a very high association with vascular injury (popliteal artery) and multiple ligament injuries.

Question 19

Which of the following bone graft options strictly provides osteoconduction, osteoinduction, and osteogenesis?

Explanation

Autograft, such as an iliac crest bone graft (ICBG), is the 'gold standard' because it is the only graft type that possesses all three properties: osteoconduction (scaffold), osteoinduction (growth factors like BMPs), and osteogenesis (living osteoprogenitor cells and osteoblasts). Allografts lack osteogenesis, and DBM lacks osteogenesis and meaningful structural osteoconduction.

Question 20

A 30-year-old male presents with sudden inability to actively extend the interphalangeal joint of his thumb. He had a non-displaced distal radius fracture treated in a cast 6 weeks ago. What is the most likely pathophysiologic mechanism for this new deficit?

Explanation

The patient has suffered a spontaneous rupture of the Extensor Pollicis Longus (EPL) tendon, a known complication following nondisplaced or minimally displaced distal radius fractures. The mechanism is ischemic avascular necrosis of the tendon in its 'watershed' area as it passes through the tight third dorsal compartment around Lister's tubercle, exacerbated by fracture hematoma and swelling. (Attritional rupture is more common with displaced fractures or prominent hardware).

Question 21

Mixing titanium and stainless steel in surgical implants can lead to galvanic corrosion. Which of the following factors primarily determines the severity of corrosion between these two metals in vivo?

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolyte solution like body fluid. The severity is driven by the electropotential difference between the metals.

Question 22

A 65-year-old patient is scheduled for an elective total hip arthroplasty. According to recent AAOS guidelines, which of the following is an appropriate venous thromboembolism (VTE) prophylaxis for a patient with standard risk and no history of bleeding disorders?

Explanation

Current AAOS guidelines support the use of aspirin for VTE prophylaxis in standard-risk patients undergoing total joint arthroplasty, balancing effective prevention with lower bleeding risks.

Question 23

A 68-year-old man presents with increasing hat size, bowing of the tibiae, and hearing loss. Radiographs show mixed lytic and sclerotic lesions. Which of the following serum parameters is most likely to be isolated and significantly elevated?

Explanation

The clinical presentation is classic for Paget's disease of bone. This condition is characterized by massive bone turnover resulting in highly elevated serum alkaline phosphatase, while calcium and phosphorus typically remain normal.

Question 24

A 35-year-old farmer sustains a severe open tibia fracture after being run over by agricultural machinery. In addition to standard broad-spectrum coverage, which antibiotic is classically recommended to specifically cover for Clostridium species due to soil contamination?

Explanation

Farm or soil-contaminated injuries have a high risk of clostridial infection (gas gangrene). High-dose intravenous penicillin is traditionally added to the antibiotic regimen to target Clostridium perfringens.

Question 25

According to the International Consensus Meeting (ICM) criteria, which of the following is considered a 'major criterion' for the definitive diagnosis of a periprosthetic joint infection (PJI)?

Explanation

The two major criteria for PJI are a sinus tract communicating with the prosthesis and two positive periprosthetic cultures with phenotypically identical organisms. The others are minor criteria.

Question 26

An 18-year-old male presents with deep knee pain and a mixed lytic/sclerotic lesion in the distal femur. Biopsy confirms high-grade intramedullary osteosarcoma. What is the standard treatment algorithm?

Explanation

High-grade osteosarcoma is typically treated with neoadjuvant chemotherapy, followed by surgical resection with wide margins, and then adjuvant chemotherapy to address systemic micrometastases.

Question 27

During an anatomical single-bundle ACL reconstruction, the surgeon must properly place the femoral tunnel. The center of the native ACL footprint is positioned anatomically in relation to which two osseous landmarks on the medial aspect of the lateral femoral condyle?

Explanation

The lateral intercondylar ridge (resident's ridge) represents the anterior margin of the ACL footprint, and the lateral bifurcate ridge separates the anteromedial and posterolateral bundle footprints.

Question 28

A 25-year-old sustains a volar laceration over the proximal phalanx of the index finger, completely transecting both the FDS and FDP tendons. According to the Verdan classification, which flexor tendon zone is injured?

Explanation

Zone II, historically called 'no man's land', extends from the proximal edge of the A1 pulley to the insertion of the flexor digitorum superficialis (FDS) tendon. Both FDS and FDP are frequently injured together here.

Question 29

A 12-year-old obese male presents with knee pain and obligatory external rotation during passive hip flexion, consistent with a slipped capital femoral epiphysis (SCFE). Why is in-situ pinning preferred over open anatomical reduction for standard, stable slips?

Explanation

Forceful anatomical reduction stretches or kinks the delicate retinacular blood supply to the femoral epiphysis, significantly increasing the risk of avascular necrosis (AVN).

Question 30

Bone morphogenetic proteins (BMPs) are used in orthopedics to promote bone healing. Which of the following is an FDA-approved indication for rhBMP-2?

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for acute, open tibial shaft fractures treated with an intramedullary nail and for anterior lumbar interbody fusion (ALIF).

Question 31

A 45-year-old patient with an acute massive L4-L5 disc herniation presents with urinary retention and saddle anesthesia. What is the most critical time-dependent variable influencing the return of bladder function?

Explanation

Cauda equina syndrome is a surgical emergency. Decompression within 48 hours of symptom onset is the most critical factor for maximizing the recovery of bladder and bowel function.

Question 32

A 22-year-old is admitted with a closed tibia fracture. Which of the following clinical signs is considered the earliest and most reliable indicator of acute compartment syndrome in an alert patient?

Explanation

Pain out of proportion to the injury, especially pain on passive stretch of the involved compartment's muscles, is the earliest and most sensitive clinical sign of acute compartment syndrome.

Question 33

During a prolonged lower extremity orthopedic surgery, a pneumatic tourniquet is utilized. What is the generally accepted maximum safe continuous tourniquet inflation time before a deflation 'breathe' period is required?

Explanation

Most literature and orthopedic guidelines recommend a maximum continuous tourniquet time of 120 minutes to minimize the risk of ischemic nerve and muscle damage.

Question 34

When comparing various orthopedic implant materials, which of the following possesses a modulus of elasticity that most closely approximates that of human cortical bone, thereby reducing stress shielding?

Explanation

Titanium alloy has a lower modulus of elasticity (closer to cortical bone) compared to stainless steel or cobalt-chromium. This similarity helps reduce stress shielding and subsequent bone resorption.

Question 35

A 60-year-old female with back pain has punched-out lytic skull lesions and a monoclonal protein spike. What is the most appropriate imaging modality to evaluate the extent of her skeletal involvement?

Explanation

Multiple myeloma lesions are purely lytic and lack reactive osteoblastic activity. Therefore, a Technetium-99m bone scan is often falsely negative; a low-dose whole-body CT or skeletal survey is the standard.

Question 36

A 72-year-old with pseudoparalysis and severe rotator cuff tear arthropathy is indicated for a reverse total shoulder arthroplasty (RTSA). Which biomechanical alteration explains the success of RTSA in restoring forward elevation?

Explanation

RTSA shifts the center of rotation medially and inferiorly. This effectively lengthens the deltoid lever arm and increases its resting tension, allowing the deltoid to compensate for the deficient rotator cuff.

Question 37

A 35-year-old sustains an acute Achilles tendon rupture. If non-operative management with an early functional weight-bearing protocol is chosen, how do outcomes compare to surgical repair according to recent high-level evidence?

Explanation

Recent RCTs utilizing early functional rehabilitation protocols show that non-operative management has equivalent re-rupture rates to surgery, while completely avoiding surgical site and soft-tissue complications.

Question 38

A 30-year-old manual laborer presents with chronic dorsal wrist pain. Radiographs reveal advanced sclerosis of the lunate (Kienböck's disease) and an ulnar minus variance. Which joint-leveling procedure is best indicated?

Explanation

In early to mid-stage Kienböck's disease with negative ulnar variance, a radial shortening osteotomy levels the radiocarpal joint, thereby decreasing the mechanical load transmitted through the avascular lunate.

Question 39

A patient arrives hypotensive after a high-speed collision, with an anteroposterior compression (APC) type III pelvic ring injury. Where is the most biomechanically effective anatomical location to apply a pelvic binder?

Explanation

A pelvic binder must be applied directly over the greater trochanters to effectively close the pelvic volume and stabilize the symphysis. Placing it higher over the iliac crests can paradoxically open the pelvis further.

Question 40

A 5-year-old boy sustains a completely displaced extension-type supracondylar humerus fracture. On examination, he is unable to make an 'A-OK' sign. Which nerve is most likely injured?

Explanation

The anterior interosseous nerve (AIN) is the most commonly injured nerve in extension-type supracondylar humerus fractures. Injury causes loss of flexion at the thumb IP and index DIP joints, preventing the 'A-OK' sign.

Question 41

To decrease wear in ultra-high-molecular-weight polyethylene (UHMWPE) components for total joint arthroplasty, highly cross-linked polyethylene is frequently used. What is the primary mechanical disadvantage of increasing the degree of cross-linking?

Explanation

Highly cross-linked polyethylene significantly reduces adhesive and abrasive wear. However, the cross-linking process alters the polymer chain mobility, which decreases the material's fatigue resistance and makes it more susceptible to fracture.

Question 42

Which of the following correctly describes the cellular mechanism of action of nitrogen-containing bisphosphonates such as alendronate?

Explanation

Nitrogen-containing bisphosphonates are internalized by osteoclasts and inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents protein prenylation, disrupting osteoclast function and promoting early apoptosis.

Question 43

During fracture fixation, maximizing the pullout strength of a cortical bone screw is critical. Which of the following modifications to the screw design will most significantly increase its pullout strength?

Explanation

Pullout strength is most heavily influenced by the outer diameter of the screw, as it dictates the volume of bone caught between the threads. Decreasing the inner diameter and decreasing the pitch also increase pullout strength, but to a lesser extent.

Question 44

During the Smith-Petersen (anterior) approach to the hip, an internervous plane is utilized to protect dynamic stabilizers. Which of the following defines the superficial internervous plane of this approach?

Explanation

The superficial internervous plane for the anterior (Smith-Petersen) approach lies between the sartorius (supplied by the femoral nerve) and the tensor fasciae latae (supplied by the superior gluteal nerve). The deep plane is between the rectus femoris and gluteus medius.

Question 45

A 15-year-old boy presents with aching knee pain that is noticeably worse at night and dramatically relieved by ibuprofen. Radiographs show a small radiolucent nidus with surrounding sclerosis in the proximal tibia. What is the primary molecular driver of his pain?

Explanation

The clinical and radiographic presentation is classic for an osteoid osteoma. The osteoblastic cells within the nidus produce extremely high levels of prostaglandins (particularly PGE2), mediating the characteristic night pain that responds to NSAIDs.

Question 46

In a patient presenting with a slipped capital femoral epiphysis (SCFE), what is the most typical direction of epiphyseal displacement relative to the femoral neck?

Explanation

In SCFE, the metaphysis (femoral neck) typically displaces anteriorly and superiorly. This results in the capital femoral epiphysis being anatomically positioned posterior and inferior relative to the neck.

Question 47

Which of the following organisms is most notoriously associated with early and robust biofilm formation on orthopedic implants, frequently resulting in indolent, chronic periprosthetic joint infections?

Explanation

Staphylococcus epidermidis, a coagulase-negative staphylococcus, is a major colonizer of orthopedic hardware. It produces a thick glycocalyx biofilm that acts as a physical barrier against both systemic antibiotics and host immune cells.

Question 48

A patient sustains a severely displaced, closed tibial shaft fracture. Which of the following absolute pressure measurements or gradients is considered the most reliable threshold for diagnosing acute compartment syndrome?

Explanation

The delta pressure (diastolic blood pressure minus absolute compartment pressure) is the most reliable physiologic indicator of acute compartment syndrome. A delta pressure of less than 30 mmHg strongly indicates critical tissue ischemia requiring urgent fasciotomies.

Question 49

A heavy machinery worker sustains a deep volar laceration in "No Man's Land" of the hand, resulting in an inability to flex the proximal and distal interphalangeal joints. Which flexor tendon zone is anatomically involved?

Explanation

Zone II extends from the proximal edge of the A1 pulley to the insertion of the flexor digitorum superficialis (FDS). It is historically termed "No Man's Land" due to the tight fibro-osseous tunnel that makes surgical repair prone to adhesions and poor functional outcomes.

Question 50

In orthopedic hardware selection, mixing certain metals can lead to destructive galvanic corrosion. Which of the following implant combinations in direct physical contact poses the highest risk for severe galvanic corrosion?

Explanation

Mixing stainless steel and titanium implants creates a strong galvanic couple due to their significant differences in electrochemical potential. The titanium acts as a large cathode, leading to rapid, destructive anodic dissolution of the stainless steel.

Question 51

A 14-year-old elite gymnast presents with mechanical lower back pain. Radiographs reveal a pars interarticularis defect at L5 with a 25% anterior translation of L5 on S1. According to the Wiltse classification, what specific type of spondylolisthesis is this?

Explanation

Isthmic spondylolisthesis (Wiltse Type II) is caused by a structural defect, elongation, or acute fracture of the pars interarticularis (spondylolysis). It is the most common cause of spondylolisthesis in adolescent athletes who perform repetitive spinal extension.

Question 52

Following a closed midshaft humerus fracture, a patient demonstrates a profound radial nerve palsy. An electromyogram (EMG) performed at 4 weeks demonstrates abundant fibrillation potentials but no voluntary motor unit action potentials. What is the minimum grade of nerve injury sustained according to Seddon's classification?

Explanation

Fibrillation potentials on an EMG indicate true muscular denervation resulting from axonal disruption. This rules out neurapraxia (which has intact axons and no fibrillations) and signifies at least an axonotmesis, if not a complete neurotmesis.

Question 53

Venous thromboembolism (VTE) prophylaxis is a standard of care following major joint arthroplasty. Which of the following oral anticoagulants exerts its effect by acting as a direct thrombin inhibitor?

Explanation

Dabigatran is a direct thrombin (Factor IIa) inhibitor used for oral VTE prophylaxis. Rivaroxaban and apixaban are direct Factor Xa inhibitors, whereas warfarin inhibits Vitamin K epoxide reductase.

Question 54

A 60-year-old man presents with a destructive sacral mass causing bowel and bladder dysfunction. Biopsy reveals cells arranged in cords with abundant bubbly cytoplasm and distinct physaliferous features. What is the most likely diagnosis?

Explanation

Chordomas are rare, low-grade malignant bone tumors arising from embryonic remnants of the notochord, most commonly located in the sacrococcygeal and spheno-occipital regions. The presence of large, vacuolated "physaliferous" cells is the pathognomonic histologic hallmark.

Question 55

The anterior cruciate ligament (ACL) provides crucial stability to the knee and is composed of two primary bundles. Which of the following statements correctly describes their varying tension during knee motion?

Explanation

The ACL has two distinct functional bundles based on their tibial insertions. The anteromedial (AM) bundle is the primary restraint to anterior translation and is tightest in flexion, while the posterolateral (PL) bundle provides rotational stability and is tightest in extension.

Question 56

When a diaphyseal fracture is fixed with a rigid dynamic compression plate (DCP) resulting in absolute stability and less than 2% interfragmentary strain, which specific process of bone healing predominates?

Explanation

Absolute fracture stability with minimal interfragmentary strain suppresses callus formation. Healing occurs via primary bone healing, wherein osteoclasts form cutting cones that cross the fracture line, followed immediately by osteoblasts laying down new lamellar bone (Haversian remodeling).

Question 57

In the evaluation of an infant for Developmental Dysplasia of the Hip (DDH), static ultrasound imaging is standard. Which specific ultrasound measurement quantifies the bony acetabular roof concavity and must be >60 degrees to be considered normal (Graf Type I)?

Explanation

In the Graf ultrasound classification for infant hips, the alpha angle measures the osseous roof of the acetabulum. An alpha angle of 60 degrees or greater indicates a normal, mature hip.

Question 58

In adult-acquired flatfoot deformity secondary to posterior tibial tendon dysfunction (PTTD), progressive collapse of the medial longitudinal arch occurs. What primary structural failure leads directly to talonavicular uncoverage and significant forefoot abduction?

Explanation

The posterior tibial tendon acts as the primary dynamic stabilizer of the arch. When it fails, excessive stress is transferred to the static stabilizers, particularly the spring (calcaneonavicular) ligament, leading to its attenuation and subsequent plantarflexion/medial rotation of the talar head.

Question 59

A surgeon applies a long, locked bridging plate to a highly comminuted midshaft femur fracture, leaving the fracture site undisturbed. This specific fixation construct relies on which biomechanical principle to promote healing?

Explanation

A bridging plate intentionally bypasses the zone of comminution, preserving fracture hematoma biology while providing relative stability. This construct allows for controlled interfragmentary strain (typically 2% to 10%), which robustly stimulates secondary bone healing via callus formation.

Question 60

Denosumab is an antiresorptive medication used for treating severe osteoporosis. What is its specific molecular mechanism of action?

Explanation

Denosumab is a fully human monoclonal antibody that directly binds to RANKL, mimicking the body's natural decoy receptor, osteoprotegerin (OPG). By blocking RANKL from binding to the RANK receptor on osteoclasts, it effectively halts osteoclast maturation, function, and survival.

Question 61

Cross-linking of ultra-high molecular weight polyethylene (UHMWPE) in total hip arthroplasty affects its mechanical properties. Highly cross-linking UHMWPE primarily results in which of the following biomechanical changes?

Explanation

Highly cross-linked polyethylene significantly improves wear resistance, which reduces osteolysis. However, this comes at the cost of reduced mechanical properties, specifically decreased fatigue strength and ductility.

Question 62

A 14-year-old boy presents with a painful mass in his distal femur. Biopsy reveals a small round blue cell tumor. Molecular testing is positive for a t(11;22) translocation. What is the most likely diagnosis and its associated fusion gene?

Explanation

Ewing sarcoma is classically characterized by the t(11;22) chromosomal translocation, which results in the EWS-FLI1 fusion gene. It typically presents as a small round blue cell tumor in children and young adults.

Question 63

Following a laceration in Zone II of the flexor tendons of the hand, a surgeon performs a primary repair. Biomechanically, which core suture parameter contributes most to the tensile strength of the repair?

Explanation

Increasing the number of core suture strands directly increases the tensile strength of a flexor tendon repair. A 4-strand or 6-strand repair provides significantly greater strength than a 2-strand technique, safely permitting early active mobilization.

Question 64

A 25-year-old male sustains a traumatic spondylolisthesis of the axis (Hangman's fracture) following an MVA. Imaging shows a pars interarticularis fracture with severe angulation and 6mm translation of C2 on C3, but normal C2-C3 facets. According to the Levine and Edwards classification, what is the most appropriate management?

Explanation

This is a Type II Hangman's fracture (translation >3mm and angulation). Treatment involves initial gentle reduction with slight compression and extension followed by Halo vest immobilization; traction is contraindicated as it may over-distract and exacerbate the injury.

Question 65

A hemodynamically unstable patient arrives after a severe crush injury. Pelvic radiographs demonstrate an anterior-posterior compression (APC) Type III pelvic ring injury. After placing a pelvic binder, the patient remains hypotensive despite massive transfusion. A FAST exam is negative. What is the most appropriate next step?

Explanation

In a hemodynamically unstable patient with a pelvic ring injury and a negative FAST exam, the pelvis is the primary source of life-threatening hemorrhage. Pre-peritoneal pelvic packing and/or pelvic angiography with embolization are the immediate interventions of choice.

Question 66

A 13-year-old obese male presents with acute exacerbation of chronic knee pain and an inability to bear weight. The affected leg is held in external rotation. What is the most severe potential complication of the definitive surgical treatment for his underlying condition?

Explanation

The patient has an unstable Slipped Capital Femoral Epiphysis (SCFE) characterized by the inability to bear weight. The most devastating complication of an unstable SCFE and its surgical stabilization is avascular necrosis (AVN) of the femoral head.

Question 67

In anterior cruciate ligament (ACL) reconstruction, bone-patellar tendon-bone (BTB) autografts are frequently utilized. Compared to the native ACL, what is the ultimate tensile load of a 10-mm wide BTB graft at the exact time of implantation?

Explanation

A 10-mm BTB graft has an ultimate tensile load of approximately 2977 N, which is about 138% of the native ACL (roughly 2160 N). However, this mechanical strength drops significantly during the necrotic and revascularization remodeling phases.

Question 68

During a total knee arthroplasty, the surgeon assesses the gaps with trial components. The knee is tight in extension and balanced in flexion. Which of the following is the most appropriate intraoperative adjustment?

Explanation

A tight extension gap with a balanced flexion gap indicates that the distal femur is under-resected. Resecting more distal femur will increase the extension space without altering the balanced flexion gap.

Question 69

A 55-year-old diabetic patient presents with a rapidly spreading erythematous leg rash, severe pain out of proportion to exam, and hemorrhagic bullae. Which laboratory parameter is NOT a component of the LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score?

Explanation

The LRINEC score utilizes CRP, total WBC count, hemoglobin, serum sodium, serum creatinine, and serum glucose to stratify the risk of necrotizing fasciitis. Serum potassium is not a component of this scoring system.

Question 70

Bone morphogenetic proteins (BMPs) induce osteogenesis by signaling through transmembrane receptors. Which intracellular signaling pathway is primarily activated by BMPs to promote osteoblast differentiation?

Explanation

BMPs bind to serine/threonine kinase receptors on the cell membrane, triggering the phosphorylation of intracellular Smad proteins (Smad 1, 5, and 8). These activated Smads form a complex with Smad 4 and translocate to the nucleus to initiate transcription of osteogenic genes.

Question 71

The "peel-back" mechanism in overhead-throwing athletes primarily contributes to the pathogenesis of which of the following shoulder lesions?

Explanation

The "peel-back" mechanism occurs during the late cocking phase of throwing (maximum abduction and external rotation). This shifts the biceps vector posteriorly, generating a torsional force that peels the superior labrum off the glenoid rim, creating a Type II SLAP tear.

Question 72

In the pathophysiology of acute compartment syndrome, the initial cascade of tissue ischemia is triggered by which of the following microvascular hemodynamic alterations?

Explanation

Acute compartment syndrome initially develops when increased intracompartmental pressure exceeds the pressure of post-capillary venules, causing venous outflow obstruction. This leads to a backup of pressure, capillary transudation, and eventual microcirculatory collapse.

Question 73

A 65-year-old male with a metal-on-metal total hip arthroplasty presents with groin pain and an enlarging pseudotumor. Histological analysis of the periprosthetic tissue will most likely demonstrate which of the following distinct features?

Explanation

Adverse local tissue reactions (ALTR) associated with metal-on-metal implants are characterized histologically by ALVAL (aseptic lymphocytic vasculitis-associated lesion). This features a dense perivascular lymphocytic infiltrate indicative of a delayed-type hypersensitivity response.

Question 74

A 40-year-old recreational athlete sustains an acute Achilles tendon rupture. Non-operative management is chosen using an early functional rehabilitation protocol. Compared to surgical repair, which of the following statements regarding non-operative management is most accurate based on recent high-level evidence?

Explanation

Recent meta-analyses demonstrate that when using an early functional rehabilitation protocol, the re-rupture rates between operative and non-operative management of acute Achilles tendon ruptures are statistically equivalent. However, operative management carries a higher risk of soft-tissue complications and nerve injury.

Question 75

A 6-month-old female with developmental dysplasia of the hip (DDH) is treated with a Pavlik harness. During a follow-up visit, she demonstrates an inability to actively extend her knee. Which of the following is the most appropriate next step?

Explanation

An inability to actively extend the knee indicates a femoral nerve palsy, a severe complication of the Pavlik harness typically caused by excessive hip flexion. Its occurrence requires the immediate cessation of harness treatment to allow the nerve to recover.

Question 76

Teriparatide is an anabolic pharmacological agent utilized in the treatment of severe osteoporosis. What is its specific mechanism of action and the maximum FDA-approved duration for continuous lifetime use?

Explanation

Teriparatide is a recombinant parathyroid hormone analog (PTH 1-34) that has a potent anabolic effect on bone by stimulating osteoblast activity when given intermittently. Its maximum FDA-approved lifetime use is restricted to 2 years due to a theoretical risk of osteosarcoma observed in animal models.

Question 77

A 30-year-old male sustains a closed midshaft humerus fracture and presents concurrently with an isolated wrist drop. Initial observation is elected. At 12 weeks post-injury, there is no clinical or electromyographic (EMG) evidence of radial nerve recovery. What is the most appropriate next step in management?

Explanation

While initial observation is appropriate for a primary radial nerve palsy associated with a closed humeral shaft fracture, the lack of clinical or EMG signs of reinnervation by 12 weeks mandates surgical exploration of the radial nerve.

Question 78

Denosumab is utilized as an adjuvant or neoadjuvant treatment for advanced Giant Cell Tumor of Bone (GCTB). At the cellular level, denosumab exerts its therapeutic effect by directly targeting and binding to which entity within the tumor microenvironment?

Explanation

In Giant Cell Tumor of Bone, the mononuclear stromal cells are the actual neoplastic elements that oversecrete RANKL. Denosumab, a monoclonal antibody, binds directly to this RANKL, preventing it from activating the non-neoplastic, bone-resorbing multinucleated giant cells.

Question 79

A 65-year-old patient presents with aseptic loosening 15 years after a total hip arthroplasty using a highly cross-linked polyethylene liner. Which of the following cells is the primary mediator of the osteolysis observed in this condition?

Explanation

Macrophages are the primary cells responsible for recognizing particulate wear debris. Upon phagocytosing polyethylene particles, they release pro-inflammatory cytokines like TNF-alpha and IL-1, which upregulate RANKL and stimulate osteoclast-mediated bone resorption.

Question 80

A 34-year-old male is brought to the trauma bay after a motorcycle accident. He is hypotensive with a mechanically unstable anteroposterior compression type III (APC III) pelvic ring injury. Application of a pelvic circumferential compression device is planned. At which anatomical landmark should this device be centered?

Explanation

To effectively reduce pelvic volume and control hemorrhage in open-book pelvic fractures, a pelvic binder must be placed at the level of the greater trochanters. Placement higher over the iliac crests is less effective and may inadvertently worsen the deformity.

Question 81

A 13-year-old obese male presents with left groin pain and a limp for 3 weeks. Radiographs confirm a stable slipped capital femoral epiphysis (SCFE). Which of the following physical exam findings is most characteristic of this condition?

Explanation

Patients with SCFE typically demonstrate obligatory external rotation as the affected hip is passively flexed. This occurs because the femoral neck displaces anteriorly and externally rotates relative to the capital femoral epiphysis.

Question 82

A 12-year-old boy presents with progressive diaphyseal leg pain. Radiographs reveal a permeative lytic lesion in the tibial diaphysis with an "onion skin" periosteal reaction. Cytogenetic analysis is most likely to reveal which of the following translocations?

Explanation

The clinical and radiographic presentation is classic for Ewing sarcoma. This tumor is strongly associated with the t(11;22) chromosomal translocation, which results in the EWS-FLI1 fusion protein.

Question 83

A 22-year-old restrained passenger is involved in a high-speed motor vehicle collision. Radiographs and CT of the lumbar spine reveal a flexion-distraction injury (Chance fracture) at L2. Which of the following associated injuries must be most highly suspected and ruled out?

Explanation

Chance fractures are high-energy flexion-distraction injuries commonly associated with seatbelt use. They carry a high rate (up to 40-50%) of associated intra-abdominal injuries, particularly to hollow viscous organs like the bowel.

Question 84

A 45-year-old carpenter presents with volar forearm pain and numbness in the radial three and a half digits. Unlike typical carpal tunnel syndrome, the patient also notes decreased sensation over the thenar eminence. Which of the following is the most likely site of nerve compression?

Explanation

The sensory deficit over the thenar eminence indicates involvement of the palmar cutaneous branch of the median nerve, which branches proximal to the carpal tunnel. This points to proximal median nerve compression, most commonly between the heads of the pronator teres in Pronator Syndrome.

Question 85

During distraction osteogenesis using an Ilizarov frame, bone healing occurs primarily through which of the following processes?

Explanation

Distraction osteogenesis promotes new bone formation primarily via intramembranous ossification, bypassing the cartilaginous intermediate phase. This occurs under conditions of stable fixation and controlled, gradual mechanical tension.

Question 86

A 58-year-old male with a ceramic-on-ceramic total hip arthroplasty presents with an audible squeaking noise from his hip during certain movements. There is no pain, and radiographs show well-fixed components. Which of the following technical factors during the index surgery most likely contributed to this issue?

Explanation

Squeaking in ceramic-on-ceramic THA is often associated with component malposition, specifically excessive acetabular cup inclination or anteversion. This malpositioning leads to edge loading, disrupting the fluid film lubrication and causing the audible squeak.

Question 87

During a posterior-stabilized total knee arthroplasty, trial reduction reveals that the knee is well-balanced in extension but unacceptably tight in flexion. Which of the following intraoperative adjustments is most appropriate to balance the knee?

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap. Downsizing the femoral component using an anterior referencing system will resect more posterior femoral condyle, thereby selectively increasing the flexion gap.

Question 88

A 6-year-old boy sustains a completely displaced supracondylar humerus fracture. After closed reduction and percutaneous pinning, the radial pulse remains unpalpable, but the hand is warm, pink, and has a capillary refill of less than 2 seconds. What is the most appropriate next step in management?

Explanation

A 'pulseless but pink' and well-perfused hand following a properly reduced supracondylar humerus fracture typically indicates adequate collateral circulation. The standard of care is close inpatient observation rather than immediate vascular exploration.

Question 89

A 24-year-old rugby player injures his midfoot. Weight-bearing radiographs reveal a 3 mm diastasis between the base of the 1st and 2nd metatarsals. An avulsion fracture (fleck sign) is noted. The injured ligament in this condition normally connects which two structures?

Explanation

The Lisfranc ligament is a strong interosseous ligament that connects the lateral aspect of the medial cuneiform to the medial base of the second metatarsal. Disruption of this ligament causes midfoot instability and requires operative stabilization.

Question 90

A 30-year-old male presents with inability to actively flex the distal interphalangeal joint of his ring finger after a rugby tackle. Radiographs and ultrasound show the flexor digitorum profundus (FDP) tendon retracted into the palm. According to the Leddy-Packer classification, what is the ideal timeframe for surgical repair of this specific injury pattern?

Explanation

A Type I FDP avulsion (Jersey finger) involves tendon retraction into the palm, disrupting its vincula and blood supply. It must be surgically repaired within 7 to 10 days to prevent permanent ischemic contracture of the tendon.

Question 91

A 55-year-old male presents with a progressively enlarging, painful mass in his proximal femur. Biopsy confirms conventional high-grade chondrosarcoma. Which of the following best describes the optimal treatment strategy for this patient?

Explanation

Conventional chondrosarcomas are notoriously resistant to both chemotherapy and radiation therapy due to their poor vascularity and slow growth fraction. Wide surgical resection is the definitive and most effective treatment.

Question 92

A 7-year-old child sustains a Bado Type I Monteggia fracture-dislocation. Which of the following nerve injuries is most classically associated with this specific injury pattern?

Explanation

Monteggia fracture-dislocations involve a proximal ulna fracture with radial head dislocation. The posterior interosseous nerve (PIN) is anatomically tethered at the arcade of Frohse and is highly susceptible to traction or direct injury, particularly in anterior and lateral dislocations.

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