Which of the following findings is considered a contraindication for posterior decompression (with or without fusion) for myelopathy?

Fixed kyphosis of more than 10°

Which of the following best describes the most common anatomic variation seen in the glenoid labrum and the middle glenohumeral ligament in the anterosuperior quadrant of the shoulder?

Labrum attached to the glenoid rim and a flat/broad middle glenohumeral ligament

-A form of renal osteodystrophy that is characterized by pure osteomalacia is caused by

Aluminum deposition in bone from oral phosphate binders

A 2-week-old infant has had diminished movement of the right upper extremity since birth. Examination reveals weakness of shoulder abduction and external rotation, elbow flexion, and forearm supination. Both pupils are equally round and responsive to

observation and range-of-motion exercises.

A 19-year-old female long-distance runner has an incomplete tension-side femoral neck stress fracture. Management should consist of

internal fixation at the time of diagnosis.

Emergent management of acute tooth displacement (luxation) includes

delaying replantation until a dentist is present.

All of the following are advantages of supine over lateral positioning during intramedullary nailing of subtrochanteric femur fractures EXCEPT:

Can be protective to an injured spine

The therapeutic effect of etanercept in the treatment of rheumatoid arthritis is primarily mediated through

antagonism of tumor necrosis factor-alpha (TNF-α).

Orthopedic Ban Review | Dr Hutaif General Orthopedics

Question 1

A surgeon uses a stainless steel screw through a titanium plate for internal fixation of a diaphyseal femur fracture.

What type of corrosion is most likely to occur due to this construct?

Explanation

Galvanic corrosion occurs when two dissimilar metals, such as stainless steel and titanium, are placed in direct physical contact within an electrolytic medium (such as bodily fluids). The metal with the lower nobility (stainless steel) acts as the anode and corrodes faster, while the more noble metal (titanium) acts as the cathode. Fretting corrosion involves mechanical micromotion, and crevice corrosion occurs in oxygen-depleted zones like screw hole interfaces.

Question 2

A hemodynamically unstable patient is brought to the trauma bay after a high-speed motor vehicle collision. The anteroposterior pelvic radiograph

shows an APC-III injury with >2.5 cm widening of the pubic symphysis. To properly apply a pelvic binder to reduce pelvic volume, over which anatomic landmark should the binder be centered?

Explanation

A pelvic binder must be applied directly over the greater trochanters to effectively close an open-book pelvic ring injury. Placing the binder higher, over the iliac crests or anterior superior iliac spines, can paradoxically worsen the pubic diastasis and is less effective at reducing pelvic volume and controlling hemorrhage.

Question 3

A 12-year-old obese male presents with a 2-week history of left thigh pain and an antalgic limp. Examination reveals obligate external rotation with passive hip flexion. A radiograph is shown

. He is diagnosed with a Slipped Capital Femoral Epiphysis (SCFE). Which of the following is the strongest indication for prophylactic pinning of the contralateral asymptomatic hip?

Explanation

Prophylactic pinning of the contralateral hip in SCFE is highly recommended for patients with an underlying endocrine disorder (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy), as they have a significantly higher risk of a subsequent bilateral slip. A low modified Oxford bone age score (<16), denoting skeletal immaturity, is also a relative indication, but a score of 20 indicates skeletal maturity.

Question 4

A 15-year-old boy presents with severe right tibial pain that occurs predominantly at night and is dramatically relieved by NSAIDs. Imaging

reveals a cortical radiolucent nidus measuring 8 mm surrounded by dense reactive sclerosis. What is the most appropriate definitive minimally invasive treatment?

Explanation

The clinical presentation and imaging are classic for an osteoid osteoma (nidus <1.5 cm, nocturnal pain relieved by NSAIDs). Radiofrequency ablation (RFA) under CT guidance is the standard of care and the most appropriate minimally invasive definitive treatment, offering excellent success rates with minimal morbidity.

Question 5

A 55-year-old male underwent a total hip arthroplasty 3 years ago utilizing a ceramic-on-ceramic bearing surface

. He presents to the clinic complaining of a new, audible 'squeaking' sound originating from his hip when walking. What is the most common mechanical etiology for this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic (CoC) total hip arthroplasty is a known complication. It is most commonly associated with edge loading caused by component malposition (such as a vertically placed or excessively anteverted cup). Edge loading disrupts the fluid lubrication film, leading to localized stripe wear on the ceramic head and resulting in the audible squeak.

Question 6

A 25-year-old male is brought to the ED after a diving accident. He is awake, alert, and cooperative. Examination reveals bilateral upper and lower extremity weakness consistent with an incomplete spinal cord injury. Imaging

demonstrates a bilateral C5-C6 facet dislocation. According to major guidelines, what is the most appropriate next step in management?

Explanation

In an awake, cooperative, and testable patient with a cervical facet dislocation, urgent closed reduction using cranial traction (e.g., Gardner-Wells tongs) with serial neurological examinations is indicated. An MRI prior to reduction is generally reserved for patients who are obtunded, uncooperative, or who fail closed reduction, as delaying reduction to obtain an MRI can prolong spinal cord ischemia.

Question 7

A 22-year-old female soccer player undergoes an anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone (BPTB) autograft

. Postoperatively, she reports a localized area of numbness on the anterior/anterolateral aspect of her proximal leg. Injury to which nerve during graft harvest is responsible for this finding?

Explanation

The infrapatellar branch of the saphenous nerve crosses the proximal anterior tibia from medial to lateral. It is highly susceptible to iatrogenic injury during the anterior longitudinal incision used for harvesting a central third bone-patellar tendon-bone autograft. Injury results in numbness over the anterior and lateral aspect of the knee and proximal leg.

Question 8

A 25-year-old rugby player presents with an inability to actively flex the distal interphalangeal (DIP) joint of his ring finger after grabbing an opponent's jersey. Radiographs

reveal a large bony avulsion fragment located at the level of the A4 pulley. Based on the Leddy-Packer classification, what type of flexor digitorum profundus (FDP) avulsion is this?

Explanation

The Leddy-Packer classification for FDP avulsions (Jersey finger): Type 1 describes retraction into the palm (blood supply disrupted, requires early repair). Type 2 retracts to the level of the PIP joint, held by the intact vincula. Type 3 is characterized by a large bony avulsion fragment that catches at the A4 pulley, preventing further proximal retraction.

Question 9

A 30-year-old construction worker drops a heavy beam on his midfoot. Radiographs and CT imaging

demonstrate a purely ligamentous Lisfranc injury with significant lateral and dorsal displacement of the 2nd through 5th metatarsals. Based on recent literature comparing operative techniques, what is the favored surgical management for purely ligamentous Lisfranc injuries?

Explanation

Recent level 1 orthopedic trauma literature (such as the study by Coetzee et al. and subsequent meta-analyses) has shown that primary arthrodesis for purely ligamentous Lisfranc injuries provides superior short- and mid-term functional outcomes and lower rates of hardware removal and secondary surgery compared to Open Reduction and Internal Fixation (ORIF).

Question 10

A 21-year-old man falls on an outstretched hand. Imaging

shows a displaced fracture through the proximal third of the scaphoid. The patient is counseled regarding a high risk of avascular necrosis (AVN). The primary blood supply to the proximal pole of the scaphoid enters the bone at which location?

Explanation

The scaphoid receives its primary blood supply (70-80%) via branches of the radial artery that enter distally at the dorsal ridge near the waist and flow retrograde to supply the proximal pole. Because of this tenuous retrograde blood supply, fractures at the waist or proximal pole carry a high risk of nonunion and avascular necrosis.

Question 11

A 45-year-old male sustains a severe high-energy knee injury. Radiographs and CT

show a Schatzker IV tibial plateau fracture with a predominant, displaced posteromedial fragment. To adequately apply a buttress plate to this fragment and prevent varus collapse, which surgical approach is most appropriate?

Explanation

Schatzker IV fractures involve the medial plateau. When a significant posteromedial fragment is present, it is best addressed with an anti-glide buttress plate. The standard posteromedial approach utilizes the interval between the medial head of the gastrocnemius (retracted laterally) and the pes anserinus (retracted medially or anteriorly) to directly access the posteromedial cortex.

Question 12

A 6-month-old female with developmental dysplasia of the hip (DDH) has failed 4 weeks of compliant Pavlik harness treatment. An ultrasound

reveals the hip remains persistently dislocated. What is the most appropriate next step in her management?

Explanation

If a Pavlik harness fails to achieve reduction of a dislocated hip after 3 to 4 weeks of compliant use, it should be abandoned to prevent "Pavlik harness disease" (damage to the posterior acetabulum). The definitive next step in management for a 6-month-old is a closed reduction under general anesthesia, usually accompanied by an arthrogram and adductor tenotomy, followed by spica casting.

Question 13

During a primary total knee arthroplasty (TKA) for a patient with a severe, fixed valgus deformity

, the surgeon employs an "inside-out" lateral release technique to balance the knee. In the classical stepwise sequence described for valgus release, which of the following structures is typically released first?

Explanation

In the stepwise "inside-out" release for a fixed valgus knee in TKA, the iliotibial band (ITB) is generally the first structure released, particularly to balance tightness in extension. If the knee remains tight in both flexion and extension, the posterolateral capsule or LCL may subsequently be sequentially released according to the specific gaps.

Question 14

A 65-year-old man presents with deteriorating handwriting, dropping objects, and frequent tripping over the past year. Examination reveals a positive Hoffman's sign and hyperreflexia. A cervical MRI

confirms severe stenosis at C4-C6. He is still able to ambulate, but requires the daily use of a cane. What is his Nurick classification grade?

Explanation

The Nurick scale assesses cervical myelopathy based on gait impairment. Grade 0: Root signs only. Grade 1: Signs of cord involvement, normal gait. Grade 2: Mild gait abnormality, but employed. Grade 3: Gait abnormality prevents employment, can walk unassisted. Grade 4: Ambulates only with assistance (cane, walker). Grade 5: Chairbound or bedridden. Because he requires a cane, he is Grade 4.

Question 15

A 40-year-old clerical worker is diagnosed with severe, recalcitrant cubital tunnel syndrome

. Intraoperatively, the ulnar nerve is found to be compressed precisely where it passes between the two heads of the flexor carpi ulnaris (FCU). What is the specific eponymous anatomical structure that forms the roof of this compression site?

Explanation

Osborne's ligament, or the cubital tunnel retinaculum, forms the roof of the cubital tunnel. It stretches from the medial epicondyle to the olecranon, spanning the two heads of the flexor carpi ulnaris (FCU). The Arcade of Struthers is a fascial band located more proximally (about 8 cm proximal to the medial epicondyle) where the ulnar nerve pierces the medial intermuscular septum.

Question 16

In the process of secondary bone healing following a diaphyseal fracture, which specific phase is characterized by the peak of angiogenesis, maximum tissue cellularity, and the replacement of soft cartilaginous callus by hard woven bone?

Explanation

Secondary bone healing occurs in three main phases: Inflammation, Repair (soft and hard callus), and Remodeling. The Reparative phase is characterized by significant angiogenesis, the proliferation of osteoblasts, and the conversion of the soft (fibrocartilaginous) callus into a hard (woven bone) callus via endochondral ossification.

Question 17

A 78-year-old female sustains a comminuted 4-part proximal humerus fracture. The surgeon elects to perform a reverse total shoulder arthroplasty (RTSA). To minimize the risk of post-operative external rotation weakness and optimize functional outcome, the surgeon must prioritize the healing of which specific bony fragment?

Explanation

In RTSA performed for proximal humerus fractures, while the implant design compensates for rotator cuff arthropathy by relying on the deltoid, healing of the greater tuberosity is strongly correlated with improved active external rotation and significantly better overall patient functional scores (e.g., ASES scores). Therefore, meticulous repair of the greater tuberosity is prioritized.

Question 18

According to the Ponseti method for the non-operative treatment of idiopathic clubfoot, serial casting must correct the components of the deformity in a highly specific order to prevent midfoot breach. What is the correct sequence of deformity correction?

Explanation

The Ponseti method dictates that the deformities of clubfoot be corrected in the CAVE sequence: first the Cavus (by elevating the first ray to supinate the forefoot), then Adductus and Varus (simultaneously corrected by abducting the foot around the head of the talus), and finally Equinus (usually requiring a percutaneous Achilles tenotomy as the last step).

Question 19

Biochemically, articular cartilage is a highly specialized connective tissue designed to resist compressive forces in joints. Which of the following collagen types forms the vast majority of the primary structural framework of normal hyaline articular cartilage?

Explanation

Type II collagen makes up 90-95% of the collagen found in normal hyaline articular cartilage. It provides the tensile framework that, combined with the swelling pressure of aggrecan (proteoglycans), allows cartilage to resist compressive loads. Type I is found in bone and fibrocartilage (e.g., meniscus, scar tissue). Type X is found in the hypertrophic zone of the growth plate.

Question 20

A 30-year-old male presents with a slow-growing, painful soft tissue mass deep in his distal thigh near the knee joint. Histopathology reveals a biphasic pattern consisting of both spindle cells and epithelial cells. Molecular testing of the biopsy specimen demonstrates a t(X;18) chromosomal translocation. What is the most likely diagnosis?

Explanation

The presence of a biphasic histologic pattern (spindle and epithelial cells) and the characteristic t(X;18)(p11;q11) chromosomal translocation, which results in the SYT-SSX fusion gene, are pathognomonic for Synovial Sarcoma. Despite its name, synovial sarcoma rarely arises directly from joint synovium, often occurring in periarticular soft tissues of young adults.

Question 21

Which of the following biomechanical material properties is represented by the total area under the stress-strain curve up to the point of failure?

Explanation

Toughness is defined as the amount of energy a material can absorb before it fractures, which corresponds to the total area under the stress-strain curve. Stiffness is the slope of the elastic portion (Young's modulus). Yield strength is the stress at which plastic deformation begins. Ductility is the amount of plastic strain a material can undergo before failure.

Question 22

In healthy articular cartilage, which zone is characterized by the highest concentration of water and collagen fibers that are oriented strictly parallel to the joint surface?

Explanation

The superficial (tangential) zone makes up the top 10-20% of articular cartilage. It contains the highest water content (approx 80%), the lowest proteoglycan content, and collagen fibers (predominantly Type II) aligned parallel to the articular surface to resist shear forces.

Question 23

A 12-year-old boy presents with frequent fractures and a classic 'rugger jersey' appearance of his spine on lateral radiographs. Genetic testing reveals a mutation in the CLCN7 gene. Which of the following best describes the underlying cellular pathophysiology of his condition?

Explanation

The clinical picture describes Osteopetrosis (Albers-Schönberg disease), characterized by dense but brittle bones. The most common genetic defect involves the CLCN7 gene, which impairs the chloride channel necessary for osteoclasts to acidify Howship's lacuna, preventing the formation of a functional ruffled border and halting bone resorption.

Question 24

Tranexamic acid (TXA) is widely utilized in orthopedic surgery to mitigate perioperative blood loss. What is its precise mechanism of action?

Explanation

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

Question 25

A 65-year-old man presents with diffuse bone pain, anemia, and hypercalcemia. Radiographs show multiple 'punched-out' lytic lesions in the pelvis and proximal femur.

Serum protein electrophoresis demonstrates a monoclonal spike. What is the most appropriate initial surgical management for an impending pathologic fracture of the subtrochanteric femur in this patient?

Explanation

The patient has Multiple Myeloma, the most common primary bone malignancy in adults. Because myeloma lesions are highly responsive to radiation and are systemic, the standard of care for impending or actual pathologic fractures in the long bones is stabilization (e.g., prophylactic intramedullary nailing) followed by postoperative radiation therapy. En bloc resection is not indicated for this systemic, radiosensitive disease.

Question 26

A 4-year-old boy presents with progressive severe bowing of his lower extremities and a waddling gait. Laboratory tests reveal normal serum calcium, significantly low serum phosphate, normal parathyroid hormone (PTH), and elevated alkaline phosphatase. What is the most likely genetic mutation responsible for this condition?

Explanation

This presentation is classic for X-linked hypophosphatemic rickets (XLH). It is caused by a mutation in the PHEX gene, which leads to an overproduction of FGF-23. High FGF-23 decreases renal reabsorption of phosphate and decreases 1-alpha-hydroxylase activity, leading to isolated profound hypophosphatemia with normal calcium and PTH levels.

Question 27

In the pathogenesis of periprosthetic joint infection, biofilm formation provides bacteria with a physical barrier against host defenses and antibiotics. What is the primary extracellular polymeric substance produced by Staphylococcus epidermidis to facilitate this structural adhesion?

Explanation

Staphylococcus epidermidis is a notorious biofilm producer in implant-related infections. The crucial structural component of this biofilm matrix is the Polysaccharide Intercellular Adhesin (PIA), also known as poly-N-acetylglucosamine (PNAG), which facilitates bacterial aggregation and immune evasion.

Question 28

A 32-year-old man sustains a closed high-energy tibial shaft fracture. Clinical concern for acute compartment syndrome arises.

According to standard orthopedic practice, which of the following objective pressure criteria is most predictive of the need for emergent fasciotomy?

Explanation

The Delta P concept is the most reliable objective measure for diagnosing acute compartment syndrome. A Delta P (Diastolic Blood Pressure - Intra-compartmental Pressure) of less than 30 mmHg is an absolute indication for emergent four-compartment fasciotomy, as muscle perfusion becomes critically compromised below this threshold.

Question 29

Which of the following mechanical and biological conditions must be strictly satisfied for primary (direct) cortical bone healing to occur without the formation of a visible intermediate cartilaginous callus?

Explanation

Primary (direct) bone healing occurs via cutting cones (osteonal remodeling) directly across the fracture site. It bypasses intermediate callus formation and requires strictly absolute mechanical stability (interfragmentary strain < 2%) and precise anatomical reduction with virtually no gap.

Question 30

In total hip arthroplasty, aseptic loosening due to osteolysis is primarily driven by the biological reaction to wear debris. In a well-functioning, accurately aligned metal-on-polyethylene articulation, which specific mechanism of wear is predominantly responsible for generating the submicron polyethylene particles that trigger this cascade?

Explanation

Adhesive wear occurs when two surfaces rub together and micro-bonds form and break, leading to the transfer or liberation of small particles. In well-functioning metal-on-polyethylene joints without third-body interposition, adhesive wear is the most significant source of the submicron (0.1 to 1.0 micrometer) particles most actively engulfed by macrophages to incite osteolysis.

Question 31

A 55-year-old woman presents with worsening thigh pain. Radiographs demonstrate a large, permeative lytic lesion in the proximal femur with intralesional 'popcorn' calcifications. An open biopsy confirms a high-grade (Grade III) conventional chondrosarcoma.

What is the most appropriate definitive treatment?

Explanation

Conventional chondrosarcoma is notoriously resistant to both chemotherapy and radiation therapy. Therefore, the mainstay of treatment for high-grade (Grade II and III) lesions is wide surgical resection alone, typically with endoprosthetic reconstruction. Curettage is reserved only for low-grade (Grade I/atypical cartilaginous tumors) in specific anatomic locations.

Question 32

A novel diagnostic test for a rare orthopedic condition is developed with a sensitivity of 95% and a specificity of 90%. If this test is utilized in a primary care population where the actual prevalence of the disease is very low (e.g., 0.1%), what is the most likely statistical effect compared to using it in an orthopedic specialty clinic where the prevalence is 40%?

Explanation

Positive Predictive Value (PPV) and Negative Predictive Value (NPV) are highly dependent on disease prevalence. In a population with very low prevalence, the absolute number of false positives outnumbers the true positives, causing the PPV to drop significantly. Sensitivity and specificity are intrinsic properties of the test and do not change with prevalence.

Question 33

Bone morphogenetic proteins (BMPs) play a pivotal role in osteoinduction during bone healing. Upon binding to their transmembrane serine/threonine kinase receptors, which specific intracellular signaling molecules are phosphorylated and translocate to the nucleus to act as transcription factors?

Explanation

BMP signaling operates primarily via the canonical Smad pathway. BMP binds to a type II serine/threonine kinase receptor, which recruits and phosphorylates a type I receptor. This complex then phosphorylates receptor-regulated Smads (Smad 1, 5, or 8), which complex with Smad 4 and translocate to the nucleus to regulate gene transcription for osteoblast differentiation.

Question 34

A 68-year-old patient undergoes elective total knee arthroplasty. Postoperatively, she is prescribed oral Rivaroxaban for deep vein thrombosis (DVT) prophylaxis. What is the precise pharmacological target of this medication?

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa in the coagulation cascade. Dabigatran inhibits direct thrombin (Factor IIa). Warfarin inhibits vitamin K epoxide reductase. Clopidogrel blocks the P2Y12 ADP receptor on platelets.

Question 35

Following a severe crush injury to the arm resulting in a Sunderland Grade IV injury of the radial nerve, Wallerian degeneration ensues.

Which of the following best describes the classical process of Wallerian degeneration?

Explanation

Wallerian degeneration is the active process of anterograde degeneration of the axon and its myelin sheath distal to the site of a severe nerve injury (axotmesis or neurotmesis). Macrophages and Schwann cells subsequently clear the debris, leaving endoneurial tubes (bands of Büngner) to guide potential regenerating axons.

Question 36

A 13-year-old obese boy is brought to the emergency department strictly unable to bear weight on his left leg after a minor slip. Radiographs confirm a severe, unstable slipped capital femoral epiphysis (SCFE).

He undergoes urgent single-screw in situ fixation. Which of the following is the most feared and highest-risk complication specifically associated with an unstable SCFE compared to a stable SCFE?

Explanation

An unstable SCFE is defined clinically by the inability of the patient to ambulate, even with crutches. Unstable slips carry a profoundly higher risk of osteonecrosis (avascular necrosis) of the femoral head (ranging from 20% to nearly 50%), whereas AVN is exceedingly rare in stable SCFE. Chondrolysis is another complication but is classically associated with unrecognized pin joint penetration.

Question 37

Tendons possess exceptionally high tensile strength owing to their highly organized composition and structural hierarchy. Which of the following pairs correctly identifies the predominant collagen type and the primary proteoglycan found in a normal, healthy tendon?

Explanation

Healthy tendon extracellular matrix is composed of approximately 85-90% Type I collagen (providing tensile strength). The most abundant proteoglycan in tendon is Decorin, which binds to Type I collagen fibrils and regulates their assembly and diameter. Type II collagen and Aggrecan are primarily found in articular cartilage.

Question 38

Fractures of the talar neck carry a famously high risk of avascular necrosis due to the tenuous, retrograde blood supply to the talar body.

Which of the following arteries provides the major contribution to the vascularity of the talar body?

Explanation

The artery of the tarsal canal (a major branch of the posterior tibial artery) provides the predominant blood supply to the body of the talus, entering via the talar neck and running in a retrograde fashion. This makes it highly vulnerable to injury in displaced talar neck fractures.

Question 39

You are consulted regarding a diabetic patient requiring lower extremity amputation due to advanced gangrene.

You counsel the patient on the anticipated increased metabolic energy expenditure required for ambulation with a prosthesis. Based on classic orthopedic data, which of the following amputation levels is associated with the highest percentage increase in energy expenditure compared to normal baseline walking?

Explanation

Energy expenditure increases significantly with higher levels of amputation, particularly in patients with vascular disease. Unilateral vascular transfemoral (Above-Knee) amputation increases energy expenditure by approximately 65-100% over baseline. Bilateral transtibial is roughly 40-41%. Unilateral vascular transtibial is ~40%. Syme is ~15%. Therefore, the vascular transfemoral amputation imposes the highest energy demand.

Question 40

A 70-year-old woman with a T-score of -3.1 is prescribed Alendronate for the treatment of osteoporosis.

What is the precise intracellular mechanism by which this nitrogen-containing bisphosphonate inhibits osteoclast function and causes osteoclast apoptosis?

Explanation

Nitrogen-containing bisphosphonates (like Alendronate, Risedronate, Zoledronate) inhibit farnesyl pyrophosphate (FPP) synthase, a key enzyme in the mevalonate pathway. This prevents the prenylation of small GTPase proteins (like Ras, Rho, and Rab) essential for osteoclast survival and cytoskeletal organization (ruffled border formation), ultimately leading to osteoclast apoptosis.

Question 41

A 65-year-old dysvascular patient undergoes a transfemoral amputation. Compared to baseline normal human gait, what is the expected increase in energy expenditure for this patient during ambulation with a properly fitted prosthesis?

Explanation

Energy expenditure during gait increases as the level of amputation moves proximally. Approximate increases in energy expenditure compared to normal baseline gait are: Syme amputation (15%), unilateral below-knee amputation (25%), bilateral below-knee amputation (41%), unilateral above-knee amputation (65%), and bilateral above-knee amputation (>200%). Dysvascular amputees often expend even more energy than traumatic amputees of the same level.

Question 42

During the stance phase of a normal gait cycle, the hip abductors fire to stabilize the pelvis and prevent a Trendelenburg drop. In which specific phase of the gait cycle does maximal contraction of the gluteus medius occur?

Explanation

The gluteus medius fires to stabilize the pelvis during the single-leg support phase of gait. Maximal contraction of the gluteus medius occurs during mid-stance, which corresponds to the time when the contralateral leg is in the swing phase, requiring maximum abductor moment to keep the pelvis level.

Question 43

Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is commonly used in total joint arthroplasty to reduce volumetric wear. Which of the following is a direct biomechanical consequence of increasing the radiation dose to maximize cross-linking in the polyethylene?

Explanation

While high-dose irradiation increases the cross-linking of UHMWPE (which significantly decreases adhesive and abrasive wear), it inversely affects the mechanical properties of the material. Highly cross-linked polyethylene exhibits decreased ultimate tensile strength, decreased yield strength, decreased fatigue limit, and decreased elongation to failure, making it more brittle than conventional UHMWPE.

Question 44

A new diagnostic biomarker is evaluated for the detection of periprosthetic joint infection (PJI). Out of 100 patients confirmed to not have PJI via gold-standard criteria, the new test correctly identifies 90 of them as negative. What statistical measure does this result (90%) directly represent?

Explanation

Specificity is defined as the true negative rate, or the proportion of patients without the disease who test negative (True Negatives / [True Negatives + False Positives]). Since 90 out of 100 disease-free patients tested negative, the specificity is 90%.

Question 45

A 14-year-old boy presents with a diaphyseal femur lesion exhibiting an 'onion-skin' periosteal reaction.

Biopsy confirms sheets of small, uniform, blue round cells with scant cytoplasm. Which of the following chromosomal translocations is most characteristic of this pathology?

Explanation

The clinical, radiographic, and histologic descriptions are classic for Ewing sarcoma. The most common chromosomal translocation associated with Ewing sarcoma is t(11;22)(q24;q12), which results in the EWS-FLI1 fusion protein. t(9;22) is seen in extraskeletal myxoid chondrosarcoma (and CML). t(2;13) is seen in alveolar rhabdomyosarcoma. t(X;18) is seen in synovial sarcoma. t(12;16) is seen in myxoid liposarcoma.

Question 46

A patient is prescribed rivaroxaban for extended deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the specific mechanism of action of this medication?

Explanation

Rivaroxaban and apixaban are oral direct Factor Xa inhibitors. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin is a vitamin K epoxide reductase inhibitor. Low molecular weight heparins (e.g., enoxaparin) act primarily by binding and activating antithrombin III, which then inactivates Factor Xa (and to a lesser extent IIa).

Question 47

During the incorporation of a cortical structural allograft, a process known as creeping substitution occurs. What physiological process characterizes the initial phase of creeping substitution in this setting?

Explanation

Creeping substitution is the process by which a bone graft is resorbed and replaced by host bone. In cortical grafts, the sequence is: (1) inflammation and neovascularization (vascular invasion), (2) osteoclastic resorption via cutting cones, and (3) osteoblastic new bone formation. Unlike cancellous grafts where osteoblastic apposition occurs early, cortical grafts must first undergo osteoclastic resorption to create space for new bone formation.

Question 48

Articular cartilage is structurally divided into four distinct zones to optimize its biomechanical properties. In which zone are the collagen fibers oriented primarily perpendicular to the joint surface to resist compressive forces?

Explanation

In articular cartilage, the superficial (tangential) zone has collagen fibers oriented parallel to the surface to resist shear forces. The middle (transitional) zone has randomly oriented fibers. The deep (radial) zone has collagen fibers oriented perpendicular to the joint surface, extending down to the tidemark, to provide maximum resistance to compressive loads. The tidemark separates the deep zone from the calcified zone.

Question 49

A 55-year-old female with malabsorption presents with diffuse bone pain, muscle weakness, and a Looser zone on radiographs.

Laboratory studies reveal low serum calcium, low serum phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone levels. What is the most likely diagnosis?

Explanation

The clinical presentation and laboratory profile (low Ca, low P, high ALP, high PTH) are characteristic of osteomalacia secondary to severe Vitamin D deficiency (often from malabsorption). The low Vitamin D leads to decreased intestinal calcium absorption, triggering secondary hyperparathyroidism (high PTH). PTH causes renal phosphate wasting (low P). Primary hyperparathyroidism would typically show high serum calcium. Paget's disease typically has normal Ca and P with a markedly elevated ALP.

Question 50

In the pathogenesis of periprosthetic joint infection, biofilm formation protects bacteria from host defenses and systemic antibiotics. What is the primary constituent of the extracellular polymeric substance (EPS) matrix in a mature staphylococcal biofilm?

Explanation

The biofilm matrix produced by staphylococci (especially S. epidermidis and S. aureus) is largely composed of an extracellular polymeric substance (EPS). A major component of this matrix is polysaccharide intercellular adhesin (PIA), also known as poly-N-acetylglucosamine (PNAG), along with extracellular DNA (eDNA) and various proteins. It provides a structural scaffold and barrier against antimicrobials.

Question 51

A peripheral nerve injury results in complete disruption of the axons and their surrounding myelin sheaths, but the endoneurial tubes remain entirely intact. Wallerian degeneration occurs distally. Which Sunderland classification best describes this injury?

Explanation

According to Sunderland's classification: First degree corresponds to neurapraxia (focal conduction block). Second degree corresponds to axonotmesis with intact endoneurium. Third degree is axon disruption with endoneurium disruption, but intact perineurium. Fourth degree is disruption of axon, endoneurium, and perineurium, with an intact epineurium (neuroma-in-continuity). Fifth degree is a complete nerve transection (neurotmesis).

Question 52

When evaluating the biomechanical holding power of a cortical bone screw, the pull-out strength is most directly proportional to which of the following screw characteristics?

Explanation

The pull-out strength of a bone screw is directly proportional to the volume of bone engaged by the threads. The formula for pull-out strength correlates most directly with the outer thread diameter, the length of thread engagement, and the shear strength of the bone material. Increasing the outer thread diameter is the most effective way to increase pull-out strength in a given cortical thickness.

Question 53

A child presenting with rhizomelic short stature, a prominent forehead, and midface hypoplasia is diagnosed with achondroplasia. What is the specific genetic and molecular basis of this condition?

Explanation

Achondroplasia is an autosomal dominant condition caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 is normally a negative regulator of chondrocyte proliferation in the growth plate; its constant activation prematurely halts endochondral ossification. COL1A1/COL1A2 mutations cause osteogenesis imperfecta. COMP mutations cause pseudoachondroplasia and multiple epiphyseal dysplasia. RUNX2 mutations cause cleidocranial dysplasia. PHEX mutations cause X-linked hypophosphatemic rickets.

Question 54

The optimal low-friction environment of healthy articular cartilage during high-load, dynamic activities (such as the stance phase of running) is primarily maintained by which of the following mechanisms?

Explanation

In articular cartilage, elastohydrodynamic lubrication occurs during high-load, dynamic movements. The cartilage deforms slightly under pressure, which traps a layer of synovial fluid between the articulating surfaces, keeping them separated. Boundary lubrication (via lubricin) dominates under static or low-speed, high-load conditions.

Question 55

Secondary bone healing is characterized by the formation of a fracture callus. During the initial soft callus phase, which type of collagen is predominantly synthesized by the proliferating chondrocytes?

Explanation

Secondary bone healing proceeds through endochondral ossification, forming a cartilaginous soft callus. Chondrocytes in the soft callus predominantly synthesize Type II collagen (the primary collagen of hyaline cartilage). As the callus matures into a hard bony callus, the chondrocytes undergo hypertrophy (expressing Type X collagen) before being replaced by osteoblasts that secrete Type I collagen.

Question 56

Fibroblast growth factor 23 (FGF-23) plays a critical role in mineral metabolism and is often significantly elevated early in the course of chronic kidney disease. What is the primary physiologic effect of FGF-23?

Explanation

FGF-23 is a hormone primarily produced by osteocytes that serves to lower serum phosphate levels. It acts on the kidneys to decrease phosphate reabsorption (causing phosphaturia) by downregulating NaPi co-transporters in the proximal tubule. It also inhibits 1-alpha-hydroxylase, decreasing the production of active Vitamin D (1,25-OH2 D3), which further reduces intestinal phosphate and calcium absorption.

Question 57

When measuring intracompartmental pressures to evaluate for acute compartment syndrome of the lower extremity, which of the following absolute or differential pressure measurements is the most reliable and generally accepted threshold indicating the need for emergency fasciotomy?

Explanation

The most widely accepted parameter for diagnosing acute compartment syndrome is the delta pressure (ΔP). A delta pressure (Diastolic Blood Pressure minus Intracompartmental Pressure) of less than 30 mmHg indicates critically impaired microcirculation and is an indication for fasciotomy. Absolute pressure thresholds (e.g., >30 or >40 mmHg) are less reliable due to individual variations in blood pressure.

Question 58

A 19-year-old male complains of severe, localized thigh pain that occurs primarily at night and is dramatically relieved by aspirin. Radiographs demonstrate an area of dense cortical sclerosis with a 6 mm radiolucent nidus. The intense pain associated with this lesion is mediated primarily by the local production of:

Explanation

The clinical presentation is classic for an osteoid osteoma. The nidus of an osteoid osteoma has a very high concentration of cyclooxygenase-2 (COX-2), which produces high levels of Prostaglandin E2 (PGE2). This massive localized PGE2 release is responsible for the intense pain, which explains why NSAIDs (which inhibit COX and thus PGE2 production) are highly effective in providing symptomatic relief.

Question 59

Slipped capital femoral epiphysis (SCFE) is a common adolescent hip disorder characterized by the displacement of the proximal femoral epiphysis. Pathologically, failure and slippage occur through which specific zone of the proximal femoral physis?

Explanation

In SCFE, the structural failure occurs through the hypertrophic zone of the physis. This zone is the weakest portion of the growth plate biomechanically due to the large size of the chondrocytes and the relatively low matrix-to-cell ratio. The hypertrophic zone is widened in SCFE, making it particularly vulnerable to shear stresses.

Question 60

Tranexamic acid (TXA) is extensively utilized in orthopedic procedures (e.g., total joint arthroplasty, trauma) to minimize perioperative blood loss. What is the specific mechanism of action of TXA?

Explanation

Tranexamic acid (TXA) is an antifibrinolytic agent. It functions as a synthetic analog of the amino acid lysine. TXA reversibly binds to the lysine receptor sites on plasminogen, which prevents plasminogen from binding to fibrin and competitively inhibits its activation into plasmin. By blocking plasmin formation, TXA prevents the degradation of fibrin clots, effectively stabilizing existing clots.

Question 61

A 15-year-old male presents with persistent knee pain. Radiographs reveal a metaphyseal lesion in the distal femur with a "sunburst" periosteal reaction.

Which of the following genetic syndromes is most strongly associated with this primary bone malignancy?

Explanation

Osteosarcoma is the most common primary bone malignancy in children and is characterized by a "sunburst" periosteal reaction. It is strongly associated with Li-Fraumeni syndrome (p53 mutation) and hereditary retinoblastoma (Rb mutation).

Question 62

Following a reamed intramedullary nailing of a closed midshaft femur fracture, which type of bone healing predominantly occurs?

Explanation

Reamed intramedullary nailing allows for relative stability and micromotion, leading to secondary bone healing. This process relies on both endochondral and intramembranous ossification, characterized by visible fracture callus.

Question 63

A 6-year-old boy presents after falling from monkey bars with an extension-type Gartland III supracondylar humerus fracture.

Examination reveals weak index finger flexion and absent flexion of the IP joint of the thumb. Which nerve is most likely injured?

Explanation

The anterior interosseous nerve (AIN) is the most commonly injured nerve in extension-type supracondylar humerus fractures. It is evaluated by checking the patient's ability to make an "OK" sign, requiring flexion of the thumb IP and index DIP joints.

Question 64

A 32-year-old male sustains a closed comminuted tibial shaft fracture. Within 8 hours, he develops severe leg pain with passive toe stretch. What is the generally accepted threshold for a diagnostic "delta p" indicating the need for immediate fasciotomy?

Explanation

A delta pressure (diastolic blood pressure minus compartment pressure) of less than 30 mmHg is the accepted threshold for diagnosing acute compartment syndrome. Absolute pressures are less reliable due to variations in systemic blood pressure.

Question 65

A 65-year-old female experiences recurrent posterior dislocations following a primary total hip arthroplasty via a posterior approach. To optimize stability, what is the ideal orientation for the acetabular component according to Lewinnek's safe zone?

Explanation

Lewinnek's safe zone dictates an inclination (abduction) of 40 degrees +/- 10 degrees, and an anteversion of 15 degrees +/- 10 degrees. Positioning the cup within this range minimizes posterior impingement and dislocation.

Question 66

A 72-year-old male is evaluated for progressive clumsiness. Examination reveals hyperreflexia in the lower extremities and a positive Hoffmann's sign. Radiographs show significant cervical spondylosis.

What is typically the earliest presenting clinical symptom in cervical spondylotic myelopathy?

Explanation

Subtle gait disturbance and loss of balance are typically the earliest presenting symptoms of cervical spondylotic myelopathy (CSM). Hand clumsiness and fine motor difficulty usually follow closely.

Question 67

A 24-year-old carpenter sustains a laceration over the volar aspect of his proximal phalanx, resulting in a Zone II flexor tendon injury. What is the primary source of nutrition to the flexor tendons in this specific zone?

Explanation

Flexor tendons in Zone II receive nutrition through a dual mechanism: synovial diffusion, which provides the majority, and vascular perfusion via the vincula (longa and brevia).

Question 68

A 17-year-old female soccer player sustains a non-contact pivoting injury to her knee, diagnosed as an anterior cruciate ligament (ACL) tear.

Which of the following is considered the most significant modifiable risk factor for ACL tears in female athletes?

Explanation

Poor neuromuscular control, specifically valgus collapse and stiff-legged landing mechanics, is the most significant modifiable risk factor for non-contact ACL injuries. Injury prevention programs specifically target these biomechanical deficits.

Question 69

A 55-year-old diabetic male presents with a swollen, erythematous, and warm right foot without open ulceration. Radiographs show early fragmentation at the tarsometatarsal joints. What is the most appropriate initial management?

Explanation

The initial treatment for acute, active (Eichenholtz stage 0 or 1) Charcot arthropathy is strict immobilization and offloading. A total contact cast (TCC) combined with non-weight bearing is the gold standard to prevent further deformity.

Question 70

A 40-year-old male sustains a severe open tibia fracture with exposed bone devoid of periosteum that cannot be closed primarily (Gustilo-Anderson IIIB). According to recent evidence, when should definitive soft tissue coverage ideally be performed to minimize infection?

Explanation

Early soft tissue coverage (ideally within 3 to 7 days) for severe open tibia fractures significantly decreases the risk of deep infection and promotes union. Delays beyond 7-10 days drastically increase complication rates.

Question 71

A 9-month-old female is referred for asymmetric thigh folds. Ultrasound reveals a dysplastic left hip with a subluxated femoral head.

She has not received any prior treatment. What is the most appropriate initial management?

Explanation

While the Pavlik harness is the gold standard for infants under 6 months with DDH, its success rate drops significantly in older infants. Closed reduction and spica casting is generally the preferred initial intervention for a child presenting at 6 to 18 months of age.

Question 72

Which zone of articular cartilage contains the highest concentration of water and has collagen fibers oriented parallel to the articular surface to resist shear forces?

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content and features collagen type II fibers aligned parallel to the joint surface. This orientation is critical for resisting shear stresses.

Question 73

A 70-year-old male presents with a painful total knee arthroplasty 2 years post-operation. Joint aspiration reveals a synovial white blood cell (WBC) count of 4,500 cells/uL with 85% polymorphonuclear leukocytes (PMNs).

Based on MSIS criteria, what is the most appropriate definitive management?

Explanation

A synovial WBC > 3,000 cells/uL or PMN% > 80% is diagnostic for chronic PJI in a knee > 4 weeks post-op. The gold standard treatment for chronic PJI in North America is a two-stage exchange arthroplasty.

Question 74

According to Perren's strain theory of fracture healing, what is the maximum strain tolerated by lamellar bone formation?

Explanation

Perren's strain theory states that lamellar bone can tolerate up to 2% strain before failing. Granulation tissue tolerates up to 100%, and cartilage up to 10%.

Question 75

A 35-year-old farm worker sustains an open tibial shaft fracture heavily contaminated with soil. Which of the following antibiotic regimens is most appropriate according to current evidence-based guidelines?

Explanation

Farm injuries are highly associated with Clostridium species. Current guidelines recommend a first-generation cephalosporin, an aminoglycoside for Gram-negative coverage, and high-dose penicillin for anaerobes.

Question 76

A 4-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip. The parents report the child has stopped kicking the right leg. On examination, the infant lacks active knee extension but has normal ankle movements. What is the most likely cause?

Explanation

Excessive hip flexion in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to femoral nerve palsy. This classically presents with absent active knee extension.

Question 77

A 14-year-old boy presents with a diaphyseal femur lesion with an "onion-skin" periosteal reaction. Biopsy confirms a small blue round cell tumor. Which of the following chromosomal translocations is most characteristic of this diagnosis?

Explanation

Ewing sarcoma is classically associated with the t(11;22)(q24;q12) translocation, resulting in the EWS-FLI1 fusion protein. This is a highly characteristic diagnostic molecular marker.

Question 78

In total hip arthroplasty, which bearing surface combination is associated with the lowest volumetric wear rate?

Explanation

Ceramic-on-ceramic bearing surfaces exhibit the lowest volumetric wear rates in total hip arthroplasty. However, they carry risks of component squeaking and catastrophic brittle fracture.

Question 79

A patient presents with a laceration over the volar aspect of the proximal phalanx of the index finger. Both the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) are severed. According to the Verdan classification, which zone of injury is this?

Explanation

Zone II extends from the proximal A1 pulley (distal palmar crease) to the FDS insertion at the middle phalanx. It is historically known as "no man's land" due to poor healing outcomes from tendon adhesions.

Question 80

A 45-year-old male presents with acute onset saddle anesthesia, bilateral radicular leg pain, and urinary retention. Which of the following MRI findings is the most absolute indication for emergent surgical decompression?

Explanation

Urinary retention with saddle anesthesia indicates Cauda Equina Syndrome. A central disc herniation compressing the cauda equina requires emergent surgical decompression to optimize functional urologic and neurologic recovery.

Question 81

A 40-year-old weekend warrior sustains an acute Achilles tendon rupture. Which clinical test is most sensitive and specific for diagnosing a complete Achilles tendon rupture?

Explanation

The Thompson test (calf squeeze test) is the most reliable clinical sign. A lack of passive plantarflexion when squeezing the calf muscles strongly indicates a complete rupture of the Achilles tendon.

Question 82

The anterior cruciate ligament (ACL) is composed of the anteromedial (AM) and posterolateral (PL) bundles. During which knee position is the PL bundle most tight?

Explanation

The posterolateral (PL) bundle of the ACL is tightest in full extension and primarily controls rotatory stability. The anteromedial (AM) bundle is tightest in flexion and primarily controls anterior translation.

Question 83

Which of the following Bone Morphogenetic Proteins (BMPs) is currently FDA-approved for use in acute, open tibial shaft fractures?

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for use in acute open tibial shaft fractures treated with an intramedullary nail. rhBMP-7 was previously approved for recalcitrant nonunions but is no longer commercially available.

Question 84

Following a displaced intracapsular femoral neck fracture, which artery provides the predominant residual blood supply to the femoral head?

Explanation

The medial femoral circumflex artery (MFCA) provides the primary blood supply to the femoral head via the lateral epiphyseal artery branches. Disruption of this blood supply leads to a high risk of avascular necrosis.

Question 85

A 5-year-old boy presents with a limp, fever of 39.0°C, a WBC count of 14,000/mm3, an ESR of 50 mm/hr, and inability to bear weight. According to the Kocher criteria, what is the approximate probability of septic arthritis?

Explanation

The four Kocher criteria are fever >38.5°C, non-weight bearing, ESR >40, and WBC >12,000. With all four criteria present, the probability of septic arthritis is approximately 99%.

Question 86

A 13-year-old boy with a slipped capital femoral epiphysis (SCFE) cannot bear weight even with crutches. According to the Loder classification, this is an unstable SCFE. What is the most significant risk associated with an unstable SCFE compared to a stable SCFE?

Explanation

An unstable SCFE (inability to bear weight with or without crutches) has a significantly higher risk of avascular necrosis (up to nearly 50%) compared to a stable SCFE, which has an AVN rate close to 0%.

Question 87

A 60-year-old woman with breast cancer presents with a lytic metastatic lesion in the peritrochanteric region of the proximal femur. It is moderately painful and involves 2/3 of the cortical diameter. What is her Mirels score and recommended management?

Explanation

The Mirels score components: Site (Lower limb = 2), Pain (Moderate = 2), Lesion nature (Lytic = 3), Size (2/3 of cortex = 3). Total = 10. A score of 9 or greater strongly warrants prophylactic internal fixation.

Question 88

A patient sustains a traumatic spondylolisthesis of the axis (Hangman's fracture). A Levine-Edwards Type II fracture is characterized by disruption of the C2-C3 disc and posterior longitudinal ligament, causing significant angulation and translation. What is the primary mechanism of injury?

Explanation

A Levine-Edwards Type II Hangman's fracture is classically caused by a hyperextension force followed by rebound flexion. It results in significant anterior translation and angulation of C2 on C3.

Question 89

During an open carpal tunnel release, the surgeon must be careful to avoid injuring the recurrent motor branch of the median nerve. What is the most common anatomical variation of this branch?

Explanation

The most common anatomical variation of the recurrent motor branch of the median nerve is extraligamentous with recurrent branching (approx 50-80%). It exits distal to the transverse carpal ligament and curves back to innervate the thenar muscles.

Question 90

A 55-year-old diabetic patient presents with a warm, swollen, erythematous left foot. Radiographs show fragmentation, joint subluxation, and debris at the tarsometatarsal joints. According to the Eichenholtz classification, what stage of Charcot arthropathy is this?

Explanation

Eichenholtz Stage I is the developmental (fragmentation) stage, characterized by clinical inflammation and radiographic evidence of osteopenia, periarticular fragmentation, subluxation, and debris.

Question 91

A 22-year-old male athlete sustains an anterior shoulder dislocation. An MRI reveals an avulsion of the anterior labrum along with the anterior band of the inferior glenohumeral ligament (IGHL) from the glenoid rim. What is the eponym for this specific lesion?

Explanation

A Bankart lesion is defined as an avulsion of the anterior-inferior labrum and the attached inferior glenohumeral ligament complex from the anterior glenoid rim. It is the most common "essential lesion" in traumatic anterior shoulder instability.

Question 92

A 30-year-old man undergoes intramedullary nailing of a closed tibial shaft fracture. Postoperatively, he develops severe pain out of proportion, not relieved by opioids. Passive stretch of the toes exacerbates the pain. Compartment pressure is 35 mmHg and diastolic blood pressure is 60 mmHg. What is the delta pressure, and what is the indicated management?

Explanation

The delta pressure (diastolic BP minus compartment pressure) is 60 - 35 = 25 mmHg. A delta pressure of < 30 mmHg is highly indicative of acute compartment syndrome, and emergent four-compartment fasciotomy is indicated.

Question 93

In articular cartilage, which zone is characterized by the highest concentration of proteoglycans and vertically aligned type II collagen fibers?

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicular to the joint surface. It has the highest concentration of proteoglycans, providing maximum resistance to compressive forces.

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