A 56-year-old woman underwent a total knee arthroplasty 2 years ago and now has pain and swelling. Radiographs of her knee are unremarkable. Her C-reactive protein (CRP) level is 3.0 (reference range [rr], 0.08–3.1 mg/L), and her erythrocyte sediment

nonsurgical treatment without antibiotics.

What is the most important genetic element that distinguishes community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) from hospital-acquired MRSA? Review Topic

Panton-Valentine leukocidin (PVL)

An ulnar nerve palsy at the level of the wrist is typically associated with deficits in the palmaris brevis, the hypothenar muscles, and what other groups of muscles?

All of the interossei, adductor pollicis, and the deep head of the flexor pollicis brevis

Figure 1 shows the radiograph of an 18-year-old patient who has severe knee pain. Treatment consisting of osteotomy should be perfomed

at or just below the tibial tubercle.

When comparing surgical and nonsurgical extremities in patients who underwent anterior cruciate ligament (ACL) reconstruction using patellar tendon or hamstrings autografts, isokinetic strength measurements obtained 6 months after the surgery would m

no significant difference between the hamstring and the pateller tendon.

A 56-year-old man who underwent a left total hip arthroplasty 8 years ago is seen following a fall from a standing height. A radiograph obtained at 2 years postoperatively is shown in Figure 55a and a current radiograph obtained in the emergency depa

Revision of the femoral component to a cementless femoral component that bypasses the fracture site by at least two cortical diameters

A 30-year-old man presents with a distal third tibia fracture that has healed in 25 degrees of varus alignment. The patient is at greatest risk of developing which of the following conditions as a result of this malunion?

Degenerative lumbar spine changes

Dr. Hutaif's General Orthopedics Review MCQ Quiz

Question 1

Which of the following bone morphogenetic proteins (BMPs) is currently FDA-approved as an alternative to autogenous bone graft for use in acute, open tibial shaft fractures treated with an intramedullary nail?

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for use in acute, open tibial shaft fractures treated with an intramedullary nail, as well as for anterior lumbar interbody fusion (ALIF). rhBMP-7 was previously available under an FDA Humanitarian Device Exemption for recalcitrant tibial nonunions but is no longer actively marketed for that specific indication.

Question 2

In the management of polytraumatized patients, Damage Control Orthopedics (DCO) is often favored over Early Total Care (ETC) in 'borderline' or 'unstable' patients. Which of the following systemic inflammatory markers, typically peaking 24 to 48 hours post-injury, has been shown to correlate most closely with the development of multiorgan failure and is frequently used to monitor systemic inflammatory response?

Explanation

Interleukin-6 (IL-6) is a key pro-inflammatory cytokine that peaks 24 to 48 hours after severe injury. Peak levels of IL-6 (especially >500 pg/mL) correlate strongly with injury severity, the magnitude of the surgical 'second hit', and the risk of developing acute respiratory distress syndrome (ARDS) and multiple organ dysfunction syndrome (MODS).

Question 3

An infant with developmental dysplasia of the hip (DDH) is treated with a Pavlik harness. During a routine follow-up visit, the infant exhibits decreased spontaneous extension of the knee on the treated side, though hip motion remains unchanged. Which of the following harness positioning errors is most likely responsible for this complication?

Explanation

The patient is presenting with a femoral nerve palsy, a known complication of the Pavlik harness resulting from excessive hip flexion. Decreasing the degree of hip flexion usually results in spontaneous recovery of the nerve. Excessive hip abduction is strongly associated with a different, severe complication: avascular necrosis (AVN) of the femoral head.

Question 4

A 24-year-old athlete undergoes an anterior cruciate ligament (ACL) reconstruction. Postoperatively, she demonstrates an inability to achieve terminal knee flexion, and physical examination reveals increasing graft tension as the knee moves from extension to flexion. What is the most likely technical error made during the surgery?

Explanation

A femoral tunnel placed too far anteriorly (anterior to Blumensaat's line) causes the ACL graft to be tight in flexion and loose in extension. This error restricts knee flexion, can lead to graft stretching or failure, and causes a 'captured knee' feeling.

Question 5

A 55-year-old active male underwent a total hip arthroplasty (THA) utilizing a ceramic-on-ceramic bearing surface. Two years postoperatively, he complains of an audible, high-pitched squeaking sound during hip movement, though he is generally pain-free. Which of the following technical factors is most strongly associated with this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic THA is a well-documented complication strongly associated with edge loading of the bearing surface. Edge loading typically results from a malpositioned acetabular component, such as steep inclination or excessive anteversion/retroversion. Other risk factors include young age, high activity level, and larger BMI.

Question 6

A 14-year-old boy presents with a high-grade intramedullary osteosarcoma of the distal femur. His family history is notable for a mother who died of early-onset breast cancer and a sister treated for adrenocortical carcinoma. Which of the following genetic mutations is most likely implicated in this patient's presentation?

Explanation

The clinical picture and family history are classic for Li-Fraumeni syndrome, an autosomal dominant disorder caused by a germline mutation in the TP53 (p53) tumor suppressor gene. Patients are at very high risk for developing osteosarcoma, breast cancer, soft tissue sarcomas, adrenocortical carcinomas, and brain tumors.

Question 7

A 65-year-old male undergoes magnetic resonance imaging (MRI) of the cervical spine to evaluate progressive hand clumsiness and gait imbalance. Which of the following MRI findings in the spinal cord is most predictive of a poor clinical neurological outcome following surgical decompression?

Explanation

Foci of increased T2 signal with corresponding decreased T1 signal in the spinal cord indicate myelomalacia (cystic necrosis or cavitation of the cord). This combination is strongly associated with permanent structural cord damage and a poor prognosis for neurological recovery after decompressive surgery for cervical spondylotic myelopathy.

Question 8

In the surgical repair of zone II flexor tendon lacerations, which biomechanical factor has been demonstrated to most directly correlate with the initial tensile yield strength of the repair construct?

Explanation

The initial yield strength and ultimate tensile strength of a flexor tendon repair are directly proportional to the number of core suture strands crossing the repair site (e.g., a 4-strand repair is stronger than a 2-strand repair). Dorsal placement of core sutures is also mechanically stronger than volar placement.

Question 9

A 58-year-old patient with long-standing, poorly controlled diabetes mellitus presents with a swollen, erythematous, and warm foot but no open ulcers. Radiographs demonstrate periarticular fragmentation, subchondral cyst formation, and joint subluxation at the tarsometatarsal joints. According to the Eichenholtz classification, what is the most appropriate initial management?

Explanation

This patient is in Eichenholtz Stage I (Development/Fragmentation) of Charcot arthropathy, characterized by acute inflammation, hyperemia, and bony fragmentation. The gold standard for initial management in this active phase is rigid immobilization and offloading, typically achieved with a total contact cast (TCC), to prevent progressive deformity until the process reaches the consolidation phase.

Question 10

According to Perren's strain theory of bone healing, what is the maximum percentage of interfragmentary strain that allows for primary (direct) bone healing to occur across a fracture site?

Explanation

Perren's strain theory states that primary (direct) bone healing via cutting cones requires absolute stability, which is defined as an interfragmentary strain of less than 2%. Strain between 2% and 10% allows for secondary bone healing (callus formation), while strain greater than 10% generally prevents bone formation and leads to nonunion or fibrous tissue formation.

Question 11

A 32-year-old male sustains a closed, high-energy tibial shaft fracture. Two hours post-injury, he complains of severe pain disproportionate to the injury. His systemic blood pressure is 120/80 mmHg. Intracompartmental pressure testing is performed. Which of the following pressure profiles is the most universally accepted absolute indication for a four-compartment fasciotomy?

Explanation

The most reliable threshold for diagnosing acute compartment syndrome and indicating a fasciotomy is a Delta P (Diastolic BP minus Intracompartmental Pressure) of less than 30 mmHg. Relying strictly on absolute compartment pressure can lead to overtreatment in normotensive patients or undertreatment in hypotensive patients.

Question 12

A 12-year-old boy presents with a left-sided slipped capital femoral epiphysis (SCFE) and undergoes in situ pinning. Prophylactic pinning of the contralateral, asymptomatic hip is most strongly indicated if the patient has which of the following concurrent conditions?

Explanation

Endocrine disorders (such as hypothyroidism, panhypopituitarism, or growth hormone deficiency) and renal osteodystrophy significantly increase the risk for bilateral SCFE. In these atypical SCFE patients, prophylactic pinning of the contralateral hip is strongly indicated to prevent future slippage.

Question 13

During a Latarjet procedure for recurrent anterior shoulder instability with significant glenoid bone loss, the coracoid process is osteotomized and transferred to the anterior glenoid. The transferred coracoid brings with it the conjoined tendon. Which of the following nerves is at greatest risk of iatrogenic injury during the mobilization and inferior transfer of the conjoined tendon?

Explanation

The musculocutaneous nerve enters the coracobrachialis muscle (which makes up part of the conjoined tendon along with the short head of the biceps) approximately 5 to 8 cm distal to the tip of the coracoid process. Aggressive inferior retraction or mobilization of the conjoined tendon puts this nerve at high risk for stretch or transection injuries.

Question 14

A 68-year-old female presents with catching and a painful 'pop' at the anterior aspect of her knee when extending from a flexed position. This symptom began 14 months after she underwent a primary total knee arthroplasty (TKA). What is the most likely underlying etiology of her symptoms?

Explanation

The patient's presentation is classic for patellar clunk syndrome, a complication most frequently associated with posterior-stabilized (PS) TKA designs. A symptomatic fibrotic nodule forms at the superior pole of the patella and catches within the intercondylar box of the PS femoral component as the knee extends from approximately 30-45 degrees of flexion.

Question 15

A 9-year-old boy presents with progressive mid-thigh pain and systemic fevers. Radiographs reveal a permeative, diaphyseal lesion of the femur with a prominent 'onion skin' periosteal reaction. A core biopsy confirms a small round blue cell tumor. Which of the following chromosomal translocations is most characteristic of this malignancy?

Explanation

The clinical and radiographic presentation points to Ewing sarcoma. Ewing sarcoma is classically driven by the t(11;22)(q24;q12) chromosomal translocation, which results in the EWS-FLI1 fusion protein in about 85-90% of cases. t(X;18) is associated with synovial sarcoma, and t(2;13) is seen in alveolar rhabdomyosarcoma.

Question 16

A 50-year-old female presents with severe, longstanding symptoms of carpal tunnel syndrome, including noticeable thenar atrophy. Electromyography (EMG) and nerve conduction velocities (NCV) are ordered. Which of the following findings on these studies indicates the most severe degree of axonal nerve injury and suggests a poorer prognosis for complete functional recovery?

Explanation

Fibrillation potentials and positive sharp waves on EMG indicate active muscle denervation resulting from axonal loss. This represents advanced, severe nerve compression (Wallerian degeneration) and portends a poorer prognosis for complete functional recovery compared to mere demyelination, which typically presents as prolonged latencies and decreased conduction velocities without EMG denervation changes.

Question 17

Which of the following clinical and anatomical features correctly differentiates degenerative spondylolisthesis from isthmic spondylolisthesis in the adult lumbar spine?

Explanation

Degenerative spondylolisthesis most commonly occurs at the L4-L5 level and features an intact pars interarticularis, driven primarily by facet joint incompetence and disc degeneration (most common in older females). Isthmic spondylolisthesis most commonly occurs at L5-S1, involves a pars interarticularis defect (spondylolysis), and typically presents earlier in life.

Question 18

A 40-year-old male undergoes percutaneous repair of an acute Achilles tendon rupture. Postoperatively, he notes numbness and paresthesias along the lateral aspect of his heel and foot. Which nerve was most likely injured during the procedure, and at what anatomical location is it at greatest risk?

Explanation

The sural nerve is at the highest risk of injury during percutaneous or minimally invasive Achilles tendon repair. It courses down the posterior leg and reliably crosses the lateral border of the Achilles tendon approximately 9.8 to 10 cm proximal to its insertion on the calcaneus.

Question 19

When dissimilar metals are used in adjacent orthopaedic implants (e.g., placing a stainless steel screw through a titanium plate), galvanic corrosion may occur. Which of the following accurately describes the primary electrochemical process governing this phenomenon?

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (like body fluid). The less noble (more reactive) metal acts as the anode and undergoes oxidation (corrosion), while the more noble metal acts as the cathode and is protected. For example, stainless steel is less noble than titanium and will preferentially corrode if the two are coupled.

Question 20

In a patient who sustains a highly unstable vertical shear or an anteroposterior compression (APC) pelvic ring fracture with severe posterior sacroiliac (SI) joint disruption, massive retroperitoneal hemorrhage is often encountered. When arterial bleeding is the primary source in the setting of a posterior ring injury, which artery is most frequently implicated?

Explanation

While the majority of pelvic hemorrhage is venous (from the presacral venous plexus) or from cancellous bone surfaces, arterial hemorrhage can be life-threatening. In posterior pelvic ring injuries (SI joint disruptions and sacral fractures), the superior gluteal artery is the most commonly injured artery as it exits the pelvis through the greater sciatic notch in close proximity to the SI joint.

Question 21

A 14-year-old boy presents with a painful diaphyseal lesion in the femur. Radiographs reveal an aggressive, permeative lytic lesion with an 'onion skin' periosteal reaction. A core needle biopsy is performed. Which of the following cytogenetic abnormalities is most closely associated with the likely diagnosis?

Explanation

The clinical and radiographic presentation is classic for Ewing sarcoma. The most common cytogenetic abnormality found in Ewing sarcoma is the t(11;22)(q24;q12) translocation, which produces the EWS-FLI1 fusion protein. Synovial sarcoma is associated with t(X;18). Myxoid liposarcoma is associated with t(12;16). Alveolar rhabdomyosarcoma is associated with t(2;13).

Question 22

A 6-week-old female infant is undergoing treatment with a Pavlik harness for developmental dysplasia of the hip (DDH). A follow-up ultrasound reveals the femoral head remains dislocated posterosuperiorly and is irreducible on dynamic testing. Continued rigid use of the Pavlik harness in this situation places the patient at highest risk for which of the following complications?

Explanation

If a hip remains persistently dislocated in a Pavlik harness, continued use can cause the femoral head to wear away the posterior lip of the acetabulum, known as 'Pavlik harness disease.' It creates a false acetabulum and makes subsequent reduction significantly more difficult. Therefore, if reduction is not achieved within 3 to 4 weeks, the harness should be abandoned. Avascular necrosis is associated with extreme abduction, and femoral nerve palsy is associated with extreme hyperflexion.

Question 23

Demineralized bone matrix (DBM) is widely used in orthopedic surgery as a bone graft substitute. Which of the following best describes the inherent biologic properties of DBM?

Explanation

Demineralized bone matrix (DBM) provides a collagen scaffold (osteoconductive) and contains bone morphogenetic proteins (BMPs) left behind after demineralization (osteoinductive). Because it undergoes processing that removes living cells, it is not osteogenic.

Question 24

Ossification of the posterior longitudinal ligament (OPLL) most commonly occurs in the cervical spine and can cause severe progressive myelopathy. Which of the following patient demographics and genetic markers is most strongly associated with this condition?

Explanation

OPLL is highly prevalent in populations of East Asian descent (e.g., Japanese, Korean). It has been strongly linked to genetic factors, particularly mutations in the collagen 6A1 (COL6A1) gene and specific HLA haplotypes. HLA-B27 is classically associated with ankylosing spondylitis.

Question 25

In total hip arthroplasty, the use of ceramic-on-ceramic bearing surfaces drastically reduces volumetric wear. Which of the following is a recognized complication uniquely associated with ceramic-on-ceramic bearings compared to metal-on-polyethylene?

Explanation

'Squeaking' is a well-documented clinical phenomenon unique to hard-on-hard bearings, particularly ceramic-on-ceramic total hip arthroplasties. It occurs due to resonance from micro-separation or stripe wear. Trunnionosis and galvanic corrosion are issues at metal-metal junctions. Polyethylene bears the issues of creep and macrophage-induced osteolysis.

Question 26

During the acute resuscitation of a hemodynamically unstable patient with an anteroposterior compression (APC) type III pelvic ring injury, a pelvic binder is applied. To optimally reduce pelvic volume and control venous hemorrhage, the binder should be centered directly over which of the following anatomic landmarks?

Explanation

Pelvic binders must be placed accurately at the level of the greater trochanters to effectively close the pelvic ring, internally rotate the hemipelvises, and maximally reduce pelvic volume. Placement higher up over the ASIS or iliac crests is less effective and can paradoxically open the pelvic ring further in certain fracture patterns.

Question 27

During an anterior cruciate ligament (ACL) reconstruction, the surgeon drills the femoral tunnel too vertically (high and anterior in the intercondylar notch). Which of the following clinical findings is most likely to result from this non-anatomic tunnel placement?

Explanation

A vertically placed femoral tunnel (common with older transtibial drilling techniques) effectively restores anterior-posterior stability (resulting in a negative Lachman test) but fails to adequately restore rotational stability. This leaves the patient with a persistent positive pivot shift test. Roof impingement with loss of extension is typically due to an anterior tibial tunnel placement.

Question 28

The Lisfranc ligament is an essential stabilizing structure of the midfoot. Which of the following describes the true anatomic attachments of the Lisfranc ligament?

Explanation

The Lisfranc ligament is a strong interosseous ligament that runs obliquely from the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal. There is no transverse intermetatarsal ligament connecting the bases of the first and second metatarsals, making this region highly susceptible to traumatic disruption.

Question 29

A 35-year-old male sustains a 'terrible triad' injury of the elbow (elbow dislocation, radial head fracture, coronoid fracture). Standard surgical management requires a specific sequence of repair. Which of the following is the most widely accepted first step in the internal fixation sequence for this injury?

Explanation

The standard surgical sequence for a terrible triad injury proceeds deep to superficial and distal to proximal: fixation of the coronoid fracture first, followed by fixation or arthroplasty of the radial head, and finally repair of the lateral ulnar collateral ligament (LUCL/LCL complex). MCL repair is generally only performed if the elbow remains unstable after the lateral side is fixed.

Question 30

Periprosthetic osteolysis in total joint arthroplasty is primarily driven by a biologic response to particulate wear debris. Which of the following cell types initially phagocytoses ultra-high-molecular-weight polyethylene wear particles, leading to the release of inflammatory cytokines (TNF-alpha, IL-1, IL-6) and subsequent osteoclast activation?

Explanation

Macrophages are the primary initial responders that phagocytose ultra-high-molecular-weight polyethylene (UHMWPE) wear particles. Once activated, they release pro-inflammatory cytokines (such as TNF-alpha, IL-1, and IL-6), which upregulate RANKL expression and promote osteoclastogenesis, ultimately leading to periprosthetic osteolysis.

Question 31

Kanavel's signs are classically used to clinical diagnose pyogenic flexor tenosynovitis of the hand. Which of the following is considered the earliest and most reliable of these signs?

Explanation

The four Kanavel signs are: 1) flexed resting posture, 2) fusiform (sausage) swelling, 3) tenderness along the flexor tendon sheath, and 4) excruciating pain with passive extension. Pain with passive extension is historically considered the earliest and most reliable clinical hallmark of pyogenic flexor tenosynovitis.

Question 32

In the evaluation of a 7-year-old boy with Legg-Calve-Perthes disease, the lateral pillar (Herring) classification is utilized to determine prognosis. This classification is primarily based on the height of the lateral pillar of the capital femoral epiphysis during which stage of the disease?

Explanation

The lateral pillar (Herring) classification relies on anteroposterior radiographs specifically taken during the fragmentation stage of Legg-Calve-Perthes disease. It assesses the maintenance of the height of the lateral pillar of the femoral head, which correlates strongly with long-term sphericity, containment, and clinical outcome.

Question 33

In the evaluation of suspected acute compartment syndrome of the lower leg, utilizing the 'delta pressure' (Delta P) is considered a more accurate indicator for intervention than the absolute compartment pressure. Which of the following accurately defines the Delta P and the threshold that strongly indicates the need for a fasciotomy?

Explanation

Delta P is defined as the Diastolic Blood Pressure minus the Compartment Pressure. A Delta P of less than or equal to 30 mmHg indicates inadequate tissue perfusion pressure, which strongly confirms acute compartment syndrome and the necessity for an emergent fasciotomy.

Question 34

During a primary total knee arthroplasty (TKA), trial components are inserted. Evaluation reveals that the knee is well-balanced and symmetric in full extension, but the joint is significantly tight both medially and laterally in 90 degrees of flexion. Which of the following surgical maneuvers is the most appropriate next step to balance the knee?

Explanation

A knee that is balanced in extension but tight in flexion indicates that the flexion gap is too small relative to the extension gap. Options to increase the flexion gap without affecting the extension gap include downsizing the femoral component (which decreases the posterior condylar offset), increasing the posterior tibial slope, or recessing the PCL (if retaining). Downsizing the femoral component is the most direct solution. Resecting more distal femur or releasing the posterior capsule would widen the extension gap.

Question 35

According to the Wiltse classification of spondylolisthesis, which type is most commonly seen at the L5-S1 level and is caused by a bilateral defect in the pars interarticularis?

Explanation

Type II (Isthmic) spondylolisthesis is due to a defect in the pars interarticularis (spondylolysis) and most frequently occurs at L5-S1. This is the most common type in young patients and athletes. Degenerative (Type III) spondylolisthesis is most common at L4-L5 in older individuals. Type I (Dysplastic) involves congenital abnormalities of the upper sacrum or L5 arch.

Question 36

A 65-year-old male presents with severe, atraumatic back pain and hypercalcemia. Radiographs show a 'punched-out' lytic lesion in the L3 vertebral body. Suspecting multiple myeloma, a workup is initiated. Which of the following imaging modalities is the LEAST sensitive for detecting additional skeletal lesions in this patient?

Explanation

Technetium-99m (Tc-99m) bone scans rely on osteoblastic activity. Multiple myeloma lesions are almost purely osteolytic and lack reactive osteoblastic bone formation; thus, they classically present as 'cold' or yield false-negative results on a bone scan. Low-dose CT, MRI, and PET are vastly superior imaging modalities for the detection of myeloma lesions.

Question 37

A 55-year-old woman presents with medial ankle pain, a progressively flattening arch, and a positive 'too many toes' sign. She is diagnosed with Stage II adult acquired flatfoot deformity (posterior tibial tendon dysfunction). Which of the following radiographic findings distinguishes Stage IIb from Stage IIa and frequently requires a lateral column lengthening procedure?

Explanation

Stage II posterior tibial tendon dysfunction involves a flexible hindfoot valgus deformity. It is subclassified into IIa (hindfoot valgus with minimal forefoot abduction) and IIb (hindfoot valgus with significant forefoot abduction). Forefoot abduction is radiographically quantified by talonavicular uncoverage on an AP foot X-ray. Uncoverage greater than 30-40% typically defines Stage IIb and often necessitates a lateral column lengthening. Rigid hindfoot/arthritis is Stage III, and ankle involvement is Stage IV.

Question 38

In young adults with high-energy femoral neck fractures, a Pauwels type III fracture pattern is notoriously difficult to treat due to high rates of nonunion and avascular necrosis. The Pauwels classification categorizes these fractures based on which of the following parameters?

Explanation

The Pauwels classification is based on the angle of the femoral neck fracture line relative to the horizontal plane. Type I is <30 degrees, Type II is 30-50 degrees, and Type III is >50 degrees. Higher angles (more vertical fracture lines) experience exponentially greater shear forces, leading to poor biomechanical stability, higher rates of fixation failure, and nonunion.

Question 39

A cyclist presents with numbness in the volar aspect of his small finger and the ulnar half of his ring finger, alongside profound weakness of the interosseous muscles. Sensation on the dorsal ulnar aspect of the hand is completely preserved. According to the zoning of Guyon's canal, which zone is most likely the site of ulnar nerve compression?

Explanation

Guyon's canal is divided into 3 zones. Zone 1 is proximal to the nerve's bifurcation and contains both motor and sensory fascicles; compression here causes mixed motor and sensory deficits in the volar digits. Zone 2 contains only the deep motor branch, and Zone 3 contains only the superficial sensory branch. Dorsal sensation is spared because the dorsal sensory branch of the ulnar nerve branches off roughly 5-8 cm proximal to the wrist crease, completely bypassing Guyon's canal. Thus, volar sensory loss plus motor loss indicates Zone 1 compression.

Question 40

A patient with a previously retained stainless steel plate for a distal femur fracture undergoes a total hip arthroplasty. The surgeon uses a titanium alloy stem that extends distally and makes physical contact with the proximal edge of the stainless steel plate. Over several years, accelerated localized corrosion occurs at the contact site. This scenario is a classic example of which type of corrosion?

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., stainless steel and titanium alloys) are placed in physical contact within an electrolyte solution (conductive body fluid). This creates an electrochemical cell, resulting in accelerated dissolution (corrosion) of the less noble metal. Fretting corrosion is mechanically driven by micromotion. Crevice corrosion occurs in shielded areas with oxygen depletion.

Question 41

Ligaments and tendons exhibit distinct viscoelastic properties. Which of the following biomechanical terms best describes the phenomenon where a tissue subjected to a constant, sustained load demonstrates progressive deformation over time?

Explanation

Creep is the progressive deformation of a viscoelastic material when it is placed under a constant load over time. Conversely, stress relaxation refers to the decrease in stress over time when the material is held at a constant length.

Question 42

Articular cartilage consists of multiple histomorphological zones. In which specific zone are the type II collagen fibers oriented primarily perpendicular to the joint surface to provide the highest resistance to compressive forces?

Explanation

In the deep (radial) zone of articular cartilage, collagen fibers are oriented perpendicular to the joint surface to maximally resist compressive loads. The superficial zone features parallel collagen fibers to resist shear and friction forces.

Question 43

According to the 2018 International Consensus Meeting (ICM) criteria for periprosthetic joint infection (PJI), which of the following synovial fluid biomarkers carries the highest diagnostic weight and serves as a standalone major diagnostic criterion?

Explanation

A positive synovial fluid alpha-defensin test is highly specific for PJI and is classified as a major criterion in modern scoring systems. Alpha-defensin is an antimicrobial peptide released by neutrophils in response to pathogens.

Question 44

A 24-year-old male presents with a scaphoid proximal pole fracture nonunion six months post-injury. The proximal pole's severe vulnerability to avascular necrosis is primarily due to its retrograde blood supply from branches of which vessel?

Explanation

The scaphoid receives a retrograde blood supply primarily from dorsal branches of the radial artery, which enter the bone distally. This anatomic peculiarity leaves the proximal pole highly susceptible to ischemia and avascular necrosis following a fracture.

Question 45

In the surgical management of an unstable slipped capital femoral epiphysis (SCFE) with single in situ screw fixation, which iatrogenic complication is most strongly associated with screw placement in the anterior-superior quadrant of the femoral head?

Explanation

Screws placed in the anterior-superior quadrant of the femoral head risk penetrating the lateral epiphyseal vessels, directly causing avascular necrosis. Screws should ideally be placed in the center-center position of the epiphysis to avoid this.

Question 46

A 14-year-old boy presents with a destructive diaphyseal bone lesion of the femur and an overlying soft tissue mass. Biopsy reveals uniform small round blue cells. Which specific chromosomal translocation is most classically characteristic of this tumor?

Explanation

Ewing sarcoma is a small round blue cell tumor typically found in the diaphysis of long bones in children and adolescents. It is classically associated with the t(11;22) translocation, which results in the oncogenic EWS-FLI1 fusion gene.

Question 47

In an obtunded polytrauma patient with a comminuted tibial shaft fracture, continuous compartment pressure monitoring is utilized. What 'delta P' threshold is the most universally accepted indication for an emergent four-compartment fasciotomy?

Explanation

A 'delta P' (diastolic blood pressure minus compartment pressure) of less than 30 mm Hg is the most reliable and validated indicator for acute compartment syndrome requiring fasciotomy. Relying solely on absolute compartment pressures can be misleading, especially in hypotensive trauma patients.

Question 48

During the physical exam of a 65-year-old man with broad-based gait instability and hand clumsiness, you rapidly flex the distal phalanx of his middle finger, which promptly elicits involuntary flexion of the thumb and index finger. What is the eponymous name of this clinical sign?

Explanation

The Hoffmann sign is indicative of an upper motor neuron lesion, strongly suggesting cervical myelopathy in this clinical context. It is elicited by flicking the distal phalanx of the middle finger, resulting in reflex flexion of the thumb and index finger.

Question 49

A 30-year-old male sustains a high-velocity gunshot wound to the thigh resulting in a comminuted midshaft femur fracture and an expanding pulsatile hematoma with absent distal pulses. In the operating room, what is the most appropriate sequence of operative management?

Explanation

In combined orthopedic and vascular extremity injuries with severe ischemia, temporary vascular shunting must be performed first to restore perfusion and minimize ischemia time. This is followed by skeletal stabilization, definitive vascular repair, and lastly prophylactic fasciotomies.

Question 50

Highly cross-linked polyethylene (HXLPE) is standardly used in modern total hip arthroplasty to reduce wear rates and subsequent osteolysis. What is the primary mechanical trade-off associated with the increased gamma radiation cross-linking of the polyethylene?

Explanation

While high cross-linking significantly reduces both adhesive and abrasive wear, it alters the mechanical properties of the polyethylene, specifically reducing its toughness, ductility, and resistance to fatigue crack propagation.

Question 51

In the assessment of Legg-Calve-Perthes disease, the Lateral Pillar (Herring) classification is widely used for determining prognosis. What specific radiographic feature defines a Lateral Pillar Group B hip on an AP radiograph?

Explanation

In the Herring Lateral Pillar classification, Group B indicates that the lateral pillar maintains >50% of its original height, yielding an intermediate prognosis. Group A has no lateral pillar height loss, while Group C has <50% height maintained, signifying a poor prognosis.

Question 52

You are applying a commercial pelvic binder to a hemodynamically unstable patient with an APC-III open-book pelvic ring injury. For maximum biomechanical efficacy and optimal reduction of pelvic volume, the binder should be centered over which anatomical landmarks?

Explanation

Pelvic binders are most effective at reducing pelvic volume and controlling life-threatening retroperitoneal hemorrhage when placed precisely at the level of the greater trochanters. Improper placement higher over the iliac crests is biomechanically inferior and frequently restricts critical abdominal access.

Question 53

A carpenter suffers a sharp laceration to the palmar aspect of the proximal phalanx, transecting both the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) tendons. This injury is located in which flexor tendon zone, historically deemed 'no man's land'?

Explanation

Zone II extends from the distal palmar crease to the middle of the middle phalanx, a tight fibro-osseous sheath where both the FDS and FDP travel together. It was historically called 'no man's land' due to the high propensity for postoperative adhesions and historically poor functional outcomes.

Question 54

Following an anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft, the tissue undergoes a biological process termed 'ligamentization'. During which specific post-operative phase is the graft mechanically at its weakest?

Explanation

The ACL graft is mechanically weakest during the early remodeling or revascularization phase, which typically occurs between 6 and 12 weeks postoperatively. During this vulnerable time, the initial graft undergoes cellular necrosis, repopulation, and profound collagen remodeling.

Question 55

In a patient presenting with massive rotator cuff tear arthropathy, the Hamada classification is utilized to grade the radiographic severity. A patient exhibiting an acromiohumeral interval of < 6mm along with distinct 'acetabularization' of the acromion is classified as:

Explanation

Hamada Grade 3 is explicitly defined by a narrowed acromiohumeral interval (< 6mm) combined with acetabularization of the undersurface of the acromion. Grade 2 involves narrowing (< 6mm) without acetabularization, while Grade 4 demonstrates true glenohumeral arthritis.

Question 56

Perren's strain theory dictates the specific type of bone healing that will occur in a fracture environment. Secondary bone healing via endochondral ossification and callus formation is optimized in a mechanical environment with what percentage of strain?

Explanation

Secondary bone healing, characterized by robust callus formation, optimally occurs in a moderate strain environment of between 2% and 10%. Strain < 2% promotes absolute stability and primary bone healing, while strain > 10% heavily promotes fibrous nonunion.

Question 57

A 22-year-old rugby player sustains an axial load injury to an extreme plantarflexed foot. Weight-bearing radiographs reveal a 3 mm diastasis between the medial cuneiform and the base of the second metatarsal. The primary deforming force pulling the 1st metatarsal medially is the insertion of which structure?

Explanation

The tibialis anterior inserts onto the medial cuneiform and the base of the first metatarsal, acting as a strong deforming force that pulls the first ray medially during a Lisfranc injury. The Lisfranc ligament itself connects the medial cuneiform to the base of the second metatarsal.

Question 58

A 60-year-old woman with metastatic breast cancer presents with a lytic lesion in the peritrochanteric region of the proximal femur, occupying half the cortical diameter, and complains of moderate pain with weight-bearing. Using the Mirels' scoring system, what is her score and the recommended management?

Explanation

Her Mirels' score is exactly 10 (Proximal femur = 3, Lytic nature = 3, Size 1/3-2/3 = 2, Moderate pain = 2). A score of 9 or greater indicates an unacceptably high risk of impending pathologic fracture, making prophylactic internal fixation the highly recommended treatment.

Question 59

A patient with a poorly functioning metal-on-metal total hip arthroplasty presents with persistent groin pain and a palpable anterior mass. Advanced imaging reveals a large, cystic pseudotumor. This adverse local tissue reaction (ALVAL) is histologically driven by which specific type of hypersensitivity response?

Explanation

Adverse Local Tissue Reaction (ALVAL) generated by metal debris in arthroplasty is primarily a Type IV delayed cell-mediated hypersensitivity reaction. The condition features dense perivascular lymphocytic infiltrates caused by T-lymphocyte sensitization to elevated cobalt and chromium ions.

Question 60

A 68-year-old male complains of bilateral leg and buttock pain that progressively worsens with walking. You instruct him to perform a clinical stationary bicycle test. The pain does not occur while pedaling in a forward-flexed posture but occurs rapidly when standing upright. This specific finding most strongly points to:

Explanation

The stationary bicycle test is highly useful for differentiating neurogenic from vascular claudication. Neurogenic claudication symptoms reliably improve with lumbar flexion (which transiently widens the spinal canal) and worsen in extension, making pedaling comfortable while upright walking causes rapid pain.

Question 61

Which phase of creeping substitution in cortical bone grafts is characterized by a temporary but significant decrease in mechanical strength?

Explanation

Cortical autografts undergo creeping substitution where osteoclastic resorption initially outpaces osteoblastic bone formation. This leads to a temporary but significant decrease in the mechanical strength of the graft.

Question 62

A 14-year-old boy presents with a destructive metaphyseal lesion of the distal femur. Biopsy reveals small round blue cells. Which of the following chromosomal translocations is most characteristic of this tumor?

Explanation

Ewing sarcoma is a small round blue cell tumor typically associated with the t(11;22) translocation. This specific genetic alteration results in the formation of the EWS-FLI1 fusion protein.

Question 63

In a hypotensive polytrauma patient with a tibial shaft fracture, which of the following is the most reliable threshold for diagnosing acute compartment syndrome using intracompartmental pressure monitoring?

Explanation

The delta pressure, calculated as diastolic blood pressure minus intracompartmental pressure, is the most reliable indicator for compartment syndrome. A delta pressure of less than 30 mmHg strongly indicates the need for emergency fasciotomy.

Question 64

A 12-year-old obese boy presents with knee pain and an obligatory external rotation of the hip during active flexion. Radiographs confirm a slipped capital femoral epiphysis (SCFE). What is the primary reason for performing an in situ single-screw fixation rather than attempting closed reduction?

Explanation

Forceful closed reduction of a SCFE significantly increases the risk of avascular necrosis of the femoral head. This complication occurs due to stretching or tearing of the delicate retinacular vessels supplying the epiphysis.

Question 65

In total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is widely used. Which of the following material property changes occurs as a direct result of the irradiation process used to increase cross-linking?

Explanation

High-dose irradiation increases cross-linking and dramatically reduces volumetric wear in polyethylene. However, it concomitantly decreases mechanical properties, specifically reducing fatigue resistance and ultimate tensile strength.

Question 66

A 45-year-old woman presents with classic symptoms of carpal tunnel syndrome. Which of the following electrodiagnostic findings is typically the earliest objective abnormality seen in compressive neuropathy of the median nerve?

Explanation

In compressive neuropathies like carpal tunnel syndrome, focal demyelination occurs first. This initial myelin damage leads to a prolongation of sensory latencies before motor fibers are objectively affected.

Question 67

An anteroposterior compression type III (APC III) pelvic ring injury is characterized by complete disruption of the symphysis pubis and which of the following posterior structures?

Explanation

An APC III injury involves a complete disruption of both the anterior and posterior sacroiliac ligaments, along with the sacrotuberous and sacrospinous ligaments. This extensive damage results in complete global instability of the hemipelvis.

Question 68

Which type of corrosion is most likely to occur at the modular head-neck taper junction of a total hip arthroplasty implant?

Explanation

Fretting corrosion occurs at the contact site between two materials under cyclical load, such as the taper junction of a modular hip implant. Micromotion disrupts the protective oxide layer, accelerating the localized corrosion process.

Question 69

A patient presents with a knee dislocation and a suspected posterolateral corner (PLC) injury. The dial test is performed. Which of the following findings is diagnostic of an isolated PLC injury without an associated PCL tear?

Explanation

The dial test shows increased external rotation of greater than 10 degrees compared to the contralateral side at 30 degrees of flexion in isolated PLC injuries. If external rotation is increased at both 30 and 90 degrees, it indicates a combined PLC and PCL injury.

Question 70

Which zone of articular cartilage has the highest concentration of collagen, with fibrils oriented parallel to the joint surface to primarily resist shear forces?

Explanation

The superficial tangential zone of articular cartilage contains the highest concentration of collagen and water. The densely packed collagen fibers are oriented parallel to the joint surface to effectively resist sheer stresses.

Question 71

A 40-year-old man presents with severe lower back pain, bilateral sciatica, and perineal numbness. He mentions he cannot feel toilet paper when wiping. Which of the following represents the most appropriate initial management step to confirm the diagnosis and plan treatment?

Explanation

While post-void residual volume supports the clinical suspicion of urinary retention in Cauda Equina Syndrome, an urgent MRI is definitively required. The MRI confirms the level and extent of compression, which is essential before emergent surgical decompression.

Question 72

According to the latest guidelines for the management of open fractures, what is the recommended prophylactic antibiotic regimen for a Gustilo-Anderson Type III open tibia fracture in a patient with no known allergies?

Explanation

For Gustilo-Anderson Type III open fractures, current guidelines typically recommend adding Gram-negative coverage to standard Gram-positive prophylaxis. This is most commonly achieved with a first-generation cephalosporin combined with an aminoglycoside.

Question 73

In the Ponseti method for correcting idiopathic clubfoot, what is the final deformity to be corrected before the application of the last cast and potential Achilles tenotomy?

Explanation

The Ponseti method corrects deformities in a strict sequence known by the acronym CAVE: Cavus, Adductus, Varus, and Equinus. Equinus is the final deformity addressed, frequently requiring a percutaneous Achilles tenotomy to finalize correction.

Question 74

A patient sustained a volar laceration over the proximal phalanx of the index finger, resulting in the inability to flex both the PIP and DIP joints. This injury is located in which flexor tendon zone?

Explanation

Zone II extends from the proximal edge of the A1 pulley to the insertion of the flexor digitorum superficialis tendon. Historically known as "no man's land," injuries here typically involve both the superficialis and profundus tendons within the tight fibro-osseous sheath.

Question 75

During a total knee arthroplasty, the surgeon notices that the knee is tight in flexion but balanced and stable in extension. Which of the following is the most appropriate surgical step to balance the knee?

Explanation

A knee that is tight in flexion but stable in extension indicates an isolated tight flexion gap. Downsizing the femoral component increases the anterior-posterior bone cut, which increases the flexion gap without altering the extension gap.

Question 76

A 65-year-old woman with a distal radius fracture is diagnosed with osteoporosis and started on an oral bisphosphonate. What is the primary mechanism of action of this medication class?

Explanation

Nitrogen-containing bisphosphonates work by inhibiting the enzyme farnesyl pyrophosphate synthase within the mevalonate pathway. This disruption impairs osteoclast function and promotes osteoclast apoptosis, thereby decreasing bone resorption.

Question 77

A 35-year-old recreational athlete sustains an acute Achilles tendon rupture. Nonoperative management with early functional rehabilitation is chosen. Compared to surgical repair, which of the following is the most established outcome difference for nonoperative management?

Explanation

While early functional rehabilitation has vastly improved outcomes for nonoperative treatment, surgical repair is still associated with a slightly lower tendon rerupture rate. However, surgery carries a higher risk of wound complications and infections.

Question 78

A 75-year-old active community ambulator sustains a displaced, completely off-ended femoral neck fracture. Which of the following is the most compelling reason to perform a total hip arthroplasty (THA) rather than a hemiarthroplasty?

Explanation

In active, independently ambulating older adults, THA is favored over hemiarthroplasty for displaced femoral neck fractures. THA significantly reduces the risk of long-term acetabular erosion and persistent groin pain, leading to better long-term functional scores.

Question 79

Which of the following types of fracture fixation provides absolute stability and promotes primary bone healing rather than secondary bone healing via callus formation?

Explanation

Primary bone healing requires conditions of absolute stability and minimal interfragmentary strain, which is achieved through techniques like compression plating or lag screw fixation. Methods like intramedullary nailing provide relative stability and heal via secondary callus formation.

Question 80

A 6-year-old boy is diagnosed with Legg-Calve-Perthes disease. According to the Herring lateral pillar classification, which radiographic finding portends the poorest prognosis for future hip joint congruency?

Explanation

The Herring lateral pillar classification determines prognosis based on the height of the lateral aspect of the femoral epiphysis. Group C, characterized by greater than 50% loss of lateral pillar height, carries the worst prognosis for maintaining femoral head sphericity.

Question 81

Which zone of the articular cartilage has the highest concentration of proteoglycans and the lowest concentration of water?

Explanation

The deep zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content. It is responsible for providing the most resistance to compressive forces.

Question 82

A 32-year-old male presents with a closed tibial shaft fracture. Which of the following continuous compartment pressure measurements is the most reliable threshold for diagnosing acute compartment syndrome and indicating fasciotomy?

Explanation

A delta pressure (diastolic blood pressure minus compartment pressure) of less than 30 mm Hg is the most reliable indicator for acute compartment syndrome. Absolute pressure thresholds can lead to over-diagnosis, especially in hypotensive patients.

Question 83

A 15-year-old boy presents with knee pain and a blastic lesion in the distal femur with a periosteal "sunburst" reaction. Biopsy confirms osteosarcoma. What is the most significant prognostic factor for long-term survival in this patient?

Explanation

The percentage of tumor necrosis following neoadjuvant chemotherapy is the most important prognostic factor for localized osteosarcoma. Greater than 90% necrosis indicates a good response and significantly better long-term survival.

Question 84

A 65-year-old female undergoes a total hip arthroplasty via a posterior approach. Postoperatively, she has a foot drop and cannot actively dorsiflex her ankle or extend her toes, but ankle inversion is preserved. Which nerve or nerve division is most likely injured?

Explanation

The peroneal division of the sciatic nerve is located laterally and is more tethered, making it highly susceptible to stretch injury during total hip arthroplasty. Preservation of ankle inversion (innervated by the tibial nerve) confirms an isolated peroneal division injury.

Question 85

A 45-year-old male presents with acute back pain, bilateral sciatica, and urinary retention following a heavy lifting injury. An MRI confirms a massive L4-L5 disc herniation compressing the cauda equina. What is the most critical factor determining the postoperative return of normal bladder function?

Explanation

The time interval from the onset of autonomic symptoms (like urinary retention) to surgical decompression is the most critical factor for functional recovery in cauda equina syndrome. Decompression within 24 to 48 hours of symptom onset significantly improves bladder outcomes.

Question 86

A 13-year-old obese male presents with acute-on-chronic left hip pain and an inability to bear weight. Radiographs show a severe slipped capital femoral epiphysis (SCFE). He undergoes urgent in-situ pinning. What is the most common devastating complication associated with this specific presentation?

Explanation

Unstable SCFE (defined clinically by the inability to bear weight) carries a high risk of osteonecrosis of the femoral head, regardless of the treatment method. The risk can approach 50% in severe, unstable slips.

Question 87

During an anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft, the surgeon places the femoral tunnel too far anteriorly. What is the most likely biomechanical consequence of this tunnel malposition?

Explanation

An anteriorly placed femoral tunnel in ACL reconstruction results in a graft that is tight in flexion and loose in extension. This can lead to restricted knee flexion and eventual graft stretching or failure.

Question 88

Which of the following terms describes the property of a viscoelastic material where the stress required to maintain a constant tissue deformation decreases over time?

Explanation

Stress relaxation is the phenomenon where less force (stress) is required over time to maintain a constant deformation (strain) in a viscoelastic material. Creep, conversely, is progressive deformation under a constant applied load.

Question 89

A 28-year-old male sustains an anteroposterior compression type III (APC-III) pelvic ring injury. Initial resuscitation includes a pelvic binder. Where is the most appropriate anatomical location to center the pelvic binder to effectively reduce pelvic volume?

Explanation

A pelvic binder should be centered directly over the greater trochanters to effectively close the pelvic ring and reduce volume. Placement higher, such as over the iliac crests or ASIS, is less effective and can paradoxically exacerbate the deformity.

Question 90

A 35-year-old carpenter sustains a volar laceration to his index finger at the level of the proximal phalanx, transecting both the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) tendons. According to the strictly defined flexor tendon zones, which zone is injured?

Explanation

Zone II, historically called "no man's land," extends from the proximal A1 pulley to the insertion of the FDS on the middle phalanx. Injuries here involve both the FDS and FDP tendons within the narrow fibro-osseous sheath, posing a high risk of postoperative adhesions.

Question 91

A patient undergoing a total knee arthroplasty has a significant preoperative flexion contracture. After initial bone cuts and soft tissue releases, the knee is balanced in extension but remains tight in flexion. Which of the following steps is the most appropriate to address this specific mismatch?

Explanation

If a knee is balanced in extension but tight in flexion, the flexion gap needs to be increased without affecting the extension gap. This is achieved by downsizing the femoral component, which decreases the posterior condylar offset and opens the flexion gap.

Question 92

A 55-year-old diabetic patient presents with a swollen, erythematous, and warm unilateral foot without any skin ulceration. Radiographs show fragmentation and subluxation of the tarsometatarsal joints. Which of the following is the most appropriate initial management?

Explanation

The clinical presentation is classic for acute Eichenholtz stage I Charcot arthropathy. The gold standard initial treatment to prevent further deformity and progression is strict non-weight bearing and immobilization, typically with a total contact cast.

Question 93

A 40-year-old smoker presents with a 9-month-old midshaft humeral fracture that has failed to heal following conservative management with a functional brace. Radiographs show a hypertrophic nonunion with an "elephant shoe" appearance. Which of the following best describes the primary underlying cause of this specific type of nonunion?

Explanation

A hypertrophic nonunion ("elephant shoe" appearance) is characterized by abundant callus formation, indicating excellent biological potential and blood supply. The primary cause of failure to unite in this scenario is inadequate mechanical stability.

Question 94

A 6-year-old boy is diagnosed with Legg-Calve-Perthes disease. According to the Herring lateral pillar classification, a patient with greater than 50% loss of lateral pillar height is placed in which prognostic group?

Explanation

The Herring lateral pillar classification categorizes Perthes based on the height of the lateral pillar on the AP radiograph. Group C is defined by a loss of more than 50% of the lateral pillar height and is associated with a poor prognosis and high risk of aspherical healing.

Question 95

Which of the following deep vein thrombosis (DVT) prophylaxis agents functions by directly inhibiting Factor Xa?

Explanation

Rivaroxaban is an oral anticoagulant that selectively and directly inhibits Factor Xa. Dabigatran is a direct thrombin inhibitor, while Enoxaparin (a low molecular weight heparin) primarily has indirect anti-Xa activity via antithrombin III.

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