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

Question 1

A patient undergoes revision total hip arthroplasty. The retrieved femoral component demonstrates evidence of galvanic corrosion at the modular head-neck junction. Which of the following material combinations is most susceptible to this specific type of corrosion?

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact in an electrolyte solution (like body fluid). A cobalt-chromium head on a titanium stem is a classic combination susceptible to galvanic corrosion due to their different resting electropotentials, leading to mechanically assisted crevice corrosion (trunnionosis). Ceramic heads do not undergo metallic corrosion.

Question 2

A hemodynamically unstable 35-year-old male is brought to the ED after a motorcycle collision.

Radiographs show an APC-III pelvic ring injury. Despite a pelvic binder and 2 units of uncrossmatched blood, the patient's BP remains 75/40. FAST is negative. What is the most rapid and definitive surgical intervention to control the primary source of pelvic bleeding?

Explanation

In a hemodynamically unstable patient with an unstable pelvic fracture and negative FAST, the source of bleeding is likely the venous presacral plexus or cancellous bone (80% of cases). If instability persists despite binder and resuscitation, preperitoneal pelvic packing or angiography with embolization is indicated. Preperitoneal packing is favored for rapid control of venous bleeding in the emergent setting.

Question 3

A 14-year-old boy presents with knee pain. Radiographs demonstrate a mixed lytic and sclerotic lesion in the distal femur metaphysis with cortical destruction and a 'sunburst' periosteal reaction.

Biopsy confirms high-grade intramedullary osteosarcoma. Which of the following genetic alterations is most consistently associated with this condition?

Explanation

High-grade intramedullary osteosarcoma is highly associated with mutations in tumor suppressor genes p53 (Li-Fraumeni syndrome) and Rb (Hereditary Retinoblastoma). t(11;22) is characteristic of Ewing sarcoma. t(X;18) is associated with synovial sarcoma. t(2;13) is seen in alveolar rhabdomyosarcoma, and GNAS mutation is found in fibrous dysplasia.

Question 4

A 13-year-old obese male presents with left knee pain and a limp. Examination reveals obligate external rotation with passive hip flexion.

A radiograph shows a slipped capital femoral epiphysis. During in situ pinning of this lesion, which of the following represents the optimal starting point for the screw to ensure maximum purchase and minimize joint penetration?

Explanation

In a classic posterior and inferior slip of the capital femoral epiphysis, an anterior starting point on the proximal femoral metaphysis allows the screw to be directed posteriorly to engage the center of the displaced epiphysis. This allows the screw to be perpendicular to the physis, maximizing fixation and minimizing the risk of out-in-out joint penetration.

Question 5

A 45-year-old male presents with acute onset back pain, bilateral lower extremity weakness, and perineal numbness after lifting a heavy box. He reports inability to void for the past 12 hours. What is the most sensitive early clinical finding for cauda equina syndrome?

Explanation

Urinary retention is the most sensitive sign for cauda equina syndrome (CES), with a sensitivity of up to 90%. If a patient with suspected CES does not have urinary retention, the diagnosis is less likely, though early incomplete CES may manifest with altered urinary sensation first. Saddle anesthesia and decreased anal tone are highly specific but less sensitive early on.

Question 6

A 25-year-old football player sustains an axial load to a plantarflexed foot.

Weight-bearing radiographs reveal a 3 mm diastasis between the base of the first and second metatarsals. What is the primary stabilizing structure of this articulation?

Explanation

The Lisfranc ligament complex connects the medial cuneiform to the base of the second metatarsal. It has three components: dorsal, interosseous, and plantar. The interosseous Lisfranc ligament is the strongest and thickest primary stabilizer of the joint. The dorsal ligament is the weakest.

Question 7

A 22-year-old male falls on an outstretched hand and sustains a fracture through the proximal pole of the scaphoid. Why is this specific fracture pattern at a very high risk for avascular necrosis?

Explanation

The scaphoid receives 70-80% of its blood supply from the dorsal carpal branch of the radial artery, which enters the scaphoid at the dorsal ridge (near the waist/distal pole) and provides intraosseous retrograde flow to the proximal pole. Fractures at the proximal pole disrupt this retrograde supply, leading to a high rate of avascular necrosis and nonunion.

Question 8

In anterior cruciate ligament (ACL) reconstruction, placing the femoral tunnel too anteriorly (shallow) will result in which of the following kinematic abnormalities?

Explanation

An anteriorly placed femoral tunnel (too shallow or anterior to the anatomic footprint) results in the graft being tight in flexion and loose in extension, often limiting full flexion. A posteriorly placed femoral tunnel results in a graft that is tight in extension and loose in flexion. Notch impingement in extension is typically caused by an excessively anterior tibial tunnel.

Question 9

During a primary total knee arthroplasty, the surgeon notes that the knee is well balanced in extension but is tight symmetrically in flexion. What is the most appropriate operative step to correct this mismatch?

Explanation

A knee that is symmetric but tight in flexion requires more space in the flexion gap. This can be achieved by decreasing the anteroposterior dimension of the femur (downsizing the femoral component or anteriorizing the component if using anterior referencing) or by increasing the posterior slope of the tibial cut. Increasing the posterior slope opens the flexion gap without significantly affecting the extension gap.

Question 10

Secondary bone healing occurs via enchondral ossification.

According to Perren's strain theory, what is the maximum interfragmentary strain that allows for the formation of woven bone?

Explanation

According to Perren's strain theory, the type of tissue that can form in a fracture gap depends on the interfragmentary strain. Lamellar bone requires <2% strain (primary healing). Woven bone can form with up to 10% strain. Fibrocartilage can tolerate up to 10-30% strain, and granulation tissue can tolerate up to 100% strain. Thus, woven bone requires strain to be less than 10%.

Question 11

A 28-year-old male sustains a closed tibia fracture and is at risk for compartment syndrome. Which of the following localized physiological factors shifts the oxyhemoglobin dissociation curve to the right, facilitating oxygen offloading in the ischemic tissues?

Explanation

In ischemic tissues (such as in early compartment syndrome), there is localized hypoxia and accumulation of CO2 and lactic acid (acidosis). Increased pCO2, increased hydrogen ions (decreased pH), increased temperature, and increased 2,3-DPG all shift the oxyhemoglobin dissociation curve to the right (Bohr effect), decreasing hemoglobin's affinity for oxygen and promoting oxygen release to the tissues.

Question 12

A 3-year-old girl is evaluated for worsening bilateral genu varum. Radiographs show medial metaphyseal beaking and an abnormal Langenskiöld stage II appearance of the proximal medial tibia. What is the primary pathological mechanism of infantile Blount disease?

Explanation

Infantile Blount disease (tibia vara) is a developmental disorder characterized by abnormal enchondral ossification of the medial aspect of the proximal tibial physis. It is caused by excessive compressive forces (Heuter-Volkmann principle) in susceptible toddlers (often early walkers and obese), leading to deceleration of growth on the medial side and resulting in progressive varus deformity.

Question 13

A 35-year-old woman presents with knee pain. Radiographs show an eccentric, lytic, expansile lesion in the epiphysis of the proximal tibia extending to the subchondral bone.

Biopsy demonstrates multinucleated giant cells in a stroma of mononuclear cells. The neoplastic stromal cells in this tumor are characterized by the excessive expression of which of the following?

Explanation

Giant cell tumor of bone is composed of neoplastic stromal cells that excessively express RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). This expression recruits and activates osteoclast-like multinucleated giant cells, which are responsible for the aggressive osteolysis characteristic of the tumor. Denosumab, a monoclonal antibody against RANKL, is used in the treatment of advanced or unresectable cases.

Question 14

A 20-year-old male undergoes arthroscopic stabilization for recurrent anterior shoulder instability. During the procedure, an anterior-inferior labral tear is identified along with an avulsed piece of the anterior-inferior glenoid rim. What is the eponymous name for this bony avulsion?

Explanation

A bony Bankart lesion is a fracture of the anterior-inferior glenoid rim associated with an anterior shoulder dislocation. A soft tissue Bankart is detachment of the anterior-inferior labrum alone. A Hill-Sachs lesion is a chondral impaction fracture of the posterosuperior humeral head. ALPSA is an anterior labroligamentous periosteal sleeve avulsion. HAGL is a humeral avulsion of the glenohumeral ligament.

Question 15

In the management of flexor tendon lacerations, 'Zone II' is classically known as 'No Man's Land' due to historically poor surgical outcomes. What are the anatomical boundaries of flexor tendon Zone II?

Explanation

Zone II of the flexor tendons extends from the proximal edge of the A1 pulley (at the distal palmar crease) to the insertion of the Flexor Digitorum Superficialis (FDS) at the middle phalanx. Both FDS and FDP travel within the narrow fibro-osseous sheath here, making repair technically demanding and highly prone to adhesion formation.

Question 16

On a standard stress-strain curve for an orthopedic biomaterial, what does the area under the curve in the elastic region represent?

Explanation

The area under the stress-strain curve in the elastic region represents the modulus of resilience, which is the amount of energy a material can absorb without undergoing permanent, plastic deformation. The total area under the entire curve (elastic + plastic regions) represents toughness (the energy absorbed before complete failure). The slope of the elastic region is the modulus of elasticity.

Question 17

A 55-year-old male presents with neck pain radiating down his right arm, associated with weakness in elbow extension and wrist flexion, and a diminished triceps reflex. Which cervical nerve root is most likely compressed?

Explanation

The clinical presentation is classic for a C7 radiculopathy. The C7 nerve root supplies the triceps (elbow extension), wrist flexors, and finger extensors. It also provides sensation to the middle finger and is tested by the triceps reflex. C5 controls the deltoid and biceps reflex. C6 controls wrist extension and the brachioradialis reflex. C8 controls finger flexion.

Question 18

A 68-year-old female undergoes a primary total hip arthroplasty via a direct posterior approach.

Postoperatively, she is found to have profound weakness in hip abduction and a positive Trendelenburg gait. Which nerve was most likely iatrogenically injured during the procedure?

Explanation

The superior gluteal nerve innervates the gluteus medius, gluteus minimus, and tensor fasciae latae, which are the primary hip abductors. Injury results in abductor weakness and a Trendelenburg gait. While a direct posterior approach typically protects this nerve, overzealous retraction superiorly or extending the approach too far proximally into the gluteus medius can injure it.

Question 19

What is the primary surgical sequence in the standard staged management of a high-energy, closed distal tibia intra-articular (Pilon) fracture with severe soft tissue swelling and fracture blisters?

Explanation

The standard of care for high-energy pilon fractures with compromised soft tissues is a staged protocol: initial management with a spanning external fixator across the ankle joint and open reduction and internal fixation (ORIF) of the fibula (to restore length and rotation), followed by definitive ORIF of the tibia 10-21 days later once soft tissue swelling has subsided (positive 'wrinkle sign') and fracture blisters have epithelized.

Question 20

Which zone of normal articular cartilage has the highest concentration of water and the lowest concentration of proteoglycans, with collagen fibers oriented parallel to the joint surface to resist shear stress?

Explanation

The superficial (tangential) zone of articular cartilage represents the top 10-20% of the cartilage thickness. It has the highest water content, the lowest proteoglycan concentration, and type II collagen fibers that are oriented strictly parallel to the articular surface to resist shear forces. The deep zone has the highest proteoglycan concentration and lowest water content, with collagen oriented perpendicularly.

Question 21

A 6-week-old female infant is evaluated for developmental dysplasia of the hip. An ultrasound is performed on the right hip. An alpha angle of 55 degrees and a beta angle of 60 degrees is noted on the coronal view. According to the Graf classification, what is the most appropriate management at this stage?

Explanation

This infant has a Graf Type IIa hip, which is defined by an alpha angle between 50-59 degrees in an infant under 3 months of age. This represents physiologic immaturity, and the vast majority of these hips will resolve spontaneously. The most appropriate management is observation and follow-up ultrasound in 2-4 weeks. A Pavlik harness is indicated for Graf Type IIb (same angles but older than 3 months), III, and IV hips.

Question 22

A 14-year-old boy presents with a painful mass in the diaphysis of the femur. Radiographs show a destructive permeative lesion with a 'onion-skin' periosteal reaction. Biopsy reveals small round blue cells. Cytogenetic analysis demonstrates a t(11;22) translocation. Which of the following fusion proteins is primarily responsible for the pathogenesis of this tumor?

Explanation

The clinical, radiographic, and histologic findings are classic for Ewing sarcoma. The t(11;22)(q24;q12) translocation is present in approximately 85% of Ewing sarcoma cases, resulting in the EWS-FLI1 fusion protein. SYT-SSX is associated with synovial sarcoma; TLS-CHOP with myxoid liposarcoma; PAX3-FKHR with alveolar rhabdomyosarcoma; and COL1A1-PDGFB with dermatofibrosarcoma protuberans.

Question 23

During a posterior-stabilized total knee arthroplasty using an anterior referencing system, the surgeon evaluates the gaps and finds that the knee is tight in flexion but well-balanced in extension. Which of the following is the most appropriate step to correct this mismatch?

Explanation

A knee that is tight in flexion and balanced in extension has an isolated tight flexion gap. Using an anterior referencing system, downsizing the femoral component shifts the posterior femoral condylar cut anteriorly (resecting more posterior bone). This effectively increases (loosens) the flexion gap without affecting the extension gap.

Question 24

A 65-year-old woman undergoes volar plate fixation for a displaced distal radius fracture. Six months postoperatively, she presents complaining of a sudden inability to bend the tip of her thumb. What is the most likely cause of this complication?

Explanation

Volar plating of the distal radius places the flexor tendons, particularly the FPL, at risk for attritional rupture if the plate is positioned distal to the watershed line of the distal radius. The loss of active interphalangeal flexion of the thumb characterizes an FPL rupture. EPL rupture is more common after nonoperative management or dorsal plating of distal radius fractures.

Question 25

A 5-year-old child sustains a completely displaced extension-type Gartland III supracondylar fracture of the humerus. Which of the following clinical findings is most specific for testing the most commonly injured nerve in this fracture pattern?

Explanation

The anterior interosseous nerve (AIN) is the most commonly injured nerve in extension-type supracondylar humerus fractures. It is a pure motor nerve that innervates the FPL, the FDP to the index and middle fingers, and the pronator quadratus. Weakness is evaluated by the 'OK' sign, which corresponds to the inability to actively flex the IP joint of the thumb and the DIP joint of the index finger.

Question 26

The scaphoid bone is highly susceptible to avascular necrosis following fracture. The predominant blood supply to the proximal pole of the scaphoid enters the bone through which of the following areas?

Explanation

The scaphoid receives its primary blood supply from branches of the radial artery. The major vessels enter the dorsal ridge (dorsal distal half) of the scaphoid and travel retrogradely to supply the proximal pole. Because of this retrograde blood supply, fractures through the waist or proximal pole disrupt the blood flow to the proximal fragment, significantly increasing the risk of avascular necrosis and nonunion.

Question 27

A 32-year-old man presents with a closed comminuted tibial shaft fracture following a motorcycle collision. He is complaining of excruciating leg pain out of proportion to the injury. His blood pressure is 110/65 mmHg. Intracompartmental pressure testing of the anterior compartment of the leg reads 45 mmHg. What is the Delta P and the recommended management?

Explanation

Delta P is calculated as Diastolic Blood Pressure minus Intracompartmental Pressure. In this patient, 65 mmHg - 45 mmHg = 20 mmHg. A Delta P of less than 30 mmHg in the setting of clinical signs is an absolute indication for emergent four-compartment fasciotomy of the leg to prevent irreversible ischemic necrosis.

Question 28

A 68-year-old man with advanced cervical spondylosis sustains a hyperextension injury to his neck during a fall. He presents to the ED with profound motor weakness in his upper extremities but is able to move his lower extremities with near-normal strength. He has variable sensory loss. Which spinal cord syndrome does this represent, and which region of the cord is primarily affected?

Explanation

This patient has Central Cord Syndrome, which typically occurs after a hyperextension injury in a patient with pre-existing cervical spondylosis. The central region of the spinal cord is bruised, affecting the centrally located fibers of the corticospinal tract (which supply the upper extremities) more severely than the peripherally located fibers (which supply the lower extremities).

Question 29

During arthroscopic repair of a Type II SLAP lesion, a suture anchor is placed at the 11 o'clock position in a right shoulder. Postoperatively, the patient complains of severe pain and weakness with external rotation. An EMG shows denervation of the infraspinatus with a normal supraspinatus. Which structure was most likely injured by errant drill or anchor placement?

Explanation

Suture anchors placed in the posterosuperior quadrant of the glenoid (10 to 12 o'clock in right shoulder, but commonly cited as 11 o'clock) place the suprascapular nerve at risk as it wraps around the spinoglenoid notch (approximately 1.5 - 2 cm medial to the glenoid rim). Injury at the spinoglenoid notch spares the supraspinatus but denervates the infraspinatus, leading to isolated external rotation weakness.

Question 30

A 4-year-old boy presents with right hip pain, a limp, and a fever of 38.6°C. He absolutely refuses to bear weight on the right leg. Blood work reveals a WBC count of 14,000/mm³ and an ESR of 45 mm/hr. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?

Explanation

The Kocher criteria are used to differentiate septic arthritis from transient synovitis of the pediatric hip. The four criteria are: (1) Non-weight-bearing on affected side, (2) ESR > 40 mm/hr, (3) Fever > 38.5°C, and (4) WBC count > 12,000/mm³. This patient meets all 4 criteria. The probability of septic arthritis is 3% for 1 criterion, 40% for 2, 93% for 3, and 99% for 4 criteria.

Question 31

When evaluating a patient with rotator cuff pathology, which of the following best describes a 'massive' rotator cuff tear according to the traditional Cofield classification?

Explanation

According to the Cofield classification of rotator cuff tears, a small tear is < 1 cm, a medium tear is 1-3 cm, a large tear is 3-5 cm, and a massive tear is > 5 cm. While Gerber defines a massive tear as involving two or more complete tendons, the Cofield system relies exclusively on the anterior-to-posterior dimension of the tear being greater than 5 cm.

Question 32

During the single-leg stance phase of gait, the abductor muscles must generate sufficient torque to balance the body weight. If the distance from the body's center of gravity to the center of the femoral head is exactly three times the distance from the abductor insertion to the center of the femoral head, what is the approximate abductor muscle force required to maintain a level pelvis?

Explanation

This illustrates the biomechanical lever arms acting around the hip joint. To maintain equilibrium (a level pelvis), the torque generated by body weight must equal the torque of the abductors. (Body Weight * 3) = (Abductor Force * 1). Therefore, Abductor Force = 3 times Body Weight. The total joint reaction force across the hip would be Body Weight + Abductor Force = 4 times Body Weight.

Question 33

A 40-year-old man sustains a sudden "pop" in the back of his heel while playing tennis. Which of the following physical examination maneuvers is the most sensitive and specific for diagnosing a complete acute Achilles tendon rupture?

Explanation

The Thompson test (calf squeeze test) is the most reliable clinical sign for a complete Achilles tendon rupture. Squeezing the calf muscle belly in a prone patient normally elicits passive plantar flexion of the ankle. Lack of this plantar flexion response indicates a loss of continuity of the Achilles tendon.

Question 34

A mechanic sustains a deep knife laceration over the volar aspect of the proximal phalanx of his ring finger. Examination reveals an inability to actively flex both the PIP and DIP joints of that finger. This injury is located in which anatomical flexor tendon zone?

Explanation

The flexor tendon zones of the hand define the anatomical location of injury. Zone II (historically called 'no man/'s land') extends from the proximal edge of the A1 pulley (distal palmar crease) to the insertion of the Flexor Digitorum Superficialis (FDS) on the middle phalanx. The volar aspect of the proximal phalanx is strictly within Zone II, containing both the FDS and FDP tendons.

Question 35

Rigid internal fixation with an absolute stability construct (e.g., a lag screw and neutralization plate) for a transverse diaphyseal fracture promotes primary bone healing. Which of the following is the primary histological mechanism by which primary bone healing occurs?

Explanation

Primary bone healing occurs without intermediate callus formation when there is absolute stability and compression across the fracture site. It is driven directly by Haversian remodeling, where osteoclasts create 'cutting cones' that cross the fracture line, followed immediately by osteoblasts laying down lamellar bone. Endochondral ossification is the hallmark of secondary bone healing (callus formation).

Question 36

A 22-year-old athlete presents with a recurrent anterior shoulder dislocation. An MRI shows an anterior labral tear and a distinct impaction fracture on the posterolateral aspect of the humeral head. Which of the following best describes this bony defect?

Explanation

An anterior shoulder dislocation can result in the posterolateral aspect of the humeral head impacting forcefully against the hard anterior glenoid rim, causing an impaction fracture known as a Hill-Sachs lesion. A reverse Hill-Sachs lesion is an anteromedial impaction fracture seen with posterior dislocations. A Bankart lesion is an avulsion of the anterior-inferior labrum from the glenoid.

Question 37

A newborn infant presents with a right upper extremity held rigidly in adduction and internal rotation, with the elbow extended, forearm pronated, and wrist flexed. The infant's grasp reflex remains fully intact. This classic presentation is due to an injury to which of the following neural structures?

Explanation

Erb-Duchenne palsy (Erb's palsy) is the most common obstetric brachial plexus palsy and involves the upper trunk, primarily affecting the C5 and C6 nerve roots. The classic 'waiter's tip' posture results from loss of shoulder abductors and external rotators, elbow flexors, and forearm supinators. Hand function (grasp reflex) is preserved because the lower roots (C8, T1) are spared.

Question 38

A 10-month-old infant is brought to the emergency department by his parents with a swollen and painful left thigh. Radiographs demonstrate a displaced spiral fracture of the femoral diaphysis. There is no clear history of trauma provided. Which of the following is the most appropriate initial step in the management of this patient?

Explanation

A diaphyseal femur fracture in a non-ambulatory infant (under 1 year of age) is a highly specific marker for non-accidental trauma (child abuse). The most critical initial step is to ensure the child's safety, which requires admission, performing a skeletal survey to identify any other healing fractures, and immediate consultation with child protective services (CPS).

Question 39

According to the Lauge-Hansen classification, a pronation-external rotation (PER) ankle fracture is characterized by a specific sequential pattern of structural failure. What is the very first structure to fail in a PER injury?

Explanation

In the Lauge-Hansen classification, the first word describes the position of the foot and the second describes the deforming force. In a Pronation-External Rotation (PER) injury, the foot is pronated, putting the medial structures under tension. Thus, Stage 1 is a transverse fracture of the medial malleolus or rupture of the deltoid ligament. This is followed by AITFL injury (Stage 2), high fibula fracture (Stage 3), and PITFL/posterior malleolus injury (Stage 4).

Question 40

A 16-year-old boy presents with severe right thigh pain that is distinctly worse at night and dramatically relieved by taking ibuprofen. Radiographs reveal a cortical thickening with a small 8 mm radiolucent nidus in the diaphysis of the femur. If a trial of conservative medical management fails, what is the most appropriate definitive treatment?

Explanation

The clinical presentation is classic for an osteoid osteoma, characterized by intense night pain relieved by NSAIDs (due to high levels of prostaglandins), and a small (<1.5 cm) radiolucent nidus surrounded by reactive sclerosis. If conservative management fails or the patient wishes for definitive treatment, CT-guided Radiofrequency Ablation (RFA) is the standard of care with excellent success rates.

Question 41

A viscoelastic orthopedic implant is subjected to a constant physiological load over a prolonged period. Over time, the material undergoes increasing progressive deformation despite the applied stress remaining unchanged. Which of the following best describes this biomechanical property?

Explanation

Creep is a viscoelastic property characterized by progressive deformation of a material under a constant load over time. This is clinically relevant in ultra-high-molecular-weight polyethylene (UHMWPE) components. Stress relaxation, in contrast, refers to a decrease in internal stress over time when the material is held at a constant deformation.

Question 42

A 28-year-old male is evaluated in the trauma bay following a fall from a 20-foot scaffold. He is hypotensive (BP 80/50 mmHg), bradycardic (HR 55 bpm), and has warm, well-perfused extremities. He lacks motor and sensory function below the umbilicus. What is the primary pathophysiologic mechanism for his hemodynamic instability?

Explanation

The patient is in neurogenic shock, characterized by hypotension, bradycardia, and warm extremities due to a loss of sympathetic outflow following acute spinal cord injury. This loss of vascular tone causes systemic vasodilation and venous pooling. Resuscitation requires judicious volume expansion followed by vasopressors.

Question 43

A 22-year-old female presents with a painless, slow-growing soft tissue mass in her popliteal fossa. MRI reveals a well-circumscribed, multilobulated mass intimately associated with an adjacent tendon sheath. Core needle biopsy demonstrates a biphasic cellular pattern consisting of epithelial-like cells and spindle cells. Which of the following chromosomal translocations is diagnostic for this neoplasm?

Explanation

The clinical and histologic description is highly characteristic of a synovial sarcoma. Synovial sarcomas are defined by the specific chromosomal translocation t(X;18)(p11;q11), leading to the fusion of the SS18 and SSX genes. Ewing sarcoma is associated with t(11;22).

Question 44

A 13-year-old obese male presents to the emergency department refusing to bear weight on his right leg after a minor twisting injury. Radiographs reveal a severe slipped capital femoral epiphysis (SCFE). Because he cannot bear weight even with crutches, this is classified as an unstable SCFE. Which of the following complications is significantly more likely in this patient compared to a patient with a stable SCFE?

Explanation

Unstable SCFE is defined by the inability to bear weight on the affected extremity and carries a much higher risk (up to 50%) of developing avascular necrosis (AVN) of the femoral head. Stable SCFE has a very low risk of AVN. Chondrolysis can occur in both, often related to prominent hardware.

Question 45

During revision total hip arthroplasty for aseptic loosening, extensive osteolysis is noted behind the acetabular component. Histologic analysis of the periprosthetic tissue reveals abundant particulate polyethylene wear debris. Which cell type is primarily responsible for internalizing these particles and initiating the inflammatory cascade leading to osteolysis?

Explanation

Macrophages are the primary effector cells that phagocytose polyethylene wear debris in periprosthetic osteolysis. Upon activation, they release pro-inflammatory cytokines (such as TNF-alpha, IL-1, and IL-6) that upregulate RANKL expression. This ultimately stimulates osteoclast-mediated bone resorption.

Question 46

A 70-year-old male with pre-existing cervical spondylosis presents after a hyperextension injury to his neck during a motor vehicle collision. On examination, he has significant weakness in his bilateral hands and arms (1/5 strength), but retains 4/5 strength in his legs. Perianal sensation is intact. What is the most likely diagnosis?

Explanation

Central cord syndrome typically occurs after a hyperextension injury in older patients with cervical spondylosis. It classically presents with motor weakness that is more pronounced in the upper extremities than in the lower extremities, along with varying degrees of sensory loss. The sacral tracts (perianal sensation) are peripherally located and typically spared.

Question 47

A 25-year-old mechanic sustains a displaced fracture of the proximal pole of the scaphoid. Nonunion and avascular necrosis are significant concerns for this fracture pattern. Which of the following best describes the predominant arterial supply to the proximal pole of the scaphoid?

Explanation

The major blood supply to the scaphoid comes from the dorsal carpal branch of the radial artery, which enters at the dorsal ridge near the waist and provides retrograde blood flow to the proximal pole. Fractures at the waist or proximal pole disrupt this retrograde supply, leading to a high risk of avascular necrosis and nonunion.

Question 48

A 32-year-old male undergoes intramedullary nailing for a closed tibial shaft fracture. Twelve hours postoperatively, he complains of severe leg pain out of proportion to the injury, unrelieved by opioids. Passive stretch of his toes elicits excruciating pain. To confirm acute compartment syndrome using intracompartmental pressure monitoring, which criterion is the most accurate indicator for emergency fasciotomy?

Explanation

The delta pressure (ΔP) is the most reliable threshold for diagnosing acute compartment syndrome, particularly in hypotensive patients. A ΔP (diastolic blood pressure minus compartment pressure) of less than 30 mmHg is an absolute indication for emergency fasciotomy to prevent irreversible muscle and nerve ischemia.

Question 49

A 20-year-old collegiate football player sustains a midfoot injury after an axial load was applied to his plantarflexed foot. On exam, there is plantar ecchymosis. Radiographs reveal a widening of the space between the medial and middle cuneiforms and a "fleck sign". The primary stabilizing ligament injured in this condition connects which two osseous structures?

Explanation

The Lisfranc ligament is an interosseous ligament that runs from the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal. It is critical for stabilizing the midfoot, and its rupture is indicated by the "fleck sign" (a bony avulsion at its attachment).

Question 50

A 65-year-old female develops a delayed prosthetic joint infection 14 months after a total knee arthroplasty. Cultures yield Staphylococcus epidermidis. The pathogenesis of this infection relies heavily on the bacteria's ability to form a biofilm. Which bacterial surface component is most critical for the accumulation phase of biofilm formation in this organism?

Explanation

Biofilm formation in coagulase-negative staphylococci (like S. epidermidis) occurs in two main phases: primary attachment and accumulation. The accumulation phase is primarily mediated by the production of polysaccharide intercellular adhesin (PIA), which is encoded by the ica operon.

Question 51

A 35-year-old male undergoes open reduction and internal fixation of a transverse radial shaft fracture using a dynamic compression plate, achieving absolute stability. Which of the following describes the primary mechanism of bone healing expected in this scenario?

Explanation

When absolute stability is achieved (e.g., rigid plate fixation with anatomic reduction), secondary fracture healing (callus formation) is suppressed. The bone heals via primary (direct) bone healing, characterized by osteoclast-led cutting cones crossing the fracture gap followed immediately by osteoblast-mediated osteonal formation.

Question 52

A 6-year-old boy falls off monkey bars and sustains a displaced supracondylar humerus fracture. Upon arrival, the hand is well-perfused but the radial pulse is not palpable. Following a closed reduction and percutaneous pinning, the hand remains pink and warm with a capillary refill of less than 2 seconds, but the radial pulse remains absent. What is the most appropriate next step in management?

Explanation

In a pediatric supracondylar humerus fracture, a "pulseless, pink" hand following closed reduction generally indicates adequate collateral circulation despite probable brachial artery spasm or tethering. The standard of care is close observation and continuous pulse oximetry monitoring rather than immediate surgical exploration.

Question 53

A 16-year-old male presents with severe right thigh pain that is uniquely worse at night and dramatically relieved by ibuprofen. Radiographs demonstrate a radiolucent nidus surrounded by dense reactive sclerosis in the proximal femur. Which of the following inflammatory mediators is produced in high levels by this lesion and is responsible for the classic clinical presentation?

Explanation

The clinical and radiographic presentation is classic for an osteoid osteoma. The nidus of an osteoid osteoma produces high levels of Prostaglandin E2 (PGE2), which causes the characteristic night pain that is rapidly alleviated by nonsteroidal anti-inflammatory drugs (NSAIDs).

Question 54

During a primary total knee arthroplasty using measured resection techniques, the surgeon trials the components. The knee achieves full extension and is stable to varus/valgus stress at 0 degrees. However, when evaluating the knee at 90 degrees of flexion, the joint is excessively tight and the trial components are difficult to insert. Which of the following technical modifications will best correct this specific imbalance?

Explanation

A tight flexion gap with a balanced extension gap implies that the anteroposterior (AP) dimension of the femoral component is too large. Downsizing the femoral component (shifting the posterior condylar cut anteriorly) will increase the size of the flexion gap without affecting the extension gap.

Question 55

A 24-year-old professional soccer player undergoes anterior cruciate ligament (ACL) reconstruction using an autologous bone-patellar tendon-bone graft. The graft must undergo a process of "ligamentization" to restore function. At what postoperative time frame is the structural graft mechanically at its weakest due to the revascularization and necrosis phase?

Explanation

The "ligamentization" of a free tendon graft involves stages of necrosis, revascularization, cellular proliferation, and remodeling. The graft is generally at its weakest biomechanical point around 6 to 8 weeks postoperatively, which must be considered when designing rehabilitation protocols to prevent premature failure.

Question 56

A 29-year-old male sustains a high-energy Pauwels type III (vertical) femoral neck fracture. He undergoes closed reduction and internal fixation with three cannulated screws. Despite an anatomic reduction, there is a significantly elevated risk of nonunion compared to less vertical fractures. What biomechanical factor primarily accounts for this increased risk?

Explanation

Pauwels type III femoral neck fractures have a high fracture angle (>50 degrees) relative to the horizontal. This vertical orientation translates axial physiological loads into high shear stresses across the fracture line, significantly increasing the risk of loss of fixation, varus collapse, and nonunion.

Question 57

A 40-year-old male "weekend warrior" presents with acute heel pain after pushing off to run during a tennis match. Examination reveals a palpable gap in the posterior ankle and lack of plantarflexion upon squeezing the calf. The injury most commonly occurs in a vascular watershed zone. Approximately how far proximal to the calcaneal insertion is this zone located?

Explanation

Acute Achilles tendon ruptures frequently occur in the hypovascular "watershed" zone of the tendon. This area of decreased blood supply is located approximately 2 to 6 cm proximal to the calcaneal insertion.

Question 58

A 25-year-old carpenter lacerates his volar index finger at the level of the proximal phalanx, resulting in an inability to flex the proximal and distal interphalangeal joints. During surgical exploration, repair of the flexor tendon sheath pulleys is considered to prevent biomechanical failure (bowstringing). Which two pulleys are most critical to preserve or reconstruct?

Explanation

The A2 (arising from the proximal phalanx) and A4 (arising from the middle phalanx) pulleys are biomechanically the most important annular pulleys in the flexor tendon sheath. Preserving or reconstructing them is crucial to prevent tendon bowstringing and ensure an effective excursion for finger flexion.

Question 59

A 45-year-old female presents with severe neck pain radiating down her right arm. Neurological examination reveals a diminished brachioradialis reflex, weakness in wrist extension, and decreased sensation over the dorsal aspect of the thumb and index finger. Which cervical nerve root is most likely compressed?

Explanation

Compression of the C6 nerve root (typically from a C5-C6 disc herniation) classically presents with weakness in wrist extension and elbow flexion, a diminished brachioradialis reflex, and sensory deficits in the thumb and index finger.

Question 60

A 38-year-old male sustains an inversion ankle injury. Radiographs show a widening of the medial clear space but no apparent fracture around the ankle mortise. Which of the following injuries MUST be ruled out to avoid missing a highly unstable injury pattern requiring operative fixation?

Explanation

A widened medial clear space without a visible distal fibular or medial malleolar fracture suggests a syndesmotic rupture extending proximally. Full-length tibia/fibula radiographs must be obtained to rule out a Maisonneuve fracture (proximal fibula fracture), which indicates a complete disruption of the syndesmotic ring requiring surgical stabilization.

Question 61

What is the primary mechanism by which denosumab affects bone metabolism?

Explanation

Denosumab is a monoclonal antibody that targets RANKL. By binding to RANKL, it prevents it from activating the RANK receptor on osteoclast precursors, thus inhibiting their maturation, function, and survival.

Question 62

A 45-year-old male presents with acute onset of severe low back pain, bilateral lower extremity weakness, and urinary retention following a heavy lifting event. Perianal numbness is noted on exam. Which of the following is the most critical next step in management?

Explanation

The patient presents with classic signs of cauda equina syndrome. This is an absolute orthopedic emergency requiring urgent MRI to confirm the diagnosis, followed by emergent surgical decompression to prevent irreversible neurological deficits.

Question 63

A 25-year-old male sustains a vertically oriented, displaced femoral neck fracture (Pauwels type III) after a fall from a height. Open reduction and internal fixation is planned. What biomechanical construct provides the most stable fixation for this specific fracture pattern?

Explanation

Pauwels type III fractures are highly unstable due to significant vertical shear forces. A fixed-angle device such as a DHS supplemented with an anti-rotation screw provides superior biomechanical stability against shear compared to parallel cancellous screws.

Question 64

A 9-year-old girl presents with a painful mass in her proximal tibia. Radiographs show a destructive, permeative lytic lesion in the diaphysis with an "onion-skin" periosteal reaction. A biopsy is performed. Which of the following translocations is most characteristic of this tumor?

Explanation

The presentation and "onion-skin" periosteal reaction are classic for Ewing sarcoma. The most common genetic abnormality associated with Ewing sarcoma is the t(11;22) translocation, which results in the EWS-FLI1 fusion gene.

Question 65

A 22-year-old soccer player sustains a twisting injury to his knee. Radiographs reveal an avulsion fracture of the lateral tibial plateau (Segond fracture). This radiographic finding is virtually pathognomonic for an injury to which of the following structures?

Explanation

A Segond fracture is an avulsion fracture of the anterolateral proximal tibia. It represents an avulsion of the anterolateral ligament (ALL) or lateral capsular attachment and is highly specific for an anterior cruciate ligament (ACL) tear.

Question 66

During a total hip arthroplasty, the surgeon opts for a highly cross-linked polyethylene liner instead of conventional polyethylene. Which of the following best describes the primary advantage of highly cross-linked polyethylene?

Explanation

High cross-linking of polyethylene significantly reduces volumetric wear, leading to a lower incidence of particle-induced osteolysis. However, the cross-linking process can decrease the material's mechanical properties, such as fracture toughness.

Question 67

A 13-year-old overweight boy presents with a 3-week history of right groin pain and a limp. Examination reveals obligatory external rotation of the hip with passive flexion. What is the most appropriate initial management?

Explanation

The presentation is classic for a Slipped Capital Femoral Epiphysis (SCFE). The standard of care for a stable SCFE is in situ percutaneous pinning with a single cannulated screw in the center of the epiphysis.

Question 68

A 40-year-old male sustains a closed posterior wall acetabular fracture with a concomitant posterior hip dislocation. Post-reduction CT scan reveals a 25% posterior wall fracture, a congruent joint, and a 2 mm intra-articular fragment. What is the most appropriate definitive management?

Explanation

Intra-articular incarcerated fragments following hip reduction are an absolute indication for operative intervention. The posterior wall should also be fixed simultaneously, as the approach is already necessary to clear the joint.

Question 69

A 30-year-old carpenter suffers a deep laceration over the volar aspect of his proximal phalanx. He is unable to flex the proximal or distal interphalangeal joints of his index finger. This injury occurred in which flexor tendon zone?

Explanation

The injury involves both the FDS and FDP tendons over the proximal phalanx, which corresponds to Zone II. This area is traditionally known as "no man's land" due to the historical difficulty of successful surgical repair and risk of adhesion.

Question 70

A 24-year-old female presents with midfoot pain after a fall from a horse with her foot plantarflexed in the stirrup. Weight-bearing radiographs show a 3 mm widening of the space between the base of the first and second metatarsals. What is the primary stabilizing structure that has most likely been injured?

Explanation

The Lisfranc ligament connects the lateral aspect of the medial cuneiform to the medial base of the second metatarsal. Injury to this ligament leads to instability of the tarsometatarsal complex.

Question 71

Which phase of fracture healing is characterized by the peak activity of chondrocytes and the formation of a soft callus?

Explanation

The reparative phase is characterized by the formation of a soft callus. During this phase, chondrocytes produce a cartilaginous matrix that bridges the fracture gap prior to endochondral ossification.

Question 72

A 65-year-old male presents with a painful total knee arthroplasty 3 years post-operatively. ESR and CRP are significantly elevated. Joint aspiration yields a WBC count of 55,000 cells/microliter with 92% neutrophils. What is the most appropriate surgical treatment?

Explanation

The patient has a chronic periprosthetic joint infection. In North America, the gold standard for managing chronic PJI is a two-stage revision arthroplasty involving component removal, placement of an antibiotic spacer, and delayed reimplantation.

Question 73

A 70-year-old male presents with deteriorating handwriting, difficulty buttoning his shirt, and a broad-based, unsteady gait. Physical examination reveals a positive Hoffman's sign and hyperreflexia in the lower extremities. What is the most likely diagnosis?

Explanation

Cervical spondylotic myelopathy classically presents with upper extremity dexterity issues, gait instability, and upper motor neuron signs (Hoffman's, hyperreflexia). It is the most common cause of spinal cord dysfunction in the elderly.

Question 74

In the evaluation of developmental dysplasia of the hip (DDH) in a 6-month-old infant, which of the following imaging modalities is most appropriate to confirm the diagnosis and assess severity?

Explanation

By 4 to 6 months of age, the capital femoral ossific nucleus begins to ossify. This makes AP and frog-leg pelvis radiographs the preferred and reliable imaging modality for evaluating DDH, replacing ultrasound.

Question 75

The "creeping substitution" process observed in the incorporation of a massive structural cortical bone allograft is primarily mediated by which of the following mechanisms?

Explanation

Creeping substitution is the process by which a bone graft is slowly resorbed by host osteoclasts and simultaneously replaced by host osteoblasts laying down new bone. Cortical allografts undergo this process much slower than cancellous autografts.

Question 76

A 32-year-old female sustains a closed midshaft tibia fracture and undergoes intramedullary nailing. Six hours post-operatively, she complains of severe pain out of proportion to the injury. Passive stretch of her toes exacerbates the pain. Compartment pressures measure 45 mmHg. What is the immediate indicated treatment?

Explanation

The clinical scenario strongly suggests acute compartment syndrome. Intracompartmental pressures above 30 mmHg (or within 30 mmHg of diastolic blood pressure) in conjunction with classic clinical signs necessitate emergent fasciotomy.

Question 77

A 32-year-old male sustains a midshaft radius fracture treated with open reduction and internal fixation using a dynamic compression plate to achieve absolute stability. Which of the following best describes the predominant mechanism of bone healing in this scenario?

Explanation

Absolute stability achieved by dynamic compression plating leads to primary bone healing. This process relies on osteoclastic cutting cones crossing the fracture site, followed by osteoblastic bone deposition, without the formation of an intermediate callus.

Question 78

A 28-year-old female presents with a closed tibial shaft fracture. She complains of severe pain out of proportion to the injury. Which of the following compartment pressure measurements is the most accepted threshold for diagnosing acute compartment syndrome and indicating the need for fasciotomy?

Explanation

Acute compartment syndrome is a clinical diagnosis, but pressure monitoring can be utilized in obtunded patients. A delta pressure (diastolic blood pressure minus compartment pressure) of less than 30 mmHg is the most widely accepted threshold for performing a fasciotomy.

Question 79

A 65-year-old man presents with back pain, fatigue, and renal insufficiency. Radiographs show a "punched-out" lytic lesion in his L4 vertebral body. Serum protein electrophoresis reveals an M-spike. Which of the following is the most appropriate next step in confirming the diagnosis?

Explanation

Multiple myeloma is the most common primary bone malignancy in adults. The definitive diagnosis requires a bone marrow biopsy demonstrating greater than 10% clonal plasma cells, even when a focal lytic lesion is present.

Question 80

In total hip arthroplasty, the use of highly cross-linked polyethylene has significantly reduced wear rates. However, the process of irradiation used for cross-linking generates free radicals. Which of the following processes is used to eliminate these free radicals and prevent subsequent oxidation and degradation of the polyethylene?

Explanation

Irradiation of polyethylene cross-links the material to reduce wear, but generates free radicals that can cause oxidative degradation over time. Thermal treatments like annealing (heating below melting point) or remelting are utilized to extinguish these free radicals and stabilize the liner.

Question 81

A 13-year-old obese male presents with a 3-week history of left knee pain and an antalgic gait. Examination reveals limited internal rotation of the left hip. Radiographs confirm a stable slipped capital femoral epiphysis (SCFE) on the left. Prophylactic pinning of the contralateral asymptomatic hip is most strongly indicated if the patient has which of the following concomitant conditions?

Explanation

Prophylactic pinning of the contralateral hip in SCFE is controversial but widely recommended in patients with underlying endocrine or metabolic disorders. These conditions, such as hypothyroidism or renal osteodystrophy, significantly increase the risk of bilateral involvement.

Question 82

A 45-year-old male presents to the emergency department with acute onset of severe lower back pain, bilateral sciatica, saddle anesthesia, and urinary retention with overflow incontinence. MRI confirms a massive L4-L5 disc herniation compressing the cauda equina. What is the most critical factor in maximizing the likelihood of neurological recovery?

Explanation

Cauda equina syndrome is an absolute surgical emergency requiring prompt intervention. Urgent decompression, ideally within 24 to 48 hours of symptom onset, is critical to maximize the potential for full neurological recovery, particularly of bowel and bladder function.

Question 83

Following a zone II flexor tendon repair of the index finger, a structured early active motion rehabilitation protocol is initiated. What is the primary biomechanical advantage of an early active mobilization protocol compared to immobilization?

Explanation

Early active mobilization protocols after flexor tendon repair promote intrinsic tendon healing over extrinsic healing. This approach significantly reduces the formation of peritendinous adhesions and improves functional glide without excessively increasing the rupture rate.

Question 84

Articular cartilage is composed of multiple zones with distinct structural properties. In which zone are the collagen fibers oriented parallel to the articular surface, providing the highest resistance to shear forces?

Explanation

Articular cartilage consists of multiple zones with specific collagen fiber orientations. The superficial (tangential) zone contains tightly packed collagen fibers aligned parallel to the joint surface, providing primary resistance to shear forces.

Question 85

During anterior cruciate ligament (ACL) reconstruction, improper placement of the femoral tunnel can lead to graft failure or loss of motion. Placing the femoral tunnel too anteriorly (shallow) within the intercondylar notch results in which of the following graft tension patterns?

Explanation

Femoral tunnel malposition is the most common cause of technical failure in ACL reconstruction. A femoral tunnel placed too anteriorly (shallow) will result in a graft that is loose in extension and pathologically tight in flexion, limiting terminal knee flexion.

Question 86

A 40-year-old male sustains a Gustilo-Anderson Type IIIB open tibial shaft fracture. According to classic principles established by Godina, within what timeframe should definitive free soft tissue coverage ideally be performed to significantly decrease the risk of flap failure and deep infection?

Explanation

In Gustilo IIIB open fractures, timing of soft tissue coverage is critical. Godina's classic studies demonstrated that definitive free tissue transfer within 72 hours significantly decreases the rates of deep infection, flap failure, and nonunion compared to delayed coverage.

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