Orthopedic Board Review: High-Yield General Orthopedics MCQs

Correct Answer: C

The patient has a stable Slipped Capital Femoral Epiphysis (SCFE), which frequently presents with referred knee pain and obligatory external rotation during hip flexion. The standard of care for a stable SCFE is in situ fixation, typically with a single central cannulated screw, to prevent further slippage. Closed reduction is strictly contraindicated as it significantly increases the risk of avascular necrosis (AVN) of the femoral head by disrupting the already tenuous retinacular blood supply.

Correct Answer: C

The inability to make an "OK" sign indicates an injury to the anterior interosseous nerve (AIN), a motor branch of the median nerve. The AIN is the most commonly injured nerve in extension-type supracondylar humerus fractures. A pulseless, pale hand (vascular compromise) in the setting of a displaced fracture requires urgent closed reduction and percutaneous pinning. Often, the pulse returns after anatomical reduction relieves tension on the brachial artery. Open exploration is reserved for cases where the hand remains dysvascular after adequate reduction.

Correct Answer: A

The clinical and radiographic presentation (diaphyseal lesion, onion-skin periosteal reaction, systemic symptoms) is classic for Ewing sarcoma. The most common genetic translocation associated with Ewing sarcoma is t(11;22)(q24;q12), which results in the EWS-FLI1 fusion protein. This translocation is present in approximately 85% of cases and is a key diagnostic marker.

Correct Answer: B

The patient has an isthmic spondylolisthesis secondary to a bilateral spondylolysis (a stress fracture or defect in the pars interarticularis). This is common in adolescent athletes who perform repetitive hyperextension and rotation (e.g., gymnasts). The "collar" on the Scotty dog represents the pars defect. Initial management for a symptomatic, low-grade (<50% slip) isthmic spondylolisthesis is nonoperative, consisting of activity modification, physical therapy (core strengthening, antilordotic exercises), and often a rigid brace (TLSO) to restrict extension and allow the pars defect to heal or become asymptomatic.

Correct Answer: C

In an elderly, independently ambulatory patient with a displaced femoral neck fracture, arthroplasty (hemiarthroplasty or total hip arthroplasty) is the treatment of choice. Internal fixation (e.g., cannulated screws or a sliding hip screw) in displaced fractures in this age group carries an unacceptably high risk of avascular necrosis and nonunion, leading to a high reoperation rate. Arthroplasty allows for immediate weight-bearing and a faster return to baseline function.

Correct Answer: B

The Ponseti method is the gold standard for treating idiopathic clubfoot (talipes equinovarus). The deformities must be corrected in a specific sequence, remembered by the acronym CAVE: Cavus (corrected first by elevating the first ray to align the forefoot with the hindfoot), Adductus, Varus, and finally Equinus. The equinus is corrected last, and often requires a percutaneous Achilles tenotomy to achieve adequate dorsiflexion.

Correct Answer: A

The supraspinatus, along with the rest of the rotator cuff, functions to depress and stabilize the humeral head within the glenoid during arm elevation, counteracting the upward pull of the deltoid muscle. A massive, chronic tear of the supraspinatus (and often infraspinatus) leads to a loss of this compressive force, allowing the unopposed pull of the deltoid to cause superior migration of the humeral head. This decreases the acromiohumeral distance and can eventually lead to rotator cuff arthropathy.

Correct Answer: D

The patient presents with classic signs of acute compartment syndrome: pain out of proportion, pain with passive stretch, and tense compartments. Palpable pulses do not rule out compartment syndrome, as arterial flow is maintained until late in the ischemic process. The diagnosis is primarily clinical. When the clinical picture is clear, immediate surgical decompression via a four-compartment fasciotomy is indicated without the need to delay for pressure measurements or imaging.

Correct Answer: B

The standard of care for high-grade, non-metastatic osteosarcoma is neoadjuvant (preoperative) chemotherapy, followed by wide surgical resection (limb-salvage surgery if feasible), and then adjuvant (postoperative) chemotherapy. This approach treats micrometastatic disease early, shrinks the primary tumor to facilitate resection, and allows for histological evaluation of tumor necrosis, which is a key prognostic factor. Osteosarcoma is generally considered radioresistant.

Correct Answer: C

Recent literature supports early functional rehabilitation for acute Achilles tendon ruptures managed nonoperatively. This involves early weight-bearing in a functional brace or boot with heel wedges (to keep the ankle in equinus and approximate the tendon ends), combined with early active range of motion exercises. This approach has been shown to have similar re-rupture rates to surgical repair while avoiding surgical complications, and it provides better functional outcomes than prolonged rigid immobilization.

Correct Answer: C

Pathophysiology: Slipped Capital Femoral Epiphysis (SCFE) is an adolescent hip disorder characterized by the displacement of the proximal femoral epiphysis on the metaphysis through the hypertrophic zone of the physis. It is most commonly seen in obese adolescents undergoing rapid growth spurts.

Clinical Presentation: Patients typically present with groin, thigh, or knee pain (referred pain via the obturator nerve) and an antalgic gait. A classic physical exam finding is obligatory external rotation of the hip during passive flexion, along with limited internal rotation.

Management: The definitive and immediate management for a stable SCFE is in situ single screw fixation to prevent further slippage and promote premature closure of the physis. Open reduction is generally reserved for unstable or severe slips due to the high risk of avascular necrosis (AVN). Spica casting is obsolete due to high rates of chondrolysis.

Correct Answer: C

Anatomy & Injury: Supracondylar humerus fractures are the most common elbow fractures in children. Extension-type fractures account for >95% of cases, where the distal fragment is displaced posteriorly.

Nerve Injury: The median nerve (specifically its anterior interosseous branch) is the most frequently injured nerve in extension-type supracondylar fractures, often due to tethering or direct contusion by the proximal fracture fragment. Median nerve compromise presents with weakness in wrist flexion, forearm pronation, and inability to flex the IP joint of the thumb and DIP joint of the index finger (weak "A-OK" sign), along with sensory deficits over the palmar aspect of the radial 3.5 digits.

Complications: A severe, feared complication of displaced supracondylar fractures is Volkmann's ischemic contracture, resulting from untreated vascular compromise or compartment syndrome.

Correct Answer: C

Epidemiology: Ewing's sarcoma is the second most common primary malignant bone tumor in children, following osteosarcoma. It typically affects the diaphysis of long bones (e.g., femur, tibia) and the pelvis.

Radiographic Findings: The classic radiographic appearance is a permeative, destructive diaphyseal lesion with an "onion-skin" (lamellated) periosteal reaction, representing sequential layers of new bone formation in response to the rapidly growing tumor.

Differential Diagnosis: Osteosarcoma typically occurs in the metaphysis and presents with a "sunburst" pattern or Codman's triangle. Chondrosarcoma is more common in adults and shows "popcorn" calcifications. Osteoid osteoma presents with a radiolucent nidus surrounded by sclerotic bone and causes night pain relieved by NSAIDs.

Correct Answer: B

Pathophysiology: Femoral neck fractures are intracapsular fractures. The blood supply to the femoral head is tenuous, relying primarily on the medial femoral circumflex artery (MFCA), which courses along the femoral neck.

Complications: Displacement of a femoral neck fracture frequently disrupts the MFCA, leading to a high risk of avascular necrosis (AVN) of the femoral head and nonunion. Because of this high risk, displaced femoral neck fractures in the elderly are typically treated with arthroplasty (hemiarthroplasty or total hip arthroplasty) rather than internal fixation.

Clinical Presentation: Patients classically present with a shortened and externally rotated lower extremity due to the unopposed pull of the iliopsoas and short external rotators.

Correct Answer: C

Definitions: Spondylolysis is a defect or stress fracture of the pars interarticularis. When bilateral pars defects lead to the anterior translation of one vertebra over another, it is termed spondylolisthesis.

Etiology: In adolescents, the most common type is isthmic spondylolisthesis, which arises from repetitive hyperextension and rotation forces (common in gymnasts, weightlifters, and football linemen) causing a fatigue fracture of the pars interarticularis.

Imaging: Oblique radiographs classically demonstrate the "Scotty dog" sign, where a break in the dog's "collar" represents the pars defect.

Management: Low-grade, asymptomatic slips are observed. Symptomatic slips are initially treated with activity modification, physical therapy, and occasionally bracing.

Correct Answer: B

Pathoanatomy: Idiopathic clubfoot (talipes equinovarus) is a complex congenital deformity involving four main components: Cavus (midfoot), Adductus (forefoot), Varus (hindfoot), and Equinus (hindfoot) - remembered by the acronym CAVE.

Treatment: The Ponseti method is the universally accepted gold standard for initial treatment. It involves a specific sequence of serial manipulations and long-leg casting to gradually correct the deformities in the order of C-A-V-E. The cavus is corrected first by elevating the first ray. The equinus is corrected last, often requiring a percutaneous Achilles tenotomy. Extensive surgical releases are now rarely performed due to long-term stiffness and pain.

Correct Answer: D

Anatomy: The rotator cuff consists of four muscles: Supraspinatus, Infraspinatus, Teres minor, and Subscapularis.

Pathology: The supraspinatus is the most commonly torn rotator cuff tendon, largely due to its vulnerable location in the subacromial space where it is susceptible to impingement and hypovascularity (critical zone).

Clinical Testing: The Jobe's test (empty can test) specifically isolates the supraspinatus muscle. The patient abducts the arms to 90 degrees, angles them forward 30 degrees (scapular plane), and internally rotates the arms (thumbs pointing down). The examiner then applies downward pressure. Pain or weakness indicates supraspinatus pathology.

Correct Answer: C

Pathophysiology: Acute compartment syndrome occurs when increased pressure within a closed osteofascial compartment compromises tissue perfusion, leading to ischemia and potential necrosis of muscles and nerves. It is a surgical emergency.

Clinical Presentation: The classic "6 Ps" are Pain out of proportion, Pallor, Paresthesias, Pulselessness, Paralysis, and Poikilothermia. However, pain with passive stretch of the muscles in the affected compartment is the most sensitive and earliest clinical sign.

Management: Urgent surgical decompression via a four-compartment fasciotomy is the definitive treatment. Elevating the leg above the heart is contraindicated as it further decreases arterial perfusion pressure to the compartment.

Correct Answer: B

Classification System: The Salter-Harris (SH) system categorizes pediatric physeal fractures:

• Type I: Slipped (fracture straight across the physis).
• Type II: Above (fracture through the physis exiting through the metaphysis).
• Type III: Lower (fracture through the physis exiting through the epiphysis).
• Type IV: Through or Two (fracture through the metaphysis, physis, and epiphysis).
• Type V: ERasure of growth plate (crush injury to the physis).

Epidemiology: SH Type II is the most common type of physeal fracture. The prognosis is generally good as the germinal layer of the physis is usually preserved with the epiphysis.

Correct Answer: C

Pathophysiology: Osgood-Schlatter disease is a traction apophysitis of the tibial tubercle. It occurs in active adolescents (typically boys aged 12-15 and girls aged 10-13) during periods of rapid growth. Repetitive microtrauma from the pull of the patellar tendon on the unossified tibial tubercle leads to inflammation and microavulsions.

Clinical Presentation: Patients present with anterior knee pain exacerbated by running, jumping, or kneeling. Examination reveals a prominent, tender tibial tubercle.

Differential Diagnosis: Sinding-Larsen-Johansson syndrome is a similar traction apophysitis but occurs at the inferior pole of the patella. Patellofemoral pain syndrome presents with diffuse anterior knee pain without localized tubercle tenderness.

Correct Answer: D (Zone of hypertrophy)

Slipped capital femoral epiphysis (SCFE) typically occurs through the zone of hypertrophy of the physis. This zone is mechanically the weakest due to the lack of collagen and the large size of the chondrocytes. The condition is most commonly seen in obese adolescents undergoing rapid growth spurts, where mechanical shear forces across the proximal femoral physis exceed the structural integrity of the hypertrophic zone.

Correct Answer: C (Anterior interosseous nerve)

The anterior interosseous nerve (AIN), a motor branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures. It innervates the flexor pollicis longus (FPL), the flexor digitorum profundus (FDP) to the index and middle fingers, and the pronator quadratus. Injury results in an inability to make an "OK" sign, as the patient cannot actively flex the IP joint of the thumb and the DIP joint of the index finger.

Correct Answer: A (Cavus, Adductus, Varus, Equinus)

The Ponseti method corrects the deformities of clubfoot in a specific, sequential order, remembered by the acronym CAVE: Cavus, Adductus, Varus, and Equinus. The cavus is corrected first by elevating the first ray to align the forefoot with the hindfoot. Subsequent casts correct the adductus and varus by abducting the foot around the head of the talus. Finally, the equinus is corrected, which often requires a percutaneous Achilles tenotomy.

Correct Answer: B (t(11;22))

The clinical and radiographic presentation is classic for Ewing sarcoma. Ewing sarcoma is characterized by the t(11;22)(q24;q12) translocation in approximately 85% of cases, which results in the EWS-FLI1 fusion protein. Other translocations include t(9;22) seen in myxoid chondrosarcoma and CML, t(12;16) seen in myxoid liposarcoma, t(X;18) seen in synovial sarcoma, and t(2;13) seen in alveolar rhabdomyosarcoma.

Correct Answer: C (Medial femoral circumflex artery)

The medial femoral circumflex artery (MFCA), specifically its lateral epiphyseal branches, provides the predominant blood supply to the weight-bearing dome of the femoral head in adults. Disruption of this vessel in displaced femoral neck fractures leads to a high rate of avascular necrosis. The artery of the ligamentum teres provides a negligible amount of blood supply in adults, though it is more significant in children.

Correct Answer: D (93%)

The Kocher criteria for differentiating septic arthritis from transient synovitis in the pediatric hip include four predictors: non-weight-bearing on the affected side, ESR > 40 mm/hr, fever > 38.5°C (101.3°F), and WBC count > 12,000/mm³. This patient meets 3 criteria (refusal to bear weight, WBC > 12,000, and ESR > 40). His temperature is below the 38.5°C threshold. The probability of septic arthritis is approximately 3% for 1 criterion, 40% for 2 criteria, 93% for 3 criteria, and 99% for 4 criteria.

Correct Answer: C (Spinoglenoid notch)

The suprascapular nerve passes through the suprascapular notch (where it innervates the supraspinatus) and then winds around the base of the scapular spine through the spinoglenoid notch to innervate the infraspinatus. It is most vulnerable to traction injury at the spinoglenoid notch during excessive medial mobilization of a retracted infraspinatus tendon. Mobilization greater than 1 to 2 cm medial to the glenoid rim significantly increases the risk of iatrogenic nerve injury.

Correct Answer: B (Venous outflow obstruction leading to increased intracompartmental pressure)

The patient is presenting with acute compartment syndrome. The pathophysiologic cascade begins when tissue pressure within a closed fascial compartment exceeds the venous capillary pressure. This leads to venous outflow obstruction, which causes further fluid transudation into the interstitial space. This secondary increase in intracompartmental pressure eventually exceeds arteriolar pressure, leading to arteriolar collapse, muscle ischemia, and nerve necrosis if not urgently decompressed via fasciotomy.

Correct Answer: C (Grade III; L5-S1 instrumented fusion)

The Meyerding classification grades the degree of anterior translation of the superior vertebra over the inferior one: Grade I (0-25%), Grade II (26-50%), Grade III (51-75%), Grade IV (76-100%), and Grade V (>100%, spondyloptosis). A 65% slip is a Grade III spondylolisthesis. For high-grade slips (Grade III and above) that are symptomatic or progressive, an instrumented spinal fusion (typically L5-S1) is the standard surgical treatment. Pars repair is reserved for patients with pure spondylolysis or very low-grade slips without significant instability.

Correct Answer: B (2 to 6 cm proximal to the calcaneal insertion)

The Achilles tendon has a relative hypovascular zone (watershed area) located approximately 2 to 6 cm proximal to its insertion on the calcaneus. This area receives a tenuous blood supply from the paratenon rather than direct osseous or muscular vessels, making it the most common site for degenerative changes, tendinopathy, and acute ruptures.

Correct Answer: B

Avascular necrosis (AVN) is the most devastating complication of Slipped Capital Femoral Epiphysis (SCFE). The risk is significantly higher in unstable slips (where the patient is unable to bear weight) and if forceful closed reduction is attempted prior to pinning. The standard of care is in situ pinning to prevent further slippage without attempting to anatomically reduce the physis, thereby protecting the tenuous blood supply. Chondrolysis is another severe complication but is less common today with the avoidance of joint penetration by hardware. Contralateral slip occurs in up to 20-40% of patients but is not as acutely devastating as AVN.

Correct Answer: B

The anterior interosseous nerve (AIN), a motor branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures. AIN palsy presents with the inability to flex the interphalangeal (IP) joint of the thumb (innervating the flexor pollicis longus) and the distal interphalangeal (DIP) joint of the index finger (innervating the flexor digitorum profundus to the index and middle fingers). This leads to an abnormal "A-OK" sign, where the patient pinches with the pulps of the fingers rather than the tips. The median nerve overall is the most frequently injured nerve in these fractures, specifically its AIN branch.

Correct Answer: A

The clinical and radiographic presentation is classic for Ewing sarcoma, a highly malignant primary bone tumor that typically affects the diaphysis of long bones in children and young adults. The characteristic chromosomal translocation is t(11;22)(q24;q12), which is found in approximately 85% of cases and results in the EWS-FLI1 fusion protein. t(9;22) is seen in chronic myelogenous leukemia (Philadelphia chromosome) and some extraskeletal myxoid chondrosarcomas. t(12;16) is characteristic of myxoid liposarcoma. t(X;18) is seen in synovial sarcoma. t(2;13) is seen in alveolar rhabdomyosarcoma.

Correct Answer: B

The patient is presenting with acute compartment syndrome. The primary pathophysiologic mechanism is an increase in interstitial pressure within a closed osteofascial compartment. This elevated pressure first collapses the low-pressure venous system, causing venous outflow obstruction. This leads to a decrease in the arteriovenous (AV) pressure gradient, which ultimately impairs local tissue perfusion. When the local tissue pressure exceeds capillary perfusion pressure, capillary collapse occurs, leading to muscle and nerve ischemia. Direct arterial occlusion is a late and rare finding, as compartment pressures rarely exceed systolic arterial pressure; thus, distal pulses are usually maintained until very late in the process.

Correct Answer: C

The Meyerding classification grades the degree of anterior translation of the superior vertebra on the inferior one: Grade I (0-25%), Grade II (26-50%), Grade III (51-75%), Grade IV (76-100%), and Grade V (spondyloptosis, >100%). A 60% slip is a Grade III spondylolisthesis. For high-grade slips (Grade III and above) with progressive neurologic deficits, surgical intervention is indicated. This typically involves decompression of the neural elements and instrumented fusion. Due to the high grade of the slip and the biomechanical forces at play, fusion often needs to extend to L4 (L4-S1) to achieve adequate stability and reduction, rather than just an isolated L5-S1 fusion.

Correct Answer: B

The lesion described is an osteochondroma, the most common benign bone tumor. Malignant transformation to secondary chondrosarcoma occurs in <1% of solitary osteochondromas (the risk is higher in multiple hereditary exostoses). The most reliable imaging sign of malignant transformation in an adult is a cartilage cap thickness greater than 2.0 cm (some sources use >1.5 cm as a threshold for concern). A cap of 2.5 cm is highly concerning for secondary chondrosarcoma and warrants biopsy or wide excision. Pedunculated morphology, location in the metaphysis of long bones, and medullary continuity are standard diagnostic features of benign osteochondromas.

Correct Answer: B

The supraspinatus is the most commonly torn rotator cuff tendon. It functions to initiate shoulder abduction and provides dynamic stabilization of the glenohumeral joint. Anatomically, the supraspinatus inserts onto the superior facet of the greater tuberosity of the humerus. The infraspinatus inserts on the middle facet, and the teres minor inserts on the inferior facet. The subscapularis, which internally rotates the shoulder, inserts on the lesser tuberosity.

Correct Answer: B

The Ponseti method is the gold standard for treating idiopathic clubfoot (talipes equinovarus). It corrects the deformities in a very specific sequence, remembered by the acronym CAVE: Cavus, Adductus, Varus, and Equinus. The cavus is corrected first by elevating the first ray to align the forefoot with the hindfoot. Then, the adductus and varus are corrected simultaneously by abducting the foot around the head of the talus. Finally, the equinus is addressed; because it is often the most rigid component, it frequently requires a percutaneous Achilles tenotomy as the final step before the last cast is applied.

Correct Answer: B

The primary blood supply to the adult femoral head is derived from the medial femoral circumflex artery (MFCA), specifically its lateral epiphyseal branches, which travel along the femoral neck in the retinaculum. Displaced femoral neck fractures frequently disrupt these vessels, leading to a high risk of avascular necrosis (AVN) and nonunion. Because of this risk, elderly patients with displaced femoral neck fractures are typically treated with arthroplasty (hemiarthroplasty or total hip arthroplasty) rather than internal fixation. The artery of the ligamentum teres provides a negligible blood supply in adults. The lateral femoral circumflex artery supplies the anterior and inferior portions of the femoral neck but is not the primary supply to the head.

Correct Answer: D

This infant has multiple significant risk factors for Developmental Dysplasia of the Hip (DDH), including female sex, breech presentation, and a positive family history. Even with a normal physical examination, infants with high-risk factors (specifically breech presentation or a positive family history) should undergo screening imaging. Ultrasound is the modality of choice for infants under 4-6 months of age because the femoral head is largely cartilaginous and not well visualized on plain radiographs. The ultrasound is typically performed around 6 weeks of age to avoid false positives from physiologic capsular laxity that is normally present at birth.

Correct Answer: L5 nerve root; neural foramen

In isthmic spondylolisthesis at the L5-S1 level, the L5 nerve root is the most commonly affected nerve. The compression typically occurs in the neural foramen. The defect in the pars interarticularis fills with a fibrocartilaginous mass (often referred to as a Gill body), which hypertrophies and directly compresses the exiting L5 nerve root against the L5 pedicle. This is in contrast to degenerative spondylolisthesis, where the traversing nerve root (e.g., the L5 root in an L4-L5 slip) is typically compressed in the lateral recess due to facet hypertrophy and ligamentum flavum buckling.

Correct Answer: The metaphysis displaces anteriorly and superiorly, while the epiphysis remains in the acetabulum.

Although the term "slipped capital femoral epiphysis" implies that the epiphysis is the structure that moves, the biomechanical reality is the opposite. The femoral epiphysis is held securely within the acetabulum by the ligamentum teres. The mechanical failure occurs through the hypertrophic zone of the physis, allowing the femoral neck (metaphysis) to displace anteriorly, superiorly, and externally rotate relative to the fixed epiphysis. This creates the classic radiographic appearance of a posterior and inferior "slip" of the epiphysis on the AP and lateral views.

Correct Answer: Cavus, Adductus, Varus, Equinus

The Ponseti method follows a strict sequence of correction summarized by the acronym CAVE: Cavus, Adductus, Varus, and Equinus. The first step is to correct the cavus deformity by supinating the forefoot and elevating the first ray to align it with the hindfoot. Once the cavus is corrected, the adductus and varus are corrected simultaneously by gradually abducting the foot around the lateral aspect of the talar head (which acts as a fulcrum). Finally, the equinus is corrected; this often requires a percutaneous Achilles tenotomy in the final stage of casting to achieve adequate dorsiflexion without causing a rocker-bottom deformity.

Correct Answer: Anterior interosseous nerve

The anterior interosseous nerve (AIN), a pure motor branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures. The AIN innervates the flexor pollicis longus (FPL), the flexor digitorum profundus (FDP) to the index and middle fingers, and the pronator quadratus. Injury is clinically assessed by asking the patient to make an "OK" sign; an inability to flex the IP joint of the thumb and the DIP joint of the index finger results in a "pincer" grasp instead, indicating AIN palsy. Ulnar nerve injuries are more commonly associated with flexion-type supracondylar fractures or iatrogenic injury during medial pin placement.

Correct Answer: t(11;22)

The clinical presentation and radiographic findings (permeative diaphyseal lesion, "onion-skin" periosteal reaction) are classic for Ewing's sarcoma. Ewing's sarcoma is a small round blue cell tumor characterized by the t(11;22)(q24;q12) chromosomal translocation in approximately 85-90% of cases. This translocation fuses the EWS gene on chromosome 22 with the FLI1 gene on chromosome 11, creating an aberrant transcription factor that drives oncogenesis. Other notable translocations include t(X;18) in synovial sarcoma, t(12;16) in myxoid liposarcoma, and t(2;13) in alveolar rhabdomyosarcoma.

Correct Answer: Lateral epiphyseal branches of the medial femoral circumflex artery

The predominant blood supply to the adult femoral head is provided by the medial femoral circumflex artery (MFCA), specifically its lateral epiphyseal branches. The MFCA forms an extracapsular arterial ring at the base of the femoral neck, giving off ascending cervical branches that pierce the joint capsule and travel along the femoral neck as retinacular vessels. These vessels are highly susceptible to disruption or tamponade from an intracapsular hematoma following a displaced femoral neck fracture, leading to avascular necrosis. The artery of the ligamentum teres (a branch of the obturator artery) provides a negligible amount of blood supply in adults.

Correct Answer: Suprascapular nerve; spinoglenoid notch

The suprascapular nerve, arising from the upper trunk of the brachial plexus (C5, C6), provides motor innervation to both the supraspinatus and infraspinatus muscles. It first passes through the suprascapular notch (under the transverse scapular ligament) to innervate the supraspinatus. It then continues laterally and inferiorly, passing through the spinoglenoid notch (under the spinoglenoid ligament) to reach and innervate the infraspinatus. Compression at the suprascapular notch affects both muscles, whereas compression at the spinoglenoid notch (e.g., by a paralabral cyst) results in isolated infraspinatus weakness.

Correct Answer: Hook of the hamate and pisiform

The carpal tunnel is a fibro-osseous canal in the wrist. The roof is formed by the transverse carpal ligament (flexor retinaculum). The floor is formed by the proximal and distal rows of carpal bones. The ulnar border is defined by the hook of the hamate and the pisiform. The radial border is defined by the scaphoid tubercle and the crest of the trapezium. The tunnel contains 10 structures: the median nerve, four flexor digitorum superficialis (FDS) tendons, four flexor digitorum profundus (FDP) tendons, and the flexor pollicis longus (FPL) tendon.

Correct Answer: Diastolic blood pressure minus compartment pressure < 30 mmHg

The diagnosis of acute compartment syndrome is primarily clinical, but intracompartmental pressure monitoring is crucial in obtunded or polytrauma patients. The most reliable objective threshold for performing a fasciotomy is a "delta P" (diastolic blood pressure minus the compartment pressure) of less than 30 mmHg. This measurement accounts for the patient's systemic perfusion pressure, which dictates capillary blood flow. Relying solely on absolute compartment pressures (e.g., > 30 mmHg) can lead to unnecessary fasciotomies in hypertensive patients or missed diagnoses in hypotensive patients.

Correct Answer: 40° ± 10° of inclination and 15° ± 10° of anteversion

The Lewinnek safe zone is a classic orthopedic concept describing the ideal orientation of the acetabular component in total hip arthroplasty to minimize the risk of dislocation. It is defined as 40° ± 10° of inclination (abduction) and 15° ± 10° of anteversion. Cups placed with excessive anteversion or inclination are prone to anterior and superior dislocations, respectively, while retroverted cups are at high risk for posterior dislocation, especially when combined with a posterior surgical approach.

BMPs bind to serine/threonine kinase receptors, leading to the phosphorylation of Smad 1, 5, and 8. These form a complex with Smad 4 to enter the nucleus and regulate transcription of osteogenic genes.

A knee that is tight in flexion and balanced in extension requires an increase in the flexion gap. Downsizing the femoral component using anterior referencing resects more posterior femoral condyle, increasing the flexion gap without affecting the extension gap.

Delta pressure is calculated as diastolic blood pressure minus intracompartmental pressure (80 - 55 = 25 mmHg). A delta pressure of less than 30 mmHg is diagnostic for acute compartment syndrome and requires emergent fasciotomy.

Osteoid osteomas characteristically cause nocturnal pain that is relieved by NSAIDs. This is due to the high levels of Prostaglandin E2 produced by the nidus, which NSAIDs effectively inhibit.

Femoral nerve palsy is a known complication of the Pavlik harness, typically caused by excessive hip flexion. It presents with absent active knee extension and usually resolves with temporary removal or adjustment of the harness.

The described test is the Hoffmann sign, which indicates an upper motor neuron lesion such as cervical myelopathy. In degenerative cervical myelopathy, the most frequently involved and compressed level is C5-C6.

The primary blood supply to the scaphoid enters distally via the dorsal carpal branch of the radial artery and flows in a retrograde fashion. Fractures at the waist or proximal pole disrupt this flow, leading to a high risk of AVN.

Harvest of the hamstring tendons for ACL reconstruction can result in a measurable deficit in deep knee flexion and internal rotation strength. Unlike bone-patellar tendon-bone autografts, hamstring grafts are not typically associated with chronic anterior knee pain.

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicularly to the joint surface, providing resistance to compressive forces. It also has the lowest water content and the highest proteoglycan concentration.

While lateral compression injuries often tear the superior gluteal artery, anteroposterior compression (APC) injuries typically cause massive hemorrhage by disrupting the extensive presacral venous plexus and anterior branches of the internal iliac artery.

Intermediate and high-grade chondrosarcomas are generally resistant to both chemotherapy and radiation therapy. The gold standard for definitive management is wide surgical resection with negative margins.

Vitamin E is added to highly cross-linked polyethylene as an antioxidant to quench free radicals generated during the irradiation process. This prevents in vivo oxidation, thereby preserving the material's mechanical properties and reducing wear.

Gamma irradiation creates cross-links that improve wear resistance but also generates reactive free radicals. Remelting the polyethylene eliminates these free radicals to prevent long-term oxidation, though it comes at the cost of reducing the material's mechanical and fatigue strength.

The corona mortis is a critical vascular anastomosis connecting the external iliac or deep inferior epigastric system with the obturator system. It is highly susceptible to injury during pelvic trauma or anterior intrapelvic surgical approaches, leading to profuse bleeding.

Hyperflexion of the hip in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to an iatrogenic femoral nerve palsy. The immediate treatment is to adjust the harness to decrease the degree of hip flexion.

The histological response to neoadjuvant chemotherapy, specifically the percentage of tumor necrosis, is the most powerful prognostic factor in osteosarcoma. Greater than 90% necrosis is classified as a good response and correlates strongly with improved survival rates.

Primary bone healing requires absolute stability, which biomechanically corresponds to an interfragmentary strain of less than 2%. Strains between 2% and 10% favor secondary bone healing with callus formation, while strains above 10% lead to nonunion.

Placement of a volar plate at or distal to the watershed line of the distal radius causes prominence of the hardware in the flexor compartment. This friction most commonly leads to attrition and subsequent rupture of the flexor pollicis longus (FPL) tendon.

A tight flexion gap with a balanced extension gap indicates the femoral component is too large posteriorly or the posterior cruciate ligament (PCL) is excessively tight. Downsizing the femoral component (anterior referencing) or releasing the PCL will balance the flexion gap without altering extension.

The Ponseti method addresses clubfoot deformities in the order of CAVE: Cavus, Adductus, Varus, and Equinus. The first critical maneuver is elevating the first ray to supinate the forefoot in alignment with the hindfoot, thereby correcting the cavus.

Acute compartment syndrome is reliably diagnosed using the Delta P, calculated as the diastolic blood pressure minus the absolute compartment pressure. A Delta P of less than 30 mmHg signifies inadequate tissue perfusion and is an absolute indication for fasciotomy.

In SNAC Stage III, arthritic changes involve both the radioscaphoid and midcarpal (scaphocapitate and lunocapitate) joints. Four-corner fusion with scaphoid excision is the preferred treatment, as a proximal row carpectomy is contraindicated when capitate arthritis is present.

Conventional chondrosarcomas are notoriously resistant to both chemotherapy and radiation therapy. The standard of care for an intermediate or high-grade conventional chondrosarcoma is wide surgical resection alone.

This patient has advanced rotator cuff tear arthropathy (Hamada Stage IV) complicated by pseudoparalysis. Reverse total shoulder arthroplasty is indicated because it medializes the center of rotation and distalizes the humerus, allowing the deltoid to compensate for the deficient cuff.

Pauwels type III fractures have a vertical orientation (fracture angle > 50 degrees). This steep angle converts physiological loads into profound shear forces, greatly increasing the risk of varus collapse, fixation failure, and nonunion.

Eichenholtz Stage I (fragmentation stage) is characterized by acute inflammation, osteopenia, and architectural breakdown. The gold standard initial management is immobilization with a total contact cast and strict non-weight-bearing to halt disease progression until it reaches the coalescence stage.

The Lisfranc ligament is the strongest interosseous restraint of the tarsometatarsal joint complex. It originates from the plantar-lateral aspect of the medial cuneiform and inserts onto the plantar-medial base of the second metatarsal.

Staphylococcus epidermidis synthesizes polysaccharide intercellular adhesin (PIA), which is essential for the aggregation of cells and the formation of the biofilm's extracellular polymeric matrix. This glycocalyx heavily shields the bacteria from host immune clearance and systemic antibiotics.

Female athletes face a higher risk of non-contact ACL tears largely due to neuromuscular factors, particularly "quadriceps dominance" and weaker hamstring co-contraction. Additionally, females generally possess a narrower intercondylar notch, increased Q angle, and increased dynamic valgus loading.

The presacral venous plexus and bleeding from fractured cancellous bone surfaces account for approximately 80% of hemorrhage in unstable pelvic ring fractures. Arterial bleeding occurs in a minority of cases, more typically involving branches of the internal iliac system such as the superior gluteal or internal pudendal arteries.

The percentage of histologic tumor necrosis following neoadjuvant chemotherapy (Huvos grading) is the most reliable prognostic indicator for overall survival in osteosarcoma. Greater than 90% necrosis indicates a good chemotherapeutic response and strongly correlates with improved long-term outcomes.

The natural history of Cervical Spondylotic Myelopathy (CSM) is classically characterized by a stepwise progressive deterioration in neurologic function. Patients typically experience periods of stable symptoms interrupted by sudden, discrete episodes of functional decline.

The anteromedial (AM) bundle of the ACL is tight in flexion and serves as the primary restraint to anterior tibial translation. Conversely, the posterolateral (PL) bundle is tight in extension and primarily acts to control rotatory stability of the knee.

Acetabular retroversion, as well as decreased femoral anteversion (retroversion), strongly predisposes a total hip arthroplasty to posterior dislocation. Excessive anteversion of either the acetabular or femoral component typically predisposes the joint to anterior dislocation.

Excessive hip flexion in a Pavlik harness can compress the femoral nerve, causing a transient femoral nerve palsy that presents as a loss of active knee extension. The appropriate management is to adjust the anterior straps to decrease the degree of hip flexion, which typically results in full neurologic recovery.

The optimal management for Zone II flexor tendon lacerations is primary repair of both the FDS and FDP tendons. Repairing both tendons helps preserve the vincula blood supply, reduces the risk of PIP joint hyperextension (bowstringing), and provides superior gliding mechanics compared to isolated FDP repair.

Bone morphogenetic proteins (BMPs) bind to serine/threonine kinase cell surface receptors that directly phosphorylate intracellular SMAD proteins (specifically SMAD 1, 5, and 8). The activated SMAD complex then translocates to the nucleus to upregulate target genes crucial for osteoblastic differentiation.

The Lisfranc ligament is a strong interosseous ligament that connects the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal. It is the primary stabilizer of the tarsometatarsal joint complex, and its avulsion is classically represented by the radiographic "fleck sign".

Acute compartment syndrome is most accurately diagnosed using the delta pressure, calculated as the patient's diastolic blood pressure minus the absolute compartment pressure. A delta pressure of less than 30 mmHg indicates critically impaired tissue perfusion and is the standard threshold for emergent fasciotomy.