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Arab Orthopaedic Board MCQs - Part 11

27 Apr 2026 59 min read 77 Views
Arab Ortho Board MCQs - Part 10

Key Takeaway

Learn more about Arab Orthopaedic Board MCQs - Part 11 and how to manage it. Practice Arab Orthopaedic Board MCQs Part 11. Review orthopedic surgery questions 501 to 550 for your board exam preparation.

Arab Orthopaedic Board MCQs - Part 11

Comprehensive 100-Question Exam


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Question 1

What is the primary mechanism of wear in a well-functioning metal-on-polyethylene total hip arthroplasty?





Explanation

Adhesive wear is the primary mechanism of wear in a well-functioning metal-on-polyethylene total hip arthroplasty. It occurs when microscopic asperities on the metal surface temporarily bond to the softer polyethylene. As the surfaces slide, these bonds break, tearing away submicron particles of polyethylene. Abrasive wear occurs when a rough, harder surface plows into a softer surface (e.g., a scratched femoral head). Third-body wear involves foreign particles (like bone or cement) acting as an abrasive between the two surfaces. Fatigue wear is due to cyclic loading leading to subsurface delamination.

Question 2

Anterior posterior compression type III (APC-III) pelvic ring injuries involve complete disruption of the symphysis pubis. Which posterior ligamentous structures are disrupted in an APC-III injury?





Explanation

According to the Young-Burgess classification, an APC-III pelvic ring injury is a highly unstable 'open book' injury characterized by disruption of the symphysis pubis anteriorly and complete disruption of the posterior arch globally. This includes tearing of the anterior sacroiliac, interosseous sacroiliac, and posterior sacroiliac ligaments, as well as the sacrotuberous and sacrospinous ligaments, leading to complete spinopelvic dissociation on the affected side.

Question 3

A 3-month-old infant with developmental dysplasia of the hip (DDH) is being treated with a Pavlik harness. During a follow-up visit, the parents note decreased spontaneous movement of the affected leg. Examination reveals active toe movement but profound weakness in knee extension. What is the most likely cause of this complication?





Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment and is most commonly caused by excessive hip flexion, which stretches or compresses the femoral nerve against the inguinal ligament or pelvic brim. The clinical presentation is an absence of active knee extension. Treatment involves immediate adjustment of the harness or temporary removal until nerve function recovers. Excessive abduction, conversely, increases the risk of avascular necrosis (AVN) of the femoral head.

Question 4

A 25-year-old rugby player presents with the inability to flex the distal interphalangeal (DIP) joint of his right ring finger after grasping an opponent's jersey. Radiographs are negative for a fracture. Ultrasound demonstrates the flexor digitorum profundus (FDP) tendon retracted to the level of the palm. What is the Leddy-Packer classification of this injury and the optimal timing for surgical repair?





Explanation

This is a Type I Leddy-Packer FDP avulsion (Jersey finger), where the tendon retracts completely into the palm. Because both vincula (longa and brevia) are ruptured, the tendon loses its blood supply and undergoes rapid necrosis and contraction. It must be repaired early, ideally within 7 to 10 days. Type II injuries retract to the level of the proximal interphalangeal (PIP) joint (vincula intact) and can be repaired up to a few weeks later. Type III involves a large bony avulsion that gets caught at the A4 pulley.

Question 5

A 45-year-old male is involved in a motor vehicle accident. Cervical spine CT reveals a traumatic spondylolisthesis of the axis (Hangman's fracture) with severe angular deformity but minimal translation. The fracture line is oblique. The application of cervical traction is strictly contraindicated. Which Levine-Edwards classification type does this represent?





Explanation

A Levine-Edwards Type IIA Hangman's fracture is characterized by severe angulation and minimal translation, with an oblique fracture line running from anterior-inferior to posterior-superior. The mechanism is flexion-distraction. Application of cervical traction is contraindicated because it will exacerbate the deformity and potentially cause neurologic injury by widening the posterior disk space. Treatment typically involves a halo vest placed in slight extension and compression.

Question 6

A 16-year-old boy presents with progressive, nocturnal thigh pain that is rapidly and completely relieved by ibuprofen. Radiographs demonstrate a 7 mm radiolucent nidus in the femoral diaphysis surrounded by dense reactive cortical sclerosis. Which inflammatory mediator is found in extraordinarily high concentrations within this nidus, explaining the efficacy of NSAIDs?





Explanation

The clinical and radiographic presentation is classic for an osteoid osteoma. The nidus of an osteoid osteoma produces enormous quantities of prostaglandins, particularly Prostaglandin E2 (PGE2), at levels 100 to 1,000 times higher than surrounding normal tissue. This massive local PGE2 production lowers the threshold of unmyelinated nerve fibers, causing the severe nocturnal pain. NSAIDs provide dramatic relief by inhibiting cyclooxygenase (COX), thereby blocking prostaglandin synthesis.

Question 7

A 55-year-old patient underwent a total hip arthroplasty utilizing a ceramic-on-ceramic bearing. At a 2-year follow-up, the patient complains of a noticeable squeaking noise with certain hip movements. Which of the following factors is most strongly and mechanically associated with squeaking in this specific bearing surface?





Explanation

Squeaking is a well-documented complication specific to ceramic-on-ceramic (CoC) total hip arthroplasties. It is strongly associated with edge loading, which occurs when the femoral head loads against the rim of the acetabular liner rather than the center. This is most often caused by cup malposition (especially steep inclination or inadequate anteversion leading to microseparation or impingement). Edge loading disrupts the fluid film lubrication and causes stripe wear, eventually leading to the audible squeak.

Question 8

A 60-year-old patient with poorly controlled type 2 diabetes presents with a swollen, erythematous, and warm painless right foot. Radiographs demonstrate extensive periarticular bony debris, fragmentation of the navicular, and subluxation of the talonavicular joint. What is the Eichenholtz stage and the most appropriate initial management?





Explanation

The patient is presenting with acute Charcot neuroarthropathy. The Eichenholtz classification is used to stage Charcot feet: Stage 0 is clinically suspected (warm, red, swollen) but radiographically normal; Stage 1 is development/fragmentation (bony debris, fragmentation, subluxation); Stage 2 is coalescence (absorption of debris, early fusion); Stage 3 is remodeling. The patient is in Stage 1. The gold standard initial treatment is offloading via total contact casting (TCC) to halt progression and prevent further deformity.

Question 9

An 18-year-old soccer player sustains a severe twisting injury to his knee. Radiographs reveal a small, elliptic bone fragment avulsed from the lateral aspect of the proximal tibia just distal to the articular surface. This pathognomonic finding is most commonly associated with which primary ligamentous injury, and what anatomical structure does the bony fragment represent?





Explanation

The described radiographic finding is a Segond fracture, which is an avulsion of the anterolateral ligament (ALL) and lateral capsule from the lateral aspect of the proximal tibia. It occurs due to internal rotation and varus stress. The presence of a Segond fracture is highly predictive (up to 75-100% in various studies) of an anterior cruciate ligament (ACL) rupture.

Question 10

According to the Sunderland classification of peripheral nerve injuries, a third-degree nerve injury involves the physical disruption of which of the following structures?





Explanation

The Sunderland classification expands on Seddon's classification. 1st degree: neurapraxia (myelin injury). 2nd degree: axonotmesis with intact endoneurium (excellent recovery). 3rd degree: axon and endoneurium are disrupted, but the perineurium is intact (recovery is variable and often incomplete due to intrafascicular scarring). 4th degree: perineurium disrupted, fascicles disorganized, but epineurium intact (requires surgery). 5th degree: neurotmesis/complete nerve transection.

Question 11

When assessing a complex proximal humerus fracture for the risk of avascular necrosis (AVN), which of the following Hertel radiographic criteria is considered the most reliable predictor of subsequent humeral head ischemia?





Explanation

Hertel et al. defined several criteria that predict ischemia of the humeral head following proximal humerus fractures. The most highly predictive factors include a lack of medial metaphyseal head extension (calcar length < 8 mm attached to the articular segment), disruption of the medial hinge (> 2 mm displacement), and an anatomical neck fracture pattern. 'Length of the dorsomedial metaphyseal extension less than 8 mm' is a key indicator that the arcuate artery blood supply has likely been compromised.

Question 12

A normal-weight 10-year-old girl presents with a unilateral slipped capital femoral epiphysis (SCFE). Given her atypical demographic profile for this condition, which underlying endocrine disorder is most commonly associated with SCFE and should prompt consideration for prophylactic pinning of the contralateral hip?





Explanation

While idiopathic SCFE typically occurs in overweight adolescents during their growth spurt (males 12-16, females 10-14), patients presenting outside of this typical age or weight demographic (e.g., <10 years old, or normal weight) have a high likelihood of an underlying endocrine or metabolic disorder. Hypothyroidism is the most common endocrine disorder associated with SCFE. Other conditions include renal osteodystrophy and growth hormone deficiency. These patients are at very high risk for contralateral disease, often necessitating prophylactic pinning.

Question 13

During a total knee arthroplasty for a severe, rigid varus deformity, the surgeon performs a standard medial release. After releasing the deep medial collateral ligament and excising all medial osteophytes, the knee remains excessively tight medially in both flexion and extension. What is the next most appropriate anatomical structure to release to balance the knee?





Explanation

In varus knee balancing, the release sequence targets specific tight structures. The deep MCL and osteophytes are released first. If the knee is tight in both flexion and extension, the superficial medial collateral ligament (sMCL) is the primary structure restricting both gaps. Releasing the sMCL (often via subperiosteal stripping off the tibia) will increase both the flexion and extension gaps symmetrically. If the knee was tight ONLY in extension, the posteromedial capsule and semimembranosus would be the next structures to release.

Question 14

In the Lenke classification system for adolescent idiopathic scoliosis, a minor curve is defined as 'structural' (and therefore requires inclusion in the surgical fusion construct) if it meets which of the following criteria?





Explanation

The Lenke classification defines a minor curve as structural if its Cobb angle remains at or above 25 degrees on maximal supine side-bending radiographs. Additionally, for thoracic curves, a regional kyphosis of +20 degrees or more (T2-T5 for proximal thoracic, T10-L2 for thoracolumbar/lumbar) also qualifies the curve as structural regardless of the side-bending coronal Cobb angle. Structural minor curves must be included in the arthrodesis.

Question 15

A 45-year-old carpenter presents with progressive weakness of the intrinsic hand muscles and numbness isolated to his ring and small fingers. Examination reveals a positive Tinel's sign approximately 8 cm proximal to the medial epicondyle. Which of the following structures is most likely compressing the involved nerve at this specific location?





Explanation

The patient has ulnar neuropathy. While the most common site of compression is at the cubital tunnel (Osborne's ligament / between the two heads of the FCU), compression can also occur proximally at the Arcade of Struthers. The Arcade of Struthers is a fascial band extending from the medial head of the triceps to the medial intermuscular septum, located approximately 8 cm proximal to the medial epicondyle. (Note: The Ligament of Struthers is associated with median nerve compression at the supracondylar process).

Question 16

A 40-year-old male sustains a Schatzker IV tibial plateau fracture. Which of the following best describes the typical pathological mechanism of this specific injury pattern and its most feared associated complication?





Explanation

A Schatzker IV fracture involves the medial tibial plateau. It typically results from a high-energy varus and axial loading force. Because the medial plateau is dense and strong, this fracture often represents a variant of a knee fracture-dislocation. Consequently, the proximal tibia may subluxate or dislocate, placing traction and shear on the popliteal artery and the common peroneal nerve. A thorough vascular examination (often including ABI or CT angiogram) is mandatory.

Question 17

During a Latarjet procedure for recurrent anterior shoulder instability, the transferred coracoid process confers stability via a 'triple blocking' effect. Which of the following anatomical structures provides the critical dynamic 'sling' effect when the arm is placed in abduction and external rotation?





Explanation

The Latarjet procedure provides stability through three mechanisms: 1) The bony block of the coracoid extending the glenoid arc; 2) The dynamic 'sling' effect of the conjoined tendon (short head of biceps and coracobrachialis) acting across the inferior subscapularis when the arm is abducted and externally rotated, effectively tensioning the capsule and subscapularis; 3) The capsule repair to the stump of the coracoacromial ligament. The conjoined tendon provides the sling effect.

Question 18

A 55-year-old female presents with severe, progressive flattening of her left foot. Examination demonstrates a rigid hindfoot valgus deformity and a completely absent ability to perform a single-limb heel rise. Radiographs confirm subtalar and talonavicular osteoarthritis. What is the appropriate classification stage of her posterior tibial tendon dysfunction (PTTD) and the most definitive surgical treatment?





Explanation

Posterior tibial tendon dysfunction (PTTD) is classified into four stages. Stage I: tendon pathology without deformity. Stage II: flexible flatfoot deformity. Stage III: fixed/rigid flatfoot deformity with degenerative joint changes in the hindfoot (subtalar/talonavicular). Stage IV: progression to involve the ankle joint (valgus talar tilt). Because this patient has a rigid hindfoot valgus with osteoarthritis, she is Stage III. The standard surgical treatment for Stage III is a corrective hindfoot arthrodesis (such as a triple or double arthrodesis).

Question 19

Vancomycin is frequently administered in orthopedic surgery for both prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. What is the precise mechanism of action by which vancomycin exerts its bactericidal effect?





Explanation

Vancomycin is a glycopeptide antibiotic that bactericidally inhibits cell wall synthesis. It works by binding non-covalently but very tightly to the D-alanyl-D-alanine terminal dipeptide of the peptidoglycan precursors, preventing their cross-linking by transpeptidases. This differs from beta-lactam antibiotics (like penicillins and cephalosporins), which bind directly to the penicillin-binding proteins (transpeptidases) themselves.

Question 20

A 14-year-old boy presents with progressive knee pain and swelling. Radiographs reveal an aggressive, ill-defined diaphyseal lesion of the distal femur with a lamellated 'onion-skin' periosteal reaction. A biopsy confirms a small round blue cell tumor. Which of the following cytogenetic abnormalities is most characteristic of this malignancy?





Explanation

The clinical, radiographic, and histological findings are highly characteristic of Ewing sarcoma. Ewing sarcoma is a small round blue cell tumor most commonly found in the diaphysis of long bones in children and adolescents. The classic cytogenetic hallmark is the t(11;22)(q24;q12) chromosomal translocation, which fuses the EWS gene on chromosome 22 with the FLI1 gene on chromosome 11, found in approximately 85% of cases.

Question 21

A 45-year-old male sustained a closed pelvic ring injury in a high-speed motor vehicle collision. Examination reveals a massive, fluctuant mass over the greater trochanter with areas of overlying skin necrosis. Aspiration yields serosanguinous fluid. What is the best initial management for this lesion?





Explanation

This is a Morel-Lavallée lesion (a closed degloving injury). When overlying skin necrosis is present, conservative measures or percutaneous drainage are inadequate and carry a high risk of deep infection. Open debridement with excision of all non-viable tissue is required, particularly before proceeding with any definitive osteosynthesis.

Question 22

A 60-year-old male presents with progressive clumsiness in his hands and gait instability. Imaging confirms Ossification of the Posterior Longitudinal Ligament (OPLL) from C3 to C6. The sagittal MRI and CT show a kyphotic cervical alignment, making the K-line negative. Which of the following is the most appropriate surgical intervention?





Explanation

The K-line is a line connecting the midpoints of the spinal canal at C2 and C7. A negative K-line means the OPLL mass extends posterior to this line, usually due to kyphosis or a massive ossification. In K-line negative OPLL, the spinal cord will not sufficiently shift backward after a posterior-only decompression (like laminoplasty), resulting in poor neurological recovery. An anterior approach (corpectomy) or a combined anterior-posterior approach is indicated.

Question 23

A 50-year-old manual laborer complains of chronic wrist pain. Radiographs demonstrate advanced joint space narrowing between the radius and the scaphoid, as well as narrowing between the capitate and the lunate. The radiolunate joint space is perfectly preserved. This radiographic appearance is pathognomonic for which stage of Scapholunate Advanced Collapse (SLAC)?





Explanation

SLAC wrist progresses in a predictable pattern. Stage I involves the radial styloid and scaphoid. Stage II involves the entire radioscaphoid fossa. Stage III involves proximal migration of the capitate with capitolunate arthritis. The radiolunate joint is characteristically spared due to the concentric shape of the articulation, even in Stage III. Stage IV (controversial) implies pancarpal arthritis including the radiolunate joint.

Question 24

A 13-year-old obese male undergoes in-situ pinning for a stable Slipped Capital Femoral Epiphysis (SCFE). Four months postoperatively, he develops severe hip stiffness, worsening pain, and a 30-degree flexion contracture. Radiographs show a 50% reduction in the joint space globally compared to the contralateral hip. What is the most significant risk factor for this specific complication?





Explanation

The clinical picture describes chondrolysis, a devastating complication of SCFE characterized by acute cartilage destruction and global joint space narrowing. The most strongly associated iatrogenic risk factor is unrecognized pin penetration into the hip joint during fixation. The use of live fluoroscopy (approach-withdraw technique) is critical to confirm the pin is completely within the femoral head.

Question 25

A 72-year-old female with advanced Parkinson's disease suffers her third posterior dislocation following a primary total hip arthroplasty (THA). Evaluation reveals her acetabular and femoral components are well-fixed and in acceptable alignment. Abductor muscle function is intact. Which of the following is the most appropriate surgical option?





Explanation

Dual mobility cups are highly effective for managing or preventing recurrent instability in patients with neuromuscular disorders like Parkinson's disease. They provide a larger effective femoral head diameter, dramatically increasing the jump distance. Because her abductors are intact, dual mobility is preferred over a constrained liner, which has a higher risk of impingement, mechanical failure, and component loosening.

Question 26

A 55-year-old diabetic male presents with an erythematous, swollen, and warm foot with no open wounds. Radiographs show fragmentation of the navicular, periarticular osseous debris, and subluxation of the midfoot joints. According to the Eichenholtz classification of Charcot arthropathy, what is the current stage and best initial management?





Explanation

Eichenholtz Stage I is the developmental (or fragmentation) stage, characterized clinically by a red, hot, swollen foot and radiographically by bone debris, fragmentation, and joint subluxation. The gold standard treatment during this active phase is offloading with a total contact cast (TCC) to prevent further deformity until the acute inflammatory process subsides (Stage II - coalescence).

Question 27

A 40-year-old patient undergoes biopsy of a heavily calcified diaphyseal lesion in the proximal femur. Pathology demonstrates malignant chondroid cells permeating the medullary bone. Molecular testing reveals a mutation in the isocitrate dehydrogenase 1 (IDH1) gene. This mutation is the hallmark of which of the following conditions?





Explanation

IDH1 and IDH2 gene mutations are found in the vast majority of central chondrosarcomas and enchondromas. They are the underlying genetic abnormality in Ollier disease and Maffucci syndrome (multiple enchondromatosis). In contrast, Multiple Hereditary Exostoses (osteochondromas) is associated with EXT1 and EXT2 mutations.

Question 28

A 25-year-old motorcyclist is brought to the trauma bay after a high-speed collision. He has massive soft tissue swelling over the left shoulder, and the left upper extremity is flail and pulseless. A chest radiograph demonstrates a widely displaced clavicle fracture and significant lateral displacement of the scapula. What is the most critical immediate step in management?





Explanation

This patient has a scapulothoracic dissociation, characterized by complete disruption of the scapulothoracic articulation. It is associated with a high incidence of life-threatening subclavian or axillary artery disruption (up to 88%) and devastating brachial plexus avulsions. Immediate angiography and vascular control/repair take precedence to save the limb and patient's life.

Question 29

During the physical examination of a patient with a suspected multiligamentous knee injury, varus stress testing at 30 degrees of knee flexion demonstrates significant gapping. Which anatomical structure is the primary static restraint preventing this displacement?





Explanation

The Fibular Collateral Ligament (LCL) is the primary static stabilizer to varus stress at both 0 and 30 degrees of knee flexion. While the popliteus complex (popliteus tendon and popliteofibular ligament) contributes to external rotation stability, the LCL is the primary check against varus displacement.

Question 30

A researcher is testing the viscoelastic properties of the anterior cruciate ligament in a laboratory setting. When a constant tensile force is applied to the ligament over an extended period, the ligament is observed to gradually elongate. Which biomechanical term best describes this phenomenon?





Explanation

Creep is the time-dependent deformation (elongation) of a viscoelastic material when subjected to a constant load over time. In contrast, stress relaxation is the time-dependent decrease in internal stress when the tissue is held at a constant deformation/strain. Hysteresis is the energy lost (as heat) during the loading and unloading cycle.

Question 31

A 32-year-old male falls from a height and presents neurologically intact. CT imaging shows an L1 burst fracture with 30% canal compromise. An MRI clearly demonstrates a wide disruption of the interspinous ligaments and facet capsules with significant edema (definite Posterior Ligamentous Complex disruption). Based on the Thoracolumbar Injury Classification and Severity (TLICS) score, what is the score and corresponding recommendation?





Explanation

The TLICS score is calculated from three categories: Morphology (Burst = 2 points), Neurologic status (Intact = 0 points), and Posterior Ligamentous Complex (PLC) status (Definite disruption = 3 points). Total score = 2 + 0 + 3 = 5. A TLICS score >4 indicates surgical intervention is the recommended treatment.

Question 32

A 6-week-old infant is being treated with a Pavlik harness for Developmental Dysplasia of the Hip (DDH). After 3 weeks of treatment, the hip remains persistently dislocated. Which of the following ultrasonographic findings is the most significant anatomic predictor of harness failure?





Explanation

An interposed inverted limbus, thick pulvinar, contracted transverse acetabular ligament, or a tight iliopsoas tendon are intra-articular and extra-articular blocks to reduction. Their presence on imaging strongly predicts the failure of non-operative management (Pavlik harness) and often necessitates a closed or open reduction.

Question 33

During a revision total knee arthroplasty, the surgeon notes that the medial collateral ligament (MCL) is severely attenuated and non-functional, resulting in gross, uncorrectable coronal plane instability. The extensor mechanism and posterior capsule remain structurally intact. Which of the following implant constraints is the most appropriate choice?





Explanation

A Constrained Condylar Knee (CCK) is indicated when there is severe collateral ligament (MCL or LCL) deficiency causing coronal instability. The CCK design features a high and wide central post within a deep femoral box to provide varus/valgus constraint. A rotating hinge is typically reserved for global (multiligamentous) instability, massive bone loss, or combined collateral and extensor mechanism deficiencies.

Question 34

A 35-year-old carpenter presents with a swollen, painful index finger 3 days after a penetrating injury. The surgeon suspects acute pyogenic flexor tenosynovitis. Which of the following is NOT one of Kanavel's four cardinal signs of this condition?





Explanation

Kanavel's four cardinal signs are: 1) Fusiform swelling (sausage digit), 2) Tenderness along the flexor tendon sheath, 3) Pain with passive extension (most sensitive early sign), and 4) Resting posture of the digit in flexion. Erythema extending proximal to the wrist crease is not a cardinal sign and may indicate a more extensive cellulitis or a deep space infection of the hand/forearm (Parona's space).

Question 35

A 40-year-old male sustains a proximal tibia fracture. Radiographs and CT show a fracture line exiting through the medial cortex, with separation and depression of the entire medial tibial plateau. This is classified as a Schatzker IV fracture. What is the classic mechanism of injury for this specific fracture pattern?





Explanation

A Schatzker type IV fracture involves the medial tibial plateau. Because the medial plateau is structurally stronger and denser than the lateral plateau, fracturing it requires a high-energy mechanism, classically a varus stress combined with axial loading. Due to this high energy, Schatzker IV fractures are frequently associated with popliteal artery injuries, peroneal nerve damage, and knee dislocation equivalents.

Question 36

Demineralized Bone Matrix (DBM) is widely used in orthopedic surgery as a bone graft substitute. DBM primarily facilitates bone healing by providing which of the following biological properties?





Explanation

Demineralized bone matrix (DBM) is created by acid extraction of allograft bone, leaving a collagenous matrix (which provides osteoconduction) and exposing naturally occurring growth factors like Bone Morphogenetic Proteins (BMPs) (which provide osteoinduction). DBM has no living cells, so it is not osteogenic, and its processing removes its structural/mechanical integrity.

Question 37

The Lisfranc ligament is critical for transverse stability of the midfoot. Which of the following accurately describes the precise origin and insertion of the main bundle of the Lisfranc ligament?





Explanation

The Lisfranc ligament is the strongest of the tarsometatarsal interosseous ligaments. It spans obliquely from the lateral aspect of the medial cuneiform to the medial aspect of the base of the second metatarsal. There is no ligamentous connection directly between the bases of the first and second metatarsals, making the Lisfranc ligament essential for tying the midfoot to the forefoot.

Question 38

A 14-year-old female undergoes 10 weeks of neoadjuvant chemotherapy followed by surgical resection of a conventional high-grade osteosarcoma in her distal femur. The pathologist examines the resected specimen. Which of the following histologic parameters is the most powerful predictor of long-term overall survival in this patient?





Explanation

The degree of tumor necrosis after neoadjuvant chemotherapy is the single most important and reliable prognostic factor in conventional osteosarcoma. According to the Huvos grading system, a 'good histologic response' is defined as >90% tumor necrosis, which strongly correlates with improved long-term disease-free and overall survival.

Question 39

A 24-year-old professional baseball pitcher complains of vague posterior shoulder pain. Physical examination demonstrates a Glenohumeral Internal Rotation Deficit (GIRD) of 25 degrees on his throwing arm compared to the contralateral side. What is the primary anatomical driver responsible for this physical exam finding?





Explanation

GIRD is frequently seen in overhead throwing athletes and is driven by repetitive microtrauma during the extreme eccentric loading of the deceleration phase of throwing. This leads to reactive fibroplasia, thickening, and contracture of the posterior-inferior capsule, specifically the posterior band of the inferior glenohumeral ligament (IGHL). This shifts the glenohumeral center of rotation posterosuperiorly, putting the athlete at risk for SLAP tears.

Question 40

A 30-year-old male is admitted with a highly comminuted diaphyseal tibia fracture. He develops severe, unremitting leg pain overnight. His blood pressure is 120/80 mmHg. Intracompartmental pressure monitoring of the anterior compartment reads 55 mmHg. What is his Delta P (ΔP), and is emergency fasciotomy indicated?





Explanation

Delta P (ΔP) is calculated as the Diastolic Blood Pressure minus the Intracompartmental Pressure. In this case, ΔP = 80 mmHg - 55 mmHg = 25 mmHg. A Delta P of less than 30 mmHg (threshold for adequate tissue perfusion) confirms the diagnosis of acute compartment syndrome and is an absolute indication for emergency four-compartment fasciotomy.

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