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1. General Principles & Basic Science MCQs

Practice Set 214 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 4261

Topic: Surgical Anatomy & Approaches
A 35-year-old man sustains an APC-III pelvic ring injury. During the ilioinguinal approach for internal fixation, massive hemorrhage occurs near the superior pubic ramus. This bleeding is most likely originating from the 'corona mortis', which represents an anastomosis between which two vascular systems?
. External iliac and internal pudendal
. Internal iliac and inferior gluteal
. External iliac and obturator
. Inferior epigastric and internal pudendal
. Superior gluteal and obturator

Correct Answer & Explanation

. External iliac and obturator

Explanation

The corona mortis is a vascular anastomosis between the external iliac system (typically via the inferior epigastric artery) and the internal iliac system (via the obturator artery). It is highly vulnerable to injury during approaches to the superior pubic ramus and acetabulum.

Question 4262

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with a lytic epiphyseal lesion of the distal femur. Biopsy reveals multinucleated giant cells in a background of mononuclear stromal cells. In the pathogenesis of this tumor, the true neoplastic cells express high levels of which of the following?

. RANKL
. RANK receptor
. Osteoprotegerin
. Runx2
. SOX9

Correct Answer & Explanation

. RANKL

Explanation

In a Giant Cell Tumor of bone, the mononuclear stromal cells are the actual neoplastic elements. They overexpress RANKL, which recruits and activates the abundant, reactive osteoclast-like multinucleated giant cells that cause the characteristic bone destruction.

Question 4263

Topic: Biology, Genetics & Bone Healing

A 30-year-old pregnant woman presents with an aggressively expanding, painful lytic lesion in the distal radius. Biopsy confirms Giant Cell Tumor (GCT) of bone. What is the primary mechanism of action of Denosumab, and why is it contraindicated in this patient?

. RANKL inhibitor; it causes fetal skeletal malformations
. Tyrosine kinase inhibitor; it causes premature closure of the fetal ductus arteriosus
. Bisphosphonate; it induces maternal renal failure
. VEGF inhibitor; it restricts placental blood flow
. RANKL inhibitor; it accelerates tumor growth during pregnancy

Correct Answer & Explanation

. RANKL inhibitor; it causes fetal skeletal malformations

Explanation

Denosumab is a monoclonal antibody against RANKL, which disrupts osteoclast function and is highly effective for GCT of bone. It is contraindicated in pregnancy because RANKL inhibition can cross the placenta and cause severe fetal skeletal malformations and impaired tooth eruption.

Question 4264

Topic: 1. General Principles & Basic Science

A 60-year-old man presents with progressive bowel and bladder dysfunction. MRI reveals a large, destructively expansile, T2-hyperintense midline mass in the sacrum. Histology shows physaliferous cells with bubbly cytoplasm. What is the most appropriate surgical management for this lesion?

. Intralesional curettage and bone grafting
. Wide en bloc surgical resection
. Debulking followed by chemotherapy
. Marginal excision with postoperative radiotherapy
. Radiofrequency ablation

Correct Answer & Explanation

. Wide en bloc surgical resection

Explanation

The clinical and histologic findings (physaliferous cells) are pathognomonic for a sacral chordoma. Chordomas are locally aggressive and highly radio- and chemo-resistant, making wide en bloc surgical resection with negative margins the gold standard for treatment to minimize recurrence.

Question 4265

Topic: 1. General Principles & Basic Science

A 62-year-old female with long-standing rheumatoid arthritis presents with an inability to actively flex the interphalangeal joint of her right thumb. Passive motion is intact. She has a history of a 'Mannerfelt-Norman lesion'. Which of the following best describes the pathoanatomy of this condition?

. Attrition rupture of the flexor pollicis longus (FPL) tendon over a bony spur on the volar lunate
. Attrition rupture of the flexor pollicis longus (FPL) tendon over a bony spur on the volar scaphoid
. Spontaneous rupture of the extensor pollicis longus (EPL) over Lister's tubercle
. Avulsion of the FPL tendon from its insertion due to chronic tenosynovitis
. Entrapment of the FPL tendon within a calcified flexor retinaculum

Correct Answer & Explanation

. Attrition rupture of the flexor pollicis longus (FPL) tendon over a bony spur on the volar scaphoid

Explanation

The Mannerfelt-Norman syndrome refers to the spontaneous attrition rupture of the flexor pollicis longus (FPL) tendon (and sometimes the flexor digitorum profundus of the index and middle fingers) in rheumatoid arthritis patients. This is caused by friction over a bony spur on the volar aspect of the scaphoid. The spur forms secondary to rotatory subluxation of the scaphoid, causing the proximal pole to abrade the volar capsule and tendons.

Question 4266

Topic: 1. General Principles & Basic Science
In cases of massive peripheral nerve defects (e.g., > 6 cm gap) or poor soft-tissue beds (e.g., heavily irradiated or scarred), a free vascularized nerve graft is sometimes indicated. When a vascularized medial femoral condyle (MFC) bone graft or an adjacent free flap is harvested with an associated sensory nerve, what is the primary arterial pedicle supplying the MFC and its adjacent tissues?
. Lateral circumflex femoral artery
. Descending genicular artery
. Inferior medial genicular artery
. Superior lateral genicular artery
. Deep femoral artery

Correct Answer & Explanation

. Descending genicular artery

Explanation

The primary vascular pedicle for the medial femoral condyle (MFC) free flap—which can include corticocancellous bone, periosteum, and occasionally skin or nerve components—is the descending genicular artery (DGA), specifically its articular and saphenous branches. If the DGA is absent or unsuitable, the superior medial genicular artery (SMGA) can sometimes serve as an alternative.

Question 4267

Topic: 1. General Principles & Basic Science
When a large cortical bone autograft is utilized to reconstruct an upper extremity bony defect, it heals via a process termed creeping substitution. During which phase of this incorporation process is the mechanical and structural strength of the cortical bone graft at its weakest?
. Immediately post-implantation
. During the initial inflammatory phase (weeks 1-4)
. During the revascularization and osteoclastic resorption phase (months 6-12)
. During the osteoblastic new bone formation phase (years 1-2)
. It maintains constant structural strength throughout the process

Correct Answer & Explanation

. During the revascularization and osteoclastic resorption phase (months 6-12)

Explanation

Cortical bone grafts incorporate via creeping substitution, which begins with osteoclastic resorption followed by osteoblastic bone formation. During the phase of revascularization and peak osteoclastic resorption (typically between 6 and 12 months, depending on the graft size), the graft becomes significantly porous. As a result, its mechanical and structural strength is at its lowest point, making it highly susceptible to fatigue fracture during this period.

Question 4268

Topic: 1. General Principles & Basic Science

A patient undergoes a staged flexor tendon reconstruction utilizing a silicone (Hunter) rod for a severe Zone II injury. During the first stage, the rod is secured and left in place to stimulate the formation of a pseudo-sheath. Which of the following best describes the biological composition and functional property of the inner lining of this newly formed pseudo-sheath?

. It is comprised of dense fibrous tissue that acts primarily to provide structural tension to the graft
. It is a synovial-like mesothelial lining that actively secretes hyaluronic acid to reduce gliding friction
. It contains high concentrations of Type II collagen to withstand compressive forces
. It functions primarily as an osteoinductive barrier to prevent heterotopic ossification
. It depends entirely on external diffusion of synovial fluid from the joint capsules for lubrication

Correct Answer & Explanation

. It is a synovial-like mesothelial lining that actively secretes hyaluronic acid to reduce gliding friction

Explanation

The implantation of a silicone (Hunter) rod induces a foreign body reaction that forms a fibrous pseudo-sheath. The inner layer of this pseudo-sheath differentiates into a synovial-like mesothelial layer. This highly specialized lining actively secretes a mucin-like fluid rich in hyaluronic acid, which provides nutrition to the future tendon graft and creates a low-friction, gliding environment essential for the success of the second-stage tendon transfer.

Question 4269

Topic: Biology, Genetics & Bone Healing
When utilizing Demineralized Bone Matrix (DBM) as a bone graft substitute to fill a benign bone cyst void in a metacarpal, its primary biological mechanism relies on osteoinductivity. Which specific components retained within the DBM are responsible for this osteoinductive property?
. Living osteoblasts and osteoprogenitor cells
. Calcium hydroxyapatite crystals
. Bone morphogenetic proteins (BMPs)
. Vascular endothelial growth factors (VEGF)
. Type III collagen meshwork

Correct Answer & Explanation

. Bone morphogenetic proteins (BMPs)

Explanation

Demineralized Bone Matrix (DBM) is created by acid extraction of the mineralized component of allograft bone, which exposes and preserves the non-collagenous proteins, specifically Bone Morphogenetic Proteins (BMPs). These BMPs induce local mesenchymal stem cells to differentiate into osteoblasts, providing the osteoinductive property. DBM lacks viable cells (so it is not osteogenic) and has poor structural integrity (minimal osteoconductivity compared to cancellous bone or synthetic ceramics).

Question 4270

Topic: 1. General Principles & Basic Science

Incorporation of bone grafts occurs through a process known as creeping substitution. Which of the following accurately describes the initial histological event distinguishing the incorporation of a cortical bone autograft from a cancellous bone autograft?

. Cortical grafts initially undergo osteoblastic apposition, whereas cancellous grafts undergo osteoclastic resorption.
. Cortical grafts initially undergo osteoclastic resorption via cutting cones, whereas cancellous grafts initially undergo osteoblastic apposition.
. Cortical grafts rely entirely on chondrocyte proliferation, whereas cancellous grafts rely on fibroblast differentiation.
. Both graft types initially undergo osteoclastic resorption, but it occurs faster in cortical grafts.
. Both graft types initially undergo osteoblastic apposition, but it occurs faster in cancellous grafts.

Correct Answer & Explanation

. Cortical grafts initially undergo osteoclastic resorption via cutting cones, whereas cancellous grafts initially undergo osteoblastic apposition.

Explanation

The incorporation of bone autografts (creeping substitution) differs fundamentally between cortical and cancellous bone. Cancellous bone is rapidly revascularized and osteoblasts lay down new bone on the existing trabecular scaffold first (osteoblastic apposition), followed by remodeling. Cortical bone is denser, meaning it must first be revascularized and resorbed by osteoclasts via 'cutting cones' before new bone can be deposited by osteoblasts. This initial osteoclastic resorption makes cortical grafts temporarily weaker during the incorporation process.

Question 4271

Topic: Biology, Genetics & Bone Healing
Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is utilized as an osteoinductive graft substitute in spinal fusion and open tibia fractures. At the cellular level, BMP-2 initiates osteoblast differentiation by binding to which type of cell surface receptor to activate the SMAD signaling pathway?
. Tyrosine kinase receptor
. G-protein coupled receptor
. Serine/threonine kinase receptor
. Intracellular nuclear receptor
. Ligand-gated ion channel

Correct Answer & Explanation

. Serine/threonine kinase receptor

Explanation

Bone Morphogenetic Proteins (BMPs) are members of the Transforming Growth Factor-beta (TGF-β) superfamily. They bind to distinct Type I and Type II cell surface receptors, which are both serine/threonine kinase receptors. Upon ligand binding, these receptors form a complex that phosphorylates intracellular SMAD proteins (specifically SMADs 1, 5, and 8), which then translocate to the nucleus to upregulate osteogenic genes like Runx2.

Question 4272

Topic: 1. General Principles & Basic Science

During a modified Brunelli tenodesis for a chronic scapholunate ligament dissociation, a tendon graft is utilized to reconstruct the vital dorsal scapholunate ligament and tether the scaphoid to prevent volar flexion. Which tendon is typically harvested or split to serve as the graft in this specific procedure?

. Extensor carpi radialis longus (ECRL)
. Flexor carpi radialis (FCR)
. Palmaris longus (PL)
. Extensor carpi ulnaris (ECU)
. Abductor pollicis longus (APL)

Correct Answer & Explanation

. Flexor carpi radialis (FCR)

Explanation

The modified Brunelli procedure (three-ligament tenodesis) uses a strip of the Flexor carpi radialis (FCR) tendon. The FCR strip is left attached distally at its insertion, passed from volar to dorsal through a bone tunnel in the distal pole of the scaphoid, routed across the dorsal radiocarpal capsule to the lunate (and often secured to the radius or radiocarpal ligaments), acting as a dynamic and static checkrein against scaphoid flexion and reconstructing the dorsal SL ligament.

Question 4273

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in orthopedic surgery to supplement fusion masses. Which of the following best describes the biological property that distinguishes DBM from purely synthetic ceramic grafts (e.g., tricalcium phosphate)?

. High compressive strength providing immediate structural support
. Presence of live, differentiating osteogenic stem cells
. Osteoinductive capacity due to retained bone morphogenetic proteins (BMPs)
. Ability to completely bypass the inflammatory phase of bone healing
. Strong osteoclastic stimulation via rapid calcium burst release

Correct Answer & Explanation

. Osteoinductive capacity due to retained bone morphogenetic proteins (BMPs)

Explanation

Demineralized bone matrix (DBM) is processed allograft bone that has had the inorganic mineral phase removed, exposing the underlying collagen matrix and trapped growth factors. While it lacks structural strength and live cells (it is NOT osteogenic), it retains osteoinductive proteins, primarily Bone Morphogenetic Proteins (BMPs), which recruit and differentiate host mesenchymal stem cells into osteoblasts. Synthetic ceramics (like TCP) are purely osteoconductive scaffolds without osteoinductive properties.

Question 4274

Topic: 1. General Principles & Basic Science

A 28-year-old aquarium worker presents with a slow-growing, erythematous, nodular lesion on his right index finger that recently ulcerated, following a minor abrasion sustained while cleaning a fish tank 3 weeks ago. What is the most appropriate culture medium and condition to identify the likely causative organism?

. Lowenstein-Jensen agar at 30°C to 32°C
. Blood agar at 37°C
. Viral transport media at 37°C
. Sabouraud dextrose agar at 25°C
. Chocolate agar at 37°C

Correct Answer & Explanation

. Lowenstein-Jensen agar at 30°C to 32°C

Explanation

The clinical scenario strongly suggests an atypical mycobacterial infection caused by Mycobacterium marinum ('fish tank granuloma'). This organism grows best at lower temperatures (30°C to 32°C) on mycobacterial specific media such as Lowenstein-Jensen or Middlebrook agar. Cultures incubated at standard body temperature (37°C) will frequently yield false-negative results.

Question 4275

Topic: 1. General Principles & Basic Science

In the surgical management of Zone II flexor tendon lacerations, which of the following suture modifications most significantly increases the ultimate tensile strength of the repair, thereby safely permitting an early active motion protocol?

. Increasing the number of core suture strands crossing the repair site
. Changing from a grasping to a locking core suture configuration
. Placing the core suture entirely in the volar half of the tendon
. Increasing the caliber of the epitendinous suture from 6-0 to 5-0
. Utilizing a braided absorbable core suture instead of monofilament non-absorbable

Correct Answer & Explanation

. Increasing the number of core suture strands crossing the repair site

Explanation

The ultimate tensile strength of a flexor tendon repair is directly proportional to the number of core suture strands crossing the repair site. Moving from a 2-strand to a 4-strand or 6-strand repair significantly increases strength and gap resistance, which is critical for early active motion protocols. Dorsal placement (not volar) increases strength due to the cross-sectional geometry of the tendon. Epitendinous sutures add strength but less significantly than increasing core strands.

Question 4276

Topic: 1. General Principles & Basic Science

In a patient with an isolated complete rupture of the scapholunate interosseous ligament (SLIL), which distinct anatomic region of the ligament is biomechanically the strongest and most critical for preventing pathologic diastasis between the scaphoid and lunate?

. Dorsal region
. Volar region
. Proximal (membranous) region
. Central region
. Palmar radiocarpal region

Correct Answer & Explanation

. Dorsal region

Explanation

The scapholunate interosseous ligament (SLIL) is a C-shaped ligament divided into dorsal, proximal (membranous), and volar regions. The dorsal region is composed of stout, transversely oriented collagen fibers and is biomechanically the thickest and strongest portion, making it the primary stabilizer of the scapholunate joint. Conversely, for the lunotriquetral (LT) ligament, the volar portion is the strongest.

Question 4277

Topic: Biology, Genetics & Bone Healing

During a corrective osteotomy for a distal radius malunion, a structural cortical bone graft is placed to maintain length. In contrast to cancellous bone grafts, which undergo rapid revascularization, cortical bone grafts incorporate primarily via a protracted process. What is the defining histologic sequence of this process?

. Osteoclastic resorption of host bone followed by osteoblastic new bone formation (creeping substitution)
. Direct intramembranous ossification from surviving transplanted osteoprogenitor cells
. Endochondral ossification beginning with a cartilaginous intermediate
. Rapid neoangiogenesis leading to direct osteoblast differentiation from endothelial cells
. Formation of woven bone directly bridging the fracture gap without prior resorption

Correct Answer & Explanation

. Osteoclastic resorption of host bone followed by osteoblastic new bone formation (creeping substitution)

Explanation

Cortical bone grafts lack the porous architecture for rapid revascularization seen in cancellous grafts. They primarily incorporate through 'creeping substitution,' a slow process where host osteoclasts first resorb the dead structural graft bone (creating cutting cones), followed immediately by host osteoblasts laying down new living bone matrix. This process temporarily weakens the graft before full incorporation occurs.

Question 4278

Topic: 1. General Principles & Basic Science

During a two-stage flexor tendon reconstruction for a severe Zone II injury using a Hunter rod, the surgeon prepares for the second stage requiring an autologous tendon graft. Which of the following donor tendons is considered 'intrasynovial' and has been shown to result in fewer adhesions and improved gliding?

. Palmaris longus
. Plantaris
. Extensor indicis proprius
. Flexor digitorum longus
. Extensor digiti minimi

Correct Answer & Explanation

. Flexor digitorum longus

Explanation

Intrasynovial tendon grafts (such as the flexor digitorum longus or flexor digitorum superficialis) retain a synovial surface that limits postoperative adhesions and improves gliding excursion in Zone II reconstructions. Extrasynovial grafts (such as palmaris longus, plantaris, and extensor indicis proprius) lack this gliding surface and historically have a higher rate of adhesions.

Question 4279

Topic: 1. General Principles & Basic Science

A volar advancement (Moberg) flap is used to cover a 1.5 cm volar pulp defect on the thumb. This flap can be safely advanced in the thumb without causing dorsal skin necrosis, unlike in the lesser digits, due to which of the following anatomical characteristics?

. The absence of Cleland's ligaments in the thumb
. The independent dorsal blood supply to the thumb skin
. The superficial location of the princeps pollicis artery
. The increased elasticity of the volar thumb fascia
. The complete separation of the flexor pollicis longus sheath

Correct Answer & Explanation

. The independent dorsal blood supply to the thumb skin

Explanation

The Moberg flap involves elevating the entire volar skin and neurovascular bundles of the thumb. In the thumb, the dorsal skin has an independent blood supply (via dorsal branches of the radial artery). In the lesser digits, the dorsal skin is supplied by branches from the proper volar digital arteries; thus, raising a true Moberg flap in the fingers would devascularize the dorsal skin, leading to necrosis.

Question 4280

Topic: 1. General Principles & Basic Science

A 35-year-old man undergoes the Masquelet technique for a 4 cm segmental bone defect in his 3rd metacarpal following a crush injury. Six weeks after the initial placement of the polymethylmethacrylate (PMMA) spacer, he is ready for the second stage. What type of bone graft is most appropriate to place within the induced membrane?

. Non-vascularized cortical strut allograft
. Non-vascularized cancellous autograft
. Free vascularized fibular graft
. Demineralized bone matrix (DBM) with BMP-2 alone
. Synthetic hydroxyapatite blocks

Correct Answer & Explanation

. Non-vascularized cancellous autograft

Explanation

The Masquelet technique relies on a foreign body reaction to a PMMA spacer to create a pseudo-synovial induced membrane that is highly vascularized and secretes growth factors (VEGF, TGF-beta). In the second stage, the spacer is removed, and the void is packed with non-vascularized cancellous autograft. The membrane provides the necessary vascularity and osteoinductive factors to incorporate the cancellous graft.

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