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1. General Principles & Basic Science MCQs

Practice Set 188 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 3741

Topic: Surgical Anatomy & Approaches
What structure has been described as having a risk of injury with retractor placement on the sacrum during combined acetabular-pelvic ring surgery using the Stoppa approach with a lateral window?
. External iliac artery
. Obturator nerve
. Corona mortis
. L5 nerve root
. Ilioinguinal nerve

Correct Answer & Explanation

. L5 nerve root

Explanation

DISCUSSION: Care must be taken when placing a retractor on the anterior aspect of the sacrum, as the L4 and L5 nerve roots are both at risk. The L5 nerve root is 10 mm medial to the sacroiliac joint at the pelvic brim.

Question 3742

Topic: Surgical Anatomy & Approaches

The direct anterior approach (Smith-Petersen) to the hip is increasingly popular for total hip arthroplasty. This approach utilizes a true internervous and intermuscular plane. Deep dissection occurs between which of the following muscles?

. Gluteus medius and tensor fasciae latae
. Rectus femoris and gluteus medius
. Sartorius and tensor fasciae latae
. Gluteus maximus and gluteus medius
. Pectineus and adductor longus

Correct Answer & Explanation

. Gluteus medius and tensor fasciae latae

Explanation

The direct anterior approach utilizes an internervous plane. Superficial dissection is between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The deep dissection continues between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

Question 3743

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic arthroplasty to minimize perioperative blood loss and reduce transfusion rates. What is the precise pharmacological mechanism of action of TXA?
. It directly inhibits the action of thrombin on fibrinogen.
. It competitively inhibits the activation of plasminogen to plasmin.
. It irreversibly binds to antithrombin III, enhancing its effect.
. It promotes the cross-linking of fibrin monomers by stimulating factor XIII.
. It inhibits cyclooxygenase enzymes, preventing platelet aggregation.

Correct Answer & Explanation

. It competitively inhibits the activation of plasminogen to plasmin.

Explanation

Tranexamic acid is an antifibrinolytic synthetic analog of the amino acid lysine. It reversibly and competitively binds to the lysine-binding sites on plasminogen, thus preventing the activation of plasminogen to plasmin, which ultimately inhibits the degradation of fibrin clots.

Question 3744

Topic: Surgical Anatomy & Approaches

During a direct anterior (Smith-Petersen) approach for total hip arthroplasty, the surgeon performs deep dissection between the sartorius and tensor fasciae latae. Which nerve is at greatest risk of iatrogenic injury if dissection is carelessly carried too superficially in this interval?

. Femoral nerve
. Obturator nerve
. Sciatic nerve
. Lateral femoral cutaneous nerve
. Superior gluteal nerve

Correct Answer & Explanation

. Femoral nerve

Explanation

The lateral femoral cutaneous nerve (LFCN) is highly vulnerable during the superficial dissection of the direct anterior approach. It courses over the sartorius and can be injured, leading to meralgia paresthetica.

Question 3745

Topic: Surgical Anatomy & Approaches

A 45-year-old male with end-stage avascular necrosis undergoes a primary total hip arthroplasty. The surgeon uses the direct anterior (Smith-Petersen) approach. Which of the following nerve injuries is most specifically associated with the superficial dissection of this approach?

. Superior gluteal nerve
. Femoral nerve
. Lateral femoral cutaneous nerve
. Sciatic nerve
. Obturator nerve

Correct Answer & Explanation

. Superior gluteal nerve

Explanation

The direct anterior approach uses the internervous plane between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve). The lateral femoral cutaneous nerve courses superficially over the sartorius and is at highest risk during the superficial dissection.

Question 3746

Topic: Surgical Anatomy & Approaches

A surgeon is performing a primary THA via the direct anterior (Smith-Petersen) approach. During the deep dissection between the tensor fasciae latae and sartorius, a vascular bundle is routinely encountered crossing the field that must be ligated to prevent excessive bleeding. This bundle represents branches of which of the following arteries?

. Medial femoral circumflex artery
. Lateral femoral circumflex artery
. Superior gluteal artery
. Inferior gluteal artery
. Obturator artery

Correct Answer & Explanation

. Medial femoral circumflex artery

Explanation

The ascending branches of the lateral femoral circumflex artery reliably cross the internervous plane of the direct anterior approach. Ligation or cauterization is necessary to maintain hemostasis.

Question 3747

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is routinely utilized in total joint arthroplasty to minimize perioperative blood loss. Which of the following describes its precise pharmacological mechanism of action?

. Direct inhibition of factor Xa
. Activation of the extrinsic coagulation cascade
. Competitive inhibition of plasminogen activation
. Irreversible binding to platelet cyclooxygenase
. Promotion of von Willebrand factor release

Correct Answer & Explanation

. Direct inhibition of factor Xa

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively inhibits the activation of plasminogen to plasmin, thereby preventing the degradation of fibrin clots (antifibrinolytic effect).

Question 3748

Topic: 1. General Principles & Basic Science

What is the typical axial plane transverse angulation of the thoracic pedicles? Review Topic

. 5 degrees medial at T1 and T2; 10 degrees from T3 to T10
. 5 degrees lateral at T1; neutral at T2; 5 degrees medial from T3 to T12
. 10 degrees medial from T1 to T10; 15 degrees medial at T11 and T12
. 10 degrees medial from T1 to T12
. 25 degrees medial at T1; 15 degrees at T2; and 10 degrees medial from T3 to T10

Correct Answer & Explanation

. 5 degrees medial at T1 and T2; 10 degrees from T3 to T10

Explanation

Thoracic pedicles typically are angled 25 degrees medially at T1 so the starting point is more lateral. T2 angles about 15 degrees, and then the pedicles average about 5 to 7 degrees down to T10. At T11 and 12, the angulation is minimal.

Question 3749

Topic: Infection, Pharmacology & VTE
Figures 32a and 32b show the AP and lateral radiographs of an 11-year-old boy who has a severe limp, a fever, and swelling and tenderness of the thigh. Aspiration of the bone reveals purulent material. The patient has most likely been symptomatic for
. 24 hours.
. 2 days.
. 5 days.
. 7 to 14 days.
. 6 months.

Correct Answer & Explanation

. 7 to 14 days.

Explanation

DISCUSSION: In patients with an osteomyelitic infection, radiographic findings at 1 to 5 days usually show soft-tissue swelling only. Seven to 14 days after symptoms begin, radiographs will most likely show the classic signs of acute osteomyelitis. Reactive bone formation would be expected by 6 months.

Question 3750

Topic: Biology, Genetics & Bone Healing

Rickets can be best characterized by which of the following radiographic changes in children?

. Narrowed physes
. Widening of the ribs anteriorly
. Rounded epiphyses
. Punched out metaphyseal defects with subperiosteal resorption
. Sclerotic bands in the upper and lower margins of each vertebra

Correct Answer & Explanation

. Narrowed physes

Explanation

Rickets is a condition of inadequate mineralization of osteoid and cartilage at the growing ends of bone in children. It is associated with a nutritional deficiency in children that affects open physes, as opposed to osteomalacia which is a deficiency in people with closed growth plates. There are classic radiographic findings and disorders that mimic rickets. Classic findings are widened physes related to widening of the physis from accumulation of nonmineralized osteoid and cartilage, irregular metaphyses, and loss of definition of the zone of provisional calcification. The changes are seen predominantly in the bones with greatest growth (tibia, distal femur, distal radius) and rarely seen in slower growing bones such as the tubular bones in the hand. Widening of the anterior ribs, the rachitic rosary, may be seen. Hyperparathyroidism with accumulation of fibrous tissue in the metaphyses can produce lucencies that may appear similar to the nonmineralized osteoid of rickets. Hyperparathyroidism has erosion around the edge of the growth plate. There are punched out lesions and resorption subperiosteally. Rounded epiphyses and marked separation of the epiphysis and metaphysis are the classic differentiation of Jansen syndrome, a dominantly inherited metaphyseal chondrodysplasia. Sclerotic metaphyseal ends are similar to rickets, but with maturation, the spaces fill with irregular calcification classic to Jansen syndrome. Sclerotic of the vertebra, or "rugger jersey" spine, is typical of renal osteodystrophy.

Question 3751

Topic: 1. General Principles & Basic Science

New computer scanning technology for socket design has achieved which of the following improvements in amputee care?

. Improved socket fit
. Reduced skin breakdown from excessive pressure on the residual limb
. Reduced the time of socket fabrication
. Reduced the cost of prosthetic devices
. Decreased pain at the limb socket interface

Correct Answer & Explanation

. Reduced the time of socket fabrication

Explanation

One of the new technologies available to the prosthetist is the use of digital scanners to obtain a model of the residual limb. Typically, a digital image of the residual limb is obtained by either running a wand over the surface anatomy, allowing the computer program to record the shape, or by using a ring-type scanner that does not make contact with the residual limb but records the shape by bouncing a laser beam off the limb. In either instance, the end result is a digital image that can then be viewed and modified on the computer to improve the weight-bearing aspects of a socket shape or take pressure off sensitive bony areas. The final shape is then carved out of a foam block for use in the socket fabrication process. Computer-aided socket design is still dependent on input from the prosthetist, and therefore does not represent an improvement in overall socket fit. Digital scanning works well on specific types of devices, such as transfemoral sockets, where there is more soft tissue relative to bone. The scanner does not have the ability to detect the density of tissue beneath the scanned surface. Heterotopic ossification and other anomalies will be missed if a thorough examination of the underlying anatomy is neglected. Therefore, the advantages of using scanning technology are for producing and fabricating a socket shape quickly, storing the shape digitally for future use, and increasing efficiency with a plasterless facility.

Question 3752

Topic: Surgical Anatomy & Approaches
When harvesting iliac crest bone graft during a posterior spinal decompression and fusion, injury to what structure can result in painful neuromas or numbness over the skin of the buttocks?
. Ilioinguinal nerve
. Superior gluteal nerve
. Superior cluneal nerves
. Iliohypogastric nerves
. Lateral femoral cutaneous nerve

Correct Answer & Explanation

. Superior cluneal nerves

Explanation

DISCUSSION: The superior cluneal nerves (L1, L2, and L3) are most at risk when harvesting iliac crest bone graft during a posterior decompression and fusion. These nerves pierce the lumbodorsal fascia and cross the posterior iliac crest, beginning 8 cm lateral to the posterior superior iliac spine.

Question 3753

Topic: Physiology & Rehabilitation

Endurance training stimulates which of the following physiologic adaptations in the athlete? Review Topic

. Selective hypertrophy of type II muscle fibers
. Decreased concentration of Krebs cycle enzymes
. Increased rate of glycogen depletion
. Increased sympathetic nervous system activity
. Increased storage and utilization of intramuscular lipids

Correct Answer & Explanation

. Increased storage and utilization of intramuscular lipids

Explanation

Endurance training causes selective hypertrophy of type I muscle fibers. It stimulates an increase in the enzymes of the Krebs cycle which increases the capacity for aerobic ATP resynthesis during exercise. There is a decrease in the rate of glycogen depletion. Depletion of glycogen has been linked to fatigue during endurance exercise. Endurance training blunts the catecholamine response and may contribute to the reduction in heart rate observed for the same exercise intensity following training. The greater use of lipid reduces the contribution of carbohydrate to ATP resynthesis and preserves muscle glycogen.

Question 3754

Topic: Biomechanics & Biomaterials

A 55-year-old female presents with acute onset of medial knee pain and a 'pop' while squatting. MRI reveals a medial meniscus posterior root tear. Biomechanically, what is the consequence to the knee joint in this condition?

. Increased contact area in the medial compartment
. Peak contact pressure decreases in the medial compartment
. Loss of hoop stresses, resulting in biomechanics equivalent to a total meniscectomy
. Increased medial joint space opening on valgus stress
. Altered patellofemoral tracking due to external rotation of the tibia

Correct Answer & Explanation

. Loss of hoop stresses, resulting in biomechanics equivalent to a total meniscectomy

Explanation

A posterior root tear of the medial meniscus leads to meniscal extrusion and complete loss of circumferential hoop stresses. Biomechanically, this is equivalent to a total meniscectomy, leading to decreased contact area and significantly increased peak contact pressures in the medial compartment, which can lead to rapid cartilage degeneration and subchondral insufficiency fractures.

Question 3755

Topic: 1. General Principles & Basic Science

A 45-year-old female undergoes transtibial pull-out repair for a medial meniscus posterior root tear. Which of the following factors is most critical for restoring the hoop stresses of the meniscus during this procedure?

. Using a non-absorbable suture rather than absorbable suture
. Tying the suture over a cortical button rather than a post
. Anatomic placement of the tibial tunnel at the native root footprint
. Performing a concomitant medial collateral ligament release
. Augmentation with platelet-rich plasma (PRP)

Correct Answer & Explanation

. Anatomic placement of the tibial tunnel at the native root footprint

Explanation

The most critical factor in restoring the biomechanical function (circumferential hoop stresses) of the meniscus after a root tear is the anatomic placement of the root repair. Non-anatomic placement, even by a few millimeters, fails to adequately restore contact pressures and contact area in the joint.

Question 3756

Topic: 1. General Principles & Basic Science

A 50-year-old female presents with acute medial knee pain after a deep flexion event. MRI demonstrates a medial meniscus posterior root tear. What is the biomechanical consequence of this injury if left untreated?

. Increased contact area in the medial compartment
. Decreased peak contact pressures in the medial compartment
. Biomechanical equivalence to a total medial meniscectomy
. Increased anterior tibial translation
. Increased varus laxity

Correct Answer & Explanation

. Biomechanical equivalence to a total medial meniscectomy

Explanation

A posterior root tear of the medial meniscus disrupts the circumferential hoop stresses of the meniscus, leading to extrusion and loss of load distribution. Biomechanical studies have shown that a posterior root tear is equivalent to a total meniscectomy in terms of peak contact pressure and contact area, ultimately predisposing the patient to rapid compartment degeneration.

Question 3757

Topic: Infection, Pharmacology & VTE

A 25-year-old professional soccer player sustains a severe valgus injury to the right knee. MRI demonstrates a complete tear of the superficial medial collateral ligament (sMCL). The distal aspect of the torn sMCL is flipped superficial to the pes anserinus. This specific finding is associated with:

. High likelihood of nonoperative healing
. A Stener-like lesion of the knee, typically requiring surgical repair
. Isolated deep MCL injury
. Spontaneous reduction with knee extension
. Concomitant popliteal artery occlusion

Correct Answer & Explanation

. A Stener-like lesion of the knee, typically requiring surgical repair

Explanation

A Stener-like lesion of the knee occurs when the distal aspect of a torn superficial MCL is displaced superficial to the pes anserinus expansion. Because the pes anserinus blocks the torn ends from approximating, this lesion often fails nonoperative management and requires surgical repair or reconstruction.

Question 3758

Topic: Physiology & Rehabilitation

A 28-year-old marathon runner presents with lateral knee pain that worsens after 3 miles of running. Examination reveals tenderness over the lateral femoral epicondyle, particularly when the knee is flexed to 30 degrees. The underlying pathophysiology of this condition involves friction of the iliotibial band over the lateral epicondyle during which phase of the gait cycle?

. Foot strike (early stance phase)
. Mid-stance
. Heel off (late stance phase)
. Mid-swing
. Late swing

Correct Answer & Explanation

. Foot strike (early stance phase)

Explanation

Iliotibial (IT) band friction syndrome occurs as the IT band passes back and forth over the lateral femoral epicondyle. Maximum friction typically occurs at approximately 30 degrees of knee flexion. During running, the knee is at roughly 30 degrees of flexion at foot strike (early stance phase), which is when the impingement and pain are most pronounced.

Question 3759

Topic: 1. General Principles & Basic Science

A 50-year-old man presents with posterior knee swelling and aching pain. MRI demonstrates a large popliteal (Baker's) cyst. Which two anatomical structures form the interval through which the synovial fluid typically herniates to form this cyst?

. Medial head of the gastrocnemius and semimembranosus
. Lateral head of the gastrocnemius and biceps femoris
. Popliteus and lateral collateral ligament
. Plantaris and lateral head of the gastrocnemius
. Semitendinosus and medial head of the gastrocnemius

Correct Answer & Explanation

. Medial head of the gastrocnemius and semimembranosus

Explanation

A Baker's cyst is a fluid-filled distension of the gastrocnemio-semimembranosus bursa. It communicates with the knee joint through a one-way valve effect in the posterior joint capsule located between the medial head of the gastrocnemius and the semimembranosus tendon.

Question 3760

Topic: 1. General Principles & Basic Science

When utilizing interference screws for soft-tissue ACL graft fixation in the tibial tunnel, which of the following screw configurations provides the optimal pullout strength and minimizes graft slippage?

. Interference screw diameter 2 mm smaller than the prepared tunnel
. Divergent screw placement of greater than 15 degrees
. Line-to-line screw diameter matching the prepared tunnel size
. Use of a fully threaded metallic screw over a bioabsorbable screw
. Screw placement on the cancellous side of the graft instead of the cortical side

Correct Answer & Explanation

. Line-to-line screw diameter matching the prepared tunnel size

Explanation

For soft tissue ACL grafts, an interference screw diameter that matches the tunnel diameter (line-to-line fit) provides optimal pullout strength. Screw divergence greater than 15 degrees relative to the tunnel significantly decreases fixation strength.

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