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1. General Principles & Basic Science MCQs

Practice Set 162 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 3221

Topic: 1. General Principles & Basic Science

When analyzing a tibia with a suspected diaphyseal deformity, lines representing the mechanical axis of the proximal segment and the mechanical axis of the distal segment are drawn.

What does the intersection of these two lines mathematically represent?

. The Center of Rotation of Angulation (CORA)
. The anatomic axis
. The mechanical axis deviation
. The center of the intermediate segment
. The magnitude of translation

Correct Answer & Explanation

. The Center of Rotation of Angulation (CORA)

Explanation

The intersection of the proximal and distal mechanical or anatomic axes defines the Center of Rotation of Angulation (CORA), which is the apex of the deformity.

Question 3222

Topic: 1. General Principles & Basic Science

A patient is evaluated for a suspected oblique plane deformity of the tibia. True AP and lateral radiographs demonstrate both varus and procurvatum. How is the true magnitude and plane of the deformity properly calculated?

. Addition of the AP and lateral angles
. Using the Paley multiplier method
. Graphic method using orthogonal CORAs to find the true oblique plane CORA
. Taking the average of the two angles
. Oblique plane deformities cannot be calculated radiographically

Correct Answer & Explanation

. Graphic method using orthogonal CORAs to find the true oblique plane CORA

Explanation

Oblique plane deformities appear as separate deformities on AP and lateral views. Their true magnitude and plane are determined using mathematical formulas or graphical methods (combining the orthogonal vectors).

Question 3223

Topic: 1. General Principles & Basic Science

During preoperative planning for a distal femoral osteotomy following Paley's Rule 2, the surgeon plans the osteotomy proximal to the CORA but positions the hinge exactly on the CORA. Which of the following is an obligatory physical consequence of this construct during correction?

. Shortening of the limb
. Translation of the bone fragments at the osteotomy site
. Opening of the joint line
. Rotational malalignment
. Creation of a secondary CORA

Correct Answer & Explanation

. Translation of the bone fragments at the osteotomy site

Explanation

Hinging at the CORA when the osteotomy is displaced from it necessitates translation of the bone ends at the osteotomy site to achieve a collinear mechanical axis.

Question 3224

Topic: 1. General Principles & Basic Science

In a patient requiring deformity correction who has severe bilateral hip arthritis precluding reliable mechanical axis line drawing from the femoral head, the surgeon decides to use the anatomic axis of the femur as a reference. How does the normal anatomic axis of the femur relate to the mechanical axis?

. They are perfectly collinear
. The anatomic axis is approximately 5 to 7 degrees valgus to the mechanical axis
. The anatomic axis is 5 to 7 degrees varus to the mechanical axis
. The anatomic axis is 10 degrees valgus to the mechanical axis
. They intersect precisely at the lesser trochanter

Correct Answer & Explanation

. The anatomic axis is approximately 5 to 7 degrees valgus to the mechanical axis

Explanation

In a normal femur, the anatomic axis diverges from the mechanical axis by approximately 5 to 7 degrees of valgus, intersecting near the intercondylar notch.

Question 3225

Topic: 1. General Principles & Basic Science

A 40-year-old undergoes an opening wedge high tibial osteotomy for a varus deformity. The CORA is at the joint line, but the osteotomy is in the proximal metaphysis. If the surgeon incorrectly hinges at the lateral cortex of the osteotomy without fragment translation, what will happen to the mechanical axis?

. Complete restoration of the mechanical axis
. The mechanical axis will remain deviated medially
. The mechanical axis will be displaced parallel to its ideal position
. The mechanical axis will be overcorrected into severe valgus
. No change in mechanical axis deviation

Correct Answer & Explanation

. The mechanical axis will be displaced parallel to its ideal position

Explanation

This scenario describes Paley's Rule 3 (osteotomy and hinge away from the CORA). This results in a parallel shift (translation) of the mechanical axis, preventing collinear restoration.

Question 3226

Topic: 1. General Principles & Basic Science

A patient is diagnosed with a multi-apical deformity of the femur. A mid-diaphyseal CORA and a distal metaphyseal CORA are identified. To restore perfect mechanical axis alignment without relying on compensatory translation at the osteotomy sites, what is the optimal surgical strategy?

. One at the mid-diaphysis
. One at the distal metaphysis
. Two, one at each CORA
. One at the knee joint line
. One at the proximal metaphysis

Correct Answer & Explanation

. Two, one at each CORA

Explanation

Multiapical deformities usually require an osteotomy at each respective CORA (following Rule 1 twice) to perfectly realign the axis without inducing translation.

Question 3227

Topic: 1. General Principles & Basic Science

A 14-year-old girl has a distal femoral valgus deformity. According to Paley's Rule 1 of osteotomy, if the osteotomy and the hinge are both located exactly at the center of rotation of angulation (CORA), what is the expected outcome of the correction?

. Pure angular correction with translation of bone ends at the osteotomy
. Pure angular correction with no translation of bone ends
. Pure translation with no angular correction
. Angular correction with resultant mechanical axis translation
. No correction of the mechanical axis deviation

Correct Answer & Explanation

. Pure angular correction with no translation of bone ends

Explanation

Paley's Rule 1 states that when the osteotomy and hinge axis both pass through the CORA, the mechanical axis is restored via pure angulation without any translation of the bone ends. This yields an anatomic restoration of the bone.

Question 3228

Topic: 1. General Principles & Basic Science

A 28-year-old male with a midshaft tibial varus deformity undergoes a corrective osteotomy. The surgeon places the hinge axis at the CORA, but makes the osteotomy 4 cm proximal to the CORA. What is the expected radiographic result of this correction based on Paley's Rule 2?

. Pure angular correction without translation
. Translation of the mechanical axis producing a secondary deformity
. Realignment of the mechanical axis with translation of the bone ends at the osteotomy site
. Failure to correct the mechanical axis deviation
. Pure translational correction of the bone ends without angulation

Correct Answer & Explanation

. Realignment of the mechanical axis with translation of the bone ends at the osteotomy site

Explanation

Paley's Rule 2 dictates that if the hinge is at the CORA but the osteotomy is at a different level, the mechanical axis is fully corrected and realigned. However, the bone ends will translate relative to each other at the osteotomy site to achieve this collinearity.

Question 3229

Topic: 1. General Principles & Basic Science

During a distal tibial osteotomy, a surgeon inadvertently places the correction hinge proximal to the CORA, while the osteotomy is made exactly at the CORA. Which of the following describes the resulting deformity according to Paley's principles?

. Realignment of the mechanical axes with no translation
. Realignment of the mechanical axes with translation at the osteotomy site
. Creation of a new translation deformity (zigzag effect) with parallel but non-collinear mechanical axes
. Pure lengthening with no angular change
. Perfect anatomic realignment

Correct Answer & Explanation

. Creation of a new translation deformity (zigzag effect) with parallel but non-collinear mechanical axes

Explanation

Paley's Rule 3 states that if the hinge axis is placed outside the CORA, the correction will result in translation of the mechanical axis. This produces a zigzag deformity where the proximal and distal axes become parallel but not collinear.

Question 3230

Topic: 1. General Principles & Basic Science

You are analyzing the joint line convergence angle (JLCA) on a standing AP radiograph of a 50-year-old with osteoarthritis. The JLCA measures 6 degrees, opening laterally. What does this finding most likely indicate in the context of deformity planning?

. A pure extra-articular diaphyseal tibial deformity
. Normal physiologic joint orientation
. Medial compartment cartilage loss or lateral ligamentous laxity
. A fixed lateral flexion contracture
. An isolated distal femoral varus deformity

Correct Answer & Explanation

. Medial compartment cartilage loss or lateral ligamentous laxity

Explanation

The normal JLCA is 0 to 2 degrees. An increased JLCA (e.g., 6 degrees opening laterally) typically indicates intra-articular pathology, such as asymmetric medial cartilage loss or lateral collateral ligament laxity.

Question 3231

Topic: 1. General Principles & Basic Science

Review the provided radiograph diagram demonstrating lower limb alignment.

When drawing the mechanical axis of the femur and the mechanical axis of the tibia to find the CORA, what represents the normal relationship of the femoral mechanical axis compared to its anatomic axis?

. They are completely collinear
. The anatomic axis is typically 5 to 7 degrees valgus relative to the mechanical axis
. The anatomic axis is typically 5 to 7 degrees varus relative to the mechanical axis
. The mechanical axis is 9 degrees valgus relative to the anatomic axis
. They intersect exactly at the lesser trochanter

Correct Answer & Explanation

. The anatomic axis is typically 5 to 7 degrees valgus relative to the mechanical axis

Explanation

The mechanical axis of the femur runs from the center of the femoral head to the center of the knee. The anatomic axis (down the intramedullary canal) typically diverges by 5 to 7 degrees of valgus relative to this mechanical axis.

Question 3232

Topic: 1. General Principles & Basic Science

During pre-operative planning for a complex post-traumatic femoral deformity, drawing the proximal, middle, and distal anatomic axes reveals two distinct intersections (two CORAs). What is the optimal surgical strategy according to Paley's principles to fully restore the anatomic axis without introducing translation?

. Perform a single osteotomy at the proximal CORA with a translation component
. Perform a single osteotomy at the distal CORA and accept the translation
. Perform two separate osteotomies, one at each CORA, with hinges at each respective CORA
. Perform a single osteotomy exactly midway between the two CORAs
. Correct only the larger magnitude deformity and leave the smaller one

Correct Answer & Explanation

. Perform two separate osteotomies, one at each CORA, with hinges at each respective CORA

Explanation

For multi-apical deformities with two distinct CORAs, Paley's principles dictate performing two separate osteotomies with hinges placed at their respective CORAs. This restores the collinearity of the axis without unwanted iatrogenic translation.

Question 3233

Topic: 1. General Principles & Basic Science

A 14-year-old male presents with mid-diaphyseal tibial procurvatum. During preoperative planning, the center of rotation of angulation (CORA) is identified. If the osteotomy and the axis of correction of angulation (ACA) are both placed exactly at the CORA, what is the geometric outcome of the correction?

. Correction of angulation is achieved without any translation at the osteotomy site.
. Correction of angulation is achieved, but translation will occur at the osteotomy site.
. A new translation deformity is created because the ACA and osteotomy are congruent.
. Angulation is undercorrected, requiring a second closing-wedge osteotomy.
. Pure translation occurs without correction of the angular deformity.

Correct Answer & Explanation

. Correction of angulation is achieved without any translation at the osteotomy site.

Explanation

According to Paley's Rule 1 of deformity correction, when the osteotomy and the ACA are both placed at the CORA, pure angular correction is achieved without translation. This ensures the proximal and distal anatomical axes remain collinear.

Question 3234

Topic: Surgical Anatomy & Approaches
During a transperitoneal approach to the L5-S1 interspace, care must be taken to protect the superior hypogastric plexus from injury. Which of the following techniques reduces the risk of neurologic injury?
. Transverse incision across the posterior peritoneum and disk space, reflecting the tissues toward the sacral promontory
. Transverse incision across the posterior peritoneum and disk space, reflecting the tissues toward the confluence of the iliac veins
. Vertical midline incision of the posterior peritoneum, reflecting the prevertebral tissues beginning at the margin of the left iliac vein and extending toward the right iliac vein
. Vertical midline incision of the posterior peritoneum, reflecting the prevertebral tissues beginning at the margin of the right iliac vein extending toward the left iliac vein
. Vertical midline incision of the posterior peritoneum, reflecting the prevertebral tissues bilaterally away from the midline

Correct Answer & Explanation

. Vertical midline incision of the posterior peritoneum, reflecting the prevertebral tissues beginning at the margin of the left iliac vein and extending toward the right iliac vein

Explanation

DISCUSSION: Retrograde ejaculation is the sequela of superior hypogastric plexus injury. This structure needs protection, especially during anterior exposure of the L5-S1 disk space. Only blunt dissection should be used, and use of monopolar electrocautery should be avoided. If possible, preserve and retract the middle sacral artery. Once the iliac veins are isolated, blunt dissection is begun along the course of the medial edge of the left iliac vein, reflecting the prevertebral tissues toward the patient’s right side. The dissection goes from left to right because the parasympathetic plexus is more adherent on the right side. REFERENCE: Transperitoneal midline approach to L4-S1, in Watkins RG (ed): Surgical Approaches to the Spine, ed 1. New York, NY, Springer Verlag, 1983, pp 123-129.

Question 3235

Topic: Biomechanics & Biomaterials
During total hip arthroplasty, what characteristic of irradiated (10 Mrad) and subsequently melted highly cross-linked polyethylene should provide a more wear-resistant construct than traditional gamma-irradiated (2.5-4 Mrad)-in-air polyethylene mated with the same head?
. Resistance to adhesive wear
. Resistance to abrasive wear
. Resistance to fatigue wear
. Resistance to creep

Correct Answer & Explanation

. Resistance to adhesive wear

Explanation

DISCUSSION: Highly cross-linked polyethylene makes material resistant to adhesive wear. Abrasive wear from third bodies does not decrease wear. The fatigue strength of such material is inferior to that of traditional polyethylene, and its resistance to creep is the same, if not lower, than that of traditional polyethylene.

Question 3236

Topic: Biology, Genetics & Bone Healing
Osteopenia is defined by the World Health Organization (WHO) as a bone mineral density (BMD) that is
. within 1 standard deviation of age-matched normals.
. within 1 and 2.5 standard deviations below age-matched normals.
. within 1 standard deviation of young normals.
. within 1 and 2.5 standard deviations below young normals.
. more than 2.5 standard deviations below age-matched normals.

Correct Answer & Explanation

. within 1 and 2.5 standard deviations below age-matched normals.

Explanation

DISCUSSION: Osteopenia, decreased bone mass without fracture risk as defined by the WHO criteria for diagnosis of osteoporosis, is when a woman’s T-score is within -1 to -2.5 SD. The T-score represents a comparison to young normals or optimum peak density. The Z-score represents a comparison of BMD to age-matched normals. Measurements of bone mineral density (BMD) at various skeletal sites help in predicting fracture risk. Hip BMD best predicts fracture of the hip, as well as fractures at other sites. REFERENCE: Kanis JA, Johnell O, Oden A, et al: Risk of hip fracture according to the World Health Organization criteria for osteopenia and osteoporosis. Bone 2000;27:585-590.

Question 3237

Topic: 1. General Principles & Basic Science
Within the menisci, the majority of the large collagen fiber bundles are oriented in what configuration?
. Radially
. Circumferentially
. Vertically
. Obliquely
. Randomly

Correct Answer & Explanation

. Circumferentially

Explanation

DISCUSSION: The majority of large collagen fibers within the menisci are oriented circumferentially. It is these fibers that develop the hoop stress with compressive loading of the menisci. Most meniscal tears are longitudinal and occur between these circumferential fibers. REFERENCES: Mow VC, et al: Structure and function relationships of the menisci of the knee, in Mow VC, Arnoczky SP, Jackson DW (eds): Knee Meniscus: Basic and Clinical Foundations. New York, NY, Raven Press, 1992, pp 37-57. DeHaven KE, Arnoczky SP: Meniscus repair: Basic science, indications for repair, and open repair. Instr Course Lect 1994;43:65-76.

Question 3238

Topic: 1. General Principles & Basic Science

-Figures 56a and 56b are the MRI scans of a 2-year-old girl who has a fever of 39°C and inability to move her left arm. She has not had any recent injury and is otherwise healthy. Radiograph findings of her left upper extremity are normal. What is the most appropriate treatment?

. Incision and drainage of the humerus
. Sling immobilization of the left upper extremity
. Total body bone scan
. A course of oral antibiotics and recheck in 1 weekDISCUSSION-The MRI scan shows a large abscess along most of the humerus. Incision and drainage of the abscess is indicated. A bone scan will not add any additional information regarding location of the problem.Immobilization will not address the origin of the problem. Oral antibiotics are not adequate for this abscess.

Correct Answer & Explanation

. Incision and drainage of the humerus

Explanation

Question 3239

Topic: Biomechanics & Biomaterials
Cortical bone demonstrates viscoelastic behavior as its mechanical properties are sensitive to strain rate and duration of applied load. Regarding longitudinal strain in cortical bone, which of the following statements regarding this characteristic is true?
. As strain rate increases, both elastic modulus and ultimate strength increase
. As strain rate increases, elastic modulus remains unchanged but ultimate strength increases
. As strain rate increases, elastic modulus increases but ultimate strength decreases
. As strain rate increases, both elastic modulus and ultimate strength decrease
. As strain rate increases, elastic modulus increases but ultimate strength remains unchanged

Correct Answer & Explanation

. As strain rate increases, both elastic modulus and ultimate strength increase

Explanation

As strain rate increases, both elastic modulus and ultimate strength increase. For LOW strain rates typical of normal activity (physiological strain rates of <0.1/s), bone is ELASTIC and DUCTILE (increasing ultimate strain with increasing strain rate). There is a ductile-to-brittle transition with increasing strain rate from normal to supranormal rates. For EXTREMELY HIGH supranormal strain rates (>0.1/s, high impact trauma), bone is VISCOELASTIC and BRITTLE (low ultimate strain with increasing strain rate). Bone also becomes stronger and stiffer (higher modulus, steeper slope of stress-strain plot) as strain rate increases. This viscoelastic property helps in damping muscle contracture. Natali and Meroi reviewed studies examining mechanical properties of bone. Mechanical properties are correlated with moisture, deformation rate, density and region of bone. Mechanical adaptation of bone is affected by strain rate (rate at which bone is deformed), strain mode (tension, compression, shear), strain direction (direction of strain relative to bone surface), strain frequency (cycles/second), stimulus duration (period over which deformation cycles are applied), strain distribution (pattern of strain magnitude across bone section) and strain energy (energy stored during deformation).

Question 3240

Topic: 1. General Principles & Basic Science
The therapeutic effect of etanercept in the treatment of rheumatoid arthritis is primarily mediated through
. antagonism of tumor necrosis factor-alpha (TNF-α).
. antagonism of matrix metalloproteinases (MMPs).
. inhibition of COX2.
. stimulation of interleukin-1 (IL-1).
. stimulation of tissue inhibitors of metalloproteinases (TIMPs).

Correct Answer & Explanation

. antagonism of tumor necrosis factor-alpha (TNF-α).

Explanation

DISCUSSION: Etanercept is a fusion protein that combines the ligand-binding domain of the TNF-α receptor to the Fc portion of human immunoglobulin G (IgG). Protein serves as a competitive inhibitor of TNF-α signaling. COX2 is the target of NSAIDs, including newer formulations that are more COX2-specific. The remaining responses are not direct targets of etanercept. REFERENCES: Weinblatt ME, Kremer JM, Bankhurst AD, et al: A trial of etanercept, a recombinant tumor necrosis factor receptor: Fc fusion protein, in patients with rheumatoid arthritis receiving methotrexate. N Engl J Med 1999;340:253-259. Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 489-530.

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