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1. General Principles & Basic Science MCQs

Practice Set 116 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 2301

Topic: Biomechanics & Biomaterials

A 16-year-old patient presents with a history of anterior physeal arrest of the proximal tibia, resulting in a significant genu recurvatum deformity. Despite the structural bony abnormality, the patient's gait is described as 'deceptively normal' by the physical therapist, with no obvious hyperextension thrust during walking. Which of the following statements best explains this paradox in a patient with normal muscle strength and tone?

. The knee joint is inherently unstable in the sagittal plane, allowing for a wide range of motion without functional impairment.
. The patient has developed significant ligamentous laxity, which paradoxically stabilizes the knee in a functional position.
. Normal gait kinematics involve the knee never fully extending during walking, and the body uses active muscle control to prevent full passive hyperextension.
. The osseous deformity is entirely compensated by increased hip extension, making the knee appear normal.
. The patient has a concomitant distal femoral procurvatum, which balances the proximal tibial recurvatum.

Correct Answer & Explanation

. Normal gait kinematics involve the knee never fully extending during walking, and the body uses active muscle control to prevent full passive hyperextension.

Explanation

Correct Answer: CThe text explains this paradox: 'Counterintuitively, a patient with a significantosseousrecurvatum deformity may present with a surprisingly normal-looking gait, provided they have normal muscle strength and tone. This paradox is explained by the kinematics of a normal walking cycle and the body's incredible capacity for compensation. Normal Gait Kinematics: The knee never fully extends during normal walking. At heel strike (initial contact), the normal knee is in approximately 5° of flexion. It then flexes further to about 20° during the loading response phase to absorb shock and transfer weight smoothly. Compensated Recurvatum Gait: A patient with a structural bony recurvatum will still initiate contact with their knee in 5° of flexion. They use active, dynamic muscle control to prevent the knee from snapping into its full, passive hyperextension.'Option A is incorrect; the knee joint is designed for stability during stance, and instability would lead to functional impairment.Option B is incorrect; ligamentous laxity would exacerbate recurvatum, not stabilize it, and is a distinct etiology.Option D is incorrect; while compensation occurs, the primary compensation for osseous knee recurvatum to achieve a plantigrade foot is at the ankle, not entirely at the hip.Option E is incorrect; a concomitant deformity that balances another would be a complex scenario, but the core explanation for the 'deceptively normal' gait lies in normal knee kinematics and active muscle control.

Question 2302

Topic: 1. General Principles & Basic Science

A 40-year-old male presents with progressive knee pain and a feeling of instability. Clinical examination reveals a noticeable knee hyperextension. A full-length lateral standing radiograph is obtained, and the following measurements are recorded: aLDFA = 82°, PPTA = 95°, ADTA = 80°, JLCA = 1°. Based on Paley's principles and the provided normative data, what is the primary sagittal plane deformity in this patient?

. Distal femoral recurvatum.
. Proximal tibial recurvatum.
. Distal tibial procurvatum.
. Ligamentous laxity of the knee.
. Normal sagittal plane alignment with functional instability.

Correct Answer & Explanation

. Proximal tibial recurvatum.

Explanation

Correct Answer: BLet's analyze the given angles against the normal values:aLDFA = 82°:Normal range is 79° to 87°. This value is within the normal range, ruling out distal femoral recurvatum.PPTA = 95°:Normal range is 77° to 84°. A PPTA > 84° indicates proximal tibial recurvatum. This patient's PPTA of 95° is significantly elevated, indicating a proximal tibial recurvatum deformity.ADTA = 80°:Normal range is 78° to 82°. This value is within the normal range, ruling out distal tibial procurvatum (which would be < 78°).JLCA = 1°:Normal range is 0° to 2°. This confirms that the joint surfaces are parallel and the deformity is extra-articular, consistent with a bony deformity.Therefore, the primary sagittal plane deformity is proximal tibial recurvatum.Option A is incorrect as the aLDFA is normal.Option C is incorrect as the ADTA is normal.Option D is incorrect; while ligamentous laxity can cause recurvatum, the clear bony angle abnormality (PPTA) points to an osseous etiology, and the normal JLCA suggests an extra-articular bony problem rather than primary intra-articular ligamentous laxity.Option E is incorrect as the PPTA clearly indicates a significant bony deformity.

Question 2303

Topic: Physiology & Rehabilitation

A 70-year-old patient with a history of stroke presents with a dynamic genu recurvatum during the stance phase of gait. Unlike patients with purely osseous recurvatum, this patient exhibits a marked hyperextension thrust that worsens with fatigue. The text highlights that the deceptively normal gait seen in compensated osseous recurvatum 'shatters completely when muscle weakness is introduced into the equation.' What is the most likely reason for the breakdown of compensated gait in the presence of muscle weakness in a patient with underlying osseous recurvatum?

. Muscle weakness directly causes the osseous deformity to worsen over time.
. The weakened muscles are unable to provide the active, dynamic control needed to prevent the knee from snapping into full passive hyperextension.
. Muscle weakness leads to increased ligamentous laxity, which then causes the recurvatum.
. The body compensates by increasing ankle dorsiflexion, which exacerbates knee recurvatum.
. Muscle weakness primarily affects the swing phase, leading to toe drag rather than stance phase instability.

Correct Answer & Explanation

. The weakened muscles are unable to provide the active, dynamic control needed to prevent the knee from snapping into full passive hyperextension.

Explanation

Correct Answer: BThe text states, 'The deceptively normal gait pattern seen in compensated osseous recurvatum shatters completely when muscle weakness is introduced into the equation. The anteroposterior stability of the knee during the stance phase is an active, dynamic process controlled by the delicate balance between the quadriceps and [hamstrings].' In the presence of muscle weakness (e.g., hamstrings or quadriceps imbalance), the patient loses the ability to actively control the knee's position, allowing the underlying bony recurvatum to manifest as a dynamic hyperextension thrust during weight-bearing.Option A is incorrect; muscle weakness does not directly alter bone shape or worsen an existing osseous deformity.Option C is incorrect; muscle weakness does not cause ligamentous laxity. Ligamentous laxity is a separate etiology for recurvatum.Option D is incorrect; the primary compensation for osseous recurvatum is ankle plantar flexion, not dorsiflexion. Increased dorsiflexion would further destabilize a recurvatum knee.Option E is incorrect; while muscle weakness can affect the swing phase, the question specifically addresses the breakdown of compensated gait during thestance phasedue to recurvatum, which is a stability issue.

Question 2304

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with a progressive gait abnormality and knee pain. She describes her knee as 'bending backward' when she stands or walks. Clinical examination reveals a significant genu recurvatum. The image below shows a clinical presentation that might be observed in such a patient. Which of the following etiologies is LEAST likely to be the primary cause of this patient's genu recurvatum if her Sagittal Mechanical Axis Deviation (MAD) is significant and her PPTA is measured at 98°?

. Anterior physeal arrest of the proximal tibia.
. Malunited fracture of the proximal tibia.
. Ehlers-Danlos syndrome with generalized ligamentous laxity.
. Rickets causing a structural bowing of the tibia.
. Post-traumatic infection leading to growth disturbance.

Correct Answer & Explanation

. Ehlers-Danlos syndrome with generalized ligamentous laxity.

Explanation

Correct Answer: CThe question provides two key pieces of information: a significant Sagittal Mechanical Axis Deviation (MAD) and a PPTA of 98°. A PPTA of 98° is significantly higher than the normal range (77-84°), which strongly indicates aproximal tibial recurvatum (hyperextension) deformityof osseous origin. The text categorizes etiologies into osseous, ligamentous, and neuromuscular.Osseous Deformity:'This is a structural bowing of the bone itself. Common causes include anterior physeal arrest of the distal femur or proximal tibia... malunited fractures, or metabolic bone diseases like rickets.' Options A, B, and D are all classic causes of osseous deformity. Option E (post-traumatic infection leading to growth disturbance) is also a common cause of physeal arrest and subsequent osseous deformity.Ligamentous Laxity:'This involves incompetence of the posterior soft tissue restraints of the knee... It is frequently seen in connective tissue disorders (e.g., Ehlers-Danlos syndrome).' While Ehlers-Danlos syndrome can cause genu recurvatum, the presence of a significantly abnormal PPTA (a bony angle) points overwhelmingly to anosseousetiology as the primary driver, rather than purely ligamentous laxity. While ligamentous laxity might coexist, it is less likely to be theprimarycause when a clear bony deformity is identified by radiographic angles.Therefore, Ehlers-Danlos syndrome, primarily causing ligamentous laxity, is the least likelyprimarycause when a definitive osseous deformity (PPTA = 98°) is identified.

Question 2305

Topic: 1. General Principles & Basic Science

A 45-year-old male presents with a long-standing genu recurvatum deformity following a childhood injury. Radiographic analysis reveals a Sagittal CORA located 5 cm distal to the knee joint line in the proximal tibia. The surgeon plans a corrective osteotomy. According to Paley's Osteotomy Rules, what is the most critical principle to follow regarding the osteotomy cut and hardware hinge placement to achieve pure angular correction without introducing a new translational deformity?

. The osteotomy cut should be performed at the level of the joint line, and the hinge placed proximally.
. The osteotomy cut should be performed at the level of the CORA, and the hinge placed at the CORA.
. The osteotomy cut should be performed 1 cm proximal to the CORA, and the hinge placed at the CORA.
. The osteotomy cut should be performed 1 cm distal to the CORA, and the hinge placed at the CORA.
. The osteotomy cut should be performed at the CORA, but the hinge can be placed anywhere along the bone.

Correct Answer & Explanation

. The osteotomy cut should be performed at the level of the CORA, and the hinge placed at the CORA.

Explanation

Correct Answer: BThe text emphasizes the critical importance of the CORA: 'Identifying the CORA is not a mere academic exercise; it is the single most important step in planning a corrective osteotomy. As we will explore later in Paley's Osteotomy Rules, the location of your osteotomy cut and the placement of your hardware hinge relative to the CORA determines whether you achieve pure angular correction or inadvertently introduce a new, deleterious translational deformity.' The fundamental principle of Paley's method for pure angular correction is that both the osteotomy cut and the hinge of the external fixator (or internal fixation device) must be placed precisely at the CORA. If the osteotomy is performed away from the CORA, or the hinge is not at the CORA, translation will occur during correction.Option A is incorrect; performing the osteotomy at the joint line and placing the hinge proximally would introduce significant translation and likely alter joint mechanics.Options C and D are incorrect; performing the osteotomy either proximal or distal to the CORA, even if the hinge is at the CORA, will result in translation. The osteotomy cut itself must be at the CORA.Option E is incorrect; placing the hinge anywhere along the bone, even if the osteotomy is at the CORA, will inevitably lead to translation during correction.

Question 2306

Topic: Biomechanics & Biomaterials

The teaching case emphasizes that while the coronal plane often takes center stage in orthopedic deformity correction, 'a true, comprehensive mastery of limb reconstruction requires a profound understanding of the sagittal plane.' Which of the following statements best summarizes the unique functional impact of sagittal plane deformities compared to coronal deformities, as highlighted in the text?

. Sagittal deformities primarily affect load distribution and joint wear, similar to coronal deformities.
. Sagittal deformities are easier to compensate for and rarely lead to significant functional deficits.
. Sagittal deformities directly disrupt the kinematic chain required for forward propulsion, unlike coronal deformities which primarily affect load distribution.
. Coronal deformities are always more complex to correct surgically than sagittal deformities.
. Both sagittal and coronal deformities primarily impact cosmetic appearance, with minimal functional consequences.

Correct Answer & Explanation

. Sagittal deformities directly disrupt the kinematic chain required for forward propulsion, unlike coronal deformities which primarily affect load distribution.

Explanation

Correct Answer: CThe introductory paragraph of the teaching case directly addresses this: 'Unlike coronal deformities, which primarily affect load distribution and joint wear, sagittal deformities directly disrupt the kinematic chain required for forward propulsion. Their correction demands a systematic, biomechanically sound approach.'Option A is incorrect because the text explicitly differentiates the primary impact: coronal affects load distribution, sagittal affects kinematics for propulsion.Option B is incorrect; the text states sagittal deformities 'can create devastating functional deficits' and their correction 'demands a systematic, biomechanically sound approach,' implying they are not easily compensated for without consequences.Option D is incorrect; the text does not make a general statement about the relative surgical complexity of coronal versus sagittal deformities, but rather emphasizes the unique challenges and importance of sagittal plane correction.Option E is incorrect; the text focuses on the profound functional deficits and disruption of gait kinematics, not primarily cosmetic impact.

Question 2307

Topic: Physiology & Rehabilitation

A 62-year-old male presents with chronic knee pain and difficulty with ambulation, noting significant fatigue after short distances. Clinical examination reveals a fixed knee flexion deformity (FFD) of 15 degrees. During the mid-stance phase of gait, which of the following biomechanical alterations is most characteristic of this patient's condition?

. The Ground Reaction Vector (GRV) passes anterior to the knee's center of rotation, creating an extension moment.
. The quadriceps muscle group remains largely inactive, relying on passive knee stability.
. The GRV passes posterior to the knee's center of rotation, necessitating persistent quadriceps contraction.
. The ankle joint is forced into plantarflexion to maintain a plantigrade foot.
. The hip joint primarily compensates by moving into increased extension to shift the center of mass posteriorly.

Correct Answer & Explanation

. The GRV passes posterior to the knee's center of rotation, necessitating persistent quadriceps contraction.

Explanation

Correct Answer: CThe case explicitly states that in the presence of a Fixed Flexion Deformity (FFD), the Ground Reaction Vector (GRV) is forced to passposteriorto the knee's center of rotation. This posterior shift instantly creates a powerful, pathological flexion moment that attempts to buckle the knee with every step. To prevent collapse, the patient must engage in persistent, active, isometric quadriceps contraction throughout the entire stance phase. The image provided illustrates this exact scenario, showing the GRV (yellow/green line) passing posterior to the knee's center of rotation (blue dot), creating a flexion moment.Option A is incorrectbecause this describes the normal, energy-efficient gait where the GRV passes anterior to the knee, creating a passive extension moment. This is disrupted in FFD.Option B is incorrectbecause, as explained, the posterior GRV in FFD necessitates constant, active quadriceps contraction, leading to significant energy expenditure and fatigue, directly contradicting the idea of passive stability.Option D is incorrect. For a mild FFD (5-15 degrees), the body attempts to keep the foot plantigrade by compensating withincreased ankle dorsiflexion, not plantarflexion. Plantarflexion would exacerbate the toe-walking tendency.Option E is incorrect. While the hip does compensate, it does so by moving intoincreased flexion(proximal compensation) and a slight anterior lean of the trunk, not extension. This attempts to shift the body's center of mass forward to reduce the flexion moment at the knee.

Question 2308

Topic: Biomechanics & Biomaterials

A 30-year-old male presents with a 20-degree fixed knee flexion deformity following a traumatic injury. Radiographic analysis reveals a normal PDFA (83°) and PPTA (81°). The patient reports significant quadriceps fatigue and difficulty with prolonged standing. Which of the following is the most direct physiological consequence of the altered Ground Reaction Vector (GRV) in this patient?

. Reduced energy expenditure during ambulation.
. Passive knee extension moment during mid-stance.
. Increased reliance on hip abductor muscles for stability.
. Relentless demand on the quadriceps mechanism.
. Improved patellofemoral joint mechanics.

Correct Answer & Explanation

. Relentless demand on the quadriceps mechanism.

Explanation

Correct Answer: DThe case explicitly details the physiological cost of abnormal gait due to FFD. It states that the most immediate and catastrophic effect of an FFD is therelentless demand on the quadriceps mechanism. Because the GRV passes posterior to the knee, creating a powerful flexion moment, the quadriceps muscle must fire isometrically and eccentrically throughout stance to counteract this moment and prevent collapse. This leads to quadriceps burnout and significant fatigue, as described in the vignette.Option A is incorrect. FFD transforms an energy-efficient, passive process into an exhausting, joint-damaging ordeal, leading toincreasedenergy expenditure, not reduced.Option B is incorrect. A passive knee extension moment occurs in normal gait when the GRV passes anterior to the knee. In FFD, the GRV passes posterior, creating a flexion moment.Option C is incorrect. While other muscles may compensate, the most direct and immediate consequence of the altered GRV at the knee is on the quadriceps, which are directly responsible for sagittal plane knee stability.Option E is incorrect. The relentless demand on the quadriceps and the altered kinematics in FFD lead topatellofemoral destructionand pain, not improved mechanics.

Question 2309

Topic: 1. General Principles & Basic Science

An osteotomy is performed to correct a lower limb deformity. The surgeon plans the cut such that the osteotomy passes exactly through the center of rotation of angulation (CORA), and the axis of correction (hinge) is also positioned at the CORA. According to Dror Paley's principles of deformity correction, what is the geometric result?

. Angulation corrects without translation.
. Angulation corrects with a purposeful translation.
. A new translational deformity is created.
. Only the length discrepancy is addressed.
. The mechanical axis is medialized without angular change.

Correct Answer & Explanation

. Angulation corrects without translation.

Explanation

According to Paley's Rule 1, when both the osteotomy and the hinge are located at the CORA, angulation corrects completely without inducing any translation. This perfectly realigns the mechanical axis.

Question 2310

Topic: Physiology & Rehabilitation

During a normal gait cycle, maximum knee flexion is critical to allow for adequate foot clearance. This maximum degree of knee flexion typically occurs during which phase of the gait cycle?

. Initial contact
. Mid-stance
. Terminal stance
. Initial swing
. Mid-swing

Correct Answer & Explanation

. Initial swing

Explanation

Maximum knee flexion during normal walking reaches approximately 60 degrees and occurs during the initial swing phase. This motion is essential for clearing the foot off the ground as the limb advances.

Question 2311

Topic: 1. General Principles & Basic Science

A patient presents with a severe varus deformity of the right lower extremity. Radiographic analysis reveals that the mechanical axis line passes significantly medial to the center of the knee joint. What is the immediate biomechanical consequence of this alignment on the knee?

. Decreased joint reaction forces in the medial compartment.
. Increased joint reaction forces in the lateral compartment.
. Increased compressive joint reaction forces in the medial compartment.
. Symmetrical distribution of forces across both tibiofemoral compartments.
. Increased tension on the medial collateral ligament.

Correct Answer & Explanation

. Increased compressive joint reaction forces in the medial compartment.

Explanation

A medial mechanical axis deviation (varus deformity) increases the moment arm of the body weight relative to the knee center, significantly increasing the compressive joint reaction forces in the medial compartment. This accelerates medial compartment osteoarthritis.

Question 2312

Topic: Physiology & Rehabilitation

A 12-year-old patient with severe external tibial torsion demonstrates 'lever arm dysfunction' during clinical gait analysis. This rotational malalignment primarily impairs the biomechanical efficiency of which muscle group during the terminal stance phase?

. Quadriceps
. Hamstrings
. Gluteus medius
. Triceps surae
. Tibialis anterior

Correct Answer & Explanation

. Triceps surae

Explanation

External tibial torsion outwardly rotates the foot progression angle, shortening the effective sagittal lever arm of the foot. This significantly reduces the push-off power generated by the triceps surae (gastrocnemius-soleus complex) during terminal stance.

Question 2313

Topic: 1. General Principles & Basic Science

A surgeon corrects a diaphyseal deformity by placing the axis of correction (hinge) exactly at the CORA. However, due to poor local soft tissues, the osteotomy is performed away from the CORA. According to Paley's Rule 2, what happens geometrically?

. Pure angulation occurs without translation.
. Angulation occurs simultaneously with translation.
. Translation occurs without any change in angulation.
. Compression occurs at the osteotomy site.
. A secondary angular deformity is created.

Correct Answer & Explanation

. Angulation occurs simultaneously with translation.

Explanation

According to Paley's Rule 2, placing the hinge at the CORA but cutting the bone outside the CORA results in angular correction accompanied by translation. This translation is necessary to re-align the mechanical axis properly.

Question 2314

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis using a circular external fixator, the formation of new regenerate bone under stable mechanical tension primarily bypasses the cartilaginous intermediate phase. Which type of ossification predominates in the distraction gap?

. Endochondral ossification
. Intramembranous ossification
. Appositional ossification
. Chondroid ossification
. Woven bone transformation

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis occurs primarily via intramembranous ossification when the fixator construct is stable and blood supply is preserved. Bone forms directly from mesenchymal cells aligning along the tension vector without a cartilaginous precursor.

Question 2315

Topic: 1. General Principles & Basic Science

In normal human gait, the vertical ground reaction force (GRF) curve is classically described as having a 'double hump' pattern. The first peak of this vertical GRF curve occurs during which specific phase?

. Heel strike
. Loading response
. Mid-stance
. Terminal stance
. Pre-swing

Correct Answer & Explanation

. Loading response

Explanation

The first peak of the vertical GRF occurs during the loading response (weight acceptance phase) as the body absorbs the impact of landing. The second peak occurs during terminal stance as the triceps surae initiates push-off.

Question 2316

Topic: 1. General Principles & Basic Science

When evaluating a standing long leg radiograph for deformity planning, the mechanical lateral distal femoral angle (mLDFA) is measured. What is the normal range for the mLDFA in a healthy adult?

. 75 to 79 degrees
. 80 to 84 degrees
. 85 to 89 degrees
. 90 to 94 degrees
. 95 to 99 degrees

Correct Answer & Explanation

. 85 to 89 degrees

Explanation

The normal mLDFA typically measures 87 degrees, with a recognized normal range of 85 to 89 degrees. This angle defines the relationship between the mechanical axis of the femur and the distal femoral joint orientation line.

Question 2317

Topic: Biomechanics & Biomaterials

Sagittal plane alignment of the distal tibia is critical for normal ankle biomechanics. What is the normal measurement of the anterior distal tibial angle (ADTA) relative to the mechanical axis of the tibia?

. 70 degrees
. 80 degrees
. 90 degrees
. 100 degrees
. 110 degrees

Correct Answer & Explanation

. 80 degrees

Explanation

The normal ADTA is approximately 80 degrees (range 78-82 degrees). Deviations from this angle indicate a procurvatum (increased angle) or recurvatum (decreased angle) deformity of the distal tibia.

Question 2318

Topic: Physiology & Rehabilitation

A patient with advanced osteoarthritis of the right hip presents with a compensated Trendelenburg gait. Which kinematic alteration best describes how this patient minimizes the required abductor force during the stance phase on the affected leg?

. Leaning the trunk away from the right hip.
. Leaning the trunk laterally over the right hip.
. Increasing lumbar lordosis dramatically.
. Flexing the trunk forward over the knee.
. Circumducting the right leg during swing.

Correct Answer & Explanation

. Leaning the trunk laterally over the right hip.

Explanation

In a compensated Trendelenburg gait (abductor lurch), the patient shifts their trunk laterally over the affected hip. This moves the center of gravity closer to the joint center, drastically reducing the moment arm of body weight and decreasing the force required by the weak abductors.

Question 2319

Topic: 1. General Principles & Basic Science

A surgeon incorrectly plans a tibial osteotomy such that both the osteotomy cut and the axis of correction (hinge) are placed proximal to the actual CORA. According to Paley's Rule 3, what geometric consequence will occur when the angulation is corrected?

. Perfect alignment of the mechanical axis without translation.
. Angulation with purposeful, beneficial translation.
. Creation of a secondary translational deformity (step-off).
. Isolated shortening of the limb.
. Isolated lengthening of the limb.

Correct Answer & Explanation

. Creation of a secondary translational deformity (step-off).

Explanation

According to Paley's Rule 3, placing both the osteotomy and the hinge at a location other than the CORA results in the creation of a new, iatrogenic translational deformity (a step-off) when the angular correction is performed.

Question 2320

Topic: Physiology & Rehabilitation

Saunders et al. described six classic 'determinants of gait' designed to minimize the vertical and lateral displacement of the body's center of gravity. Which determinant is primarily responsible for lowering the highest point (apex) of the center of gravity trajectory during the stance phase?

. Pelvic rotation
. Pelvic tilt
. Knee flexion in stance
. Foot and ankle mechanisms
. Lateral displacement of the pelvis

Correct Answer & Explanation

. Knee flexion in stance

Explanation

Knee flexion during the stance phase (typically around 15 degrees) serves to lower the body's center of gravity at the peak of its trajectory, thereby flattening the arc of motion and conserving energy.

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