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1. General Principles & Basic Science MCQs

Practice Set 144 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 2861

Topic: 1. General Principles & Basic Science

A 45-year-old male with medial compartment osteoarthritis and varus deformity is scheduled for a High Tibial Osteotomy (HTO). His mechanical medial proximal tibial angle (mMPTA) is measured at 81 degrees. What is the normal range for the mMPTA, and what does this patient's value indicate?

. Normal is 85-90 degrees; the patient has a proximal tibial varus deformity.
. Normal is 85-90 degrees; the patient has a proximal tibial valgus deformity.
. Normal is 75-80 degrees; the patient has a normal proximal tibia.
. Normal is 79-83 degrees; the patient has a proximal tibial valgus deformity.
. Normal is 90-95 degrees; the patient has a proximal tibial varus deformity.

Correct Answer & Explanation

. Normal is 85-90 degrees; the patient has a proximal tibial varus deformity.

Explanation

The normal mMPTA is 85 to 90 degrees (average 87 degrees). An mMPTA of 81 degrees is less than normal, indicating that the proximal tibia is contributing to the varus deformity.

Question 2862

Topic: 1. General Principles & Basic Science

To accurately measure joint orientation angles and the mechanical axis on a long-leg radiograph, the patient must be positioned correctly. Which of the following is the most critical positioning requirement to prevent rotational artifact from altering the perceived coronal plane alignment?

. The feet must be externally rotated 15 degrees.
. The feet must be placed perfectly parallel to each other.
. The patella must be facing strictly anteriorly.
. The pelvis must be tilted 10 degrees anteriorly.
. The knee must be flexed 10 degrees.

Correct Answer & Explanation

. The patella must be facing strictly anteriorly.

Explanation

Accurate radiographic evaluation of coronal plane deformity requires a 'patella forward' position. If the leg is rotated, the true coronal deformity will be distorted, projecting a false representation of the mechanical axis and joint orientation angles.

Question 2863

Topic: 1. General Principles & Basic Science

A patient presents with a severe varus deformity of the lower extremity. The Joint Line Convergence Angle (JLCA) is measured at 6 degrees (normal is 0-2 degrees). What is the most likely cause of this abnormal JLCA?

. A diaphyseal deformity of the femur.
. A diaphyseal deformity of the tibia.
. Intra-articular cartilage loss or collateral ligament laxity.
. A severe rotational deformity of the femur.
. An inaccurate radiograph taken with the knee in 30 degrees of flexion.

Correct Answer & Explanation

. Intra-articular cartilage loss or collateral ligament laxity.

Explanation

The JLCA measures the angle between the femoral and tibial articular surfaces. An increased JLCA (>2 degrees) typically indicates intra-articular pathology, such as asymmetric cartilage wear (e.g., medial compartment osteoarthritis) or ligamentous laxity.

Question 2864

Topic: Biomechanics & Biomaterials

A surgeon plans a medial opening wedge high tibial osteotomy (HTO) for a patient with medial compartment osteoarthritis. If the osteotomy is performed proximal to the tibial tubercle, what is the most predictable effect on the patellofemoral joint?

. Increased patellar height (patella alta).
. Decreased patellar height (patella baja).
. Lateral subluxation of the patella.
. Medial subluxation of the patella.
. No change in patellofemoral kinematics.

Correct Answer & Explanation

. Decreased patellar height (patella baja).

Explanation

A medial opening wedge HTO performed proximal to the tibial tubercle increases the distance between the tibial tubercle and the joint line. This effectively decreases the patellar height relative to the joint, leading to patella baja (infera).

Question 2865

Topic: 1. General Principles & Basic Science

When planning a corrective osteotomy for a uni-apical deformity, drawing the proximal and distal mechanical axes helps identify the Center of Rotation of Angulation (CORA). If a joint is found to have a compensatory deformity, how does this affect the planning?

. The CORA must automatically be moved to the intra-articular space.
. The compensatory deformity should always be ignored to focus on the primary bone.
. Joint line orientation angles may appear falsely normal if the compensatory deformity perfectly balances the primary one.
. A double osteotomy is contraindicated in the presence of compensatory deformities.
. The mechanical axis will strictly remain within normal limits despite the structural bow.

Correct Answer & Explanation

. Joint line orientation angles may appear falsely normal if the compensatory deformity perfectly balances the primary one.

Explanation

A compensatory deformity in an adjacent bone (e.g., valgus tibia compensating for a varus femur) can shift the mechanical axis back toward the center of the knee. However, the joint line orientation angles will be abnormal, reflecting the zig-zag alignment of the limb.

Question 2866

Topic: 1. General Principles & Basic Science

During an opening wedge high tibial osteotomy (HTO) for a varus deformity, what is the geometric relationship between the width of the opening wedge at the medial cortex and the degree of angular correction achieved?

. 1 mm of opening typically provides 3 degrees of angular correction.
. 1 mm of opening typically provides 1 degree of angular correction.
. 1 mm of opening typically provides 0.5 degrees of angular correction.
. The opening wedge width is unrelated to the angular correction; it only affects translation.
. 1 cm of opening is required for every 2 degrees of angular correction.

Correct Answer & Explanation

. 1 mm of opening typically provides 1 degree of angular correction.

Explanation

As a reliable surgical rule of thumb in the proximal tibia, approximately 1 mm of opening wedge gap at the posteromedial cortex corresponds to 1 degree of angular correction in the coronal plane.

Question 2867

Topic: 1. General Principles & Basic Science

According to Paley's first rule of osteotomy, if both the osteotomy cut and the hinge axis are placed exactly at the Center of Rotation of Angulation (CORA), what is the resultant effect on the bone segments?

. Pure angulation combined with length loss
. Pure angulation without translation
. Translation without angulation
. Angulation with collateral translation of the bone ends
. Pure translation without angulation

Correct Answer & Explanation

. Pure angulation without translation

Explanation

Paley's Rule 1 states that when the osteotomy and the correction hinge axis are both located at the CORA, the bone realigns through pure angulation without any translation of the bone ends.

Question 2868

Topic: 1. General Principles & Basic Science

A surgeon is planning to correct a diaphyseal tibial deformity. Due to poor soft tissue quality at the apex, the osteotomy is planned at a different level than the Center of Rotation of Angulation (CORA), but the hinge axis remains exactly at the CORA. According to Paley's second rule, which of the following describes the resulting correction?

. Angulation without translation
. Pure translation
. Collinear mechanical axes with translation of the bone ends at the osteotomy site
. Angulation with non-collinear, parallel mechanical axes
. Failure to correct the mechanical axis deviation

Correct Answer & Explanation

. Collinear mechanical axes with translation of the bone ends at the osteotomy site

Explanation

Paley's Rule 2 states that if the hinge is at the CORA but the osteotomy is at a different level, the mechanical axes will successfully become collinear, but the bone ends at the osteotomy site will translate.

Question 2869

Topic: 1. General Principles & Basic Science

In a distal femoral deformity correction, a surgeon incorrectly places both the osteotomy and the correction hinge at a level proximal to the Center of Rotation of Angulation (CORA). According to Paley's third rule, what will be the resulting alignment?

. Parallel but non-collinear mechanical axes, resulting in a translation deformity
. Collinear mechanical axes with ideal correction
. Pure angulation without translation
. Complete correction of mechanical axis deviation with intentional lengthening
. Pure rotational correction only

Correct Answer & Explanation

. Parallel but non-collinear mechanical axes, resulting in a translation deformity

Explanation

Paley's Rule 3 dictates that if both the hinge and the osteotomy are placed outside the CORA, the mechanical axes of the proximal and distal segments will end up parallel but non-collinear, creating a new translation deformity.

Question 2870

Topic: 1. General Principles & Basic Science

When planning a distal femoral osteotomy, the surgeon must account for the difference between the anatomic and mechanical axes of the femur. What is the typical normal relationship between the anatomic and mechanical axes of the femur?

. The anatomic axis is typically 7 degrees valgus to the mechanical axis.
. The anatomic axis is typically 7 degrees varus to the mechanical axis.
. The axes are parallel and separated by 10 mm.
. The anatomic axis is typically 3 degrees varus to the mechanical axis.
. The axes are perfectly collinear in the coronal plane.

Correct Answer & Explanation

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

Explanation

Due to the lateral offset of the greater trochanter, the anatomic axis of the femur typically diverges from the mechanical axis by about 7 degrees (range 5-9 degrees) in a valgus direction.

Question 2871

Topic: Biology, Genetics & Bone Healing

A 20-year-old undergoes femoral lengthening with an external fixator. Five weeks into the distraction phase, radiographs show dense bone bridging the gap, and the patient is unable to turn the distraction nut. What is the most appropriate management for this complication?

. Increase the distraction rate to 2 mm per day immediately
. Reverse the distractor to compress the site for one week
. Perform an open osteoclasis or repeat osteotomy
. Administer bisphosphonates to slow bone healing
. Remove the frame and convert to an intramedullary nail

Correct Answer & Explanation

. Perform an open osteoclasis or repeat osteotomy

Explanation

Premature consolidation occurs when the regenerate bone heals faster than the distraction rate. Once bridging bone forms and distraction is impossible, surgical intervention via repeat osteotomy or osteoclasis is required to resume lengthening.

Question 2872

Topic: 1. General Principles & Basic Science

The Taylor Spatial Frame (TSF) utilizes computer-assisted software to correct complex limb deformities based on the Stewart-Gough platform. How many degrees of freedom does the TSF simultaneously correct?

. Three
. Four
. Five
. Six
. Eight

Correct Answer & Explanation

. Six

Explanation

The Taylor Spatial Frame utilizes six variable-length struts connecting two circular rings, allowing simultaneous correction of deformity in all six degrees of freedom (angulation and translation in the coronal, sagittal, and axial planes).

Question 2873

Topic: 1. General Principles & Basic Science

During the preoperative planning for a severe tibial deformity, a resident places both the osteotomy and the hinge (axis of correction) distal to the calculated Center of Rotation of Angulation (CORA). According to Paley's Rule 3, what is the expected outcome of this configuration?

. Perfect collinear realignment of the anatomic axes
. Collinear axes with severe translation at the osteotomy site
. Angulation correction that results in a parallel translation of the anatomic axes (a zig-zag deformity)
. Complete correction of mechanical axis deviation with no effect on joint orientation
. Lengthening of the limb without any change in angular deformity

Correct Answer & Explanation

. Angulation correction that results in a parallel translation of the anatomic axes (a zig-zag deformity)

Explanation

Paley's Rule 3 dictates that if both the osteotomy and the hinge are placed away from the CORA, the proximal and distal anatomic axes will end up parallel to each other rather than collinear. This introduces a secondary translation or 'zig-zag' deformity.

Question 2874

Topic: 1. General Principles & Basic Science

A patient undergoing distraction osteogenesis for a post-traumatic tibial shortening presents to the clinic 4 weeks postoperatively. Radiographs show a distinct radiolucent gap at the distraction site with tapered, poorly mineralized bone ends (atrophic regenerate). Which of the following technical errors is most likely responsible for this complication?

. A distraction rate of 0.5 mm per day
. A distraction rate of 2.0 mm per day
. A latent period of 10 days before beginning distraction
. Performing a low-energy metaphyseal corticotomy
. Rigid stability provided by the external fixator

Correct Answer & Explanation

. A distraction rate of 2.0 mm per day

Explanation

Atrophic regenerate is typically caused by a distraction rate that is too rapid (e.g., 2.0 mm/day), which outpaces angiogenesis and osteogenesis. Conversely, a distraction rate that is too slow (e.g., <0.5 mm/day) typically results in premature consolidation.

Question 2875

Topic: 1. General Principles & Basic Science

A patient undergoes a distal femoral varus-producing osteotomy (DFO) for isolated lateral compartment osteoarthritis with a valgus knee. Assuming an accurate intraoperative correction, what is the anticipated effect on the Mechanical Axis Deviation (MAD)?

. It will shift the MAD from a lateral position to a central or slightly medial position
. It will shift the MAD further laterally to decompress the medial joint
. It will not alter the MAD, only the joint line convergence angle
. It will reverse the mechanical axis of the tibia
. It will create an iatrogenic patella baja

Correct Answer & Explanation

. It will shift the MAD from a lateral position to a central or slightly medial position

Explanation

A varus-producing distal femoral osteotomy is used to treat a valgus knee. By correcting the valgus, the mechanical axis (MAD) is shifted from the diseased lateral compartment toward the center or slightly into the medial compartment.

Question 2876

Topic: 1. General Principles & Basic Science

During the distraction osteogenesis process, what is the definition and physiologic purpose of the 'latent period'?

. The duration between fixator removal and full weight-bearing to allow cortical maturation
. The time between the surgical corticotomy and the initiation of distraction to allow early fibrovascular tissue and angiogenesis
. The pause taken between the distraction and consolidation phases
. The time taken to acutely correct an angular deformity before lengthening
. The delay in bone healing seen when the distraction rate exceeds 2.0 mm/day

Correct Answer & Explanation

. The time between the surgical corticotomy and the initiation of distraction to allow early fibrovascular tissue and angiogenesis

Explanation

The latent period is the time interval (typically 5-7 days) between the corticotomy and the start of distraction. It allows for the resolution of the acute inflammatory phase and the establishment of a robust fibrovascular network necessary for successful regenerate formation.

Question 2877

Topic: 1. General Principles & Basic Science

A 50-year-old male is recovering from a medial opening wedge high tibial osteotomy (HTO). Postoperative radiographs reveal that the patellar height has changed compared to the preoperative imaging. What is the most common effect of a standard medial opening wedge HTO proximal to the tibial tubercle on patellar height?

. Produces patella alta
. Produces patella baja (infera)
. Does not alter patellar height
. Shifts the patella laterally causing subluxation
. Increases the patellar tilt without changing vertical height

Correct Answer & Explanation

. Produces patella baja (infera)

Explanation

A medial opening wedge HTO performed proximal to the tibial tubercle elevates the joint line relative to the tibial tubercle. This effectively shortens the distance from the patella to the joint line, producing a relative patella baja (infera).

Question 2878

Topic: 1. General Principles & Basic Science

A 28-year-old patient presents with a pure angular valgus deformity of the proximal tibia, with the CORA precisely located at the metaphyseal apex of the deformity. The surgeon plans a corrective osteotomy and fixation with a circular external fixator. According to Paley's principles, which of the following approaches will achieve a perfect correction without creating any secondary translation?

. Perform the osteotomy 2 cm distal to the CORA and place the hinge at the CORA.
. Perform the osteotomy at the CORA and place the hinge 2 cm distal to the CORA.
. Perform the osteotomy at the CORA and place the hinge at the CORA.
. Perform the osteotomy 2 cm distal to the CORA and place the hinge 2 cm distal to the CORA.
. Perform the osteotomy at the CORA and apply a translational force during correction.

Correct Answer & Explanation

. Perform the osteotomy at the CORA and place the hinge at the CORA.

Explanation

Correct Answer: CThis scenario describes a pure angular deformity where the CORA is located at the apex of the deformity. According to Paley's Rule 1: 'If the osteotomy is performed at the CORA and the hinge is placed at the CORA, then angulation is perfectly corrected without creating any secondary translation.' This is the ideal, straightforward scenario for simple angular deformities, where the bone segments pivot around their natural geometric center, resulting in perfectly collinear proximal and distal anatomical axes.Options A, B, and D describe situations where either the osteotomy or the hinge (or both) are not at the CORA, which, according to Paley's Rule 3, would result in the creation of a new, secondary translation deformity (a 'residual bump'). Option E is incorrect because applying a translational force would be unnecessary and potentially detrimental in a pure angular deformity corrected according to Rule 1.

Question 2879

Topic: Surgical Anatomy & Approaches

A 60-year-old patient requires correction of a pure angular deformity in the tibia. The surgeon plans an osteotomy and places the Angulation Correction Axis (hinge) precisely at the CORA. According to Paley's Osteotomy Rules, what is the expected outcome of this surgical approach?

. The angulation will be corrected, but a new iatrogenic translation will be created.
. Both angulation and translation will occur at the osteotomy site, but the axes will become collinear.
. Pure angular correction will be achieved, with the proximal and distal anatomical axes becoming perfectly collinear and no induced translation.
. The deformity will be corrected, but a 'two-bump' problem will inevitably result.
. The osteotomy will fail to correct the angulation, requiring a secondary procedure.

Correct Answer & Explanation

. Pure angular correction will be achieved, with the proximal and distal anatomical axes becoming perfectly collinear and no induced translation.

Explanation

Correct Answer: CThis scenario perfectly describes Paley Osteotomy Rule One: 'The Pure Angular Correction'. The text states: 'Condition: The osteotomy is performed exactly AT the CORA, and the Angulation Correction Axis (hinge) is placed exactly AT the CORA. Result: Pure angular correction. The proximal and distal anatomical axes become perfectly collinear with no induced translation. Clinical Application: This is the ideal scenario for a pure angular deformity. By cutting at the apex and hinging at the apex, the bone straightens perfectly.'Option A is incorrectas this describes the outcome of Paley's Rule Three, where both the osteotomy and hinge are away from the CORA.Option B is incorrectas this describes the outcome of Paley's Rule Two, where the osteotomy is away from the CORA but the hinge is at the CORA.Option D is incorrectas the 'two-bump' problem is associated with strategies that correct angulation and then translate the bone at the osteotomy site, often when the osteotomy is not at the CORA or when dealing with angulation-translation deformities.Option E is incorrectas this rule describes a successful correction strategy for pure angular deformities.

Question 2880

Topic: 1. General Principles & Basic Science
A surgeon is planning to correct a complex angulation-translation deformity of the femur. The CORA is located in an area of poor soft tissue, making an osteotomy at that exact point undesirable. The surgeon decides to perform the osteotomy at a different level, away from the CORA, but still places the Angulation Correction Axis (hinge) precisely at the CORA. Which of Paley's Osteotomy Rules is being applied, and what is the expected outcome?
. Rule One: Pure angular correction with no induced translation.
. Rule Two: Both angulation and translation will occur at the osteotomy site, but the proximal and distal axes will become perfectly collinear.
. Rule Three: Angulation will be corrected, but a new iatrogenic translation deformity will be created.
. Rule One: A 'two-bump' problem will be created due to the osteotomy location.
. Rule Three: The deformity will be overcorrected, leading to a recurvatum deformity.

Correct Answer & Explanation

. Rule Two: Both angulation and translation will occur at the osteotomy site, but the proximal and distal axes will become perfectly collinear.

Explanation

Correct Answer: B. This scenario describes Paley Osteotomy Rule Two: 'The Strategic Correction'. The text states: 'Condition: The Angulation Correction Axis (hinge) is placed at the CORA, but the osteotomy is performed at a different level (either proximal or distal to the CORA). Result: The proximal and distal axes still become perfectly collinear. However, at the osteotomy site itself, both angulation and translation will occur. Clinical Application: This is the most powerful rule for treating angulation-translation deformities. By intentionally placing the osteotomy away from the angulation-translation CORA, the induced translation from Rule Two can be used to perfectly cancel out the pre-existing translation of the deformity.' Option A is incorrect as Rule One applies when both the osteotomy and hinge are at the CORA, resulting in pure angular correction without induced translation. Option C is incorrect as Rule Three applies when both the osteotomy and hinge are away from the CORA, resulting in iatrogenic translation. Option D is incorrect as the 'two-bump' problem is a consequence of certain strategies, not a direct result of Rule One, which aims for perfect collinearity. Option E is incorrect as Rule Three results in iatrogenic translation, not necessarily overcorrection or recurvatum.

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