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1. General Principles & Basic Science MCQs

Practice Set 462 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 9221

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity correction, what is the expected result when both the osteotomy and the hinge axis are placed exactly at the Center of Rotation of Angulation (CORA)?

. Pure translation without angulation
. Angulation with a secondary translational deformity
. Pure angulation without translation
. Angulation combined with inherent limb shortening
. Pure length change without axis correction

Correct Answer & Explanation

. Pure angulation without translation

Explanation

Paley's Rule 1 states that when the osteotomy and the hinge axis are both located at the CORA, pure angulation occurs without translation. This completely realigns the proximal and distal anatomical axes collinearly.

Question 9222

Topic: 1. General Principles & Basic Science

A patient with severe genu varum presents with a Mechanical Axis Deviation (MAD) measuring 30 mm medial to the center of the knee. What is the expected biomechanical consequence in the knee joint?

. Increased tensile forces on the medial collateral ligament
. Shift of compressive loads primarily to the lateral compartment
. Increased contact pressures in the medial compartment
. Uniform distribution of forces across the knee joint
. Decreased strain on the lateral collateral ligament

Correct Answer & Explanation

. Increased contact pressures in the medial compartment

Explanation

A medial shift of the mechanical axis creates a varus moment, increasing the compressive loads and contact pressures in the medial compartment. This leads to premature medial compartment osteoarthritis and increased tensile strain on the lateral collateral structures.

Question 9223

Topic: 1. General Principles & Basic Science

A 45-year-old male undergoes a medial opening wedge high tibial osteotomy (HTO) for medial compartment arthritis. Postoperatively, what predictable biomechanical change regarding the extensor mechanism is most likely to occur?

. Patella alta
. Patella baja (infera)
. Increased Q-angle
. Anterior subluxation of the tibia
. Decreased retropatellar contact pressures

Correct Answer & Explanation

. Patella baja (infera)

Explanation

Medial opening wedge HTO predictably decreases patellar height, leading to patella baja (infera). This occurs because the osteotomy is typically proximal to the tibial tubercle, elevating it relative to the joint line as the wedge is opened.

Question 9224

Topic: Biology, Genetics & Bone Healing

When planning a deformity correction using an external fixator for distraction osteogenesis, a latency period of 7 to 10 days is typically observed. What is the primary biological purpose of this phase?

. To allow rigid consolidation of the osteotomy site
. To permit the initial inflammatory phase and soft callus formation
. To completely eliminate the risk of pin tract infections
. To allow the periosteum to completely detach from the cortex
. To promote immediate cortical bridging prior to distraction

Correct Answer & Explanation

. To permit the initial inflammatory phase and soft callus formation

Explanation

The 7-10 day latency period allows for the resolution of acute inflammation and the initiation of soft callus formation with mesenchymal stem cell aggregation. Immediate distraction disrupts this vital early phase, leading to poor regenerate bone formation.

Question 9225

Topic: 1. General Principles & Basic Science

A surgeon plans an osteotomy for a diaphyseal tibial deformity. The osteotomy is performed proximal to the CORA due to poor soft tissues, but the hinge of the frame is placed exactly on the CORA. According to Paley's rules, what is the expected outcome?

. Pure angulation without translation
. Angulation with a translational deformity (iatrogenic translation)
. Collinear alignment of the axes with an expected translation at the osteotomy site
. Pure translation without angulation
. Complete failure of axis correction

Correct Answer & Explanation

. Angulation with a translational deformity (iatrogenic translation)

Explanation

Paley's Rule 2 dictates that if the hinge is at the CORA but the osteotomy is at a different level, the mechanical axes will realign collinearly. However, the bone ends will undergo translation at the osteotomy site, which must be planned for to maintain bone contact.

Question 9226

Topic: 1. General Principles & Basic Science

According to the principles of lower limb deformity correction, if an osteotomy is performed exactly at the Center of Rotation of Angulation (CORA) and the mechanical axis lines are aligned around a hinge at this same location, what is the biomechanical outcome?

. Correction of angulation with secondary translation
. Correction of angulation without translation
. Correction of translation without angulation
. Creation of a secondary deformity in the coronal plane
. Leg lengthening without angular correction

Correct Answer & Explanation

. Correction of angulation without translation

Explanation

Paley's Osteotomy Rule 1 states that when the osteotomy and the hinge (axis of correction) are both placed at the CORA, angulation is perfectly corrected without translation of the bone segments.

Question 9227

Topic: Biology, Genetics & Bone Healing

During gradual distraction osteogenesis for lower limb lengthening, what is the primary mode of bone formation observed within the distraction gap?

. Endochondral ossification
. Intramembranous ossification
. Appositional ossification
. Creeping substitution
. Enchondral sequence

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Bone formation during classic distraction osteogenesis (Ilizarov technique) occurs primarily via intramembranous ossification. This process requires stable fixation, proper latency, and an appropriate distraction rhythm.

Question 9228

Topic: 1. General Principles & Basic Science

A patient undergoes a medial opening-wedge high tibial osteotomy (HTO) for varus gonarthrosis. How does this procedure typically affect patellar height and posterior tibial slope if the anterior gap is opened the exact same amount as the posterior gap?

. Increases patellar height and decreases posterior slope
. Decreases patellar height (patella baja) and increases posterior slope
. Increases patellar height and increases posterior slope
. Decreases patellar height and decreases posterior slope
. No effect on either parameter

Correct Answer & Explanation

. Decreases patellar height (patella baja) and increases posterior slope

Explanation

A medial opening wedge HTO classically decreases patellar height relative to the joint line (patella baja). Because the proximal tibia has a triangular shape, opening the anterior and posterior gaps equally will inadvertently increase the posterior tibial slope.

Question 9229

Topic: 1. General Principles & Basic Science

According to Paley's first rule of osteotomy for lower limb deformity, if the osteotomy is performed exactly at the Center of Rotation of Angulation (CORA) and the correction hinge is placed on the transverse bisector line, what is the geometric result?

. Correction of angulation without translation
. Correction of angulation with expected translation
. Creation of a secondary compensatory deformity angle
. Pure translation without angular correction
. Mechanical axis deviation to the lateral compartment

Correct Answer & Explanation

. Correction of angulation without translation

Explanation

Osteotomy Rule 1 states that an osteotomy through the CORA with the hinge on the bisector line results in pure angular correction without translation. The anatomical and mechanical axes are realigned perfectly.

Question 9230

Topic: 1. General Principles & Basic Science

A surgeon applies Osteotomy Rule 2 for a proximal tibial deformity. The osteotomy is performed at a level distinct from the CORA, but the hinge is maintained on the bisector line of the CORA. What is the expected outcome of this correction?

. Pure angulation with no translation
. Correction of the angular deformity accompanied by translation at the osteotomy site
. Incomplete correction of the mechanical axis
. Creation of an intentional new CORA at the osteotomy site
. Failure to achieve bony apposition, requiring massive bone grafting

Correct Answer & Explanation

. Correction of the angular deformity accompanied by translation at the osteotomy site

Explanation

Osteotomy Rule 2 dictates that if the osteotomy is outside the CORA but the hinge remains on the bisector line, the mechanical axis will be completely corrected. However, this is achieved at the expense of translation at the osteotomy site.

Question 9231

Topic: 1. General Principles & Basic Science

In a skeletally mature adult with normal coronal alignment, where does the mechanical axis of the lower extremity (Mikulicz line) typically pass in relation to the center of the knee joint?

. Exactly through the center of the intercondylar notch
. 8 to 10 mm medial to the center of the knee joint
. 8 to 10 mm lateral to the center of the knee joint
. Through the lateral compartment
. Directly through the medial collateral ligament

Correct Answer & Explanation

. 8 to 10 mm medial to the center of the knee joint

Explanation

The normal mechanical axis of the lower limb passes slightly medial (approximately 8-10 mm) to the geometric center of the knee. This contributes to a naturally higher load-sharing ratio in the medial compartment.

Question 9232

Topic: 1. General Principles & Basic Science

During preoperative planning for a varus distal femoral deformity, the surgeon measures the mechanical lateral distal femoral angle (mLDFA). What is the accepted normal population average for the mLDFA?

. 81 degrees
. 87 degrees
. 93 degrees
. 99 degrees
. 105 degrees

Correct Answer & Explanation

. 87 degrees

Explanation

The normal mechanical lateral distal femoral angle (mLDFA) is 87 degrees, with a typical range of 85 to 90 degrees. Deviations from this indicate a distal femoral coronal plane deformity.

Question 9233

Topic: Biology, Genetics & Bone Healing

A 25-year-old male undergoing tibial distraction osteogenesis at a rate of 1 mm/day is noted on 4-week follow-up radiographs to have premature consolidation of the regenerate. What is the most appropriate next step in management?

. Increase the distraction rate to 2 mm/day
. Administer systemic bisphosphonates to inhibit osteoblasts
. Return to the operating room for re-osteotomy
. Decrease the distraction rate to 0.25 mm/day
. Apply localized extracorporeal shockwave therapy

Correct Answer & Explanation

. Return to the operating room for re-osteotomy

Explanation

Premature consolidation occurs when the rate of bone formation outpaces the distraction rate. Once consolidation bridges the gap, closed distraction is impossible, and surgical re-osteotomy is required.

Question 9234

Topic: Biology, Genetics & Bone Healing

When performing a diaphyseal tibial corticotomy for Ilizarov distraction osteogenesis in an adult, what is the standard recommended latency period before initiating distraction?

. 0 to 1 days
. 2 to 3 days
. 7 to 10 days
. 14 to 21 days
. 28 days

Correct Answer & Explanation

. 7 to 10 days

Explanation

A latency period of 7 to 10 days is optimal for diaphyseal distraction in adults. This allows for initial fracture hematoma organization and the beginning of the soft callus phase prior to applying tension.

Question 9235

Topic: 1. General Principles & Basic Science

A surgeon is performing a medial opening-wedge high tibial osteotomy (HTO). If the anterior aspect of the osteotomy gap is inadvertently opened wider than the posterior aspect, what is the biomechanical consequence on the sagittal alignment?

. Decreased posterior tibial slope
. Increased posterior tibial slope
. Unintended patella alta
. Posterior translation of the mechanical axis
. Direct injury to the posterior cruciate ligament

Correct Answer & Explanation

. Increased posterior tibial slope

Explanation

The normal proximal tibia slopes inferiorly from anterior to posterior. Opening the anterior gap more than the posterior gap tilts the articular surface further posteriorly, increasing the posterior tibial slope.

Question 9236

Topic: Physiology & Rehabilitation

During normal human gait, the joint reaction force across the knee is highest during which specific phase?

. Heel strike (Initial contact)
. Single-limb support (Mid-stance)
. Toe-off (Preswing)
. Mid-swing
. Terminal swing

Correct Answer & Explanation

. Single-limb support (Mid-stance)

Explanation

The knee joint reaction force peaks during the stance phase, specifically at single-limb support (mid-stance), where it can reach approximately 3 times body weight due to muscle contraction and body mass.

Question 9237

Topic: 1. General Principles & Basic Science

According to Paley's Rule 3, if a corrective osteotomy is performed outside the CORA and the hinge is placed at the osteotomy site rather than on the bisector line, what is the geometric consequence?

. Complete correction of both angulation and translation
. Correction of translation without affecting the angular deformity
. Correction of the angular deformity with creation of a new translation deformity (MAD)
. Perfect realignment of the mechanical axis with leg lengthening
. Failure to alter the anatomic axis

Correct Answer & Explanation

. Correction of the angular deformity with creation of a new translation deformity (MAD)

Explanation

Osteotomy Rule 3 dictates that placing the hinge at an osteotomy site that is outside the CORA will correct the angulation but simultaneously create a new translation deformity, resulting in persistent mechanical axis deviation.

Question 9238

Topic: 1. General Principles & Basic Science

When planning a deformity correction, an osteotomy is performed at a level different from the center of rotation of angulation (CORA), but the mechanical axis is realigned. According to Paley's rules of osteotomy, what is the expected outcome at the osteotomy site?

. No translation occurs
. Pure rotation occurs
. Translation occurs
. A secondary angular deformity is induced
. The joint line convergence angle increases

Correct Answer & Explanation

. Translation occurs

Explanation

According to Paley's Rule 2, if the osteotomy is performed at a level different from the CORA but the hinge is placed at the CORA, the mechanical axis is restored but translation will occur at the osteotomy site.

Question 9239

Topic: 1. General Principles & Basic Science

During tibial lengthening using distraction osteogenesis, the standard protocol involves a distraction rate of 1 mm per day. If serial radiographs reveal premature consolidation of the regenerate, which modification is most appropriate?

. Increase the distraction rate to 1.5 mm/day
. Decrease the distraction rate to 0.5 mm/day
. Change the rhythm to 0.25 mm once daily
. Stop distraction and perform bone grafting
. Compress the site by 2 mm then resume 1 mm/day

Correct Answer & Explanation

. Increase the distraction rate to 1.5 mm/day

Explanation

Premature consolidation indicates the bone is mineralizing faster than the distraction gap is widening. Increasing the distraction rate temporarily (e.g., to 1.5 mm/day) helps overcome rapid mineralization before the gap fully fuses.

Question 9240

Topic: 1. General Principles & Basic Science

The Taylor Spatial Frame (TSF) utilizes the principles of a Stewart platform to correct complex multiplanar deformities. How many degrees of freedom does this hexapod system allow for simultaneous correction?

. 3
. 4
. 5
. 6
. 8

Correct Answer & Explanation

. 6

Explanation

The hexapod configuration of the TSF acts as a Stewart platform, permitting simultaneous correction in all 6 degrees of freedom (translation and rotation along the x, y, and z axes).

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