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1. General Principles & Basic Science MCQs

Practice Set 135 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 2681

Topic: 1. General Principles & Basic Science
During a gradual fibular transport procedure using a circular external fixator, the surgeon is preparing to place the olive wire for capturing the proximal fibula. According to the Paley method, what is the critical aspect of this wire placement to ensure both effective transport and patient safety?
. The wire should be drilled from anteromedial to posterolateral, with the olive seated against the anteromedial cortex.
. The wire should be placed in the distal fibular diaphysis, away from the fibular head.
. The wire must be drilled from posterolateral to anteromedial through the fibular head, ensuring the olive is firmly seated against the posterolateral cortex, while carefully avoiding the common peroneal nerve.
. Multiple wires should be used to capture the fibular head to maximize stability and prevent rotation.
. The wire trajectory is not critical as long as it passes through the fibula, as the external fixator provides all necessary stability.

Correct Answer & Explanation

. The wire must be drilled from posterolateral to anteromedial through the fibular head, ensuring the olive is firmly seated against the posterolateral cortex, while carefully avoiding the common peroneal nerve.

Explanation

The case provides specific 'Surgical Pearl: Fibular Wire Placement' details: 'A single 1.8-mm olive wire is typically the workhorse for capturing and transporting the proximal fibula. It must be drilled from posterolateral to anteromedial directly through the fibular head, ensuring the 'olive' (stopper) is firmly seated against the posterolateral cortex of the fibula to allow for a distal pull. CRITICAL: The trajectory of this wire is paramount. It must be placed to avoid the common peroneal nerve, which runs posterior and distal to the wire's intended path.'

Question 2682

Topic: 1. General Principles & Basic Science

A 42-year-old patient presents with a varus knee deformity, a positive lateral thrust on gait analysis, and a JLCA of 5° on single-leg stance radiographs. The mLDFA is 87°, and the MPTA is 80°. Bilateral varus stress radiographs show 6mm of lateral joint space opening on the affected side compared to 2mm on the contralateral side. According to the Paley blueprint, what is the most appropriate surgical strategy?

. Perform a high tibial osteotomy (HTO) to achieve 8-10° of mechanical axis valgus overcorrection to offload the lateral compartment.
. Perform an acute fibular head advancement to tighten the LCL by 4mm, followed by a distal femoral osteotomy to correct the mLDFA.
. Perform a proximal tibial osteotomy to correct the MPTA to 87°, and simultaneously address the LCL laxity with a gradual fibular transport to normalize the JLCA.
. Perform an isolated LCL repair, as the mLDFA is normal, indicating no bony deformity requiring osteotomy.
. Perform a distal femoral osteotomy to correct the mLDFA to 87°, as the MPTA is within normal limits for a varus knee.

Correct Answer & Explanation

. Perform a proximal tibial osteotomy to correct the MPTA to 87°, and simultaneously address the LCL laxity with a gradual fibular transport to normalize the JLCA.

Explanation

Correct Answer: CThis question requires integrating multiple pieces of information from the case. The patient has a varus knee deformity (MPTA 80°, normal is 87°), LCL laxity (positive lateral thrust, JLCA 5° > 2°, 4mm asymmetric lateral joint space opening on stress views). The mLDFA is normal (87°).The Paley blueprint emphasizes a two-pronged attack: 'The preoperative plan must explicitly separate the pathology into two distinct problems that require two distinct solutions: 1. The Bony Deformity: This is corrected with a precisely calculated osteotomy (femoral, tibial, or both) to normalize the mLDFA and MPTA. 2. The Soft Tissue Deformity: This is corrected with a targeted ligamentous procedure to retension the lateral structures and normalize the JLCA.'Given the MPTA of 80° (normal 87°), a proximal tibial osteotomy is indicated to correct the bony deformity. Given the LCL laxity (lateral thrust, JLCA > 2°, asymmetric joint space opening), a ligamentous procedure is also required. The case strongly advocates for gradual fibular transport for LCL retensioning due to its safety and effectiveness, especially when combined with bony correction using the same fixator.Option A is incorrectbecause the case explicitly condemns the 'overcorrection fallacy' of intentionally creating valgus to compensate for LCL laxity, stating it is 'fundamentally flawed and should be abandoned.'Option B is incorrectbecause the mLDFA is normal (87°), so a distal femoral osteotomy is not indicated. Also, acute fibular head advancement has significant risks and limitations compared to gradual transport, and the amount of tightening should correspond to the joint space difference (4mm in this case), but the method itself is less preferred.Option D is incorrectbecause while the mLDFA is normal, the MPTA is 80°, indicating a significant tibial varus deformity that requires bony correction. An isolated LCL repair would not address the underlying bony malalignment.Option E is incorrectbecause the mLDFA is already normal (87°), so a distal femoral osteotomy is not indicated. The MPTA of 80° is abnormal and indicates a tibial deformity, not a normal value for a varus knee.

Question 2683

Topic: 1. General Principles & Basic Science

In the context of gradual fibular transport for LCL retensioning, the fibular osteotomy is performed in the proximal fibular diaphysis. What is the primary reason for choosing this specific location and technique for the osteotomy?

. To maximize the amount of acute fibular head advancement possible.
. To ensure the osteotomy is directly at the CORA of the fibula for optimal mechanical correction.
. To keep the osteotome safely away from the common peroneal nerve and minimize thermal necrosis for better regenerate formation.
. To facilitate rapid consolidation of the osteotomy site, preventing delayed union.
. To allow for simultaneous correction of the medial collateral ligament (MCL) laxity.

Correct Answer & Explanation

. To keep the osteotome safely away from the common peroneal nerve and minimize thermal necrosis for better regenerate formation.

Explanation

Correct Answer: CThe case details the 'Step 2: The Fibular Osteotomy' for gradual fibular transport: 'A low-energy osteotomy is performed in the proximal fibular diaphysis. This location is chosen specifically because it is well distal to the LCL and biceps femoris insertions, and it keeps the osteotome safely away from the common peroneal nerve as it wraps around the fibular neck.' It also advises: 'Avoid using a high-speed oscillating saw, which can cause thermal necrosis and impair bone healing (regenerate formation). Instead, utilize a multiple drill-hole technique along the planned osteotomy line... to ensure a complete, clean break of the periosteum and cortex without displacing the fragments.'Option A is incorrectbecause this technique is for gradual transport, not acute advancement, and the location is chosen for safety and healing, not to maximize acute movement.Option B is incorrectbecause the CORA method applies to the primary deformed bone (femur or tibia) for mechanical axis correction, not typically for the fibular osteotomy itself in this context. The fibular osteotomy is for ligamentous retensioning.Option D is incorrectbecause while bone healing is desired, the emphasis on low-energy technique is to prevent thermal necrosis andimpairmentof bone healing (regenerate formation), not necessarily to facilitate rapid consolidation beyond normal physiological rates.Option E is incorrectbecause fibular transport is specifically for LCL retensioning and lateral stability, not MCL laxity.

Question 2684

Topic: 1. General Principles & Basic Science

According to Paley's rules of deformity correction, if an osteotomy is performed outside the Center of Rotation of Angulation (CORA) and the mechanical axes are completely realigned, what is the expected outcome at the osteotomy site?

. Angulation without translation
. Translation of the bone segments
. Rotational deformity
. Significant limb shortening
. Loss of joint line congruity

Correct Answer & Explanation

. Translation of the bone segments

Explanation

Paley's Osteotomy Rule 2 dictates that if the osteotomy is at a different level than the CORA, the mechanical axes will only align if the bone ends translate relative to each other.

Question 2685

Topic: 1. General Principles & Basic Science

A 50-year-old patient with severe varus deformity has an mLDFA of 94 degrees and an MPTA of 81 degrees. The JLCA is 2 degrees. If an isolated high tibial osteotomy (HTO) is performed to completely correct the mechanical axis deviation, what is the most likely biomechanical consequence?

. Subluxation of the patellofemoral joint
. Unacceptable joint line obliquity
. Postoperative LCL laxity
. Overcorrection into valgus
. Limb length discrepancy greater than 3 cm

Correct Answer & Explanation

. Unacceptable joint line obliquity

Explanation

Correcting a combined femoral (mLDFA 94°) and tibial (MPTA 81°) varus deformity solely in the tibia creates an abnormal shear angle across the knee. This results in unacceptable joint line obliquity and accelerated articular wear.

Question 2686

Topic: 1. General Principles & Basic Science

During an anterior opening-wedge high tibial osteotomy for a varus knee, the surgeon must be mindful of changes to patellofemoral mechanics. How does an opening-wedge HTO proximal to the tibial tubercle typically affect patellar height?

. Increases patellar height (patella alta)
. Decreases patellar height (patella baja)
. No change in patellar height
. Translates the patella laterally
. Translates the patella medially

Correct Answer & Explanation

. Decreases patellar height (patella baja)

Explanation

An opening-wedge HTO proximal to the tibial tubercle lengthens the tibia distal to the joint line but does not alter the patellar tendon insertion, effectively lowering the patella relative to the joint line and causing patella baja.

Question 2687

Topic: 1. General Principles & Basic Science

When calculating the total angle of correction for a varus knee with documented LCL laxity (manifesting as a widened lateral JLCA on standing view), how should the surgeon determine the appropriate osteotomy wedge size?

. Based on MPTA deviation alone
. Based solely on the Mechanical Axis Deviation (MAD)
. The sum of the structural osseous deformity and the degree of abnormal JLCA
. Subtracting the JLCA from the MPTA
. Matching the contralateral knee's mLDFA

Correct Answer & Explanation

. The sum of the structural osseous deformity and the degree of abnormal JLCA

Explanation

To completely eliminate the dynamic varus thrust and restore alignment, the correction angle must account for both the bony structural deformity (MPTA) and the soft tissue laxity (abnormal JLCA component > 2°).

Question 2688

Topic: Physiology & Rehabilitation

A patient with a significant varus thrust and underlying LCL laxity during the stance phase of gait will most likely utilize which compensatory mechanism to reduce the knee adduction moment?

. Exaggerated hip flexion
. Contralateral pelvic drop
. Lateral trunk lean toward the affected side
. Medial trunk lean away from the affected side
. Circumduction gait pattern

Correct Answer & Explanation

. Lateral trunk lean toward the affected side

Explanation

A lateral trunk lean toward the affected side during the stance phase shifts the body's center of mass closer to the knee joint center. This decreases the external knee adduction moment, mitigating the varus thrust.

Question 2689

Topic: 1. General Principles & Basic Science

According to Paley's Rule 3 of deformity correction, what occurs if the osteotomy and axis of hinge are located outside the CORA, and the correction is achieved purely by angulation?

. The mechanical axis is fully restored without translation
. The mechanical axes remain parallel but translated
. A secondary translation deformity is created
. The limb undergoes substantial lengthening
. Joint line obliquity is perfectly corrected

Correct Answer & Explanation

. A secondary translation deformity is created

Explanation

Paley's Rule 3 states that if the osteotomy and axis of hinge are outside the CORA and correction is made by angulation alone, a secondary translation deformity arises, resulting in parallel but non-collinear mechanical axes.

Question 2690

Topic: 1. General Principles & Basic Science

A 45-year-old male presents with varus gonarthrosis and noticeable lateral thrust during gait. Weight-bearing radiographs reveal a joint line convergence angle (JLCA) of 8 degrees. According to the Paley Method, what is the normal range of the JLCA, and what does this patient's value signify?

. Normal is 0-2 degrees; the elevated value signifies significant lateral collateral ligament (LCL) laxity and intra-articular deformity.
. Normal is 3-5 degrees; the elevated value signifies medial collateral ligament contracture.
. Normal is 5-7 degrees; the elevated value represents a bony varus deformity of the proximal tibia.
. Normal is 0-2 degrees; the elevated value signifies severe patellofemoral osteoarthritis.
. Normal is -2 to 0 degrees; the elevated value indicates a primary distal femoral deformity.

Correct Answer & Explanation

. Normal is 0-2 degrees; the elevated value signifies significant lateral collateral ligament (LCL) laxity and intra-articular deformity.

Explanation

The normal JLCA ranges from 0 to 2 degrees. An elevated JLCA in a varus knee typically represents dynamic lateral joint opening due to lateral collateral ligament (LCL) laxity or significant cartilage loss.

Question 2691

Topic: 1. General Principles & Basic Science

According to the Paley Method of deformity correction, which of the following is the expected outcome if an osteotomy is performed exactly at the center of rotation of angulation (CORA) and the deformity is corrected by angulation alone?

. The proximal and distal mechanical axes will remain translated relative to one another.
. The proximal and distal mechanical axes will become perfectly collinear without translation.
. A secondary translational deformity will be induced at the osteotomy site.
. The joint line convergence angle (JLCA) will obligatorily increase.
. The osteotomy will require a closing wedge technique to prevent limb lengthening.

Correct Answer & Explanation

. The proximal and distal mechanical axes will become perfectly collinear without translation.

Explanation

Paley's Osteotomy Rule 1 states that if the osteotomy and the hinge (axis of correction) pass through the CORA, correction by angulation alone will realign the mechanical axes perfectly without translation. This prevents the creation of a secondary deformity.

Question 2692

Topic: Physiology & Rehabilitation

When analyzing the joint line convergence angle (JLCA) in a patient with a varus knee and a dynamic lateral thrust, what radiographic finding is most consistent with a significant soft-tissue (ligamentous) contribution to the overall varus deformity?

. A JLCA of 0 degrees on a weight-bearing AP view.
. A JLCA that is larger on a weight-bearing radiograph compared to a supine non-weight-bearing radiograph.
. A JLCA that decreases during the stance phase of gait.
. A JLCA that measures exactly 2 degrees on both stress and resting views.
. An abnormally high MPTA on the weight-bearing view.

Correct Answer & Explanation

. A JLCA that is larger on a weight-bearing radiograph compared to a supine non-weight-bearing radiograph.

Explanation

The normal JLCA is 0 to 2 degrees. In a varus knee with LCL laxity, weight-bearing forces open the lateral joint space, resulting in a larger JLCA on weight-bearing or varus stress views compared to supine views. This signifies a soft-tissue contribution to the varus.

Question 2693

Topic: 1. General Principles & Basic Science

A surgeon is planning a medial opening wedge high tibial osteotomy (HTO) for a varus knee. To avoid inadvertently increasing the posterior tibial slope, which of the following intraoperative gap ratios (anterior gap to posterior gap) is generally recommended?

. The anterior gap should be approximately equal to the posterior gap.
. The anterior gap should be approximately half the size of the posterior gap.
. The anterior gap should be approximately twice the size of the posterior gap.
. The anterior gap should be maximally opened while the posterior gap is kept closed.
. The anterior gap should be measured strictly from the tibial tubercle, regardless of the posterior gap.

Correct Answer & Explanation

. The anterior gap should be approximately half the size of the posterior gap.

Explanation

Because the proximal tibia is triangular in cross-section, opening the anterior cortex the same amount as the posterior cortex will inadvertently increase the posterior tibial slope. To maintain the native slope, the anterior opening should typically be about half the size of the posteromedial opening.

Question 2694

Topic: 1. General Principles & Basic Science

During preoperative planning for a patient with genu varum,

you determine the CORA is located in the proximal tibial metaphysis. If you perform an osteotomy outside the CORA, apply angulation, and intentionally translate the distal segment to realign the mechanical axes, which Paley Osteotomy Rule are you following?

. Rule 1
. Rule 2
. Rule 3
. Rule 4
. The Rule of Squares

Correct Answer & Explanation

. Rule 3

Explanation

Paley's Osteotomy Rule 3 states that if the osteotomy is performed at a level independent of the CORA, correction requires both angulation and translation to make the proximal and distal mechanical axes collinear. This avoids the secondary translational deformity seen in Rule 2.

Question 2695

Topic: Physiology & Rehabilitation

A patient with a varus knee and a documented dynamic lateral thrust is scheduled for surgery. The surgeon performs a medial opening wedge high tibial osteotomy (HTO). How does this bony correction primarily address the patient's chronic lateral soft-tissue laxity?

. By functionally shortening the LCL through proximal displacement of the fibular head.
. By shifting the weight-bearing line laterally, which persistently tensions the LCL during the stance phase.
. By allowing scarring of the iliotibial band into the medial joint space.
. By directly imbricating the lateral soft tissues via a lateral hinge.
. Bony correction cannot address lateral laxity; simultaneous LCL reconstruction is always required.

Correct Answer & Explanation

. By shifting the weight-bearing line laterally, which persistently tensions the LCL during the stance phase.

Explanation

Creating a mechanical valgus alignment shifts the weight-bearing forces laterally. During the stance phase of gait, this alignment dynamically tensions the lateral structures (including the stretched LCL) and eliminates the lateral varus thrust, making LCL reconstruction unnecessary in most cases.

Question 2696

Topic: 1. General Principles & Basic Science

In the assessment of normal lower limb alignment, what is the expected relationship between the mechanical axis of the femur and the anatomical axis of the femur?

. They are perfectly collinear.
. The mechanical axis is in approximately 5 to 7 degrees of valgus relative to the anatomical axis.
. The anatomical axis is in approximately 5 to 7 degrees of valgus relative to the mechanical axis.
. The anatomical axis diverges 10 degrees medially relative to the mechanical axis.
. They intersect precisely at the lesser trochanter.

Correct Answer & Explanation

. The mechanical axis is in approximately 5 to 7 degrees of valgus relative to the anatomical axis.

Explanation

The mechanical axis of the femur (center of femoral head to center of knee) and the anatomical axis of the femur (down the medullary canal) typically diverge by about 5 to 7 degrees, with the anatomical axis being in valgus relative to the mechanical axis.

Question 2697

Topic: 1. General Principles & Basic Science

An orthopaedic surgeon evaluates a 60-year-old patient with right knee pain, a varus thrust, and LCL laxity.

To definitively assess whether the deformity is purely intra-articular (soft tissue or cartilage loss) versus extra-articular (bony), which specific angle must be calculated on the full-length radiograph?

. Mechanical lateral distal femoral angle (mLDFA)
. Medial proximal tibial angle (MPTA)
. Anatomical tibiofemoral angle (aTFA)
. Joint line convergence angle (JLCA)
. Posterior proximal tibial angle (PPTA)

Correct Answer & Explanation

. Joint line convergence angle (JLCA)

Explanation

The joint line convergence angle (JLCA) quantifies the intra-articular contribution to deformity (due to asymmetric cartilage loss or ligamentous laxity). The mLDFA and MPTA evaluate extra-articular bony deformities.

Question 2698

Topic: Biomechanics & Biomaterials

Following a medial opening wedge high tibial osteotomy to correct a severe varus deformity, the patient exhibits persistent knee extension lag and complains of anterior knee pain. What intraoperative technical error is most likely responsible for this complication?

. Overcorrection of the mechanical axis into 4 degrees of valgus.
. Failure to release the superficial medial collateral ligament distally.
. Distalization of the tibial tubercle leading to patella baja.
. Inadvertent lateral cortical hinge fracture.
. Use of a gap ratio that increased the posterior tibial slope.

Correct Answer & Explanation

. Distalization of the tibial tubercle leading to patella baja.

Explanation

A medial opening wedge HTO elongates the proximal tibia. If the osteotomy is proximal to the tibial tubercle, it relative distalizes the patella, creating patella baja. This alters patellofemoral kinematics, often leading to anterior knee pain and extensor lag.

Question 2699

Topic: 1. General Principles & Basic Science

When calculating the Mechanical Axis Deviation (MAD) on a standing full-length AP radiograph, a measurement of 15 mm lateral to the center of the knee joint indicates which of the following?

. Normal alignment.
. A pathologic varus deformity.
. A physiologic varus alignment.
. A valgus deformity.
. A completely collapsed medial compartment.

Correct Answer & Explanation

. A pathologic varus deformity.

Explanation

MAD measures the distance from the mechanical axis of the lower extremity to the center of the knee. A line passing medial to the knee center indicates varus, whereas a line passing lateral to the knee center indicates valgus.

Question 2700

Topic: 1. General Principles & Basic Science

A surgeon is performing a lateral closing wedge high tibial osteotomy. To safely protect the peroneal nerve during the proximal fibular osteotomy and lateral tibial cortex resection, what is the most critical anatomical relationship to respect?

. The nerve wraps around the fibular neck approximately 2 to 3 cm distal to the fibular head.
. The nerve travels anterior to the anterior tibial artery at the level of the joint line.
. The nerve lies directly medial to the medial collateral ligament.
. The nerve bifurcates proximal to the biceps femoris tendon insertion.
. The nerve courses directly posterior to the popliteus muscle.

Correct Answer & Explanation

. The nerve wraps around the fibular neck approximately 2 to 3 cm distal to the fibular head.

Explanation

The common peroneal nerve is highly vulnerable during a lateral closing wedge HTO, particularly during the required fibular osteotomy. It courses directly over the fibular neck, typically 2 to 3 cm distal to the tip of the fibular head, and must be carefully protected.

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