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1. General Principles & Basic Science MCQs

Practice Set 114 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 2261

Topic: Surgical Anatomy & Approaches

A surgeon is planning to correct a complex, multi-apical femoral deformity involving both diaphyseal varus and distal metaphyseal valgus, along with significant procurvatum. Due to time constraints and a desire to minimize surgical invasiveness, the surgeon decides to perform a single osteotomy at the mid-diaphysis, attempting to correct all frontal and sagittal plane deformities simultaneously by angulating the bone around this single cut. Based on Paley's Three Osteotomy Rules, what is the most likely outcome of this surgical approach?

. The deformity will be perfectly corrected with pure angulation, as long as the osteotomy is performed at the single, global CORA.
. The deformity will be corrected by a combination of angulation and translation, resulting in a stable, flush bone-to-bone interface.
. The original angular deformity will be traded for a massive translational deformity, and the mechanical axis will remain malaligned, leading to biomechanical failure.
. The bone ends will align flush, but the limb will experience significant shortening due to the acute correction.
. The correction will be stable, but the patient will experience increased pain due to the creation of a new, iatrogenic rotational deformity.

Correct Answer & Explanation

. The original angular deformity will be traded for a massive translational deformity, and the mechanical axis will remain malaligned, leading to biomechanical failure.

Explanation

Correct Answer: CThe scenario described is a direct violation of Paley's Osteotomy Rule Three. The case explicitly states that a multi-apical deformity (like the described femoral diaphyseal varus and distal metaphyseal valgus, plus procurvatum) has multiple distinct CORAs. Attempting to correct such a deformity with a single osteotomy performedawayfrom all individual CORAs, and then angulating around an axis of correction alsoawayfrom the true CORAs, will inevitably lead to the creation of a new, iatrogenic deformity. This results in a massive translational step-off, malalignment of the mechanical axis, and biomechanical failure, as the original angular deformity is simply traded for a translational one. This is described as a 'catastrophic surgical error' in the text.Option A is incorrect because a multi-apical deformity does not have a single, global CORA that can perfectly correct all apices with one cut. Option B describes Paley's Rule Two, which applies when the osteotomy is away from the CORA but the axis of correction isatthe CORA, leading to controlled translation. This is not the scenario described. Option D is incorrect; while some shortening can occur with acute corrections, the primary issue with violating Rule Three is malalignment and translation, not necessarily just shortening. Option E introduces a rotational deformity, which is not the primary consequence described for violating Paley's Rule Three in this context.

Question 2262

Topic: 1. General Principles & Basic Science

A 30-year-old male presents with knee pain and a 'knock-kneed' appearance. Radiographic analysis reveals a Mechanical Lateral Distal Femoral Angle (mLDFA) of 80° and a Medial Proximal Tibial Angle (MPTA) of 95°. The Joint Line Convergence Angle (JLCA) is 1°. Based on these measurements and Paley's principles, what is the most accurate interpretation of this patient's frontal plane alignment?

. The patient has a combined femoral varus and tibial varus deformity, with significant intra-articular pathology.
. The patient has a combined femoral valgus and tibial valgus deformity, with normal joint space.
. The patient has isolated distal femoral varus, with compensatory proximal tibial valgus.
. The patient has isolated proximal tibial varus, with compensatory distal femoral valgus.
. The patient has a normal mLDFA and MPTA, indicating that the 'knock-kneed' appearance is due to soft tissue laxity only.

Correct Answer & Explanation

. The patient has a combined femoral valgus and tibial valgus deformity, with normal joint space.

Explanation

Correct Answer: BAccording to the provided table of Joint Orientation Angles:mLDFA:Normal range is 85° to 90° (Avg 87°). A value <87° indicates femoral valgus. This patient's mLDFA of 80° indicates significant femoral valgus.MPTA:Normal range is 85° to 90° (Avg 87°). A value >87° indicates tibial valgus. This patient's MPTA of 95° indicates significant tibial valgus.JLCA:Normal range is 0° to 2°. This patient's JLCA of 1° is within the normal range, suggesting no significant intra-articular pathology, cartilage loss, or ligamentous laxity contributing to the angular deformity.Therefore, the patient has a combined femoral valgus and tibial valgus deformity, with a normal joint space (JLCA). This combination would result in a 'knock-kneed' (genu valgum) appearance.Option A is incorrect as both angles indicate valgus, not varus. Option C and D are incorrect as both femur and tibia contribute to the valgus deformity, not isolated or compensatory. Option E is incorrect as both mLDFA and MPTA are outside their normal ranges, indicating bony deformity, not just soft tissue laxity.

Question 2263

Topic: Infection, Pharmacology & VTE

In the management of a patient with a profoundly complex, multi-apical femoral deformity and a complex tibial deformity, the surgical team decides to stage the procedures, addressing the femur first and the tibia in a secondary operation several weeks later. Which of the following is the *most critical* advantage of this staged approach, particularly in a patient with compromised osteoporotic bone stock?

. It allows for immediate weight-bearing on the corrected femur, accelerating rehabilitation.
. It provides the surgeon an opportunity to dynamically adjust the subsequent tibial plan based on the femoral correction's outcome.
. It significantly reduces the overall cost of the surgical intervention by minimizing implant usage in a single setting.
. It completely eliminates the risk of systemic complications such as DVT and PE.
. It ensures that the patient's cosmetic outcome is prioritized over functional restoration.

Correct Answer & Explanation

. It provides the surgeon an opportunity to dynamically adjust the subsequent tibial plan based on the femoral correction's outcome.

Explanation

Correct Answer: BThe case highlights several critical advantages of staging procedures. While physiological tolerance and complication mitigation are important, the text specifically mentions: 'Intraoperative Adjustment: Provides the surgeon an opportunity to assess the clinical and radiographic outcome of the initial correction. If the femoral correction slightly alters the global limb length or mechanical axis unexpectedly, the subsequent tibial plan can be dynamically adjusted to compensate.' This ability to fine-tune the overall limb alignment based on the first stage's outcome is a paramount advantage in complex, multi-level corrections.Option A is incorrect; while early mobilization is a goal, immediate full weight-bearing after multi-level osteotomies in osteoporotic bone is unlikely and not the primary reason for staging. Option C is incorrect; staging procedures often increases overall costs due to multiple hospitalizations and anesthetic events. Option D is incorrect; staging reduces theriskof complications but does noteliminatethem. Option E is incorrect; functional restoration and biomechanical alignment are the primary goals, with cosmesis being a secondary benefit.

Question 2264

Topic: 1. General Principles & Basic Science

A surgeon is planning a proximal tibial osteotomy for a patient with significant tibial valgus and recurvatum, complicated by poor bone stock. The goal is to achieve simultaneous multiplanar correction with minimal limb length change and maximal bone-on-bone healing surface. Which osteotomy technique, as described in the case, is best suited for this scenario?

. A medial opening wedge osteotomy, requiring a structural bone graft to fill the void.
. A lateral closing wedge osteotomy, which shortens the limb and sacrifices bone stock.
. A focal dome osteotomy, centered on the CORA, allowing multiplanar correction with a large congruent healing surface.
. A transverse diaphyseal osteotomy, followed by gradual distraction with an external fixator.
. A simple oblique osteotomy, relying on soft tissue tension for stability and correction.

Correct Answer & Explanation

. A focal dome osteotomy, centered on the CORA, allowing multiplanar correction with a large congruent healing surface.

Explanation

Correct Answer: CThe case specifically advocates for the focal dome osteotomy in complex cases like the proximal tibia with valgus and recurvatum, especially in osteoporotic bone. It states: 'A curvilinear, cylindrical cut centered exactly on the CORA. It allows for massive, multiplanar angular correction (e.g., simultaneous varus and flexion) with minimal to no change in overall limb length. Most importantly, it creates a large, highly congruent, bone-on-bone surface area for healing. This maximizes intrinsic stability and biological healing potential.'Option A (opening wedge) is less ideal in poor bone stock due to the need for grafting and increased soft tissue tension. Option B (closing wedge) sacrifices bone stock and shortens the limb, which may not be desired, and is less versatile for multiplanar correction. Option D (transverse diaphyseal osteotomy for distraction) is primarily for lengthening, not necessarily for acute multiplanar angular correction with maximal bone contact. Option E (simple oblique osteotomy) lacks the precision, stability, and multiplanar correction capabilities of a dome osteotomy and would be unstable.

Question 2265

Topic: Biomechanics & Biomaterials

A 60-year-old patient with osteoporotic bone stock requires a complex tibial realignment using an external fixator, as depicted in the clinical image below. To maximize pin purchase and minimize the risk of pin loosening or bone failure in this compromised bone, which of the following external fixation pearls is most critical?

. Using standard stainless steel half-pins to ensure maximum rigidity.
. Relying solely on fine wires for all fixation, as they are less invasive.
. Utilizing hydroxyapatite (HA) coated half-pins to increase bone-to-pin integration.
. Mounting the external fixator rings obliquely to the bone segments to allow for greater adjustability.
. Performing daily pin site care with hydrogen peroxide to aggressively sterilize the sites.

Correct Answer & Explanation

. Utilizing hydroxyapatite (HA) coated half-pins to increase bone-to-pin integration.

Explanation

Correct Answer: CThe case provides specific 'Surgical Pearls: External Fixation in Osteoporotic Bone.' It states: 'Always use hydroxyapatite (HA) coated half-pins. HA coating significantly increases bone-to-pin integration, drastically improving purchase and pull-out strength in weak, osteoporotic bone.' This directly addresses the challenge of osteoporotic bone stock.Option A is incorrect; standard stainless steel pins have less bone integration than HA-coated pins, making them less ideal in osteoporotic bone. Option B is partially correct in that tensioned fine wires are excellent for metaphyseal fixation in osteoporotic bone, but the question asks about maximizingpinpurchase, and half-pins are also used. Relyingsolelyon fine wires for all fixation might not be appropriate for all segments or constructs. Option D is incorrect; the text explicitly warns against this: 'If mounted obliquely, any subsequent distraction or adjustment will introduce iatrogenic translational forces.' Option E is incorrect; while meticulous daily pin site care is paramount, the text does not specify hydrogen peroxide, and aggressive sterilization can sometimes be detrimental to healing. The focus here is on thehardware choicefor osteoporotic bone.

Question 2266

Topic: 1. General Principles & Basic Science

A 55-year-old patient with a history of Paget's disease presents with a complex, multiapical femoral deformity. Preoperative planning is initiated. According to the foundational principles of deformity planning outlined in the case, what are the two overarching, non-negotiable goals of surgical correction for this patient?

. To achieve a Mechanical Axis Deviation (MAD) of exactly zero millimeters and ensure weight-bearing joints are parallel to the ground.
. To perform the osteotomy precisely at the Center of Rotation of Angulation (CORA) and use an intramedullary nail.
. To minimize surgical time and reduce blood loss during the procedure.
. To restore the bone's original length and prevent any rotational malalignment.
. To eliminate all pain and restore full range of motion in adjacent joints.

Correct Answer & Explanation

. To achieve a Mechanical Axis Deviation (MAD) of exactly zero millimeters and ensure weight-bearing joints are parallel to the ground.

Explanation

Correct Answer: AThe case explicitly states: 'The overarching goal of deformity correction is twofold: 1. To normalize the overall limb alignment, which is mathematically represented by the Mechanical Axis Deviation (MAD). 2. To ensure that the weight-bearing joints are perfectly parallel to the ground during the stance phase of gait, represented by the Joint Orientation Angles.'Option B is incorrectbecause while identifying the CORA and using an IM nail are crucialmethodsin modern correction, they are not the overarchinggoalsthemselves. The CORA dictates osteotomy placement to achieve the goals of alignment.Option C is incorrectbecause minimizing surgical time and blood loss are general surgical principles, not the specific, primary biomechanical goals of deformity correction.Option D is incorrectbecause while restoring length and preventing rotational malalignment are important aspects of a complete correction, they are sub-goals that contribute to the primary goals of MAD and joint orientation, which encompass overall limb alignment.Option E is incorrectbecause while pain relief and improved range of motion are desired clinical outcomes, they are not the direct, measurable biomechanical goals of deformity correction as defined in the text.

Question 2267

Topic: 1. General Principles & Basic Science

The case emphasizes that rigorous, exhaustive geometric analysis is paramount before surgery. Which of the following statements best encapsulates the fundamental reason why this meticulous preoperative planning is considered 'non-negotiable' for complex lower extremity deformities?

. To determine the patient's eligibility for insurance coverage for the procedure.
. To minimize the duration of the patient's hospital stay post-surgery.
. To definitively identify the Center of Rotation of Angulation (CORA) and predict the geometric outcome of correction, serving as the blueprint for surgical success.
. To select the appropriate antibiotic prophylaxis regimen for the patient.
. To educate the patient about the potential cosmetic benefits of the surgery.

Correct Answer & Explanation

. To definitively identify the Center of Rotation of Angulation (CORA) and predict the geometric outcome of correction, serving as the blueprint for surgical success.

Explanation

Correct Answer: CThe case states: 'Before a single scalpel is lifted or a single incision is made, a rigorous, exhaustive geometric analysis of the patient's deformity is absolutely paramount. This is not merely an academic exercise to be glossed over; it is the definitive blueprint for surgical success.' It further emphasizes: 'Identifying the CORA is non-negotiable. It dictates the ideal biomechanical location for the osteotomy and defines the exact pivot point around which the bone segments must be manipulated to restore a straight, collinear axis.'Option A is incorrectbecause insurance eligibility is an administrative concern, not a surgical planning principle.Option B is incorrectbecause while good planning can contribute to a smoother recovery, minimizing hospital stay is a secondary outcome, not the fundamental reason for geometric analysis.Option D is incorrectbecause antibiotic prophylaxis is a standard perioperative measure, unrelated to geometric deformity analysis.Option E is incorrectbecause patient education, including cosmetic benefits, is important, but it is not the fundamental reason for the detailed geometric analysis that dictates surgical execution.

Question 2268

Topic: Surgical Anatomy & Approaches

A surgeon is planning a distal femoral osteotomy for a patient with a valgus deformity. Preoperative planning identifies the Center of Rotation of Angulation (CORA) at the junction of the distal metaphysis and diaphysis. The surgeon decides to perform a focal dome osteotomy precisely at the CORA and uses an external fixator as a temporary reduction tool, with its hinge axis also passing through the CORA. During the procedure, the deformity is acutely corrected. According to Paley's Three Laws of Osteotomy, what is the expected outcome of this surgical approach?

. Angulation with intentional translation, as the osteotomy is metaphyseal.
. Pure angular correction without any translation or change in limb length.
. Iatrogenic translation deformity due to the use of an external fixator.
. Angulation with shortening of the limb segment.
. Angulation with lengthening of the limb segment.

Correct Answer & Explanation

. Pure angular correction without any translation or change in limb length.

Explanation

Correct Answer: BThis scenario perfectly describes Paley's Osteotomy Rule One: 'When the osteotomy and the hinge axis both pass directly through the CORA, pure angular correction is achieved without any translation.' This is the surgical ideal, maximizing bone-to-bone contact and promoting robust healing. A focal dome osteotomy centered at the CORA is a classic example of achieving pure angular correction.Option A is incorrect:Angulation with intentional translation occurs when the hinge axis passes through the CORA, but the osteotomy is performed at a different level (Rule Two).Option C is incorrect:Iatrogenic translation deformity (Rule Three) occurs when both the hinge axis and the osteotomy are separate from the CORA, leading to misaligned mechanical axes.Options D and E are incorrect:A focal dome osteotomy centered at the CORA, performing pure angular correction, does not typically result in significant limb shortening or lengthening. These are more associated with large opening or closing wedge osteotomies or specific lengthening/shortening procedures.

Question 2269

Topic: 1. General Principles & Basic Science

A surgeon is performing a distal femoral osteotomy for a patient with a complex multi-planar deformity. The surgeon chooses a focal dome osteotomy, as it is considered biomechanically and biologically superior. Post-osteotomy, the segments are held with a temporary external fixator, as shown in the image. Which of the following is a key advantage of the focal dome osteotomy over a simple transverse cut or wedge osteotomy?

. It allows for easier limb lengthening procedures.
. It creates a massive, highly congruent surface area of cancellous bone contact.
. It inherently creates a controlled translation, useful for Rule Two corrections.
. It is simpler and faster to perform than other osteotomy types.
. It minimizes the need for internal fixation, relying more on external support.

Correct Answer & Explanation

. It creates a massive, highly congruent surface area of cancellous bone contact.

Explanation

Correct Answer: BThe case explicitly highlights the advantages of a focal dome osteotomy. One of its profound benefits is that, unlike a wedge osteotomy which often creates gaps, a dome osteotomy creates a massive, highly congruent surface area of cancellous bone contact. This promotes rapid, robust endosteal and periosteal healing, which is crucial for successful deformity correction.Option A is incorrect:While deformity correction can be combined with lengthening, the dome osteotomy itself is not primarily designed for easier lengthening compared to other osteotomy types; its advantage lies in angular correction and stability.Option C is incorrect:When the center of the dome's radius is placed precisely at the CORA, it perfectly fulfills Paley's Osteotomy Rule One, allowing forpure angular correction without translation. It does not inherently create controlled translation; that is a feature of Rule Two when the osteotomy is separate from the CORA.Option D is incorrect:A focal dome osteotomy requires meticulous drill-hole placement along a pre-marked arc and careful connection with an osteotome, making it arguably more technically demanding and not necessarily simpler or faster than a straightforward transverse or wedge cut.Option E is incorrect:The dome osteotomy provides inherent rotational and translational stability, whichreducesstress on the internal hardware, but it does not minimize the need for definitive internal fixation (like an IM nail) in a FAN procedure. The internal hardware is still essential for load sharing and long-term stability.

Question 2270

Topic: 1. General Principles & Basic Science

A patient is undergoing surgical correction of a mid-diaphyseal tibial varus deformity. The surgeon performs the osteotomy 5 cm proximal to the Center of Rotation of Angulation (CORA), but mechanically maintains the Angulation Correction Axis (ACA) exactly at the CORA. According to Paley's Osteotomy Rules, what is the expected geometric result of this maneuver?

. Pure angulation without translation, resulting in collinear mechanical axes
. Angulation combined with translation, resulting in collinear mechanical axes
. Angulation combined with translation, resulting in parallel but non-collinear mechanical axes
. Pure translation without angulation, correcting only the mechanical axis deviation
. A multi-apical zig-zag deformity with severe joint line divergence

Correct Answer & Explanation

. Angulation combined with translation, resulting in collinear mechanical axes

Explanation

According to Paley's Rule 2, when the osteotomy is made away from the CORA but the ACA passes through the CORA, the mechanical axes will realign to be collinear. However, this inherently requires the bone ends at the osteotomy site to translate.

Question 2271

Topic: 1. General Principles & Basic Science

According to Paley's osteotomy principles, performing a corrective osteotomy at a level significantly different from the CORA and placing the Angulation Correction Axis (ACA) directly at the osteotomy site (Rule 3) will result in which of the following mechanical outcomes?

. Collinear mechanical axes with no translation at the osteotomy site
. Collinear mechanical axes with significant translation at the osteotomy site
. Pure lengthening of the segment without angular correction
. Parallel but non-collinear mechanical axes, creating a zig-zag bony contour
. Loss of joint line parallelism with unaltered diaphyseal mechanical axes

Correct Answer & Explanation

. Parallel but non-collinear mechanical axes, creating a zig-zag bony contour

Explanation

Paley's Rule 3 states that if the osteotomy and ACA are both separate from the CORA, the correction will result in mechanical axes that are parallel but translated (non-collinear). This resolves overall mechanical axis deviation but creates a structural zig-zag deformity.

Question 2272

Topic: 1. General Principles & Basic Science

A surgeon is planning a single-level diaphyseal osteotomy to correct a multi-apical femoral deformity. To achieve completely collinear alignment of the proximal and distal mechanical joint axes utilizing a single cut, which of the following trade-offs is mathematically unavoidable?

. Significant bony translation at the osteotomy site
. A guaranteed loss of limb length of at least 2 cm
. The creation of an iatrogenic rotational malalignment
. Placement of the ACA exactly midway between the two local CORAs without translation
. Altering the normal Mechanical Lateral Distal Femoral Angle (mLDFA) to >95 degrees

Correct Answer & Explanation

. Significant bony translation at the osteotomy site

Explanation

Correcting a multi-apical deformity with a single osteotomy requires the ACA to be placed at the single 'global' CORA representing the total combined deformity. Because the osteotomy cannot simultaneously be at multiple local CORAs, significant translation at the osteotomy site (Rule 2) is required to achieve collinear mechanical axes.

Question 2273

Topic: 1. General Principles & Basic Science

When planning a true opening wedge osteotomy for correcting a diaphyseal varus deformity of the proximal tibia, where must the Angulation Correction Axis (ACA) be positioned biomechanically?

. In the central medullary canal
. On the convex (lateral) cortex of the bone
. On the concave (medial) cortex of the bone
. At an infinite distance from the bone (infinity)
. Exactly at the knee joint line

Correct Answer & Explanation

. On the convex (lateral) cortex of the bone

Explanation

An opening wedge osteotomy requires the ACA (hinge point) to be located on the convex side of the deformity. For a varus deformity (apex lateral, concave medial), placing the ACA on the lateral (convex) cortex forces the medial (concave) side to open.

Question 2274

Topic: 1. General Principles & Basic Science

Preoperative planning for a complex tibial deformity determines that an osteotomy will be performed directly at the Center of Rotation of Angulation (CORA), and the Angulation Correction Axis (ACA) will also be centered exactly at the CORA. Based on Paley's Rule 1, what is the expected structural outcome at the osteotomy site?

. Pure angular correction with collinear mechanical axes and no translation
. Angular correction with parallel mechanical axes and a 1 cm translation
. Pure translation without any change in angular deformity
. Lengthening of the limb by precisely the width of the bone
. Rotational correction without frontal or sagittal plane alteration

Correct Answer & Explanation

. Pure angular correction with collinear mechanical axes and no translation

Explanation

Paley's Rule 1 dictates that if both the osteotomy and the ACA pass exactly through the CORA, the deformity corrects with pure angulation. The mechanical axes become perfectly collinear without any translation required at the osteotomy site.

Question 2275

Topic: 1. General Principles & Basic Science

During precise preoperative planning for a distal femoral osteotomy, the Mechanical Lateral Distal Femoral Angle (mLDFA) and the Medial Proximal Tibial Angle (MPTA) are evaluated. Which of the following pairs represents the standard accepted population averages for mLDFA and MPTA in a normal knee?

. mLDFA: 81 degrees, MPTA: 93 degrees
. mLDFA: 90 degrees, MPTA: 81 degrees
. mLDFA: 93 degrees, MPTA: 87 degrees
. mLDFA: 95 degrees, MPTA: 95 degrees
. mLDFA: 87 degrees, MPTA: 87 degrees

Correct Answer & Explanation

. mLDFA: 87 degrees, MPTA: 87 degrees

Explanation

The normal mechanical Lateral Distal Femoral Angle (mLDFA) is approximately 87 degrees (range 85-90 degrees). The normal Medial Proximal Tibial Angle (MPTA) is independently also approximately 87 degrees (range 85-90 degrees), providing joint line parallelism.

Question 2276

Topic: 1. General Principles & Basic Science

A surgeon corrects a 15-degree varus deformity of the proximal tibia using an osteotomy where the ACA is located exactly halfway between the medial and lateral cortices, at the level of the CORA. What type of geometric correction does this produce?

. A pure opening wedge osteotomy
. A pure closing wedge osteotomy
. A pure translation without angular change
. A neutral wedge osteotomy involving both opening and closing components
. An oblique lengthening osteotomy

Correct Answer & Explanation

. A neutral wedge osteotomy involving both opening and closing components

Explanation

When the ACA is placed centrally within the bone (between the convex and concave cortices), correction produces a neutral wedge osteotomy. This technique involves an opening gap on the concave side and a closing wedge on the convex side, thereby preserving the overall axial length of the segment.

Question 2277

Topic: 1. General Principles & Basic Science

A surgeon plans a deformity correction for a mid-diaphyseal tibial varus. The osteotomy is performed exactly at the Center of Rotation of Angulation (CORA), and the Axis of Correction of Angulation (ACA) also passes through the CORA. According to Paley's rules, what is the expected outcome at the osteotomy site?

. Angulation with translation
. Angulation without translation
. Translation without angulation
. Incomplete axis realignment
. Length discrepancy without angulation

Correct Answer & Explanation

. Angulation without translation

Explanation

Paley's Rule 1 states that when the osteotomy and the ACA both pass through the CORA, the mechanical and anatomic axes will realign completely without translation at the osteotomy site.

Question 2278

Topic: 1. General Principles & Basic Science

During preoperative planning for a distal femoral valgus deformity, the surgeon notes the CORA is juxta-articular. To allow adequate distal fixation, the osteotomy is planned 3 cm proximal to the CORA, but the ACA will remain at the CORA. What is the expected mechanical consequence?

. The mechanical axis will not realign.
. Angulation and translation will occur at the osteotomy site, and the axes will be collinear.
. Pure translation without angulation will occur at the osteotomy site.
. A zig-zag deformity will be created.
. The bone will shorten by exactly 3 cm.

Correct Answer & Explanation

. Angulation and translation will occur at the osteotomy site, and the axes will be collinear.

Explanation

Under Paley's Rule 2, if the osteotomy is separate from the CORA but the ACA passes through the CORA, the axes will successfully realign. However, obligatory translation will occur at the osteotomy site.

Question 2279

Topic: 1. General Principles & Basic Science

A patient presents with severe medial compartment osteoarthritis and a mechanical axis deviation (MAD) of 45 mm medial. Weight-bearing radiographs reveal a Joint Line Convergence Angle (JLCA) of 6 degrees opening laterally. If an extra-articular osteotomy is planned using the anatomic axis alone without accounting for the JLCA, what is the most likely postoperative outcome?

. Overcorrection into valgus
. Undercorrection of the varus deformity
. Posterior slope reversal
. Medial collateral ligament rupture
. Sagittal plane translation

Correct Answer & Explanation

. Overcorrection into valgus

Explanation

The JLCA represents intra-articular deformity or ligamentous laxity. Failing to account for a laterally opening JLCA during extra-articular varus correction typically leads to valgus overcorrection once weight-bearing resumes.

Question 2280

Topic: 1. General Principles & Basic Science

A surgeon executes a closing wedge osteotomy for a diaphyseal deformity. The osteotomy is performed at a site remote from the CORA, and the ACA is located at the convex cortex of the osteotomy site (away from the CORA). According to Paley's osteotomy rules, what is the resulting alignment?

. Collinear mechanical axes with translation at the osteotomy.
. Collinear mechanical axes without translation at the osteotomy.
. A translated mechanical axis resulting in a zig-zag deformity.
. Complete normalization of the joint line orientation without secondary deformity.
. Lengthening of the limb segment.

Correct Answer & Explanation

. A translated mechanical axis resulting in a zig-zag deformity.

Explanation

Paley's Rule 3 states that if both the osteotomy and the ACA are placed away from the CORA, the mechanical axis will not realign, resulting in an unintended translation (zig-zag deformity).

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