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1. General Principles & Basic Science MCQs

Practice Set 130 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 2581

Topic: 1. General Principles & Basic Science

In evaluating a patient with a suspected sagittal plane deformity of the femur, the surgeon measures the anatomic posterior distal femoral angle (aPDFA). Which of the following values represents the expected normal aPDFA?

. 75 degrees
. 83 degrees
. 90 degrees
. 95 degrees
. 102 degrees

Correct Answer & Explanation

. 83 degrees

Explanation

The normal anatomic posterior distal femoral angle (aPDFA) is approximately 83 degrees. This angle reflects the normal anterior bow of the femur and the natural joint orientation in the sagittal plane.

Question 2582

Topic: 1. General Principles & Basic Science

A 24-year-old male has a midshaft tibial angular deformity. The center of rotation of angulation (CORA) is identified at the deformity apex. The surgeon plans an osteotomy 5 cm proximal to the CORA but aligns the hinge axis exactly on the CORA. According to Paley's osteotomy rules, what will be the resulting biomechanical effect?

. Pure angular correction with no translation
. Angular correction with translation at the osteotomy site
. Pure translation with no angular correction
. An opening wedge deformity without translation
. Correction of joint line obliquity without altering the mechanical axis

Correct Answer & Explanation

. Angular correction with translation at the osteotomy site

Explanation

According to Paley's Osteotomy Rule 2, if the osteotomy is made at a different level than the CORA but the hinge axis is placed on the CORA, angular correction is achieved at the expense of translation at the osteotomy site. This is often utilized when local bone quality dictates a non-apical osteotomy.

Question 2583

Topic: 1. General Principles & Basic Science

A 45-year-old female undergoes a distal femoral osteotomy for symptomatic valgus malalignment. Postoperatively, the mechanical axis passes exactly through the center of the knee. To achieve a normal joint line orientation during preoperative planning, what target mechanical lateral distal femoral angle (mLDFA) should the surgeon aim for?

. 81 degrees
. 87 degrees
. 90 degrees
. 93 degrees
. 98 degrees

Correct Answer & Explanation

. 87 degrees

Explanation

The normal mechanical lateral distal femoral angle (mLDFA) is approximately 87 degrees (range 85-90). Restoring this angle is crucial during deformity correction to ensure proper joint line orientation and prevent shear stresses across the articular cartilage.

Question 2584

Topic: Biology, Genetics & Bone Healing

A 35-year-old patient is undergoing tibial lengthening via distraction osteogenesis at a rate of 1 mm per day. Radiographs at 4 weeks demonstrate a thin, hour-glass shaped regenerate with a central radiolucent gap exceeding 5 mm. What is the most appropriate next step in management to optimize biomechanical strength and healing?

. Increase the distraction rate to 1.5 mm/day to stimulate osteoblastic activity
. Continue the current distraction rate and prescribe oral bisphosphonates
. Pause distraction and compress the regenerate slightly (accordion maneuver)
. Immediately perform an autologous iliac crest bone graft
. Remove the external fixator and place the limb in a patellar tendon-bearing cast

Correct Answer & Explanation

. Pause distraction and compress the regenerate slightly (accordion maneuver)

Explanation

An hour-glass regenerate or a gap >5 mm indicates inadequate bone formation, often due to an excessively rapid distraction rate or poor biology. Pausing or compressing the regenerate (the accordion maneuver) stimulates osteogenesis before considering more invasive options like bone grafting.

Question 2585

Topic: Physiology & Rehabilitation

A 30-year-old athlete presents with a history of chronic knee pain and a subtle gait abnormality. On physical examination, the knee appears to 'lock' securely in full extension during the stance phase of gait without significant quadriceps effort. Based on the principles outlined in the case, which of the following best describes the normal sagittal mechanical axis alignment at the knee joint that facilitates this efficient gait?

. The mechanical axis passes directly through the center of the knee joint.
. The mechanical axis passes slightly posterior to the center of the knee joint, creating a passive flexion moment.
. The mechanical axis passes slightly anterior to the center of the knee joint, creating a passive extension moment.
. The mechanical axis passes through the posterior third of the tibial plateau, ensuring stability.
. The mechanical axis is highly variable at the knee joint, depending on individual anatomy.

Correct Answer & Explanation

. The mechanical axis passes slightly anterior to the center of the knee joint, creating a passive extension moment.

Explanation

Correct Answer: CThe case explicitly states: 'This mechanical line, originating from the body's center of gravity, passes through the center of the femoral head, drops slightlyanteriorto the center of the knee joint, and continues through the center of the ankle joint. This slight anterior positioning at the knee is a biomechanical masterpiece: it creates a natural, passive extension moment. This allows the knee to 'lock' securely in full extension during the stance phase of the gait cycle, requiring minimal active quadriceps effort to maintain an upright posture.'Option A is incorrectbecause while it's close, the normal axis isslightlyanterior, which is critical for the passive extension moment.Option B is incorrectbecause passing posterior would create a flexion moment, requiringmorequadriceps effort, which is characteristic of procurvatum, not normal alignment.Option D is incorrectas the description of the mechanical axis passing through the posterior third of the tibial plateau is not the standard definition of the sagittal mechanical axis at the knee joint.Option E is incorrectas while there's some individual variation, the fundamental principle of the mechanical axis passing slightly anterior to the knee for a passive extension moment is a consistent biomechanical truth for normal alignment.

Question 2586

Topic: Physiology & Rehabilitation

A 40-year-old patient with a history of femoral procurvatum is being evaluated for surgical correction. The surgeon is concerned about potential postoperative hyperextension. The provided case highlights the 'neuromuscular feedback loop' and the role of dynamic restraints. Which of the following statements accurately describes the primary mechanism by which the hamstrings prevent pathologic hyperextension in a neuromuscularly intact patient?

. They act as static restraints, providing rigid stability at the end range of motion.
. They passively shorten after an extension osteotomy, mechanically blocking hyperextension.
. They serve as a 'dynamic checkrein,' receiving efferent signals from the CNS to prevent hyperextension.
. They primarily provide anterior stability to the tibia, preventing posterior subluxation.
. They stretch over time in response to procurvatum, leading to compensatory hyperextension.

Correct Answer & Explanation

. They serve as a 'dynamic checkrein,' receiving efferent signals from the CNS to prevent hyperextension.

Explanation

Correct Answer: CThe case states: 'Proprioceptive mechanoreceptors within the joint capsule, ligaments, and tendons send continuous afferent signals to the central nervous system (CNS). The CNS, in turn, fires efferent signals to the hamstrings, commanding them to act as a 'dynamic checkrein.' This prevents pathologic hyperextension during the swing and stance phases.' This describes the active, neurologically controlled role of the hamstrings.Option A is incorrectbecause the case differentiates static restraints (capsule, ligaments) from dynamic restraints (musculature like hamstrings).Option B is incorrectbecause while an extension osteotomy does relatively shorten posterior soft tissues, the primary mechanism for preventingpathologichyperextension in a neuromuscularly intact patient is the active, dynamic control by the hamstrings, not just passive mechanical shortening.Option D is incorrectbecause the hamstrings primarily provide posterior stability to the knee and act as knee flexors, not anterior stability to the tibia in the context of preventing hyperextension.Option E is incorrectbecause while the posterior capsulestretchesin response to chronic procurvatum, the hamstrings' role is topreventpathologic hyperextension through active contraction, not to stretch and cause it.

Question 2587

Topic: Physiology & Rehabilitation

A 28-year-old patient with a history of poliomyelitis presents with a 35-degree femoral procurvatum and a clinical fixed flexion deformity (FFD) of 20 degrees, indicating 15 degrees of compensatory hyperextension. The patient has significant hamstring weakness and atrophy. The surgeon is planning a distal femoral extension osteotomy. Based on the 'Surgical Pearls for the Neuromuscularly Compromised' section, what is the MOST appropriate surgical strategy for this patient?

. Perform a full 35-degree extension osteotomy to correct the entire osseous deformity, expecting a proprioceptive reset.
. Perform a 20-degree extension osteotomy to match the clinical FFD, leaving 15 degrees of residual procurvatum.
. Perform a deliberate under-correction of the osseous deformity (e.g., 20 degrees) to utilize the remaining bony deformity as a mechanical block against hyperextension.
. Perform a 35-degree extension osteotomy combined with a posterior capsular plication to tighten the lax capsule.
. Perform a 35-degree extension osteotomy and then refer the patient for intensive hamstring strengthening rehabilitation.

Correct Answer & Explanation

. Perform a deliberate under-correction of the osseous deformity (e.g., 20 degrees) to utilize the remaining bony deformity as a mechanical block against hyperextension.

Explanation

Correct Answer: CThe case specifically highlights this exception: 'The major exception is the patient with weak, paralyzed, or atrophied hamstrings... In these patients, the dynamic checkrein is absent. ...correcting the full 30° of bone deformitywillunmask the 10° of static capsular laxity, resulting in a devastating, pathologic hyperextension thrust during the stance phase of gait. In these specific, high-risk cases, the surgeon must carefully plan adeliberate under-correctionof the osseous deformity (e.g., correcting only 20° of the 30° bow) to utilize the remaining bony deformity as a mechanical block against hyperextension.' In this patient's case, correcting only 20 degrees of the 35-degree deformity would leave 15 degrees of residual procurvatum, which would then act as a mechanical block against the 15 degrees of compensatory hyperextension, preventing pathologic recurvatum.Option A is incorrectbecause the proprioceptive reset relies on a functioning neuromuscular system, which is compromised in this patient. Full correction would lead to pathologic hyperextension.Option B is incorrectbecause while 20 degrees matches the FFD, the principle is to under-correct theosseous deformityto leave a mechanical block, not just match the FFD. The example in the text shows correcting 20 of 30 degrees, leaving 10 degrees of procurvatum, which then blocks the 10 degrees of hyperextension. So, correcting 20 degrees of a 35-degree deformity is an under-correction, but the rationale is key.Option D is incorrectbecause while capsular plication might seem logical, the Paley method emphasizes bony correction and the dynamic checkrein. The text does not suggest capsular plication as the primary solution for neuromuscularly compromised patients; deliberate under-correction of the bone is the described strategy.Option E is incorrectbecause while rehabilitation is important, it cannot restore function to paralyzed or severely atrophied muscles to the extent needed to prevent pathologic hyperextension if the dynamic checkrein is truly absent. The surgical strategy must account for the permanent neuromuscular deficit.

Question 2588

Topic: 1. General Principles & Basic Science

A 42-year-old patient presents with a chief complaint of a 'bent knee' that will not straighten. Clinical examination reveals a maximum active and passive knee extension locked at 20 degrees of flexion (clinical FFD = 20°). Full-length weight-bearing lateral radiographs show a normal PPTA of 80 degrees, but a PDFA of 54 degrees. Based on the case's 'Deconstructing Femoral Procurvatum' section, what is the magnitude of the true osseous femoral procurvatum deformity, and how much compensatory joint hyperextension is present?

. Osseous deformity: 20 degrees; Compensatory hyperextension: 0 degrees.
. Osseous deformity: 29 degrees; Compensatory hyperextension: 9 degrees.
. Osseous deformity: 30 degrees; Compensatory hyperextension: 10 degrees.
. Osseous deformity: 54 degrees; Compensatory hyperextension: 34 degrees.
. Osseous deformity: 83 degrees; Compensatory hyperextension: 63 degrees.

Correct Answer & Explanation

. Osseous deformity: 30 degrees; Compensatory hyperextension: 10 degrees.

Explanation

Correct Answer: CThe case provides a direct example that matches this scenario: 'Normal PDFA (83°) - Measured PDFA (54°) = 29° (which we round to30° of femoral procurvatumfor surgical planning).'For compensatory hyperextension: 'Bone Deformity (30°) - Clinical FFD (20°) =10° of compensatory joint hyperextension.'Therefore, the true osseous femoral procurvatum is 30 degrees, and there are 10 degrees of compensatory joint hyperextension.Option A is incorrectas it miscalculates both values.Option B is incorrectas while 29 degrees is the precise calculation, the case rounds it to 30 degrees for surgical planning, and the compensatory hyperextension would then be 10 degrees.Option D is incorrectas 54 degrees is the measured PDFA, not the magnitude of the deformity, and the hyperextension calculation is incorrect.Option E is incorrectas 83 degrees is the normal PDFA, not the deformity, and the hyperextension calculation is incorrect.

Question 2589

Topic: Physiology & Rehabilitation

A 70-year-old patient with a long-standing history of knee flexion deformity due to femoral procurvatum is being considered for surgical correction. The patient has no known neurological deficits, and clinical assessment confirms intact hamstring strength. The surgeon plans a distal femoral extension osteotomy to correct the full 30-degree osseous deformity, despite 10 degrees of compensatory joint hyperextension. According to Paley's principles for a neuromuscularly intact patient, what is the expected outcome regarding the compensatory hyperextension postoperatively?

. The 10 degrees of compensatory hyperextension will persist, leading to a floppy, hyperextended knee.
. The extension osteotomy will functionally lengthen the posterior soft tissues, exacerbating the hyperextension.
. The proprioceptive feedback loop will reset, and the hamstrings will engage to define a new, healthy terminal extension at 0 degrees.
. The patient will require a secondary posterior capsular plication to address the persistent laxity.
. The knee will remain in 10 degrees of fixed flexion due to the uncorrected soft tissue contracture.

Correct Answer & Explanation

. The proprioceptive feedback loop will reset, and the hamstrings will engage to define a new, healthy terminal extension at 0 degrees.

Explanation

Correct Answer: CThe case explicitly addresses this scenario for a neuromuscularly intact patient: 'The ideal, biomechanically sound treatment is a 30° distal femoral extension osteotomy performed precisely at the CORA. ...More importantly, dynamic knee extension is governed by proprioception. Once the bone is surgically straightened, the CNS no longer needs to aggressively force the knee into hyperextension just to achieve an upright stance. The neural feedback loop resets instantly. The hamstrings (the dynamic checkrein) engage normally to define a new, healthy terminal extension point at exactly 0°. The postoperative FFD becomes 0°, and the compensatory hyperextension vanishes.'Option A is incorrectbecause this is the fear of trainees, but the text explains why it does not happen in a neuromuscularly intact patient.Option B is incorrectbecause the extension osteotomy functionallyshortens and tightensthe posterior soft tissues, taking up the slack, not lengthening them.Option D is incorrectbecause a secondary capsular plication is not typically needed in a neuromuscularly intact patient due to the proprioceptive reset.Option E is incorrectbecause the full correction of the osseous deformity, combined with the proprioceptive reset, is expected to resolve the FFD to 0 degrees, not leave it in flexion.

Question 2590

Topic: 1. General Principles & Basic Science

A 50-year-old female presents with a 15° fixed flexion deformity of the knee. Radiographic analysis reveals a PDFA of 78° and a normal PPTA of 82°. The CORA is identified in the distal femoral metaphysis. According to Paley's principles, what is the most accurate quantification of the osseous and soft tissue contributions to this patient's FFD?

. Osseous: 5° femoral procurvatum; Soft tissue: 10° contracture
. Osseous: 7° femoral recurvatum; Soft tissue: 8° contracture
. Osseous: 5° tibial procurvatum; Soft tissue: 10° contracture
. Osseous: 10° femoral procurvatum; Soft tissue: 5° contracture
. Osseous: 15° femoral procurvatum; Soft tissue: 0° contracture

Correct Answer & Explanation

. Osseous: 5° femoral procurvatum; Soft tissue: 10° contracture

Explanation

Correct Answer: AThe total clinical FFD is 15°. The normal PDFA is 83°. The measured PDFA is 78°. Therefore, the osseous contribution from the femur is 83° - 78° = 5°. A decreased PDFA indicates femoral procurvatum. The PPTA is normal (82°), so there is no tibial osseous contribution. The remaining FFD is due to soft tissue contracture: Total FFD (15°) - Osseous contribution (5°) = 10°. Thus, the deformity is composed of 5° femoral procurvatum and 10° soft tissue contracture.Option B is incorrectbecause a PDFA of 78° indicates procurvatum (decreased angle), not recurvatum (increased angle).Option C is incorrectbecause the PPTA is normal, ruling out tibial procurvatum, and the calculation for soft tissue is correct but the osseous component is misattributed.Option D is incorrectbecause the osseous contribution is 5°, not 10°, and consequently, the soft tissue contribution is 10°, not 5°.Option E is incorrectbecause the osseous contribution is 5°, not 15°, and there is a significant soft tissue component.

Question 2591

Topic: Surgical Anatomy & Approaches

A surgeon is planning a distal femoral osteotomy to correct a sagittal plane deformity. The Center of Rotation of Angulation (CORA) has been precisely identified in the distal femoral metaphysis. The surgeon decides to perform the osteotomy *at the CORA* and places the hinge of correction *at the CORA*. According to Paley's Three Immutable Laws of Osteotomy, what is the expected outcome of this surgical approach?

. The deformity will be corrected, but a secondary translation of the entire mechanical axis will occur.
. The deformity will be corrected, but the bone ends will translate at the osteotomy site, creating a 'dog-leg' deformity.
. The deformity will be corrected perfectly without any translation of the bone fragments, and the anatomic axes will realign seamlessly.
. The deformity will be overcorrected, leading to an iatrogenic recurvatum.
. The deformity will be undercorrected, requiring a secondary soft tissue release to achieve full extension.

Correct Answer & Explanation

. The deformity will be corrected, but a secondary translation of the entire mechanical axis will occur.

Explanation

Correct Answer: CThis scenario describes Paley's Rule 1 (Anatomic Correction). If the osteotomy is performedat the CORAand the hinge of correction (the mechanical axis of the hinge) is placedat the CORA, the deformity corrects perfectly without any translation of the bone fragments. The anatomic axes realign seamlessly, making this the gold standard for deformity correction when feasible.Option A is incorrectas this describes the outcome of Rule 3, where both the osteotomy and hinge are away from the CORA.Option B is incorrectas this describes the outcome of Rule 2, where the osteotomy is away from the CORA but the hinge is at the CORA.Option D and E are incorrectas these describe errors in magnitude of correction, not the geometric outcome of osteotomy placement relative to the CORA and hinge.

Question 2592

Topic: 1. General Principles & Basic Science

A 40-year-old male presents with a complex sagittal plane deformity of the tibia, with the CORA located in the proximal tibial epiphysis, close to the joint line. Due to concerns about damaging the articular cartilage and poor bone stock at the CORA, the surgeon decides to perform the osteotomy 2 cm distal to the CORA in the metaphysis. However, the hinge of correction is meticulously placed *at the CORA*. Based on Paley's Three Immutable Laws of Osteotomy, what is the anticipated geometric outcome of this surgical plan?

. The deformity will be corrected perfectly without any translation of the bone fragments.
. The deformity will be corrected, but a secondary translation of the entire mechanical axis will occur.
. The deformity will be corrected, but the bone ends will translate at the osteotomy site.
. The osteotomy will result in an iatrogenic fixed flexion deformity.
. The correction will be unstable, leading to early hardware failure.

Correct Answer & Explanation

. The deformity will be corrected, but the bone ends will translate at the osteotomy site.

Explanation

Correct Answer: CThis scenario describes Paley's Rule 2 (Correction with Translation). If the osteotomy is performedaway from the CORA(in this case, 2 cm distal) but the hinge of correction remainsat the CORA, the axes will align correctly, but the bone ends will translate at the osteotomy site. This is a common and acceptable modification, often necessary when the CORA is in an unfavorable location for osteotomy (e.g., too close to a joint or in poor bone quality). While there is translation at the osteotomy, the overall alignment of the bone's anatomic axes is restored.Option A is incorrectas this describes Rule 1, where both the osteotomy and hinge are at the CORA.Option B is incorrectas this describes Rule 3, where both the osteotomy and hinge are away from the CORA, leading to mechanical axis translation.Option D and E are incorrectas these describe potential complications or errors in planning/execution, not the direct geometric outcome of applying Rule 2.

Question 2593

Topic: 1. General Principles & Basic Science

A 55-year-old patient presents with a 20° fixed flexion deformity (FFD) of the knee. A lateral radiograph, taken at maximum extension, reveals a PDFA of 74° and a normal PPTA of 80°. The CORA is located in the distal femoral metaphysis. The diagram below illustrates the initial deformity and potential treatment strategies. Based on this information and the case's detailed analysis, what is the precise breakdown of the osseous and soft tissue contributions to this patient's FFD?

. 10° femoral procurvatum and 10° joint contracture.
. 20° femoral procurvatum and 0° joint contracture.
. 10° femoral recurvatum and 10° joint contracture.
. 5° femoral procurvatum and 15° joint contracture.
. 20° joint contracture with no osseous deformity.

Correct Answer & Explanation

. 10° femoral procurvatum and 10° joint contracture.

Explanation

Correct Answer: AAs detailed in the case study, the total clinical FFD is 20°. The normal PDFA is 83°. The measured PDFA is 74°. Therefore, the osseous contribution from the femur (femoral procurvatum, as the angle is decreased) is 83° - 74° = 9°, which is rounded to 10° for practical planning. The PPTA is normal (80°), indicating no tibial osseous contribution. The remaining FFD is attributed to soft tissue contracture: Total FFD (20°) - Osseous contribution (10°) = 10°. Thus, the 20° FFD is caused equally by a 10° femoral procurvatum and a 10° posterior soft tissue contracture, as depicted in Panel (i) of the provided diagram.Option B is incorrectbecause the osseous contribution is 10°, not 20°, and there is a significant soft tissue component.Option C is incorrectbecause a decreased PDFA (74° vs. 83°) indicates procurvatum, not recurvatum.Option D is incorrectbecause the calculation for osseous deformity is 10°, not 5°, and consequently, the soft tissue component is 10°, not 15°.Option E is incorrectbecause the abnormal PDFA clearly indicates an osseous deformity is present.

Question 2594

Topic: 1. General Principles & Basic Science

A 48-year-old male presents with a crouched gait and significant anterior knee pain. Clinical examination reveals a 15° fixed flexion deformity. A lateral radiograph is obtained, as shown below. Based on the image and the case's principles, if the PDFA is measured at 76° and the PPTA is 80°, what is the most appropriate initial surgical strategy following the anatomic restoration approach?

. Perform a 15° distal femoral extension osteotomy without soft tissue release.
. Perform a 7° distal femoral extension osteotomy followed by an 8° posterior soft tissue release.
. Perform an 8° distal femoral extension osteotomy followed by a 7° posterior soft tissue release.
. Perform a 15° posterior soft tissue release without any osseous correction.
. Perform a 7° proximal tibial extension osteotomy followed by an 8° posterior soft tissue release.

Correct Answer & Explanation

. Perform a 7° distal femoral extension osteotomy followed by an 8° posterior soft tissue release.

Explanation

Correct Answer: BFirst, deconstruct the deformity: Total FFD = 15°. Normal PDFA = 83°. Measured PDFA = 76°. Osseous contribution (femoral procurvatum) = 83° - 76° = 7°. The PPTA is normal (80°), so no tibial osseous deformity. Soft tissue contribution = Total FFD (15°) - Osseous contribution (7°) = 8°. The anatomic restoration approach, as described in the case, addresses each component separately. Therefore, the ideal treatment is a 7° distal femoral extension osteotomy to correct the osseous deformity, followed by an 8° posterior soft tissue release to address the contracture.Option A is incorrectbecause it uses a compensatory approach (correcting the entire FFD with bone) and ignores the soft tissue component, which would lead to an overcorrected PDFA.Option C is incorrectbecause the osseous contribution is 7°, not 8°, and the soft tissue contribution is 8°, not 7°.Option D is incorrectbecause it ignores the significant osseous deformity (7° femoral procurvatum), which must be corrected for long-term success.Option E is incorrectbecause the deformity is femoral procurvatum, not tibial, and the osseous correction magnitude is incorrect.

Question 2595

Topic: 1. General Principles & Basic Science

A 68-year-old patient with severe knee osteoarthritis and a 25° fixed flexion deformity is being evaluated for surgical correction. Radiographic analysis shows a PDFA of 70° and a PPTA of 85°. The CORA for the femoral deformity is in the distal metaphysis, and for the tibial deformity, it is in the proximal metaphysis. Which of the following statements accurately reflects the osseous contributions to this patient's FFD?

. 13° femoral procurvatum and 4° tibial procurvatum.
. 13° femoral procurvatum and 4° tibial recurvatum.
. 13° femoral recurvatum and 4° tibial recurvatum.
. 10° femoral procurvatum and 5° tibial recurvatum.
. No significant osseous deformity; the FFD is primarily due to soft tissue contracture.

Correct Answer & Explanation

. 13° femoral procurvatum and 4° tibial recurvatum.

Explanation

Correct Answer: BLet's calculate each osseous component:Femoral Deformity:Normal PDFA = 83°. Measured PDFA = 70°. Deviation = 83° - 70° = 13°. Since the measured angle is decreased, this indicates 13° of femoral procurvatum.Tibial Deformity:Normal PPTA = 81°. Measured PPTA = 85°. Deviation = 85° - 81° = 4°. Since the measured angle is increased, this indicates 4° of tibial recurvatum (increased posterior slope).Therefore, the osseous contributions are 13° femoral procurvatum and 4° tibial recurvatum.Option A is incorrectbecause the tibial deformity is recurvatum (increased angle), not procurvatum (decreased angle).Option C is incorrectbecause the femoral deformity is procurvatum (decreased angle), not recurvatum (increased angle).Option D is incorrectbecause the calculated magnitudes (13° and 4°) are different from 10° and 5°.Option E is incorrectbecause both PDFA and PPTA are significantly abnormal, indicating substantial osseous deformities.

Question 2596

Topic: Biomechanics & Biomaterials
A surgeon is considering a 'compensatory strategy' for a patient with a 20° FFD caused by 10° femoral procurvatum and 10° soft tissue contracture, as depicted in Panel (iii) of the provided diagram. Which of the following statements accurately describes the outcome and implications of this compensatory approach?
. A 10° femoral extension osteotomy is performed, restoring the PDFA to normal, and the remaining 10° FFD is corrected by soft tissue release.
. A 20° femoral extension osteotomy is performed, making the leg clinically straight but resulting in an intentionally overcorrected (increased) PDFA.
. A 20° femoral extension osteotomy is performed, making the leg clinically straight and restoring the PDFA to a normal value of 83°.
. A 10° soft tissue release is performed, and the remaining 10° FFD is corrected by a femoral extension osteotomy, leaving the PDFA undercorrected.
. This approach is considered the gold standard as it avoids soft tissue releases and minimizes surgical complexity.

Correct Answer & Explanation

. A 20° femoral extension osteotomy is performed, making the leg clinically straight but resulting in an intentionally overcorrected (increased) PDFA.

Explanation

As described in the case and illustrated in Panel (iii) of the diagram, the compensatory strategy involves performing a larger osteotomy than anatomically required to correct the osseous deformity. In this specific example (20° FFD, 10° bone, 10° soft tissue), a 20° femoral osteotomy is performed. This single osseous intervention makes the leg clinically straight (0° extension) but leaves the joint with an intentionally abnormal, overcorrected PDFA (e.g., if normal is 83° and initial was 74°, a 20° correction would make it 94°, which is recurvatum). This approach 'compensates' for the soft tissue contracture by overcorrecting the bone.

Question 2597

Topic: Biomechanics & Biomaterials

A 70-year-old patient undergoes a distal femoral osteotomy for correction of a 15° fixed flexion deformity. Postoperatively, the patient continues to experience significant anterior knee pain, a persistent crouched gait, and reports difficulty with terminal knee extension. Radiographs show that the coronal alignment is excellent, but the sagittal plane correction resulted in a PDFA of 90°. Based on the case's discussion, what is the most likely underlying cause of the patient's persistent symptoms?

. Inadequate correction of a coronal plane deformity, leading to persistent mechanical axis deviation.
. Overcorrection of the femoral procurvatum, resulting in iatrogenic femoral recurvatum and altered knee kinematics.
. Undercorrection of the soft tissue contracture, leading to persistent hamstring tightness.
. Development of a new tibial procurvatum deformity due to compensatory loading.
. Avascular necrosis of the distal femur, causing pain and limited range of motion.

Correct Answer & Explanation

. Overcorrection of the femoral procurvatum, resulting in iatrogenic femoral recurvatum and altered knee kinematics.

Explanation

Correct Answer: BThe normal PDFA is 83° (range 79° to 87°). A postoperative PDFA of 90° indicates an overcorrection of the femoral procurvatum, resulting in iatrogenic femoral recurvatum (a posterior bow). As highlighted in the case, overlooking sagittal plane malalignment or creating an iatrogenic one can lead to persistent anterior knee pain, abnormal kinematics, and profound patient dissatisfaction, even with a perfectly executed coronal correction. Femoral recurvatum would place increased stress on the anterior knee structures and alter the normal passive extension moment, contributing to the crouched gait and difficulty with terminal extension.Option A is incorrectas the question states coronal alignment is excellent.Option C is incorrectbecause while undercorrection of soft tissue can cause FFD, the specific finding of a 90° PDFA points to an osseous overcorrection as the primary issue here, which itself can cause pain and kinematic problems.Option D is incorrectbecause while compensatory loading can occur, the direct and immediate cause of symptoms with a 90° PDFA is the iatrogenic femoral recurvatum.Option E is incorrectas avascular necrosis is a serious complication but is not directly indicated by the described symptoms and radiographic finding of an abnormal PDFA; the symptoms are more consistent with biomechanical malalignment.

Question 2598

Topic: 1. General Principles & Basic Science

According to the case, overlooking a sagittal plane malalignment, such as femoral procurvatum or tibial recurvatum, can have significant long-term consequences for the patient. Which of the following is NOT listed as a potential consequence of failing to respect sagittal biomechanics?

. Persistent anterior knee pain.
. Rapid cartilage wear.
. Profound patient dissatisfaction.
. Abnormal kinematics.
. Increased risk of deep vein thrombosis (DVT) due to prolonged immobilization.

Correct Answer & Explanation

. Increased risk of deep vein thrombosis (DVT) due to prolonged immobilization.

Explanation

Correct Answer: EThe case explicitly states that 'Overlooking a sagittal plane malalignment... can easily undermine an otherwise perfectly executed coronal plane correction. Failure to respect sagittal biomechanics leads to persistent anterior knee pain, abnormal kinematics, rapid cartilage wear, and profound patient dissatisfaction.' All options A, B, C, and D are directly mentioned as consequences.Option E (Increased risk of deep vein thrombosis (DVT) due to prolonged immobilization) is incorrectbecause while DVT is a general surgical risk, it is not specifically listed in the case as a direct consequence offailing to respect sagittal biomechanicsin terms of long-term functional outcomes or joint health. The question asks what isNOTlisted as a potential consequence of failing to respect sagittal biomechanics.

Question 2599

Topic: 1. General Principles & Basic Science

A 48-year-old patient underwent a distal femoral osteotomy for valgus knee realignment. The post-operative radiograph is shown. While the mechanical axis appears well-corrected, the surgeon notes a significant increase in the joint line obliquity. According to Paley's principles, what is a potential long-term consequence of an unaddressed or overcorrected joint line obliquity?

. Increased risk of nonunion at the osteotomy site.
. Development of patellofemoral pain and osteoarthritis.
. Recurrence of valgus deformity due to ligamentous laxity.
. Increased risk of deep vein thrombosis.
. Accelerated degeneration of the medial compartment.

Correct Answer & Explanation

. Development of patellofemoral pain and osteoarthritis.

Explanation

Correct Answer: BPaley's principles emphasize not only correcting the mechanical axis but also restoring or preserving the joint line orientation. An excessive increase in joint line obliquity (i.e., making the joint line too steep) can lead to abnormal patellofemoral biomechanics, increasing stress on the patellofemoral joint. This can manifest as patellofemoral pain, instability, and ultimately accelerate the development of patellofemoral osteoarthritis. While the mechanical axis may be corrected, an abnormal joint line can create new problems.Option A is incorrectbecause nonunion is related to factors like surgical technique, bone biology, and fixation stability, not directly to joint line obliquity.Option C is incorrectbecause recurrence of valgus deformity is typically due to insufficient correction, hardware failure, or progression of underlying disease, not primarily due to joint line obliquity itself.Option D is incorrectbecause DVT is a general surgical complication, not specifically linked to joint line obliquity.Option E is incorrectbecause the goal of valgus realignment is to offload the lateral compartment and shift load to the medial compartment. While overcorrection into excessive varus could theoretically overload the medial compartment, an increased joint line obliquity itself primarily affects the patellofemoral joint, not directly accelerating medial compartment degeneration in this context.

Question 2600

Topic: 1. General Principles & Basic Science

The case highlights the importance of Paley's foundational principles in valgus knee realignment. Which of the following is a core principle for accurately planning and executing an osteotomy to correct an angular deformity, such as a valgus knee?

. Always perform the osteotomy at the level of the joint line to minimize soft tissue disruption.
. Correct the deformity at the apex of the deformity (CORA) to avoid creating a new deformity.
. Prioritize limb lengthening over angular correction to improve gait mechanics.
. Utilize only closing wedge osteotomies for maximum stability and faster healing.
. Perform all corrections in the sagittal plane first, then address the coronal plane.

Correct Answer & Explanation

. Correct the deformity at the apex of the deformity (CORA) to avoid creating a new deformity.

Explanation

Correct Answer: BA fundamental principle in deformity correction, as emphasized by Paley, is to perform the osteotomy at the Center of Rotation of Angulation (CORA). The CORA is the point around which the distal segment rotates relative to the proximal segment. Correcting the deformity precisely at the CORA ensures that the mechanical axis is realigned without creating a translational deformity (shift) or a new angular deformity (secondary angulation) in the adjacent segment. This leads to a more predictable and anatomically correct outcome.Option A is incorrectbecause performing the osteotomy at the joint line is often not the CORA and can lead to joint line obliquity or other issues if the deformity is not truly juxta-articular.Option C is incorrectbecause angular correction to realign the mechanical axis is the primary goal in valgus knee realignment for LCOA. Limb lengthening is a secondary consideration, only addressed if a significant limb length discrepancy exists and the chosen osteotomy technique (e.g., opening wedge) allows for it.Option D is incorrectbecause both opening and closing wedge osteotomies have their indications and advantages. The choice depends on factors like the desired correction, limb length, and surgeon preference. Paley's principles advocate for the appropriate technique based on the specific deformity and goals.Option E is incorrectbecause deformity correction is typically planned and executed in all three planes (coronal, sagittal, axial) simultaneously or sequentially based on the specific deformity. There is no universal rule to address sagittal plane first; the most significant deformity is often addressed first, or a comprehensive plan is made for all planes.

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