ABOS Part I & AAOS OITE Orthopedic Review: Knee Deformity

Question 1

A 30-year-old patient presents with 20 degrees of knee hyperextension on passive examination. Their full-length lateral radiograph shows a Mechanical Posterior Distal Femoral Angle (mPDFA) of 84° and a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 80°. The clinical presentation is analogous to Panel (i) in the provided diagram.

clinical image

Explanation

Correct Answer: C

The case content explicitly states that if the mPDFA and mPPTA are strictly within normal limits despite significant clinical hyperextension, the deformity is extra-osseous (soft tissue). The normal range for mPDFA is 80-85°, and for mPPTA is 77-84°. This patient's mPDFA of 84° and mPPTA of 80° are both within these normal ranges. Therefore, the 20 degrees of clinical hyperextension is due to laxity of the posterior soft tissue envelope (capsule, ligaments), as depicted in Panel (i) of the provided image. This single, vital diagnostic step prevents the surgeon from performing a disastrous, unnecessary, and ultimately harmful bone osteotomy.

Options A, B, and D are incorrect because the bony angles (mPDFA and mPPTA) are within normal limits, ruling out osseous deformity. Option E is incorrect because while hamstring dysfunction can lead to recurvatum, the question describes a passive examination finding and normal bony angles, pointing to a fixed soft tissue laxity rather than a purely dynamic muscular issue, although hamstring weakness could contribute to the development of such laxity over time.

Question 2

A 55-year-old male presents with significant knee recurvatum. Preoperative planning reveals a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 88° and a normal Mechanical Posterior Distal Femoral Angle (mPDFA) of 82°. The surgeon, aiming for a 'straight leg,' performs a distal femoral flexion osteotomy to correct the clinical hyperextension.

Explanation

Correct Answer: B

The case content emphasizes the critical axiom: 'You must correct the deformity in the bone where it actually exists.' The patient has a reversed posterior tibial slope (mPPTA > 84°), indicating that the tibia is the true source of the recurvatum. The mPDFA is normal, meaning the femur is not deformed. By performing a flexion osteotomy of the distal femur (the wrong bone), the femoral condyles are now pointing abnormally downward onto a tibial plateau that is still sloped backward. The text explicitly states: 'With every single step, weight-bearing forces will cause the femur to literally slide off the back of the tibia, creating a devastating iatrogenic posterior knee subluxation.'

Option A is incorrect; anterior subluxation would occur if femoral recurvatum were corrected in the tibia. Option C (patella baja) is typically associated with proximal tibial osteotomies performed incorrectly relative to the tibial tuberosity, not distal femoral osteotomies. Options D and E are general surgical complications but not the specific biomechanical catastrophe predicted by violating Paley's fundamental rule in this scenario.

Question 3

A 40-year-old patient with a history of distal femoral fracture malunion presents with 15 degrees of knee recurvatum. Radiographic analysis reveals a Mechanical Posterior Distal Femoral Angle (mPDFA) of 98° (normal 80-85°) and a normal Mechanical Posterior Proximal Tibial Angle (mPPTA) of 81° (normal 77-84°). The Center of Rotation of Angulation (CORA) is identified in the distal femoral metaphysis.

Explanation

Correct Answer: C

The case content defines the CORA as 'the apex of the deformity—the precise mathematical point where the proximal and distal anatomical (or mechanical) axes of a deformed bone intersect.' It further states that 'Identifying the CORA is not a mere academic exercise; it is the single most important step in preoperative planning. The CORA dictates the ideal location for your surgical osteotomy.' According to Paley's Osteotomy Rule 1: 'If the osteotomy is performed exactly at the CORA, simple angular correction will perfectly realign the proximal and distal bone axes without creating any unwanted translation.' In this patient, the deformity is clearly femoral (mPDFA = 98°), and the CORA is located in the distal femoral metaphysis. Therefore, performing the osteotomy at this CORA allows for a precise angular correction without inducing secondary translation.

Option A is incorrect; a joint-line CORA indicates a soft tissue deformity, not a bony one, and would necessitate translation. Options B, D, and E are incorrect because the deformity is in the distal femur, and performing the osteotomy in the tibia or away from the CORA in the femur would either violate the principle of correcting the deformity where it lives or necessitate additional translation (Rule 2), which is not the ideal scenario when the CORA is accessible.

Question 4

A patient with a severe knee deformity undergoes full-length weight-bearing lateral radiography. A plumb line dropped from the center of the femoral head passes significantly posterior to the center of the knee joint.

Explanation

Correct Answer: B

The case content describes the normal sagittal mechanical axis: 'In a normal, healthy standing posture... a plumb line dropped from the center of the femoral head should pass... Anterior to the center of the knee joint... This specific anterior positioning creates a natural extension moment at the knee.' It then states: 'Conversely, excessive posterior deviation, where the mechanical axis falls behind the center of the knee, signifies a hyperextension deformity (recurvatum).' Therefore, a plumb line passing significantly posterior to the knee joint indicates recurvatum.

Option A is incorrect; excessive anterior deviation of the distal femur or proximal tibia indicates a flexion deformity (procurvatum). Option C is incorrect as the axis should pass anterior to the knee. Options D and E describe coronal plane deformities, which are not assessed by the sagittal mechanical axis.

Question 5

A 12-year-old patient with cerebral palsy presents with a 'recurvatum thrust' during the stance phase of gait, despite having normal Mechanical Posterior Distal Femoral Angle (mPDFA) and Mechanical Posterior Proximal Tibial Angle (mPPTA) measurements. The clinical presentation is analogous to Panel (iii) in the provided diagram.

clinical image

Explanation

Correct Answer: C

The case content highlights the crucial role of hamstrings: 'They are the primary dynamic guardians against knee hyperextension.' It further explains that in patients with neuromuscular conditions like cerebral palsy, 'this dynamic check-rein is often lost. The knee is driven into hyperextension with every single step. This repetitive micro-trauma gradually attenuates the posterior capsule and cruciate ligaments, ultimately transforming a purely dynamic muscle imbalance into a fixed, static ligamentous laxity.' Panel (iii) of the image specifically illustrates 'Dynamic Recurvatum' due to 'atrophied, weak, or paralyzed hamstrings.' The normal mPDFA and mPPTA rule out a primary osseous deformity.

Option A is incorrect as bony angles are normal. Option B and E describe specific ligamentous or capsular injuries, which can cause recurvatum, but in the context of a neuromuscular condition and dynamic thrust with normal bony angles, the primary underlying mechanism is hamstring dysfunction leading to secondary laxity. Option D is incorrect; quadriceps contracture typically leads to flexion contracture, not hyperextension.

Question 6

A 60-year-old patient with severe, long-standing knee flexion contracture (FFD) of 45 degrees presents for evaluation. A lateral radiograph shows the tibia appearing significantly translated posteriorly relative to the femur.

Explanation

Correct Answer: B

The case content explicitly addresses this diagnostic pitfall: 'One of the most dangerous traps in sagittal plane analysis is misinterpreting apparent subluxation in the setting of a severe Fixed Flexion Deformity (FFD).' It states that 'When a knee is locked in a flexion contracture, the tibia naturally appears to be translated posteriorly relative to the femur on a standard lateral radiograph.' The radiographic clue for apparent subluxation is that 'The posterior translation mathematically resolves as the flexion deformity is corrected.' The correct treatment is to 'Focus entirely on correcting the flexion contracture (e.g., performing a distal femoral extension osteotomy or soft tissue release).'

Option A is incorrect as it misinterprets apparent subluxation as true subluxation and suggests an inappropriate treatment (distraction). Option C is incorrect; while PCL rupture causes true subluxation, the context of severe FFD points to apparent subluxation. Option D is incorrect because while it's a common finding, it's not 'normal' in the sense of being benign; it's a consequence of the FFD that needs to be understood for correct treatment. Option E (tibial tubercle distalization) is used for patella alta, not for reducing posterior subluxation in this context.

Question 7

A surgeon is planning a proximal tibial flexion osteotomy for a patient with tibial recurvatum (Mechanical Posterior Proximal Tibial Angle (mPPTA) = 86°). The patient also has patella alta.

Explanation

Correct Answer: B

The case content provides specific guidance for proximal tibial osteotomies and patellar tendon insertion: 'According to advanced Paley principles, if the patellar tendon insertion is at a normal anatomic level, the osteotomy must be made distal to the tibial tuberosity. This is vital to avoid creating an iatrogenic patella baja (low-riding patella).' However, it then states: 'Conversely, if the patellar tendon insertion is abnormally proximal (patella alta), the osteotomy should be made proximal to the tibial tuberosity. In this specific scenario, an opening wedge correction will simultaneously bring the patellar tendon back down to its normal level and indirectly reduce any associated posterior knee subluxation.'

Option A is incorrect because it describes the rule for a normal patellar tendon insertion, not patella alta. Option C is incorrect as the level is highly relevant. Option D is incorrect; a combined osteotomy is not indicated for patella alta in this context. Option E is incorrect; the osteotomy itself can address the patella alta without separate tendon lengthening.

Question 8

During a distal femoral flexion osteotomy via a lateral sub-vastus approach for femoral recurvatum, the surgeon is performing an anterior opening wedge osteotomy.

Explanation

Correct Answer: C

Under 'Surgical Pearls: Distal Femoral Osteotomy,' the case content explicitly states: 'Hinge Integrity: The medial cortex (when using a lateral approach) must be meticulously preserved as the bony hinge. A fractured hinge leads to immediate instability, translation, and loss of the planned correction.' This is a critical technical detail for successful osteotomy.

Option A is incorrect; the approach is lateral sub-vastus, protecting the vastus lateralis, not releasing the vastus medialis. Option B is incorrect; the lateral cortex is the side of the osteotomy, but the medial cortex is preserved as the hinge. Option D is incorrect; while a posterior closing wedge is biomechanically stable, an anterior opening wedge is also a valid option, especially if limb lengthening is desired, and the question describes an anterior opening wedge. Option E is not a standard or necessary step for this specific osteotomy and could lead to lateral knee instability.

Question 9

A 28-year-old patient presents with 18 degrees of clinical knee hyperextension. Full-length lateral radiographs reveal a Mechanical Posterior Distal Femoral Angle (mPDFA) of 82° (normal 80-85°) and a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 89° (normal 77-84°).

Explanation

Correct Answer: B

The case content provides a clear diagnostic algorithm: 'If the mPDFA is > 85°, the source of the deformity is femoral. If the mPPTA is > 84°, the source of the deformity is tibial.' In this patient, the mPDFA of 82° is within the normal range, ruling out femoral osseous deformity. However, the mPPTA of 89° is significantly greater than the normal upper limit of 84°, indicating a flattened or reversed posterior slope of the tibial plateau. This directly points to tibial recurvatum as the primary source of the deformity.

Option A is incorrect because the mPDFA is normal. Option C is incorrect because the mPPTA is abnormal, indicating an osseous deformity. Option D is incorrect because only the tibia shows an osseous deformity. Option E is a potential etiology but the question asks for the primary source of the deformity based on the given radiographic measurements, which clearly point to a structural tibial issue.

Question 10

A patient with a distal femoral extension deformity (Mechanical Posterior Distal Femoral Angle (mPDFA) = 90°, Mechanical Posterior Proximal Tibial Angle (mPPTA) = 81°) undergoes a proximal tibial flexion osteotomy to correct their clinical hyperextension.

Explanation

Correct Answer: B

The case content provides a direct warning against this specific surgical error: 'Correcting Femoral Recurvatum in the Tibia (THE WRONG WAY).' The problem is a distal femoral extension deformity (mPDFA > 85°), meaning the femur is the source. The mistake is performing a flexion osteotomy of the proximal tibia to compensate. The result is that 'The tibial plateau now has an excessively increased posterior slope. The abnormally extended femoral condyles will drive the tibia violently forward during the stance phase, creating a severe iatrogenic anterior knee subluxation and placing immense, tearing strain on the PCL.'

Option A is incorrect; posterior subluxation occurs when tibial recurvatum is corrected in the femur. Option C (patella alta) is a pre-existing condition or can be caused by certain osteotomy designs, but not the primary biomechanical consequence of this specific error. Option D is a long-term consequence of instability but not the immediate biomechanical complication. Option E is a general surgical complication but not the specific iatrogenic subluxation described.

Question 11

A 62-year-old patient presents with a chronic, progressive crouched gait and significant anterior knee pain, particularly with ambulation. Clinical examination reveals a fixed flexion deformity (FFD) of the knee. The patient reports rapid quadriceps fatigue even with short distances. Based on the biomechanical principles outlined in the case, which of the following is the MOST accurate explanation for the patient's symptoms?

clinical image

Explanation

Correct Answer: C

The case explicitly states that when the knee cannot fully extend, the quadriceps mechanism is forced to fire continuously throughout the stance phase. This constant, unrelenting isometric contraction is metabolically demanding, leading to rapid muscle fatigue. Furthermore, this continuous quadriceps activity subjects the patellofemoral joint to massive, abnormal compressive loads, rapidly leading to chondromalacia, severe pain, and early-onset osteoarthritis (anterior knee pain). The crouched gait is a compensatory mechanism, not a primary cause of reduced anterior knee pain.

Option A is incorrect because while hamstrings can contribute to FFD, the primary biomechanical consequence described for fatigue and anterior knee pain relates to the quadriceps. Option B is incorrect; increased patellar tendon tension is a consequence of quadriceps overactivity, but patellar subluxation is not the primary or most direct biomechanical consequence described. Option D is incorrect as the crouched gait alters the center of gravity and places immense strain on the hips and lower back, but it does not reduce anterior knee pain; rather, it's a compensatory mechanism for the knee's inability to extend. Option E is incorrect; while the gastrocnemius can contribute to soft tissue contracture, the primary mechanism for fatigue and anterior knee pain is the quadriceps' continuous firing.

Question 12

A 48-year-old male presents with a sagittal plane knee deformity. To accurately quantify the bony architecture, a true lateral radiograph is obtained. Which of the following statements correctly defines the Posterior Distal Femoral Angle (PDFA) and its normal range, according to Paley's principles?

diagram of angles

Explanation

Correct Answer: C

The case defines the Posterior Distal Femoral Angle (PDFA) as 'the angle formed between the anatomic axis of the femur and the joint line of the distal femoral condyles.' It also states the normal value range for PDFA is '83° ± 4°'.

Option A describes the PPTA and its normal range is incorrect for PDFA. Option B correctly defines PDFA but provides the normal range for PPTA. Option D incorrectly refers to the mechanical axis instead of the anatomic axis. Option E describes the PPTA and its normal range, not the PDFA.

Question 13

A 35-year-old patient with a history of congenital knee deformity undergoes radiographic evaluation. On a true lateral radiograph, the measured Posterior Distal Femoral Angle (PDFA) is 75°, and the Posterior Proximal Tibial Angle (PPTA) is 86°. Based on Paley's principles and the provided normal values (PDFA 83° ± 4°, PPTA 81° ± 4°), what do these measurements indicate?

diagram of angles

Explanation

Correct Answer: B

According to the case, a decreased PDFA signifies femoral procurvatum, and an increased PDFA signifies femoral recurvatum. A decreased PPTA signifies tibial procurvatum, and an increased PPTA signifies tibial recurvatum.

PDFA: Measured at 75°. Normal range is 83° ± 4° (79° to 87°). Since 75° is less than 79°, this indicates a decreased PDFA, which signifies femoral procurvatum.
PPTA: Measured at 86°. Normal range is 81° ± 4° (77° to 85°). Since 86° is greater than 85°, this indicates an increased PPTA, which signifies tibial recurvatum.

Therefore, the patient has femoral procurvatum and tibial recurvatum.

Question 14

A 55-year-old patient presents with a clinical Fixed Flexion Deformity (FFD) of 30°. A true lateral radiograph is obtained for detailed analysis. The measured Posterior Proximal Tibial Angle (PPTA) is 65°. Using the standard normal reference values from the case (PDFA 84°, PPTA 80°), what is the calculated contribution of tibial procurvatum to the overall FFD?

radiograph with measurements

Explanation

Correct Answer: C

The case outlines the calculation for tibial procurvatum: Normal PPTA - Measured PPTA. Using the standard normal reference of 80° for PPTA:

Normal PPTA: 80°
Measured PPTA: 65°
Tibial procurvatum = 80° - 65° = 15°

This 15° represents the contribution of the proximal tibial bony deformity to the overall FFD.

Question 15

A 70-year-old patient presents with a severe crouched gait and a clinical Fixed Flexion Deformity (FFD) of 35°. Radiographic analysis using Paley's principles reveals a Posterior Distal Femoral Angle (PDFA) of 70° and a Posterior Proximal Tibial Angle (PPTA) of 72°. Using the standard normal reference values from the case (PDFA 84°, PPTA 80°), what is the calculated true soft tissue flexion contracture component?

radiograph with measurements

Explanation

Correct Answer: C

To calculate the true soft tissue flexion contracture, we must first determine the total bony deformity:

Femoral Procurvatum: Normal PDFA (84°) - Measured PDFA (70°) = 14°
Tibial Procurvatum: Normal PPTA (80°) - Measured PPTA (72°) = 8°
Total Bony Deformity: 14° (Femur) + 8° (Tibia) = 22°
Soft Tissue Contracture: Clinical FFD (35°) - Total Bony Deformity (22°) = 13°

The patient has a 13° true soft tissue flexion contracture.

Question 16

A 40-year-old patient presents with a 40° clinical Fixed Flexion Deformity (FFD). Radiographic analysis, as depicted in the case example, reveals a 10° femoral procurvatum, a 20° tibial procurvatum, and a 10° soft tissue flexion contracture. According to the Paley Doctrine of Anatomic Correction, what is the ideal surgical strategy for this patient?

radiograph with measurements

Explanation

Correct Answer: C

The case emphasizes that the ideal treatment strategy is a coordinated, three-part procedure that addresses each component precisely at its anatomic source. For the specific example given (10° femoral procurvatum, 20° tibial procurvatum, 10° soft tissue contracture), the anatomically correct treatment is:

A 10° distal femoral extension osteotomy performed exactly at the femoral CORA.
A 20° proximal tibial extension osteotomy performed exactly at the tibial CORA.
A posterior soft tissue release (or gradual distraction) to specifically address the 10° of true joint contracture.

Options A, B, and D represent flawed strategies that either overcorrect bone for soft tissue or fail to address all components, leading to joint incongruity and poor outcomes. Option E is a plausible strategy for soft tissue in specific cases (like irradiated knees), but combining it with a 30° tibial osteotomy is not the precise correction for the given breakdown of deformities.

Question 17

An inexperienced orthopedic surgeon attempts to correct a 30° Fixed Flexion Deformity (FFD) by performing a 30° proximal tibial extension osteotomy, without addressing the underlying 10° femoral procurvatum and 10° soft tissue contracture. Based on the principles discussed, what is the MOST likely long-term consequence of this flawed surgical approach?

clinical image

Explanation

Correct Answer: C

The case explicitly warns against the 'flawed alternative strategy' where a surgeon attempts to correct the entire deformity within a single bone or by overcorrecting bone to compensate for tight soft tissues. This approach 'is fundamentally doomed to fail.' By overcorrecting the bone (e.g., 30° tibial osteotomy for a 10° tibial deformity + 10° femoral deformity + 10° soft tissue contracture), the surgeon creates a joint that is only congruent in a state of hyperextension. The pathologically tight posterior soft tissues will dramatically increase joint contact pressures, wedge the joint open anteriorly, and ultimately pull the knee right back into a flexion contracture. This iatrogenic joint malalignment guarantees postoperative stiffness, severe pain, and rapid-onset early arthritis.

Options A, B, D, and E describe positive or compensatory outcomes that contradict the severe negative consequences detailed in the case for such a flawed approach.

Question 18

A 50-year-old patient presents with a 34° Fixed Flexion Deformity (FFD) of the knee following extensive radiation therapy for a distal femoral sarcoma. Radiographic analysis reveals a 14° femoral procurvatum and a 12° tibial procurvatum. The calculated soft tissue contracture is 8°. Given the patient's history of radiation, which of the following is the MOST appropriate strategy for addressing the soft tissue component of the deformity?

clinical image

Explanation

Correct Answer: C

The case specifically addresses 'The Irradiated or Severely Scarred Knee,' stating that 'Radiation creates a profoundly hostile soft-tissue envelope characterized by severe microvascular damage, profound fibrosis, and chronic tissue hypoxia.' It explicitly warns that 'attempting an open posterior soft tissue release is fraught with extreme peril, carrying an unacceptably high risk of catastrophic wound breakdown, deep tissue necrosis, and devastating neurovascular injury.'

For such cases, the implied and generally accepted strategy is gradual distraction (often with an external fixator) to safely stretch the contracted soft tissues over time, minimizing the risk of wound complications and neurovascular injury. The case example for post-radiation contracture implies this approach by stating the need to address the soft tissue component without suggesting an open release.

Options A and B are contraindicated due to the high risk of complications in irradiated tissue. Option D is not a standard or effective treatment for severe fibrotic contractures. Option E is incorrect, as ignoring the soft tissue component will lead to joint incongruity and recurrence of the FFD, as discussed in the 'Flawed Alternative Strategy' section.

Question 19

According to Paley's principles, the Center of Rotation of Angulation (CORA) is a critical concept for precise deformity correction. For a patient presenting with an isolated femoral procurvatum deformity, where would the CORA typically be located?

diagram of angles

Explanation

Correct Answer: B

The case states, 'A decreased PDFA signifies that the distal femoral joint surface is pathologically tilted anteriorly (into extension) relative to the femoral shaft. This creates a femoral procurvatum deformity. The CORA for this specific deformity is located in the distal femur.' While the exact point within the distal femur can vary, it is generally proximal to the joint line, where the angulation occurs.

Option A is incorrect as it describes the location for a tibial deformity. Option C is incorrect; a CORA at the joint line would imply a joint-level deformity, not a specific bony angulation within the femur. Option D is incorrect; mid-diaphyseal CORAs are typically associated with diaphyseal bowing, not juxta-articular procurvatum. Option E is unrelated to the CORA of a femoral procurvatum.

Question 20

A 28-year-old patient presents with a long-standing history of a crouched gait, difficulty with prolonged standing, and recurrent anterior knee pain. Clinical examination reveals a significant fixed flexion deformity of the knee. The patient denies any acute trauma. Based on the case, which of the following is the MOST accurate initial diagnostic approach for this patient's FFD?

clinical image

Explanation

Correct Answer: C

The case explicitly states, 'The critical first step in preoperative planning is a paradigm shift: an FFD is a clinical sign, not a final diagnosis. It is a symptom that can arise from three distinct anatomic sources, often presenting in complex combinations: bony deformity of the distal femur, bony deformity of the proximal tibia, and soft tissue contracture.' It further emphasizes the need to 'meticulously quantify the bony architecture using standardized joint orientation angles on a high-quality, true lateral radiograph.'

Options A, D, and E are incorrect because they assume a single etiology for FFD and jump to specific treatments or less comprehensive diagnostic steps without first differentiating the underlying components. Option B is incorrect because while patellofemoral issues are a consequence, a CT scan is not the initial or primary tool for differentiating the bony and soft tissue components of FFD in the sagittal plane; a true lateral radiograph is paramount for Paley's angle measurements.

Question 21

A 28-year-old patient presents with a painful knee recurvatum deformity following a previous trauma. Radiographs reveal a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 96° (normal 77°-84°). Which ligamentous structure is subjected to the highest strain due to this specific bony deformity?

Explanation

An mPPTA >84° indicates an anterior tilt of the proximal tibial articular surface (anterior slope). This anterior slope forces the tibia posteriorly relative to the femur during weight-bearing, abnormally increasing strain on the PCL.

Question 22

When planning an anterior opening wedge high tibial osteotomy (HTO) to correct a severe sagittal plane recurvatum deformity, what associated modification must be considered to prevent iatrogenic patella infera (baja)?

Explanation

An anterior opening wedge osteotomy proximal to the tibial tubercle effectively elongates the anterior tibia, pulling the tibial tubercle distally and creating patella infera. This is prevented by performing the osteotomy distal to the tubercle or utilizing a sliding tubercle osteotomy.

Question 23

According to Paley's principles of deformity correction, if an osteotomy is performed at a level outside the Center of Rotation of Angulation (CORA), but the mechanical hinge is placed exactly at the CORA, what is the geometric result of the correction?

Explanation

This describes Paley's Osteotomy Rule 2. When the osteotomy is outside the CORA but the hinge is at the CORA, the mechanical axes will fully realign collinearly, but it requires and results in local translation at the osteotomy site.

Question 24

A 45-year-old patient exhibits a unilateral fixed equinus contracture of the ankle. What is the classic compensatory sagittal plane deformity observed at the ipsilateral knee during the stance phase of gait?

Explanation

To maintain a plantigrade foot during the stance phase of gait in the presence of a fixed ankle equinus contracture, the knee must hyperextend, leading to a compensatory knee recurvatum deformity.

Question 25

A normal sagittal plane mechanical axis of the lower extremity is evaluated by dropping a plumb line from the center of the femoral head to the center of the ankle. In a normal individual standing with full knee extension, where does this line pass in relation to the knee joint center?

Explanation

The sagittal mechanical axis (plumb line) normally passes anterior to the center of rotation of the knee joint. This anterior position helps maintain passive knee extension during stance, reducing the energy requirement of the quadriceps.

Question 26

A 35-year-old patient presents with 20 degrees of clinical knee recurvatum. Radiographic evaluation shows a Mechanical Posterior Distal Femoral Angle (mPDFA) of 83° and an mPPTA of 81°. What is the most appropriate primary intervention for this patient?

Explanation

An mPDFA of 83° and an mPPTA of 81° are within normal limits, indicating no primary bony sagittal deformity. The recurvatum is therefore driven by soft tissue, capsular, or ligamentous laxity, and bony osteotomy is generally contraindicated as the primary solution.

Question 27

A surgeon applies Paley's Rule 3 to correct a severe distal femoral procurvatum deformity. The osteotomy is performed proximal to the CORA, and the mechanical hinge is also placed proximal to the CORA. What is the expected postoperative alignment?

Explanation

Under Paley's Rule 3, if both the osteotomy and the axis of rotation (hinge) are located away from the CORA, the correction will result in parallel but non-collinear mechanical axes, creating a translation deformity.

Question 28

A patient sustained a distal femur fracture managed non-operatively 10 years ago. A standing full-length lateral radiograph reveals a Mechanical Posterior Distal Femoral Angle (mPDFA) of 70°. What is the precise nature of this sagittal plane deformity?

Explanation

Normal mPDFA is approximately 83°. An mPDFA of 70° indicates that the posterior angle is decreased, meaning the distal articular surface is tilted posteriorly. This corresponds to an apex anterior bowing of the distal femur, which is clinically defined as distal femoral procurvatum.

Question 29

During a distal femoral osteotomy to correct a sagittal plane deformity, the mechanical hinge axis is inadvertently aligned obliquely rather than perfectly perpendicular to the sagittal plane. What is the primary biomechanical consequence?

Explanation

If the axis of correction (hinge) is not strictly perpendicular to the plane of the deformity, angular correction will couple out of the primary plane, unintentionally inducing a secondary angulation (varus or valgus) in the coronal plane.

Question 30

A surgeon is considering a focal dome osteotomy to correct a 25-degree recurvatum deformity of the proximal tibia. What is the primary geometric advantage of utilizing a dome osteotomy centered perfectly on the CORA?

Explanation

A focal dome osteotomy with the axis of rotation placed at the CORA (Rule 1) allows pure angular correction. Because the cut is arcuate, it maintains bony contact without the limb shortening seen in closing wedges or the gap/lengthening seen in opening wedges.

Question 31

A patient undergoes a proximal tibial osteotomy that inadvertently overcorrects the sagittal alignment, creating an mPPTA of 70°. This excessive posterior tibial slope will place maximum detrimental strain on which of the following post-operative conditions?

Explanation

An mPPTA of 70° corresponds to a very high posterior tibial slope. Excessive posterior slope forces the tibia anteriorly relative to the femur during weight-bearing, significantly increasing the strain on the Anterior Cruciate Ligament (ACL) or its graft.

Question 32

Which radiographic study is considered the gold standard for accurately measuring a bony sagittal plane deformity of the lower extremity prior to deformity correction surgery?

Explanation

Accurate assessment of sagittal mechanical axes and joint line orientation (mPDFA, mPPTA) requires a full-length lateral radiograph of the limb under load, specifically positioned in maximum possible active extension.

Question 33

A patient with a distal femoral recurvatum deformity (mPDFA 98°) also demonstrates a compensatory deformity to maintain a horizontal foot flat during stance. What is the most likely ipsilateral compensatory bony deformity?

Explanation

To keep the foot flat on the ground and the trunk upright, a recurvatum (apex posterior) deformity of the femur is typically compensated by a procurvatum (apex anterior) deformity of the tibia, effectively 'Z-ing' the limb.

Question 34

When calculating the mPDFA for preoperative planning of a sagittal deformity, the mechanical axis of the femur in the sagittal plane must be drawn. Which two anatomic landmarks properly define this axis?

Explanation

The sagittal mechanical axis of the femur is defined by a line connecting the center of rotation of the femoral head to the center of the distal femoral joint space on a true lateral radiograph.

Question 35

A patient presents with a severe fixed flexion contracture of the knee (35 degrees) secondary to a malunited distal femur fracture. If acute correction via an extension closing wedge osteotomy is planned, what is the most critical limiting factor for the amount of acute correction obtainable?

Explanation

Acute correction of severe knee flexion contractures places immediate, high stretch on the posterior neurovascular structures. The sciatic nerve, and particularly its common peroneal branch, is highly sensitive to traction injury, often limiting acute correction.

Question 36

When analyzing the Joint Line Convergence Angle (JLCA) in the sagittal plane of a normal knee, how do the distal femoral and proximal tibial joint lines relate to one another?

Explanation

In the normal knee, the sagittal joint lines of the distal femur and proximal tibia are roughly parallel (JLCA near 0 degrees). Significant deviation indicates either cartilage loss, ligamentous laxity, or intra-articular deformity.

Question 37

A patient has a tibial procurvatum (apex anterior) deformity resulting in a lack of full extension. An anterior closing wedge high tibial osteotomy is performed to restore the mechanical axis. What is a known consequence of this specific technique?

Explanation

An anterior closing wedge osteotomy removes bone stock to close the deformity. While it successfully corrects procurvatum, it inherently results in limb shortening, which must be accounted for in preoperative planning.

Question 38

A 50-year-old patient undergoes a distal femoral extension osteotomy to correct a significant procurvatum deformity. Postoperatively, the patient's mechanical alignment is restored, but they complain of a new-onset, significant limitation in knee flexion. What is the primary biomechanical reason for this?

Explanation

Correcting a procurvatum deformity via an extension osteotomy shifts the entire arc of motion towards extension. If the patient had adapted their soft tissues to the flexed position, this shift typically reduces maximum terminal flexion postoperatively.

Question 39

In applying Paley's Rule 1 to correct a sagittal deformity of the distal femur, which of the following statements strictly characterizes the surgical technique?

Explanation

Paley's Rule 1 dictates that both the osteotomy cut and the mechanical axis of rotation (hinge) are located at the Center of Rotation of Angulation (CORA), resulting in pure angular correction without translation.

Question 40

A patient requires an osteotomy for a combined angulation and translation deformity in the sagittal plane of the tibia. Which of the following describes the correct identification of the CORA in this specific combined deformity?

Explanation

Even in combined angulation and translation deformities, the CORA is defined by the intersection of the proximal and distal anatomical (or mechanical) axes. If there is angulation, these lines will intersect at a specific definable point.

Question 41

When evaluating a patient for sagittal plane knee deformity, accurate measurement of the mechanical axes is critical. What are the generally accepted normal values for the Mechanical Posterior Distal Femoral Angle (mPDFA) and the Mechanical Posterior Proximal Tibial Angle (mPPTA)?

Explanation

Normal sagittal joint line orientation relies on a mPDFA of approximately 83° (range 79°-87°) and an mPPTA of approximately 81° (range 77°-84°). Deviations from these values indicate structural recurvatum or procurvatum.

Question 42

A 45-year-old patient presents with a clinically apparent knee procurvatum (flexion deformity). Full-length sagittal radiographs reveal a normal mPPTA of 82° and an abnormal femoral parameter. Which of the following mPDFA values confirms an apex anterior (procurvatum) deformity of the distal femur?

Explanation

An mPDFA significantly less than 80° indicates an apex anterior bow (procurvatum) of the distal femur, leading to a fixed flexion deformity. An mPDFA greater than 85° indicates recurvatum.

Question 43

According to Paley's principles of deformity correction, if a surgeon plans an osteotomy to correct a severe sagittal plane distal femoral deformity, what is the geometric outcome if the osteotomy is made exactly at the Center of Rotation of Angulation (CORA) and the hinge is also placed exactly at the CORA?

Explanation

Paley's Osteotomy Rule 1 states that if both the osteotomy and the hinge (axis of correction) are located at the CORA, pure angular correction is achieved without any translation of the mechanical axis.

Question 44

A patient requires a distal femoral osteotomy for a severe recurvatum deformity. Due to poor metaphyseal bone stock, the surgeon places the osteotomy in the diaphysis, significantly proximal to the CORA. However, the hinge (axis of rotation) is placed exactly at the CORA. What is the expected outcome based on Paley's Rule 2?

Explanation

Paley's Rule 2 states that if the osteotomy is placed away from the CORA, but the hinge remains at the CORA, the mechanical axes will realign perfectly, but intended translation will occur at the osteotomy site.

Question 45

A surgeon corrects a proximal tibial procurvatum deformity. Both the osteotomy and the hinge are inadvertently placed 3 cm distal to the true CORA. According to Paley's Rule 3, what is the mechanical consequence of this execution?

Explanation

Paley's Rule 3 dictates that if both the osteotomy and the hinge are located away from the CORA, the resulting mechanical axes will be parallel to each other but translated, creating a secondary translation deformity.

Question 46

A 22-year-old male presents with 20 degrees of genu recurvatum. Radiographic analysis shows an mPDFA of 83° and an mPPTA of 81°. What is the most likely etiology of this patient's deformity?

Explanation

Normal sagittal bony parameters (mPDFA ~83°, mPPTA ~81°) in the presence of clinical recurvatum indicate a soft-tissue etiology, such as posterior capsular or ligamentous laxity, rather than a structural osseous deformity.

Question 47

A patient with a chronic distal femoral fracture malunion develops a fixed bony recurvatum deformity (mPDFA = 96°). To maintain a plantigrade foot and an upright posture over time, what compensatory bony or positional change is most likely to develop in the ipsilateral tibia?

Explanation

To compensate for a femoral extension deformity (recurvatum), the tibia will often develop a compensatory flexion deformity (procurvatum) to keep the leg relatively straight for weight-bearing. Procurvatum of the tibia increases the mPPTA.

Question 48

Altering the sagittal alignment of the proximal tibia significantly impacts knee ligament biomechanics. If a surgeon performs an osteotomy that decreases the posterior tibial slope (increases mPPTA), which ligament is placed under increased strain?

Explanation

Decreasing the posterior tibial slope shifts the resting position of the tibia posteriorly relative to the femur, increasing tension on the PCL. Wait, decreasing posterior slope reduces anterior tibial translation, increasing tension on the PCL.

Question 49

A 16-year-old athlete presents with genu recurvatum following a history of severe Osgood-Schlatter disease. Radiographs confirm an osseous deformity. Which of the following radiographic findings is most characteristic of this condition?

Explanation

Premature closure of the anterior aspect of the proximal tibial physis leads to continued posterior growth, resulting in an apex posterior deformity (recurvatum). This is radiographically defined by an abnormally decreased mPPTA.

Question 50

A 50-year-old female undergoes an anterior opening-wedge High Tibial Osteotomy (HTO) to correct a complex deformity, effectively decreasing her mPPTA. What biomechanical effect does this specific sagittal change have on the anterior cruciate ligament (ACL)?

Explanation

Decreasing the mPPTA means increasing the posterior tibial slope. An increased posterior slope drives the tibia anteriorly relative to the femur during axial loading, thereby increasing strain on the ACL.

Question 51

During a distal femoral extension osteotomy to correct a severe fixed flexion deformity (procurvatum), what secondary complication regarding the extensor mechanism must the surgeon be highly vigilant about?

Explanation

An extension osteotomy of the distal femur typically translates the femoral condyles anteriorly relative to the shaft. This stretches the extensor mechanism, creating a relative patella baja and significantly increasing patellofemoral contact pressures.

Question 52

A surgeon corrects a clinically severe genu recurvatum caused entirely by a proximal tibial deformity (mPPTA = 68°). To 'straighten the leg' without operating on the tibia, the surgeon performs a distal femoral flexion osteotomy. What is the primary long-term consequence of this compensatory correction?

Explanation

Correcting a tibial deformity by operating on the femur creates parallel mechanical axes but an oblique joint line in the sagittal plane. This unphysiologic orientation induces shear forces and accelerates joint degeneration.

Question 53

When performing a standard medial opening-wedge High Tibial Osteotomy (HTO) for a coronal varus deformity, what is the most common unintended iatrogenic change in the sagittal plane if the gap is opened equally at the anterior and posterior cortices?

Explanation

Due to the triangular cross-section of the proximal tibia, opening the osteotomy gap equally anteriorly and posteriorly inadvertently increases the posterior tibial slope (decreases mPPTA). The anterior gap must be smaller to maintain the normal slope.

Question 54

A patient with a distal femoral recurvatum deformity (mPDFA = 95°) is planned for a corrective anterior opening wedge osteotomy using an external circular fixator. To adhere to Paley's Rule 1 and avoid translation, where must the hinge be strategically placed?

Explanation

For an opening wedge osteotomy that achieves pure angulation without translation (Rule 1), the hinge must be placed on the convex cortex (anterior cortex for recurvatum) exactly at the level of the CORA.

Question 55

A patient presents with a severe knee recurvatum deformity. Radiographs reveal a mechanical posterior distal femoral angle (mPDFA) of 96 degrees and a mechanical posterior proximal tibial angle (mPPTA) of 81 degrees. According to Paley's principles, where is the primary site of the bony deformity?

Explanation

The normal mPDFA is 83 degrees. An increased mPDFA (96 degrees) indicates the distal articular surface is extended relative to the shaft, representing a distal femoral apex posterior deformity (recurvatum).

Question 56

A surgeon plans to correct a distal femoral procurvatum deformity using Paley's Osteotomy Rule 1. If the osteotomy is performed exactly at the Center of Rotation of Angulation (CORA) and the hinge is placed at the CORA, what is the expected geometric outcome?

Explanation

Paley's Rule 1 states that if the osteotomy and the hinge are both located at the CORA, pure angular correction is achieved without any translation of the bone segments.

Question 57

A 45-year-old male presents with symptomatic knee hyperextension. Preoperative analysis shows a normal distal femur (mPDFA = 83 degrees) but an abnormal proximal tibia with an mPPTA of 95 degrees. What compensatory change in knee ligament mechanics is most likely occurring due to this tibial morphology?

Explanation

An increased mPPTA implies a decreased or reversed posterior tibial slope (apex posterior deformity/recurvatum). This abnormal anterior tilt of the tibial plateau increases posterior tibial translation forces, thereby increasing tension on the PCL.

Question 58

A patient with a distal femoral recurvatum deformity (mPDFA = 98 degrees) undergoes a compensatory flexion osteotomy of the proximal tibia instead of the femur. What is the most significant long-term biomechanical consequence of this mismatch correction?

Explanation

Correcting a femoral deformity with a tibial osteotomy creates a compensatory deformity. While the overall leg may appear straight, the knee joint line becomes oblique to the ground in the sagittal plane, drastically increasing shear forces and altering kinematics.

Question 59

When analyzing the sagittal plane alignment of the lower extremity using Paley's principles, where should the normal mechanical axis (plumb line from the center of the femoral head) pass relative to the knee joint?

Explanation

In the sagittal plane, the normal mechanical axis (plumb line) drops from the center of the femoral head and passes slightly anterior to the center of the knee joint, terminating at the center of the ankle.

Question 60

During preoperative planning for a proximal tibial deformity, an orthopedic surgeon measures a mechanical posterior proximal tibial angle (mPPTA) of 68 degrees (normal 77-84 degrees). Which of the following clinical findings best corresponds to this measurement?

Explanation

A decreased mPPTA (68 degrees) means the posterior angle is smaller than normal, indicating the joint line is tilted posteriorly relative to the shaft. This equates to an apex anterior deformity (procurvatum) and an increased posterior tibial slope.

Question 61

A surgeon applies Paley's Osteotomy Rule 2 to correct a distal femoral sagittal deformity. The CORA is at the knee joint line, but the osteotomy is performed 5 cm proximal in the metaphysis. If the hinge is maintained at the CORA, what is the radiographic result?

Explanation

Paley's Rule 2 states that if the osteotomy is away from the CORA but the hinge is at the CORA, the correction will result in both angulation and translation. This combination restores collinearity to the mechanical axis.

Question 62

A 35-year-old female presents with clinical knee recurvatum. Her standing full-length lateral radiograph shows a normal mPDFA (82 degrees) and normal mPPTA (81 degrees). However, there is a prominent Sagittal Joint Line Convergence Angle (sJLCA). What is the primary etiology of her deformity?

Explanation

A normal mPDFA and mPPTA indicate the bones themselves do not have a sagittal deformity. An increased sJLCA indicates the joint space is opening asymmetrically, pointing to soft tissue laxity or capsular hyperextension as the cause.

Question 63

While performing a medial opening wedge high tibial osteotomy (HTO) for a coronal varus deformity, the surgeon inadvertently opens the anterior gap more than the posterior gap. What is the expected iatrogenic effect in the sagittal plane?

Explanation

Opening the anterior cortex more than the posterior cortex in an HTO tilts the tibial plateau posteriorly. This increases the posterior tibial slope, which is an apex anterior (procurvatum) morphologic change, increasing strain on the ACL.

Question 64

A patient has a distal femoral diaphyseal fracture malunion with an apex anterior (procurvatum) deformity. The surgeon performs an osteotomy at the distal metaphysis (away from the diaphyseal CORA) and places the hinge at the osteotomy site. According to Paley's Rule 3, what is the biomechanical outcome?

Explanation

Paley's Rule 3 states that when the osteotomy and the hinge are both located away from the CORA, angular correction occurs but a secondary translation deformity is created (the proximal and distal axes become parallel but not collinear).

Question 65

Which of the following interventions is most appropriate for a 28-year-old patient with an isolated, symptomatic 15-degree bony recurvatum of the proximal tibia (mPPTA = 96 degrees) with a CORA located 4 cm distal to the joint line?

Explanation

The deformity is in the proximal tibia (recurvatum/apex posterior). To correct this (decrease the mPPTA and restore slope), an anterior opening wedge osteotomy or a posterior closing wedge osteotomy of the proximal tibia is required.

Question 66

A patient with cerebral palsy presents with severe bilateral knee flexion posturing during gait. Sagittal radiographs show an mPDFA of 83 degrees and an mPPTA of 81 degrees. The popliteal angle is 70 degrees. What is the most appropriate initial management strategy?

Explanation

Normal mPDFA and mPPTA values indicate the bony architecture is normal. The knee flexion is due to soft tissue contracture (hamstring spasticity), making soft tissue lengthening the appropriate initial management rather than bony osteotomy.

Question 67

When planning an anterior closing wedge osteotomy of the distal femur to correct a symptomatic procurvatum deformity, the surgeon must counsel the patient on which inherent consequence of this specific osteotomy technique?

Explanation

A closing wedge osteotomy removes a segment of bone, inherently resulting in some degree of limb shortening. This must be factored into preoperative planning, especially if a leg length discrepancy already exists.

Question 68

A 50-year-old patient requires a distal femoral osteotomy for a combined 10-degree valgus and 15-degree recurvatum deformity. The surgeon plans a single-cut oblique osteotomy. In which plane does the true deformity exist?

Explanation

A multi-planar deformity (coronal and sagittal) is geometrically a single angular deformity occurring in an oblique plane. A single-cut osteotomy perpendicular to this oblique plane can correct both deformities simultaneously.

Question 69

During evaluation of a sagittal knee deformity, you utilize <br/><br/>. According to Paley's principles, what is the defining radiographic landmark for the proximal mechanical axis of the femur in the sagittal plane?

Explanation

The mechanical axis of the femur in any plane (coronal or sagittal) is defined by a line connecting the center of the femoral head to the center of the knee joint.

Question 70

An adult patient presents with a 'back-knee' (recurvatum) gait thrust. Upon clinical examination, the patient's knee anatomy is entirely normal, but they lack active and passive ankle dorsiflexion past neutral. What is the mechanism of this compensatory knee recurvatum?

Explanation

An ankle equinus contracture prevents normal forward progression of the tibia over the foot during the stance phase of gait. To keep the foot flat on the ground, the knee is forced into compensatory hyperextension (recurvatum).

Question 71

A surgeon analyzes a femur with severe bowing. Drawing the proximal and distal anatomic axes does not intersect at the maximum point of clinical deformity. Instead, the bowing spans the entire diaphysis. How should this multi-apical sagittal deformity be analyzed using Paley's method?

Explanation

For multi-apical or sweeping deformities (like a bowed femur), the bone is divided into proximal, middle, and distal segments. Intersecting the axes of these individual segments defines multiple CORAs required to plan a multi-level correction.

Question 72

When correcting a severe distal femoral apex posterior (recurvatum) deformity with an anterior opening wedge osteotomy, what is a crucial patellofemoral biomechanical change that the surgeon must anticipate?

Explanation

An anterior opening wedge osteotomy at the distal femur effectively lengthens the anterior column, which can alter the extensor mechanism vector, increasing patellofemoral contact pressures and functionally tightening the extensor mechanism.

Question 73

A patient sustained a proximal tibial fracture resulting in malunion. The current mPPTA is 88 degrees (normal 81 degrees). The patient complains of giving way. Which ligament is most likely rendered functionally incompetent by this osseous malalignment?

Explanation

An mPPTA of 88 degrees means the proximal tibia is in recurvatum (decreased/reversed posterior slope). A flattened or reversed tibial slope shifts the resting position of the tibia posteriorly and forces the femur anteriorly, dramatically reducing the functional tension and efficiency of the ACL.

Question 74

A 16-year-old with a history of a distal femoral physeal arrest presents with 20 degrees of knee procurvatum. Radiographs demonstrate an mPDFA of 70 degrees. To perform a corrective osteotomy following Paley's Rule 1, where must the hinge be located?

Explanation

Paley's Rule 1 requires that the osteotomy and the hinge point both reside on the bisector line of the angle formed by the proximal and distal mechanical axes (the CORA). This ensures pure angular correction without translation.

Question 75

A 40-year-old patient presents with 25 degrees of knee recurvatum. Full-length standing lateral radiographs reveal a Mechanical Posterior Distal Femoral Angle (mPDFA) of 83° and a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 68°. Which of the following is the primary source of the deformity?

Explanation

The normal mPPTA is 77°-84°. A decreased mPPTA (e.g., 68°) indicates that the posterior joint angle is diminished, resulting in an abnormal posterior slope and proximal tibial recurvatum.

ABOS Part I Orthopaedic Deformity Correction, Limb Reconstruction & Gait Analysis Review | Part 21914

ABOS Part I & AAOS OITE Orthopedic Review: Sagittal Knee Deformity, Paley's Principles & Osteotomy | Part 21917

Key Takeaway

ABOS Part I & AAOS OITE Orthopedic Review: Sagittal Knee Deformity, Paley's Principles & Osteotomy | Part 21917

Chapter Index