This practice set contains high-yield board review questions covering key concepts in Lower Extremity Trauma. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Question 161
Topic: Lower Extremity Trauma
A surgeon performs a medial opening wedge high tibial osteotomy (HTO) for a varus knee. If the anterior osteotomy gap is inadvertently opened significantly more than the posteromedial gap, what is the expected change to the proximal tibia?
Correct Answer & Explanation
. Increase in posterior tibial slope.
Explanation
The proximal tibia has a triangular cross-section. To maintain the native sagittal slope during a medial opening wedge HTO, the anterior gap must be about half the size of the posteromedial gap. Opening the anterior gap excessively will tilt the plateau posteriorly, increasing the posterior tibial slope.
Question 162
Topic: Lower Extremity Trauma
A 48-year-old female presents with chronic knee pain. Radiographs show a mechanical axis that passes 10 mm lateral to the center of the knee joint. The mLDFA is 80°, and the MPTA is 87°. The Joint Line Convergence Angle (JLCA) is 1°. Which of the following statements accurately describes the primary deformity and its implications?
Correct Answer & Explanation
. The patient has a distal femoral valgus deformity, leading to lateral compartment overload.
Explanation
Correct Answer: BThe mechanical axis passing 10 mm lateral to the center of the knee indicates a negative MAD, which signifies a valgus alignment. This valgus alignment leads to lateral compartment overload. To identify the source, we look at the joint orientation angles: the mLDFA is 80°. The normal mLDFA range is 85° to 90°. An mLDFA less than 85° indicates a distal femoral valgus deformity. The MPTA is 87°, which is normal (85° to 90°), ruling out a proximal tibial deformity. The JLCA of 1° is also normal (0° to 2°), suggesting no significant ligamentous laxity or cartilage loss contributing to joint line opening. Therefore, the primary deformity is a distal femoral valgus, causing lateral compartment overload.Option A is incorrectbecause the mechanical axis is lateral (valgus), not medial (varus), and the MPTA is normal, ruling out proximal tibial varus.Option C is incorrectbecause the mLDFA is abnormal, indicating a bony deformity in the distal femur, not primarily an intra-articular issue.Option D is incorrectbecause a JLCA of 1° is normal. A JLCA > 2° would suggest ligamentous laxity or cartilage loss.Option E is incorrectbecause a MAD of 10 mm lateral is outside the normal range (4-8 mm medial), indicating significant valgus malalignment.
Question 163
Topic: Lower Extremity Trauma
A 28-year-old athlete presents with left knee pain and a progressive genu valgum deformity. A full-length standing AP radiograph is obtained, as shown below. Based on the principles of deformity analysis, where is the primary anatomical location of the angular deformity in this patient?
Correct Answer & Explanation
. Primarily in the distal femur, indicated by a decreased mLDFA.
Explanation
Correct Answer: CThe image shows a genu valgum deformity. To determine the primary location of the deformity (femoral vs. tibial), one assesses the mechanical axis deviation and the joint line orientation. In genu valgum, the mechanical axis passes lateral to the knee. The mLDFA (normal 87° ± 3°) measures the angle between the mechanical axis of the femur and the distal femoral joint line. A decreased mLDFA (e.g., 80° or less) indicates a valgus deformity originating in the distal femur. The MPTA (normal 87° ± 3°) measures the angle between the mechanical axis of the tibia and the proximal tibial joint line. An increased MPTA (e.g., 95° or more) indicates a valgus deformity originating in the proximal tibia. Visually, the image suggests that the distal femur is angled more laterally relative to the femoral shaft, while the tibial plateau appears relatively horizontal. Therefore, a decreased mLDFA, indicating a valgus deformity of the distal femur, is the most likely primary location. An increased mLDFA (Option A) would indicate femoral varus. A decreased MPTA (Option B) would indicate tibial varus. An increased MPTA (Option D) would indicate tibial valgus. Option E is incorrect as there is clear malalignment.
Question 164
Topic: Lower Extremity Trauma
A 50-year-old patient presents with medial compartment knee pain and a varus deformity. A close-up radiograph of the knee is shown below. To accurately quantify the angular deformity and plan a corrective osteotomy, which of the following measurements is most critical for determining the contribution of the proximal tibia to the overall malalignment?
Correct Answer & Explanation
. Medial proximal tibial angle (MPTA).
Explanation
Correct Answer: BThe image shows a close-up of a knee joint, likely with a varus deformity given the clinical context. To determine the contribution of the proximal tibia to the overall malalignment, the Medial Proximal Tibial Angle (MPTA) is the most critical measurement. The MPTA is formed by the intersection of the mechanical axis of the tibia and the medial aspect of the tibial plateau. A normal MPTA is 87° ± 3°. In a varus deformity originating from the proximal tibia, the MPTA will be decreased (e.g., <84°). The mLDFA (Option A) assesses the distal femur. The JLCA (Option C) indicates joint space narrowing or opening but does not directly quantify bone deformity. The aLDFA (Option D) uses the anatomical axis, which is less relevant for mechanical alignment. The PTS (Option E) is measured on a lateral radiograph and relates to sagittal plane alignment, not coronal plane varus/valgus.
Question 165
Topic: Lower Extremity Trauma
A 70-year-old female presents with severe valgus deformity of her left knee. Preoperative planning involves measuring joint orientation angles. Her mLDFA is measured at 80°, and her MPTA is 87°. The Mechanical Axis Deviation (MAD) is 18 mm lateral. Based on these measurements and the Paley method, what is the primary anatomical source of this patient's valgus malalignment?
Correct Answer & Explanation
. D. Distal femoral valgus deformity
Explanation
Correct Answer: DThe case defines normal values for joint orientation angles: mLDFA (Mechanical Lateral Distal Femoral Angle) is normally 88° (range 85°-90°), and MPTA (Medial Proximal Tibial Angle) is normally 87° (range 85°-90°).The patient's mLDFA is 80°. The case states, 'An mLDFA < 85° signifies a distal femoral valgus deformity.' This measurement is significantly below the normal range, indicating a valgus deformity originating from the distal femur.The patient's MPTA is 87°. This value falls within the normal range (85°-90°), indicating that there is no significant proximal tibial deformity contributing to the malalignment.Given the 18 mm lateral MAD (consistent with valgus malalignment) and the specific angle measurements, the primary source of the valgus deformity is the distal femur.Incorrect Options:A. Proximal tibial varus deformity:This would be indicated by an MPTA < 85°, which is not present (MPTA is 87°).B. Distal tibial valgus deformity:This would be indicated by an abnormal LDTA, which is not provided, but the primary deformity is clearly identified in the femur.C. Proximal femoral varus deformity:This would be indicated by an abnormal LPFA or NSA, which are not provided, but the mLDFA points to a distal femoral issue.E. Combined proximal tibial and distal femoral varus deformity:This is incorrect. The MPTA is normal, ruling out proximal tibial deformity, and the femoral deformity is valgus, not varus.
Question 166
Topic: Lower Extremity Trauma
A 35-year-old active duty soldier sustained a complex tibial shaft fracture that healed with significant angulation and translation. Preoperative planning for corrective osteotomy involves identifying the Center of Rotation of Angulation (CORA). Which of the following best describes the CORA and its significance in surgical planning?
Correct Answer & Explanation
. C. The point of intersection of the proximal mechanical axis and the distal mechanical axis of the deformed bone segment, dictating the ideal osteotomy site and hinge position.
Explanation
Correct Answer: CThe case defines the CORA precisely: 'The CORA is defined as the point of intersection of the proximal mechanical axis and the distal mechanical axis of the deformed bone segment.' It further emphasizes its significance: 'Finding the CORA is the absolute key to surgical planning because it dictates the biomechanical reality of the deformity. It tells the surgeon exactly where the osteotomy should ideally be performed and how the correction hinge must be positioned.'Incorrect Options:A. The point where the anatomic axis of the proximal segment intersects the anatomic axis of the distal segment, indicating the ideal site for intramedullary nail insertion:While anatomic axes are used for IM nailing, the CORA is defined by mechanical axes and is for angular deformity correction, not IM nail insertion site.B. The perpendicular distance from the mechanical axis to the center of the knee, quantifying the global limb malalignment:This describes the Mechanical Axis Deviation (MAD), not the CORA.D. The angle between the distal femoral joint line and the femoral mechanical axis, defining the orientation of the knee joint:This describes the Mechanical Lateral Distal Femoral Angle (mLDFA), not the CORA.E. The point where the ground reaction force passes through the limb during the single-leg stance phase, representing the load-bearing line:This describes the mechanical axis of the lower extremity, not the CORA.
Question 167
Topic: Lower Extremity Trauma
A 40-year-old male presents with a 10-year history of progressive right knee pain and a varus deformity. Standing long AP radiographs show a Mechanical Axis Deviation (MAD) of 15 mm medial to the center of the knee. His MPTA is 80°, and his mLDFA is 88°. Which of the following statements accurately describes the significance of these findings according to the Paley method?
Correct Answer & Explanation
. D. The primary source of the varus malalignment is a proximal tibial varus deformity, as evidenced by the MPTA.
Explanation
Correct Answer: DLet's break down the measurements based on the case:MAD of 15 mm medial:The case states, 'Normal Alignment: The mechanical axis normally passes 1 to 8 mm medial to the exact center of the knee.' A MAD of 15 mm medial is significantly outside this normal range, indicating varus malalignment.MPTA of 80°:The normal MPTA is 87° (range 85°-90°). An MPTA < 85° signifies a proximal tibial varus deformity. This patient's 80° MPTA clearly indicates a proximal tibial varus deformity.mLDFA of 88°:The normal mLDFA is 88° (range 85°-90°). This patient's mLDFA is perfectly normal, indicating no distal femoral deformity.Therefore, the primary source of the varus malalignment is a proximal tibial varus deformity.Incorrect Options:A. The normal MPTA indicates that the deformity is primarily located in the distal femur:The MPTA of 80° isabnormal, indicating a proximal tibial deformity. The mLDFA is normal, ruling out a distal femoral deformity.B. The 15 mm medial MAD is within the normal physiological range, suggesting no significant malalignment:This is incorrect. The normal range for MAD is 1-8 mm medial. 15 mm medial is significant varus malalignment.C. The mLDFA of 88° indicates a distal femoral valgus deformity contributing to the overall varus:An mLDFA of 88° is normal. A distal femoral valgus deformity would be indicated by an mLDFA < 85°.E. The deformity is multiapical, requiring complex spatial frame correction due to both femoral and tibial involvement:Since the mLDFA is normal, there is no femoral deformity. The deformity is primarily uni-apical in the proximal tibia.
Question 168
Topic: Lower Extremity Trauma
When evaluating a full-length standing lower extremity radiograph for deformity correction, the surgeon measures the angle between the mechanical axis and the anatomical axis of the femur (AMA). In a normally aligned lower extremity, what is the expected approximate value of this angle?
Correct Answer & Explanation
. 7 degrees
Explanation
The anatomic-mechanical angle (AMA) of the femur normally averages 7 degrees (range 5 to 9 degrees). This angle reflects the mechanical axis running from the femoral head center to the knee center, while the anatomic axis follows the medullary canal of the femoral shaft.
Question 169
Topic: Lower Extremity Trauma
A 42-year-old male undergoes a high tibial osteotomy (HTO) for medial compartment osteoarthritis. The surgeon aims to shift the mechanical axis to the Fujisawa point to optimize load distribution. Where is the Fujisawa point located on the tibial plateau?
Correct Answer & Explanation
. 62.5% from the medial edge of the tibial plateau
Explanation
The Fujisawa point is located approximately 62-62.5% across the width of the tibial plateau, measured from medial to lateral. Shifting the mechanical weight-bearing axis to this point optimally unloads the medial compartment while protecting the lateral compartment from rapid breakdown.
Question 170
Topic: Lower Extremity Trauma
A 30-year-old female presents with bilateral knee pain. Full-length standing radiographs reveal a mechanical axis deviation (MAD) falling 25 mm medial to the center of the right knee. Joint orientation measurements demonstrate a mechanical lateral distal femoral angle (mLDFA) of 96° and a medial proximal tibial angle (MPTA) of 87°. Where is the primary site of deformity?
Correct Answer & Explanation
. Distal femur
Explanation
The normal mLDFA is 87°±3° and normal MPTA is 87°±3°. An mLDFA of 96° indicates a significant varus deformity in the distal femur. Since the MPTA is normal, the deformity is localized to the femur.
Question 171
Topic: Lower Extremity Trauma
A 32-year-old female is evaluated for right knee pain. Standing full-length radiographs show a mechanical axis deviation (MAD) of 20 mm medial to the center of the knee. The mechanical lateral distal femoral angle (mLDFA) is 96 degrees, and the mechanical proximal tibial angle (MPTA) is 87 degrees. What is the primary source of the patient's deformity?
Correct Answer & Explanation
. Distal femoral varus
Explanation
The normal mLDFA is approximately 87 degrees (range 85-90). An mLDFA of 96 degrees indicates a varus deformity of the distal femur, while the MPTA of 87 degrees is normal. Therefore, the medial mechanical axis deviation is driven entirely by the distal femur.
Question 172
Topic: Lower Extremity Trauma
During distraction osteogenesis utilizing an Ilizarov frame, a patient's post-operative radiographs at 4 weeks show an 'hourglass' shaped regenerate with a very narrow central zone. What is the most appropriate next step in management?
Correct Answer & Explanation
. Decrease the rate of distraction or perform a temporary compression.
Explanation
An 'hourglass' or tapering regenerate indicates poor bone formation, usually due to a distraction rate that is too fast for the patient's osteogenic potential. Decreasing the rate of distraction, or temporarily compressing the site, stimulates osteogenesis and improves the regenerate caliber.
Question 173
Topic: Lower Extremity Trauma
During preoperative planning for a femoral diaphyseal deformity, the surgeon notes two distinct Centers of Rotation of Angulation (CORAs). The surgeon opts to perform a single osteotomy at the level of the normal diaphyseal bone between the two deformities. Which of the following corrections is strictly required at the osteotomy site to perfectly realign the mechanical axis?
Correct Answer & Explanation
. Angular correction with simultaneous translation.
Explanation
When a multi-apical deformity is corrected with a single osteotomy that does not pass through either CORA (or their intersection), a combination of angular correction and translation is required to perfectly restore the mechanical axis.
Question 174
Topic: Lower Extremity Trauma
A 55-year-old man presents with a severe varus knee deformity. Full-length standing radiographs show a mechanical axis passing medial to the knee. The mLDFA is 88 degrees, and the medial proximal tibial angle (MPTA) is 87 degrees. The joint line convergence angle (JLCA) is measured at 8 degrees (apex lateral). What is the primary source of the varus deformity?
Correct Answer & Explanation
. Intra-articular space loss or ligamentous laxity
Explanation
Normal mLDFA and MPTA values indicate there is no significant bony deformity in the distal femur or proximal tibia. A high JLCA (normal 0-2 degrees) indicates that the varus malalignment is driven by intra-articular factors, such as medial cartilage loss or lateral ligamentous laxity.
Question 175
Topic: Lower Extremity Trauma
A 55-year-old male presents with chronic knee pain and difficulty ambulating due to a 'bent knee' that he cannot straighten. Clinical examination reveals a fixed flexion deformity (FFD) of 25 degrees. Radiographic analysis confirms a significant sagittal plane deformity. According to the provided case, which of the following statements BEST describes the primary biomechanical consequence of a procurvatum deformity leading to this patient's symptoms?
Correct Answer & Explanation
. It forces the knee into a functional fixed flexion deformity, requiring increased quadriceps effort and leading to early joint degeneration.
Explanation
Correct Answer: CThe case explicitly states that 'A procurvatum deformity forces the knee into a functional fixed flexion deformity (FFD), triggering a massive cascade of compensatory mechanisms that increase energy expenditure, fatigue the quadriceps, and eventually lead to early-onset joint degeneration.' This directly aligns with the patient's symptoms of a 'bent knee' and difficulty ambulating. The increased quadriceps effort is required to maintain an upright posture against the constant flexion moment.Option A is incorrectbecause varus/valgus stress relates to coronal plane deformities, not primarily sagittal plane procurvatum.Option B is incorrectbecause a normal sagittal mechanical axis passesanteriorto the knee, creating a passive extension moment. A procurvatum deformity shifts the mechanical axisposteriorto the knee, creating aflexionmoment, not an extension moment, thusincreasingquadriceps effort, not overloading it due to a passive extension moment.Option D is incorrectbecause a procurvatum deformity is characterized by adecreasedPDFA, not an increased one, indicating anterior bowing of the distal femur. Patellofemoral tracking issues are secondary and not the primary biomechanical consequence described.Option E is incorrectbecause while a decreased PPTA can contribute to a flexion deformity (tibial procurvatum), the statement describes it as 'mechanically blocking full knee extension,' which is a consequence, but the primary biomechanical disruption is the creation of a functional FFD and the resulting compensatory cascade, which is a more comprehensive answer.
Question 176
Topic: Lower Extremity Trauma
A 60-year-old patient presents with a long-standing history of a 'bent knee' deformity. Clinical examination reveals a fixed flexion deformity (FFD) of 15 degrees. Full-length weight-bearing lateral radiographs show a true osseous femoral procurvatum deformity of 25 degrees. Based on Paley's principles, what does this discrepancy between the osseous deformity and the clinical FFD signify?
Correct Answer & Explanation
. The patient has 10 degrees of compensatory joint hyperextension due to stretching of the posterior capsule.
Explanation
Correct Answer: BThe case explicitly addresses this critical concept: 'When the true osseous deformity (e.g., 30° of structural femoral procurvatum) isgreaterthan the clinically measured fixed flexion deformity (e.g., 20° FFD), it signifies that the posterior capsule has stretched. It has allowed the joint to pathologically hyperextend by 10° simply to minimize the severe flexion crouch.' In this patient's scenario, 25° (osseous deformity) - 15° (clinical FFD) = 10° of compensatory joint hyperextension.Option A is incorrectbecause a soft tissue contracture wouldaddto the FFD, making itgreaterthan the osseous deformity, not less.Option C is incorrectbecause while quadriceps weakness can affect active extension, the discrepancy described here specifically points to passive soft tissue stretching to compensate for the bone deformity, allowing the knee to extendmorethan the bone deformity would otherwise dictate.Option D is incorrectas the scenario provides specific measurements and asks for their interpretation, assuming the measurements are correct for the purpose of the question.Option E is incorrectbecause the question specifies a 'true osseous femoral procurvatum deformity,' indicating the location is already identified.
Question 177
Topic: Lower Extremity Trauma
A 35-year-old patient presents with a 'bent knee' deformity. Radiographic analysis is performed using Paley's method. The surgeon measures the angle between the anatomical axis of the femur and the distal femoral joint line (tangent to the most posterior aspects of the femoral condyles) and finds it to be 68 degrees. What is this angle, and what does this measurement indicate?
Correct Answer & Explanation
. Posterior Distal Femoral Angle (PDFA); indicates anterior bowing of the distal femur (procurvatum).
Explanation
Correct Answer: BThe case defines the Posterior Distal Femoral Angle (PDFA) as 'the angle between the anatomical axis of the femur and the distal femoral joint line (drawn as a tangent to the most posterior aspects of the femoral condyles).' The normal value for PDFA is 83° (± 4°). A measured value of 68° is significantly decreased (< 79°), which 'definitively indicates anterior bowing of the distal femur, which mechanically forces the knee into a flexed posture,' i.e., procurvatum.Option A is incorrectbecause the description is for the femur, not the tibia, and the PPTA relates to the tibia.Option C is incorrectbecause adecreasedPDFA indicates procurvatum (anterior bowing), while anincreasedPDFA (> 87°) would indicate recurvatum (posterior bowing).Option D is incorrectbecause the Mechanical Lateral Distal Femoral Angle (mLDFA) is a coronal plane measurement, not sagittal, and indicates varus/valgus deformity.Option E is incorrectbecause 'Anterior Distal Femoral Angle' is not one of the key sagittal angles described, and 68° is highly abnormal, not normal.
Question 178
Topic: Lower Extremity Trauma
A 50-year-old patient presents with a functional knee flexion deformity. Radiographic analysis using Paley's method reveals a normal Posterior Distal Femoral Angle (PDFA) of 82 degrees. However, the angle between the anatomical axis of the tibia and the proximal tibial joint line (representing the posterior slope of the tibial plateau) is measured at 75 degrees. What is this measured angle, and what is its significance in this patient?
Correct Answer & Explanation
. Posterior Proximal Tibial Angle (PPTA); indicates an excessive posterior slope of the tibial plateau (tibial procurvatum).
Explanation
Correct Answer: BThe case defines the Posterior Proximal Tibial Angle (PPTA) as 'the angle between the anatomical axis of the tibia and the proximal tibial joint line (representing the posterior slope of the tibial plateau).' The normal value for PPTA is 81° (± 4°). A measured value of 75° is decreased (< 77°), which 'indicates an excessive posterior slope of the tibial plateau. This causes the femur to slide posteriorly, functionally contributing to a knee flexion deformity,' i.e., tibial procurvatum.Option A is incorrectbecause the description is for the tibia, not the femur, and the PDFA relates to the femur. Also, 82 degrees PDFA is normal, and 75 degrees PPTA indicates procurvatum, not femoral recurvatum.Option C is incorrectbecause adecreasedPPTA indicates anexcessiveposterior slope (procurvatum), while anincreasedPPTA (> 85°) would indicate insufficient posterior slope (recurvatum).Option D is incorrectbecause the Mechanical Medial Proximal Tibial Angle (mMPTA) is a coronal plane measurement, not sagittal, and indicates varus/valgus deformity.Option E is incorrectbecause 'Anterior Proximal Tibial Angle' is not one of the key sagittal angles described, and 75° is highly abnormal, not normal.
Question 179
Topic: Lower Extremity Trauma
A 65-year-old patient with a history of severe osteomyelitis in childhood presents with a significant tibial procurvatum deformity. Clinical examination reveals a marked knee flexion deformity and a gait pattern characterized by a 'crouch.' Based on the case's description of tibial procurvatum, which of the following best explains the biomechanical consequence of this deformity?
Correct Answer & Explanation
. The anterior bow of the proximal tibia increases the posterior slope of the tibial plateau, causing posterior subluxation of the femur.
Explanation
Correct Answer: BThe case states: 'Tibial procurvatum creates a remarkably similar clinical picture to femoral deformity, but the mechanical culprit lies distal to the joint line. The anterior bow of the proximal tibia drastically increases the posterior slope of the tibial plateau. This steep slope causes the rounded femoral condyles to slide and subluxate posteriorly during weight-bearing, creating a severe functional flexion deformity.'Option A is incorrectbecause tibial procurvatumincreasesthe posterior slope, and this causesposteriorsubluxation of the femur, not anterior.Option C is incorrectbecause a varus thrust is characteristic of coronal plane deformities, not primarily sagittal plane tibial procurvatum.Option D is incorrectbecause tibial procurvatum is characterized by adecreasedPPTA (indicating an excessive posterior slope), not an increased one.Option E is incorrectbecause tibial procurvatum leads to aflexiondeformity (crouch gait), not a fixed extension deformity.
Question 180
Topic: Lower Extremity Trauma
A 58-year-old male presents with chronic left knee pain, worse with activity, and a noticeable deformity. Clinical examination reveals the appearance shown in the image. Radiographs confirm lateral compartment osteoarthritis (LCOA) and a valgus mechanical axis deviation. According to Paley's principles for valgus knee realignment, what is the primary biomechanical goal of surgical correction in this patient?
Correct Answer & Explanation
. To shift the mechanical axis medially, typically aiming for 2-4 degrees of mechanical varus.
Explanation
Correct Answer: CThe primary biomechanical goal of valgus knee realignment for lateral compartment osteoarthritis (LCOA) is to shift the mechanical axis medially. This offloads the diseased lateral compartment and transfers weight-bearing forces to the healthier medial compartment. While a truly 'neutral' mechanical axis (0 degrees) might seem ideal, studies and clinical experience, particularly following principles like those advocated by Paley, suggest that a slight overcorrection into 2-4 degrees of mechanical varus is often beneficial for long-term pain relief and delaying progression of OA in the affected compartment. This slight varus ensures consistent offloading of the lateral compartment.Option A is incorrectbecause passing the mechanical axis through the center of the lateral compartment would maintain or exacerbate the existing LCOA, as it would continue to bear the primary load. The goal is to offload it.Option B is incorrectbecause restoring the anatomical axis to 0 degrees is not the primary goal; the mechanical axis is the critical determinant of load distribution across the knee joint. Furthermore, the anatomical axis is inherently in slight valgus (typically 5-7 degrees) in a normal knee.Option D is incorrectbecause while patellofemoral tracking can be affected by severe valgus, it is not the primary biomechanical goal of a valgus realignment osteotomy for LCOA. The main focus is on tibiofemoral load distribution.Option E is incorrectbecause increasing the MPTA to 90 degrees would correct a varus deformity at the tibia, not a valgus deformity. In a valgus knee, the MPTA is often normal or slightly decreased, and the primary deformity is usually in the distal femur (decreased mLDFA).
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