ABOS Orthopedic Board Review: Lower Limb Deformity Correction, Gait, & Guided Growth | Part 11

Question 1

A surgeon is performing a simple, uniapical varus correction in the proximal femur. To achieve a perfect correction where the mechanical axis is restored to a straight line without any displacement, which of Paley's rules must be followed?

• A) The osteotomy is made at the CORA, but the hinge of correction is placed distally.
• B) The osteotomy is made distal to the CORA, and the hinge of correction is placed at the osteotomy site.
• C) The osteotomy and the hinge of correction (ACA) are both placed exactly at the CORA.
• D) The osteotomy is made distal to the CORA, but the hinge of correction is placed at the CORA.
• E) The osteotomy is performed as a double-level cut bracketing the CORA.

Question 2

A 40-year-old patient has a proximal femoral deformity with the CORA located in a region of poor, osteopenic bone. The surgeon decides to perform the osteotomy 3 cm distal to the CORA where the bone quality is better. To achieve a perfectly collinear mechanical axis, what must be done?

• A) The hinge of correction (ACA) must be placed at the osteotomy site.
• B) The hinge of correction (ACA) must be placed at the CORA, which will require a planned translation at the osteotomy site.
• C) The angular correction must be reduced by 50% to avoid translation.
• D) A bone graft must be used to fill the gap at the CORA.
• E) The osteotomy must be oblique to compensate for the distance from the CORA.

Question 3

A patient undergoes a subtrochanteric osteotomy for a varus deformity. Postoperatively, the limb appears visually straight, but a full-length radiograph reveals that the mechanical axis passes through the hip and ankle centers but deviates medially, missing the center of the knee. This "dog-leg" deformity is known as Mechanical Axis Deviation (MAD). What is the most likely surgical error?

• A) The surgeon overcorrected the varus into valgus.
• B) The surgeon undercorrected the varus deformity.
• C) The surgeon placed both the osteotomy and the hinge of correction at a location different from the CORA.
• D) The surgeon used an external fixator instead of a blade plate.
• E) The surgeon failed to use bone graft at the osteotomy site.

Question 4

A 65-year-old male is evaluated for gait instability. During the stance phase, his quadriceps are observed to be continuously firing. A long-leg lateral radiograph is obtained with the knee in terminal extension. Which of the following radiographic findings would best explain the need for constant quadriceps activation during stance?

• A) The sagittal mechanical axis passes anterior to the knee's center of rotation.
• B) The sagittal mechanical axis passes posterior to the knee's center of rotation.
• C) The sagittal mechanical axis passes directly through the knee's center of rotation.
• D) The anatomic posterior proximal tibial angle (aPPTA) is 81°.
• E) The mid-sagittal width of the lateral femoral condyle is aligned with the tibial plateau.

Question 5

A 45-year-old female with a history of poliomyelitis presents with a gait disturbance. She ambulates by thrusting her hip forward to achieve knee stability. This compensatory mechanism is designed to manipulate the ground reaction force and sagittal mechanical axis. What is the primary biomechanical goal of this gait pattern?

• A) To shift the sagittal mechanical axis posterior to the knee, engaging the hamstrings.
• B) To shift the sagittal mechanical axis anterior to the knee, creating a passive extension moment.
• C) To medialize the mechanical axis, offloading the lateral compartment.
• D) To decrease the flexion moment at the hip joint.
• E) To increase ankle dorsiflexion to clear the foot during swing phase.

Question 6

A 28-year-old male sustains a tibial shaft fracture that heals with an apex posterior deformity (recurvatum). He is able to walk with a near-normal gait pattern despite the significant bony deformity seen on radiographs. Which compensatory mechanism is he most likely utilizing?

• A) Increased ankle plantarflexion
• B) Increased hip extension
• C) Persistent knee flexion during stance
• D) Persistent knee hyperextension during stance
• E) Pelvic obliquity

Question 7

A 35-year-old female presents with a distal femoral procurvatum deformity following a malunited fracture. To compensate and maintain a functional limb alignment, which joint motion is required?

• A) Knee flexion
• B) Knee hyperextension
• C) Ankle dorsiflexion
• D) Hip flexion
• E) Hip internal rotation

Question 8

A 70-year-old patient from a culture where deep squatting is a daily activity undergoes a total knee arthroplasty. During the procedure, significant cartilage loss is noted. Based on biomechanical studies of knee joint loading, where are these osteoarthritic lesions most likely to be predominantly located?

• A) Anterior aspect of the femoral condyles
• B) Posterior aspect of the femoral condyles
• C) Medial tibial plateau exclusively
• D) Lateral tibial plateau exclusively
• E) Patellofemoral joint

Question 9

A 55-year-old male with chronic knee instability is evaluated with a lateral radiograph in full extension. The surgeon measures the distance between the mid-sagittal line of the lateral femoral condyle and the mid-sagittal line of the tibial plateau. A measurement of 5 mm is recorded, with the tibia displaced anteriorly. What is the correct diagnosis?

• A) Normal knee alignment
• B) Pathologic anterior subluxation
• C) Pathologic posterior subluxation
• D) Femoral procurvatum
• E) Tibial recurvatum

Question 10

A surgeon is performing a sagittal plane Malalignment Test (MAT) on a patient with a suspected deformity. A long lateral radiograph is taken with the knee in maximum passive extension. The test is positive for flexion malalignment. What does this finding signify?

• A) The mechanical axis passes anterior to the knee's center of rotation.
• B) The mechanical axis does not pass anterior to the knee's center of rotation.
• C) The overall axes of the tibia and femur are in more than 5° of hyperextension.
• D) The anatomic posterior proximal tibial angle (aPPTA) is less than 77°.
• E) The anatomic posterior distal femoral angle (aPDFA) is greater than 87°.

Question 11

An orthopedic resident is evaluating a patient with a significant distal femoral procurvatum deformity. The standing lateral radiograph, however, shows a relatively normal overall limb alignment. Why is the sagittal Malalignment Test (MAT) often considered misleading in such cases?

• A) The frontal plane deformity masks the sagittal plane deformity.
• B) The patient's compensatory joint motion can hide the underlying bony deformity.
• C) The MAT is only accurate for deformities greater than 20°.
• D) Radiographic magnification errors are too high in the sagittal plane.
• E) The test does not account for patellar height.

Question 12

When performing a sagittal plane Malorientation Test (MOT) of the proximal tibia, the anatomic posterior proximal tibial angle (aPPTA) is measured. What is the normal range for this angle?

• A) 70° ± 5°
• B) 81° ± 4°
• C) 83° ± 4°
• D) 90° ± 2°
• E) 170° ± 5°

Question 13

A surgeon is evaluating a lateral radiograph of a distal femur to assess for sagittal plane deformity. The anatomic posterior distal femoral angle (aPDFA) is measured. What is the normal value for this angle?

• A) 80° ± 2°
• B) 81° ± 4°
• C) 83° ± 4°
• D) 90° ± 3°
• E) 170° ± 5°

Question 14

A 22-year-old patient has a healed tibial fracture with a suspected sagittal plane deformity. A Malorientation Test (MOT) is performed. The measured anatomic posterior proximal tibial angle (aPPTA) is 72°. What does this measurement indicate?

• A) Normal proximal tibial alignment
• B) Proximal tibial procurvatum (apex anterior)
• C) Proximal tibial recurvatum (apex posterior)
• D) Anterior knee subluxation
• E) Distal tibial procurvatum

Question 15

A 40-year-old male has a malunited distal femur fracture. On the lateral radiograph, his anatomic posterior distal femoral angle (aPDFA) is measured to be 92°. How is this deformity best described?

• A) Distal femoral procurvatum
• B) Distal femoral recurvatum
• C) Normal distal femoral alignment
• D) Proximal femoral varus
• E) Posterior knee subluxation

Question 16

A surgeon is performing an overall sagittal plane Malorientation Test (MOT) for the femur in a patient with a mid-shaft deformity. The modified posterior distal femoral angle (mPDFA) is measured to be 75°. What is the correct interpretation of this finding?

• A) Overall femoral recurvatum
• B) Overall femoral procurvatum
• C) Normal overall femoral alignment
• D) Soft tissue flexion contracture
• E) Soft tissue hyperextension laxity

Question 17

An overall sagittal plane MOT of the tibia is performed on a patient with a complex post-traumatic deformity. The modified posterior proximal tibial angle (mPPTA) is calculated to be 90°. What does this value signify?

• A) Overall tibial procurvatum
• B) Normal overall tibial alignment
• C) Overall tibial recurvatum
• D) Anterior knee subluxation
• E) Flexion contracture of the knee

Question 18

During a preoperative evaluation for a supramalleolar osteotomy, a surgeon measures the anatomic anterior distal tibial angle (aADTA) on a lateral radiograph. The measured angle is 75°. What deformity is present?

• A) Distal tibial procurvatum
• B) Distal tibial recurvatum
• C) Normal distal tibial alignment
• D) Ankle valgus
• E) Ankle varus

Question 19

According to Paley's 4-step protocol for sagittal deformity analysis, what is the first step in quantifying the clinical deformity?

• A) Measure the aPPTA.
• B) Measure the aPDFA.
• C) Measure the angle between the anterior cortical lines of the femur and tibia with the knee in maximal extension.
• D) Assess for knee subluxation using the 3mm rule.
• E) Draw the modified mechanical axis of the femur.

Question 20

A 30-year-old patient has a 20° fixed flexion deformity (FFD) on clinical exam. Radiographic analysis reveals a distal femoral procurvatum of 12° (aPDFA = 71°) and a proximal tibial procurvatum of 8° (aPPTA = 73°). Using Paley's reconciliation formula, what is the contribution of soft tissue to this deformity?

• A) 20° of soft tissue flexion contracture
• B) 10° of soft tissue flexion contracture
• C) 0° (no soft tissue component)
• D) 10° of soft tissue hyperextension laxity
• E) 20° of soft tissue hyperextension laxity

Question 21

A patient presents with a clinical 30° fixed flexion deformity (FFD). The sagittal MOT reveals a 15° femoral procurvatum and a 5° tibial procurvatum. There is no recurvatum deformity. Based on the 4-step reconciliation protocol, what is the underlying soft tissue pathology?

• A) The bony deformity is fully responsible for the FFD.
• B) There is a 10° soft tissue knee flexion contracture.
• C) There is a 10° soft tissue knee hyperextension laxity.
• D) There is a 20° soft tissue knee flexion contracture.
• E) There is a 5° soft tissue knee hyperextension laxity.

Question 22

A 42-year-old male has a clinical fixed flexion deformity (FFD) of 10°. Radiographic analysis shows a 15° distal femoral procurvatum and a 5° proximal tibial procurvatum. What is the correct interpretation of these findings?

• A) A 10° soft tissue flexion contracture is present.
• B) The bone deformity is fully explained by the FFD.
• C) A 20° soft tissue flexion contracture is present.
• D) Compensatory knee joint hyperextension laxity of 10° is present.
• E) The radiographic measurements must be incorrect.

Question 23

A patient is evaluated for knee hyperextension (HE) of 15°. The sagittal MOT shows a 10° femoral recurvatum and a 5° tibial recurvatum. There is no procurvatum. What is the soft tissue contribution to this deformity?

• A) 15° of soft tissue hyperextension laxity
• B) 10° of soft tissue hyperextension laxity
• C) 5° of soft tissue flexion contracture
• D) 10° of soft tissue flexion contracture
• E) 0° (no soft tissue component)

Question 24

A 25-year-old patient has a clinical knee hyperextension (HE) of 20°. Radiographic analysis reveals a total bony recurvatum of 12° and no procurvatum. According to Paley's reconciliation protocol, what is the soft tissue diagnosis?

• A) 8° of soft tissue knee flexion contracture
• B) 8° of soft tissue knee hyperextension laxity
• C) 12° of soft tissue knee hyperextension laxity
• D) The bony deformity fully explains the clinical picture.
• E) 20° of soft tissue knee flexion contracture

Question 25

A 55-year-old male undergoes gait analysis for progressive right knee pain. At a normal walking speed, the analysis reveals that the time from his right heel strike to the subsequent right heel strike is 1.0 second. What is the approximate duration of the stance phase for his right leg?

• A) 0.12 seconds
• B) 0.38 seconds
• C) 0.50 seconds
• D) 0.62 seconds
• E) 1.00 second

Question 26

A 30-year-old runner is evaluated for anterior shin pain. Physical examination reveals weakness of the tibialis anterior muscle. Dysfunction of this muscle would most directly impair which phase of the gait cycle?

• A) First (heel) rocker
• B) Second (ankle) rocker
• C) Third (forefoot) rocker
• D) Mid-swing
• E) Terminal swing

Question 27

A 62-year-old female with severe ankle arthritis presents for evaluation. Her gait is characterized by an inability to advance her tibia over her planted foot. To maintain forward progression, she forcefully drives her ipsilateral knee into hyperextension during mid-stance. This compensatory pattern indicates a failure of which rocker mechanism?

• A) First (heel) rocker
• B) Second (ankle) rocker
• C) Third (forefoot) rocker
• D) Double support phase
• E) Swing phase initiation

Question 28

A surgeon is planning a distal femoral osteotomy for a 45-year-old male with a valgus deformity. Preoperative planning on a full-length standing radiograph shows the line from the center of the femoral head to the center of the ankle passes 25 mm lateral to the center of the knee. This measurement is defined as the:

• A) Center of Rotation of Angulation (CORA)
• B) Mechanical Axis Deviation (MAD)
• C) Joint Line Congruency Angle (JLCA)
• D) Mechanical Lateral Distal Femoral Angle (mLDFA)
• E) Anatomical-Mechanical Axis Angle

Question 29

A 58-year-old female presents with medial-sided knee pain and a varus deformity. A standing radiograph demonstrates that the mechanical axis passes medial to the knee center. This alignment creates which pathological force across the knee during the single limb stance phase?

• A) Abduction moment
• B) Adduction moment
• C) Flexion moment
• D) Extension moment
• E) Torsional moment

Question 30

A 25-year-old patient has a 20-degree procurvatum deformity of the distal tibia. To achieve a plantigrade foot for standing, the patient must sacrifice motion at the adjacent ankle joint. What is the specific motion that is consumed by this compensation?

• A) 20 degrees of plantarflexion
• B) 20 degrees of dorsiflexion
• C) 20 degrees of inversion
• D) 20 degrees of eversion
• E) 20 degrees of subtalar motion

Question 31

During preoperative planning for a tibial osteotomy, the surgeon identifies the point where the proximal mechanical axis intersects the distal mechanical axis. According to Paley's principles, what is this critical point called?

• A) Mechanical Axis Deviation (MAD)
• B) Joint Line Orientation Point (JLOP)
• C) Center of Rotation of Angulation (CORA)
• D) Apex of Deformity (AOD)
• E) Hinge Point of Correction (HPC)

Question 32

A surgeon performs a proximal tibial osteotomy for a varus deformity. The osteotomy and the hinge of correction are both placed precisely at the CORA. According to Paley's osteotomy rules, what is the expected outcome?

• A) Pure angular correction without translation
• B) Angular correction with secondary translation
• C) Pure translation without angular correction
• D) Limb lengthening with angular correction
• E) Iatrogenic malorientation of the joint line

Question 33

A 19-year-old male with a history of a malunited clubfoot deformity presents with a limp. His gait is characterized by a long step with his affected leg and a noticeably short, hurried step with his normal, contralateral leg. This gait asymmetry is most directly caused by:

• A) Weakness of the contralateral hip abductors
• B) Pain in the affected foot during initial contact
• C) Premature termination of the terminal stance phase of the affected leg
• D) Over-compensation by the contralateral quadriceps
• E) A fixed pelvic obliquity

Question 34

A 65-year-old female has a severe valgus deformity of her left knee. Radiographic analysis reveals a Mechanical Lateral Distal Femoral Angle (mLDFA) of 78 degrees. What is the normal range for this angle?

• A) 75° - 80°
• B) 80° - 85°
• C) 85° - 90°
• D) 90° - 95°
• E) 95° - 100°

Question 35

A 40-year-old male is evaluated for a painful varus ankle. His radiographs show a Mechanical Lateral Distal Tibial Angle (mLDTA) of 80 degrees. How does this malorientation primarily affect his gait?

• A) It causes a recurvatum thrust at the knee.
• B) It forces him to walk on the lateral border of his foot.
• C) It increases the adduction moment at the knee.
• D) It leads to a functional leg length discrepancy.
• E) It causes excessive hip abduction during swing phase.

Question 36

A gait analysis is performed on a healthy 28-year-old. The period when both feet are in contact with the ground simultaneously during weight transfer is measured. According to normative data, what percentage of the total gait cycle does one of these "double stance support" periods occupy?

• A) 12%
• B) 24%
• C) 38%
• D) 50%
• E) 62%

Question 37

A 50-year-old patient with limited ankle motion due to a previous pilon fracture requires a minimum of 10 degrees of ankle dorsiflexion for normal gait. This motion is biomechanically essential for the successful completion of which rocker mechanism?

• A) First (heel) rocker
• B) Second (ankle) rocker
• C) Third (forefoot) rocker
• D) Loading response
• E) Pre-swing

Question 38

A 60-year-old male with a valgus knee deformity is shown in the clinical image. This alignment results in an overload of the lateral compartment of the knee. This pathological loading is caused by which of the following biomechanical forces?

• A) A medial Mechanical Axis Deviation (MAD) creating an adduction moment
• B) A lateral Mechanical Axis Deviation (MAD) creating an abduction moment
• C) An increased Joint Line Congruency Angle (JLCA)
• D) A decreased Mechanical Proximal Tibial Angle (MPTA)
• E) A varus thrust during mid-stance

Question 39

A surgeon plans a tibial osteotomy but places the osteotomy and the corrective hinge 3 cm distal to the CORA. To avoid creating a secondary deformity, what additional surgical maneuver must be performed?

• A) No additional maneuver is needed.
• B) The bone must be lengthened by 3 cm.
• C) The bone must be shortened by 3 cm.
• D) A planned translation must be incorporated at the osteotomy site.
• E) A rotational correction must be added.

Question 40

A 22-year-old female presents with posterior knee pain and instability. Her clinical gait is shown in the image. This gait pattern is a classic secondary compensation for a primary pathology that has exhausted motion at which joint?

• A) Ipsilateral hip
• B) Ipsilateral ankle
• C) Contralateral knee
• D) Lumbar spine
• E) Subtalar joint

Question 41

A 48-year-old male has a varus deformity primarily located in his proximal tibia. Preoperative radiographic assessment reveals a Mechanical Proximal Tibial Angle (MPTA) of 78 degrees. What is the average normal value for the MPTA?

• A) 81°
• B) 84°
• C) 87°
• D) 90°
• E) 93°

Question 42

The powerful, explosive push-off that initiates the swing phase is the primary function of which rocker mechanism and is powered mainly by which muscle group?

• A) First rocker; Tibialis anterior
• B) Second rocker; Quadriceps
• C) Third rocker; Gastroc-soleus complex
• D) Second rocker; Tibialis anterior
• E) Third rocker; Peroneals

Question 43

A 60-year-old patient with knee osteoarthritis has a standing radiograph showing that the femoral and tibial articular surfaces are not parallel, with the joint space widened laterally. The angle between the tangent to the femoral condyles and the tangent to the tibial plateau measures 5 degrees. This measurement defines the:

• A) Mechanical Axis Deviation (MAD)
• B) Mechanical Proximal Tibial Angle (MPTA)
• C) Mechanical Lateral Distal Femoral Angle (mLDFA)
• D) Center of Rotation of Angulation (CORA)
• E) Joint Line Congruency Angle (JLCA)

Question 44

The fundamental objective of lower extremity deformity correction is to restore normal biomechanics. For physiological gait, the articular surfaces of the hip, knee, and ankle should be oriented in what way relative to the ground during the single-limb stance phase?

• A) Perpendicular
• B) Parallel
• C) Oblique at 7 degrees
• D) Angled posteriorly
• E) In slight varus

Question 45

A 35-year-old male has a 15-degree procurvatum deformity of the distal tibia. He complains of anterior ankle pain, especially when trying to walk uphill. The physical "hard stop" to his compensatory ankle dorsiflexion is caused by impingement between which two structures?

• A) Posterior malleolus and calcaneus
• B) Medial malleolus and talar body
• C) Anterior lip of the tibia and the neck of the talus
• D) Fibula and lateral process of the talus
• E) Calcaneus and cuboid

Question 46

A surgeon performs an osteotomy for a tibial deformity at a level different from the CORA, but places the hinge of correction at the CORA. According to Paley's Rule 2, what will be the result at the osteotomy site?

• A) The bone ends will angulate without translation.
• B) The bone ends will translate, but the mechanical axis will be restored.
• C) A secondary angular deformity will be created.
• D) The joint line will become oblique.
• E) The limb will be unintentionally shortened.

Question 47

A 58-year-old male presents with progressive right knee pain and a noticeable "bow-legged" appearance. A full-length standing radiograph demonstrates a significant medial Mechanical Axis Deviation (MAD). According to the principles of deformity correction, what is the primary biomechanical consequence of this finding?

• A) Overload of the lateral compartment cartilage
• B) Attenuation of the medial collateral ligament
• C) Exponential increase in joint reactive forces on the medial compartment
• D) Pathologic stretching of the anterior cruciate ligament
• E) Decreased Anatomic-Mechanical Angle (AMA)

Question 48

A 65-year-old female undergoes a total knee arthroplasty (TKA). Postoperatively, she has persistent medial knee pain. Radiographs reveal a well-fixed TKA but a previously unrecognized 15-degree varus deformity in the distal femur. Failure to correct this extra-articular deformity most commonly leads to which complication?

• A) Aseptic loosening of the femoral component
• B) Eccentric loading and early catastrophic failure of the polyethylene liner
• C) Periprosthetic fracture of the distal femur
• D) Patellar maltracking and anterior knee pain
• E) Common peroneal nerve palsy

Question 49

An orthopedic resident is learning to perform preoperative planning for a limb deformity. They are asked to define the mechanical axis of the lower limb. Which of the following descriptions is the most accurate?

• A) A line drawn down the center of the medullary canal of the femur and tibia
• B) A straight line from the center of the femoral head to the center of the ankle joint
• C) A line parallel to the anatomic axis of the tibia, passing through the knee center
• D) A line from the anterior superior iliac spine to the medial malleolus
• E) The bisector of the angle formed by the proximal and distal joint lines

Question 50

A 45-year-old patient with a post-traumatic malunion of the tibia is being evaluated. On a full-length standing radiograph, the line from the femoral head to the ankle center passes 30 mm medial to the center of the knee. What is the correct term for this finding?

• A) Joint Line Convergence Angle (JLCA)
• B) Anatomic-Mechanical Angle (AMA)
• C) Center of Rotation of Angulation (CORA)
• D) Mechanical Axis Deviation (MAD)
• E) Lateral Distal Femoral Angle (LDFA)

Question 51

A 22-year-old female presents with lateral knee pain and instability. Her clinical examination and radiographs are consistent with a significant valgus deformity of the lower limb. Chronic malalignment in this pattern leads to progressive strain and attenuation of which structure?

• A) Medial collateral ligament
• B) Lateral collateral ligament
• C) Anterior cruciate ligament
• D) Posterior cruciate ligament
• E) Patellar tendon

Question 52

A 19-year-old with a history of metabolic bone disease has a long, sweeping varus bow of his femur. During preoperative planning (Step 3 of the Paley method), the surgeon draws a single proximal anatomic axis line and a single distal anatomic axis line. They do not accurately represent the curvature of the bone. What does this indicate?

• A) The deformity is uniapical.
• B) The deformity is likely multiapical and requires additional mid-diaphyseal lines.
• C) Mechanical axis planning must be used instead of anatomic planning.
• D) The deformity is primarily rotational and cannot be planned in the frontal plane.
• E) The patient has a significant leg length discrepancy.

Question 53

A surgeon is planning a correction for a femoral deformity as shown in the image. A proximal axis line and a distal axis line have been drawn to represent the two main segments of the bone.

The point where these two lines intersect is best defined as the:

• A) Center of Rotation of Angulation (CORA)
• B) Mechanical Axis Deviation (MAD)
• C) Joint Line Convergence Angle (JLCA)
• D) Anatomic-Mechanical Angle (AMA)
• E) Osteotomy hinge point

Question 54

A 30-year-old patient has a complex tibial deformity, and the preoperative plan is shown in the image. The plan involves two separate osteotomies.

What is the most likely reason for planning two osteotomies instead of one?

• A) To achieve simultaneous limb lengthening.
• B) The deformity is multiapical, with two distinct CORAs.
• C) The patient has poor bone quality requiring staged correction.
• D) A single osteotomy would result in excessive rotation.
• E) The surgeon prefers using two plates for enhanced stability.

Question 55

A surgeon misinterprets a multiapical femoral varus deformity as uniapical. They perform a single, large angular correction at the distal CORA only. What is the most predictable iatrogenic consequence of this action?

• A) Over-correction into a valgus deformity
• B) Creation of a significant translational deformity
• C) Shortening of the limb
• D) Iatrogenic rotational deformity
• E) Failure to correct the distal joint orientation

Question 56

During deformity planning for a tibia with a complex bow, a surgeon draws a proximal anatomic axis line, a distal anatomic axis line, and one additional mid-diaphyseal anatomic axis line to accurately map the bone's shape. According to the "Rule of Intersecting Lines," how many CORAs and magnitudes of angulation will be identified?

• A) One CORA, one magnitude
• B) Two CORAs, two magnitudes
• C) Three CORAs, three magnitudes
• D) One CORA, two magnitudes
• E) Two CORAs, one magnitude

Question 57

A surgeon is performing preoperative planning for a femoral osteotomy. They note that the line representing the center of the medullary canal and the line from the femoral head center to the knee center are not parallel. What is the term for the angle of divergence between these two lines?

• A) Mechanical Axis Deviation (MAD)
• B) Lateral Proximal Femoral Angle (LPFA)
• C) Anatomic-Mechanical Angle (AMA)
• D) Joint Line Convergence Angle (JLCA)
• E) Center of Rotation of Angulation (CORA)

Question 58

When performing frontal plane deformity planning for the tibia, what is the typical relationship between the anatomic axis and the mechanical axis?

• A) They are perpendicular.
• B) They diverge by approximately 7 degrees.
• C) They are essentially parallel.
• D) The anatomic axis is always medial to the mechanical axis.
• E) The mechanical axis is always medial to the anatomic axis.

Question 59

A surgeon is comparing the CORA derived from mechanical axis planning versus anatomic axis planning for a femoral deformity. In which region of the femur will the locations of the mechanical CORA and anatomic CORA be the farthest apart?

• A) Distal metaphysis
• B) Distal diaphysis
• C) Mid-diaphysis
• D) Proximal diaphysis
• E) Proximal femur (metaphysis)

Question 60

In the provided image, a surgeon is analyzing the intersection of proximal and distal axis lines for a femoral deformity. A dotted line is shown cutting the angle of deformity exactly in half.

According to Paley's principles, what does this dotted line represent?

• A) The planned osteotomy cut
• B) The mechanical axis of the limb
• C) The bisector line of the deformity
• D) The anatomic axis of the femur
• E) The line of desired translation

Question 61

During preoperative planning for a distal femoral varus deformity, a surgeon identifies both the mechanical CORA and the anatomic CORA, which are in slightly different locations. To determine the true transverse level of the angulation for planning the osteotomy, which geometric construct should be prioritized?

• A) The mechanical CORA point
• B) The anatomic CORA point
• C) The bisector line of the deformity angle
• D) The midpoint between the two CORAs
• E) The narrowest point of the diaphysis

Question 62

A 40-year-old male has a 20-degree varus deformity in his distal femur. A surgeon is deciding between mechanical and anatomic axis planning. According to the provided text, what is the relationship between the bisector lines generated by these two methods for a distal femoral deformity?

• A) They are identical.
• B) The difference between them is negligible.
• C) The mechanical bisector is always superior to the anatomic bisector.
• D) They are significantly different, leading to different osteotomy levels.
• E) The anatomic bisector is always proximal to the mechanical bisector.

Question 63

A 35-year-old patient requires a corrective osteotomy for a femoral malunion. The surgeon plans to use a locked intramedullary nail for fixation. Which method of preoperative planning is most advantageous in this scenario?

• A) Mechanical axis planning
• B) Anatomic axis planning
• C) Uniapical planning only
• D) Multiapical planning only
• E) Joint line orientation planning

Question 64

An orthopedic surgeon is teaching a resident the principles of mechanical axis planning for a femoral deformity. How is the Mechanical CORA correctly defined?

• A) Intersection of the Proximal Anatomic Axis (PAA) and Distal Anatomic Axis (DAA)
• B) Intersection of the Proximal Mechanical Axis (PMA) and Distal Mechanical Axis (DMA)
• C) Intersection of the Proximal Mechanical Axis (PMA) and Distal Anatomic Axis (DAA)
• D) The point on the bisector line that is closest to the convex cortex
• E) The center of the narrowest part of the medullary canal

Question 65

A 15-year-old male with a history of a malunited proximal femur fracture presents with a limp and knee pain. On examination, a line drawn from the center of his femoral head to the center of his ankle joint passes 25 mm medial to the center of his knee. What does this line represent?

• A) Anatomic axis of the femur
• B) Mechanical axis of the lower extremity
• C) Sagittal femoral axis
• D) Joint Line Convergence Angle (JLCA)
• E) Anatomic Medial Proximal Femoral Angle (aMPFA)

Question 66

A 45-year-old female presents with progressive right knee pain. Radiographs reveal a significant proximal femoral varus deformity. Her mechanical axis is found to pass 30 mm medial to the knee center. What is the correct term for this finding?

• A) Center of Rotation of Angulation (CORA)
• B) Articulo Trochanteric Distance (ATD)
• C) Mechanical Axis Deviation (MAD)
• D) Joint Line Convergence Angle (JLCA)
• E) Physiologic valgus alignment

Question 67

A surgeon is evaluating a standing, full-length radiograph of a healthy 25-year-old athlete with no complaints. In a normally aligned lower limb, where should the mechanical axis pass relative to the center of the knee joint?

• A) Exactly through the center of the knee
• B) 15-20 mm lateral to the center of the knee
• C) 8 ± 7 mm medial to the center of the knee
• D) 8 ± 7 mm lateral to the center of the knee
• E) Directly through the medial tibial spine

Question 68

A 12-year-old with developmental coxa vara presents for evaluation. Radiographs confirm a neck-shaft angle of 105°. According to the provided text, what is the primary biomechanical consequence of this deformity on the knee joint?

• A) Exponentially increased load on the lateral compartment of the knee
• B) Stretching and attenuation of the lateral collateral ligament (LCL)
• C) Pathologic overloading of the patellofemoral joint
• D) Exponentially increased load on the medial compartment of the knee
• E) A shift of the mechanical axis laterally

Question 69

A 50-year-old patient with a history of untreated coxa vara now has severe medial-sided knee pain and imaging consistent with advanced osteoarthritis. This clinical scenario is a direct result of which biomechanical principle?

• A) A laterally deviated mechanical axis
• B) A negative Articulo Trochanteric Distance (ATD)
• C) A medially deviated mechanical axis
• D) An increased Joint Line Convergence Angle (JLCA)
• E) Excessive femoral anteversion

Question 70

A 16-year-old female with cerebral palsy has developed bilateral coxa valga with neck-shaft angles of 150°. She now complains of lateral knee pain. What is the expected finding on a full-length standing radiograph?

• A) A medially shifted mechanical axis
• B) A varus alignment of the lower limb
• C) A laterally shifted mechanical axis
• D) A decreased mechanical Lateral Distal Femoral Angle (mLDFA)
• E) Increased loading of the medial knee compartment

Question 71

A patient with long-standing, uncorrected coxa valga is being evaluated. Which of the following is a direct biomechanical consequence of this deformity?

• A) Pathologic overloading of the lateral compartment of the knee
• B) Increased compressive forces on the medial collateral ligament (MCL)
• C) A bow-legged appearance of the lower extremities
• D) Medial Mechanical Axis Deviation (MAD)
• E) Shortening of the abductor lever arm

Question 72

A surgeon is planning a proximal femoral osteotomy for a 19-year-old with a complex deformity. The surgeon measures the angle between the femoral head/neck complex and the true mechanical axis of the femur. What is this cornerstone angle called?

• A) Neck Shaft Angle (NSA)
• B) Anatomic Medial Proximal Femoral Angle (aMPFA)
• C) Mechanical Lateral Proximal Femoral Angle (mLPFA)
• D) Articulo Trochanteric Distance (ATD)
• E) Joint Line Convergence Angle (JLCA)

Question 73

A preoperative radiograph of a 30-year-old male shows a Mechanical Lateral Proximal Femoral Angle (mLPFA) of 75°. What does this value indicate?

• A) A normal hip alignment
• B) A valgus deformity
• C) A varus deformity
• D) A flexion deformity
• E) A rotational deformity

Question 74

During preoperative planning for a patient with a severe diaphyseal femur deformity, the surgeon is unable to accurately draw the mechanical axis. Which angle serves as the most vital fallback measurement in this scenario?

• A) Neck Shaft Angle (NSA)
• B) Anatomic Medial Proximal Femoral Angle (aMPFA)
• C) Articulo Trochanteric Distance (ATD)
• D) Joint Line Convergence Angle (JLCA)
• E) Mechanical Lateral Proximal Femoral Angle (mLPFA)

Question 75

A resident is measuring angles on a proximal femur radiograph. They measure the angle between the femoral head/neck complex and the anatomic axis of the proximal femur. What is the normal range for this angle?

• A) 85-95°
• B) 124-136°
• C) 0-2°
• D) 10-25 mm
• E) 80-89°

Question 76

A 40-year-old patient has a post-traumatic deformity of the hip. The surgeon notes that the Neck Shaft Angle (NSA) appears normal at 130°, but the mLPFA is pathologically low. Why is the mLPFA considered biomechanically more important than the NSA for complex deformity planning?

• A) The NSA is more difficult to measure accurately.
• B) The NSA only applies to pediatric patients.
• C) The NSA fails to account for the femur's natural anterior bow and lateral sweep.
• D) The NSA is a measure of sagittal plane alignment only.
• E) The NSA relates to the mechanical axis, not the anatomic axis.

Question 77

A 22-year-old female presents with a painful, non-weightbearing gait. On examination, she has a profound Trendelenburg gait. Radiographs show that the tip of her greater trochanter is 5 mm superior to the center of the femoral head. Which measurement is abnormal?

• A) Joint Line Convergence Angle (JLCA)
• B) Mechanical Lateral Proximal Femoral Angle (mLPFA)
• C) Neck Shaft Angle (NSA)
• D) Articulo Trochanteric Distance (ATD)
• E) Anatomic Medial Proximal Femoral Angle (aMPFA)

Question 78

During surgical planning for a valgus intertrochanteric osteotomy, the surgeon aims to restore a normal abductor lever arm. What is the target normal range for the Articulo Trochanteric Distance (ATD)?

• A) 0-2 mm
• B) -5 to 5 mm
• C) 85-95 mm
• D) 10-25 mm
• E) 124-136 mm

Question 79

A 55-year-old male with a proximal femoral varus deformity is being evaluated. Standing radiographs show that the angle between the distal femoral joint line and the proximal tibial joint line is 6°. What does this measurement represent?

• A) Mechanical Axis Deviation (MAD)
• B) Mechanical Lateral Proximal Femoral Angle (mLPFA)
• C) Joint Line Convergence Angle (JLCA)
• D) Anatomic Medial Proximal Femoral Angle (aMPFA)
• E) A normal finding

Question 80

A surgeon is planning a proximal femoral osteotomy to correct a valgus deformity. Preoperative assessment reveals a Joint Line Convergence Angle (JLCA) of 8°. What is the clinical significance of this finding?

• A) It indicates the primary deformity is in the tibia.
• B) It confirms the mLPFA measurement is accurate.
• C) It suggests the patient may require a concurrent or staged knee surgery.
• D) It is a contraindication to performing a femoral osteotomy.
• E) It guarantees an excellent outcome from the hip surgery alone.

Question 81

A resident is learning the Paley methodology for deformity correction. How is the Center of Rotation of Angulation (CORA) geometrically defined?

• A) The point of maximum bone density in the proximal femur.
• B) The intersection of the normal proximal axis and the abnormal distal axis of the bone.
• C) The center of the intramedullary canal at the level of the lesser trochanter.
• D) The geometric center of the femoral head.
• E) The midpoint of the planned osteotomy cut.

Question 82

When planning a correction for a complex, multi-planar proximal femoral deformity, how is the coronal plane CORA located on a radiograph?

• A) By intersecting the anatomic axis of the shaft with a line parallel to the ground.
• B) By finding the narrowest point of the femoral neck.
• C) By intersecting the normal proximal mechanical axis with the mechanical axis of the distal femoral shaft.
• D) By drawing a line from the greater trochanter to the lesser trochanter.
• E) By identifying the location of the physeal scar.

Question 83

A surgeon is planning a closing wedge osteotomy for a femoral neck non-union where the CORA is located precisely within the planned osteotomy site in the mid-neck. The surgeon performs the cut and angulates the fragments around a hinge at the osteotomy site. Which of Paley's Osteotomy Rules is being applied?

• A) Osteotomy Rule One
• B) Osteotomy Rule Two
• C) Osteotomy Rule Three
• D) The 3D Box Diagram Rule
• E) The Joint Line Convergence Rule

Question 84

A surgeon is performing a femoral neck osteotomy according to Paley's Rule One. What is the expected result if this rule is followed perfectly?

• A) The deformity is corrected with pure translation.
• B) The deformity is corrected with a combination of angulation and translation.
• C) The deformity is corrected with pure angulation and no translation.
• D) A new, iatrogenic translational deformity is created.
• E) The mechanical axis remains malaligned.

Question 85

Despite being the "anatomic ideal," why is an osteotomy performed at the CORA in the femoral neck (Rule One) rarely advisable in the proximal femur?

• A) It provides inadequate correction of varus.
• B) It is technically too difficult to perform.
• C) It creates a significant leg length discrepancy.
• D) It carries an unacceptably high risk of Avascular Necrosis (AVN).
• E) It fails to correct the mechanical axis.

Question 86

A surgeon plans a valgus-producing intertrochanteric osteotomy to correct coxa vara. The CORA is located in the femoral head. The osteotomy is performed distally in the intertrochanteric region. To achieve a perfect correction of the mechanical axis, the axis of correction (ACA) must pass through which point?

• A) The center of the osteotomy cut
• B) The tip of the greater trochanter
• C) The center of the lesser trochanter
• D) The true CORA in the femoral head
• E) The center of the knee joint

Question 87

A surgeon is performing a valgus intertrochanteric osteotomy for coxa vara, applying Paley's Rule Two. The osteotomy is performed distal to the CORA. What additional maneuver is mathematically required at the osteotomy site besides angulation?

• A) Shortening of the distal fragment
• B) Derotation of the distal fragment
• C) Medial translation of the distal fragment
• D) Lateral translation of the distal fragment
• E) No additional maneuver is needed

Question 88

A 10-year-old boy presents with progressively worsening bowlegs. On examination, he has significant genu varum. Radiographs confirm the deformity, and the mechanical axis passes medial to the knee. According to the Heuter-Volkmann law, what is the primary biological driver of this progressive deformity?

• A) Increased compression on the medial physis inhibits its growth, while the lateral physis continues to grow.
• B) Increased tension on the lateral physis stimulates its growth, causing it to outpace the medial side.
• C) Bone remodeling in the diaphysis (Wolff's law) is the primary cause of the angular change.
• D) Pathological ossification of the medial physeal perichondral ring of LaCroix.
• E) Decreased compression on the medial physis stimulates its growth, leading to overgrowth.

Question 89

A 12-year-old girl undergoes successful guided growth for genu valgum. Over 18 months, her mechanical axis normalizes. Which biological principle is primarily responsible for the subsequent remodeling of the femoral and tibial metaphyses to align with the new, corrected mechanical axis?

• A) Wolff's Law
• B) Heuter-Volkmann Law
• C) The Phemister technique
• D) The law of Laplace
• E) The Starling principle

Question 90

A surgeon is evaluating a full-length, weight-bearing AP radiograph of a 9-year-old boy with knock-knees. To quantify the overall severity of the lower extremity malalignment, a line is drawn from the center of the femoral head to the center of the ankle mortise. What is this measurement called?

• A) Mechanical Axis Deviation (MAD)
• B) Anatomic Axis Deviation (AAD)
• C) Joint Line Convergence Angle (JLCA)
• D) Mechanical Lateral Distal Femoral Angle (mLDFA)
• E) Center of Rotation of Angulation (CORA)

Question 91

An 11-year-old girl presents with genu valgum. Her full-length radiograph shows a Mechanical Axis Deviation (MAD) of 30 mm lateral to the knee center. Measurement of her joint orientation angles reveals a mechanical Lateral Distal Femoral Angle (mLDFA) of 80°. The Medial Proximal Tibial Angle (MPTA) is 88°. What is the primary location of her deformity?

• A) Distal femur
• B) Proximal tibia
• C) Distal tibia
• D) Knee joint ligamentous laxity
• E) Femoral diaphysis

Question 92

A 13-year-old boy has a varus deformity of his lower limb. Radiographic analysis shows a normal mLDFA of 87° but a Medial Proximal Tibial Angle (MPTA) of 80°. What is the correct interpretation of these findings?

• A) Tibia vara
• B) Femur varum
• C) Tibia valga
• D) Femur valgum
• E) Ankle varus

Question 93

During preoperative planning for a developmental genu varum deformity in an 8-year-old, the surgeon identifies the intersection point of the proximal and distal mechanical axes of the tibia. What does this point represent?

• A) Center of Rotation of Angulation (CORA)
• B) Mechanical Axis Deviation (MAD)
• C) Joint Line Convergence Angle (JLCA)
• D) The ideal location for a diaphyseal osteotomy
• E) The center of the knee joint

Question 94

A 16-year-old female with nearly closed physes presents with a painful 20° genu valgum deformity. She has significant remaining growth predicted to be less than 0.5 cm. What is the most appropriate surgical treatment?

• A) Distal femoral osteotomy
• B) Medial distal femoral hemi-epiphysiodesis with a tension-band plate
• C) Medial proximal tibial hemi-epiphysiodesis with staples
• D) Brace treatment until skeletal maturity
• E) Observation

Question 95

A 7-year-old boy with idiopathic genu valgum is being considered for guided growth. His parents are concerned about the procedure being permanent. Which of the following is a key advantage of using modern tension-band plates or staples for hemi-epiphysiodesis?

• A) The procedure is reversible upon hardware removal.
• B) It provides instantaneous correction.
• C) It requires a bone graft to be effective.
• D) It is only effective for varus deformities.
• E) It permanently arrests all growth in the limb.

Question 96

A surgeon is planning a hemi-epiphysiodesis for a 9-year-old child. To accurately predict the remaining growth and properly time the intervention and subsequent hardware removal, which of the following is most critical?

• A) Assessment of skeletal age using a Greulich and Pyle atlas
• B) The patient's chronological age
• C) The patient's body mass index (BMI)
• D) The mid-parental height
• E) The magnitude of the deformity in degrees

Question 97

A 4-year-old child presents with a significant genu valgum deformity. The surgeon is hesitant to perform a hemi-epiphyseal stapling. What is the primary technical concern with performing this procedure in a very young child, as described in the text?

• A) Risk of staple pull-out due to the highly cartilaginous epiphysis
• B) High likelihood of permanent, irreversible growth arrest
• C) Inability to obtain accurate preoperative radiographs
• D) The growth rate is too slow to achieve correction
• E) Increased risk of neurovascular injury

Question 98

A 12-year-old undergoes guided growth for a 15° femoral varus deformity. A follow-up radiograph 6 months later shows the tines of the staple have spread apart slightly. What is the clinical significance of this "tine spread"?

• A) It demonstrates the powerful force of physeal growth acting against the implant.
• B) It indicates imminent implant failure and requires immediate revision surgery.
• C) It is a sign of infection around the implant.
• D) It suggests the staple was placed incorrectly across the physis.
• E) It confirms that overcorrection has occurred.

Question 99

Two 11-year-old patients have identical 15° valgus deformities and similar growth rates. Patient A's deformity is in the distal femur (wider physis), and Patient B's deformity is in the distal tibia (narrower physis). Both are treated with hemi-epiphysiodesis. Which patient's deformity is expected to correct more quickly, and why?

• A) Patient B, because a narrower physis has a smaller "turning radius."
• B) Patient A, because a wider physis generates more corrective force.
• C) Both will correct at the same rate because the deformity magnitude is identical.
• D) Patient A, because the femur has a better blood supply.
• E) Correction speed is independent of physeal width.

Question 100

A surgeon is performing a lateral distal femoral hemi-epiphysiodesis using a tension-band plate for genu varum. To minimize the risk of secondary deformities, what is the most critical aspect of implant placement as seen on the lateral radiograph?

• A) The implant must be perfectly centered over the physis.
• B) The implant must be placed as anteriorly as possible.
• C) The implant must be placed as posteriorly as possible.
• D) The screws must be parallel to the joint line.
• E) The plate must be placed sub-periosteally.