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Orthopedic Ob Reconstru Review | Dr Hutaif Hip & Knee R -...

TKR Component Malalignment: Oral Examination Question Uncovered

23 Apr 2026 84 min read 155 Views
Illustration of oralexamination question malalignment - Dr. Mohammed Hutaif

Key Takeaway

This article provides essential research regarding TKR Component Malalignment: Oral Examination Question Uncovered. Oralexamination question malalignment of total knee replacement (TKR) components, particularly internal rotation of the femoral component, can cause significant complications. This malposition is implicated in patellofemoral maltracking, leading to anterior knee pain, subluxation, fracture, wear, and aseptic loosening. It also results in a tight flexion gap on the medial side of the knee.

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Question 1

A 68-year-old female presents with persistent anterior knee pain and crepitus 6 months after a total knee arthroplasty. Clinical examination reveals difficulty with terminal knee extension and a positive 'J' sign during flexion. Radiographs show a well-fixed patellar component without obvious tilt. Which of the following component malalignments is the most likely cause?





Explanation

Persistent anterior knee pain with a positive 'J' sign post-TKA is highly suggestive of patellofemoral maltracking, often caused by internal rotation of the femoral component. This effectively lateralizes the patella in relation to the trochlear groove, increasing lateral patellar facet pressure and causing symptoms. External rotation of the femoral component would tend to medialize the patella. Tibial valgus or posterior slope would not directly cause a 'J' sign. Patellar component medialization would generally improve tracking, not worsen it.

Question 2

A patient undergoes a primary total knee arthroplasty. Postoperatively, they complain of a persistent flexion contracture of 15 degrees, despite aggressive physical therapy. Radiographs show adequately sized components. Which of the following intraoperative technical errors is the most probable cause?





Explanation

A persistent flexion contracture post-TKA is frequently caused by placing the femoral component in excessive flexion. This elevates the anterior femoral condyles relative to the mechanical axis, impinging on the extensor mechanism in extension. Insufficient posterior femoral condylar resection would lead to a tight flexion gap, not necessarily a contracture in extension. Over-resection of the anterior femoral condyle could cause patella alta or patellar instability. Excessive tibial posterior slope would cause laxity in flexion and potentially hyperextension. Excessive tibial valgus primarily affects coronal alignment and stability.

Question 3

A 72-year-old male develops early aseptic loosening of his tibial component 3 years after a TKA for varus osteoarthritis. What is the most common coronal plane malalignment associated with early aseptic loosening of the tibial component?





Explanation

Tibial component varus malalignment (i.e., less than 0-3 degrees valgus, or frankly varus) is strongly correlated with early aseptic loosening, particularly on the medial side. A varus alignment shifts the load medially, leading to increased stress on the medial bone-implant interface and polyethylene wear. A tibial component placed in 5 degrees of valgus is generally considered within an acceptable range (often 0-3 degrees valgus). Femoral component malalignment or overall mechanical axis restoration would impact loosening differently or not be the primary driver for tibial component aseptic loosening in this scenario.

Question 4

Regarding rotational alignment in TKA, which anatomical landmark is considered the most reliable guide for external rotation of the femoral component?





Explanation

The Transepicondylar Axis (TEA) is considered the most reliable and anatomically consistent reference for femoral component rotation, representing the functional flexion axis of the knee. The femoral component is typically aligned parallel or slightly externally rotated (3-5 degrees) to the TEA. Whiteside's line (or the anteroposterior axis) is perpendicular to the TEA. The posterior condylar line can be unreliable in osteoarthritic knees due to posterior condylar wear. The femoral shaft axis guides coronal alignment, not rotation.

Question 5

A patient presents with a feeling of instability and giving way in full extension after TKA. Radiographs demonstrate well-fixed components with appropriate sizing. Which sagittal plane malalignment is the most likely culprit?





Explanation

Excessive tibial posterior slope can lead to an extensor lag and instability in extension. It creates a relatively 'loose' extension gap and a 'tight' flexion gap, pushing the femur posteriorly on the tibia in extension and potentially causing hyperextension or feeling of giving way. Insufficient tibial posterior slope typically leads to a tight flexion gap and difficulty with flexion. Femoral component placed in excessive flexion causes a flexion contracture. Tibial component placed in excessive extension is an unusual term, usually referred to as insufficient posterior slope. Patellar baja is related to patellofemoral mechanics, not directly extension instability.

Question 6

What is the primary consequence of significant internal rotation of the tibial component in a TKA?





Explanation

Significant internal rotation of the tibial component creates an asymmetrical flexion gap, often leading to a relatively tighter medial compartment and a looser lateral compartment during knee flexion. This can manifest as lateral instability in flexion, subluxation, or even impingement in some cases. It can also contribute to patellofemoral tracking issues but primarily affects the tibiofemoral kinematics in flexion. Medial patellofemoral impingement is less common, and ligament tension changes are usually complex rather than simply increased MCL tension.

Question 7

A 55-year-old active male reports persistent knee stiffness and difficulty achieving full flexion after TKA. Radiographs show a well-aligned implant without obvious issues. What subtle malalignment or technical error could contribute to this 'tight knee' sensation, particularly in flexion?





Explanation

Oversizing of the femoral component (especially in the anterior-posterior dimension) can lead to a 'tight' flexion gap by effectively increasing the volume within the knee, preventing full flexion. It can also cause impingement of the posterior capsule or soft tissues. Excessive tibial posterior slope typically leads to a loose flexion gap. Femoral component undersizing can cause instability or aseptic loosening. Insufficient posterior soft tissue release would make extension difficult, rather than flexion. Excessive femoral external rotation can cause medial laxity and not necessarily stiffness.

Question 8

For accurate assessment of overall mechanical axis post-TKA, which imaging study is considered the gold standard?





Explanation

A full-length standing anteroposterior (AP) radiograph of both lower extremities (often called a 'long leg alignment view') is the gold standard for assessing the overall mechanical axis of the lower limb. This view allows measurement from the center of the femoral head to the center of the ankle, passing through the knee, providing a comprehensive assessment of the coronal alignment and load transmission. Other views are useful for specific details but don't provide the complete mechanical axis picture.

Question 9

What is the primary biomechanical advantage of achieving a neutral mechanical axis (0 ± 3 degrees varus/valgus) in TKA?





Explanation

The primary biomechanical advantage of achieving a neutral mechanical axis in TKA is the even distribution of load across the tibial polyethylene insert. This minimizes peak stresses on one side, which is critical for reducing polyethylene wear, preventing aseptic loosening, and improving the long-term survival of the implant. While other benefits may exist, load distribution is paramount for longevity.

Question 10

A patient experiences a medial collateral ligament (MCL) tear during a TKA. Which femoral component rotational malposition is most likely to predispose to this complication if the flexion gap is aggressively balanced?





Explanation

Insufficient femoral external rotation (i.e., internal rotation) during TKA can lead to a tight medial flexion gap. If the surgeon attempts to balance this aggressively with releases, or if significant force is applied during reduction or range of motion, it can overstress and potentially tear the MCL. Excessive femoral external rotation would make the medial flexion gap loose. Coronal alignment (varus/valgus) and sagittal alignment (flexion) primarily affect different aspects of stability and range of motion.

Question 11

Which of the following is considered the most common cause of patellofemoral complications after TKA?





Explanation

Rotational malalignment of either the femoral or tibial components is the most common cause of patellofemoral complications (e.g., maltracking, anterior knee pain, patellar tilt) after TKA. Incorrect rotation can alter the patellofemoral kinematics, leading to lateralization or medialization of the patella within the trochlear groove. Other options have different primary consequences.

Question 12

When performing a measured resection technique, what is the desired amount of external rotation for the femoral component relative to the posterior condylar line in most valgus knees?





Explanation

In a measured resection technique, the femoral component is typically placed in 3-5 degrees of external rotation relative to the posterior condylar line to avoid internal rotation of the femoral component and to align with the transepicondylar axis. This compensates for the natural internal rotation of the posterior condyles relative to the surgical epicondylar axis. In severe valgus knees with hypoplastic lateral condyles, using the posterior condylar line may still result in internal rotation, and the TEA or Whiteside's line should be considered the primary reference.

Question 13

A 70-year-old patient presents with recurrent knee effusions and a grinding sensation 2 years after TKA. Radiographs show no obvious loosening or infection. On examination, there's a palpable clunk during knee flexion and extension. A CT scan is obtained and reveals significant component impingement. Which type of malalignment is most likely causing this issue?





Explanation

Femoral component oversizing, particularly in the anterior-posterior dimension, can lead to impingement of the posterior soft tissues (e.g., posterior capsule) during flexion or the extensor mechanism in extension, causing a clunk, grinding, stiffness, and recurrent effusions. Excessive tibial posterior slope usually causes laxity in extension. Tibial component undersizing can cause subsidence. Patellar component tilt primarily causes patellofemoral pain. Insufficient femoral external rotation leads to patellofemoral maltracking or medial compartment tightness.

Question 14

Which of the following is a potential complication of placing the tibial component with insufficient posterior slope?





Explanation

Insufficient tibial posterior slope (i.e., the tibial cut being too flat or even anteriorly sloped) can create a relatively 'tight' flexion gap, making it difficult to achieve full knee flexion. It can also cause anterior impingement. Hyperextension instability is associated with excessive posterior slope. Increased wear of the anterior polyethylene is less direct. Increased PCL tension can occur, but difficulty with flexion is a more primary functional consequence. Lateral patellar subluxation is usually related to rotational alignment.

Question 15

What is the consequence of placing the femoral component in excessive external rotation (beyond 5-7 degrees relative to TEA)?





Explanation

Placing the femoral component in excessive external rotation can lead to a relatively loose medial flexion gap, potentially causing medial collateral ligament (MCL) laxity in flexion and varus instability. It effectively 'opens up' the medial side. Increased medial patellofemoral pressure is more typical of internal rotation. Tightening of the lateral flexion gap is also incorrect. Patellar baja is related to patellar component positioning. Condyle fracture is less likely than instability.

Question 16

When assessing TKA alignment on postoperative radiographs, what is the acceptable range for the mechanical axis in the coronal plane?





Explanation

The generally accepted range for achieving optimal mechanical axis in the coronal plane post-TKA is within 3 degrees of neutral (i.e., 3 degrees varus to 3 degrees valgus). Malalignment outside this range has been shown to be associated with increased rates of polyethylene wear and aseptic loosening. While a perfectly neutral axis is ideal, a small deviation is tolerated.

Question 17

Which surgical technique specifically aims to avoid rotational malalignment of the femoral component by referencing the functional flexion-extension axis?





Explanation

Navigation-assisted surgery and robotics are designed to precisely control component alignment, including rotational alignment, by referencing anatomical landmarks and often the functional flexion-extension axis. While both measured resection and gap balancing techniques aim for good alignment, navigation provides real-time feedback and often uses a registration process to define axes more accurately, helping to avoid rotational malalignment based on the functional axis. Conventional guides rely on external or internal landmarks that can be variable or affected by deformity.

Question 18

What is the most accurate imaging modality for assessing subtle rotational malalignment of the femoral and tibial components after TKA?





Explanation

Computed Tomography (CT) scan is considered the most accurate imaging modality for assessing subtle rotational malalignment of both femoral and tibial components post-TKA. It allows for precise measurement of component rotation relative to anatomical landmarks (e.g., transepicondylar axis, tibial tubercle). Standard radiographs and long leg views are less effective for detailed rotational assessment. MRI can assess soft tissues well but is not superior to CT for bone-implant rotational measurements. Bone scintigraphy assesses metabolic activity, not alignment.

Question 19

A patient reports a 'giving way' sensation and recurrent effusions after TKA, particularly when pivoting. Clinical examination reveals mild laxity in flexion. What is a common cause of this type of instability?





Explanation

All listed options can contribute to instability in flexion. Excessive femoral component external rotation can lead to MCL laxity. Excessive tibial posterior slope creates a relatively loose flexion gap. Inadequate soft tissue balancing (e.g., insufficient release of a tight side or excessive release of a loose side) directly causes gap asymmetry and instability. Femoral component undersizing in the A-P dimension can also lead to a loose flexion gap. Therefore, 'All of the above' is the best answer as these factors often combine or are isolated causes of flexion instability.

Question 20

Which of the following describes the 'Whiteside's Line' used in rotational alignment of the femoral component?





Explanation

Whiteside's Line is an important reference for femoral rotation. It is defined as a line perpendicular to the transepicondylar axis (TEA), typically passing through the deepest part of the trochlear groove anteriorly and the intercondylar notch posteriorly. It is used as an axis for femoral component rotation, ideally aligning with the AP axis of the femoral component. The TEA connects the medial and lateral epicondyles.

Question 21

In a TKA for a severe varus deformity, what is a common pitfall in tibial component placement regarding coronal alignment, if not properly addressed?





Explanation

In a severe varus knee, the medial tibial plateau is typically worn and depressed. If the surgeon simply resects bone parallel to this worn surface, the tibial component will inadvertently be placed in varus, which is a common cause of early loosening. The goal is to create a neutral or slight valgus (0-3 degrees) alignment relative to the mechanical axis of the tibia, which requires resecting more bone from the intact (lateral) side relative to the worn (medial) side, or using proper alignment guides. Over-resection of the lateral tibial plateau could lead to valgus malalignment, but the most common pitfall when not properly addressed is varus.

Question 22

What effect does persistent patella alta after TKA typically have on patellofemoral mechanics?





Explanation

Patella alta (high-riding patella) after TKA typically leads to reduced patellofemoral contact pressure in early flexion because the patella engages the femoral trochlear groove later. This can cause instability, a feeling of 'giving way', or difficulty initiating flexion. Patellar baja (low-riding patella) is associated with increased contact pressure, crepitus, and a higher risk of patellar clunk syndrome. Improved tracking and reduced anterior knee pain are unlikely with patella alta.

Question 23

Which of the following is the most appropriate strategy to correct a tight extension gap and a loose flexion gap during TKA?





Explanation

A tight extension gap suggests insufficient distal femoral resection, while a loose flexion gap often indicates over-resection of the posterior femoral condyles or an overall loose flexion space. To address a tight extension gap, re-resecting more distal femur is appropriate. This will also slightly loosen the flexion gap, which is already loose, so further consideration of flexion gap balancing would be needed. Increasing femoral component size would tighten both gaps. Increasing poly thickness would tighten both gaps. Re-resecting proximal tibia would further loosen the extension gap. Decreasing tibial posterior slope would tighten the flexion gap, but wouldn't directly address the tight extension gap.

Question 24

Failure to externally rotate the femoral component adequately, relative to the surgical epicondylar axis, results in what common alignment issue?





Explanation

Failure to externally rotate the femoral component adequately (or internally rotating it) relative to the surgical epicondylar axis is a common cause of femoral component internal rotation. This can lead to patellofemoral maltracking, lateral patellar subluxation, and an asymmetric flexion gap (tight medially, loose laterally). Valgus or flexion malalignment are different planes of malalignment. Excessive anterior tibial slope and patella baja are unrelated to femoral rotational errors.

Question 25

What is the primary concern with gross oversizing of the tibial component in TKA?





Explanation

Gross oversizing of the tibial component, particularly anteriorly, posteriorly, or medially/laterally, can lead to impingement of the surrounding soft tissues (e.g., patellar tendon, posterior capsule, MCL, pes anserinus tendons). This can cause pain, stiffness, and reduced range of motion. While stress shielding can occur with any implant, and wear is multifactorial, direct impingement is a more immediate and painful consequence of oversizing. Undersizing is more associated with subsidence.

Question 26

Which factor is most predictive of early failure in medial unicompartmental knee arthroplasty (UKR)?





Explanation

Postoperative varus alignment (e.g., 5 degrees varus) in a medial UKR significantly increases the load on the medial compartment, leading to accelerated polyethylene wear and higher rates of early aseptic loosening and failure. UKRs typically aim for a slight varus or neutral mechanical axis to shift the load slightly to the lateral compartment. A 3-degree valgus alignment would shift too much load laterally and also be detrimental, but 5 degrees varus is a more direct cause of failure in a medial UKR. Other factors are less critical for early mechanical failure.

Question 27

A TKA patient complains of a clunk and anterior knee pain. During surgical exploration, a fibrous nodule is found superior to the patellar component, within the quadriceps tendon. This is characteristic of:





Explanation

This clinical description (clunk, anterior knee pain, fibrous nodule superior to the patellar component in the quadriceps tendon) is characteristic of 'patellar clunk syndrome.' It is more commonly associated with patellar baja or femoral component design issues that allow impingement of the suprapatellar pouch. Patella alta or rotational malalignment would typically present with different patellofemoral tracking issues rather than a specific fibrous nodule.

Question 28

What is the consequence of placing the femoral component in an excessively posterior position (e.g., due to insufficient anterior femoral cut)?





Explanation

Placing the femoral component in an excessively posterior position (effectively 'anteriorizing' the knee) can lead to anterior impingement of the patella or extensor mechanism, restricting full flexion. It can also make the extension gap too tight. A flexion contracture is more associated with an excessively flexed femoral component or posterior condylar over-resection. Hyperextension instability is related to excessive tibial posterior slope. Posterior impingement usually occurs with an oversized femoral component. Patellar tendon rupture is not directly related to femoral AP position.

Question 29

When using an extramedullary guide for tibial resection, what is the most important anatomical landmark for achieving correct coronal alignment?





Explanation

When using an extramedullary guide for tibial resection, the center of the talus (or the midpoint between the malleoli) is the critical distal reference point. The goal is to align the tibial cut perpendicular to the mechanical axis, which passes from the center of the knee to the center of the talus. The tibial tubercle is a rotational reference, and the malleoli define the ankle, but the center of the talus represents the mechanical axis origin in the ankle.

Question 30

Which rotational guide for the femoral component is considered 'anatomic' and least affected by femoral condylar wear?





Explanation

The Transepicondylar Axis (TEA), connecting the most prominent points of the medial and lateral epicondyles, is considered the most anatomically consistent and reliable reference for femoral component rotation. It represents the functional flexion-extension axis of the knee and is least affected by femoral condylar wear compared to the posterior condylar axis. Whiteside's Line (AP axis) is perpendicular to the TEA. The femoral shaft axis relates to coronal alignment.

Question 31

A patient with a primary TKA is found to have polyethylene wear predominantly on the posterior aspect of the lateral tibial insert. What malalignment is most consistent with this pattern of wear?





Explanation

Excessive femoral component external rotation can lead to an asymmetric flexion gap, often causing medial laxity and increased loading on the lateral compartment, particularly in flexion. This can result in increased wear on the posterior-lateral aspect of the tibial polyethylene. Excessive femoral internal rotation (or insufficient external rotation) would typically cause medial side issues and patellofemoral tracking. Excessive tibial posterior slope would cause anterior loading/impingement in flexion or hyperextension. Tibial varus would cause medial wear.

Question 32

What is the primary risk associated with a persistently tight medial compartment after TKA, despite appropriate bone cuts?





Explanation

A persistently tight medial compartment can severely limit knee flexion due to impingement and can place excessive tension on the medial collateral ligament (MCL). This can lead to MCL failure (rupture) during surgery or postoperatively, or chronic MCL strain and pain. Lateral instability, patellofemoral issues, and increased lateral wear are more associated with a loose medial compartment or specific rotational errors. Early aseptic loosening is more common with varus malalignment.

Question 33

When balancing the extension gap in a TKA, what is the ideal soft tissue tension?





Explanation

The ideal soft tissue tension in the extension gap should be evenly balanced and stable, but not overtly tight or loose. It should allow for 1-2mm of distraction with firm manual stress. This provides stability without restricting motion or causing impingement. Visibly tight or loose gaps are indicative of malalignment or inadequate balancing. The goal is to achieve a rectangular gap, equal to the flexion gap.

Question 34

A patient presents with a TKA reporting that their knee feels 'too tight' and they cannot fully flex. Radiographs show a well-aligned femoral component but a tibial component with an unusually steep posterior slope. What is the likely consequence of this tibial slope?





Explanation

An unusually steep (excessive) posterior slope of the tibial component creates a relatively loose flexion gap and can lead to posterior instability, particularly during flexion. It also predisposes to hyperextension. A flexion contracture is associated with insufficient posterior slope or femoral component flexion. Anterior impingement is usually with insufficient slope. Increased patellofemoral forces are not directly caused by tibial slope, though instability can indirectly affect the patella.

Question 35

What is the 'kinematic alignment' philosophy in TKA aiming to achieve regarding component placement?





Explanation

Kinematic alignment (KA) in TKA aims to reproduce the patient's pre-arthritic constitutional knee alignment and the native joint kinematics. This often results in a slight varus or valgus overall alignment, rather than a forced neutral mechanical axis. It contrasts with mechanical alignment (MA) which strives for a neutral mechanical axis. The goal is to avoid overstuffing or understuffing the joint based on individual anatomy.

Question 36

Which of the following describes the 'windshield wiper effect' in the context of TKA component malalignment?





Explanation

The 'windshield wiper effect' refers to the movement of the tibial component relative to the underlying bone, particularly at the keel or stem, when the component is not well-fixed. This micromotion can cause particulate wear, osteolysis, and eventual aseptic loosening. It's often associated with inadequate cementation, poor bone quality, or significant malalignment leading to high focal stresses.

Question 37

In a TKA, a common cause of recurrent lateral patellar subluxation or dislocation is:





Explanation

Internal rotation of the femoral component is a common cause of lateral patellar subluxation or dislocation. It effectively lateralizes the trochlear groove relative to the patella, predisposing to tracking issues. External rotation of the tibial component could also contribute but femoral rotational malalignment is a more potent factor. Medial patellar placement would tend to stabilize. Insufficient posterior slope and overall valgus malalignment are less directly linked to patellar tracking.

Question 38

A TKA patient develops chronic anterior knee pain and a feeling of 'catch' or 'clunk' in mid-flexion. Radiographs are unremarkable. Which component malalignment would most likely be implicated in anterior impingement of the patella or extensor mechanism in flexion?





Explanation

Excessive anterior positioning of the femoral component (resulting from inadequate resection of the anterior femur or an oversized component) can lead to anterior impingement of the patella or extensor mechanism, causing a clunk or catch in mid-flexion. This effectively narrows the patellofemoral space. Undersizing might cause instability, not impingement. Excessive posterior tibial slope would cause posterior instability. Rotational or tilt issues lead to tracking problems, not typically anterior impingement in mid-flexion in this manner.

Question 39

What is the most common consequence of significant varus malalignment of the femoral component in TKA?





Explanation

Significant varus malalignment of the femoral component leads to lateral collateral ligament (LCL) laxity, particularly in extension, and can result in varus instability. It effectively opens up the lateral compartment. Valgus malalignment of the femoral component would lead to MCL laxity. Increased wear typically occurs on the side of increased loading, which is medial with varus tibial or overall limb malalignment, but for femoral component varus, the LCL becomes loose.

Question 40

Which of the following is most strongly associated with the 'opening up' of the medial compartment in flexion and leading to medial laxity?





Explanation

Excessive femoral component external rotation leads to an asymmetrical flexion gap where the medial side becomes loose and the lateral side becomes tight. This causes medial laxity, particularly in flexion, and can result in medial instability or varus stress laxity in flexion. Femoral internal rotation would tighten the medial side. Excessive tibial posterior slope primarily affects overall gap balance and hyperextension. Insufficient distal femoral resection affects the extension gap. Tibial component varus affects coronal stability in extension mainly.

Question 41

To correct an extension gap that is tight laterally but appropriately balanced medially, what specific soft tissue release might be considered?





Explanation

If the extension gap is tight laterally while the medial side is balanced, it indicates tightness of the lateral structures. A popliteus tendon release, or a more comprehensive posterolateral corner release (depending on the degree of tightness and specific structures involved), would be indicated to balance the lateral compartment in extension. MCL releases are for medial tightness. PCL release addresses a tight flexion gap when the PCL is causative. Pes anserinus release primarily affects flexion contracture in some cases.

Question 42

What is a potential consequence of placing the patellar component with excessive medial tilt?





Explanation

Placing the patellar component with excessive medial tilt leads to increased pressure on the medial facet of the patella against the femoral trochlea. This results in increased medial patellofemoral pressure and can cause anterior knee pain, crepitus, and accelerated wear of the medial patellar polyethylene. Lateral tilt would cause increased lateral pressure. Lateral patellar subluxation is usually due to femoral rotational malalignment. Patellar clunk syndrome is due to suprapatellar scarring.

Question 43

When assessing the sagittal alignment of the femoral component on a true lateral radiograph, which line should be parallel to the anterior femoral cortex?





Explanation

On a true lateral radiograph, the anterior femoral condylar line of the component should be parallel to the anterior femoral cortex. This indicates proper sagittal positioning of the femoral component, avoiding notching or anterior impingement. The posterior condylar line indicates flexion/extension relative to the shaft. The other options are for rotational or overall mechanical alignment.

Question 44

What is the primary technical goal of using a 'gap balancing' technique in TKA?





Explanation

The primary technical goal of the 'gap balancing' technique in TKA is to achieve equal and rectangular flexion and extension gaps. This is done by assessing the soft tissue tension in both flexion and extension and making bone resections and soft tissue releases to create balanced, symmetrical gaps of the same dimension. This ensures stability throughout the range of motion. While mechanical axis restoration is a goal, gap balancing focuses on the soft tissue envelopes.

Question 45

A patient with a TKA reports chronic posterior knee pain and a feeling of instability during staircase ascent. A lateral radiograph shows slight posterior subluxation of the femoral component on the tibial tray. Which malalignment is most likely?





Explanation

Excessive posterior slope of the tibial component creates a relatively loose flexion gap and can lead to posterior subluxation of the femoral component on the tibial tray, particularly during activities like staircase ascent which involve high flexion and posterior shear forces. It effectively allows the femur to slide posteriorly. Insufficient posterior slope would cause tightness in flexion. Femoral undersizing might cause instability, but posterior subluxation is highly indicative of excessive posterior slope.

Question 46

Which of the following describes the potential consequence of placing the femoral component in an overly extended position (e.g., too much anterior femoral cut)?





Explanation

Placing the femoral component in an overly extended position (or insufficient resection of the posterior femoral condyles) makes the extension gap excessively tight. This can lead to a flexion contracture as the knee cannot achieve full extension. Hyperextension is often linked to excessive tibial posterior slope. Anterior impingement in flexion is more associated with an anteriorized or oversized femoral component. Patellar clunk is a specific syndrome.

Question 47

What is the consequence of placing the tibial component in an excessively external rotation position?





Explanation

Excessive external rotation of the tibial component can cause the tibial tubercle to be too far laterally, potentially leading to medial patellar subluxation as the patella is drawn medially relative to the trochlear groove. It can also lead to an asymmetrical flexion gap, with tightening of the lateral compartment and loosening of the medial compartment, but medial patellar subluxation is a direct patellofemoral consequence.

Question 48

When templating for TKA, what is the most important measurement to ensure proper restoration of limb length and joint line?





Explanation

To ensure proper restoration of limb length and joint line, it is crucial to measure the preoperative distal femoral length and proximal tibial length relative to fixed anatomical landmarks (e.g., femoral head, ankle joint, fibular head). This helps guide bone resections to avoid either lengthening or shortening the limb significantly and to maintain the natural joint line, preventing patella baja or alta. Other options are important but not directly for both limb length and joint line restoration.

Question 49

Which complication is more likely with an undersized femoral component in the anterior-posterior dimension?





Explanation

An undersized femoral component in the anterior-posterior dimension creates a relatively loose flexion gap. This can lead to posterior instability in flexion, where the femur can subluxate posteriorly on the tibial tray. Stiffness and anterior impingement are more common with oversized or anteriorized components. Fracture of the anterior femoral cortex is a risk with notching during distal femoral cuts. Patellar clunk syndrome has a different etiology.

Question 50

What is the preferred reference for rotational alignment of the tibial component?





Explanation

The preferred reference for rotational alignment of the tibial component is typically a line connecting the center of the tibial tubercle to the center of the posterior cruciate ligament (PCL) insertion (or the middle of the medial third of the tibial tuberosity to the center of the ankle joint). This ensures proper orientation relative to the extensor mechanism and the native knee anatomy. The intermalleolar axis is a valid external reference, but the internal anatomical landmarks are key for component placement.

Question 51

A TKA patient develops severe pain, swelling, and warmth 3 months postoperatively. Aspiration confirms acute periprosthetic joint infection. What component malalignment, if present, might have indirectly contributed to this infection risk?





Explanation

While direct causation is rare, any significant component malalignment leading to chronic soft tissue irritation, persistent effusions, pain, or instability can compromise the local biological environment, potentially increasing the risk of infection. Chronic inflammation, repeated injections, and potentially compromised vascularity due to abnormal mechanics can be contributing factors. Neutral alignment, specific rotations or patella alta do not inherently increase infection risk unless they are symptomatic and lead to other interventions or complications.

Question 52

A patient with a severe fixed valgus deformity undergoes TKA. During surgery, significant tightness of the lateral compartment in both flexion and extension is noted. What is the most appropriate initial soft tissue release to address this?





Explanation

For a severe fixed valgus deformity with tightness of the lateral compartment in both flexion and extension, the primary structures causing this tightness are the lateral collateral ligament (LCL) and the popliteus tendon. Releasing these structures, along with the posterolateral capsule, is typically required to balance the lateral side. MCL and pes anserinus releases are for medial tightness. PCL release is for a tight flexion gap.

Question 53

When performing TKA, the anterior femoral cortex is accidentally 'notched' during distal femoral resection. What malalignment or surgical error predisposes to this?





Explanation

Notching of the anterior femoral cortex occurs when the intramedullary guide rod for distal femoral resection is placed with an overly anterior entry point, leading to an oblique cut that compromises the anterior cortex. This can predispose to periprosthetic fracture. It is not directly related to femoral component sizing, slope, or rotation, but rather to the distal femoral cutting block's positioning. Insufficient distal femoral resection would lead to a tight extension gap, not notching.

Question 54

Which intraoperative assessment confirms adequate rotational alignment of the tibial component relative to the femoral component in flexion?





Explanation

Adequate rotational alignment of the tibial component relative to the femoral component, especially in flexion, is confirmed when the medial and lateral flexion gaps are equal and rectangular when evaluated with a spacer block. This indicates that the tibiofemoral articulation is balanced and symmetrical in the rotational plane. While central patellar tracking is a good sign, the gap assessment is a direct measure of tibiofemoral rotation. Other options describe different aspects of alignment.

Question 55

What is the potential consequence of restoring the joint line too proximally in TKA?





Explanation

Restoring the joint line too proximally (i.e., making the distal femoral cut and/or proximal tibial cut more proximally than the native joint line) can lead to patella baja (low-riding patella). This shortens the patellar tendon moment arm, increases patellofemoral contact forces, can cause anterior knee pain, crepitus, and potentially patellar clunk syndrome. Patella alta is due to a more distally restored joint line.

Question 56

What is a characteristic symptom of symptomatic patella baja after TKA?





Explanation

Symptomatic patella baja (low-riding patella) after TKA typically manifests as difficulty initiating knee flexion, increased patellofemoral contact pressure, anterior knee pain, crepitus, and sometimes patellar clunk syndrome. It can also lead to a functional shortening of the quadriceps moment arm. Lateral patellar subluxation and a 'J' sign are more indicative of patella alta or rotational malalignment. Hyperextension is related to tibial slope. Posterior knee pain and clunking in deep flexion often relate to posterior impingement or loose bodies.

Question 57

A TKA patient develops progressively worsening pain and swelling with eventual radiographic evidence of early osteolysis around the tibial component. Which specific malalignment is most strongly implicated in initiating this process?





Explanation

Tibial component varus malalignment (e.g., 5 degrees of varus) leads to uneven loading and significantly higher stresses on the medial compartment. This accelerates polyethylene wear, producing wear particles that can trigger an inflammatory response and lead to osteolysis, ultimately causing aseptic loosening. Other malalignments can cause pain and dysfunction but are less directly implicated in early osteolysis from accelerated wear than coronal plane malalignment leading to uneven load distribution.

Question 58

Which of the following describes the functional consequence of restoring the mechanical axis in 7 degrees of valgus in a standard TKA (designed for neutral alignment)?





Explanation

Restoring the mechanical axis in 7 degrees of valgus (i.e., excessive valgus alignment) in a standard TKA shifts the load predominantly to the lateral compartment. This will lead to increased polyethylene wear on the lateral side of the tibial insert, and can also cause medial collateral ligament (MCL) laxity and valgus instability. Varus instability would be caused by varus malalignment. Patellofemoral issues are typically rotational. Reduced range of motion is less directly caused by coronal malalignment.

Question 59

What is the clinical significance of a persistent 'quadriceps lag' after TKA, despite good surgical alignment and rehabilitation?





Explanation

A persistent quadriceps lag (inability to actively extend the knee fully, even if passive extension is full) after TKA, when alignment is otherwise good, often indicates persistent extensor mechanism weakness (e.g., due to preoperative atrophy, pain, or nerve injury) or a subtle, persistent flexion contracture that is difficult to overcome. It is not directly indicative of patella alta or baja (though these can cause extensor dysfunction), nor an infection or specific rotational error in this general context.

Question 60

When using a computer navigation system for TKA, what is the primary benefit regarding component malalignment prevention?





Explanation

The primary benefit of computer navigation systems in TKA regarding component malalignment prevention is that they provide real-time, objective data on bone cuts and component orientation. This minimizes manual measurement errors and allows the surgeon to verify and adjust alignment precisely, especially in complex cases, ultimately leading to more accurate component placement. It does not eliminate the need for releases, isn't fully automatic, often increases surgical time, and doesn't guarantee sterility.

Question 61

What is the most accurate method to assess the patellar height after TKA?





Explanation

All listed indices (Insall-Salvati, Blackburne-Peel, Caton-Deschamps) are commonly used to assess patellar height on a lateral knee radiograph. The choice of index may depend on surgeon preference or specific clinical scenarios, but a true lateral radiograph is essential for applying these measurements accurately. Therefore, 'All of the above indices on a lateral knee radiograph' is the most complete answer.

Question 62

Which factor is most challenging to correct once established post-TKA and can significantly impact long-term outcomes and patient satisfaction?





Explanation

Persistent component rotational malalignment, especially of the femoral component, leading to ongoing patellofemoral dysfunction (e.g., anterior knee pain, maltracking, clunking) is a very challenging problem to correct once established. It often requires complex revision surgery to address. Other issues like mild swelling, incisional pain, transient weakness, or small LLDs are usually self-limiting or easily manageable. Significant rotational malalignment is a major cause of patient dissatisfaction and poor outcomes.

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Dr. Mohammed Hutaif
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