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Orthopedic Examination Question Patellar Instability Decoded

23 Apr 2026 90 min read 108 Views
Structured oral examination question 8: Patellar instability

Key Takeaway

This article provides essential research regarding Orthopedic Examination Question Patellar Instability Decoded. For an examination question patellar instability, assessment involves a detailed history and clinical exam. Key investigations include lateral and axial radiographs for patellar tilt/height and trochlear depth, MRI for articular lesions and MPFL integrity, and CT for femoral anteversion, tibial torsion, and TT-TG distance. Risk factors like trochlear dysplasia are crucial for diagnosis.

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Question 1

A 16-year-old male presents with recurrent lateral patellar dislocations. Clinical examination reveals a positive J-sign, patellar hypermobility, and a positive apprehension test at 20 degrees of knee flexion. Imaging shows significant trochlear dysplasia, a TT-TG distance of 22 mm, and patella alta. The patient has failed conservative management. Which of the following surgical interventions would be MOST appropriate to address the multiple anatomical risk factors in this patient?





Explanation

This patient presents with a severe form of patellar instability characterized by multiple significant anatomical risk factors: severe trochlear dysplasia, markedly increased TT-TG distance (normal < 15-20 mm), and patella alta. Isolated MPFL reconstruction would address the medial restraint but not the underlying bony deformities. VMO advancement and lateral retinacular release are typically insufficient for severe bony dysplasia. Tibial tubercle medialization alone would only address the TT-TG and not the trochlear dysplasia or patella alta. Therefore, a comprehensive approach involving trochleoplasty (for the severe dysplasia), MPFL reconstruction (for the medial restraint), and a tibial tubercle osteotomy for both medialization (for TT-TG) and distalization (for patella alta) is indicated for optimal outcomes and recurrence prevention. This combination addresses all major identified risk factors.

Question 2

Regarding the medial patellofemoral ligament (MPFL), which statement is most accurate concerning its anatomy and function?





Explanation

The MPFL is recognized as the primary static restraint to lateral patellar translation, particularly in the initial 20-30 degrees of knee flexion, where the trochlear groove is shallowest. At full knee extension, the joint is less constrained, but the MPFL's role is critical. The femoral attachment is variable but typically found distal and posterior to the adductor tubercle, often blended with the adductor magnus tendon and medial gastrocnemius origin, not consistently on the medial epicondyle. The patellar attachment is usually on the superior medial patella. While avulsions can occur at either end, femoral avulsions are more common in acute dislocations.

Question 3

A 14-year-old female presents with her first traumatic lateral patellar dislocation. She has significant knee swelling and pain. Lateral X-ray shows patella alta, and MRI confirms a partial tear of the MPFL at its femoral insertion, extensive bone bruising of the lateral femoral condyle and medial patella, and a small osteochondral fragment off the medial patellar facet. What is the most appropriate initial management strategy?





Explanation

The presence of a significant osteochondral fragment following a first-time dislocation is an absolute indication for surgical intervention, typically involving fixation or removal of the fragment. Given her age and the acute nature, fixation is preferred if the fragment is salvageable. While conservative management is often appropriate for first-time dislocations without significant concomitant injuries, the osteochondral fragment necessitates surgical intervention. MPFL reconstruction may be considered concurrently or at a later stage depending on residual instability, but the immediate priority is addressing the intra-articular injury. Tibial tubercle osteotomy is too aggressive for a first-time dislocation unless there are severe underlying malalignment issues, and initial conservative management or fragment fixation would precede. Closed reduction is already done, and immobilization in full extension is outdated and detrimental to recovery.

Question 4

Which of the following is considered the MOST significant risk factor for recurrent patellar instability?





Explanation

Severe trochlear dysplasia, especially Dejour Types B, C, or D, is consistently identified as the single most significant anatomical risk factor for recurrent patellar instability. The flattened or convex trochlear groove provides inadequate bony constraint against lateral patellar translation. Generalized ligamentous laxity is a risk factor but less potent than severe dysplasia. Dislocation at a younger age (especially under 15) is associated with higher recurrence rates, not older age. A torn MPFL is characteristic of acute dislocation, but its absence doesn't preclude recurrence if other factors exist; its presence increases recurrence risk if left untreated. A Q-angle less than 10 degrees would typically be protective or normal, not a risk factor; an increased Q-angle is a risk factor.

Question 5

During an MPFL reconstruction using a semitendinosus autograft, the most critical step to prevent iatrogenic patellar fracture or over-constraining the patella is:





Explanation

Over-constraining the patella is a known complication of MPFL reconstruction, leading to patellofemoral pain and stiffness. The MPFL is isometric in the initial 0-30 degrees of flexion. Tensioning the graft with the knee in 30 degrees of flexion is crucial. If the graft is tensioned in full extension or hyperflexion, it becomes too tight in mid-flexion, causing increased patellofemoral contact pressures and potentially pain or articular cartilage damage. Fluoroscopy for femoral tunnel placement is essential to avoid violating the physis in skeletally immature patients or drilling too anterior/posterior, but it doesn't directly prevent over-tensioning. Patellar fixation is standard; lateral retinacular release is not routinely performed with MPFL reconstruction unless specific lateral tightness is present.

Question 6

A patient with a history of recurrent patellar instability undergoes an MRI. The report indicates a TTPG (Tibial Tubercle-Trochlear Groove) distance of 20 mm. What is the clinical significance of this finding?





Explanation

A TT-TG distance of 20 mm is considered significantly elevated. Normal values are typically less than 15-20 mm, with values over 20 mm strongly correlating with patellofemoral instability due to a lateralized pull of the patellar tendon and quadriceps mechanism relative to the trochlear groove. It is a key factor indicating bony malalignment. While patella alta can coexist, TT-TG specifically measures the transverse plane relationship, not patellar height. It's a significant risk factor but doesn't necessarily dictate immediate surgery if asymptomatic or if conservative management is successful. Quadriceps imbalance can contribute but isn't directly measured by TT-TG.

Question 7

Which of the following physical examination maneuvers is most specific for diagnosing patellar instability?





Explanation

The patellar apprehension test (or 'Fairbank's test') involves attempting to laterally translate the patella with the knee in varying degrees of flexion while observing for the patient's anxiety, muscle guarding, or resistance, which signifies impending dislocation. This test is highly specific for patellar instability. The other tests are for collateral ligaments (valgus stress), ACL (Lachman), meniscal injury (McMurray), or patellofemoral pain syndrome (patellar grind), not patellar instability directly.

Question 8

A 12-year-old male with open physes experiences his second lateral patellar dislocation. X-rays show no fracture. MRI confirms MPFL rupture and normal trochlear morphology. He has no significant patella alta or increased TT-TG distance. What is the most appropriate surgical approach?





Explanation

For skeletally immature patients with recurrent patellar instability, MPFL reconstruction is the preferred procedure. Given the open physes, techniques that avoid or protect the growth plates are critical, such as an all-epiphyseal (transphyseal without violating growth plates) or transphyseal tunnels placed carefully to minimize growth disturbance. Tibial tubercle osteotomies and trochleoplasty are generally avoided in skeletally immature patients due to the risk of growth arrest, unless there are severe underlying bony deformities that supersede this risk (which are explicitly ruled out in this question). Conservative management has failed after the second dislocation, and lateral release alone is insufficient for MPFL rupture.

Question 9

What is the primary anatomical feature that contributes to the 'J-sign' observed in patients with patellar instability?





Explanation

The J-sign describes the sudden, exaggerated lateral deviation of the patella as the knee approaches full extension during active extension from a flexed position. This phenomenon is a dynamic manifestation of patellar instability and is primarily caused by an underlying trochlear dysplasia (a shallow or flat trochlear groove) that fails to adequately engage and constrain the patella until the very end of extension, leading to a 'jump' laterally. While other factors like lateral retinacular tightness or VMO weakness can contribute to patellar tracking issues, the J-sign itself is most directly linked to the patella failing to engage the trochlear groove early in extension, often due to trochlear dysplasia.

Question 10

A 28-year-old female presents with persistent anterior knee pain and crepitus following an MPFL reconstruction performed 1 year ago for recurrent patellar dislocations. She reports no further dislocations but finds stairs and squatting painful. Physical exam shows no apprehension, but diffuse tenderness around the patellofemoral joint. Patellar height is normal. What is the most likely cause of her symptoms?





Explanation

Persistent anterior knee pain, particularly with activities like stairs and squatting, after an MPFL reconstruction that successfully prevented recurrence, strongly suggests patellofemoral overload or over-constraining. This is a common complication if the MPFL graft is tensioned too tightly or fixed in an incorrect position, leading to increased patellofemoral contact pressures. Recurrence is ruled out by the history. Infection would typically present with different symptoms (fever, warmth, redness, systemic signs). Insufficient medialization would lead to continued instability, not just pain without apprehension. Graft rupture would lead to recurrence.

Question 11

When performing a trochleoplasty, what is the primary goal of the procedure?





Explanation

Trochleoplasty is a bony procedure specifically designed to address severe trochlear dysplasia. The primary goal is to reshape the distal femur by deepening the trochlear groove and often creating a medial facet, thus improving the bony containment and engagement of the patella, thereby reducing the risk of lateral dislocation. It does not directly affect quadriceps length, patellar tendon insertion point, lateral retinaculum tension (though it indirectly reduces lateral force), or patellar height.

Question 12

Which radiographic measurement is used to assess patellar height?





Explanation

The Insall-Salvati ratio (patellar tendon length to patellar diagonal length on a lateral X-ray) and modified Insall-Salvati ratio are standard measurements for assessing patellar height (patella alta or baja). The Q-angle measures quadriceps alignment, TT-TG measures tibial tubercle lateralization, Dejour classifies trochlear dysplasia, and bisect offset is used for patellar tilt on axial views. Therefore, Insall-Salvati ratio is the correct answer for patellar height.

Question 13

A 30-year-old competitive athlete with chronic patellofemoral pain and a history of recurrent patellar subluxation presents. MRI shows mild trochlear dysplasia, increased TT-TG (18mm), and a normal MPFL. She has failed a comprehensive rehabilitation program. Which procedure would be most appropriate?





Explanation

This patient has chronic subluxation with an increased TT-TG and failed conservative management, but a normal MPFL. While an MPFL reconstruction would usually be the first-line surgical treatment for patellar instability, the question states the MPFL is normal, implying the instability is due to a primary bony malalignment. With an increased TT-TG of 18mm and mild trochlear dysplasia, a tibial tubercle osteotomy for medialization (e.g., Elmslie-Trillat or modified Fulkerson) would address the primary mechanical driver of her subluxation. Trochleoplasty is generally reserved for more severe dysplasia. Lateral retinacular release is rarely indicated as an isolated procedure. VMO advancement is less effective for bony malalignment. Isolated MPFL reconstruction would be redundant if the MPFL is intact and functional.

Question 14

Which of the following describes the most accurate anatomical reference for the femoral attachment of the MPFL?





Explanation

The femoral attachment of the MPFL is consistently found in a sulcus located distal and posterior to the adductor tubercle and anterior to the posterior cortex of the femur, between the adductor tubercle and the medial epicondyle. This 'Schottle's Point' or 'Blumensaat's Line' position is critical for isometric reconstruction. Incorrect placement can lead to graft over-tensioning or laxity.

Question 15

A 15-year-old female presents with bilateral recurrent patellar instability. She has generalized joint hypermobility (Beighton score 7/9) and a family history of patellar dislocations. Imaging shows normal trochlear morphology, minimal patella alta, and normal TT-TG distance bilaterally. What is the most appropriate initial management?





Explanation

For patients with generalized ligamentous laxity and recurrent patellar instability, conservative management, specifically targeted physical therapy, is the cornerstone of initial treatment. Surgical intervention is often less successful in this population and should be considered only after extensive failure of conservative measures. Bony procedures are usually not indicated if bony alignment is normal. While genetic counseling may be relevant for severe generalized laxity, it's not the 'initial management' for the instability itself. Bilateral MPFL reconstruction is an aggressive surgical intervention and should not be the first step, especially with normal bony alignment. Bracing can be an adjunct but not the primary management.

Question 16

Which of the following describes a Type D trochlear dysplasia according to Dejour's classification?





Explanation

Dejour's classification of trochlear dysplasia is based on axial imaging. Type A is a shallow trochlea, Type B has a supratrochlear spur, Type C has a crossover sign (the medial facet lies lateral to the lateral facet) but no spur, and Type D (the most severe) has both a crossover sign and a supratrochlear spur, often with a 'cliff-like' appearance and clear signs of patellar subluxation. The 'cliff-like' description specifically refers to the combination of these features.

Question 17

Post-operative stiffness is a known complication following patellar stabilization surgery. Which factor is most strongly associated with an increased risk of post-operative arthrofibrosis?





Explanation

Delayed initiation of range of motion (ROM) exercises post-operatively is a significant risk factor for arthrofibrosis and stiffness following knee surgery, including patellar stabilization. Early, controlled ROM is crucial to prevent adhesions and maintain joint mobility. While aggressive rehabilitation without proper protection can cause other issues, it's delayed ROM that directly leads to stiffness. Early weight-bearing (if allowed) can be beneficial for healing. The type of anchor is less relevant than rehabilitation. Concomitant articular repair might necessitate a slower rehab but the core issue for stiffness is ROM.

Question 18

In a patient presenting with an acute patellar dislocation, what is the most important initial radiographic view to obtain?





Explanation

Following an acute patellar dislocation, after reduction, it is crucial to obtain a lateral view of the knee. This view is essential to assess for any osteochondral fragments (which can avulse from the medial patella or lateral femoral condyle), patellar height (patella alta), and gross alignment. An AP view is also standard but less informative for patellar stability-specific injuries. Axial views are important for patellar tilt/subluxation but usually obtained later. Long leg alignment views and stress views are not for acute dislocations.

Question 19

What is the primary rationale for distalizing a patellar tendon insertion during a tibial tubercle osteotomy for patellar instability?





Explanation

Tibial tubercle distalization (e.g., part of a Fulkerson osteotomy) is performed to address patella alta, which is a risk factor for instability and can also lead to increased patellofemoral contact pressures. By moving the patellar tendon insertion distally, the patella is lowered, improving its engagement in the trochlear groove and reducing stress. Correcting an increased Q-angle involves medialization, not distalization. Patella baja is the opposite and would be exacerbated by distalization. While VMO function might indirectly improve with better tracking, it's not the primary aim. Preventing lateral subluxation is a general goal of instability surgery, but distalization specifically targets patellar height.

Question 20

Which of the following statements regarding the role of lateral retinacular release in patellar instability surgery is most accurate?





Explanation

Lateral retinacular release (LRR) as an isolated procedure is rarely indicated for recurrent patellar instability, especially in the presence of MPFL insufficiency or bony malalignment. Historically, it was overused, leading to medial instability or patellofemoral pain. Its primary indication now is typically for severe lateral patellar tilt without instability or as an adjunct in cases of persistent lateral tracking after comprehensive realignment procedures, where lateral tightness is proven. It does not address trochlear dysplasia, patella alta, or directly MPFL deficiency, and performing it alone for recurrent instability can lead to iatrogenic medial instability. It is generally not performed routinely with MPFL reconstruction unless specific lateral tightness exists.

Question 21

A 17-year-old female undergoes MPFL reconstruction. Postoperatively, she develops numbness and tingling along the medial aspect of her lower leg and foot. Which nerve is most likely involved?





Explanation

The saphenous nerve is a branch of the femoral nerve that provides sensation to the medial aspect of the lower leg and foot. It runs in close proximity to the surgical field during MPFL reconstruction, particularly when harvesting hamstring autografts or during the dissection for femoral tunnel placement. Injury to the saphenous nerve or its infrapatellar branch is a known, though uncommon, complication of this procedure. The other nerves listed innervate different regions or have different primary functions.

Question 22

What is the typical age range at which trochlear dysplasia begins to clinically manifest as patellar instability?





Explanation

Patellar instability due to trochlear dysplasia most commonly manifests clinically during late childhood to adolescence (10-16 years old). This is often when activity levels increase, and the growth plates are still open, but the patellofemoral joint is undergoing significant remodeling. While the dysplasia is congenital, symptoms typically emerge during growth spurts and increased biomechanical stress on the knee.

Question 23

Which of the following is an absolute contraindication to performing a tibial tubercle osteotomy in a patient with patellar instability?





Explanation

An open proximal tibial physis is an absolute contraindication for a standard tibial tubercle osteotomy (e.g., Fulkerson or Elmslie-Trillat) due to the significant risk of growth arrest, angular deformities, or leg length discrepancies. In skeletally immature patients, if a bony procedure is absolutely necessary, techniques that spare the physis (e.g., physis-sparing MPFL reconstruction) or physeal bridging procedures with careful monitoring are considered. Patella alta, severe trochlear dysplasia, and generalized ligamentous laxity are risk factors that may necessitate a tibial tubercle osteotomy, not contraindications. A prior MPFL reconstruction does not contraindicate a subsequent tibial tubercle osteotomy if malalignment persists.

Question 24

In the setting of an acute, first-time traumatic patellar dislocation without osteochondral fragments, what is the most appropriate initial treatment regimen?





Explanation

For a first-time acute patellar dislocation without significant osteochondral injury, the standard of care is non-operative management. This includes closed reduction, often followed by a period of protected weight-bearing, use of a knee brace (often set to limit extension and encourage early flexion to engage the trochlea), and a comprehensive physiotherapy program focusing on quadriceps strengthening (especially VMO) and proprioception. Surgical intervention (MPFL reconstruction, LRR, osteotomy) is generally reserved for recurrent instability or specific concomitant injuries. Immobilization in full extension is outdated and can lead to stiffness.

Question 25

What is the primary mechanism by which the vastus medialis obliquus (VMO) muscle contributes to patellar stability?





Explanation

The VMO is the most distal and medial portion of the quadriceps femoris. Its unique fiber orientation (approximately 50-55 degrees to the femoral shaft) allows it to exert a significant medial and superior pull on the patella, particularly in the last 20-30 degrees of knee extension. This dynamic medializing force is crucial for centering the patella within the trochlear groove and preventing lateral subluxation or dislocation. It is a dynamic stabilizer, whereas the MPFL is a static stabilizer.

Question 26

A 19-year-old male presents with recurrent patellar instability. His MRI shows a TTPG distance of 25mm, severe trochlear dysplasia (Dejour Type D), and patella alta (Insall-Salvati ratio 1.5). He has failed extensive physical therapy. What is the MOST comprehensive surgical plan for this patient?





Explanation

This patient presents with severe patellar instability driven by multiple, significant bony risk factors: very high TT-TG, severe trochlear dysplasia, and patella alta. To achieve a stable outcome, all major contributors to instability should be addressed. Trochleoplasty will correct the severe trochlear dysplasia. MPFL reconstruction will restore the medial soft tissue restraint. Tibial tubercle osteotomy for medialization (to correct the TT-TG) and distalization (to correct patella alta) will address the extensor mechanism malalignment. A combined approach is necessary for such complex cases.

Question 27

What is the role of patellofemoral bracing in the conservative management of patellar instability?





Explanation

Patellofemoral braces, especially those with a J-shaped buttress or similar design, are used in conservative management to provide mechanical support, help guide the patella medially, and offer proprioceptive feedback. They are not foolproof in preventing all dislocations but can reduce the risk during activity and provide confidence. They limit motion to a controlled degree for protection, but their main role is dynamic support. They do not replace the MPFL or alter bony alignment like TT-TG.

Question 28

A patient with Ehlers-Danlos Syndrome presents with chronic, recurrent patellar dislocations. Surgical stabilization is being considered. What is a key consideration unique to this patient population?





Explanation

Patients with Ehlers-Danlos Syndrome or other connective tissue disorders often have generalized ligamentous laxity, which leads to poor tissue quality. This poor tissue quality can compromise the integrity and strength of autografts used in procedures like MPFL reconstruction, increasing the risk of graft failure and recurrent instability. They also have an increased risk of wound healing complications. While patella alta can occur, poor tissue quality and graft failure are the most critical unique surgical considerations. Isolated LRR is rarely effective, and autograft is not necessarily contraindicated but has a higher failure rate, leading some to consider allografts or specialized techniques.

Question 29

Which finding on a true lateral knee radiograph is indicative of patella alta?





Explanation

Patella alta is diagnosed radiographically by an elevated patellar position relative to the femoral trochlea. Using the Insall-Salvati ratio (patellar tendon length / patellar articular length), a ratio greater than 1.2 is generally indicative of patella alta. A crossover sign and increased sulcus angle are related to trochlear dysplasia. Decreased patellar tilt means the patella is flatter, not higher. Reduced medial patellar facet height is not a standard measure for patellar height.

Question 30

During MPFL reconstruction, the surgeon places the femoral tunnel at Schottle's point. What is the anatomical landmark that is consistently used to identify Schottle's point?





Explanation

Schottle's point, a commonly used landmark for the isometric femoral attachment of the MPFL, is identified by specific radiographic or anatomical relationships: it is distal and posterior to the adductor tubercle, anterior to the posterior femoral cortex, and proximal to the level of the posterior femoral condylar cartilage. Specifically, on a lateral radiograph, it's typically described as the intersection of a line extending proximally from the posterior femoral cortex and a line drawn perpendicular to Blumensaat's line, passing through the posterior aspect of the trochlear groove. The option describes a specific radiographic method. The most consistent anatomical reference is its position relative to the adductor tubercle, but the description given in option 3 more accurately reflects a precise radiographic identification often used.

Question 31

A 16-year-old active female undergoes MPFL reconstruction with a hamstring autograft. Which of the following is the most appropriate post-operative rehabilitation guideline for the initial 6 weeks?





Explanation

Post-MPFL reconstruction rehabilitation typically involves a period of protected weight-bearing (crutches) to protect the healing graft and fixation, along with a knee brace to control motion. Early, controlled range of motion (e.g., 0-90 degrees) is initiated to prevent stiffness while protecting the graft. Immediate full weight-bearing or aggressive strengthening is too early. Non-weight-bearing without controlled motion is also not ideal. Immobilization in 45 degrees flexion is detrimental. The goal is controlled progression to restore function without jeopardizing the repair. So, protected weight-bearing, a brace allowing controlled flexion, and gentle exercises are appropriate.

Question 32

Which of the following describes the 'crossover sign' on an axial MRI of the patellofemoral joint?





Explanation

The 'crossover sign' is a key feature of trochlear dysplasia, particularly Dejour Types C and D. It is present when the line representing the lateral facet of the trochlea appears to cross over the line representing the medial facet, meaning the deepest part of the trochlear groove is lateral to the most anterior aspect of the medial condyle. This indicates a flattened or even convex trochlear shape, leading to inadequate patellar containment.

Question 33

In a patient presenting with an acute patellar dislocation, extensive edema and ecchymosis around the knee. Which concurrent injury should be specifically ruled out due to its potential for significant morbidity?





Explanation

While meniscal tears and ACL tears can occur with patellar dislocations, a neurovascular injury is a critical and potentially devastating complication that must be ruled out immediately in an acute, swollen knee following a dislocation (especially knee dislocations, but patellar dislocations can also be associated, or cause compartment syndrome from swelling). Compromise of the popliteal artery or peroneal nerve requires urgent intervention to prevent limb-threatening consequences. Femoral shaft fracture is less common but can be obvious on X-ray. MCL laxity is often present but not limb-threatening.

Question 34

What is the primary anatomical structure that guides patellar tracking into the trochlear groove as the knee flexes?





Explanation

While the VMO and MPFL play crucial roles in dynamic and static medial patellar stability, respectively, the primary anatomical structure that guides the patella into the trochlear groove and contains it during flexion is the bony morphology of the trochlear groove itself. A well-formed, deep trochlear groove provides the primary constraint, especially beyond 20-30 degrees of flexion where the MPFL becomes relatively less important. Dysplasia of this groove is a major cause of instability.

Question 35

A 10-year-old child with an open growth plate presents with recurrent patellar dislocations. The family is concerned about the effects of surgery on growth. Which MPFL reconstruction technique is generally preferred in this population?





Explanation

For skeletally immature patients, all-epiphyseal (or physeal-sparing) techniques for MPFL reconstruction are generally preferred. These techniques aim to place tunnels or fixation points entirely within the epiphysis or metaphysis, or use techniques like soft tissue fixation on the femur and patella, to avoid violating the growth plates and prevent growth disturbance. Transphyseal tunnels are generally avoided unless carefully planned to minimize physeal damage (e.g., small diameter tunnels, specific locations, or using a drill guide perpendicular to the physis). Tibial tubercle osteotomies are usually contraindicated. The key is to avoid permanent physeal damage.

Question 36

Which of the following factors is considered to be a strong predictor of failure after MPFL reconstruction?





Explanation

MPFL reconstruction primarily addresses the soft tissue medial restraint. If significant bony malalignment (such as a severely increased TT-TG distance, or severe trochlear dysplasia like Dejour Type C or D) remains uncorrected, the biomechanical forces predisposing to instability persist, leading to a high risk of failure (re-dislocation or persistent subluxation) even after a technically adequate MPFL reconstruction. Mild patella alta or Type A dysplasia may not always require concomitant bony procedures. Chondral damage is a complication but not a direct cause of MPFL reconstruction failure in terms of recurrence. Age can influence healing but is not as strong a predictor of failure as uncorrected bony malalignment.

Question 37

In evaluating a patient for patellar instability, what information obtained from an axial CT scan is most critical for surgical planning?





Explanation

An axial CT scan is the gold standard for accurately measuring the Tibial Tubercle-Trochlear Groove (TT-TG) distance. This measurement quantifies the lateralization of the extensor mechanism relative to the trochlear groove and is a crucial parameter for determining the need for and extent of tibial tubercle medialization osteotomy. The Insall-Salvati ratio is for patellar height (lateral X-ray). Q-angle is clinical or plain X-ray. Osteochondral fragments and effusion are better assessed by MRI or plain X-rays respectively. Thus, TT-TG is the most critical information derived from an axial CT.

Question 38

Which of the following surgical procedures is specifically designed to address patella alta?





Explanation

Tibial tubercle distalization osteotomy is a bony procedure specifically aimed at lowering the patellar position. By moving the tibial tubercle (the insertion of the patellar tendon) distally on the tibia, the patella is brought down into a more appropriate height relative to the femoral trochlea, thus correcting patella alta. The other procedures address lateral tightness, medial soft tissue restraint, trochlear morphology, or VMO function, but not patellar height directly.

Question 39

A 22-year-old female presents with recurrent patellar dislocations. MRI shows an intact MPFL but a markedly increased TT-TG distance (24mm) and patellar tilt. There is no significant trochlear dysplasia or patella alta. Which procedure is most appropriate?





Explanation

Given an intact MPFL and the primary issue being a markedly increased TT-TG distance and patellar tilt, a tibial tubercle medialization osteotomy is the most appropriate procedure. This addresses the lateralization of the extensor mechanism and realigns the patella. Isolated MPFL reconstruction is not indicated if the MPFL is intact. Isolated LRR is rarely indicated for instability. Trochleoplasty is for trochlear dysplasia, which is not significant here. VMO advancement is less potent for significant bony malalignment.

Question 40

What is the typical mechanism of injury for an acute, primary lateral patellar dislocation?





Explanation

Acute, primary lateral patellar dislocations most commonly occur with a combination of knee flexion (often 20-30 degrees), valgus stress, and external rotation of the tibia on the femur (or internal rotation of the femur on the tibia). This creates a powerful lateralizing force on the patella, especially when the trochlear groove is shallowest. A direct blow to the lateral aspect of the patella is a less common but possible mechanism.

Question 41

Which of the following is considered a primary static stabilizer of the patella against lateral displacement?





Explanation

The MPFL is widely recognized as the primary static (passive) stabilizer of the patella, resisting lateral translation, especially in the initial 0-30 degrees of knee flexion. The VMO is a dynamic stabilizer. The rectus femoris and patellar tendon are components of the extensor mechanism, primarily involved in knee extension. The lateral retinaculum provides lateral soft tissue constraint.

Question 42

A patient undergoing MPFL reconstruction has a history of knee effusions. Which type of graft would be least likely to cause post-operative knee effusions and pain?





Explanation

While any graft can potentially cause post-operative effusions, harvesting autografts (semitendinosus, gracilis, quadriceps tendon) can lead to donor site morbidity, pain, and sometimes increased inflammation or effusion. Allografts avoid donor site morbidity. The adductor magnus tendon, specifically the aponeurotic extension of the adductor magnus that forms the proximal part of the native MPFL, can be used for reconstruction. This technique is 'quadriceps-sparing' and often associated with less anterior knee pain and potentially fewer effusions compared to hamstring or quad tendon autografts as it avoids injury to the extensor mechanism and a separate graft harvest site.

Question 43

Which of the following anatomical variations is LEAST likely to be a risk factor for patellar instability?





Explanation

A deep trochlear groove provides excellent bony constraint and is protective against patellar instability. A shallow or dysplastic trochlear groove is a significant risk factor. The other options (patella alta, increased Q-angle, generalized ligamentous laxity, hypoplastic medial femoral condyle) are all recognized risk factors for patellar instability.

Question 44

What is the primary concern when performing a lateral retinacular release in an individual with no signs of medial patellar instability?





Explanation

One of the most significant and well-documented complications of isolated lateral retinacular release, especially when performed in patients without severe lateral tightness or if over-released, is iatrogenic medial patellar instability. This can result in medial subluxation or even dislocation, which is often more challenging to treat than the initial lateral instability. Persistent lateral instability would suggest the release was insufficient. Patella alta is unrelated. Saphenous nerve damage is more associated with medial approaches or hamstring harvest. Arthrofibrosis can occur but isn't the primary concern unique to LRR.

Question 45

Which type of trochleoplasty procedure involves lifting and advancing a block of cartilage and subchondral bone to create a new, deeper groove?





Explanation

Deepening trochleoplasty (e.g., Bereiter, Dejour techniques) involves lifting a flap of articular cartilage and a thin layer of subchondral bone from the dysplastic trochlea, excising deeper cancellous bone, and then repositioning the cartilage-bone flap into the newly deepened groove. Recession trochleoplasty involves removing bone to make the trochlea deeper. Resection trochleoplasty removes only the spur. Therefore, deepening trochleoplasty accurately describes the technique of creating a new groove by manipulating the cartilage and subchondral bone.

Question 46

Following an acute patellar dislocation, what is the most common site of injury to the medial patellofemoral ligament (MPFL)?





Explanation

While MPFL injuries can occur at any point, femoral avulsions are the most common site of MPFL rupture in acute patellar dislocations. This typically occurs through an avulsion of a small bone fragment from the medial femoral condyle (often called a 'sleeve avulsion' or 'avulsion fracture'). Patellar avulsions are less common than femoral avulsions but can also occur. Mid-substance tears are less frequent.

Question 47

A patient presents with a 'double contour' sign on an axial patellofemoral CT scan. This finding is indicative of:





Explanation

The 'double contour' sign on an axial patellofemoral CT scan is a radiological indicator of trochlear dysplasia. It refers to the appearance where the posterior aspect of the lateral trochlear facet is more anterior than the anterior border of the medial trochlear facet, suggesting a flat or even convex trochlear groove rather than a concave one. This is a characteristic feature of more severe forms of trochlear dysplasia (e.g., Dejour Types C and D).

Question 48

Which of the following statements regarding patellofemoral contact pressures after MPFL reconstruction is most accurate?





Explanation

Excessive tensioning of the MPFL graft during reconstruction is a well-recognized cause of iatrogenic patellofemoral pain and increased patellofemoral contact pressures. This can lead to anterior knee pain, stiffness, and accelerate patellofemoral arthritis. The optimal tension is crucial, and typically, the graft is tensioned with the knee in 30 degrees of flexion to achieve stability without over-constraining. Over-tensioning does not cause patella alta; that is a matter of patellar height. While graft type can affect other outcomes, it does not directly determine contact pressures as much as graft tension and placement.

Question 49

In a patient undergoing surgery for recurrent patellar instability, the surgeon notes a significant deficiency of the vastus medialis obliquus (VMO) muscle. Which surgical adjunct could specifically target this deficiency?





Explanation

VMO advancement or plication is a surgical technique aimed at improving the medializing pull of the VMO on the patella. This involves mobilizing the VMO muscle and suturing it more distally and laterally onto the patella or its tendon, or tightening the medial capsule. It is specifically used to augment the dynamic medial patellar stabilization, especially in cases of VMO insufficiency. The other procedures address bony alignment or static restraints.

Question 50

Which imaging modality is considered the most comprehensive for evaluating the full spectrum of risk factors for patellar instability, including trochlear morphology, patellar height, TT-TG distance, and MPFL integrity?





Explanation

Magnetic Resonance Imaging (MRI) is the most comprehensive imaging modality for evaluating patellar instability. It can assess soft tissues (MPFL integrity, chondral damage, effusion, bone bruising) as well as provide information on bony morphology (trochlear dysplasia, patellar height, TT-TG distance with sequences that mimic CT measurements). While plain radiographs are initial, and CT is excellent for bony measurements like TT-TG, MRI offers the best overall picture including all relevant soft tissue and bony components simultaneously.

Question 51

What is the typical presentation of a patient with iatrogenic medial patellar instability following an inappropriate lateral retinacular release?





Explanation

Iatrogenic medial patellar instability, a known complication of excessive or unwarranted lateral retinacular release, presents as apprehension or actual subluxation/dislocation of the patella medially. Patients often describe a feeling of the patella 'falling off' to the medial side, which can be elicited with a specific medial apprehension test. Continued lateral apprehension would suggest the LRR was insufficient. Pain with deep flexion can be general patellofemoral pain, not specific to medial instability. Fixed patella baja is not related. Recurrent effusions are non-specific.

Question 52

The Dejour classification for trochlear dysplasia identifies four types (A, B, C, D). Which type is characterized by a 'crossover sign' but without a supratrochlear spur?





Explanation

According to Dejour's classification: Type A is a shallow trochlea. Type B has a supratrochlear spur (bump). Type C has a 'crossover sign' (the medial facet lies lateral to the lateral facet) but no supratrochlear spur. Type D is the most severe, combining both a crossover sign and a supratrochlear spur, often with a 'cliff-like' appearance. Therefore, Type C is the correct answer.

Question 53

A 14-year-old female presents with persistent patellofemoral pain after a first-time patellar dislocation treated non-operatively. MRI shows mild trochlear dysplasia, a normal TT-TG distance, no patella alta, and a healed MPFL. What is the most likely cause of her ongoing pain?





Explanation

Given that the MPFL has healed and there are no significant bony malalignments or instability, persistent pain in this scenario often points to unresolved patellar maltracking or residual patellofemoral overload. The mild trochlear dysplasia, even if not causing overt instability, can contribute to poor tracking and increased contact pressures. Osteochondritis dissecans would typically be visible on MRI. Infection would have different symptoms. Primary valgus deformity would be a bony malalignment risk factor, which is stated as not significant. Recurrent MPFL insufficiency is ruled out by a healed MPFL. Therefore, subtle maltracking or altered patellofemoral mechanics due to the mild dysplasia is the most likely culprit for persistent pain, even without overt instability.

Question 54

What is the surgical principle behind medializing a tibial tubercle osteotomy in the management of patellar instability?





Explanation

Tibial tubercle medialization osteotomy (e.g., Elmslie-Trillat or modified Fulkerson) aims to reduce the TT-TG distance. By moving the tibial tubercle medially, the line of pull of the quadriceps mechanism (via the patellar tendon) is shifted medially, bringing the patella into better alignment with the trochlear groove and reducing the lateralizing force. Distalization addresses patella alta. The procedure does not directly deepen the trochlear groove or release the lateral retinaculum.

Question 55

Which physical examination finding is most suggestive of patellofemoral hypermobility rather than true instability?





Explanation

A Beighton score of 7/9 indicates generalized ligamentous laxity or hypermobility. While hypermobility is a risk factor for instability, a high Beighton score itself suggests a more generalized condition and can manifest as patellofemoral hypermobility without necessarily progressing to overt instability (dislocation). A positive J-sign or apprehension test, and audible clunk, are direct signs of instability or impending instability. Hemarthrosis suggests acute traumatic dislocation. Therefore, a high Beighton score is most indicative of generalized hypermobility.

Question 56

When assessing the TT-TG distance on an axial CT scan, which anatomical plane is used for measurement?





Explanation

The Tibial Tubercle-Trochlear Groove (TT-TG) distance is measured in the transverse (axial) plane on a CT scan or MRI. This involves superimposing an axial cut through the deepest part of the trochlear groove onto an axial cut through the center of the tibial tubercle and measuring the horizontal distance between these two points. This measures the lateralization of the tibial tubercle relative to the trochlear groove.

Question 57

A patient with recurrent patellar instability, patella alta, and a normal TT-TG distance would most appropriately be treated with which surgical procedure?





Explanation

For a patient with patella alta and recurrent instability, but a normal TT-TG distance (meaning no significant lateralization of the extensor mechanism) and no mention of trochlear dysplasia, a tibial tubercle distalization osteotomy (e.g., using a Maquet or Elmslie-Trillat type osteotomy with a distal shift) is the most appropriate procedure to lower the patella and improve its engagement in the trochlear groove. Isolated lateral release is rarely sufficient. MPFL reconstruction would address the soft tissue but not the underlying patella alta. Trochleoplasty is for dysplasia. Tibial tubercle medialization is for increased TT-TG, which is normal here.

Question 58

Which type of MPFL reconstruction graft has shown promising results in terms of avoiding donor site morbidity while providing adequate strength?





Explanation

Allograft (e.g., tibialis anterior or semitendinosus allograft) for MPFL reconstruction avoids donor site morbidity associated with autograft harvest (hamstring weakness, anterior knee pain with quadriceps tendon harvest). While autografts are generally preferred for their biological integration, allografts are a viable option, especially in patients with small hamstrings, previous hamstring harvest, or for revision cases. Patellar tendon autograft is primarily for ACL reconstruction and is not typically used for MPFL. All choices except 'ipsilateral patellar tendon autograft' are valid graft sources; however, allograft is specifically chosen to avoid donor site morbidity, hence it's the most appropriate answer to the question.

Question 59

A surgeon is considering performing a trochleoplasty for a patient with severe trochlear dysplasia and recurrent patellar instability. What is a critical intraoperative maneuver to confirm the adequacy of the trochleoplasty?





Explanation

After performing a trochleoplasty, it is crucial to dynamically assess patellar tracking and stability through a full range of motion (often by flexing and extending the knee while manually attempting to sublux the patella). This allows the surgeon to confirm that the newly created trochlear groove adequately contains the patella and that there is no residual apprehension or instability. The other options are either not related to the adequacy of the trochleoplasty itself, or are separate procedures/measurements.

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Dr. Mohammed Hutaif
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