Question 1

When planning a deformity correction, an osteotomy is performed at a level different from the center of rotation of angulation (CORA), but the mechanical axis is aligned using the CORA as the hinge point. What is the expected geometric outcome according to established osteotomy rules?

Explanation

According to Paley's Osteotomy Rule 2, if the osteotomy and the hinge are at different levels but the hinge is placed directly on the CORA, the correction will result in both angulation and translation at the osteotomy site. This achieves a straight mechanical axis but with an intentional structural step-off.

Question 2

A 45-year-old active male underwent a total hip arthroplasty with a ceramic-on-ceramic bearing. Two years postoperatively, he complains of an audible squeaking sound from the hip during deep flexion. What is the most common mechanical etiology for this phenomenon?

Explanation

Squeaking in Ceramic-on-Ceramic THA is most commonly associated with edge loading caused by microseparation or component malposition. Microseparation allows the femoral head to momentarily lift out of the cup and strike the rim during the swing phase, leading to the squeaking phenomenon.

Question 3

An 11-year-old obese male presents with acute severe groin pain and inability to bear weight on his right leg after a minor fall. Radiographs reveal an unstable slipped capital femoral epiphysis (SCFE). Which of the following interventions has the highest risk of causing avascular necrosis (AVN) of the femoral head in this setting?

Explanation

Forceful or non-gentle closed reduction of an unstable SCFE is highly associated with an increased risk of AVN due to kinking or disruption of the fragile retinacular vessels. Current best practices favor either in situ fixation with incidental reduction or an open reduction (e.g., modified Dunn procedure).

Question 4

During treatment of a complex tibial deformity with a hexapod circular external fixator, the surgeon notes a residual varus and procurvatum deformity after completing the initial correction schedule. What is the most appropriate next step to correct the residual deformity?

Explanation

The primary advantage of a hexapod circular frame is the ability to easily correct residual multiplanar deformities. The surgeon should obtain new orthogonal radiographs, re-measure the parameters, and enter them into the software to generate a precise residual correction schedule.

Question 5

During a primary total knee arthroplasty in a patient with a severe, unyielding 20-degree varus deformity, what is the widely accepted standard sequence for sequential medial soft tissue release?

Explanation

The standard sequence for a medial soft tissue release in a varus TKA begins with the deep MCL. This is followed sequentially by the posteromedial capsule (and semimembranosus), the superficial MCL (periosteal sleeve release), and finally the pes anserinus if severe contracture persists.

Question 6

A 5-month-old female with developmental dysplasia of the hip (DDH) has been treated in a Pavlik harness for 4 weeks. Ultrasound demonstrates continued complete dislocation of the left hip with no signs of reduction. What is the most appropriate next step in management?

Explanation

If a hip remains completely dislocated after 3 to 4 weeks in a Pavlik harness, it must be discontinued to prevent damage to the posterior acetabulum (Pavlik harness disease). The subsequent step in a child of this age is typically a closed reduction under anesthesia followed by spica casting.

Question 7

A newborn is diagnosed with Proximal Focal Femoral Deficiency (PFFD). Radiographs demonstrate absence of the proximal femur, but an MRI confirms a cartilaginous connection between the present femoral head and the femoral shaft. According to the Aitken classification, this represents which class, and what is the typical long-term functional procedure if a severe leg-length discrepancy is expected?

Explanation

Aitken Class A PFFD is characterized by a present femoral head and a cartilaginous connection to the shaft that will eventually ossify. Due to severe leg-length discrepancies, early lengthening is often contraindicated, and definitive functional procedures like a Van Nes rotationplasty or Syme amputation with a prosthesis are commonly performed.

Question 8

A 55-year-old female with a metal-on-metal total hip arthroplasty presents with groin pain and a palpable mass 6 years postoperatively. Aspiration yields thick, dark fluid with a low nucleated cell count. MRI shows a large periarticular cystic collection. Histology of this tissue would most likely demonstrate:

Explanation

Adverse local tissue reactions (ALTR) or pseudotumors in metal-on-metal implants are driven by a type IV delayed hypersensitivity to metal ions. The histological hallmark of this reaction is an aseptic lymphocytic vasculitis-associated lesion (ALVAL).

Question 9

Which of the following radiographic findings in Legg-Calvé-Perthes disease is considered one of Catterall's 'head-at-risk' signs, indicating a potentially poorer prognosis?

Explanation

Catterall's 'head-at-risk' signs include Gage's sign (a V-shaped radiolucency in the lateral epiphysis/physis), lateral subluxation of the femoral head, calcification lateral to the epiphysis, a horizontal growth plate, and diffuse metaphyseal reactions. These suggest an increased risk for severe deformity.

Question 10

When applying an Ilizarov circular frame for tibial lengthening, which frame modification most effectively increases the axial stiffness of the construct?

Explanation

Frame stability and axial stiffness in circular fixators are increased by using smaller diameter rings, which decreases the bone-to-ring distance. Other methods to increase stiffness include increasing wire tension, using olive wires, and crossing wires at angles closer to 90 degrees.

Question 11

During a primary total knee arthroplasty, the surgeon inadvertently places the femoral component in 5 degrees of internal rotation. What is the most likely biomechanical consequence of this specific error?

Explanation

Internal rotation of the femoral component medializes the trochlear groove relative to the tibial tubercle. This effectively increases the Q-angle, causing the patella to track laterally, which can lead to lateral patellar subluxation or dislocation.

Question 12

In the Ponseti method for the treatment of idiopathic clubfoot, what is the strictly required sequence of deformity correction during serial casting?

Explanation

The Ponseti method follows the CAVE mnemonic for the order of correction: Cavus (corrected first by supinating the forefoot and elevating the first ray), Adductus, Varus, and finally Equinus (which often requires a percutaneous Achilles tenotomy).

Question 13

A 12-year-old boy presents with a proximal tibial deformity. Radiographic analysis reveals the center of rotation of angulation (CORA) is located at the level of the physis. To prevent growth arrest, the surgeon plans to perform a diaphyseal osteotomy distal to the CORA. To fully correct the mechanical axis without creating a secondary translation deformity, where should the hinge axis be placed?

Explanation

According to Paley's rules of deformity correction, if the osteotomy is performed at a level different from the CORA, the hinge axis must be placed at the CORA to fully align the mechanical axis. This results in angulation and translation at the osteotomy site.

Question 14

A 14-year-old obese male presents with acute onset of severe hip pain and inability to bear weight. Radiographs confirm an unstable slipped capital femoral epiphysis (SCFE). He undergoes urgent in situ single-screw fixation. Which of the following complications is most highly associated with this specific presentation?

Explanation

Unstable SCFE (defined by the inability to bear weight) carries a high risk of avascular necrosis (up to 50%), regardless of the treatment method, due to the disruption of the epiphyseal blood supply.

Question 15

During a primary total knee arthroplasty for a patient with a severe fixed varus deformity, the surgeon removes medial osteophytes and releases the deep medial collateral ligament, but the medial compartment remains significantly tight in extension. Which structure should typically be sequentially released next to balance the extension gap?

Explanation

In a varus TKA, the sequential medial release typically proceeds from deep MCL and osteophytes, to the posteromedial capsule, and then the superficial MCL or semimembranosus.

Question 16

A 4-year-old girl is diagnosed with developmental dysplasia of the hip (DDH). Radiographs demonstrate an acetabular index of 40 degrees with anterolateral acetabular deficiency. The surgeon decides to perform a Pemberton osteotomy. What is the primary hinge point for this specific pelvic osteotomy?

Explanation

The Pemberton osteotomy is an incomplete pericapsular osteotomy that hinges on the flexible triradiate cartilage, allowing the acetabular roof to be hinged downward, reducing acetabular volume and improving anterolateral coverage.

Question 17

A 45-year-old highly active male undergoes a total hip arthroplasty using a ceramic-on-ceramic bearing surface. At his 2-year follow-up, he complains of an audible squeaking sound during certain movements. Which of the following factors is most strongly associated with this phenomenon?

Explanation

Squeaking is a known complication of ceramic-on-ceramic THA, occurring in up to 10% of cases. It is strongly associated with component malpositioning (e.g., steep cup angle), edge loading, and impingement or microseparation.

Question 18

When utilizing a hexapod circular external fixator (e.g., Taylor Spatial Frame) for complex lower extremity deformity correction, what is its primary biomechanical and software advantage over a traditional Ilizarov frame?

Explanation

The hexapod frame uses computer software and six variable-length struts to allow simultaneous correction of angulation, translation, and rotation (six degrees of freedom) without needing to manually change hinges and construct components like a traditional Ilizarov frame.

Question 19

A 9-year-old girl presents with severe, progressive infantile Blount's disease. Radiographs reveal a Langenskiöld stage VI lesion with a complete medial physeal bar and severe depression of the medial tibial plateau. Which of the following surgical strategies is most appropriate?

Explanation

In Langenskiöld stage V and VI (advanced Blount's), there is a medial physeal bar and significant joint incongruity (medial plateau depression). Treatment requires elevation of the medial plateau to restore the joint line, along with a metaphyseal osteotomy to correct the overall mechanical axis.

Question 20

During a total knee arthroplasty for a patient with a severe fixed valgus deformity, the surgeon plans a lateral soft tissue release. To avoid iatrogenic injury, what structure must be carefully protected during the release of the posterolateral capsule and popliteus tendon?

Explanation

The common peroneal nerve is at significant risk during lateral and posterolateral releases in valgus TKA, as well as from traction injury when correcting the valgus alignment.

Question 21

An infant with a severe idiopathic clubfoot is being treated with the Ponseti method of serial casting. The physician is manipulating the foot to correct the sequence of deformities. What is the final deformity to be corrected, often requiring a percutaneous tenotomy?

Explanation

The sequence of correction in the Ponseti method is CAVE: Cavus, Adductus, Varus, and finally Equinus. Equinus is corrected last, and a percutaneous Achilles tenotomy is required in approximately 80-90% of cases to achieve dorsiflexion.

Question 22

In distraction osteogenesis for limb lengthening, a latency period is strictly observed before starting distraction. Following latency, what is the generally accepted optimal rate and rhythm of distraction to promote high-quality bone regenerate while preventing premature consolidation?

Explanation

The optimal rate of distraction for bone regeneration, originally described by Ilizarov, is 1.0 mm per day. The optimal rhythm is frequent, small increments, typically 0.25 mm four times a day.

Question 23

A 6-year-old boy is diagnosed with Legg-Calvé-Perthes disease. Which of the following radiographic classifications is most reliable for determining the long-term prognosis and likelihood of a spherical femoral head?

Explanation

The Herring lateral pillar classification evaluates the height of the lateral aspect of the capital femoral epiphysis during the fragmentation stage and is the most reliable prognostic indicator for final head shape in Perthes disease.

Question 24

A surgeon is performing a primary total hip arthroplasty using the direct anterior approach (Smith-Petersen). The superficial internervous plane lies between which two muscles?

Explanation

The superficial interval in the direct anterior approach to the hip is between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve).

Question 25

In deformity correction principles, if an osteotomy is performed at a level different from the Center of Rotation of Angulation (CORA), but the hinge is placed exactly at the CORA, what is the geometric result of the correction?

Explanation

Placing the hinge at the CORA always restores collinearity of the axes. If the osteotomy is at a different level than the CORA, correction will result in both angulation and simultaneous translation at the osteotomy site.

Question 26

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following is considered a major criterion for the diagnosis of chronic periprosthetic joint infection (PJI)?

Explanation

The 2018 ICM major criteria for PJI include having two positive periprosthetic cultures with phenotypically identical organisms, or the presence of a sinus tract communicating with the joint. The other options are considered minor criteria.

Question 27

A 2-year-old child presents with bilateral genu varum. Radiographs reveal a metaphyseal-diaphyseal angle (MDA) of 18 degrees bilaterally. Which of the following is the most appropriate management?

Explanation

An MDA greater than 16 degrees in a young child strongly predicts progression to infantile Blount's disease rather than physiologic bowing. The standard initial treatment for a child under 3 years with an MDA > 16 degrees is bracing with KAFOs.

Question 28

What is the primary advantage of the 'lengthening over a nail' (LON) technique compared to traditional Ilizarov lengthening?

Explanation

Lengthening over a nail significantly reduces the time the external fixator must remain on the patient, thereby lowering the external fixation index. The fixator can be removed once the desired length is achieved, while the locked nail maintains length during consolidation.

Question 29

During a total knee arthroplasty, trial reduction reveals that the knee is tight in full extension but appropriately balanced in 90 degrees of flexion. Which of the following is the most appropriate next step to balance the knee?

Explanation

A knee that is tight in extension but balanced in flexion indicates an isolated tight extension gap. Resecting additional distal femur increases the extension gap specifically without affecting the flexion gap.

Question 30

Which of the following findings is the most reliable determinant of 'instability' in a slipped capital femoral epiphysis (SCFE) according to the Loder classification?

Explanation

The Loder classification defines an unstable SCFE based strictly on the clinical inability of the patient to bear weight, even with assistive devices like crutches. Unstable slips carry a significantly higher risk of avascular necrosis.

Question 31

In distraction osteogenesis of the tibia, what is the primary physiological rationale for maintaining a latency period of 7 to 10 days prior to initiating distraction?

Explanation

A latency period of 7-10 days allows the initial fracture hematoma to revascularize and multipotent stem cells to populate the osteotomy gap. Distracting too early disrupts this fragile neovascular network, leading to poor regenerate formation and delayed union.

Question 32

A 72-year-old female sustains a periprosthetic femur fracture around her cementless total hip arthroplasty. Radiographs show a fracture at the tip of the stem. The stem is radiographically loose, but she has excellent proximal bone stock. According to the Vancouver classification, what is the most appropriate treatment?

Explanation

This describes a Vancouver B2 fracture (loose stem, adequate bone stock). The standard of care is revision to a longer cementless stem that bypasses the fracture site by at least two cortical diameters, often supplemented with cerclage cables.

Question 33

During the Ponseti method for correcting idiopathic clubfoot, the cavus deformity must be addressed first. Which of the following describes the correct initial manipulation?

Explanation

The cavus deformity is driven by relative pronation of the forefoot compared to the hindfoot. It is corrected by elevating (dorsiflexing) the first ray to supinate the forefoot, bringing it into proper alignment with the hindfoot before subsequent abduction maneuvers.

Question 34

When planning an opening wedge osteotomy to correct an angular deformity, placing the hinge on the convex cortex precisely at the level of the Center of Rotation of Angulation (CORA) will result in:

Explanation

Placing the hinge on the convex cortex at the CORA produces an opening wedge osteotomy. Because bone is strictly added to the concave side without removal, this geometric maneuver inherently results in a net lengthening of the limb segment.

Question 35

A patient with a ceramic-on-ceramic total hip arthroplasty complains of a new-onset audible 'squeaking' during walking. Radiographic evaluation is most likely to show which of the following component positions?

Explanation

Squeaking in ceramic-on-ceramic THA is highly associated with edge loading, microseparation, and stripe wear. Edge loading typically occurs due to component malposition, such as excessive acetabular inclination (e.g., >50 degrees) or abnormal version.

Question 36

According to the Herring Lateral Pillar Classification for Legg-Calvé-Perthes disease, a patient whose lateral pillar height is maintained at 40% of its normal height falls into which group, and what is the general prognosis?

Explanation

Herring Group C is defined by a lateral pillar height of less than 50% of the normal height. This group has a generally poor prognosis, carrying a significantly higher risk of aspherical head remodeling and early osteoarthritis.

Question 37

When utilizing a hexapod external fixator (e.g., Taylor Spatial Frame) for deformity correction, the concept of 'chronic' parameters primarily refers to:

Explanation

In hexapod circular fixation, 'chronic' (or mounting) parameters define the precise spatial relationship between the reference ring (usually the proximal ring) and its attached reference bone segment in the coronal, sagittal, and axial planes.

Question 38

According to Paley's osteotomy rules, if the osteotomy and the hinge of the correction are both located at the Center of Rotation of Angulation (CORA), what is the resultant effect on the mechanical axis?

Explanation

Paley's Rule 1 states that if the osteotomy passes through the CORA and the hinge is at the CORA, correction results in pure angulation without translation. This perfectly realigns the bone segments without inducing secondary deformities.

Question 39

A 65-year-old patient presents with end-stage knee osteoarthritis and a 25-degree extra-articular diaphyseal varus deformity of the femur. What is the most appropriate management?

Explanation

Extra-articular deformities greater than 20 degrees in the coronal plane typically require an extra-articular osteotomy to properly restore the mechanical axis. Standard intra-articular cuts for such large deformities compromise collateral ligament attachments and destabilize the knee.

Question 40

In the Ponseti method for clubfoot casting, which of the following represents the correct sequential order of deformity correction?

Explanation

The Ponseti method strictly corrects the deformities in the order of CAVE: Cavus, Adductus, Varus, and finally Equinus. The cavus is corrected first by elevating the first ray to align the forefoot with the hindfoot.

Question 41

When planning a deformity correction, if the osteotomy is performed at a level different from the CORA but the hinge remains exactly at the CORA, what is the expected outcome according to Paley's Rule 2?

Explanation

Paley's Rule 2 dictates that an osteotomy outside the CORA with the hinge at the CORA results in angulation and translation at the osteotomy site. This successfully realigns the mechanical axis without creating a secondary "zig-zag" deformity.

Question 42

A 45-year-old female with developmental dysplasia of the hip (DDH) Crowe type IV undergoes a total hip arthroplasty. To safely reduce the hip to the true acetabulum and minimize the risk of sciatic nerve palsy, which surgical maneuver is most frequently required?

Explanation

In Crowe IV DDH, the femoral head is highly dislocated. Reducing the hip to the anatomic true acetabulum stretches the sciatic nerve; a subtrochanteric shortening osteotomy is commonly required to avoid stretch injury to the nerve.

Question 43

Which patient with Legg-Calvé-Perthes disease would show the most significant radiographic benefit from a surgical containment procedure (e.g., proximal femoral or pelvic osteotomy)?

Explanation

Surgical containment provides the greatest benefit in children over 8 years of age at disease onset who have Herring lateral pillar B or B/C border involvement. Patients in group C generally have poor outcomes regardless of the intervention.

Question 44

In a medial opening wedge high tibial osteotomy (HTO) for a varus knee, how does the correction typically alter the sagittal plane alignment if the anterior and posterior gaps are opened equally?

Explanation

Opening the anterior and posterior gaps equally in a proximal tibial osteotomy increases the posterior tibial slope due to the triangular cross-section of the proximal tibia. To maintain the original slope, the anterior gap must be opened approximately half as much as the posterior gap.

Question 45

A 12-year-old obese male presents with acute-on-chronic hip pain and inability to bear weight. Radiographs show a severe slipped capital femoral epiphysis (SCFE). Intraoperatively, a capsulotomy is performed before pinning. What is the primary rationale for this capsulotomy?

Explanation

In unstable SCFE, an acute hemarthrosis significantly elevates intracapsular pressure, compromising retinacular vessel flow. A capsulotomy decompresses this hematoma, theoretically restoring blood flow and lowering the high risk of AVN.

Question 46

A 72-year-old woman with a history of a malunited midshaft femur fracture (30 degrees of apex anterior bowing) presents for a total knee arthroplasty (TKA). If standard intra-articular cuts are used, which adjustment to the distal femoral cut is required to avoid anterior notching and knee component hyperextension?

Explanation

An apex anterior bow in the femur creates a recurvatum effect on the mechanical axis. To compensate during intra-articular TKA resection and prevent anterior notching, the femoral component must be placed in relative flexion.

Question 47

You are evaluating a 2-year-old with infantile tibia vara (Blount's disease). During radiographic follow-up, which finding according to the Langenskiöld classification indicates an irreversible physeal injury that typically requires surgical intervention?

Explanation

Langenskiöld Stage IV is defined by the formation of a physeal bar (bony bridge) across the medial metaphysis and epiphysis. This arrests medial growth, requiring surgical intervention such as bar excision or osteotomy to prevent worsening deformity.

Question 48

When performing an extensive external fixation lengthening of the tibia, what is the most common adjacent joint complication that often necessitates extending the frame across the joint?

Explanation

Tibial lengthening resists the stretch of the thick posterior gastrocnemius-soleus complex, leading to an equinus contracture. Prophylactic measures include intensive physical therapy, Achilles tendon lengthening, or spanning the frame across the ankle.

Question 49

A 6-year-old child weighing 25 kg sustains a completely displaced, isolated diaphyseal femur fracture. What is the standard of care for definitive surgical fixation?

Explanation

For children aged 5-11 years with weight under 50 kg, flexible intramedullary nailing (TENs) is the preferred treatment for length-stable diaphyseal femur fractures. Rigid nailing in this age group carries an unacceptable risk of iatrogenic avascular necrosis of the femoral head.

Question 50

A patient with a significant post-traumatic valgus deformity of the proximal tibia is undergoing a primary TKA. Through a standard medial parapatellar arthrotomy, which structure is most commonly released first to balance the fixed valgus knee?

Explanation

In a fixed valgus knee, the lateral side is tight. Soft tissue balancing requires a sequential release of the tight lateral structures, most commonly starting with the iliotibial band and posterolateral capsule, followed by the popliteus and LCL if needed.

Question 51

A 10-year-old child is treated with eight-Plates (tension band constructs) for bilateral genu valgum. Eighteen months later, the deformity is fully corrected, and the hardware is removed. The parents should be counseled on which common post-removal phenomenon?

Explanation

The "rebound phenomenon" frequently occurs after the removal of tension band plates for guided growth, especially in young children with significant remaining growth potential. For this reason, mild overcorrection is sometimes recommended.

Question 52

During a femoral lengthening procedure utilizing the Lengthening Over a Nail (LON) technique, what is the primary advantage compared to lengthening with an external fixator alone?

Explanation

Lengthening over a nail (LON) allows the external fixator to be removed immediately once the desired length is achieved, with the intramedullary nail locked to maintain length during the consolidation phase. This drastically reduces the time the patient is burdened by the external frame.

Question 53

According to the principles of deformity correction, if an opening wedge osteotomy is performed with the axis of the hinge placed exactly at the Center of Rotation of Angulation (CORA), which of the following best describes the resulting correction?

Explanation

Rule 1 of osteotomy states that if the osteotomy and the hinge are both located at the CORA, angular correction occurs without translation. This perfectly aligns the proximal and distal mechanical axes.

Question 54

A 65-year-old patient with a 25-degree coronal plane extra-articular bowing deformity of the midshaft femur presents for a Total Knee Arthroplasty. Which of the following is the most appropriate management?

Explanation

For extra-articular deformities >20 degrees in the coronal plane, intra-articular compensatory bone cuts will compromise collateral ligament attachments. A staged or simultaneous extra-articular osteotomy is indicated.

Question 55

An infant with developmental dysplasia of the hip (DDH) is being treated with a Pavlik harness. During a follow-up visit, the parents report the infant is not kicking the affected leg. Examination reveals lack of knee extension. Which of the following harness adjustments is required?

Explanation

Femoral nerve palsy is a known complication of excessive hip flexion in a Pavlik harness. The appropriate management is to decrease the flexion of the anterior straps and observe for clinical recovery.

Question 56

A 4-year-old girl with severe infantile Blount's disease undergoes a proximal tibial osteotomy. During preoperative planning, you note Langenskiöld stage V changes. What additional procedure is most commonly required in this stage compared to stage II?

Explanation

Langenskiöld stage V and VI infantile Blount's disease typically involves severe depression of the medial tibial plateau and often a physeal bar. Medial tibial plateau elevation combined with a corrective osteotomy is required to restore joint congruity.

Question 57

A 13-year-old obese male presents to the ED with a 2-day history of severe left hip pain and inability to bear weight. Radiographs demonstrate a Slipped Capital Femoral Epiphysis (SCFE). Which of the following factors best defines this as an 'unstable' SCFE?

Explanation

The Loder classification defines unstable SCFE as the patient's inability to bear weight on the affected limb, even with the use of crutches. Unstable SCFEs have a significantly higher risk of avascular necrosis.

Question 58

During a total hip arthroplasty for a patient with Crowe IV developmental dysplasia of the hip, a subtrochanteric shortening osteotomy is planned. Which nerve is at the highest risk of injury during the reduction of the hip into the true acetabulum?

Explanation

The sciatic nerve is highly susceptible to stretch injury when lengthening the limb during THA for severe hip dysplasia. A subtrochanteric shortening osteotomy is often performed to mitigate this risk and allow reduction without excessive tension.

Question 59

A 55-year-old female with a metal-on-metal total hip arthroplasty presents with groin pain and a pseudotumor. Histological examination of the periprosthetic tissue is most likely to reveal which of the following?

Explanation

Adverse local tissue reactions (ALTR) in metal-on-metal implants are histologically characterized by Aseptic Lymphocytic Vasculitis-Associated Lesions (ALVAL). This represents a type IV delayed hypersensitivity reaction.

Question 60

A 7-year-old child presents with a 'gunstock' deformity of the right elbow following a supracondylar humerus fracture treated conservatively 2 years ago. The deformity is primarily caused by malunion in which plane?

Explanation

Cubitus varus (gunstock deformity) is a 3-dimensional malunion primarily caused by a failure to correct coronal tilt (varus) and horizontal rotation (internal rotation) of the distal fragment.

Question 61

When applying the Ponseti method for the treatment of idiopathic clubfoot, what is the correct sequence of deformity correction?

Explanation

The Ponseti method systematically corrects deformities in the CAVE sequence: Cavus (by elevating the first ray), Adductus, Varus, and finally Equinus (often requiring a percutaneous Achilles tenotomy).

Question 62

During a Total Knee Arthroplasty in a patient with a severe fixed varus deformity, what is the standard sequential soft tissue release performed on the medial side?

Explanation

The classic sequential medial release for a fixed varus knee begins with osteophyte excision, followed by the deep MCL, posteromedial capsule, semimembranosus insertion, and finally the superficial MCL if further correction is needed.

Question 63

A 15-year-old male is undergoing femoral lengthening with a unilateral external fixator. If the bone is lengthened along the anatomical axis of the femur rather than the mechanical axis, what secondary deformity will be induced?

Explanation

Because the anatomical axis of the femur is normally in 5-7 degrees of valgus relative to the mechanical axis, lengthening strictly along the anatomical axis lateralizes the distal mechanical axis, creating a valgus deformity (lateral MAD).

Question 64

According to Rule 2 of deformity correction, if an osteotomy is performed at a level different from the CORA, but the axis of the hinge is placed exactly at the CORA, what is the geometric result?

Explanation

Rule 2 states that when the hinge is at the CORA but the osteotomy is at a different level, the angulation is corrected and the mechanical axes become collinear. However, this relies on an intentional and necessary translation at the osteotomy site.

Question 65

A 70-year-old patient presents with a painful total knee arthroplasty 3 years postoperatively. Joint aspiration yields synovial fluid with a WBC count of 4,500 cells/uL and 85% PMNs. According to the MSIS criteria, how should this be interpreted?

Explanation

According to the Musculoskeletal Infection Society (MSIS) criteria for late PJI (>90 days post-op), a synovial fluid WBC count > 3,000 cells/uL or > 80% PMNs is considered a major diagnostic indicator for infection.

Question 66

When placing the acetabular component during a Total Hip Arthroplasty, what is the Lewinnek 'safe zone' to minimize the risk of dislocation?

Explanation

The Lewinnek safe zone for acetabular cup placement is defined as 40° ± 10° of inclination (abduction) and 15° ± 10° of anteversion. Placement outside this zone is associated with a significantly higher risk of impingement and dislocation.

Question 67

According to Paley's rules of deformity correction, if an osteotomy and the hinge (axis of rotation) are both placed at a level outside the center of rotation of angulation (CORA), what is the resulting geometric effect on the bone?

Explanation

Osteotomy Rule 3 states that if both the osteotomy and the hinge are outside the CORA, the mechanical axes will become parallel but translated (non-collinear). Rule 1 yields pure angulation, and Rule 2 yields angulation with collinear translated axes.

Question 68

A 64-year-old man presents with a painful swelling in his right groin 5 years after a primary total hip arthroplasty using a titanium stem, cobalt-chromium modular head, and highly cross-linked polyethylene liner. Aspiration yields sterile, cloudy, yellowish fluid. Blood tests reveal elevated serum cobalt levels with normal chromium levels. Which of the following is the most likely source of the problem?

Explanation

Elevated serum cobalt out of proportion to chromium in a metal-on-polyethylene THA is highly indicative of mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck junction. This can cause adverse local tissue reactions (ALTR) presenting as groin masses.

Question 69

In a 5-year-old child with spastic quadriplegic cerebral palsy, routine radiographic surveillance shows a Reimers migration percentage of 45% in the left hip. The child is symptomatic with limited hip abduction. Which of the following interventions is most appropriate?

Explanation

A Reimers migration index greater than 40% in a child with cerebral palsy indicates progressive hip subluxation that typically requires bony reconstruction. Soft tissue release combined with a varus derotational osteotomy (VDRO) and possible pelvic osteotomy is the standard of care.

Question 70

During a primary total knee arthroplasty, the surgeon evaluates the gaps and finds the knee is well-balanced and stable in extension, but exceptionally tight in 90 degrees of flexion. Which of the following maneuvers is the most appropriate next step to balance the knee?

Explanation

A knee that is tight in flexion but balanced in extension requires increasing the flexion gap without altering the extension gap. Downsizing the femoral component (utilizing anterior referencing) effectively increases the flexion gap without affecting the extension gap.

Question 71

A 6-week-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During follow-up, the mother notes the infant has stopped kicking her right leg, and clinical examination reveals decreased active knee extension on that side. Which of the following harness adjustments should have been avoided to prevent this complication?

Explanation

Excessive hip flexion in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to a femoral nerve palsy characterized by decreased active knee extension. Excessive hip abduction risks avascular necrosis (AVN) of the femoral head.

Question 72

A 3-year-old overweight boy presents with progressive bilateral genu varum. Standing radiographs demonstrate an abrupt varus angulation at the proximal medial tibial metaphysis with a metaphyseal-diaphyseal angle (MDA) of 18 degrees. What is the most appropriate management?

Explanation

This child has infantile Blount disease, as indicated by age, risk factors, and an MDA greater than 16 degrees. For children under 3-4 years of age with early-stage infantile Blount disease (Langenskiold Stage I or II), bracing with KAFOs is the first-line treatment.

Question 73

A patient develops patellar subluxation postoperatively following a total knee arthroplasty. On CT scan evaluation, which of the following component malpositions is most likely responsible for lateral patellar maltracking?

Explanation

Internal rotation of either the femoral or tibial components effectively lateralizes the tibial tubercle relative to the trochlear groove, increasing the Q-angle. This exacerbates lateral patellar maltracking and subluxation.

Question 74

A 10-year-old girl is diagnosed with a unilateral slipped capital femoral epiphysis (SCFE). Which of the following patient profiles represents the strongest indication for prophylactic in situ pinning of the contralateral, asymptomatic hip?

Explanation

Prophylactic pinning of the contralateral hip is strongly recommended in patients with endocrine disorders (e.g., hypothyroidism, renal osteodystrophy) or prior pelvic radiation. These patients have a significantly higher risk of developing bilateral SCFE.

Question 75

According to the principles of deformity correction, if the center of rotation of angulation (CORA) is identified, but both the osteotomy and the hinge are placed at a level proximal to the CORA, what is the expected geometric outcome upon alignment of the mechanical axes?

Explanation

According to Paley's Osteotomy Rule 3, if the hinge and osteotomy are both located at a level different from the CORA, correction of the angulation will result in translation of the bony fragments. Rule 1 yields pure angulation, while Rule 2 yields colinear axes with translation.

Question 76

During a posterior-stabilized total knee arthroplasty, the surgeon notes that the joint is symmetrically balanced in extension but excessively tight in flexion. Which of the following is the most appropriate next step to balance the knee?

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap without altering the extension gap. Downsizing the femoral component (using anterior referencing) decreases the posterior condylar offset, thereby opening the flexion gap.

Question 77

A 7-year-old boy presents with an insidious onset of a painless limp. Radiographs demonstrate fragmentation of the capital femoral epiphysis with exactly 50% maintenance of the lateral pillar height. According to the Herring lateral pillar classification, what is the most appropriate management?

Explanation

The patient has Herring Lateral Pillar Group borderline B/C (exactly 50%). In children over 8 years, or those 6-8 years old with lateral pillar B or B/C, surgical containment (such as a proximal femoral varus osteotomy) yields significantly better radiographic outcomes than nonoperative management.

Question 78

When constructing a circular external fixator (Ilizarov) for tibial lengthening, which of the following modifications most significantly increases the axial stiffness of the construct?

Explanation

Axial stiffness in a circular frame is most significantly increased by decreasing the ring diameter (keeping the bone as central as possible), increasing wire diameter, and increasing wire tension. Wires crossed at 90 degrees provide greater stability than those intersecting at acute angles.

Question 79

A 62-year-old female with a metal-on-polyethylene total hip arthroplasty presents with new-onset groin pain 5 years postoperatively. Radiographs show well-fixed components. Laboratory workup reveals an elevated serum cobalt-to-chromium ratio of 5:1. What is the most likely source of the elevated metal ions?

Explanation

An elevated cobalt-to-chromium ratio (often >2:1 or 3:1) in a metal-on-polyethylene THA strongly suggests mechanically assisted crevice corrosion (MACC) at the modular head-neck junction, known as trunnionosis. Bearing wear in MoP would not cause selective cobalt elevation.

Question 80

During the Ponseti casting treatment for a rigid idiopathic clubfoot in a 4-week-old infant, the midfoot has been fully abducted. The heel varus has resolved, and the forefoot is abducted to 70 degrees. However, ankle dorsiflexion remains at -10 degrees. What is the correct next step in management?

Explanation

In the Ponseti method (CAVE: Cavus, Adductus, Varus, Equinus), heel varus corrects simultaneously with forefoot abduction. Once forefoot abduction reaches 60-70 degrees, equinus is the final deformity addressed, typically requiring a percutaneous Achilles tenotomy.

Question 81

A patient requires correction of a valgus deformity of the proximal tibia.

To accurately plan the correction, the surgeon must map the normal mechanical axis. Where does the mechanical axis line (MAD) typically fall in relation to the center of the knee joint in a normal patient?

Explanation

In a normal lower extremity, the mechanical axis line passes approximately 8 mm (range 3-17 mm) medial to the center of the knee joint. This corresponds to the typical slight mechanical varus alignment of the native knee.

Question 82

Which of the following pediatric patients presenting with a unilateral slipped capital femoral epiphysis (SCFE) has the strongest indication for prophylactic in situ pinning of the contralateral hip?

Explanation

Prophylactic pinning of the contralateral hip is strongly indicated in patients with endocrine disorders (e.g., hypothyroidism, renal osteodystrophy) due to an exceedingly high risk of bilateral involvement. It is also highly recommended in children presenting at a young age (<10 years).

Question 83

A 55-year-old male with a metal-on-metal total hip arthroplasty presents with a palpable groin mass and neuropathic pain radiating down the anterior thigh. MARS-MRI demonstrates a large cystic mass. Intraoperatively, the mass shows extensive tissue necrosis and an aseptic lymphocytic infiltrate. This reaction is best classified as:

Explanation

Adverse local tissue reactions (ALTR) or pseudotumors in metal-on-metal hips are characterized histologically by an aseptic lymphocytic vasculitis-associated lesion (ALVAL). This represents a delayed Type IV (cell-mediated) hypersensitivity reaction to metal ions.

Question 84

When utilizing a hexapod circular frame (e.g., Taylor Spatial Frame) for simultaneous six-axis deformity correction, what does the concept of the "virtual hinge" represent?

Explanation

In hexapod frame systems, physical hinges are absent. Instead, the software utilizes a "virtual hinge"—a mathematical point in space (usually set at the CORA)—around which all translation and angulation corrections are calculated and executed via strut adjustments.

Question 85

A 2-year-old girl presents with bilateral bowing of the lower extremities.

Radiographs show medial beaking of the proximal tibial metaphysis. Which radiographic measurement is most reliable in differentiating infantile Blount's disease from physiologic genu varum?

Explanation

Drennan's metaphyseal-diaphyseal angle (MDA) is critical in distinguishing infantile Blount's disease from physiologic bowing. An MDA greater than 16 degrees is highly predictive of Blount's disease and disease progression.

Question 86

A surgeon is performing a primary total hip arthroplasty utilizing the direct anterior approach. Which two nerves supply the muscles defining the superficial internervous plane of this approach?

Explanation

The direct anterior approach (Smith-Petersen) utilizes a superficial internervous plane between the tensor fasciae latae (supplied by the superior gluteal nerve) and the sartorius (supplied by the femoral nerve). The deep plane is between the rectus femoris and gluteus medius.

Question 87

A 15-year-old male presents with a predicted leg length discrepancy of 6.5 cm at skeletal maturity secondary to a physeal arrest of the distal femur. What is the most appropriate definitive management to equalize leg lengths?

Explanation

For predicted leg length discrepancies greater than 5 cm, surgical lengthening of the affected limb is the standard of care. Contralateral epiphysiodesis or shortening is generally reserved for discrepancies of 2-5 cm to avoid unacceptable loss of overall adult height.

Question 88

A 6-week-old female infant born in breech presentation undergoes a screening ultrasound for developmental dysplasia of the hip (DDH). The alpha angle is reported as 45 degrees. According to Graf's classification, what is the most appropriate management?

Explanation

An alpha angle less than 60 degrees indicates a shallow acetabulum consistent with dysplasia (Graf Type IIc or III depending on the beta angle). The first-line treatment for an infant under 6 months with a dysplastic or subluxated hip is a Pavlik harness.

Question 89

In lower extremity deformity correction, an osteotomy is planned to correct a significant angular deformity. According to established osteotomy rules, if both the osteotomy cut and the hinge axis are placed away from the Center of Rotation of Angulation (CORA), what is the resultant geometric effect on the bone segments after angular correction?

Explanation

According to Paley's osteotomy rule 3, if both the osteotomy and the hinge are placed away from the CORA, the angular correction will inevitably result in translation of the bone segments. This principle is utilized when simultaneous translation is desired or unavoidable due to soft tissue constraints.

Question 90

An 8-year-old boy is diagnosed with Legg-Calvé-Perthes disease. According to the Herring Lateral Pillar classification, which of the following radiographic findings places him in Group C and predicts the poorest long-term prognosis?

Explanation

The Herring Lateral Pillar classification predicts outcome based on the height of the lateral portion of the epiphysis on the AP radiograph. Group C is defined by >50% collapse (less than 50% maintained height) of the lateral pillar, which indicates a poor prognosis, particularly in children older than 8 years.

Question 91

A 62-year-old female presents with groin pain and a palpable anterior mass 6 years after a metal-on-polyethylene total hip arthroplasty utilizing a large-diameter cobalt-chromium femoral head on a titanium stem. Blood tests reveal elevated serum cobalt levels with normal chromium levels. What is the most likely etiology of her symptoms?

Explanation

Trunnionosis (mechanically assisted crevice corrosion) occurs at the modular head-neck junction. It is characterized by elevated serum cobalt disproportionate to chromium and adverse local tissue reactions (ALTR) in metal-on-polyethylene implants, particularly those utilizing large-diameter heads.

Question 92

A 6-week-old infant with developmental dysplasia of the hip is being treated with a Pavlik harness. During a follow-up visit, the parents report the child has stopped actively extending the knee on the treated side. What is the most appropriate next step in management?

Explanation

Active inability to extend the knee while in a Pavlik harness strongly suggests a femoral nerve palsy secondary to hyperflexion of the hip. The appropriate management is to temporarily discontinue the harness or loosen the anterior straps to relieve tension on the femoral nerve.

Question 93

A 4-year-old girl presents with progressive genu varum. Radiographs demonstrate a sharp varus angulation at the proximal tibial metaphysis with a metaphyseal-diaphyseal angle of 18 degrees and profound medial physeal depression. She is diagnosed with infantile Blount's disease (Langenskiold stage III). What is the most appropriate management?

Explanation

By age 4, children with stage III or higher infantile Blount's disease have a very low rate of spontaneous resolution or bracing success. A proximal tibial valgus-producing osteotomy with a fibular osteotomy is indicated to correct the deformity, unload the medial physis, and prevent further physeal damage.

Question 94

During a cruciate-retaining total knee arthroplasty, the surgeon finds that the knee is well balanced and symmetric in full extension, but tight symmetrically in 90 degrees of flexion. Which of the following is the most appropriate intervention to balance the knee?

Explanation

A knee that is symmetric in extension but tight symmetrically in flexion in a cruciate-retaining implant often has a tight PCL. Releasing the PCL, increasing the posterior tibial slope, or downsizing the femoral component will increase the flexion gap without affecting the extension gap.

Question 95

A 13-year-old boy with a BMI of 38 presents with a stable slipped capital femoral epiphysis (SCFE) of the left hip. Routine preoperative blood work reveals untreated hypothyroidism. After in situ pinning of the left hip, what is the most appropriate recommendation regarding the right hip?

Explanation

Patients with SCFE and underlying endocrinopathies (such as hypothyroidism) or renal failure are at an exceptionally high risk for bilateral involvement. Prophylactic pinning of the contralateral hip is strongly recommended in these high-risk populations to prevent future displacement.

Question 96

A 24-year-old male is undergoing femoral lengthening over a nail (LON) using a monoplanar external fixator. During the consolidation phase after achieving 4 cm of length, the fixator is removed prematurely before the intramedullary nail is proximally locked. What is the most likely complication?

Explanation

In lengthening over a nail (LON), the external fixator controls length and rotation during the distraction phase. If the fixator is removed before the nail is properly locked with interlocking screws across the regenerate segment, the limb will acutely collapse axially.

Question 97

A 72-year-old female sustains a fall 5 years after an uncemented total hip arthroplasty. Radiographs show a spiral periprosthetic femur fracture occurring around the stem. The stem is visibly subsided by 1 cm compared to previous films, but there is excellent bone stock proximally and distally. What is the appropriate Vancouver classification and standard treatment?

Explanation

A fracture around the stem with a loose implant but adequate bone stock is classified as a Vancouver B2 fracture. The standard of care is revision of the femoral component to a longer diaphyseal-engaging stem (typically fluted and tapered) to bypass the fracture and provide stability.

Question 98

A 14-year-old boy is undergoing complex multiplanar tibial deformity correction using a hexapod circular external fixator. Midway through the strut adjustment schedule, orthogonal radiographs demonstrate that angular correction is proceeding appropriately, but a new unintended 5 mm medial translation has developed at the osteotomy site. What is the most appropriate management?

Explanation

Hexapod frames rely on precise software modeling. If an unintended deformity such as translation occurs during treatment, the standard protocol is to obtain new radiographs, update the mounting parameters, and generate a new 'residual' prescription to correct the ongoing deformity.

Question 99

A 68-year-old male presents with inability to perform a straight leg raise 3 months following a primary total knee arthroplasty. Ultrasound confirms a complete avulsion of the patellar tendon from the tibial tubercle. Given the chronic nature of the tear and poor native tissue quality, reconstructive surgery is planned. Which of the following techniques provides the most reliable long-term functional outcome?

Explanation

Chronic patellar tendon disruptions post-TKA have notoriously high failure rates with direct repair. Extensor mechanism allograft reconstruction (or synthetic mesh reconstruction) provides the most reliable robust fixation and long-term functional restoration when native tissue is compromised.

Question 100

A 5-year-old girl is evaluated for a congenital femoral deficiency. Her current absolute femoral length discrepancy is 3 cm. Using the Paley multiplier method to estimate her discrepancy at skeletal maturity, which specific patient demographic factor is strictly required to select the correct multiplier coefficient?

Explanation

The Paley multiplier method predicts limb length discrepancy at maturity using a specific multiplier coefficient. This coefficient is strictly determined by the patient's current chronological age and gender, assuming the discrepancy increases proportionally with normal growth.

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

Master ABOS Board Review: Deformity Correction, Arthroplasty & Pediatric Orthopedics | Part 12

Key Takeaway

Master ABOS Board Review: Deformity Correction, Arthroplasty & Pediatric Orthopedics | Part 12

Chapter Index