Question 1

A 13-year-old boy presents with severe groin pain and inability to bear weight. Radiographs demonstrate a severe slipped capital femoral epiphysis (SCFE) with a slip angle of 60 degrees. The surgeon performs an open surgical dislocation and a subcapital realignment (modified Dunn procedure). What is the primary blood supply at critical risk during the subcapital osteotomy, requiring the careful creation of a retinacular flap?

Explanation

The deep branch of the medial femoral circumflex artery (MFCA) provides the primary blood supply to the femoral head. It is at significant risk during a Dunn osteotomy and must be meticulously protected by developing a retinacular flap.

Question 2

When correcting a lower extremity angular deformity, if the osteotomy is performed at a level different from the center of rotation of angulation (CORA) but the hinges of the fixator are placed exactly at the CORA, what secondary effect will occur during correction?

Explanation

According to Paley's rules of osteotomy, if the osteotomy is outside the CORA but the hinge is at the CORA, the bone will undergo simultaneous angulation and translation to properly realign the mechanical axis.

Question 3

A 7-year-old boy with Legg-Calvé-Perthes disease demonstrates a 'hinge abduction' on dynamic arthrography, causing significant mechanical restriction and pain. Which of the following is the most appropriate surgical management?

Explanation

Hinge abduction occurs when the extruded, deformed lateral femoral head impinges against the lateral acetabular margin. A valgus extension osteotomy repositions the deformed segment away from the margin, relieving the hinge effect and improving joint congruency.

Question 4

During tibial lengthening over a nail (LON) using a circular fixator, a patient develops a progressive equinus contracture despite daily physical therapy. Which of the following is the most appropriate initial management?

Explanation

The initial management for an equinus contracture during distraction osteogenesis is to decrease or halt the rate of distraction while increasing aggressive stretching and splinting. Operative intervention is reserved for refractory cases.

Question 5

Which of the following pelvic osteotomies used for developmental dysplasia of the hip (DDH) is an incomplete, volume-reducing osteotomy that hinges on the triradiate cartilage?

Explanation

The Pemberton osteotomy is an incomplete pericapsular osteotomy that hinges on the flexible triradiate cartilage. It changes the volume and shape of the acetabulum, making it ideal for a dysplastic, capacious acetabulum.

Question 6

A 3-year-old girl is diagnosed with infantile Blount disease (Langenskiöld stage III). Conservative management with knee-ankle-foot orthoses (KAFOs) has failed, and the deformity is progressive. What is the most appropriate surgical intervention?

Explanation

For infantile Blount disease failing bracing by age 3 or presenting at stage III or higher, a proximal tibial valgus-derotation osteotomy is indicated to correct both the varus and the internal tibial torsion before irreversible physeal damage occurs.

Question 7

A 28-year-old male athlete presents with anterior groin pain worsened by deep hip flexion. Radiographs reveal a crossover sign, a prominent ischial spine sign, and a positive posterior wall sign. Which type of femoroacetabular impingement (FAI) is most strongly suggested by these findings?

Explanation

The crossover sign, prominent ischial spine sign, and posterior wall sign are classic radiographic markers for acetabular retroversion, which causes a focal anterior overcoverage leading to pincer-type FAI.

Question 8

When utilizing a hexapod circular fixator (e.g., Taylor Spatial Frame) to correct a complex multi-planar tibial deformity, what parameter is essential for the software to establish the 'origin' from which all corrections are calculated?

Explanation

The reference fragment (usually the proximal or distal ring) must be clearly defined in the software. It dictates the spatial origin, and the software calculates the movement of the non-reference fragment relative to it.

Question 9

A 12-year-old boy undergoes in situ pinning with a single screw for a stable slipped capital femoral epiphysis (SCFE). Two years later, he presents with limited hip internal rotation and a positive impingement test. The screw is radiographically extra-articular. What is the most likely cause of his symptoms?

Explanation

In situ pinning leaves the residual slippage uncorrected. The resulting anterior metaphyseal prominence frequently abuts the acetabular rim during flexion and internal rotation, causing secondary cam-type femoroacetabular impingement.

Question 10

According to Ilizarov's principles of distraction osteogenesis, what is the optimal rate of distraction to balance robust bone regeneration with soft tissue accommodation in a healthy adult tibia?

Explanation

The Ilizarov principle dictates an optimal distraction rate of 1.0 mm per day, classically divided into four equal increments of 0.25 mm, to optimize osteogenesis while preventing premature consolidation or soft tissue injury.

Question 11

A 22-year-old female undergoes a Bernese periacetabular osteotomy (PAO) for symptomatic hip dysplasia. Postoperatively, she demonstrates weakness in ankle dorsiflexion and great toe extension. Which nerve was most likely injured during the procedure?

Explanation

The sciatic nerve is at significant risk during the posterior column osteotomy of the PAO. Misdirection of the osteotome exiting too far posteriorly can injure the sciatic nerve, typically manifesting as a peroneal division deficit (foot drop).

Question 12

A 45-year-old man with an Ilizarov frame for a tibial non-union presents with localized pain, erythema, and soft tissue tenting at a tensioned wire site. There is no purulent drainage. What is the most appropriate initial step in management?

Explanation

Tenting of the skin by a wire causes focal ischemia, pain, and erythema, mimicking infection. Relieving the skin tension by extending the incision locally with a scalpel is the most appropriate initial step and resolves most cases.

Question 13

A 35-year-old man on chronic corticosteroids presents with bilateral hip pain. MRI shows Ficat stage II avascular necrosis (AVN) of both femoral heads involving 20% of the weight-bearing surface, with no evidence of subchondral collapse. What is the most appropriate surgical management?

Explanation

Core decompression is indicated for early-stage AVN (Ficat Stage I or II) before subchondral collapse occurs, particularly when the necrotic lesion is small to moderate in size. It aims to reduce intraosseous pressure and promote revascularization.

Question 14

A 9-year-old boy presents with idiopathic bilateral genu valgum. Standing radiographs show the mechanical axis falls in the lateral zone 3 of the knee. Tension-band plating (guided growth) is planned. Where should the plates be placed to correct the deformity?

Explanation

Genu valgum is corrected by tethering the medial physis of the distal femur and/or proximal tibia. This restricts medial growth while allowing the lateral side to continue growing, effectively correcting the valgus alignment.

Question 15

A 5-year-old child presents with a severe limp. Radiographs reveal complete resorption of the right femoral head and neck with a high-riding trochanter (Choi type IV) as a sequela of neonatal MRSA septic arthritis. Which salvage procedure provides the most stable fulcrum for ambulation and equalizes leg length?

Explanation

A pelvic support osteotomy utilizes a proximal femoral valgus-extension osteotomy to abut the pelvis (creating a fulcrum) combined with distal femoral lengthening. It is a highly effective salvage for unsalvageable post-infectious hip defects in children.

Question 16

In evaluating a normal lower extremity via long standing radiographs, the mechanical axis deviation (MAD) is typically located in which position relative to the center of the knee joint?

Explanation

The normal mechanical axis of the lower extremity passes slightly medial to the exact center of the knee joint. This is typically measured as a mechanical axis deviation (MAD) of roughly 0 to 8 mm medially.

Question 17

A 30-year-old woman with developmental hip dysplasia complains of lateral hip pain. Radiographs reveal a lateral center edge angle (LCEA) of 15 degrees. Which of the following findings would make her a POOR candidate for a Bernese periacetabular osteotomy (PAO)?

Explanation

Advanced osteoarthritis (Tönnis grade 2 or 3) is a strict contraindication for a joint-preserving PAO due to unacceptably high rates of early failure and rapid conversion to total hip arthroplasty.

Question 18

A 1-year-old is diagnosed with Aitken Class A proximal focal femoral deficiency (PFFD). The femoral head is present in the acetabulum, but a severe subtrochanteric varus pseudarthrosis is identified. What is the most important early surgical intervention to optimize the extremity for future lengthening?

Explanation

In Aitken Class A PFFD, addressing the proximal varus deformity and healing the pseudarthrosis with a valgus osteotomy is critical early in life. This establishes a biomechanically sound proximal femur capable of withstanding future lengthening.

Question 19

During an open reduction and subcapital realignment (modified Dunn procedure) for a severe slipped capital femoral epiphysis (SCFE), how is the surgical approach optimized to protect the medial femoral circumflex artery (MFCA)?

Explanation

The modified Dunn procedure utilizes a surgical hip dislocation via a trochanteric flip osteotomy. This extensile approach allows direct visualization and protection of the retinacular vessels, which are meticulously peeled back to preserve the MFCA.

Question 20

When applying a circular external fixator to the proximal tibia, placing transverse wires carries a risk of neurovascular injury. To safely avoid the common peroneal nerve laterally, a lateral-to-medial wire should be optimally inserted in which manner?

Explanation

The common peroneal nerve winds around the fibular neck. A wire can be safely passed directly through the center of the fibular head because the nerve lies posterior and distal to this specific structure, keeping it safely out of the wire's path.

Question 21

When performing a corrective osteotomy for a uniplanar tibial deformity, what is the geometric consequence of placing the osteotomy and the hinge at a level distant from the Center of Rotation of Angulation (CORA)?

Explanation

When the osteotomy and hinge are placed away from the CORA, correcting the angulation will induce an unintended translation of the bone fragments. To achieve pure angular correction without translation, the hinge must be placed on the bisector line of the CORA.

Question 22

A 4-year-old child presents with a waddling gait and a painless limp. Radiographs reveal a decreased neck-shaft angle and a vertically oriented proximal femoral physis. Measurement of the Hilgenreiner epiphyseal angle (HEA) is 65 degrees. What is the most appropriate management?

Explanation

Developmental coxa vara with a Hilgenreiner epiphyseal angle greater than 60 degrees has a high risk of progression and pseudarthrosis. Proximal femoral valgus osteotomy is the standard treatment to alter the shear forces across the physis.

Question 23

A 4-year-old girl with residual acetabular dysplasia requires a pelvic osteotomy. The surgeon plans a redirectional osteotomy that hinges at the pubic symphysis. Which of the following osteotomies is described?

Explanation

The Salter innominate osteotomy is a complete, redirectional osteotomy that cuts through the ilium to the sciatic notch and hinges at the pubic symphysis. The Pemberton and Dega are incomplete shaping osteotomies that hinge at the triradiate cartilage.

Question 24

A 13-year-old obese boy presents with severe right hip pain and inability to bear weight after a minor fall 2 days ago. Radiographs confirm a slipped capital femoral epiphysis. According to the Loder classification, what is his primary risk for the most devastating complication of this specific type of slip?

Explanation

This is an unstable SCFE (defined by the inability to bear weight), which carries a high risk (up to 47%) of avascular necrosis (AVN). Stable slips have a much lower AVN risk but may lead to FAI or chondrolysis.

Question 25

During preoperative planning for a distal femoral varus deformity, the mechanical lateral distal femoral angle (mLDFA) and the mechanical proximal tibial angle (mPTA) are measured. What are the normal population averages for these respective angles?

Explanation

The normal mechanical lateral distal femoral angle (mLDFA) is approximately 88 degrees, and the normal mechanical proximal tibial angle (mPTA) is 87 degrees. These standard parameters are crucial for defining and analyzing lower extremity deformities.

Question 26

A patient with a multiplanar tibial deformity is treated with a hexapod external fixator. Following the initial correction schedule, a residual 5-degree varus deformity is noted. To generate a residual correction program, which of the following frame parameters MUST be updated in the software?

Explanation

When generating a residual program for a hexapod fixator, the mounting parameters must be updated based on new orthogonal radiographs. These parameters define the spatial relationship of the reference ring to the reference bone fragment, which changes as the deformity corrects.

Question 27

A 3-year-old girl weighing above the 95th percentile presents with bilateral genu varum. Standing radiographs demonstrate a metaphyseal-diaphyseal angle (Drennan's angle) of 18 degrees and medial metaphyseal beaking. What is the most appropriate initial treatment?

Explanation

The patient has infantile Blount's disease, suggested by age, weight, and a metaphyseal-diaphyseal angle > 16 degrees. For children under 3 to 4 years of age with Langenskiold stage I or II, daytime use of KAFOs is the standard initial non-operative treatment.

Question 28

An 8-year-old boy is diagnosed with Legg-Calve-Perthes disease. Radiographs show that 40% of the lateral pillar height is maintained. According to the Herring lateral pillar classification, what is his classification and associated prognosis?

Explanation

Herring Group C is defined by less than 50% maintenance of lateral pillar height. It carries a poor prognosis, and studies show little to no benefit from surgical containment in this group, particularly in older children.

Question 29

A 45-year-old man with a history of high-dose corticosteroid use presents with groin pain. Hip radiographs show a crescent sign without flattening of the femoral head. What is the Ficat and Arlet stage of his disease?

Explanation

A crescent sign indicates subchondral collapse without overt flattening of the femoral head, corresponding to Ficat Stage III. Core decompression is generally ineffective once Stage III is reached, often necessitating joint arthroplasty.

Question 30

In the context of distraction osteogenesis via the Ilizarov method, what is the optimal latency period prior to initiating distraction after the corticotomy?

Explanation

A latency period of 5 to 7 days is optimal for establishing early vascularization and primitive callus formation before distraction begins. Shorter latency risks poor regenerate formation, while longer latency risks premature consolidation.

Question 31

An AP pelvis radiograph of a 25-year-old man with groin pain reveals the anterior wall of the acetabulum crossing over the posterior wall before reaching the lateral sourcil. What underlying pathomorphology does this crossover sign indicate?

Explanation

The crossover sign indicates acetabular retroversion, a form of pincer-type femoroacetabular impingement (FAI). This morphology causes focal anterior overcoverage of the femoral head, leading to labral damage.

Question 32

A 55-year-old female with adult sequelae of DDH is scheduled for a total hip arthroplasty. Her preoperative radiograph shows the femoral head is superiorly displaced by 60% of the normal pelvic height. According to the Crowe classification, what type of DDH does she have?

Explanation

Crowe IV is defined as proximal displacement of the femoral head greater than 100% of the femoral head diameter or >20% of the pelvic height. This severe displacement often requires a subtrochanteric shortening osteotomy during THA to safely reduce the hip.

Question 33

During an acute correction of a severe valgus deformity of the proximal tibia using a closing wedge osteotomy, the patient develops a foot drop postoperatively. Which structure is most likely compromised?

Explanation

Acute correction of genu valgum stretches the lateral structures, placing the common peroneal nerve at high risk for traction neurapraxia or palsy. Prophylactic peroneal nerve decompression is often considered in severe acute varus-producing corrections.

Question 34

A 10-year-old boy undergoes placement of a tension-band construct (eight-Plate) on the medial distal femur for a valgus deformity. Which of the following is the mechanism of action of this device?

Explanation

Guided growth (hemiepiphysiodesis) relies on the Hueter-Volkmann principle, which states that increased compression across a physis slows longitudinal bone growth. Medial tethering slows medial growth while the lateral physis continues to grow, correcting the valgus.

Question 35

A newborn is diagnosed with congenital femoral deficiency. Radiographs reveal a complete absence of the proximal femur, including the femoral head, and no acetabular development. Which class does this represent in the Aitken classification?

Explanation

Aitken Class D represents the most severe form of congenital femoral deficiency, characterized by the complete absence of the femoral head, neck, and acetabulum. Class A features a present femoral head and adequate acetabulum with a subtrochanteric varus.

Question 36

In a patient with Legg-Calve-Perthes disease, which of the following is considered a head at risk sign as described by Catterall?

Explanation

Catterall's head-at-risk signs indicate a poorer prognosis in LCP disease. They include Gage sign (a V-shaped radiolucency in the lateral epiphysis/metaphysis), lateral subluxation, calcification lateral to the epiphysis, and a horizontal growth plate.

Question 37

When performing a deformity correction, if the osteotomy and the axis of correction of angulation (ACA) are both located exactly at the center of rotation of angulation (CORA), what is the expected geometric outcome?

Explanation

Placing both the osteotomy and the ACA exactly at the CORA ensures pure angular correction without translation. If the osteotomy is made away from the CORA but the ACA remains at the CORA, angulation will be corrected but translation of the bone ends will occur.

Question 38

A 6-week-old infant is treated with a Pavlik harness for developmental dysplasia of the hip. At the two-week follow-up, the parents report the infant has stopped kicking the affected leg. On exam, there is absent active knee extension. Which of the following positioning errors most likely caused this complication?

Explanation

Excessive hip flexion (typically greater than 120 degrees) in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to a femoral nerve palsy. Excessive abduction is associated with avascular necrosis of the femoral head.

Question 39

According to the Loder classification, an unstable slipped capital femoral epiphysis (SCFE) is defined by which of the following criteria, and carries what primary complication risk?

Explanation

The Loder classification defines an unstable SCFE by the patient's inability to ambulate, even with crutches. Unstable SCFE carries a significantly higher risk of avascular necrosis (up to nearly 50%) compared to stable SCFE.

Question 40

In the Herring lateral pillar classification for Legg-Calvé-Perthes disease, a Type B hip is characterized by:

Explanation

In the Herring classification, Type B is defined by the preservation of >50% of the lateral pillar height. Type A has no lateral pillar involvement, and Type C has <50% of the lateral pillar maintained.

Question 41

The Bernese periacetabular osteotomy (PAO) involves multiple bone cuts to reorient the acetabulum. Which of the following pelvic structures is deliberately left intact to maintain pelvic ring stability?

Explanation

The PAO preserves the posterior column of the pelvis, which maintains the continuity of the pelvic ring. This crucial structural preservation allows for earlier mobilization and weight-bearing compared to other pelvic osteotomies.

Question 42

In distraction osteogenesis using the Ilizarov method, what is the primary biological consequence of initiating distraction with a latency period of less than 3 days?

Explanation

A sufficient latency period (typically 7-10 days) is required to allow mesenchymal stem cells and vascular invasion to populate the osteotomy site. Distracting too early impairs the formation of robust regenerate, leading to poor bone formation and atrophic nonunion.

Question 43

A 4-year-old child with infantile Blount's disease is noted to have a permanent metaphyseal-epiphyseal bony bridge on imaging. This complete medial physeal bar corresponds to which Langenskiöld stage?

Explanation

Langenskiöld Stage VI is characterized by the formation of a true bony bridge (physeal bar) across the medial physis. This requires complex surgical management, often involving bar resection or concurrent physeal distraction.

Question 44

Cam-type femoroacetabular impingement (FAI) is most commonly characterized by abnormal bone morphology in which specific region of the proximal femur?

Explanation

Cam impingement is defined by a loss of spherical contour and decreased offset at the femoral head-neck junction. This asphericity most commonly occurs in the anterosuperior quadrant of the proximal femur.

Question 45

When performing a medial opening wedge high tibial osteotomy (HTO) for varus gonarthrosis, failing to make the anterior gap smaller than the posterior gap will typically result in which unintended sagittal plane deformity?

Explanation

Because the proximal tibia is triangular, opening the osteotomy equally anteriorly and posteriorly actually increases the posterior tibial slope. To maintain normal slope, the anterior opening must typically be about half the size of the posterior opening.

Question 46

In a patient with congenital coxa vara, surgical intervention (such as a valgus producing subtrochanteric osteotomy) is generally indicated when the Hilgenreiner epiphyseal angle (HEA) exceeds what threshold?

Explanation

A Hilgenreiner epiphyseal angle (HEA) greater than 60 degrees is a classic indication for surgical correction in congenital coxa vara, as it is associated with progression of the deformity. An HEA of less than 45 degrees usually resolves or remains stable.

Question 47

During a lower extremity deformity correction, the osteotomy is made proximal to the CORA, but the axis of correction of angulation (ACA) is placed exactly at the CORA. What is the resulting mechanical effect upon correction?

Explanation

When the ACA is aligned with the CORA but the osteotomy is performed at a different level (off-CORA osteotomy), angular correction is achieved but it is necessarily accompanied by translation of the osteotomy fragments.

Question 48

When performing a closed reduction and spica casting for developmental dysplasia of the hip (DDH), the 'safe zone' of Ramsey defines the range between:

Explanation

Ramsey's safe zone is the range of abduction between the angle of re-dislocation (when the hip is adducted) and maximum abduction. Keeping the hip within this zone minimizes the risk of re-dislocation while mitigating the risk of avascular necrosis caused by forced extreme abduction.

Question 49

Prophylactic in situ pinning of the contralateral asymptomatic hip in a patient with a unilateral slipped capital femoral epiphysis (SCFE) is most strongly indicated in which of the following scenarios?

Explanation

Prophylactic contralateral pinning is highly recommended in patients with SCFE related to underlying endocrinopathies or metabolic bone diseases (like chronic renal failure), as well as in patients undergoing radiation therapy or those under 10 years of age, due to the high risk of bilateral involvement.

Question 50

In the treatment of Legg-Calvé-Perthes disease, surgical containment yields the most significant improvement in radiographic outcomes compared to nonoperative treatment in which specific patient population?

Explanation

Studies (e.g., Herring et al.) have demonstrated that surgical containment provides significantly better radiographic outcomes than nonoperative management in children who are over 8 years old at symptom onset and have Lateral Pillar B or B/C border disease. Type C hips perform poorly regardless of treatment.

Question 51

On an anteroposterior radiograph of the pelvis, the 'cross-over sign' is indicative of which acetabular morphology?

Explanation

The cross-over sign occurs when the anterior wall of the acetabulum crosses over the posterior wall on a well-centered AP pelvic radiograph. It is a hallmark sign of focal or global acetabular retroversion, often contributing to pincer-type FAI.

Question 52

A 22-year-old female presents with symptomatic genu valgum. A lateral opening-wedge distal femoral osteotomy is planned. Compared to a medial closing-wedge osteotomy, what is a primary biomechanical or anatomic advantage of the lateral opening-wedge technique?

Explanation

A lateral opening-wedge osteotomy of the distal femur adds bone stock and lengthens the limb, which is advantageous if the patient has a concomitant leg length discrepancy (affected leg is shorter). Conversely, a medial closing-wedge osteotomy shortens the limb.

Question 53

The Taylor Spatial Frame utilizes a specialized software program to calculate strut adjustments based on a 6-axis deformity analysis. Which of the following is NOT a required radiographic or clinical parameter for the software to generate a prescription?

Explanation

The software requires precise mechanical parameters including AP, lateral, and axial offsets, as well as rotational and angular data relative to a reference ring. Bone density scores (DEXA) are not inputted into the spatial frame software for kinematic calculations.

Question 54

In the Ficat and Arlet classification for avascular necrosis (osteonecrosis) of the femoral head, the defining radiographic feature of Stage III disease is:

Explanation

Ficat Stage III is defined by subchondral collapse, evidenced radiographically by the 'crescent sign' or frank flattening of the femoral head. Stage IV involves advanced arthritic changes with joint space narrowing.

Question 55

A 7-year-old boy undergoes temporary hemiepiphysiodesis using tension band plates for genu valgum. Following complete correction and implant removal, the family should be counseled that the risk of 'rebound deformity' is highest in which demographic?

Explanation

Rebound deformity after hardware removal in guided growth is most frequently observed in younger children with substantial remaining growth, requiring close clinical and radiographic monitoring. Overcorrection is sometimes recommended in this high-risk group.

Question 56

When planning a corrective osteotomy for a lower extremity deformity, if the osteotomy is performed at a level different from the Center of Rotation of Angulation (CORA) but the correction axis passes through the CORA, what is the expected resulting deformity?

Explanation

According to Paley's rules of deformity correction (Rule 2), if the osteotomy is away from the CORA but the angulation axis passes through the CORA, the mechanical axis is restored but a translation deformity is induced at the osteotomy site.

Question 57

A 12-year-old obese male presents with acute-on-chronic left hip pain and inability to bear weight. Radiographs confirm an unstable slipped capital femoral epiphysis (SCFE). What is the most significant risk factor for developing avascular necrosis (AVN) following surgical fixation?

Explanation

Preoperative instability (inability to bear weight even with crutches) is the highest risk factor for AVN in SCFE. The risk of AVN in unstable SCFE can be up to 50%, compared to near zero in stable slips.

Question 58

A 4-year-old girl is diagnosed with Langenskiöld stage III infantile Blount's disease. What is the most appropriate management?

Explanation

Langenskiöld stage III in a child older than 3 years is unlikely to spontaneously resolve or respond to bracing. A proximal tibial and fibular osteotomy is the gold standard to correct varus and internal tibial torsion.

Question 59

In a 7-year-old boy with Legg-Calvé-Perthes disease, which of the following radiographic "head-at-risk" signs (Catterall) suggests a poor prognosis and potential need for surgical containment?

Explanation

Lateral subluxation of the femoral head is a critical "head-at-risk" sign indicating loss of containment and impending hinge abduction. This finding often prompts surgical intervention, such as a varus derotational osteotomy or pelvic osteotomy.

Question 60

A neonate presents with an anteromedial bowing of the tibia, a shortened leg, and an absent lateral ray of the foot. Radiographs confirm fibular hemimelia. Which associated ligamentous deficiency is most commonly seen in the knee of this patient?

Explanation

Fibular hemimelia is frequently associated with congenital anterior cruciate ligament (ACL) deficiency, leading to anteroposterior knee instability. Ball-and-socket ankle joint and tarsal coalitions are also common associations.

Question 61

A 24-year-old male hockey player presents with anterior groin pain exacerbated by hip flexion and internal rotation. Imaging demonstrates a "pistol grip" deformity and an alpha angle of 65 degrees. The primary pathomechanical process in this condition involves:

Explanation

Cam impingement (characterized by a high alpha angle and pistol grip deformity) causes shear forces at the chondrolabral junction. This leads to outside-in chondral delamination and labral detachment from the acetabular rim.

Question 62

During distraction osteogenesis using an external fixator for a 5 cm tibial lengthening, a patient develops an equinus contracture. What is the most appropriate initial management?

Explanation

Soft tissue contractures, particularly equinus during tibial lengthening, are common complications. Initial management involves aggressive physical therapy, dynamic splinting, and sometimes slowing the distraction rate before considering surgical release.

Question 63

A 16-year-old female presents with persistent lateral hip pain. Radiographs show a lateral center edge angle (LCEA) of 15 degrees and a Tönnis angle of 18 degrees with an intact Shenton's line. Joint space is preserved. What is the most appropriate surgical treatment?

Explanation

This patient has symptomatic developmental dysplasia of the hip (DDH) with preserved joint space. PAO allows powerful reorientation of the acetabulum while preserving the posterior column, making it the ideal treatment for symptomatic dysplasia in adolescents and young adults.

Question 64

A 12-year-old boy presents with progressive bilateral genu valgum. Mechanical axis deviation is lateral to the center of the knee. What is the most appropriate site and technique for guided growth (hemiepiphysiodesis) to correct the deformity?

Explanation

For genu valgum (knock knees), the mechanical axis is lateral, and the medial aspect of the knee grows relatively faster. Tension band plating of the medial distal femur (and/or medial proximal tibia depending on CORA) tethers the medial side, allowing the lateral side to catch up.

Question 65

A 35-year-old female on chronic corticosteroids for SLE presents with groin pain. MRI reveals bilateral femoral head avascular necrosis (Ficat Stage II). What is the primary rationale for performing a core decompression?

Explanation

Core decompression aims to reduce the elevated intraosseous pressure in the femoral head caused by venous stasis and edema. This provides a channel for neoangiogenesis and potentially halts disease progression in pre-collapse stages (Ficat I and II).

Question 66

To maximize the stiffness of a unilateral external fixator applied for a tibial shaft fracture, which of the following modifications is most effective?

Explanation

Moving the connecting rod closer to the bone significantly increases the stiffness of the external fixator construct. Increasing pin diameter is also highly effective, as stiffness is proportional to the pin radius to the fourth power.

Question 67

A 5-year-old boy presents with a painless limp and a positive Trendelenburg sign. Radiographs show a neck-shaft angle of 90 degrees and an inverted Y-shaped radiolucency in the inferior femoral neck. What is the most appropriate surgical treatment?

Explanation

The presentation and "inverted Y" or "triangle" fragment (Fairbank's triangle) are classic for congenital coxa vara. A proximal femoral valgus osteotomy is indicated when the Hilgenreiner-epiphyseal (H-E) angle is >60 degrees to convert shear forces into compressive forces.

Question 68

According to Ilizarov principles of distraction osteogenesis, what is the optimal rate and rhythm for bone lengthening?

Explanation

Ilizarov found that a high-frequency, small-step rhythm (e.g., 0.25 mm four times daily for a total of 1 mm/day) provides the best environment for bone regeneration while minimizing soft tissue complications.

Question 69

A 70-year-old woman presents with recurrent posterior dislocations 6 months following a primary total hip arthroplasty via a posterior approach. Radiographs show a well-fixed cup with 10 degrees of anteversion and 45 degrees of abduction, and a well-fixed stem with 5 degrees of retroversion. What is the most appropriate definitive management?

Explanation

The combined anteversion is approximately 5 degrees (10 cup + (-5) stem), which is well below the safe zone of 25-45 degrees. The retroverted femoral stem is the primary cause of posterior instability and requires revision to increase anteversion.

Question 70

A 4-year-old child with Osteogenesis Imperfecta presents with severe anterior bowing of bilateral femurs preventing ambulation. What is the gold standard surgical management to correct the deformity and prevent further fractures?

Explanation

The Sofield-Millar operation (multiple osteotomies) stabilized by a telescoping intramedullary rod (like the Fassier-Duval) is the gold standard for correcting severe long bone deformities in growing children with Osteogenesis Imperfecta.

Question 71

A 13-year-old boy undergoes in situ pinning of a stable, moderate left SCFE. One year later, he presents with progressive stiffness and pain in the left hip. Examination reveals severe global restriction of hip motion. Radiographs show joint space narrowing and subchondral sclerosis without focal collapse. What is the most likely diagnosis?

Explanation

Chondrolysis is a severe complication of SCFE, presenting with global loss of motion and joint space narrowing. It is commonly associated with unrecognized pin penetration into the joint but can also occur idiopathically in severe slips.

Question 72

When using a hexapod circular fixator for deformity correction, accurate data entry into the software is crucial. Which parameter specifically dictates the spatial relationship between the reference ring and the bone segment it attaches to?

Explanation

In hexapod frame systems, the mounting parameters define the exact position (translation and rotation in all planes) of the reference ring relative to the bone segment (specifically the reference point/CORA). This is essential for the software to calculate accurate strut adjustments.

Question 73

A 4-week-old female infant has a positive Ortolani test on the right hip. An ultrasound is performed. What alpha angle measurement is considered the threshold for a normal hip (Graf Type I)?

Explanation

According to Graf's ultrasound classification for DDH, an alpha angle greater than 60 degrees indicates a normal, well-developed bony acetabular roof (Type I hip). Angles less than 60 degrees indicate varying degrees of dysplasia.

Question 74

A 5-year-old boy presents with progressive, asymmetric hypertrophy of his right lower extremity, cutaneous capillary malformations (port-wine stains), and varicose veins. Which condition is the most likely diagnosis?

Explanation

Klippel-Trenaunay syndrome is a rare congenital vascular disorder characterized by the triad of capillary malformations (port-wine stains), venous varicosities, and bony and soft tissue hypertrophy, typically involving one extremity.

Question 75

In metal-on-metal hip resurfacing arthroplasty, which patient demographic and anatomical profile has the highest risk of early failure and adverse local tissue reaction (ALTR)?

Explanation

Female gender, small component size (<50 mm), and hip dysplasia are well-recognized risk factors for early failure in metal-on-metal hip resurfacing. These factors increase the risk of edge loading, accelerated wear, and subsequent metallosis/ALTR.

Question 76

According to the principles of deformity correction (Paley's Rule 1), if an osteotomy and the correction hinge are both placed exactly at the Center of Rotation of Angulation (CORA), what is the resulting effect on the bone segments after realignment?

Explanation

Paley's Osteotomy Rule 1 states that if both the osteotomy and the hinge are positioned at the CORA, the mechanical axes will realign via pure angulation with no translation.

Question 77

A 28-year-old hockey player presents with groin pain worsened by deep hip flexion and internal rotation. Radiographs display an alpha angle of 65 degrees. What is the primary pathomechanism of cartilage damage in this specific condition?

Explanation

Cam impingement (high alpha angle) involves a non-spherical femoral head entering the acetabulum, creating shear forces at the chondrolabral junction. This leads to inside-out delamination of the acetabular cartilage.

Question 78

In the evaluation of a 7-year-old boy with Legg-Calvé-Perthes disease, the Herring lateral pillar classification dictates prognosis and treatment. Which of the following radiographic findings correctly defines a Herring Group C classification?

Explanation

The Herring classification assesses the height of the lateral pillar on AP radiographs during the fragmentation phase. Group C is defined by >50% loss of height, portending a poorer prognosis and a higher likelihood of non-spherical healing.

Question 79

When analyzing the mechanical axis of the lower extremity for deformity planning, what is the accepted normal range for the mechanical lateral distal femoral angle (mLDFA)?

Explanation

The normal mLDFA is approximately 87 degrees, with an acceptable range of 85 to 90 degrees. This references the lateral angle formed between the mechanical axis of the femur and the knee joint line.

Question 80

A patient presents with severe genu varum. Standing long-leg radiographs show a mechanical axis deviation (MAD) falling completely medial to the medial tibial plateau (Zone 3). During an acute correction using a high tibial opening wedge osteotomy, what is the primary soft tissue structure at risk?

Explanation

Acute correction of severe varus deformities places significant stretch on the lateral structures, particularly the common peroneal nerve. Prophylactic peroneal nerve decompression is frequently indicated in substantial corrections.

Question 81

A 13-year-old obese male sustains an acute-on-chronic slipped capital femoral epiphysis (SCFE) and is unable to bear weight even with crutches. He is treated with single in situ screw fixation. What is the most devastating, yet relatively common, complication specifically associated with this variant of SCFE?

Explanation

By the Loder classification, the inability to bear weight defines an unstable SCFE. Unstable slips carry a high risk of avascular necrosis (up to 47%), resulting from kinking or disruption of the vulnerable retinacular vessels.

Question 82

A 14-year-old female undergoes femoral lengthening using distraction osteogenesis. During the consolidation phase, her surgeon calculates the External Fixator Index (EFI). How is the EFI defined?

Explanation

The External Fixator Index (EFI) represents the total duration the frame is worn per centimeter of length gained. It is typically expressed in months/cm or days/cm, serving as a standardized measure of treatment duration.

Question 83

A 35-year-old female with secondary osteoarthritis due to severe developmental dysplasia of the hip (Crowe Type IV) requires a total hip arthroplasty. To successfully place the acetabular cup in the true acetabulum and safely reduce the hip, which adjunctive procedure is most frequently required?

Explanation

Crowe Type IV DDH involves a high, completely dislocated hip. Bringing the femoral head down to the true acetabulum heavily stretches the sciatic nerve, routinely requiring a subtrochanteric shortening osteotomy to prevent nerve palsy.

Question 84

When programming a Taylor Spatial Frame (hexapod fixator) for multiplanar lower extremity deformity correction, what does the "mounting parameter" mathematically communicate to the software?

Explanation

Mounting parameters in a hexapod fixator define the spatial orientation (translation and rotation across all planes) of the reference ring relative to the targeted bone segment. This data is critical for the software to generate an accurate correction prescription.

Question 85

A 4-year-old boy presents with a limp, right hip pain, a temperature of 38.6°C (101.5°F), and refusal to bear weight. His laboratory values show WBC 14,000/mm³, ESR 45 mm/hr, and CRP 25 mg/L. According to Kocher's criteria, what is the approximate probability of this child having septic arthritis?

Explanation

Kocher's criteria include non-weight bearing, fever >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm³. The presence of all four predictors yields an approximately 99% probability of septic arthritis.

Question 86

According to Paley's osteotomy rules, if the osteotomy is executed at a level separate from the CORA, and the correction hinge is placed directly at the osteotomy site, what is the biomechanical outcome upon correction of the angulation?

Explanation

Paley's Rule 3 indicates that if both the osteotomy and the hinge are placed away from the CORA, correcting the angulation will simultaneously induce a translational deformity. This results in parallel but misaligned mechanical axes.

Question 87

A 42-year-old male with chronic corticosteroid use presents with significant groin pain. Plain radiographs are completely normal. MRI reveals a serpiginous low-signal intensity line in the anterosuperior femoral head on T1-weighted sequences. What is the most appropriate initial surgical management?

Explanation

The patient has early, pre-collapse (Ficat/Steinberg Stage I) avascular necrosis of the femoral head. Core decompression is the standard initial surgical treatment to reduce intraosseous pressure and promote revascularization.

Question 88

The Paley multiplier method provides accurate predictions of leg length discrepancy (LLD) at skeletal maturity. At what specific age is the skeletal multiplier for girls exactly 2.0?

Explanation

For girls, the Paley multiplier is approximately 2.0 at exactly 2 years of age, meaning they have achieved half of their mature limb length. For boys, the multiplier is 2.0 closer to 3 years of age.

Question 89

When planning a deformity correction using a circular fixator, the surgeon places the hinge at the center of rotation of angulation (CORA) but performs the osteotomy at a different level. According to Paley's osteotomy rules, what is the expected outcome at the osteotomy site?

Explanation

According to Osteotomy Rule 2, when the osteotomy is separate from the CORA but the hinge is placed at the CORA, the mechanical axes will realign properly. However, this configuration inevitably causes translation at the osteotomy site.

Question 90

A 5-year-old girl with developmental dysplasia of the hip (DDH) requires a pelvic osteotomy. The surgeon plans an incomplete osteotomy through the ilium, hinging on the triradiate cartilage, to reduce the acetabular volume and improve anterior and lateral coverage. Which osteotomy is described?

Explanation

The Pemberton osteotomy is an incomplete pericapsular osteotomy that hinges on the triradiate cartilage. It actively alters the shape of the acetabulum and reduces its volume, making it highly effective for true acetabular dysplasia.

Question 91

A 4-year-old child presents with severe infantile Blount disease. Radiographs show a Langenskiöld stage IV lesion with a prominent medial metaphyseal beak and a step-off in the epiphysis. What is the most appropriate surgical management?

Explanation

Langenskiöld stage IV infantile Blount disease involves the formation of a medial physeal bar. Management requires excision of the bony bridge (bar) with fat interposition and a concurrent valgus-producing proximal tibial osteotomy.

Question 92

A 28-year-old male athlete presents with anterior groin pain. Imaging reveals a CAM-type femoroacetabular impingement. At which clock-face location on the femoral head-neck junction is the maximum CAM deformity most commonly located?

Explanation

CAM deformities represent an abnormal femoral head-neck offset. They are most frequently located in the anterosuperior quadrant of the femoral head-neck junction, which corresponds to the 1:00 to 3:00 position on the clock face.

Question 93

A 12-year-old obese male presents with a unilateral stable slipped capital femoral epiphysis (SCFE). Which of the following is the strongest clinical indication for prophylactic in situ pinning of the contralateral asymptomatic hip?

Explanation

Endocrine or metabolic disorders (e.g., hypothyroidism, renal osteodystrophy) carry a very high risk of bilateral involvement in SCFE. This makes underlying endocrinopathy a strong, widely accepted indication for prophylactic pinning of the contralateral hip.

Question 94

A 5-year-old boy is evaluated for a painless waddling gait. Radiographs show developmental coxa vara. The Hilgenreiner's epiphyseal angle (HEA) is measured at 65 degrees. What is the most appropriate management?

Explanation

An HEA greater than 60 degrees in developmental coxa vara generally indicates a progressive deformity that will not resolve spontaneously. A proximal femoral valgus osteotomy is required to correct the neck-shaft angle and mechanical axis.

Question 95

A 45-year-old male presents with early-onset hip osteoarthritis. He has a history of Legg-Calvé-Perthes disease as a child. Radiographs show an enlarged, flat femoral head that is congruent with a similarly flattened acetabulum. This presentation most closely correlates with which Stulberg classification from childhood?

Explanation

Stulberg III describes an aspherical but congruent joint (coxa magna), which leads to mild-to-moderate osteoarthritis in middle age. Stulberg IV and V are aspherical and incongruent, typically leading to severe, early arthritis before age 40.

Question 96

Review the lower extremity deformity shown.

When analyzing a diaphyseal deformity with two distinct centers of rotation of angulation (CORAs), which of the following mechanical axis lines must be established to determine the intervening segment's true axis?

Explanation

In multi-apical deformities, the axis of the middle segment is defined by a line connecting the two CORAs. These CORAs are found at the intersections of this intervening line with the respective proximal and distal mechanical or anatomic axes.

Question 97

A 2-year-old child with Proximal Focal Femoral Deficiency (PFFD) has a severely short femur, but a normal, stable knee and ankle. The foot is at the level of the contralateral knee. To optimize the child for a functional prosthesis, the surgeon considers a Van Nes rotationplasty. What critical prerequisite must be met for this procedure to be successful?

Explanation

For a successful Van Nes rotationplasty, the ankle must be fully functional and have near-normal range of motion. Following the 180-degree rotation, the ankle joint will function as the new knee joint to power the prosthesis.

Question 98

When applying a hexapod circular external fixator for complex lower extremity deformity correction, accurately inputting mounting parameters is essential. Which of the following defines the "axial translation" mounting parameter?

Explanation

In hexapod frame software, axial translation refers to the vertical (proximal-distal) distance from the reference ring's center to the deformity's origin (CORA). Anteroposterior and lateral translations denote the orthogonal offsets.

Question 99

A 6-month-old girl undergoes closed reduction and spica casting for developmental dysplasia of the hip. Which of the following positions during casting is most heavily associated with the development of iatrogenic avascular necrosis (AVN) of the femoral head?

Explanation

Immobilization in extreme hip abduction (the 'frog-leg' position) increases pressure on the delicate retinacular vessels. This dramatically increases the risk of iatrogenic avascular necrosis of the femoral head in DDH treatment.

Question 100

A 16-year-old patient presents with a combined leg length discrepancy and complex femoral deformity. A proximal femoral osteotomy and external fixation are performed.

When distracting a fixator over a newly formed regenerate in the proximal femur, what soft tissue structure is at highest risk of causing an apex-anterior (procurvatum) and varus bowing of the regenerate?

Explanation

During proximal femoral lengthening, the unopposed pull of the iliopsoas (flexing the proximal fragment) and hip abductors (abducting the proximal fragment) creates a deforming force. This classically results in a varus and procurvatum deformity at the regenerate site.

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

Mastering Lower Extremity Deformity & Hip Pathology: Orthopaedic Board Review | Part 15

Key Takeaway

Mastering Lower Extremity Deformity & Hip Pathology: Orthopaedic Board Review | Part 15

Chapter Index