This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Question 2421
Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with right hip pain, a limp, and refusal to bear weight. Temperature is 38.8°C. Blood tests show an ESR of 55 mm/hr and WBC of 14,000/mm³. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis rather than transient synovitis?
Correct Answer & Explanation
. 99%
Explanation
The Kocher criteria include non-weight-bearing, temperature >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm³. Having all four predictors yields a 99% probability of septic arthritis.
Question 2422
Topic: 1. General Principles & Basic Science
A 14-year-old boy presents with severe limb shortening, Trendelenburg gait, and a completely destroyed proximal femur/acetabulum secondary to infantile septic arthritis (Choi type IV). Which of the following is the most appropriate reconstructive option to restore mechanics and leg length?
Correct Answer & Explanation
. Pelvic support osteotomy (Ilizarov hip reconstruction)
Explanation
A pelvic support osteotomy involves a proximal femoral valgus-extension osteotomy to eliminate Trendelenburg gait and a distal varus-lengthening osteotomy to restore length and mechanical axis. It is the gold standard for severe post-septic hip sequelae in adolescents.
Question 2423
Topic: Infection, Pharmacology & VTE
A 2-year-old girl is diagnosed with a septic hip. Gram stain is negative, but PCR and BACTEC blood culture systems eventually isolate a fastidious Gram-negative coccobacillus. Which of the following organisms is most likely responsible?
Correct Answer & Explanation
. Kingella kingae
Explanation
Kingella kingae is a fastidious Gram-negative organism increasingly recognized as a leading cause of pediatric septic arthritis in toddlers (6 months to 4 years). It is best isolated using PCR or inoculation into aerobic BACTEC blood culture vials.
Question 2424
Topic: 1. General Principles & Basic Science
During preoperative planning for deformity correction, the surgeon identifies the Center of Rotation of Angulation (CORA).
According to Paley's osteotomy rules (Rule 1), if the osteotomy and the hinge are both placed exactly at the CORA, what will be the result upon correction?
Correct Answer & Explanation
. Angulation correction without translation
Explanation
Paley's Rule 1 states that when the osteotomy and the hinge are co-located at the CORA, the bone ends angulate around each other without translation, perfectly restoring the mechanical axis.
Question 2425
Topic: Infection, Pharmacology & VTE
A 3-year-old child presents with suspected septic arthritis of the hip. The child holds the hip in a characteristic "resting position." This position minimizes intracapsular pressure to reduce the risk of avascular necrosis. What is this classic position?
Correct Answer & Explanation
. Flexion, abduction, and external rotation
Explanation
The hip capsule has its maximum volume in flexion, abduction, and external rotation. Children with joint effusions from septic arthritis reflexively hold the hip in this position to minimize pressure and pain.
Question 2426
Topic: Infection, Pharmacology & VTE
In the evaluation of a limping child with hip pain, a C-reactive protein (CRP) value greater than what threshold is considered the strongest independent laboratory predictor of septic arthritis versus transient synovitis?
Correct Answer & Explanation
. 2.0 mg/dL
Explanation
Studies (e.g., Caird et al.) demonstrated that a CRP > 2.0 mg/dL is a strong independent predictor of septic arthritis. It is often considered more reliable than ESR in the acute setting due to its rapid rise and fall.
Question 2427
Topic: Infection, Pharmacology & VTE
A 2-week-old neonate born at 32 weeks gestation is evaluated for decreased movement of the right leg. The infant is afebrile but demonstrates pain with diaper changes. Ultrasound shows a right hip effusion. What is the most common causative organism for septic arthritis in this specific age group?
Correct Answer & Explanation
. Staphylococcus aureus
Explanation
Even in neonates, Staphylococcus aureus is the most common cause of septic arthritis. Group B Streptococcus and Gram-negative enteric bacilli are also prevalent but less common than S. aureus. Neonates often lack fever, presenting instead with pseudoparalysis.
Question 2428
Topic: Biomechanics & Biomaterials
When applying a Taylor Spatial Frame (TSF) for complex multi-planar deformity correction, the software requires specific mounting parameters to calculate the strut adjustments. Which of the following is NOT one of the standard TSF mounting parameters?
Correct Answer & Explanation
. Bone regenerate density coefficient
Explanation
TSF mounting parameters include AP, Lateral, Axial, and Rotary offsets (identifying the position of the reference ring relative to the origin). Bone regenerate density is not a geometric parameter used in the kinematics software.
Question 2429
Topic: Surgical Anatomy & Approaches
An 18-month-old presents with a septic hip requiring urgent surgical irrigation and debridement. The surgeon utilizes the anterior (Smith-Petersen) approach. Which two internervous planes define the superficial interval of this approach?
Correct Answer & Explanation
. Femoral nerve and Superior gluteal nerve
Explanation
The superficial interval of the Smith-Petersen approach is between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The deep interval is between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).
Question 2430
Topic: 1. General Principles & Basic Science
According to Paley's Rule 2 of osteotomy, if the osteotomy is made at a level distinct from the CORA, but the hinge is placed at the CORA, what will occur during the correction?
Correct Answer & Explanation
. Angulation combined with translation to realign the mechanical axis
Explanation
Paley's Rule 2 dictates that if the hinge is at the CORA but the osteotomy is elsewhere, the correction will result in both angulation and translation at the osteotomy site. This translation is necessary to fully restore the collinearity of the mechanical axis.
Question 2431
Topic: Biomechanics & Biomaterials
When optimizing the biomechanics of an Ilizarov circular fixator for a tibial lengthening, which of the following modifications will most effectively increase the axial stiffness of the construct?
Correct Answer & Explanation
. Increasing the crossing angle of the wires toward 90 degrees
Explanation
Axial and torsional stiffness of a circular fixator are maximized by increasing wire diameter, increasing wire tension, decreasing ring diameter, placing rings closer to the bone, and crossing wires at an angle as close to 90 degrees as anatomically possible.
Question 2432
Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with right hip pain and refusal to bear weight. His temperature is 38.8°C (101.8°F). Laboratory studies reveal a WBC count of 13,500/mm³ and an ESR of 55 mm/hr. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
Correct Answer & Explanation
. 99.6%
Explanation
The Kocher criteria for differentiating septic arthritis from transient synovitis include: non-weight bearing, temperature >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm³. The probability of septic arthritis with 4 criteria present is approximately 99.6%.
Question 2433
Topic: Surgical Anatomy & Approaches
When utilizing the Kaplan approach for exposure of the radial head in a terrible triad injury, the surgical interval is developed between which two muscle bellies?
Correct Answer & Explanation
. Extensor digitorum communis (EDC) and extensor carpi radialis brevis (ECRB)
Explanation
The Kaplan approach utilizes the interval between the EDC and the ECRB. In contrast, the Kocher approach utilizes the interval between the ECU and the anconeus.
Question 2434
Topic: 1. General Principles & Basic Science
A 55-year-old male presents with chronic right knee pain and a progressive varus deformity. A standing long-leg alignment radiograph is obtained, and the following measurements are recorded using the Mechanical Axis Test (MAT):
Based on these findings, what is the primary osseous source of the patient's varus malalignment?
Correct Answer & Explanation
. Distal femoral varus
Explanation
Correct Answer: CThe normal range for the Mechanical Lateral Distal Femoral Angle (mLDFA) is 85°-90°. An mLDFA greater than 90° indicates a femoral varus deformity, which contributes to medial Mechanical Axis Deviation (MAD). In this patient, the mLDFA is 94°, which is outside the normal range and indicates a distal femoral varus deformity. The Medial Proximal Tibial Angle (MPTA) is 87°, which is within the normal range of 85°-90°, indicating no significant tibial deformity. The Joint Line Convergence Angle (JLCA) is 0°, which is within the normal range of 0°-2° medial convergence, ruling out significant ligamentous laxity or cartilage loss as the primary source of the osseous malalignment. Therefore, the primary osseous source of the varus malalignment is distal femoral varus.
Question 2435
Topic: 1. General Principles & Basic Science
A 62-year-old female presents with severe bilateral knee pain and a progressive valgus deformity. A standing long-leg alignment radiograph of her left lower extremity reveals the following measurements:
Which of the following best describes the combined sources of her valgus malalignment?
Correct Answer & Explanation
. Distal femoral valgus and proximal tibial valgus
Explanation
Correct Answer: CThe normal range for the Mechanical Lateral Distal Femoral Angle (mLDFA) is 85°-90°. An mLDFA less than 85° indicates a femoral valgus deformity, contributing to lateral Mechanical Axis Deviation (MAD). In this case, the mLDFA is 82°, indicating distal femoral valgus. The normal range for the Medial Proximal Tibial Angle (MPTA) is 85°-90°. An MPTA greater than 90° indicates a tibial valgus deformity, also contributing to lateral MAD. Here, the MPTA is 92°, indicating proximal tibial valgus. The Joint Line Convergence Angle (JLCA) is 1° lateral, which is within the normal range of 0°-2° medial convergence, suggesting no significant medial ligamento-capsular laxity or lateral cartilage loss as a primary source of the osseous malalignment. Therefore, the combined sources of her valgus malalignment are distal femoral valgus and proximal tibial valgus.
Question 2436
Topic: 1. General Principles & Basic Science
A 68-year-old patient presents with chronic medial knee pain and a varus deformity on a standing long-leg radiograph. The Joint Line Convergence Angle (JLCA) is measured at 4° of medial convergence. The surgeon suspects either lateral collateral ligament laxity or significant medial compartment cartilage loss.
What additional radiographic study would be most beneficial to differentiate between these two potential sources of the increased JLCA?
Correct Answer & Explanation
. A varus stress radiograph of the affected knee
Explanation
Correct Answer: CThe text states that the JLCA should be compared between films obtained with the patient in weight-bearing and non-weight-bearing positions to separate joint line convergence due to loss of cartilage height and ligamentous laxity. Furthermore, stress radiographs can also be used (Chaps. 3, 14, and 16). A varus stress radiograph (Fig. 3-10a) specifically assesses the integrity of the lateral collateral ligament and the stability of the lateral compartment. If the JLCA significantly increases under varus stress compared to a non-weight-bearing film, it indicates lateral collateral ligament laxity. If the JLCA remains similar to the weight-bearing film but is reduced on a non-weight-bearing film, it suggests cartilage loss as the primary factor. A valgus stress radiograph (Option D) would assess the medial collateral ligament, which is not the primary concern for a medially convergent JLCA in varus. Single-leg stance (Option A) and non-weight-bearing (Option B) AP radiographs can provide some information but are less specific than a stress view for differentiating ligamentous laxity from cartilage loss. A lateral view (Option E) assesses sagittal plane alignment and is not relevant for this frontal plane issue.
Question 2437
Topic: Biology, Genetics & Bone Healing
A 60-year-old patient presents with severe knee osteoarthritis and a suspected varus deformity of the right lower extremity. Before proceeding with detailed tibial axis planning, the surgeon performs a Malalignment Test (MAT) as the initial step. Which of the following best describes the primary purpose and components of this crucial prerequisite step?
Correct Answer & Explanation
. To assess the overall lower limb alignment by drawing global mechanical axes, measuring Mechanical Axis Deviation (MAD), and evaluating joint orientation angles (mLDFA, MPTA, JLCA).
Explanation
Correct Answer: CThe case explicitly states, "Before drawing any tibial axes, you must assess the entire lower limb macroscopically. This is Step 0—the absolute prerequisite to all localized planning." It then details the components: "1. Draw the Global Mechanical Axes... 2. Measure the Mechanical Axis Deviation (MAD)... 3. Measure Joint Orientation Angles (mLDFA, MPTA, and the Joint Line Convergence Angle (JLCA) on both sides)." The clinical criticality is also explained: "It tells youwherethe deformity is originating from. Is the massive MAD caused by a tibial deformity, a distal femoral deformity, or a combination of both?"Option A is incorrect. Bone density assessment is not part of the MAT for deformity planning.Option B is incorrect. While CORA identification is a later step in planning, the MAT is a global assessment, and a CT scan is not the primary tool for initial MAT.Option D is incorrect. Limb length measurement is a separate assessment, not the primary purpose of the MAT.Option E is incorrect. Soft tissue evaluation is important but not the core component of the radiographic MAT.
Question 2438
Topic: 1. General Principles & Basic Science
A 22-year-old patient requires a distal femoral osteotomy for valgus deformity. The surgeon is meticulously planning the correction using mechanical axis principles. Which of the following represents the normal average Mechanical Lateral Distal Femoral Angle (mLDFA) that should be targeted for correction?
Correct Answer & Explanation
. 87°
Explanation
Correct Answer: BThe "High-Yield Joint Orientation Angles (Frontal Plane)" table in the case explicitly lists the normal average for the Mechanical Lateral Distal Femoral Angle (mLDFA) as87°, with a normal range of 85° - 90°. This is a critical value to memorize for board exams and clinical planning.Options A, C, D, and E are incorrectas they do not match the specified normal average for the mLDFA.
Question 2439
Topic: 1. General Principles & Basic Science
A surgeon is planning a complex osteotomy for a patient with a severe multiapical tibial deformity. Due to the complexity and the need for gradual, multi-planar correction, the surgeon opts for a hexapod circular external fixator. According to Paley's Osteotomy Rules, if the surgeon places both the osteotomy and the hinge of the fixator away from the true CORA(s) of the deformity, what is the most likely outcome?
Correct Answer & Explanation
. A massive translation deformity will be created, and the mechanical axis will not be fully corrected.
Explanation
Correct Answer: CThe case outlines "Rule of Osteotomy 3": "When the hinge and the osteotomy are both placed away from the CORA, a massive translation deformity is created, and the mechanical axis willnotbe fully corrected. This is a surgical failure." This rule highlights the critical importance of CORA-based planning to achieve both anatomic and mechanical axis correction.Option A is incorrect. This describes Rule of Osteotomy 1, where both the osteotomy and hinge are at the CORA.Option B is incorrect. This describes Rule of Osteotomy 2, where the hinge is at the CORA, but the osteotomy is at a different level.Option D is incorrect. Placing the osteotomy and hinge away from the CORA leads to instability and poor alignment, which would hinder, not accelerate, healing.Option E is incorrect. While overcorrection is a risk, the primary and most severe consequence of violating Rule 3 is uncorrected mechanical axis and massive translation, which is a fundamental failure of the correction.
Question 2440
Topic: 1. General Principles & Basic Science
A 50-year-old patient presents with a complex varus deformity of the proximal tibia, with the apex of the deformity located very close to the knee joint line (juxta-articular). The remaining proximal tibial segment is too short to reliably draw a mid-diaphyseal line. According to the principles of anatomic axis planning, what is the critical approach for drawing the axis line of such a short juxta-articular segment?
Correct Answer & Explanation
. Reference it off the joint line itself, using known normal population angles of the anatomic axis relative to the joint line.
Explanation
Correct Answer: BThe case addresses this challenge under "Principles of Axis Planning - Anatomic Axis Planning - Metaphyseal and Juxta-Articular Deformities": "When the CORA is located very near the joint line, the remaining bone segment is too short, and the metaphysis flares out widely. You physically cannot draw an accurate mid-diaphyseal line on the articular side because there is no 'diaphysis' left to measure. To draw the axis line of a short juxta-articular segment, you must reference it off the joint line itself. If you know the normal intersection point and the normal population angle of the anatomic axis relative to the joint line, you can mathematically reconstruct the anatomic axis of that short segment."Option A is incorrect. Extrapolating from a distal segment for a proximal juxta-articular deformity is not the correct method and would likely lead to error.Option C is incorrect. Ignoring a significant part of the deformity will lead to incomplete correction and malalignment.Option D is incorrect. While the femoral mechanical axis is used in some scenarios for theproximal tibial mechanical axis, this question specifically asks aboutanatomic axis planningfor a short juxta-articular segment, which requires referencing the joint line itself.Option E is incorrect. While MRI can show the medullary canal, the planning principles described rely on radiographic measurements and known angles relative to the joint line for reconstruction, not direct MRI drawing for this specific problem.
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