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 4001
Topic: 1. General Principles & Basic Science
A surgeon is planning a corrective osteotomy for a 60-year-old man with severe fixed sagittal imbalance. The surgeon decides to perform a pedicle subtraction osteotomy (PSO) at L3. Approximately how many degrees of sagittal correction can realistically be expected from a single-level lumbar PSO?
Correct Answer & Explanation
. 5 to 10 degrees
Explanation
A pedicle subtraction osteotomy (PSO) is a three-column closing wedge osteotomy hinged at the anterior longitudinal ligament. It typically provides approximately 30 to 35 degrees of lordotic correction at a single level.
Question 4002
Topic: Biology, Genetics & Bone Healing
A 4-year-old girl is diagnosed with Klippel-Feil syndrome. She exhibits a low posterior hairline, short neck, and limited cervical range of motion. Because of known systemic associations with this syndrome, which of the following screening tests is most highly recommended?
Correct Answer & Explanation
. Electrocardiogram (ECG)
Explanation
Klippel-Feil syndrome is associated with congenital anomalies due to abnormal embryogenesis. Genitourinary anomalies (e.g., unilateral renal agenesis) occur in approximately 30% of patients, making screening renal ultrasound mandatory.
Question 4003
Topic: 1. General Principles & Basic Science
When applying a halo vest orthosis, placing the anterior pins 1 cm superior to the orbital rim and lateral to the supraorbital notch specifically avoids injury to which of the following structures?
Correct Answer & Explanation
. Facial nerve
Explanation
Anterior halo pins must be placed in the safe zone: lateral to the supraorbital notch (or lateral two-thirds of the orbit) and medial to the temporalis fossa. This positioning explicitly avoids injuring the supratrochlear and supraorbital nerves.
Question 4004
Topic: Biomechanics & Biomaterials
Which of the following statements best characterizes polymethylmethacrylate (PMMA) when it is used to secure joint components in bone and to distribute the forces evenly across the bone-implant interface?
Correct Answer & Explanation
. Porosity reduction increases the fatigue strength of PMMA.
Explanation
PMMA has no adhesive properties and can be more accurately described as grout than glue. It does not chemically bond to bone or implants; however, mechanical bonding is accomplished with porous or coated components and with cancellous bone. PMMA is approximately three times stronger in compression than in tension. Peak blood levels of monomer are usually seen approximately 3 minutes after the cement is placed. The monomer is cleared by the lungs. Associated hypotension is more closely related to diminished blood volume than to circulating monomer levels. High porosity decreases the tensile and fatigue properties of cement. Manually mixed cement may have porosity as high as 27%. Porosity may be reduced to less than 1% through vacuum mixing or centrifugation of the cement. When adding antibiotics to cement, the compressive and tensile forces are not appreciably decreased, but the overall fatigue strength may be reduced.
Question 4005
Topic: Surgical Anatomy & Approaches
A surgeon utilizes the direct anterior approach for a total hip arthroplasty. To safely access the hip joint, an internervous plane is developed superficially. Which two nerves supply the muscles that form the boundaries of this superficial surgical interval?
Correct Answer & Explanation
. Femoral nerve and Superior gluteal nerve
Explanation
The direct anterior approach (Smith-Petersen) utilizes a superficial internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep plane is between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).
Question 4006
Topic: Surgical Anatomy & Approaches
During an ilioinguinal approach for the open reduction and internal fixation of an anterior pelvic ring fracture, the surgeon encounters brisk arterial bleeding near the superior pubic ramus. Which of the following vascular structures or anastomoses is the most likely source of this bleeding?
Correct Answer & Explanation
. An anastomosis between the external iliac system and the obturator system
Explanation
The source of the bleeding is likely the 'corona mortis' (crown of death), which is a vascular anastomosis between the external iliac or inferior epigastric vessels and the obturator vessels. It is located on the posterior aspect of the superior pubic ramus, typically 4 to 9 cm from the pubic symphysis, and can cause significant hemorrhage if inadvertently injured during surgical approaches to the anterior pelvis or acetabulum.
Question 4007
Topic: Biomechanics & Biomaterials
A 55-year-old male is 15 years post-operative from a total hip arthroplasty utilizing a highly cross-linked polyethylene (HXLPE) liner. Which of the following best describes the wear and mechanical characteristics of HXLPE compared to conventional ultra-high-molecular-weight polyethylene?
Correct Answer & Explanation
. Decreased volumetric wear but increased susceptibility to fatigue cracking and fracture
Explanation
Highly cross-linked polyethylene (HXLPE) is manufactured using irradiation to create cross-links between polymer chains, followed by a heating process (melting or annealing) to eliminate free radicals. This significantly reduces adhesive and abrasive volumetric wear. However, the cross-linking process alters the mechanical properties, leading to a reduction in ductility, yield strength, and ultimate tensile strength, which increases its susceptibility to fatigue cracking and rim fracture, particularly in thin liners or with malpositioned components.
Question 4008
Topic: Infection, Pharmacology & VTE
A 10-year-old boy who has had progressive low back and right buttock pain for the past 3 days is now unable to bear weight on the right side secondary to pain. He has a temperature of 101.3 degrees F (38.5 degrees C). Examination reveals full hip range of motion; but he reports pain on the right side with external rotation. Pain is elicited with compression of the iliac wings and with direct palpation of the right sacroiliac (SI) joint. An MRI scan of the pelvis shows no abscess, but there is inflammation of the SI joint. Management should consist of
Correct Answer & Explanation
. bed rest, blood cultures, and IV antibiotics.
Explanation
The clinical presentation and MRI findings are consistent with an acute infection of the SI joint. Bed rest and nonsteroidal anti-inflammatory drugs alone are insufficient to treat the problem. Staphylococcus aureus is the causative organism in most of these infections; therefore, unless there is an unusual factor in the history such as IV drug use, immune system compromise, or unusual travel, SI joint aspiration is unnecessary. It is often difficult to enter the SI joint, even under radiographic guidance. Management should consist of hospital admission and IV antibiotics. Blood cultures may be positive and should be obtained prior to starting antibiotics. Surgical fusion of the SI joint is not indicated.
Question 4009
Topic: 1. General Principles & Basic Science
Figure 18 is the radiograph of a 52-year-old woman who has leg length inequality and chronic activity-related buttock discomfort. This has been a life-long problem, but it is getting worse and increasingly causing back pain. What is the best current technique for total hip arthroplasty?
Correct Answer & Explanation
. Anatomic hip center with subtrochanteric shortening osteotomy
Explanation
A high hip center is not recommended for Crowe IV hips because of the lack of acetabular bone and altered hip biomechanics. An anatomic center is a better option but necessitates a technique to address the tight soft-tissue envelope. A trochanteric osteotomy with progressive femoral shortening has been described but can be prone to trochanter nonunion. Iliofemoral lengthening prior to surgery has been described but may not be tolerated by all patients. A shortening subtrochanteric osteotomy avoids trochanter nonunion and allows adjustment of femoral anteversion. Fixation of the osteotomy can include a stem with distal rotational control, plate fixation, a step vs. oblique cut, or strut grafts.
Question 4010
Topic: 1. General Principles & Basic Science
A patient with rheumatoid arthritis has a rupture of the extensor digitorum communis to 4 and 5. You are planning to perform an extensor indicis proprius (EIP) tendon transfer. What effect will this have on index finger extension?
Correct Answer & Explanation
. No effect
Explanation
EIP transfer results in no functional deficit. If the tendon is cut proximal to the sagittal band, there will be no extensor deficit.
Question 4011
Topic: Surgical Anatomy & Approaches
The anterior approach to the hip (iliofemoral or Smith-Peterson) puts which of the following anatomic structures at greatest risk?
Correct Answer & Explanation
. Lateral femoral cutaneous nerve
Explanation
The lateral femoral cutaneous nerve is at risk during the anterior approach to the hip (Smith-Peterson approach) as it passes near the interval between the tensor fasciae latae and the sartorius muscles.
Question 4012
Topic: 1. General Principles & Basic Science
A 45-year-old construction worker complains of posterior knee pain and a feeling of 'giving way'. An MRI of the knee is shown.
Which of the following biomechanical phenomena is the most direct consequence of the pathology demonstrated?
Correct Answer & Explanation
. Loss of hoop stresses and lateral extrusion of the medial meniscus.
Explanation
The clinical presentation and location of the pain strongly suggest a medial meniscus posterior root tear. The posterior root anchor serves a vital biomechanical function by converting axial compressive loads into circumferential 'hoop stresses' within the meniscus. When the root is avulsed, the meniscus can no longer resist these forces, leading to medial meniscal extrusion (often >3 mm) and a profound loss of hoop stresses. Biomechanically, this functions equivalently to a total meniscectomy, significantly increasing medial compartment peak contact pressures.
Question 4013
Topic: Surgical Anatomy & Approaches
A surgeon utilizes the direct anterior approach (DAA) for a total hip arthroplasty using the internervous plane between the tensor fasciae latae (TFL) and the sartorius. During deep dissection, a nerve passing over the anterior aspect of the iliacus muscle is at risk of iatrogenic traction injury. What is the clinical consequence of an injury to this specific nerve?
Correct Answer & Explanation
. Numbness or paresthesias over the anterolateral aspect of the thigh.
Explanation
The nerve described is the Lateral Femoral Cutaneous Nerve (LFCN), which provides sensory innervation to the anterolateral thigh. During the direct anterior approach (Smith-Petersen), the superficial internervous plane is between the TFL (superior gluteal nerve) and the sartorius (femoral nerve). The LFCN is highly variable in its course but typically runs medial to the ASIS and passes over the anterior aspect of the sartorius/iliacus fascia. Retraction in this area places it at high risk for neurapraxia or transection, leading to meralgia paresthetica (numbness/burning of the anterolateral thigh). Hip abduction weakness (Option A) implies superior gluteal nerve injury. Weakness in knee extension (Option D) implies femoral nerve injury.
Question 4014
Topic: Surgical Anatomy & Approaches
The direct anterior approach (DAA) to the hip is increasingly popular for primary THA due to its use of a true internervous and intermuscular plane. Which of the following accurately describes the superficial internervous plane utilized in the direct anterior approach?
Correct Answer & Explanation
. Between the gluteus medius (superior gluteal nerve) and the tensor fasciae latae (superior gluteal nerve)
Explanation
The direct anterior approach (Smith-Petersen) utilizes a true superficial internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep internervous plane is between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve). A key risk during the superficial dissection is injury to the lateral femoral cutaneous nerve.
Question 4015
Topic: Biomechanics & Biomaterials
A 65-year-old male presents with new-onset right groin pain 5 years after an uncomplicated metal-on-polyethylene total hip arthroplasty. Inflammatory markers are normal. Aspiration yields cloudy fluid with negative cultures, but significantly elevated cobalt levels compared to chromium. What is the primary mechanism of failure?
Correct Answer & Explanation
. Galvanic corrosion at the head-neck junction
Explanation
Mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck junction can occur in metal-on-polyethylene THAs. It classically presents with elevated serum or synovial cobalt levels out of proportion to chromium.
Question 4016
Topic: Infection, Pharmacology & VTE
What do the bone scan findings represent?
Correct Answer & Explanation
. Osteonecrosis
Explanation
The bone scan shows no uptake of the tracer, which indicates osteonecrosis. The MRI scan of the shoulder reveals sepsis with a focus on osteomyelitis. A CT scan will not add more useful information and will delay treatment. A sequestrum is a piece of dead bone that has become separated from normal/solid bone during the osteonecrosis process. It appears as a radiopacity on plain radiograph. The involucrum is new bone formed by an elevated periosteum and can be seen on radiograph. Heterotopic ossification appears as radiopacity within the soft tissues. Late recognition of pediatric shoulder sepsis has been reported, and damage to the joint can be extensive. Septic joints are one of the few true orthopaedic emergencies. The methodology of drainage in shoulder sepsis is controversial (aspiration vs open drainage vs arthroscopic lavage), but the joint must be drained and sterilized to prevent cartilage damage.
Question 4017
Topic: 1. General Principles & Basic Science
To control most spontaneous bleeding into the knee in children with hemophilia, factor VIII must be replaced to what percentage of normal?
Correct Answer & Explanation
. 40% to 50%
Explanation
The knee is the most common location of spontaneous bleeding in children with hemophilia. Treatment generally requires replacement to 40% to 50% of normal. For surgery, the replacement should be to 100%. The plasma level generally rises 2% for every unit (per kg body weight) of factor VIII administered.
Question 4018
Topic: 1. General Principles & Basic Science
After open reduction and internal fixation of long bone fractures, at what time period should C-reactive protein start to decrease?
Correct Answer & Explanation
. 48 hours
Explanation
C-reactive protein (CRP) should plateau at approximately 48 hours after surgical fixation of bony orthopedic injuries, and decrease thereafter. This is important to recognize, as an increasing CRP after 48 hours is predictive for postoperative infection.
Question 4019
Topic: Biology, Genetics & Bone Healing
A 4-year-old child has droopy shoulders. Examination shows that the child has a large head, short stature, and a narrow chest. Radiographs of the spine and chest show absent clavicles, delayed ossification of the pubis and ischium, and mild coxa vara. What is the inheritance pattern for this condition?
Correct Answer & Explanation
. Autosomal dominant
Explanation
The child has the clinical and radiographic features of cleidocranial dysostosis. This is a disorder of bones formed by intramembranous ossification. It is inherited as an autosomal-dominant condition. About two thirds of cases are familial.
Question 4020
Topic: Biology, Genetics & Bone Healing
A 28-year-old woman who is an avid runner reports pain about the left hip with activities. Nonsurgical management has failed to provide relief. An MRI arthrogram is shown in Figure 47. What is the most likely diagnosis? Review Topic
Correct Answer & Explanation
. Osteonecrosis
Explanation
The MRI arthrogram reveals dye extravasation into the labrum, consistent with a labral tear. The MRI findings are not typical of osteonecrosis, stress fracture, or transient osteoporosis. There is no increase in bone marrow edema in the neck or femoral head.
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