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 11401
Topic: 1. General Principles & Basic Science
Which zone of normal articular cartilage has the highest concentration of water and the lowest concentration of proteoglycans, with collagen fibers oriented parallel to the joint surface to resist shear stress?
Correct Answer & Explanation
. Superficial (tangential) zone
Explanation
The superficial (tangential) zone of articular cartilage represents the top 10-20% of the cartilage thickness. It has the highest water content, the lowest proteoglycan concentration, and type II collagen fibers that are oriented strictly parallel to the articular surface to resist shear forces. The deep zone has the highest proteoglycan concentration and lowest water content, with collagen oriented perpendicularly.
Question 11402
Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with right hip pain, a limp, and a fever of 38.6°C. He absolutely refuses to bear weight on the right leg. Blood work reveals a WBC count of 14,000/mm³ and an ESR of 45 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%
Explanation
The Kocher criteria are used to differentiate septic arthritis from transient synovitis of the pediatric hip. The four criteria are: (1) Non-weight-bearing on affected side, (2) ESR > 40 mm/hr, (3) Fever > 38.5°C, and (4) WBC count > 12,000/mm³. This patient meets all 4 criteria. The probability of septic arthritis is 3% for 1 criterion, 40% for 2, 93% for 3, and 99% for 4 criteria.
Question 11403
Topic: Physiology & Rehabilitation
During the single-leg stance phase of gait, the abductor muscles must generate sufficient torque to balance the body weight. If the distance from the body's center of gravity to the center of the femoral head is exactly three times the distance from the abductor insertion to the center of the femoral head, what is the approximate abductor muscle force required to maintain a level pelvis?
Correct Answer & Explanation
. Equal to body weight
Explanation
This illustrates the biomechanical lever arms acting around the hip joint. To maintain equilibrium (a level pelvis), the torque generated by body weight must equal the torque of the abductors. (Body Weight * 3) = (Abductor Force * 1). Therefore, Abductor Force = 3 times Body Weight. The total joint reaction force across the hip would be Body Weight + Abductor Force = 4 times Body Weight.
Question 11404
Topic: Biology, Genetics & Bone Healing
Rigid internal fixation with an absolute stability construct (e.g., a lag screw and neutralization plate) for a transverse diaphyseal fracture promotes primary bone healing. Which of the following is the primary histological mechanism by which primary bone healing occurs?
Correct Answer & Explanation
. Endochondral ossification
Explanation
Primary bone healing occurs without intermediate callus formation when there is absolute stability and compression across the fracture site. It is driven directly by Haversian remodeling, where osteoclasts create 'cutting cones' that cross the fracture line, followed immediately by osteoblasts laying down lamellar bone. Endochondral ossification is the hallmark of secondary bone healing (callus formation).
Question 11405
Topic: Biomechanics & Biomaterials
A viscoelastic orthopedic implant is subjected to a constant physiological load over a prolonged period. Over time, the material undergoes increasing progressive deformation despite the applied stress remaining unchanged. Which of the following best describes this biomechanical property?
Correct Answer & Explanation
. Creep
Explanation
Creep is a viscoelastic property characterized by progressive deformation of a material under a constant load over time. This is clinically relevant in ultra-high-molecular-weight polyethylene (UHMWPE) components. Stress relaxation, in contrast, refers to a decrease in internal stress over time when the material is held at a constant deformation.
Question 11406
Topic: Infection, Pharmacology & VTE
A 65-year-old female develops a delayed prosthetic joint infection 14 months after a total knee arthroplasty. Cultures yield Staphylococcus epidermidis. The pathogenesis of this infection relies heavily on the bacteria's ability to form a biofilm. Which bacterial surface component is most critical for the accumulation phase of biofilm formation in this organism?
Correct Answer & Explanation
. Protein A
Explanation
Biofilm formation in coagulase-negative staphylococci (like S. epidermidis) occurs in two main phases: primary attachment and accumulation. The accumulation phase is primarily mediated by the production of polysaccharide intercellular adhesin (PIA), which is encoded by the ica operon.
Question 11407
Topic: Biology, Genetics & Bone Healing
A 35-year-old male undergoes open reduction and internal fixation of a transverse radial shaft fracture using a dynamic compression plate, achieving absolute stability. Which of the following describes the primary mechanism of bone healing expected in this scenario?
Correct Answer & Explanation
. Endochondral ossification with robust soft callus formation
Explanation
When absolute stability is achieved (e.g., rigid plate fixation with anatomic reduction), secondary fracture healing (callus formation) is suppressed. The bone heals via primary (direct) bone healing, characterized by osteoclast-led cutting cones crossing the fracture gap followed immediately by osteoblast-mediated osteonal formation.
Question 11408
Topic: Biology, Genetics & Bone Healing
What is the primary mechanism by which denosumab affects bone metabolism?
Correct Answer & Explanation
. Directly induces apoptosis of osteoclasts
Explanation
Denosumab is a monoclonal antibody that targets RANKL. By binding to RANKL, it prevents it from activating the RANK receptor on osteoclast precursors, thus inhibiting their maturation, function, and survival.
Question 11409
Topic: Biomechanics & Biomaterials
During a total hip arthroplasty, the surgeon opts for a highly cross-linked polyethylene liner instead of conventional polyethylene. Which of the following best describes the primary advantage of highly cross-linked polyethylene?
Correct Answer & Explanation
. Increased resistance to catastrophic fatigue failure
Explanation
High cross-linking of polyethylene significantly reduces volumetric wear, leading to a lower incidence of particle-induced osteolysis. However, the cross-linking process can decrease the material's mechanical properties, such as fracture toughness.
Question 11410
Topic: Biology, Genetics & Bone Healing
Which phase of fracture healing is characterized by the peak activity of chondrocytes and the formation of a soft callus?
Correct Answer & Explanation
. Inflammation
Explanation
The reparative phase is characterized by the formation of a soft callus. During this phase, chondrocytes produce a cartilaginous matrix that bridges the fracture gap prior to endochondral ossification.
Question 11411
Topic: Biology, Genetics & Bone Healing
The "creeping substitution" process observed in the incorporation of a massive structural cortical bone allograft is primarily mediated by which of the following mechanisms?
Correct Answer & Explanation
. Direct differentiation of host mesenchymal stem cells into osteocytes
Explanation
Creeping substitution is the process by which a bone graft is slowly resorbed by host osteoclasts and simultaneously replaced by host osteoblasts laying down new bone. Cortical allografts undergo this process much slower than cancellous autografts.
Question 11412
Topic: Biology, Genetics & Bone Healing
A 32-year-old male sustains a midshaft radius fracture treated with open reduction and internal fixation using a dynamic compression plate to achieve absolute stability. Which of the following best describes the predominant mechanism of bone healing in this scenario?
Correct Answer & Explanation
. Endochondral ossification
Explanation
Absolute stability achieved by dynamic compression plating leads to primary bone healing. This process relies on osteoclastic cutting cones crossing the fracture site, followed by osteoblastic bone deposition, without the formation of an intermediate callus.
Question 11413
Topic: 1. General Principles & Basic Science
Articular cartilage is composed of multiple zones with distinct structural properties. In which zone are the collagen fibers oriented parallel to the articular surface, providing the highest resistance to shear forces?
Correct Answer & Explanation
. Superficial (tangential) zone
Explanation
Articular cartilage consists of multiple zones with specific collagen fiber orientations. The superficial (tangential) zone contains tightly packed collagen fibers aligned parallel to the joint surface, providing primary resistance to shear forces.
Question 11414
Topic: Biomechanics & Biomaterials
During total hip arthroplasty, what characteristic of irradiated (10 Mrad) and subsequently melted highly
cross-linked polyethylene should provide a more wear-resistant construct than traditional gamma- irradiated (2.5-4 Mrad)-in-air polyethylene mated with the same head?
Correct Answer & Explanation
. Resistance to adhesive wear
Explanation
Highly cross-linked polyethylene makes material resistant to adhesive wear. Abrasive wear from third bodies does not decrease wear. The fatigue strength of such material is inferior to that of traditional polyethylene, and its resistance to creep is the same, if not lower, than that of traditional polyethylene.
Question 11415
Topic: 1. General Principles & Basic Science
Figure below depicts the radiograph obtained from a 52-year-old woman who has leg-length inequality
and chronic, activity-related buttock discomfort. This problem has been lifelong, but it is getting worse and increasingly causing back pain. What is the best current technique for total hip arthroplasty?
Correct Answer & Explanation
. High hip center
Explanation
A high hip center is not recommended for Crowe type 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 versus oblique cut, or strut grafts.
Question 11416
Topic: 1. General Principles & Basic Science
A 61-year-old man with a body mass index of 31 had a 6-month gradual onset of right medial knee pain.
Examination revealed a small effusion, stable ligaments, a normally tracking patella, and mild medial joint line tenderness. Standing radiographs show mild medial joint space narrowing. Effective treatment at this stage of early medial compartmental osteoarthritis includes
Correct Answer & Explanation
. glucosamine 1,500 mg/day and chondroitin sulfate 800 mg/day.
Explanation
According to the 2008 AAOS Clinical Practice Guideline, Treatment of Osteoarthritis of the Knee (Nonarthroplasty), level 1 evidence confirms that weight loss and exercise benefit patients with knee osteoarthritis. The other responses have either inclusive evidence (a valgus-directing brace) or no evidence to support their use (glucosamine 1,500 mg/day and chondroitin sulfate 800 mg/day as well asarthroscopic debridement and lavage).
Question 11417
Topic: 1. General Principles & Basic Science
A surgeon prepares a medial gastrocnemius rotational flap to cover a medial proximal tibia defect at the
time of revision knee replacement surgery. To optimize coverage, the surgeon must optimally mobilize which artery?
Correct Answer & Explanation
. Profunda femoris
Explanation
The medial sural arteries vascularize the gastrocnemius, plantaris, and soleus muscles proximally. These arteries arise from the popliteal artery. If this artery is not adequately mobilized, a gastrocnemius soleus flap can be devascularized.
Question 11418
Topic: Infection, Pharmacology & VTE
Hip pain of 1-month duration has developed in a 72-year-old man with a previous total hip arthroplasty. He underwent dental work 6 weeks ago. Aspiration shows a white blood cell count of more than 6,000 cells/μL (reference range 4,500 to 11,000 cells/μL) and the presence of gram-positive cocci in clusters on Gram stain. The orthopaedic surgeon recommends urgent debridement and irrigation. Fixation of the components is judged to be stable, and the surgeon elects to retain the implants. The patient has a final culture that reveals methicillin-resistant Staphylococcus aureus (MRSA). If the attending physician recommends the two-stage protocol, including the use of an antibiotic-cement spacer, what is the most likely prognosis for this patient?
Correct Answer & Explanation
. Poorer prognosis for eradication of infection than that associated with infection from sensitive organisms
Explanation
The patient has a late infection of at least 4 weeks symptomatic duration that most likely is hematogenous in etiology. This infection is not an acute hematogenous infection that can successfully be treated with irrigation and debridement. Retention of the implants with debridement and irrigation alone has been associated with a poor prognosis. In a recent study, the success rate was only 44% in a series of 104 patients at a mean 5.7-year follow-up. In one study of 50 infections attributable to MRSA or methicillin-resistant Staphylococcus epidermidis organisms treated with a two-stage protocol, the failure rate was 21%. Patients who experienced successful infection treatment had lower functional outcome measures using the Western Ontario and McMaster Universities Osteoarthritis Index, the University of California Los Angeles Activity Score, and the 12-item Oxford Knee Score, however.
Question 11419
Topic: Infection, Pharmacology & VTE
An 80-year-old African American woman who lives in a large city is scheduled for total hip arthroplasty
to address primary osteoarthritis. Part of the presurgical protocol includes nasal swab screening to assess for methicillin-resistant Staphylococcus aureus (MRSA) colonization. Which demographic factor places this patient at highest risk for a positive result?
Correct Answer & Explanation
. Gender
Explanation
Demographic factors are associated with increased risk for MRSA colonization, so it is important to identify vulnerable patients. Female gender and advanced age reduce the risk for colonization, whereas African American race increases this risk. Urban environments do not influence MRSA colonization.
Question 11420
Topic: Infection, Pharmacology & VTE
Figure below shows the abdominal radiograph obtained from a 70-year-old woman who experiences
nausea and abdominal tightness 48 hours following left total knee arthroplasty performed under general anesthesia. She received 24 hours of cefazolin antibiotic prophylaxis and a patient-controlled analgesia narcotic pump for pain management. She has been receiving warfarin for thromboembolic prophylaxis. Her severe abdominal distension and markedly decreased bowel sounds are most likely secondary to the administration of
Correct Answer & Explanation
. general anesthesia.
Explanation
The radiograph reveals severe intestinal dilatation, which has occurred as the result of acute colonic pseudo-obstruction and is associated with excessive narcotic administration following total joint arthroplasty. Anesthetic type, antibiotic administration, and warfarin have not been associated with this obstruction. Electrolyte imbalances such as hypokalemia have been associated with postsurgical acute colonic pseudo-obstruction.
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