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1. General Principles & Basic Science MCQs

Practice Set 63 of 789

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 1241

Topic: Physiology & Rehabilitation

Which of the following statements about the gait cycle is true:

. The swing phase is longer than the stance phase and lasts for 62% of the cycle.
. From heel rise to toe-off, the tibia goes into external rotation.
. At heel strike, the anterior tibialis muscle is quiescent.
. At toe-off, the gastroc-soleus complex is eccentric contracting.
. From heel strike to toe-off, the transverse tarsal joint unlocks.

Correct Answer & Explanation

. From heel rise to toe-off, the tibia goes into external rotation.

Explanation

Discussion Because gait cycle questions are common on examinations, remember the following points: Stance phase: 62% of cycle Swing phase: 38% of cycle Muscle firing Electromyography findings during gait cycle: Muscle Activity Heel strike Anterior tibialis Gastroc-soleus Eccentric contraction Quiet Foot flat Anterior tibialis Gastroc-soleus Quiet Eccentric contraction Heel-off Gastroc-soleus C oncentric contraction Toe-off Gastroc-soleus C oncentric contraction Subtalar joint Heel strike to foot flat: Three important points Eversion of the subtalar joint Unlocking of the transverse tarsal joint Internal rotation of the tibia Heel rise to toe-off Inversion of the subtalar joint Locking of the transverse tarsal joint External rotation of the tibia

Question 1242

Topic: Infection, Pharmacology & VTE

Which of the following medications is an effective alternative to intravenous vancomycin for the treatment of severe soft tissue infections caused by methicillin-resistant Staphylococcus aureus (MRSA):

. C iprofloxacin
. Dicloxacillin
. Linezolid
. Gentamicin
. C lindamycin

Correct Answer & Explanation

. Linezolid

Explanation

Oral linezolid (600 mg twice a day) is an effective oral alternative to intravenous vancomycin. Below is a summary of a recent prospective, randomized study showing the efficacy of linezolid. Staphylococcus aureus complicates soft tissue and skin infections. Approximately 30% of S aureus infections are methicillinresistant. Although vancomycin has been the treatment of choice for MRSA, linezolid inhibits bacterial protein synthesis by blocking formation of the 70S initiation complex and can be administered orally, which is an advantage over vancomycin. This is a single-center study of adult patients. Investigators randomized 60 patients with S aureus (culture proven) to intravenous vancomycin or oral linezolid. The median length of therapy was 10 days. Seven patients in the vancomycin group required amputation, whereas no amputations were performed in the linezolid group. The median length of hospital stay was shorter in the linezolid group, and outpatient therapy was $100 per day less expensive (approximately $6,500 was saved on the hospital stay). A higher clinical cure rate (94%) was reported with the linezolid group compared to 84% with vancomycin. Linezolid is given orally, 600 mg every 12 hours, and it is well tolerated. No adverse effects were reported in this study. Other studies have had similar results. This is an important study for orthopedic surgeons because the number of patients presenting with MRSA infections is increasing. Athletes may be at an increased risk for the infection because of the potential for spread in locker rooms. This can be a limb-threatening infection and must be taken seriously.

Question 1243

Topic: Infection, Pharmacology & VTE

The mechanism of action of linezolid is:

. Inhibition of cell wall synthesis
. Inhibition of ribonucleic acid synthesis
. Inhibition of deoxyribonucleic acid synthesis
. Inhibition of the 70S initiation complex
. Inhibition of protein prehylation

Correct Answer & Explanation

. Inhibition of the 70S initiation complex

Explanation

Oral linezolid (600 mg twice a day) is an effective oral alternative to intravenous vancomycin. Below is a summary of a recent prospective, randomized study showing the efficacy of linezolid. Staphylococcus aureus complicates soft tissue and skin infections. Approximately 30% of S aureus infections are methicillinresistant. Although vancomycin has been the treatment of choice for methicillin- resistant S aureus (MRSA), linezolid inhibits bacterial protein synthesis by blocking formation of the 70S initiation complex and can be administered orally, which is an advantage over vancomycin. This is a single-center study of adult patients. Investigators randomized 60 patients with S aureus (culture proven) to intravenous vancomycin or oral linezolid. The median length of therapy was 10 days. Seven patients in the vancomycin group required amputation, whereas no amputations were performed in the linezolid group. The median length of hospital stay was shorter in the linezolid group, and outpatient therapy was $100 per day less expensive (approximately $6,500 was saved on the hospital stay). A higher clinical cure rate (94%) was reported with the linezolid group compared to 84% with vancomycin. Linezolid is given orally, 600 mg every 12 hours, and it is well tolerated. No adverse effects were reported in this study. Other studies have had similar results. This is an important study for orthopedic surgeons because the number of patients presenting with MRSA infections is increasing. Athletes may be at an increased risk for the infection because of the potential for spread in locker rooms. This can be a limb-threatening infection and must be taken seriously.

Question 1244

Topic: Infection, Pharmacology & VTE

A 25-year-old minor league baseball player has a severe soft tissue infection on the sole of his foot. The infection has not responded to oral cephalexin. There is 4 cm of surrounding erythema and induration, and a small amount of exudate can be expressed. The most likely organism is:

. Streptococcus
. Staphyloccus aureus
. Methicillin-resistant S aureus (MRSA)
. Corynebacterium
. Enteroccocus

Correct Answer & Explanation

. Methicillin-resistant S aureus (MRSA)

Explanation

Staphylococcus aureus complicates soft tissue and skin infections. Approximately 30% of S aureus infections are methicillinresistant. Although vancomycin has been the treatment of choice for MRSA, linezolid inhibits bacterial protein synthesis by blocking formation of the 70S initiation complex and can be administered orally, which is an advantage over vancomycin. This is a single-center study of adult patients. Investigators randomized 60 patients with S aureus (culture proven) to intravenous vancomycin or oral linezolid. The median length of therapy was 10 days. Seven patients in the vancomycin group required amputation, whereas no amputations were performed in the linezolid group. The median length of hospital stay was shorter in the linezolid group, and outpatient therapy was $100 per day less expensive (approximately $6,500 was saved on the hospital stay). A higher clinical cure rate (94%) was reported with the linezolid group compared to 84% with vancomycin. Linezolid is given orally, 600 mg every 12 hours, and it is well tolerated. No adverse effects were reported in this study. Other studies have had similar results. This is an important study for orthopedic surgeons because the number of patients presenting with MRSA infections is increasing. Athletes may be at an increased risk for the infection because of the potential for spread in locker rooms. This can be a limb-threatening infection and must be taken seriously.

Question 1245

Topic: Surgical Anatomy & Approaches

The direct anterior approach to the hip for total hip arthroplasty utilizes a true internervous plane. Which two muscles define this superficial surgical interval?

. Gluteus medius and Tensor fasciae latae
. Tensor fasciae latae and Sartorius
. Sartorius and Rectus femoris
. Rectus femoris and Tensor fasciae latae
. Gluteus maximus and Gluteus medius

Correct Answer & Explanation

. Tensor fasciae latae and Sartorius

Explanation

The superficial internervous plane for the direct anterior (Smith-Petersen) approach is between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve).

Question 1246

Topic: Biology, Genetics & Bone Healing

A 35-year-old female is diagnosed with a giant cell tumor of the distal femur. If medical therapy is considered for an unresectable lesion, denosumab may be used. What is the mechanism of action of denosumab?

. Monoclonal antibody against the RANK receptor on osteoclasts
. Monoclonal antibody against RANKL, preventing osteoclast activation
. Direct inhibition of osteoblast apoptosis
. Stimulation of osteoclast differentiation and apoptosis
. Binding directly to osteoprotegerin to increase bone mass

Correct Answer & Explanation

. Monoclonal antibody against RANKL, preventing osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), preventing it from activating RANK on the surface of osteoclasts, thereby inhibiting bone resorption.

Question 1247

Topic: Biology, Genetics & Bone Healing

A 68-year-old female on long-term bisphosphonate therapy presents with a non-traumatic thigh ache. Radiographs reveal an incomplete atypical femoral fracture. Where does the cortical thickening and fracture initiation typically occur in these injuries?

. Medial cortex with a spiral pattern
. Medial cortex as a tension failure
. Lateral cortex as a tension failure with a transverse or short oblique pattern
. Anterior cortex of the femoral neck
. Posterior cortex of the intertrochanteric line

Correct Answer & Explanation

. Lateral cortex as a tension failure with a transverse or short oblique pattern

Explanation

Atypical femur fractures associated with prolonged bisphosphonate use characteristically originate at the lateral cortex (the tension side) with localized periosteal thickening and a transverse or short oblique fracture pattern.

Question 1248

Topic: 1. General Principles & Basic Science

A 43-year-old diabetic patient has had an ulcer on the plantar aspect of her foot for 9 months. She has no systemic symptoms. There is minimal drainage from the ulcer, and she has no pain in the foot. Initial management of this patient must include:

. C ulture and sensitivity of the ulcer with initiation of culture-specific antibiotic therapy
. A technetium bone scan to determine the presence of osteomyelitis
. An indium scan to determine the presence of osteomyelitis
. A total contact cast
. Irrigation and debridement of the ulcer, deep tissue cultures, and appropriate antibiotic therapy

Correct Answer & Explanation

. A total contact cast

Explanation

This neuropathic ulcer is stable. There is minimal drainage and no clinical findings to suggest an active infection. C ulture of the ulcer yields multiple nonpathogenic organisms and antibiotic therapy is not indicated. Treatment is initiated with either a total contact cast or a total contact walker boot.C orrect Answer: A total contact cast

Question 1249

Topic: 1. General Principles & Basic Science

A 53-year-old woman presents for treatment of recurrent symptoms following excision of a third web space interdigital neuroma. She was asymptomatic for 6 months following surgery. On examination, pain is present in the third web space and reproduced with compression of the forefoot. The likelihood of a good result following revision surgery is:

. 50%
. 60%
. 70%
. 80%
. 90%

Correct Answer & Explanation

. 50%

Explanation

The reported results following revision surgery following recurrence of symptoms after excision of an interdigital neuroma are poor. In a large series, Stamatis and Myerson reported less than a 50% good outcome following revision surgery.

Question 1250

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) and BMP-7 promote bone healing primarily through which of the following molecular intracellular pathways?

. Inhibition of osteoclastogenesis via RANKL blockade
. Direct stimulation of angiogenesis via VEGF upregulation
. Activation of the SMAD signaling pathway
. Enhancement of Wnt/beta-catenin signaling
. Suppression of sclerostin production

Correct Answer & Explanation

. Activation of the SMAD signaling pathway

Explanation

BMPs bind to serine/threonine kinase receptors on mesenchymal stem cells, phosphorylating intracellular SMAD proteins (SMAD 1/5/8). These proteins then translocate to the nucleus to induce osteogenic gene transcription.

Question 1251

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with an acute limp, fever of 38.8°C, refusal to bear weight, and a WBC count of 14,000/mm³. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. Less than 10%
. Approximately 40%
. Approximately 93%
. Greater than 99%

Correct Answer & Explanation

. Approximately 93%

Explanation

The Kocher criteria evaluate four predictors: non-weight-bearing, ESR >40 mm/hr, fever >38.5°C, and WBC >12,000/mm³. Having three of these four predictors yields a 93% probability of septic arthritis.

Question 1252

Topic: Infection, Pharmacology & VTE

A 60-year-old patient with poorly controlled diabetes presents with a deep, non-healing plantar ulcer probing to bone. MRI confirms osteomyelitis of the first metatarsal head. Which of the following is the most definitive method to identify the causative organism and direct targeted antibiotic therapy?

. Superficial swab of the ulcer base
. Blood cultures
. Fine needle aspiration of the surrounding cellulitis
. Bone biopsy for culture and histology
. MRI with gadolinium enhancement

Correct Answer & Explanation

. Bone biopsy for culture and histology

Explanation

Bone biopsy is the gold standard for diagnosing osteomyelitis and accurately directing pathogen-specific antibiotic therapy. Superficial swabs often isolate colonizing flora rather than the true bone pathogen, leading to inadequate treatment.

Question 1253

Topic: 1. General Principles & Basic Science

The most common complication after resection of a plantar fibromatosis is:

. A recurrent fibroma
. Infection
. Wound dehiscence
. Injury to the medial plantar nerve
. Injury to the lateral plantar nerve

Correct Answer & Explanation

. A recurrent fibroma

Explanation

The most common complication after resection of plantar fibromatosis is recurrence. Although other complications (nerve injury and wound dehiscence) do occur, they occur less frequently. The most reliable treatment for plantar fibromatosis is observation and shoe wear modification if the lesion is painful.

Question 1254

Topic: 1. General Principles & Basic Science

The most reliable indication of an interdigital neuroma in the second web space is:

. Pain upon compression of the web space
. A painful click in the web space when compressing the forefoot
. Absent sensation between the second and third toes
. Burning, tingling, and numbness of the third toe
. A neuroma of the second web space visible on magnetic resonance image

Correct Answer & Explanation

. Pain upon compression of the web space

Explanation

A click when compressing the forefoot (referred to as a positive Mulder sign) is not diagnostic of a neuroma and is present due to an enlarged intermetatarsal bursa. The sensation of pain and burning is varied, and some patients report only a vague numbness. Magnetic resonance imaging can have a false positive and false negative result; therefore, it must not be relied upon for diagnosis. The most reliable finding on physical examination is pain on compression of the affected web space.

Question 1255

Topic: 1. General Principles & Basic Science

The strongest plantarflexor of the metatarsophalangeal (MP) joint of the lesser toes is the:

. Long flexor tendon
. Volar plate
. Lumbrical tendon
. Short flexor tendon
. Interosseous tendon

Correct Answer & Explanation

. Interosseous tendon

Explanation

Although the short flexor tendon plantarflexes the MP joint of the lesser toes, the interosseous tendons are stronger. When intrinsic atrophy or dysfunction of the forefoot is present, an intrinsic minus deformity occurs. The long flexor tendon does not flex the MP joint.

Question 1256

Topic: Biology, Genetics & Bone Healing

A closed tibia fracture is treated with a long leg cast. The fracture heals primarily through callus formation. This type of bone healing relies fundamentally on which cellular process?

. Intramembranous ossification
. Endochondral ossification
. Haversian remodeling
. Primary bone healing
. Creeping substitution

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary bone healing (callus formation), typically seen with cast immobilization or relative stability, occurs mainly via endochondral ossification. In this process, a cartilage model is initially formed and subsequently replaced by bone.

Question 1257

Topic: Biology, Genetics & Bone Healing

A 45-year-old man undergoes open reduction and internal fixation of a transverse radial shaft fracture using a dynamic compression plate providing absolute stability. Which of the following histologic processes predominantly characterizes the bone healing in this scenario?

. Endochondral ossification
. Intramembranous ossification with bridging callus
. Primary bone healing via cutting cones
. Fibrous tissue interposition followed by calcification
. Chondrocyte hypertrophy and apoptosis

Correct Answer & Explanation

. Primary bone healing via cutting cones

Explanation

Rigid internal fixation providing absolute stability and anatomic reduction bypasses callus formation. It relies on primary (direct) bone healing via osteoclast cutting cones that cross the fracture gap, followed directly by osteoblastic bone deposition.

Question 1258

Topic: Biology, Genetics & Bone Healing

A basic science researcher is studying the mechanics of fracture healing.

Under conditions of absolute stability, such as rigid compression plating where the fracture site experiences less than 2% interfragmentary strain, which biological process predominantly dictates bone healing?

. Endochondral ossification
. Primary bone healing via cutting cones
. Secondary bone healing with robust callus formation
. Fibrocartilaginous callus maturation
. Intramembranous ossification alone

Correct Answer & Explanation

. Primary bone healing via cutting cones

Explanation

Absolute stability yielding less than 2% strain suppresses callus formation and permits primary bone healing. This process occurs directly via osteoclastic cutting cones crossing the fracture gap, closely followed by osteoblasts laying down new lamellar bone.

Question 1259

Topic: Biology, Genetics & Bone Healing

A diaphyseal tibial fracture is treated with a rigid locked intramedullary nail. Which type of bone healing predominantly occurs in this scenario?

. Primary bone healing via cutting cones
. Secondary bone healing with callus formation
. Intramembranous ossification exclusively
. Endochondral ossification exclusively
. Creeping substitution

Correct Answer & Explanation

. Secondary bone healing with callus formation

Explanation

Intramedullary nailing provides relative stability rather than absolute stability. This biomechanical environment promotes secondary bone healing through the formation of a soft and hard fracture callus.

Question 1260

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with refusal to bear weight on his right leg. He has a temperature of 38.8°C (101.8°F), an ESR of 50 mm/hr, and a WBC count of 14,000/mm³. Based on Kocher's criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

Kocher's criteria include non-weight-bearing, fever >38.5°C, ESR >40, and WBC >12,000. With all 4 criteria present, the predicted probability of septic arthritis is approximately 99%.

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