Prosthetic placement in a cement-filled canal creates highest peak elevations in pressure when:

1) Using a cement restrictor

3) Using mechanical pressurization

2) Using a retrograde filling

5) Inserting the prosthesis early, while the cement is extremely soft

4) Inserting the prosthesis late in the setting phase

Prosthetic placement in the cement-filled femoral canal creates transiently higher peak elevations in pressure when inserted late in the setting phase. It creates higher pressures than those obtained with a cement restrictor, retrograde filling, or mechanical pressurization.Correct Answer: Inserting the prosthesis late in the setting phase

1. (2649) Q1-3140:

   The time it takes for the polymer/monomer mixing until polymerization is sufficient to maintain the implant in its correct position is known as:

   1) Doughing time

   3) Setting time

   2) Working time

   5) Polymerization time

   4) Mixing time

   The setting process is described by three critical time periods, which include doughing time, working time, and setting time. The doughing time begins when the polymer and the monomer are mixed until the time when the mixture will not adhere to a gloved hand anymore. Working time implies the time from the start of kneading until the cement is too stiff to be delivered in the bone. The setting time implies the time from the polymer/monomer mixing until polymerization is sufficient to maintain the correct implant position.Correct Answer: Setting time

(2650) Q1-3141:

Cement takes longer to set when using a:

1) Roughened stem

3) Polished femoral stem

2) Precoated femoral stem

5) Cement setting time is not affected by the femoral stem.

4) Irregular femoral stem

Cement sets sooner when using a roughened or precoated femoral stem. It sets later when using a finely polished femoral stem because the cement-prosthesis bond is not influenced by the wetness of the cement.Correct Answer: Polished femoral stem

(2651) Q1-3142:

Acrylic bone cement is composed of:

1) A polymer powder and a polymer liquid component

3) A polymer powder and a monomer liquid component

2) A monomer powder and a monomer liquid component

5) Polymethylmethacrylate (PMMA) only

4) A monomer powder and a polymer liquid component

Polymethylmethacrylate (PMMA) is one of the ingredients of acrylic bone cement. The two components of bone cement are a polymer powder component and a monomer liquid component. A blend of ingredients in the polymer and monomer (which includes PMMA) gives cement its unique characteristics.Correct Answer: A polymer powder and a monomer liquid component

The chemical composition of acrylic bone cement is:

1) Benzoyl peroxide and barium sulfate

3) Methylmethacrylate-styrene-copolymer and polymethylmethacrylate

2) Methylmethacrylate-styrene-copolymer

5) Polymethylmethacrylate and dimethyl-p-toluidine

4) Methylmethacrylate-styrene-copolymer, polymethylmethacrylate, and barium sulfate

When the monomer liquid is added to the polymer powder, the polymer powder dissolves and releases benzoyl peroxide from the polymer. The benzoyl peroxide initiates a reaction with n,n-dimethyl-p-toluidine in the monomer, which accelerates the chemical reaction and polymerization. When complete, acrylic bone cement is composed of 75% methylmethacrylate-styrene-copolymer, 15% polymethylmethacrylate, and 10% barium sulfate.Correct Answer: Methylmethacrylate-styrene-copolymer, polymethylmethacrylate, and barium sulfate

(2653) Q1-3144:

Bone cement was first used commercially:

1) During World War II in the production of airplane windshields

3) By John Charnley for bonding total hip joints to bone

2) In dentistry for filling cavities

5) As a base material for dentures

4) By neurosurgeons for replacement of skull defects

Otto Rohm, MD, developed polymethylmethacrylate and introduced it into commercial application. In the 1930s, bone cement was first used commercially as a base material for dentures.Correct Answer: As a base material for dentures

(2654) Q1-3145:

The longest period of survival for cemented total joints is associated with which type of cementation technique:

1) Grade A

3) Grade C 1

2) Grade B

5) Grade D

4) Grade C 2

The grade A cementation technique is the most advantageous and is associated with the longest period of survival in total joint replacement. One cannot clearly distinguish between the edge of the cement and the edge of the surrounding bone.Correct Answer: Grade A

(2655) Q1-3146:

Which of the following prosthetic areas is classified as a grade 4 Gruen zone radiographic defect:

1) The medullary distal tip of the prosthesis and the cement

3) The lateral lower third of the prosthesis

2) The lateral middle part of the prosthesis

5) The middle part, medial of the prosthesis

4) The medial distal third of the prosthesis

Gruen zones are an effective international classification system whereby radiographic defects or errors are evaluated and documented according to zones around a prosthesis. The classification begins with grade 1, which is lateral in the area of the greater trochanter to just below the lesser trochanter. Grade 4 is a radiographic defect located at the medullary distal tip of the prosthesis and the cement.Correct Answer: The medullary distal tip of the prosthesis and the cement

Which of the following grades classifies the mode of failure of cemented femoral components in which the whole proximal part of the prosthesis is denude of bone cement and rocks back and forth in the distal part that is fixed with bone cement:

1) Grade Ia

3) Grade III

2) Grade II

5) Grade Ib

4) Grade IV

Modes of failure of cemented femoral components are classified into four grades. In a grade Ia, subsidence of the metal prosthesis in the cement mantle is present. Grade Ib implies that the cement and stem are pistoning distalward. Grade II implies medial migration of the proximal stem and lateral migration of the distal stem. Grade III is classified by a pivot of the calcar part of the prosthesis. Grade IV implies that the whole proximal part of the prosthesis is denude of bone cement and rocks back and forth in the distal part that is fixed with bone cement.Correct Answer: Grade IV

(2657) Q1-3148:

Which of the following latex-free gloves are destroyed by bone cement:

1) Allegard latex-free gloves (Johnson & Johnson, New Brunswick, NJ)

3) Neotech (Regent Medical)

2) Biogel (Regent Medical, Norcross, GA)

5) No latex-free gloves are destroyed by bone cement.

4) Duraprene

Not all brands of latex-free gloves are equally effective. Bone cement destroys Allegard latex-free gloves.Correct Answer: Allegard latex-free gloves (Johnson & Johnson, New Brunswick, NJ)

(2658) Q1-3149:

Which of the following is not a factor in the setting time of cement:

1. Storage temperature of bone cement

   3) Handling and kneading of bone cement

   2) Ambient temperature

   5) Introducing bone cement in a warm environment

   4) Use of a cement gun

   Storage temperature, ambient temperature, handling and kneading of bone cement, and introducing cement in a warm environment are factors of the setting time of cement. Use of a cement gun is not a factor.Correct Answer: Use of a cement gun

2. (3067) Q1-3575:

With the use of perineural catheters, improvement in all of the following outcomes can be anticipated except:

1. Lower pain scores

   3) Reduced incidence of nausea and vomiting

   2) Narcotic sparing effect

   5) Shortened length of stay

   4) Increased sleep disturbances

   Double blind placebo controlled randomized trials the use of perineural catheters led to improved pain scores, decreased narcotic usage and narcotic related side effects, and fewer sleep disturbances.

   Length of stay was shortened by the use of perineural catheters as compared to epidural or IV PCA analgesia in several studies. In pilot studies, the use of perineural catheters in carefully selected patients allowed ambulatory total shoulder arthroplasty and single day admissions for total hip arthroplasty and total knee arthroplasty.Correct Answer: Increased sleep disturbances

   The addition of a sciatic nerve block to a femoral nerve block will:

Enhance analgesia following knee surgery

3) Provide complete anesthesia to the knee

2) Improve mobility

5) Decrease DVT formation

4) Increase the likelihood of nerve injury

Pain from the posterior aspect of the knee joint is diminished with the addition of a sciatic nerve block to complement a femoral nerve block.

The use of combined femoral sciatic nerve block impairs ambulation because of the degree of extensive motor block of the quadriceps and muscles of the lower leg. In addition, proprioception that aids in balance is diminished with peripheral nerve block.

The obturator nerve, which contributes to the innervation of the knee capsule, is more frequently anesthetized with a lumbar plexus (posterior approach) than an anterior femoral nerve block. Because of the variability of the cutaneous innervation of the obturator nerve, the only reliable test for measuring obturator nerve block is motor block of the adductors of the thigh. The addition of a sciatic nerve block will not improve obturator nerve blockade.

Nerve injury after peripheral nerve block of lower extremity is uncommon (<1 in 5,000). The incidence is no higher after combined femoral sciatic nerve blocks than after single nerve blocks.

Theoretically, the likelihood of DVT formation should be decreased in patients receiving a combined femoral and sciatic nerve blocks compared to patients who receive no regional anesthesia because of the profound degree of vasodilatation induced by the sympathetic block to the lower extremity. To date, no large studies have been performed to prove or disprove this theoretical advantage.

Correct Answer: Enhance analgesia following knee surgery

395. (3238) Q1-4060:

What percent of asymptomatic osteonecrosis (Stage I Steinberg) with steroid use, alcohol abuse, or an idiopathic etiology progress to painful symptoms:

1) 10%

3) 50%

2) 30%

5) 90%

4) 70%

In several combined studies that involved 83 asymptomatic stage 1 osteonecrosis of the femoral head associated with steroid use, alcohol abuse, or idiopathic etiology, only 27 (33%) hips progressed to symptoms after 6 to 36 months.

TABLE II. Review of the Literature of the Evolution for other Asymptomatic Stage-I Hips Treated Nonoperatively

Study	Number of Hips	Duration of Follow-up(mo)	Symptomatic Progression
Stulberg et al	3	26.8	2 of 3
Kopecky et al	25	16	7 of 25
Takatori et al	32	20.9	14 of 32
Fordyce and Solomon	5	36	2 of 5
Mulliken et al	11	22	0 of 11
Davidson	7	6.5	2 of 7
Total			27 of 83

Correct Answer: 30%

In addition to developing pain, what percent of patients with asymptomatic osteonecrosis and sickle cell disease will have hips that collapse:

1) 10%

3) 50%

2) 30%

5) 90%

4) 70%

Seventy-seven percent of 121 asymptomatic hips studied by Hernigou and colleagues went on to collapse. Their results suggest that patients with sickle cell disease with asymptomatic stage I and II osteonecrosis is more rapid and frequent than previously assumed with osteonecrosis related to steroid or alcohol use.Correct Answer: 70%

(3240) Q1-4062:

Which of the following percentages represents the number of patients with homozygous sickle cell disease that will develop osteonecrosis of the femoral head by age 35:

1) 10%

3) 50%

2) 30%

5) 90%

4) 70%

Osteonecrosis of the femoral head is a common complication in patients with sickle cell disease, and the prevalence of complications peaks in adolescence. Osteonecrosis of the femoral head develops by the age of 35 in nearly half of all patients with homozygous sickle cell disease.Correct Answer: 50%

(3241) Q1-4063:

Bilateral hip involvement with osteonecrosis is seen in what percent of patients with sickle cell disease:

1) 5%

3) 20%

10%

5) 50%

4) 30%

Bilateral hip involvement in patients with sickle cell disease with osteonecrosis is found in 40% to 90% of all patients. Without intervention, the rate of femoral head collapse in patients with sickle cell disease is 87% within 5 years after initial diagnosis of the osteonecrosis, but it can be as high as 90% within 2 years after the initial diagnosis.Correct Answer: 50%

Failure rates, based on pain and limitation of motion, after total hip replacements (THR) in patients with sickle cell disease is:

1) 10%

(3242) Q1-4064:

1. 50%

25%

5) 90%

4) 75%

Seventy-five percent of patients with sickle cell disease who had undergone THR were found to have ongoing pain and substantial limitation of motion. Because of these unfavorable results, there is considerable interest in evaluating treatment regimens that will postpone the need for THR in this population.Correct Answer: 75%

What is the prevalence of sickle cell disease among African Americans:

1) 1/6

1. 1/600

1/60

5) 1/60,000

4) 1/6000

Sickle cell disease denotes all genotypes containing one sickle cell gene and another variant hemoglobin encoding gene (eg, HbC, HbS, HbD). These result in phenotypes where HbS constitutes at least 50% of the present hemoglobin. It is estimated that 1 of every 600 African Americans has sickle cell disease. Six major subsets of sickle cell disease exist, with mutation type determining disease severity.Correct Answer: 1/600

401. (3244) Q1-4067:

In patients with sickle cell disease, what are the most commonly affected locations for osteonecrosis:

1. Distal radial and distal humerus

1. Distal femur and proximal tibia

1. Head of femur and head of humerus

5) Metacarpals and phalanges

4) Head of humerus and proximal tibia

The prevalence of osteonecrosis in patients with sickle cell disease is as high as 37% to 50%. Osteonecrosis most commonly occurs in the humeral and femoral heads, due to their limited arterial network, which can easily succumb to occlusion by sickled cells.Correct Answer: Head of femur and head of humerus

402. (3245) Q1-4068:

Appropriate indications for preoperative transfusion therapy in patients with sickle cell include:

1) Hemoglobin <5g/dL with clinical signs/symptoms of anemia.

3) Acute chronic anemia with severe aplastic anemia.

2) Pulmonary acute chest syndrome with multisegmental disease or hypoxia.

5) Hemoglobin <5g/dL with clinical signs/symptoms of anemia, acute chronic anemia with severe aplastic anemia, and pulmonary acute chest syndrome with multisegmental disease or hypoxia.

4) Hemoglobin <5g/dL with clinical signs/symptoms of anemia, and acute chronic anemia with severe aplastic anemia.

The need for transfusion therapy is based on the overall clinical history of the individual patient. Commonly cited indications include:

Patients with hemoglobin <5 g/dL and significant signs of anemia Pulmonary acute chest syndrome with multisegmental disease or hypoxia Acute or chronic anemias with severe aplastic anemias

Correct Answer: Hemoglobin <5g/dL with clinical signs/symptoms of anemia, acute chronic anemia with severe aplastic anemia, and pulmonary acute chest syndrome with multisegmental disease or hypoxia.

403. (3246) Q1-4069:

What is the most common postoperative complication in patients with sickle cell disease:

1) Acute chest syndrome

3) Neurological events

2) Vaso-occulsive crisis

5) None of the above

4) Renal events

Postoperative management consists of intravenous hydration, supplemental oxygen, intravenous antibiotics, chest physiotherapy, and incentive spirometry. Common complications encountered in the early postoperative period include acute chest syndrome (12%), vaso-occlusive crisis (9%), and less commonly, neurological and renal events.Correct Answer: Acute chest syndrome

1) Cardiac rhythm monitoring

3) Active warming

2) Oxygen saturation monitoring

5) All of the above

4) Blood pressure monitoring

The most common intraoperative complications are excessive blood loss (53%), followed by hypothermia (11%). Therefore, patients require extensive monitoring of cardiac rhythm, blood pressure, temperature, and oxygen saturation. They also need active intraoperative warming, which usually consists of a combination of a warming blanket, humidifier, blood/fluid warmer, and heat lamp.Correct Answer: All of the above

405. (3248) Q1-4071:

Which of the following postoperative thromboembolic prophylaxis options is of greatest benefit in patients with sickle cell disease:

1) Low-molecular-weight heparin

3) Warfarin

2) Low-dose heparin

5) Aspirin

4) Warfarin and foot pumps

Few published reports exist on the risk of deep vein thrombosis (DVT) in patients with sickle cell disease following orthopedic procedures. In sickle cell disease, platelets do not contribute to the pathophysiology of microvascular occlusion. However, due to splenic sequestration, patients with sickle cell disease often have thrombocytopenia. Factors associated with vaso-occlusion include the increased adhesion of the sickle cells to the endothelium and the activation of the clotting cascade with thrombin formation. Thrombin induces endothelial retraction resulting in the exposure of proadhesive extracellular components. It also upregulates endothelial expression of P-selectin, which increases binding among erythrocytes, white cells, platelets, and endothelial cells. Both of these events can facilitate thrombus formation. Following hip surgery, there is already a definable risk of DVT attributable to surgical trauma and immobility.

The goal of lower limb arthroplasty is optimal pain control with early mobilization to minimize the risk of respiratory and thromboembolic complications. Results of a meta-analysis of DVT after hip surgery suggest that patients with sickle cell disease undergoing THR are best managed with foot pumps and warfarin postoperatively to decrease the likelihood of thromboses in these patients.

Correct Answer: Warfarin and foot pumps

406. (3249) Q1-4072:

Which of the following is the most common indication for total hip arthroplasty in patients with sickle cell disease:

1) Septic arthritis

3) Osteoarthritis

2) Avascular necrosis

5) Fracture

4) Pain crisis

The mean age of patients with sickle cell disease undergoing hip surgery is approximately 34 years, with the most frequent procedure being THR for avascular necrosis. Some patients undergo bipolar hemiarthroplasty, which can be complicated by acetabular protrusio. Because hip surgery often is more complex in patients with sickle cell disease, it often is associated with longer anesthesia time and greater blood loss. Mean blood loss in THR in patients with sickle disease is approximately 1200 mL, which is significantly greater than in patients without sickle cell disease.Correct Answer: Avascular necrosis

1) Chromosome 2

3) Chromosome 11

2) Chromosome 8

5) Chromosome 14

4) Chromosome X

The common genetic basis of sickle cell disease is a mutation on chromosome 11 that results in an amino-acid substitution of valine for glutamic acid at the sixth position of the beta-globin subunit of hemoglobin that results in hemoglobin S (HbS). In the heterozygote carrier, this sickle gene mutation offers potential resistance to endemic Plasmodium falciparum malaria infections. Diagnosis of the disease is confirmed by hemoglobin electrophoresis.Correct Answer: Chromosome 11

408. (3251) Q1-4074:

In the heterozygote carrier, the presence of this sickle gene mutation offers potential resistance to:

1) Bartonella infections

3) Pneumococcal infections

2) Clostridium infections

5) Typhoid fever

4) Plasmodium falciparum malaria infections

The common genetic basis of sickle cell disease is a mutation on chromosome 11 that results in an amino-acid substitution of valine for glutamic acid at the sixth position of the beta-globin subunit of hemoglobin that results in hemoglobin S (HbS). In the heterozygote carrier, this sickle gene mutation offers potential resistance to endemic Plasmodium falciparum malaria infections. Diagnosis of the disease is confirmed by hemoglobin electrophoresis.Correct Answer: Plasmodium falciparum malaria infections

409. (3252) Q1-4076:

The minimally invasive surgical technique for unicondylar knee arthroplasty (UKA):

1) Everts the patella

3) Subluxes the patella

2) Resurfaces the patella

5) Violates the suprapatellar synovial pouch

4) Removes a portion of the patella

New surgical technique and instrumentation leads to less invasion of the extensor mechanism. The patella is not everted, and the suprapatellar synovial pouch remains untouched.Correct Answer: Subluxes the patella

410. (3253) Q1-4077:

The early failures of unicondylar knee arthroplasty (UKA) were due to:

1) Patient selection

3) Surgical technique

2) Implant design

5) Patient selection, implant design, and surgical technique

4) Implant design and surgical technique

The initial high failure rate of UKA in early reports was related to improper patient selection, incorrect surgical technique, and poor implant design.Correct Answer: Patient selection, implant design, and surgical technique

1) The medial collateral ligament should be released

3) The medial collateral ligament should not be changed

2) The medial collateral ligament should be tightened

5) Knee alignment is corrected to 6° of valgus

4) The lateral collateral ligament should be tightened

In total knee arthroplasty (TKA), knee alignment is corrected to an anatomic 6º or 7º of valgus. In UKA, this alignment leads to excessive medial compartment tightness and overload of the opposite lateral compartment. A varus knee in UKA should remain in neutral or a few degrees of varus. In TKA, a flexion contracture can be readily corrected with additional resection of both femoral condyles. In UKA, resection of the single distal femoral condyle helps to correct the flexion contracture but also changes the distal femoral valgus. Ligament releases in UKA are not as predictable as in TKA because only one compartment is replaced in the UKA, and the forces on the opposite compartment are more difficult to balance.Correct Answer: The medial collateral ligament should not be changed

412. (3255) Q1-4079:

In comparing high tibial osteomtomy to unicondylar knee arthroplasty (UKA):

1) Patients with high tibial osteotomy recover faster than patients with UKA.

3) High tibial osteotomy has better early results than UKA.

2) High tibial osteotomy has better 10-year results than UKA.

5) High tibial osteotomy has fewer operative complications than UKA.

4) High tibial osteotomy is better for patients who work as heavy laborers.

Although a successful UKA can eliminate pain and improve the patientâs function, heavy labor and high impact athletic activities are not encouraged. High tibial osteotomy allows a patient to perform more aggressive activities.Correct Answer: High tibial osteotomy is better for patients who work as heavy laborers.

413. (3256) Q1-4080:

Contraindications to unicondylar knee arthroplasty (UKA) includes all of the following except:

1) Bilateral knee disease

3) Varus deformity >15°

2) Tibial subluxation

5) >10° flexion contracture

4) Inflammatory arthritis

A patientâs symptoms and physical findings should be isolated to one tibiofemoral compartment, but disease can be present in both the right and left knee as long as its just one compartment. Patient history must be thoroughly evaluated to ensure that there are no associated patellofemoral symptoms in the opposite compartment.Correct Answer: Bilateral knee disease

414. (3257) Q1-4082:

Patellofemoral arthritis in the knee undergoing unicondylar knee arthroplasty (UKA):

1) Is an absolute contraindication

3) Does not affect the result of UKA

2) Is a relative contraindication

5) Is more symptomatic than patellar impingement

4) Is always present in UKA

Kozinn and Scott have emphasized that pain in the patellofemoral joint is a relative contraindication for UKA surgery. Degenerative changes of the patellofemoral joint also affected patient function, but the symptoms were less severe than in patients with patellar impingement. If patients report significant symptoms related to the patellofemoral joint, then UKA is contraindicated.Correct Answer: Is a relative contraindication

1) With a thickness of >10 mm

3) With a thickness of >6 mm

2) With a thickness of >8 mm

5) With a thickness of >2 mm

4) With a thickness of >4 mm

Manufacturing of polyethylene is improving, and cross-linking processes are increasing the wear properties. Most surgeons believe that it is safest to use a thickness of at least 6 mm with conventional polyethylene.Correct Answer: With a thickness of >6 mm

416. (3259) Q1-4085:

Radiographs of the UKA over a period of years after surgery show:

1) Some progression of arthritis in the opposite compartment

3) Advanced arthritis in the opposite compartment

2) No arthritis in the opposite compartment

5) Unacceptable rate of subsidence of the tibial compartment

4) No arthritis in the patellofemoral joint

Marmor reported no significant increase in the opposite compartment. Kozinn and Scott reported failures due to progression in the opposite compartment; however, this may have been due to over correction of the knee. Berger and colleagues reported minimal change in the opposite compartment with 12-year follow-up radiographs.Correct Answer: Some progression of arthritis in the opposite compartment

417. (3260) Q1-4086:

The minimally invasive surgical technique for unicondylar knee arthroplasty(UKA)

1) Everts the patella

3) Subluxes the patella

2) Resurfaces the patella

5) Violates the suprapatellar pouch

4) Removes a portion of the patellar

The minimally onvasive surgical technique for UKA subluxes the patella and leads to less invasion of the extensor mechanism. The patella is not everted and the suprapatellar synovial pouch remains untouched.Correct Answer: Subluxes the patella

418. (3450) Q1-4377:

The most common organism identified in bone cultures taken from patients with sickle cell disease with osteomyelitis is:

1) Salmonella typhimurium

3) Haemophilus influenzae

2) Staphylococcus aureus

5) Staphylococcus epidermis

4) Plasmodium falciparum

Although Salmonella infections are highly specific to patients with sickle cell disease, the most common organism identified in bone cultures taken from patients with sickle cell disease with osteomyelitis is S aureus. Due to autoinfarction, 95% of individuals develop functional asplenia by age 5 years. This condition has been associated with a decrease in opsonin production and phagocytic activity. Thus, in infants with sickle cell disease the major cause of death is pneumococcal sepsis. It has been recommended that patients with sickle cell disease have pneumococcal vaccine administered every 3 to 5 years.Correct Answer: Staphylococcus aureus

1) Cement is hand-packed in the shaft of the femur.

3) Cement is hand-mixed, medullary lavage is performed, and a canal plug is used.

2) The medullary canal is rinsed out by medullary lavage.

5) External pressurization is used.

4) The canal is brushed, jet lavage is performed, and a vacuum or centrifuge machine is used.

First-generation cement technique implies that cement is hand-packed in the shaft of the femur. A cement plug is not used and a lavage of the femoral canal is not performed. Second-generation technique implies that cement is hand-mixed in a bowl, medullary lavage is performed, and a canal plug is used. Third-generation technique refers to performing high-pressure jet lavage of the femoral canal, brushing the canal of all particles, using a vacuum or centrifuge machine in the mixing procedure, and using external pressurization on a closed canal.Correct Answer: Cement is hand-mixed, medullary lavage is performed, and a canal plug is used.

420. (3464) Q1-4399:

When comparing syringe-mixing versus bowl-mixing of bone cement, which of the following is not true:

1) Syringe-mixed bone cement has a greater density.

3) Syringe-mixed bone cement has a lesser bending modulus.

2) Syringe-mixed bone cement has a greater bending modulus.

5) Centrifuged or syringe-mixed bone cement, under vacuum conditions, is of greater strength than aerated bowl-mixed cement.

4) Syringe-mixed bone cement has a higher bending strain.

When analyzing bone cement for void content and failure in four-part bending, the results show that syringe-mixed bone cement has a greater density and a greater bending modulus and is of greater strength than aerated bowl-mixed cement.Correct Answer: Syringe-mixed bone cement has a lesser bending modulus.

421. (3486) Q1-4426:

In an obese patient undergoing unicondylar knee arthroplasty (UKA):

1) The results are worse than in a normal weight patient.

3) The results are not predictably better or worse.

2) The results are better than in a normal weight patient.

5) Results are gender dependent.

4) The results depend on the design of the prosthesis.

The knee should have less than 15° of deformity in varus or valgus and less than 10° flexion contracture. Inflammatory or crystalline-induced arthritis, knee subluxation, gross ligamentous laxity, and obesity are relative contraindications to the procedure. Scott and colleagues found that increased body weight contributed to failure in UKA and suggested that the best candidates are less than 180 lb.Correct Answer: The results are worse than in a normal weight patient.

422. (3489) Q1-4431:

The percentage of patients with a natural history of untreated asymptomatic osteonecrosis of the femoral head with sickle cell disease that will develop progression to pain is:

1) 10%

3) 50%

2) 30%

5) 90%

4) 70%

In a study involving 121 patients with untreated asymptomatic osteonecrosis of the femoral head, 110 of the patients went on to develop significant hip pain. Spontaneous resolution of osteonecrosis of the femoral head was not observed in asymptomatic hips.Correct Answer: 90%

1) Sickle cell patients with total hip replacement have outcomes equivalent to patients with osteonecrosis secondary to steroid use.

3) Core decompression alone is the most effective means of treatment in sickle cell patients with osteonecrosis.

2) Physical therapy alone is the most effective means of treatment in sickle cell patients with osteonecrosis.

5) Bone grafting has the best outcome for sickle cell patients.

4) Physical therapy alone is as effective as hip core decompression followed by physical therapy.

In a randomized prospective study performed by Neumayr and colleagues, physical therapy alone appeared to be as effective as hip core decompression followed by physical therapy in improving hip function and postponing the need for additional surgical intervention at a mean of 3 years after treatment.Correct Answer: Physical therapy alone is as effective as hip core decompression followed by physical therapy.

424. (3505) Q1-4456:

In the varus knee, unicondylar knee arthroplasty (UKA) should correct the deformity:

1. 7° of anatomic valgus

   3) 0°

2. 10° of anatomic valgus

   5) 5° of anatomic varus

   4) Permit implant positioning with 2 mm of laxity in flexion and full extension

   In the medial UKA with preoperative varus, most of the reviews suggest an alignment of 0° with reference to the anatomic axis of the lower extremity or slightly less than 0° with reference to the mechanical axis. In the study by Kennedy and White on 100 UKAs, they reported that superior results were obtained when the postoperative mechanical axis of the operated limb fell in the center of the knee or slightly medial to the center.Correct Answer: 0°

   425. (3547) Q1-4542:

   The most common risk factors for stress fractures is:

   1) Leg length discrepancy

   3) Muscle strength

   2) Training regimen

   5) Footwear

   4) Low bone mineral density

   Numerous risk factors for stress fracture exist. Most commonly, the scenario is doing âtoo much too soon.â Survey data have shown 86% of runners suffering stress fracture have had a change in duration, frequency, or intensity of training immediately prior to injury. The best independent predictors for stress fracture development in women appear to be age of menarche and calf girth.Correct Answer: Training regimen

   426. (3548) Q1-4543: