2009 Total Joint Arthroplasty/Joint Salvage

Question 1

Which of the following findings is a prerequisite for a high tibial valgus osteotomy for medial compartment gonarthrosis? 1. Inflammatory arthritis 2. Ligamentous instability 3. Lateral tibial subluxation 4. Preoperative arc of motion of at least 90° 5. Narrowing of the lateral compartment cartilaginous joint space

Answer 1

PREFERRED RESPONSE: 4 DISCUSSION: The indications for high tibial valgus osteotomy include a physiologically young age, arthritis confined to the medial compartment, 10 to 15° of varus alignment on weight-bearing radiographs, a preoperative arc of motion of at least 90°, flexion contracture of less than 15°, and a motivated, compliant patient. Contraindications include lateral compartment narrowing of the articular cartilage, lateral tibial subluxation of greater than 1 cm, medial compartment bone loss, ligamentous instability, and inflammatory arthritis. REFERENCES Naudie D, Bourne RB, Rorabeck CH, Bourne TT: The Insall Award: Survivorship of the high tibial valgus osteotomy: A 10- to 22-year followup study. Clin Orthop Relat Res 1999;367:18-27. Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 255-264.

Question 2

What is the main benefit of using metal-backed tibial components in total knee arthroplasty? 1. Improve the conformity of the articular surfaces 2. Reduce the maximum compressive stresses on the underlying cancellous bone 3. Increase the tensile forces on the other condyle when one is loaded 4. Decrease the thickness of the polyethylene tray 5. Decrease the compressive forces on the polyethylene tray

Answer 2

PREFERRED RESPONSE: 2 DISCUSSION: In a normal knee, the hard subchondral bone helps to distribute loads across the joint surface. A metal-backed tibial component in total knee arthroplasty decreases the compressive stresses on the underlying, softer cancellous bone by distributing the load over a larger surface area, particularly when one condyle is loaded. Although metallic base plates also increase the tensile forces on the other condyle when one is loaded and may decrease the thickness of the polyethylene tray, these are not benefits. Compressive forces on the polyethylene tray are increased with metal backing. The conformity of the articular surfaces is not affected by metal backing of the tibial component. REFERENCE Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 265-274.

Question 3

A 32-year-old woman with systemic lupus erythematosus treated with methotrexate and oral corticosteroids reports right groin pain with ambulation and night pain. Examination reveals pain with internal and external rotation and flexion that is limited to 105° because of discomfort. Laboratory studies show a serum WBC of 9.0/mm3 and an erythrocyte sedimentation rate of 35 mm/h. Figures 1A and 1B show AP and lateral radiographs of the right hip. Further evaluation should include 1. examination under fluoroscopy. 2. MRI. 3. a bone scan. 4. arthrography. 5. aspiration and arthrography.

Answer 3

PREFERRED RESPONSE: 2 DISCUSSION: The radiographs show Ficat and Arlet stage 2 osteonecrosis. The femoral head remains round, and there are sclerotic changes in the superolateral quadrant. Patients with systemic lupus erythematosus are at risk for osteonecrosis because of prednisone use and the underlying metabolic changes associated with the condition (hypofibrinolysis and thrombophilia). MRI is the best diagnostic method for detecting osteonecrosis, with a greater than 98% sensitivity and specificity. For this patient, an MRI can assess the contralateral hip for any involvement and can quantify the extent of the lesion. REFERENCES Mont MA, Jones LC, Sotereanos DG, Amstutz HC, Hungerford DS: Understanding and treating osteonecrosis of the femoral head. Instr Course Lect 2000;49:169-185. Koval KJ (ed): Orthopaedic Knowledge Update 7. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 417-451.

Question 4

Which of the following factors can contribute to patellar subluxation following routine total knee arthroplasty? 1. External rotation of the femoral component 2. Internal rotation of the tibial component 3. Symmetric patellar resection 4. Lateral placement of the tibial component 5. Neutral alignment of the mechanical axis

Answer 4

PREFERRED RESPONSE: 2 DISCUSSION: Excessive resection of the lateral facet of the patella can lead to subluxation. Rotational alignment of the components can have a significant impact on patellar tracking. Internal rotation of the femoral component leads to more lateral alignment of the patella within the trochlear groove. Internal rotation and medial placement of the tibial component results in lateralization of the tibial tubercle with an increase in the Q angle. Excessive valgus alignment of the mechanical axis, or insufficient correction of preoperative valgus, has a similar effect on the Q angle, and both can result in a higher rate of tracking problems. REFERENCE Ayers DC, Dennis DA, Johanson NA, Pelligrini VD: Common complications of total knee arthroplasty. J Bone Joint Surg Am 1997;79:278-311.

Question 5

During total knee arthroplasty using a posterior cruciate-retaining design, excessive tightness in flexion is noted, while the extension gap is felt to be balanced. Which of the following actions will effectively balance the knee? 1. Resect more distal femur. 2. Resect more anterior tibia. 3. Use a larger femoral component. 4. Use a smaller polyethylene insert. 5. Recess the posterior cruciate ligament.

Answer 5

PREFERRED RESPONSE: 5 DISCUSSION: Excessive flexion gap tightness can be addressed with a variety of techniques; including: (a) recess and release the posterior cruciate ligament; (b) resect a posterior slope in the tibia; (c) avoid an oversized femoral component that moves the posterior condyles more distally; (d) resect more posterior femoral condyle and use a smaller femoral component placed more anteriorly; and (e) release the tight posterior capsule and balance the collateral ligaments. REFERENCE Ayers DC, Dennis DA, Johanson NA, Pelligrini VD: Common complications of total knee arthroplasty. J Bone Joint Surg Am 1997;79:278-311.

Question 6

Figures 2A and 2B show the current radiographs of a 58-year-old man who underwent total knee arthroplasty with a cruciate ligament-sparing prosthesis 7 years ago. Examination reveals boggy synovitis and moderate pain, particularly anteriorly. Management should consist of 1. follow-up radiographs. 2. alendronate, with follow-up examinations every 6 months. 3. revision to a posterior stabilized prosthesis. 4. exchange of the tibial insert through a limited incision. 5. surgical exploration with revision or exchange based on the findings.

Answer 6

PREFERRED RESPONSE: 5 DISCUSSION: The patient has symptoms of synovitis that are most likely the result of the release of particles from the tibial polyethylene. While observation may be warranted in a completely asymtomatic knee, some intervention is indicated for this patient as there is clear radiographic evidence of lysis in both the tibia and femur. The decision about the extent of the revision should be made at the time of surgery. A limited incision technique is not indicated. Grafting (or using graft substitute) the defect is the most appropriate approach for treating the osteolytic lesions. While a posterior stabilized prosthesis might be the solution, surgical findings might dictate otherwise. REFERENCE Brassard MF, Insall JN, Scuderi GR: Complications of total knee arthroplasty, in Insall JN, Scott WN (eds): Surgery of the Knee, ed 3. Philadelphia, PA, Churchill Livingstone, 2001, vol 2, pp 1801-1844.

Question 7

What is the correct order of the elastic modulus of the following materials from greatest to least? 1. Stainless steel, cobalt-chromium, titanium, polymethylmethacrylate (PMMA), alumina ceramic 2. Cobalt-chromium, stainless steel, titanium, alumina ceramic, PMMA 3. Alumina ceramic, titanium, cobalt-chromium, stainless steel, PMMA 4. Alumina ceramic, cobalt-chromium, stainless steel, titanium, PMMA 5. Titanium, cobalt-chromium, alumina ceramic, stainless steel, PMMA

Answer 7

PREFERRED RESPONSE: 4 DISCUSSION: In Young’s modulus of elasticity, E is a measure of the stiffness of a material and its ability to resist deformation. In the elastic region of the stress-stain curve, E = stress/strain. The moduli of elasticity for these materials are alumina ceramic = 380 Gigapascals (GPa), cobalt-chromium = 210 GPa, stainless steel = 190 GPa, titanium = 116 GPa, and PMMA = 1.1 to 4.1 GPa. REFERENCES Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 182-215.

Question 8

Figure 3 shows the radiograph of a 75-year-old woman who reports the sudden onset of disabling medial knee pain. What is the most likely diagnosis? 1. Osteoarthritis 2. Osteonecrosis 3. Meniscal tear 4. Metastatic lesion 5. Synovial osteochondromatosis

Answer 8

PREFERRED RESPONSE: 2 DISCUSSION: Idiopathic osteonecrosis of the medial femoral condyle occurs predominantly in women older than age 60 years. It is characterized by pain centered in the medial anterior aspect of the knee, and onset is sudden. Flattening, sclerosis, and the radiolucent crescent sign are radiographic indicators of osteonecrosis. The radiographs show no narrowing of the joint space or osteophyte formation to indicate osteoarthritis, and there are no loose bodies to indicate synovial osteochondromatosis. A meniscal tear is not consistent with the radiographic findings shown here. Meniscal tears can coexist with osteonecrosis, but the pain is not eliminated merely by partial meniscectomy. Metastatic lesions to the distal femoral epiphysis are exceedingly rare. REFERENCES Urbaniak JR, Jones JP Jr (eds): Osteonecrosis: Etiology, Diagnosis, and Treatment. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1997, pp 413-418. Insall JN, Windsor RE, Scott WN, Kelly MA, Aglietti P (eds): Surgery of the Knee, ed 2. New York, NY, Churchill Livingstone, 1993, pp 609-634.

Question 9

When using highly cross-linked ultra-high molecular weight polyethylene as an articulating surface for total knee arthroplasty, what property of the material raises concern? 1. Decreased volumetric wear 2. Decreased ductility 3. Increased mobility of the ultra-high molecular weight polyethylene chains in the material 4. Increased fatigue resistance 5. Increased fracture toughness

Answer 9

PREFERRED RESPONSE: 2 DISCUSSION: The decreased mobility of the polymer chains from cross-linking leads to decreased volumetric wear but also to decreases in ductility and fatigue resistance. Stresses at the knee are higher and varied in the point of application, leading to the concern for fatigue resistance and fracture. REFERENCE Koval KJ (ed): Orthopaedic Knowledge Update 7. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 193-199.

Question 10

An otherwise healthy 57-year-old man has persistent, severe hip pain after undergoing total hip arthroplasty 3 months ago. What is the next most appropriate step in management? 1. Serial radiographs to assess progressive radiolucency from osteolysis or mechanical loosening 2. Assessment of C-reactive protein, erythroctye sedimentation rate, and CBC, followed by aspiration 3. Technetium and/or indium-labeled leukocyte scintigraphy 4. A trial of broad-spectrum cefalosporin antibiotics to assess for a change in pain intensity 5. Injection with lidocaine and methylprednisolone acetate

Answer 10

PREFERRED RESPONSE: 2 DISCUSSION: Any patient who is severely symptomatic this quickly after surgery must be evaluated for infection. Loosening is also a possible cause, but infection must be ruled out. Bone scans are not helpful at this early postoperative stage. Normal laboratory values argue strongly against infection, but when abnormal, need to be supplemented with a hip aspiration. Aspiration remains the most selective and sensitive measure, especially when linked to a WBC count of the synovial tissues in the joint. There is no indication for an antibiotic trial because it may make future culture sensitivity more difficult. REFERENCES Drancourt M, Stein A, Argenson JN, et al: Oral rifampin plus ofloxacin for treatment of staphylococcus-infected orthopedic implants. Antimicrob Agents Chemother 1993;37:1214-1218. Duncan CP, Beauchamp C: A temporary antibiotic-loaded joint replacement system for the management of complex infections involving the hip. Orthop Clin North Am 1993;24:751-759. Oyen WJ, Claessens RA, van Horn JR, et al: Scintiographic detection of bone and joint infections with indium-111-labeled nonspecifonal human immunoglobulin G. J Nucl Med 1990;31:403-412.

Question 11

Which of the following treatments of polyethylene results in the highest amount of oxidative degradation? 1. Ethylene oxide sterilization 2. Gamma irradiation in air 3. Gamma irradiation in an inert environment 4. Gamma irradiation followed by cross-linking 5. Gas plasma sterilization

Answer 11

PREFERRED RESPONSE: 2 DISCUSSION: Oxidative degradation of polyethylene occurs as a function of time in an air environment. In an environment such as argon, nitrogen, or a vacuum, the process is reduced. Ethylene oxide is an alternative for sterilization in which the cross-link degradation is minimized because of the absence of oxidative interactions. Gamma sterilization or use of ethylene oxide gas is the industry standard; however, oxygen concentrations are now reduced to a minimal level to retard the oxidation phenomenon. REFERENCES Sanford WM, Saum KA: Accelerated oxidative aging testing of UHMWPE. Trans Orthop Res Soc 1995;20:119. Sun DC, Schmidig G, Stark C, et al: On the origins of a subsurface oxidation maximum and its relationship to the performance of UHMWPE implants. Trans Soc Biomater 1995;18:362. Callaghan JJ, Dennis DA, Paprosky WA, Rosenberg AG (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1995, pp 35-41. McKellop HA: Bearing surfaces in total hip replacement: State of the art and future developments. Instr Course Lect 2001;50:165-179.

Question 12

Consider the theoretic articulation shown in Figure 4 as femoral and tibial components of a total knee prosthesis in which the components fit like a “roller in trough.” Which of the following best describes the articulation? 1. Constrained to anteroposterior translation, unconstrained to medial-lateral translation, high contact stress on edge (ie, varus-valgus) loading 2. Constrained to anteroposterior translation, unconstrained to medial-lateral translation, low contact stress on edge (ie, varus-valgus) loading 3. Unconstrained to anteroposterior translation, constrained to medial-lateral translation, high contact stress on edge (ie, varus-valgus) loading 4. Unconstrained to anteroposterior translation, constrained to medial-lateral translation, low contact stress on edge (ie, varus-valgus) loading 5. Constraint is dependent on the status of the posterior cruciate ligament

Answer 12

PREFERRED RESPONSE: 1 DISCUSSION: The theoretic total knee components will resist anteroposterior motion by making the femoral component “climb the walls” of the tibial component. As drawn, there is no constraint to medial-lateral translation. The cylinder is not rounded on the edges, so varus-valgus motion will impart load from the cylinder to the trough over a small area, thus having a high contact stress. REFERENCE Alicea J: Scoring systems and their validation for the arthritic knee, in Insall JN, Scott WN (eds): Surgery of the Knee, ed 3. Philadelphia, PA, Churchill Livingstone, 2001, vol 2, pp 1507-1515.

Question 13

Wear particles of ultra-high molecular weight polyethylene that are generated by total hip implants are predominantly of what diameter? 1. Less than 1 micron 2. 10 to 50 microns 3. 100 to 200 microns 4. 500 to 750 microns 5. Greater than 1,000 microns

Answer 13

PREFERRED RESPONSE: 1 DISCUSSION: Multiple studies have shown that the size of an ultra-high molecular weight polyethylene particle generated by total hip implants is typically less than 1 micron. This finding is significant in that particles of that size are readily phagocytized by macrophages. REFERENCES Campbell P, Ma S, Yeom B, McKellop H, Schmalzried TP, Amstutz HC: Isolation of predominantly submicron-sized UHMWPE wear particles from periprosthetic tissues. J Biomed Mater Res 1995;29:127-131. Shanbhag AS, Jacobs JJ, Glant TT, Gilbert JL, Black J, Galante JO: Composition and morphology of wear debris in failed uncemented total hip replacement. J Bone Joint Surg Br 1994;76:60-67. Maloney WJ, Smith RL, Schmalzried TP, Chiba J, Huene D, Rubash H: Isolation and characterization of wear particles generated in patients who have had failure of a hip arthroplasty without cement. J Bone Joint Surg Am 1995;77:1301-1310.

Question 14

Which of the following best describes the resultant forces on an increased offset stem when compared with a standard offset stem? 1. Increased joint reaction force, increased torsional load 2. Increased joint reaction force, decreased torsional load 3. Decreased joint reaction force, increased torsional load 4. Decreased joint reaction force, decreased torsional load 5. No change in joint reaction force or torsional load

Answer 14

PREFERRED RESPONSE: 3 DISCUSSION: The increased emphasis on restoring offset in total hip arthroplasty has implications for the forces applied to the components and the fixation interfaces. Static analysis has shown that with an increased affect, joint reaction force on the articulation is decreased. When the resultant load on the hip is “out of plane” (ie, directed anterior to posterior), there is increased torsion where the stem is turned into more retroversion. REFERENCES Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 134-180. Hurwitz DE, Andriaacchi TP: Biomechanics of the hip, in Callaghan J, Rosenberg AG, Rubash HE (eds): The Adult Hip. Philadelphia, PA, Lippincott-Raven, 1998. Pauwels F: Biomechanics of the Normal and Diseased Hip. New York, NY, Springer-Verlag, 1976.

Question 15

During total knee arthroplasty, what component position aids in proper tracking and stability of the patellar component? 1. Femoral component in external rotation 2. Tibial component in internal rotation 3. Medialization of the tibial tray 4. Lateralization of the patellar component 5. Medialization of the femoral component

Answer 15

PREFERRED RESPONSE: 1 DISCUSSION: The femoral component should be implanted with enough external rotation to facilitate patellar tracking. Proper tracking requires a normal Q angle and is affected by axial and rotational alignment of the femur and tibia. An excessive Q angle can result from internal rotation of either component, medialization of the tibial tray, or lateralization of the patellar component. REFERENCES Beaty JH (ed): Orthopaedic Knowledge Update 6. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 559-582. Lonner JH, Lotke PA: Aseptic complications after total knee arthroplasty. J Am Acad Orthop Surg 1999;7:311-324.

Question 16

A 60-year-old woman reports anterior knee pain 2 years after undergoing primary total knee arthroplasty for rheumatoid arthritis. A Merchant view of the patella is shown in Figure 5. What is the most likely cause of her pain? 1. Elevation of the joint line 2. Lateral placement of the femoral component 3. Medial placement of the patellar component 4. Internal rotation of the femoral component 5. External rotation of the tibial component

Answer 16

PREFERRED RESPONSE: 4 DISCUSSION: Patellar complications commonly occur after primary total knee arthroplasty; therefore, proper component positioning is critical in obtaining a successful result. This patient has lateral tilting and subluxation of the patellar component. Internal rotation of the femoral component has the most deleterious effect on patellar tracking. Lateral placement of the femoral component, medial placement of the patellar component, and external rotation of the tibial component have beneficial effects on patellar tracking. Elevation of the joint line, if not excessive, should not impact patellar tracking. REFERENCES Rand JA: Patellar resurfacing in total knee arthroplasty. Clin Orthop Relat Res 1990;260:110-117. Healy WL, Wasliewski SA, Takei R, Oberlander M: Patellofemoral complications following total knee arthroplasty: Correlation with implant design and patient risk factors. J Arthroplasty 1995;10:197-201.

Question 17

The anterior portal of a hip arthroscopy places what structure at greatest risk for injury? 1. Ascending branch of the lateral circumflex femoral artery 2. Ascending branch of the medial circumflex femoral artery 3. Femoral nerve 4. Lateral femoral cutaneous nerve 5. Superior gluteal nerve

Answer 17

PREFERRED RESPONSE: 4 DISCUSSION: The average location of the anterior portal is 6.3 cm distal to the anterior superior iliac spine. The lateral femoral cutaneous nerve typically has divided into three or more branches at the level of the anterior portal. The portal usually passes within several millimeters of the most medial branch. Injury to the nerve can lead to meralgia paresthetica. The femoral nerve lies an average minimum distance of 3.2 cm from the anterior portal. The ascending branch of the lateral circumflex artery lies approximately 3.7 cm inferior to the anterior portal. Neither the ascending branch of the medial circumflex artery nor the superior gluteal nerve are at risk. REFERENCES Byrd JWT: Operative Hip Arthroscopy. New York, NY, Thieme Medical Publishers, 1998, pp 83-91. Arendt EA (ed): Orthopaedic Knowledge Update: Sports Medicine 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 281-289.

Question 18

A 32-year-old man has posttraumatic arthritis after undergoing open reduction and internal fixation of a left acetabular fracture. A total hip arthroplasty is performed, and the radiograph is shown in Figure 6. What is the most common mode of failure leading to revision in this group of patients? 1. Infection 2. Heterotopic ossification 3. Dislocation 4. Periprosthetic fracture 5. Acetabular component loosening

Answer 18

PREFERRED RESPONSE: 5 DISCUSSION: Acetabular component loosening has been reported as the most common mode of failure following total hip arthroplasty in patients with a previous acetabular fracture. Following acetabular fracture and subsequent open reduction and internal fixation, the bone quality and vascularity are compromised, thus reducing the success rate of acetabular component cementless fixation. REFERENCES Jimenez ML, Tile M, Schenk RS: Total hip replacement after acetabular fracture. Orthop Clin 1997;28:435-446. Romness DW, Lewallen DG: Total hip arthroplasty after fracture of the acetabulum: Long-term results. J Bone Joint Surg Br 1990;72:761-764.

Question 19

A 42-year-old man sustained the periprosthetic fracture shown in Figures 7A and 7B. The femoral component is well fixed. What is the next most appropriate step in management? 1. Closed reduction and bracing 2. Retrograde femoral intramedullary nailing 3. Open reduction and internal fixation of the fracture, leaving the femoral stem in place 4. Open reduction and internal fixation of the fracture and insertion of a proximally porous-coated stem 5. Open reduction and internal fixation of fracture fragments and insertion of a fully porous-coated femoral stem with diaphyseal fixation distal to the fracture

Answer 19

PREFERRED RESPONSE: 3 DISCUSSION: The patient has a periprosthetic fracture below the femoral stem. The component is porous coated and well fixed. Open reduction and internal fixation, leaving the stem in place, can be performed when bone quality is good. Plating with or without allograft struts and supplemental cerclage fixation generally is acceptable. If the component is loose, revision to a longer device is recommended with appropriate stabilization of the fracture using the aforementioned methods. If bone loss has occurred, allograft supplementation or a tumor prosthesis may be indicated. Fractures located well below the stem tip can be treated without regard for the prosthesis. Closed reduction and bracing is not associated with good results for periprosthetic femoral fractures. Retrograde intramedullary nailing is not appropriate for this fracture. REFERENCES Duncan CP, Masri BA: Fractures of the femur after hip replacement. Instr Course Lect 1995;44:293-304. Bono JV, McCarthy JC, Thornhill TS, Bierbaum BE, Turner RH (eds): Revision Total Hip Arthroplasty. New York, NY, Springer Verlag, 1999, pp 530-592.

Question 20

A homebound 75-year-old woman with diabetes mellitus has had progressive left knee pain and swelling for the past 6 weeks. She is febrile with a temperature of 103°F (39.5°C). History reveals that she underwent arthroplasty 5 years ago. Examination shows passive range of motion of 0° to 100° with no active extension. Knee aspiration reveals purulent fluid with a Gram stain showing gram-negative rods. A radiograph is shown in Figure 8. In addition to IV antibiotics, which of the following management options offers the best chance of a successful outcome? 1. Incision and drainage with repair of the extensor mechanism 2. Removal of components and delayed revision knee arthroplasty with an allograft extensor mechanism 3. Removal of components and immediate exchange revision total knee arthroplasty 4. Removal of components and delayed knee arthrodesis 5. Removal of components and delayed revision knee arthroplasty with extensor mechanism repair

Answer 20

PREFERRED RESPONSE: 4 DISCUSSION: The patient has an infected total knee arthroplasty and an interrupted extensor mechanism. A late infection of a total knee arthroplasty in a patient with diabetes mellitus and a virulent organism requires removal of the components, debridement, antibiotic spacers, and surveillance to ensure eradication of the infection. Reconstruction of an incompetent extensor mechanism in an infected knee is extremely unlikely to be successful. Arthrodesis is the procedure of choice if a revision total knee arthroplasty is not likely to succeed. Resection arthroplasty is recommended only as a long-term solution if the patient is medically unable to undergo further surgery. REFERENCES Koval KJ (ed): Orthopaedic Knowledge Update 7. Rosemont, IL, American Academy of Orthopaedic Surgery, 2002, pp 513-536. Hanssen AD, Rand JA: Evaluation and treatment of infection at the site of a total hip or knee arthroplasty. Instr Course Lect 1999;48:111-122.

Question 21

Varus intertrochanteric osteotomy for coxa valga commonly produces which of the following results? 1. Decreased abductor lever arm 2. Increased hip joint reaction force 3. Increased center edge angle 4. Abductor lag and lurch 5. Lengthening of the leg

Answer 21

PREFERRED RESPONSE: 4 DISCUSSION: The greater trochanter is raised as a by-product of varus osteotomy, and a temporary abductor lag and lurch is common for 6 months following surgery. In the absence of hip joint subluxation, varus intertrochanteric osteotomy has no effect on the center edge angle of Wiberg. Varus osteotomy typically increases femoral offset, thereby improving the abductor lever arm and reducing the hip joint reaction force. Even without taking a wedge, varus osteotomy always produces some degree of shortening. REFERENCE Millis MB, Murphy SB, Poss R: Osteotomies about the hip for the prevention and treatment of osteoarthrosis. Instr Course Lect 1996;45:209-226.

Question 22

During a posterior cruciate ligament-sacrificing total knee arthroplasty with anterior referencing, 8 mm of distal femur is resected. It is noted that the flexion gap is tight and the extension gap appears stable. What is the next most appropriate step in management? 1. Cut more proximal tibia. 2. Cut more distal femur. 3. Cut both the proximal tibia and distal femur. 4. Decrease the size of the femoral component. 5. Decrease the tibial polyethylene insert thickness.

Answer 22

PREFERRED RESPONSE: 4 DISCUSSION: If the flexion gap is tight and the extension gap is correct, it is preferable to change only the flexion gap and leave the extension gap unchanged; therefore, the treatment of choice is to decrease the size of the femoral component. The smaller component will be smaller in both medial-lateral as well as anterior-posterior dimensions. A smaller anterior-posterior size will allow more space for the flexion gap without significantly affecting the extension gap. Decreasing the size of the tibial polyethylene insert thickness or cutting more proximal tibia will affect both the flexion and extension gaps. Cutting more distal femur will increase the extension gap and not change the flexion gap, making the described situation worse. Cutting both the proximal tibia and distal femur will increase both the flexion and extension gaps. REFERENCE Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 281-286, 339-365.

Question 23

A 58-year-old man has anterior knee pain after undergoing total knee arthroplasty for osteoarthritis 2 years ago. He denies any history of trauma. A Merchant view is shown in Figure 9. What is the most likely cause of his pain? 1. External rotation of the femoral component 2. Overstuffing of the patellofemoral joint 3. Less than 12 mm of bony patella remaining after resection 4. Lateral retinacular release 5. Use of a cemented patellar component

Answer 23

PREFERRED RESPONSE: 3 DISCUSSION: The patient has a patellar stress fracture after resurfacing in a total knee arthroplasty. Several studies have shown that over-resection of the patella to less than 12 to 15 mm increases anterior patellar surface strains to a point where the risk of fracture is increased. Increasing the patellar thickness, positioning of the femoral component, lateral releases, and component types have not been clearly associated with increased fracture risk. REFERENCES Reuben JD, McDonald CL, Woodard PL, Hennington LJ: Effect of patella thickness on patella strain following total knee arthroplasty. J Arthroplasty 1991;6:251-258. Hsu HC, Luo ZP, Rand JA, An KN: Influence of patellar thickness on patellar tracking and patellofemoral contact characteristics after total knee arthroplasty. J Arthroplasty 1996;11:69-80. Greenfield MA, Insall JN, Case GC, Kelly MA: Instrumentation of the patellar osteotomy in total knee arthroplasty: The relationship of patellar thickness and lateral retinacular release. Am J Knee Surg 1996;9:129-131.

Question 24

Etanercept is a recombinant genetically engineered fusion protein used to treat rheumatoid arthritis. What is its mode of action? 1. Monoclonal antibody that binds TNF-α 2. Blocks the binding of IL-1 to receptors 3. Soluble receptor that binds TNF-α 4. Soluble factor that binds rheumatoid factor 5. Directly inhibits pyrimidine synthesis

Answer 24

PREFERRED RESPONSE: 3 DISCUSSION: Etanercept is a molecule consisting of the Fc portion of IgG fused to the extracellular domain of the p76 human THF-α receptor. It is soluble and binds TNF-α. Infliximab is the monoclonal antibody that binds TNF-α. IL-1 receptor antagonists are still in development. Leflunomide is a drug that inhibits pyrimidine synthesis and is similar to methotrexate as an antimetabolite. REFERENCE Koval KJ (ed): Orthopaedic Knowlegde Update 7. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 193-199.

Question 25

A 68-year-old woman underwent a successful total right hip arthroplasty with a metal-on-metal articulation and cementless porous-coated components. Three months later, she underwent identical surgery on the left hip. Three months after surgery on the left hip, she reports groin pain on ambulation. Examination reveals significant groin discomfort with passive hip motion, particularly at the extremes of motion. Radiographs are shown in Figures 10A and 10B. Laboratory studies show an erythrocyte sedimentation rate of 35 mm/h and a C-reactive protein of 0.9. Aspiration yields scant growth of Staphylococcus epidermidis in the broth only, with no evidence of loosening on arthrography. A second aspiration yields scant growth of S epidermidis in the broth only. What is the most likely cause of the patient's pain? 1. Allergic metal synovitis 2. Aseptic loosening of the acetabular component 3. Septic loosening of the acetabulum 4. Deconditioning following hip arthroplasty 5. Iliopsoas tendinitis

Answer 25

PREFERRED RESPONSE: 3 DISCUSSION: The difference in the clinical results combined with the laboratory findings points to infection. While there is a significant risk of false-positive findings with aspiration, the fact that two successive aspirations grew the same organism strongly suggests infection. The radiograph shows that there is more radiolucency around the left acetabular component than the right component. REFERENCES White RE: Evaluation of the painful total hip arthroplasty, in Callaghan JJ, Rosenberg AG, Rubash HE (eds): The Adult Hip. Philadelphia, PA, Lippincott-Raven, 1998, vol 2, pp 1377-1385. Barrack RL, Harris WH: The value of aspiration of the hip joint before revision total hip arthroplasty. J Bone Joint Surg Am 1993;75:66-76.

Question 26

Which of the following findings best describes the effects of increasing conformity of a fixed tibial bearing component and femoral component in total knee arthroplasty? 1. Increased peak contact stress, decreased component edge loading 2. Increased peak contact stress, increased component wear rates 3. Decreased peak contact stress, increased component wear rates 4. Decreased peak contact stress, decreased component wear rates 5. Decreased peak contact stress, decreased component edge loading

Answer 26

PREFERRED RESPONSE: 4 DISCUSSION: In the design of tibial and femoral components, a compromise must be made between contact stresses and constraint. Increased conformity increases constraint, limits motion, and potentially increases stress on the knee-cement interface. By increasing conformity, the surface area over which force is applied is increased, resulting in decreased peak contact stresses and decreased component wear rates. REFERENCES Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 265-274. Bartel DL, Rawlinson JJ, Burstein AH, Ranawat CS, Flynn WF Jr: Stresses in polyethylene components of contemporary total knee replacements. Clin Orthop Relat Res 1995;317:76-82.

Question 27

Figure 11 shows the radiographs of a 56-year-old woman who has pain and varus knee deformity after undergoing total knee arthroplasty 8 years ago. Aspiration and studies for infection are negative. During revision surgery, management of the tibial bone loss is best achieved by 1. a custom tibial implant. 2. a hinged prosthesis. 3. reconstruction with structural allograft. 4. reconstruction with iliac crest bone graft. 5. filling the defect with cement.

Answer 27

PREFERRED RESPONSE: 3 DISCUSSION: Massive bone loss encountered in revision total knee arthroplasty remains a significant challenge. Recent reports have shown high success rates using structural allograft to reconstruct massive bone defects. Custom and hinged prostheses in this setting are no longer favored. The defect shown is segmental and is too large to be filled with cement or iliac crest bone graft. REFERENCES Mow CS, Wiedel JD: Structural allografting in revision total knee arthroplasty. J Arthroplasty 1996;11:235-241. Engh GA, Herzwurm PJ, Parks NL: Treatment of major defects of bone with bulk allografts and stemmed components during total knee arthroplasty. J Bone Joint Surg Am 1997;79:1030-1039. Clatworthy MG, Ballance J, Brick GW, Chandler HP, Gross AE: The use of structural allograft for un-contained defects in revision total knee arthroplasty: A minimum five-year review. J Bone Joint Surg Am 2001;83:404-411.

Question 28

A 62-year-old man who underwent total knee arthroplasty 6 months ago now reports pain after falling on the anterior portion of the knee. Examination reveals weakness of knee extension but no extensor lag. Flexion that had once measured 115° is now limited to 70° because of pain. A radiograph is shown in Figure 12. Management should now consist of 1. immediate repair of the ruptured patellar tendon insertion. 2. knee joint aspiration and injection of a local anesthetic to facilitate examination. 3. joint aspiration for culture, broad-spectrum antibiotics, and immobilization. 4. immobilization until comfortable, followed by protected range of motion and strengthening. 5. immediate fracture repair.

Answer 28

PREFERRED RESPONSE: 4 DISCUSSION: The patient has a type IIIB patellar fracture (inferior pole fracture with an intact patellar tendon). Non-surgical management is the treatment of choice if there is little displacement and the extensor mechanism is intact. REFERENCES Brown TE, Diduch DR: Fractures of the patella, in Insall JN, Scott WN (eds): Surgery of the Knee, ed 3. Philadelphia, PA, Churchill Livingstone, 2001, vol 2, pp 1290-1312. Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 323-337.

Question 29

During primary total knee arthroplasty, what is the maximum distance the joint line can be raised or lowered before poor motion, joint instability, and increased chance of revision occur? 1. 4 mm 2. 8 mm 3. 12 mm 4. 16 mm 5. 20 mm

Answer 29

PREFERRED RESPONSE: 2 DISCUSSION: Positioning of the femoral and tibial components is a common cause of early failure of total knee arthroplasty. Two modes of possible position are raising or lowering the joint line from its anatomic level. Raising or lowering the joint line beyond an established threshold can cause limited range of motion, poor patellar function, and possible instability. It has been determined that a threshold of approximately 8 mm provides consistently good results after knee arthroplasty. REFERENCE Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 339-365.

Question 30

Failure of high tibial osteotomy (HTO) is most closely associated with which of the following factors? 1. Patient age of less than 50 years at the time of surgery 2. Stable fixaton of the osteotomy 3. Development of deep venous thrombosis postoperatively 4. Type of osteotomy performed (ie, opening wedge versus dome osteotomy) 5. Presence of a lateral tibial thrust preoperatively

Answer 30

PREFERRED RESPONSE: 5 DISCUSSION: Long-term survivorship studies have attempted to clarify patient factors related to good outcomes in HTO. One particular study showed that a patient age of less than 50 years was related to good outcomes in those who had good preoperative knee flexion. The same study found no relation between HTO failure and the presence of postoperative infection or deep venous thrombosis. The presence of a lateral tibial thrust is a contraindication to performing this surgery. As expected, good patient selection is critical to obtaining good long-term results with HTO. REFERENCES Naudie D, Borne RB, Rorabeck CH, Bourne TJ: Survivorship of the high tibial valgus osteotomy: A 10- to 22-year followup study. Clin Orthop Relat Res 1999;367:18-27. Rinonapoli E, Mancini GB, Corvaglia A, Musiello S: Tibial osteotomy for varus gonarthrosis: A 10- to 21-year followup study. Clin Orthop Relat Res 1998;353:185-193. Coventry MB, Ilstrup DM, Wallrichs SL: Proximal tibial osteotomy: A critical long-term study of eighty-seven cases. J Bone Joint Surg Am 1993;75:196-201.

Question 31

Figure 13 shows the radiograph of a 47-year-old woman who has severe right hip pain and a limp. Management should consist of 1. acetabular osteotomy. 2. femoral and acetabular osteotomy. 3. total hip arthroplasty using standard trochanter osteotomy and cementless components. 4. total hip arthroplasty using femoral shortening osteotomy and cementless components. 5. total hip arthroplasty using femoral shortening osteotomy, a cemented socket, and a cementless femoral component.

Answer 31

PREFERRED RESPONSE: 4 DISCUSSION: Femoral shortening osteotomy for a Crowe type IV hip dislocation has been shown to provide superior results with minimal complications. Cementless fixation of the stem allows for modular implants that greatly simplify the reconstruction. REFERENCE Jaroszynski G, Woodgate IG, Saleh KJ, Gross AE: Total hip replacement for the dislocated hip. Instr Course Lect 2001;50:307-316.

Question 32

A 72-year-old woman with rheumatoid arthritis who underwent primary total knee arthroplasty 2 years ago has had diffuse knee pain that developed shortly after the surgery. The patient has difficulty with stair descent and arising from chairs. Evaluation for infection is negative. AP and lateral radiographs are shown in Figure 14. Management should now consist of 1. anti-inflammatory drugs. 2. a knee brace. 3. physical therapy for quadriceps strengthening. 4. revision to a thicker polyethylene insert. 5. revision to a posterior stabilized implant.

Answer 32

PREFERRED RESPONSE: 5 DISCUSSION: The radiographs show posterior flexion instability that is the result of flexion-extension gap imbalance and/or posterior cruciate ligament incompetence after a posterior cruciate-retaining total knee arthroplasty. The radiographs also show anterior femoral displacement on the tibia. Pagnano and associates reported on a series of patients with painful total knee arthroplasties who had been previously diagnosed as having pain of unknown etiology, showing that the pain was secondary to flexion instability. Pain relief was achieved by revision to a posterior stabilized implant. REFERENCES Pagnano MW, Hanssen AD, Lewallen DG, Stuart MJ: Flexion instability after primary posterior cruciate retaining total knee arthroplasty. Clin Orthop Relat Res 1998;356:39-46. Fehring TK, Valadie AL: Knee instability after total knee arthroplasty. Clin Orthop Relat Res 1994;299:157-162. Fehring TK, Odum S, Griffin WL, Mason B, Nadaud M: Early failures of total knee arthroplasty. Clin Orthop Relat Res 2001;392:315-318.

Question 33

During the implantation of a cementless acetabular component in total hip arthroplasty, placement of a screw in the anterior superior quadrant puts which of the following structures at risk for damage? 1. Sciatic nerve 2. Internal iliac vessels 3. External iliac vessels 4. Femoral vessels 5. Obturator vessels

Answer 33

PREFERRED RESPONSE: 3 DISCUSSION: A knowledge of the safe quadrants for screw placement for acetabular component implantation is essential when performing total hip arthroplasty. The external iliac vessels are on the inner wall of the pelvis, corresponding to the anterior superior quadrant of the acetabulum. REFERENCES Keating EM, Ritter MA, Faris PM: Structures at risk from medially placed acetabular screws. J Bone Joint Surg Am 1990;72:509-511. Wasielewski RC, Cooperstein L, Kruger MP, Rubash HE: Acetabular anatomy and the transacetabular fixation of screws in total hip arthroplasty. J Bone Joint Surg Am 1990;72:501-508.

Question 34

Figure 15 shows the AP radiograph of an 18-year-old woman with progressive and severe right hip pain. Nonsteroidal anti-inflammatory drugs no longer control her pain. What is the next most appropriate step in management? 1. Total hip arthroplasty 2. Single innominate (Salter) osteotomy 3. Chiari osteotomy 4. Periacetabular osteotomy 5. Varus intertrochanteric osteotomy

Answer 34

PREFERRED RESPONSE: 4 DISCUSSION: A concentric hip with acetabular dysplasia in a symptomatic patient is best treated by periacetabular osteotomy. The Salter osteotomy is less optimal because the method has limited correction, is uniaxial, cannot be tailored to the deformity, and lateralizes the entire hip joint, thereby increasing the joint reactive forces. Because the hyaline cartilage of the joint is histologically normal, rotating the hyaline cartilage into an optimal position is preferable to augmenting the acetabulum with a shelf or by Chiari osteotomy. Varus intertrochanteric osteotomy has no significant role in the treatment of acetabular dysplasia. Total hip arthroplasty may be required in the future but should not be the first choice. REFERENCE Millis MB, Murphy SB, Poss R: Osteotomies about the hip for the prevention and treatment of osteoarthritis. Instr Course Lect 1996;45:209-226.

Question 35

A 52-year-old man has had groin and deep buttock pain for the past 2 months. Examination reveals that hip range of motion is mildly restricted, and he has pain with both weight bearing and at rest. An MRI scan is shown in Figure 16. Management should consist of 1. protected weight bearing and anti-inflammatory drugs. 2. core decompression of the femoral head. 3. vascularized free fibular grafting to the femoral head. 4. bipolar hemiarthroplasty of the hip. 5. total hip arthroplasty.

Answer 35

PREFERRED RESPONSE: 1 DISCUSSION: The MRI findings show highly increased signal through the entire femoral head and neck that is diagnostic of transient osteoporosis of the femoral head. This recently described entity is often seen in middle-aged men and should be treated nonsurgically with protected weight bearing and anti-inflammatory drugs. The natural history is that of self-resolution. REFERENCES Guerra JJ, Steinberg ME: Distinguishing transient osteoporosis from avascular necrosis of the hip. J Bone Joint Surg Am 1995;77:616-624. Urbanski SR, de Lange EE, Eschenroeder HC Jr: Magnetic resonance imaging of transient osteoporosis of the hip. A case report. J Bone Joint Surg Am 1991;73:451-455.

Question 36

Figure 17 shows the radiograph of an 80-year-old woman who has right groin pain. She underwent a total hip arthroplasty 15 years ago and has no history of hip dislocation; however, she now reports that the pain results in functional impairment. Preoperative findings reveal that the component used has been discontinued, the locking mechanism is poor, and there is no replacement polyethylene available from the company. During surgery, the acetabular component is found to be well fixed, it is in satisfactory position, and adequate access can be obtained through the screw holes in the component to debride the osteolytic cavities. What is the best course of action for revision? 1. Remove the component and replace it with a "jumbo" cup with bone graft or substitute. 2. Remove the component and replace it with a bipolar component with bone graft or substitute. 3. Remove the component and replace it with a support ring with graft or graft substitute and cement a cup into the support ring. 4. Score the component for improved cement interdigitation and cement a cup into the retained socket with bone graft or substitute. 5. Use a structural acetabular graft to reconstruct the acetabulum and cement a cup into the structural graft.

Answer 36

PREFERRED RESPONSE: 4 DISCUSSION: The clinical result in this patient has been good, with no dislocations, suggesting that the components are in reasonably good position. The radiograph and examination at the time of surgery suggest that the acetabular component is well fixed. The surrounding bone of the acetabulum is osteopenic and there would most likely be considerable bone loss if the acetabular component is removed. Access to the osteolytic lesions is possible. Cementing an acetabular component into the retained socket will cause the least amount of bone loss, shorten the procedure, and most likely result in a functional hip. REFERENCES Maloney WJ: Socket retention: Staying in place. Orthopedics 2000;23:965-966. Blaha JD: Well-fixed acetabular component retention or replacement: The whys and the wherefores. J Arthroplasty 2002;17:157-161.

Question 37

Figures 18A and 18B show the AP and lateral radiographs of a 67-year-old woman who has severe left knee pain when ambulating. History reveals that she underwent primary total knee arthroplasty 7 years ago. The patient reports increasing deformity over the past several years and uses a knee brace and a cane. Examination reveals that she walks with a varus thrust and has an uncorrectable varus deformity with valgus force. What is the primary reason for implant failure? 1. Osteolysis 2. Polyethylene wear 3. Tibial component fixation failure 4. Modular tibial component failure 5. Posterior cruciate ligament retention

Answer 37

PREFERRED RESPONSE: 3 DISCUSSION: Both cemented and cementless total knee arthroplasties depend on adequate fixation of the tibial component to promote long-term survivorship. An effective stem and adequate peripheral fixation of the tibial component to the cancellous-cortical portion of the proximal tibia are necessary for cementless fixation. Peripheral screws and pegs can serve as adjunctive fixation to decrease micromotion and shear forces and allow bone ingrowth to occur. Careful preparation of the proximal tibial surface can minimize fixation failure. Cemented fixation of the tibial stem should be performed in addition to the plateau. Osteolysis, polyethylene wear, and failure at the insert/tray locking mechanism have not occurred. Posterior cruciate ligament retention has not caused the tibial component fixation failure. REFERENCE Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 275-279

Question 38

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? 1. PMMA is stronger in tension than compression. 2. Porosity reduction increases the fatigue strength of PMMA. 3. Hypotension that occasionally results after PMMA is placed in the femoral canal is independent of a patient's intraoperative blood volume. 4. Inclusion of antibiotics does not alter the strength of PMMA. 5. PMMA bonds chemically to bone and the implant surface.

Answer 38

PREFERRED RESPONSE: 2 DISCUSSION: 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. REFERENCES Canale ST (ed): Campbell's Operative Orthopaedics, ed 9. St Louis, MO, Mosby, 1998, pp 221-224. Callaghan JJ, Dennis DA, Paprosky WG, Rosenberg AG (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1995, pp 27-33.

Question 39

A 35-year-old male laborer with isolated posttraumatic degenerative arthritis of the right hip undergoes the procedure shown in Figure 19. What is the most appropriate position of the right lower extremity? 1. 0° of flexion, 10° of abduction, 0° of rotation 2. 15° of flexion, 20° of abduction, 15° of external rotation 3. 20° of flexion, 10° of abduction, and 5° of external rotation 4. 30° of flexion, 5° of adduction, and 5° of external rotation 5. 45° of flexion, 10° of adduction, 0° of rotation

Answer 39

PREFERRED RESPONSE: 4 DISCUSSION: The primary indication for hip arthrodesis is isolated unilateral hip disease in a young, active patient. Avoiding abductor damage and preserving proximal femoral anatomy are imperative to allow conversion to a future total hip arthroplasty. Optimal positioning is 30° of flexion to allow swing-through. Neutral abduction and adduction and slight external rotation allow the most efficient gait while allowing sufficient support in stance. A small degree of adduction is acceptable for a successful hip arthrodesis. REFERENCES Callaghan JJ, Brand RA, Pedersen DR: Hip arthrodesis: A long term follow-up. J Bone Joint Surg Am 1985;67:1328-1335. Koval KJ (ed): Orthopaedic Knowledge Update 7. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 417-451.

Question 40

Which of the following bearing materials is most resistant to scratching from third-body debris? 1. Alumina 2. Stainless steel 3. Forged cobalt-chromium 4. Ion bombarded and forged cobalt-chromium 5. Oxidized titanium

Answer 40

PREFERRED RESPONSE: 1 DISCUSSION: Alumina is the hardest of all the materials listed. Clinical retrieval demonstrates resistance to scratching from third-body debris. REFERENCE Cooper JR, Dowson D, Fisher J, Jobbins B: Ceramic bearing surfaces in total articular joints: Resistance to third body damage from bone cement particles. J Med Eng Technol 1991;15:63-67.

Question 41

A 48-year-old woman has knee pain that is worse with weight bearing. She reports no night pain or pain at rest. History reveals that she underwent total knee arthroplasty with cementless components 2 years ago. Examination reveals tenderness along the medial joint line. Figures 20A through 20C show radiographs and a bone scan. What is the most likely cause of the patient's pain? 1. Deep infection 2. Malalignment 3. Fibrous ingrowth of the femoral component 4. Fibrous ingrowth of the tibial component 5. Patellar component loosening

Answer 41

PREFERRED RESPONSE: 4 DISCUSSION: The radiographs show a halo-like sclerotic margin around the tibial stem and lucency under the baseplate. The bone scan shows markedly increased uptake under the tibial component, particularly on the medial side (not diffusely through the knee as seen with infection). These studies indicate lack of bone ingrowth fixation of the cementless porous-coated tibial component. The recent report of Fehring and associates has identified failure of ingrowth of a porous-coated implant as a dominant mode of early failure of total knee arthroplasties. REFERENCES Fehring TK, Odum S, Griffin WL, Mason B, Nadaud M: Early failures of total knee arthroplasty. Clin Orthop Relat Res 2001;392:315-318. Fehring TK: Revision TJA corrects flexion extension gap imbalance. Orthop Today 2002;22:44.

Question 42

A 65-year-old woman has nausea, vomiting, and abdominal distention after undergoing total knee arthroplasty 48 hours ago. An abdominal radiograph is shown in Figure 21. Associated risk factors for this disorder include 1. hypokalemia. 2. administration of warfarin. 3. administration of antibiotics. 4. general anesthesia. 5. early mobilization and physical therapy.

Answer 42

PREFERRED RESPONSE: 1 DISCUSSION: The prevalence of postoperative ileus associated with total joint arthroplasty has been reported to be as high as 3%. Metabolic abnormalities such as hypokalemia are believed to contribute to the onset of ileus and Ogilvie syndrome (acute pseudo-obstruction of the colon). Prolonged bed rest also has been associated with the development of ileus and Ogilvie syndrome. Untreated Ogilvie syndrome can result in cecal perforation. Ileus usually is not accompanied by mechanical obstruction. Antibiotic administration and the type of anesthesia used have not been correlated with development of ileus. Administration of warfarin has been associated with elevated prothrombin time/partial thromboplastin time and international normalized ratio levels when ileus is managed with a nasogastric tube and suction. Metabolic imbalances must be corrected to reverse the ileus process. REFERENCES Iorio R, Healy WL, Appleby D: The association of excessive warfarin anticoagulation and postoperative ileus after total joint replacement surgery. J Arthroplasty 2000;15:220-223. Clarke HD, Berry DJ, Larson DR: Acute pseudo-obstruction of the colon as a postoperative complication of hip arthroplasty. J Bone Joint Surg Am 1997;79:1642-1647.

Question 43

Which of the following methods is considered effective in decreasing the dislocation rate following a total hip arthroplasty using a posterior approach to the hip? 1. Use of a shorter neck length 2. Use of a smaller diameter head with a skirted neck extension 3. Reconstruction of the external rotators and capsular attachments during closure 4. Placement of the acetabular component in 60° of abduction as opposed to 45° of abduction 5. Placement of the acetabular component in neutral (0°) anteversion as opposed to 15° to 20° of anteversion

Answer 43

PREFERRED RESPONSE: 3 DISCUSSION: A total hip arthroplasty using the posterior approach has resulted in hip dislocation under certain circumstances. Reconstruction of the external rotator/capsular complex is recognized as a stability-enhancing mechanism for the posterior approach. Although the correct position for an acetabular component has not been definitively determined, many surgeons prefer to place the acetabular component in 15° to 20° of anteversion and approximately 45° of abduction. Relative retroversion is a risk factor for posterior dislocation. High abduction angles result in edge loading of the polyethylene and possible early failure, as well as an increased risk of dislocation. Smaller diameter heads and skirted neck extensions used together decrease the range of motion that is allowed before impingement occurs, and this can result in dislocation. Shorter neck lengths generally result in soft-tissue envelope laxity. If laxity occurs, increased offset, neck length, or both can improve stability. REFERENCES Pellicci PM, Bostrom M, Poss R: Posterior approach to total hip replacement using enhanced posterior soft tissue repair. Clin Orthop Relat Res 1998;355:224-228. Morrey BF: Difficult complications after hip joint replacement: Dislocation. Clin Orthop Relat Res 1997;344:179-187.