Orthopedics Hyperguide Review | Dr Hutaif General Ortho -...

Autopsy studies show that the loosening of cemented components occurs at the cement-bone interface. Loosening occurs first at the periphery and proceeds toward the dome. The bone resorption at the cement-bone interface is a response to polyethylene debris

Placing screws in the acetabular cup in the anterior-superior or anterior-inferior quadrant is not advised due to the proximity of the external iliaCvein and the obturator artery, respectively

Frozen section analysis is important in revision surgery to determine why a component has become loose. Ten polymorphonuclear cells per high-powered field lower the sensitivity for infection but do not reduce the specificity to diagnose an infection. Five polymorphonuclear cells per high-powered field are the current standard accepted as diagnostiCfor an infection. Mononuclear cells can be present in the face of aseptiCloosening or polywear disease. Polymorphonuclear cells are diagnostiCof biologiCinfectious response

Malunion fractures in the trochanter region and shortening, lengthening, or derotation osteotomies to realign the extremity are indications for an intertrochanteriCosteotomy. Avascular necrosis involving more than 50% of the femoral head is a contraindication for intertrochanteriCosteotomy

Normal activities increase forces over the hip to three times body weight. Jogging increases forces across the hip by five to eight times body weight

Principles of osteotomy include improving congruency by restoring proper mechanics, reorienting the weight bearing surfaces to transfer load in compression rather than shear, bone-to-bone aposition, and timely intervention with minimal arthrosis

Technical goals of osteotomy include eliminating impingement, correcting deformity, and restoring a pain-free functional range of motion. Motion should not be gained or lost, but the range can be altered

Literature from Europe and North America suggests that a patient with acetabular dysplasia whose anteroposterior radiograph shows a center edge angle of Wiberg less than 15° is a good candidate for periacetabular osteotomy

From the long-term observations of radiograph changes occurring around well-performed cemented total hip arthroplasties, fatigue fracture of cement, especially in areas of thin cement mantles, leads to loss of stability of the femoral component within the cement mantle

Loosening on the acetabular side most often occurs at the bone-cement interface. Histiocyte cell membrane proliferation incited by particulate generation proceeds from the periphery of the bone-cement interface to the dome of the acetabulum with eventual loosening

Cold-worked, cold-forged micrograin femoral components provide greater fatigue strength than original casting techniques. Coated stainless steel and coated chromium cobalt have less fatigue strength then the other answer choices

Titanium has one-half the material modulus, or stiffness, of chromium cobalt or stainless steel irrespective of the type of porous coating. Titanium also has a high corrosion resistance that is attributed to an oxide layer which is chemically nonreactive to the surrounding tissue

Cement is stronger in compression than in tension. Stem designs incorporate a taper to the mid and distal stem geometry to transfer the load from the stem to the cement primarily in compression

Femoral components with polished, smooth surfaces and low RA surfaces have proved to be more durable than devices with a rougher finish

Implants must resist translation in the axial, medial-lateral, and anteroposterior planes, as well as resisting rotation in the parasagittal, transverse, and coronal planes

The metaphysis provides axial and torsional stability for most wedge-shaped, proximally porous-coated, metaphyseal-filling implants. The other types of implants give stability in other areas than the metaphyses

Modularity in noncemented femoral components is popular because it allows more versatility in matching proximal and distal femoral geometry. However, additional research is needed to determine if particulate debris leads to osteolysis and failure

Patch porous-coated femoral implants failed because they provided channels for the particulate debris to move distally, resulting in diaphyseal osteolysis. A poor proximal fit permits the polyethylene particulate debris to erode around the femoral component

Thick hydroxyapatite coatings of 200 µm or more are at risk for fracture and delamination, and thin coatings of 20 µm or less may be resorbed too quickly. The best compromise appears to be 50 µm, which is thick enough so that resorption does not take place too quickly

Stress shielding, osteolysis, and implant extraction result in bone loss and must be minimized to maintain bone stock. Impaction grafting is a technique used to increase bone stock

Stress shielding occurs secondary to cemented femoral implants, noncemented femoral implants, and stiffer, longer implants that allow more distal bone growth. Stress shielding is also related to the geometry of the implant and bone quality. Modular designs alone do not cause stress shielding

Thigh pain in noncemented implants is frequently a consequence of stem loosening and fibrous stabilization. Thigh pain has not been associated with bony stabilization of the implant because there is no stem loosening if there is adequate bony stabilization

Providing external porous coatings to the tip of the stem, reducing contact between the tip of the stem and cortical bone, and tapering the stem tip are strategies that have been used to reduce micromotion. Cementing the femoral component will also reduce micromotion

Stems with slots, diaphyseal cutouts, and hollow distal stems have been used to reduce stem stiffness. Enlarging the distal stem tip increases the modulus of elasticity of the distal stem

Anchoring the prosthetiCfemoral head to the femur and substituting for the femoral head and neck are the major biomechanical functions of the femoral component in total hip arthroplasty. One can decrease or increase leg lengths by changing the size of a femoral component, specifically the neck length

Displaced transcervical fractures of the cervical neck of the femur are the most common cause of osteonecrosis of the femoral head. Although corticosteroid use, nitrogen bubbles, coagulopathies, and sickle cell disease can also cause osteonecrosis, the highest incidence is seen with displaced transcervical fractures

In the United States, approximately 10% of primary total hip replacements are performed due to osteonecrosis. The majority of total hip replacements occur secondary to osteoarthritis

Adults between 25 and 45 years old are most frequently affected with osteonecrosis, and the condition is bilateral in more than
50% of patients. The condition is usually secondary to alcoholism, corticosteroid use, sickle cell disease, and coagulopathies, as opposed to transcervical neck fractures seen in the elderly

Factors causing intravascular coagulation or thrombosis, not hemodilation, are the most important mechanisms implicated in causing osteonecrosis

Excessive alcohol intake and chroniCsteroid administration are the common factors implicated in the development of osteonecrosis. Although there have been case reports indicating nonsteroidal anti-inflammatory drugs, it is questionable if this was the cause

Less than 5% of patients exposed to heavy alcohol consumption develop osteonecrosis

Five percent to 10% of patients who receive high doses of corticosteroids develop avascular necrosis. Why only a small percentage of patients develop avascular necrosis is poorly understood, and there may be some genetiCpredisposition

Seventy percent of patients with osteonecrosis have some subtle coagulation defect

The crescent sign is caused by subchondral trabeculae collapse before flattening of the articular surface. The success of core decompression is markedly diminished after this finding is seen on radiographs

Cartilage receives its nutrition through the synovial fluid. Only after collapse of the head is articular cartilage subjected to abnormal mechanical pressures that lead to degeneration

Stage II of osteonecrosis has good cartilage space without collapse, and a dense necrotiClesion with sclerotiCborder but does not have a crescent sign. Stage I is detected on magnetiCresonance imaging, and stages III and IV are advanced forms of osteonecrosis

If present, radiographiCchanges are detected by MRI in more than 90% of cases. MRI remains the most sensitive test for osteonecrosis and becomes positive before changes are present on the roentgenogram

Approximately 70% of hips diagnosed clinically with osteonecrosis go on to femoral head collapse. The majority of hips progress to the severe form of the disease and will ultimately require total joint arthroplasty

The results of a multicenter study show promising results with pulsing electromagnetiCfields. Pulsing electromagnetiCfields were found effective as a symptomatiCmanagement in precollapsed lesion and as effective as core decompression

Core decompression is affected by a number of mechanisms including decreasing the intraosseous pressure, opening channels for vascular ingrowth, and stimulating the repair process through increased vascularity. Core decompression does not increase structural integrity of the area

Urbaniak and associates reported a success rate of 70% with mild collapse and 80% before collapse. Their results have not been duplicated as yet. The results of their study are much better than those reported with fibular graft

The incidence of deep infection in primary total hip replacement is 1%. After revision hip surgery, the percentage increases 3% to
4%. Repeated revisions are associated with increasing infection rates

Staphylococcus epidermidis accounts for 50% to 75% of all arthroplasty infections. This is the most common organism cultured from the skin of preoperative patients

AntibiotiCresistance, the organismâs ability to form a glycocalyx or polysaccharide biofilm, and a slime layer enable the organism to survive on implants. This is one of the reasons why it is difficult to clear up an infection using only antibiotics

Preoperatively, 25% of skin swabs taken in 100 patients undergoing total hip replacement were MRSE resistant. This is probably a direct result of the overuse of antibiotics by practicing physicians

The Swedish Registry found the lowest risk of revision was in patients who had palacos-gentamicin cement. No effect was found with ventilated suits or laminar flow

The ESR takes more than a year to return to normal after a total hip replacement

With an ESR of 30 mm/hr to 35 mm/hr, sensitivities have been reported from 0.60 to 0.96 and specificities from 0.65 to
1