arthroplasty Flashcards
severe valgus deformity w/ attenuation of MCL. What kind of prosthesis
varus-valgus constrained TKA prosthesis.
In older patients, the constrained implant is likely to last a lifetime, with several studies documenting excellent survivorship (96%) at 10 years
In younger patients, there is concern that the extra prosthetic constraint may shorten the longevity of the prosthetic fixation.Complete release of the LCL will leave the knee grossly unstable medially and laterally, and could necessitate a hinged prosthesis.
Which of the following factors is responsible for causing the **distal femur to pivot about a medial axis **as the knee moves from full extension into early flexion?
Differential radius of curvature between the medial and lateral femoral condyles
The radius of curvature of the distal femur is greater over the distal aspect of the lateral femoral condyle than the distal aspect of the medial femoral condyle. As the femur rolls posteriorly during early knee flexion, both condyles undergo similar angular changes equal to the amount of flexion. With a similar amount of angular rotation, the sphere with the larger radius experiences greater net rollback, producing a pivoting motion.
nueropathic joints are ____ and need what kind of TKA prosthesis
at risk for instability 2/2 ligamentous laxity and need semiconstrained prosthesis
Increasing articular conformity of the tibial polyethylene insert of a fixed-bearing total knee arthroplasty (TKA) prosthesis will have which of the following biomechanical effects? What are the advantages?
Increasing articular conformity increases the surface area for contact between the polyethylene and the femoral component.
* lower peak contact stress within the polyethylene
* less risk of polyethylene fatigue failure
A potential disadvantage of increasing conformity includes some restriction in tibial rollback.
Modest changes in conformity have not been shown to alter the rate of mechanical loosening. If conformity was increased to the extent of significant constraint, a potential increased risk of loosening would be expected, not a decrease. Design of modern TKAs includes a compromise in achieving enough constraint to lower polyethylene stress, without providing so much constraint as to limit kinematics and stress the fixation interfaces.
How does external rotaion of the tibial component help patellar stability?
Slight external rotation of the tibial component will cause a net medialization of the tibial tubercle when the knee is articulated. This will help centralize the extensor mechanism over the trochlear groove and minimize the tendency for lateral subluxation.
Increasing tibial polyethylene conformity can have what effect on fixed bearing total knee arthroplasty? What does this lead too? what is an undesirable consequence?
Increased conformity **increases the contact area **and thereby reduces contact stress within the polyethylene. lead to less risk of polyethylene wear, fracture, and delamination.
increasing conformity limits the ability of femoral roll back during flexion, may transfer increased shear stress to fixation surface
typical kinematic behavior for Posterior cruciate-retaining
Unpredictable anterior femoral condylar translation from full extension to 90 degrees of flexion
anterior femoral condylar translation during deep knee flexion was most commonly observed in posterior cruciate-retaining knees.
kinematic behavior of the knee during motion from full extension to flexion?
medial tibiofemoral contact point moves very little (translates) in the anterior-posterior direction, whereas the lateral contact point moves much greater in the anterior-posterior direction (translates), resulting in more lateral translation, rollback, and medial pivoting.
Method to improve wear performance of poly during manufacturing?
Gamma-irradiation of polyethylene in an inert gas improves the wear performance of polyethylene
Gamma radiation is the most common way to sterilize polyethylene implants. When oxygen is present, the polyethylene becomes oxidized as opposed to cross-linked. Cross-linking helps to improve resistance to both adhesive and abrasive wear, which are the most common mechanisms of failure of current polyethylene implants. Without cross-linking, the polyethylene can delaminate and crack propagation is more common - these can lead to rapid wear of the implants given the uneven articulation surfaces that they create.
How are free radicals removed from highly cross-linked polyethylene?
Thermal processing of irradiated poly removes free radicals. TP is the heat tx of cross-linked poly to remove free radicals Another strategy is vit E (anti-oxidant)
Cross-linking of polyethylene improves its wear property via a series of steps including irradiation, thermal processing, and sterilization. Irradiation breaks carbon-hydrogen bonds in polyethylene and creates covalent bonds during cross-linking. Both low- and high-dose irradiation create free radicals that can interact with oxygen to weaken the polyethylene. Oxidation is the process through which oxygen is introduced into the polyethylene and possibly generates free radicals. Thermal processing of irradiated polyethylene removes these free radicals. Thermal processing is the heat treatment of cross-linked polyethylene to remove free radicals. Annealing and remelting are 2 thermal processing types, with annealing being the preferred technique because it results in better mechanical properties of polyethylene. Another strategy that can remove free radicals is to add an antioxidant such as vitamin E. Sterilization is the final step before the packaging of polyethylene implants.
What polyethylene processing step results in increased polyethylene wear and subsequent osteolysis?
Gamma irradiation in air
Cross-linking and thermal stabilization are 2 important techniques. Remelting and annealing are thermal stabilization methods intended to reduce the number of free radicals that are present as a result of the cross-linking process. Both remelting and heat annealing have been shown to reduce wear and osteolysis.
What process has the most positive effect on the wear-resistance characteristics of UHMWPE?
Radiation is used to sterilize and cross-link.
Modern UHMWPE is highly cross-linked with higher doses of radiation (5.0-10 Mrad) in an inert environment. The level of radiation directly increases the amount of cross-linking and also improves wear resistance via cross-linking. Free radicals are still generated during the radiation process and are quenched by either remelting or annealing.
UHMWPE is a long polyethylene polymer with a high molecular weight. It is manufactured via ram bar extrusion and compression molding. Radiation is used to sterilize and cross-link. Historically, gamma was irradiated in air at 2.5-4.0 Mrad. This created free radicals, resulting in early oxidative degradation with high wear rates, delamination, and fracture. Modern UHMWPE is highly cross-linked with higher doses of radiation (5.0-10 Mrad) in an inert environment. The level of radiation directly increases the amount of cross-linking and also improves wear resistance via cross-linking. Free radicals are still generated during the radiation process and are quenched by either remelting or annealing. Remelting is the heating of the polyethylene above its melt point, changing it from the partial crystalline state to the amorphous state and removing all free radicals, but also reducing wear characteristics. In annealing, the UHMWPE is heated below the melting point, which avoids the reduction in crystallinity but leaves more free radicals. Ethylene oxide is used in the sterilization process. Highly cross-linked polyethylene has shown significantly decreased wear rates compared to conventional polyethylene in both clinical and simulator studies. There is still some concern regarding decreased mechanical properties.
What process changes polyethylene from its partial crystalline state to its amorphous state?
Remelting is the heating of the polyethylene above its melt point, changing it from the partial crystalline state to the amorphous state and removing all free radicals, but also reducing wear characteristics.
Several techniques have been developed to improve the wear characteristics of polyethylene. What technique results in the largest reduction of free radicals?
Thermal stabilization through remelting
Thermal stabilization techniques are designed to minimize the number of remaining free radicals available to react with oxygen. Remelting is the most efficient method to reduce free radicals.
Free radicals, which are generated when polyethylene is exposed to ionizing radiation, are highly reactive and can be quenched by cross-linking with each other or via oxidation in the presence of oxygen. Thermal stabilization techniques are designed to minimize the number of remaining free radicals available to react with oxygen. Remelting is the most efficient method to reduce free radicals. Annealing also greatly reduces the number of free radicals, but cannot quench as many free radicals as remelting. Vitamin E has been shown to protect against oxidation by quenching free radicals; however, vitamin C has not shown the same benefit.
High cross-linke poly vs conventional poly wear characteristics in THA?
A highly cross-linked polyethylene bearing has superior wear characteristics compared to a conventional polyethylene bearing.
). The improved wear is seen with larger-diameter heads as well. The volumetric wear rate of highly cross-linked polyethylene is equivalent to slightly higher with a larger head than a 28-mm head. Incidence of periarticular osteolysis is lower with highly cross-linked polyethylene.
What is the difference between annealed (below the melting temperature) and remelted highly crossed-linked polyethelyne?
Polyethylene is remelted to remove free radicals that formed during the radiation process for cross-linking. The disadvantage of remelting polyethylene is that it reduces the mechanical properties of the material. Annealing of polyethylene maintains its mechanical properties but is less effective at removing free radicals, leaving the polyethylene more susceptible to oxidation. However, both annealed and remelted polyethylene have shown in vivo oxidation.
. What is the principal negative effect of increasingly high crosslinking?
poly loses fatique strength
All other factors equal, the fatigue strength of UHMW polyethylene decreases somewhat as the level of crosslinking increases. Some types of crosslinking may impart a slight yellowish or grey color, but this has no clinical consequence. Crosslinking also has no substantial effect on dimensional stability. Although radiation crosslinking induces free radicals in the polyethylene that could lead to oxidation, these can be neutralized using suitable post-crosslinking thermal treatments, or by the addition of antioxidants, such as vitamin E.
poly packaged in air and sterilized using gamma radiation stored unoped on the shelf for 5 years should not be used why?
Sterilization using gamma radiation induces free radicals (uncombined electrons) in the polyethylene. During storage in air, oxygen will diffuse into the material and react with the free radicals, causing breakage of the molecular chains. This oxidation can markedly weaken the material, making it much more susceptible to wear and fatigue fracture. The gamma dose used for sterilization, in the range of 2.5 to 4 Mrads, induces a moderate amount of crosslinking, which (in the absence of oxidation) improves the wear resistance compared to noncrosslinked polyethylene. If the packaging has not been damaged, the component should still be sterile, even after 5 years of storage. Creep distortion should not be a problem because the component has not been under load, and the design may still be appropriate for clinical use.
what poly manufacturing process generates the greatest degree of poly oxidation?
Oxidation occurs after polyethylene has been irradiated in the presence of oxygen. Gamma irradiation has been commonly employed to sterilize the polyethylene prior to sterile packaging.
Over the last decade, several methods of reducing oxidation of polyethylene have been used. These include irradiation in an inert gas (such as argon or nitrogen), irradiation in vacuum packaging, and avoiding irradiation altogether and sterilizing the polyethylene with ethylene oxide, gas plasma, or vaporized hydrogen peroxide. Cross-linking polyethylene has been done with gamma irradiation and electron beam irradiation. Heating/melting the material after irradiation allows the free radical chains within the polyethylene to cross-link together rather than oxidize.
What mechanical properties are observed in polyethylene used for total knee arthroplasty after the material undergoes oxidation?
decrease in strength and ductility, and an increase in the elastic modulus. This makes the material more brittle, and leaves it vulnerable to delamination, fracture, and pitting
Changes to the properties of ultra-high molecular weight polyethylene with increasing irradiation dose include
Increased irradiation doses cause a decrease in the mechanical properties of the polyethylene, resulting in a** decrease in ultimate tensile strength, fracture toughness, and resistance to crack propagation. ** Irradiation leads to the production of free radicals, requiring a step in the manufacturing process (melting, annealing, vitamin E doping) to stabilize the free radicals and reduce the potential for oxidation. Wear resistance is improved with irradiation; however, there is minimal benefit with doses of greater than 10 Mrads.
When comparing unaged, radiated, cross-linked, ultra-high molecular weight polyethylenes (XPE) treated with remelting or annealing, annealed XPE has
More free radicals, better mechanical wear characteristics, and equivalent wear than remelted xpe. advantage of annealing is improved mechanical properties by avoiding disruption of the crystalline areas that occurs with remelting.
Cross-linking polyethylene with radiation improves the wear properties. Persistent free radical formation within the crystalline areas of polyethylene can become oxidized in vivo. Remelting (heating above the melting point) or annealing (heating below the melting point) are processing techniques that decrease the retained free radicals. The advantage of remelting is more complete removal of persistent free radicals compared with annealing. The advantage of annealing is improved mechanical properties by avoiding disruption of the crystalline areas that occurs with remelting. Other free radical squelching methods (eg, addition of the free radical scavengers such as vitamin E) are being used to achieve both goals (free radical removal and maintenance of improved mechanical properties). To date, no significant difference has been demonstrated in wear rates between the two materials.
In TKA, in vitro testing has shown that cross-linking can diminish the rate of polyethylene wear by 30% to 80%. What other change in material properties is possible when polyethylene is highly cross-linked?
most important concern regarding highly cross-linked polyethylene relates to decreased mechanical properties. Cross-linking results in reduced ductility, tensile strength, and fatigue crack propagation resistance
hese problems have not been identified as causing implant failure in most recent clinical trials, but remain the most important mechanical issues associated with current material processing methods.
macrophage induced osteolysis inflammatory cytokines
PDGF: platelet-derived growth factor
PGE2: prostaglandin E2
TNF-alpha
IL-1
IL-6
Marker/test for osteolysis
N-telopeptide urine level is a marker for bone turnover and is elevated in osteolysis
Urinary N-telopeptide is a marker of increased bone turnover and is a breakdown product of Type 1 collagen.
MoM association with elevated serum ion levels?
smaller femoral head diameter and acetabular cup abduction angle >55 degrees are associated with elevated serum metal ion levels. Cup abduction angles of greater than 55 degrees lead to a more vertical cup and edge loading.
Wear rates of highly cross-linked UHMW liner and head size?
Wear rates of highly cross-linked UHMW polyethylene liners are independent of femoral head size between 22 and 46 mm in diameter.
osteolysis under the tibial baseplate,
micromotion and fretting between the backside of the polyethylene insert and the tibial tray can generate significant amounts of wear debris, sufficient to cause substantial osteolysis.
Stress shielding is not a likely cause in this case because there is no intramedullary stem. In general, articulation of metal against polyethylene generates insignificant amounts of metal wear debris.
MoM compared to Metal on x-linked poly:
MoM:
* higher serum metal ions
* smaller wear particals
* lower volumetric wear rates
* vol wear rate greater than metal on ceramic
MoM stimulates lymphocytes and serum ion levels greater w/ cup abduction >55 and small component size
Wear rates above ? per year are at significant risk of osteolysis.
Wear rates above 0.1 mm per year are at significant risk of osteolysis.
Osteolysis after THA w/ polyliner is associated with what risk factors?
increasing the rate of wear
the one variable that correlates closest with the likelihood of osteolysis (and the magnitude of osteolysis) is the wear rate of the bearing couple. **Wear can be measured linearly or volumetrically. ** Both correlate with the development of osteolysis.
The development of osteolysis appears to be multifactorial. Patient activity, component positioning, polyethylene oxidation level, and bearing surface all appear to contribute. They contribute, however, by increasing the rate of wear.
Osteoprotegrin (OPG) binds to what structure to inhibit particle-induced osteolysis?
Osteoprotegrin (OPG) binds to RANK ligand (RANKL) to inhibit it from binding to RANK which are present on osteoclast-precursor cells. Normally, RANKL interacts with RANK to stimulate activation of osteoclasts.
primary mechanism of polyethylene wear in the hip?
adhesion and abrasion
previous theories on acetabular wear implicated fatigue cracking and delamination as primary wear mechanisms, these have actually manifested as major modes of polyethylene wear in knees
failur of poly in TKA, primary mechanism
Fatigue and delamination is predominant in total knee arthroplasty where stresses are maximum just below the surface of the polyethylene component, causing fatigue over time with subsequent delamination. In contrast, hip wear occurs primarily at the surface of the polyethylene component.
? occurs in fatigue cracks with low oxygen tension (under screw heads, etc). ? consists of cyclical abrading of the outer surface from small movements.
Crevice corrosion occurs in fatigue cracks with low oxygen tension (under screw heads, etc). Oscillatory fretting consists of cyclical abrading of the outer surface from small movements.
pain and subluxation of patella, what imaging is needed, and what are the factors that cause this?
** Axial CT views from the supracondylar distal femur to the proximal tibia below the tibial tubercle**
laterally positioned patellar component, a tibial tray that is internally rotated and translated to the medial side of the proximal tibial surface, and a femoral component that is markedly internally rotated about 10 degrees. All of these findings will be apparent on a CT scan.
Merchant’s view shows the basic problem.
A bone scan does not provide information about component malposition. Axial CT views from the supracondylar distal femur to the proximal tibia below the tibial tubercle
normal tibio-femoral joint kinematics?
Tibia: internal rotation w/ knee flexion, tibia EXternally rotates on femurs as the knee Extends.
medial femoral condyle does not move much from 0 to 120 degrees of flexion. lateral femoral condyle and the contact area between that condyle and the tibia move posteriorly and tibial internal rotation occurs with knee flexion. They found that from 120 degrees to full flexion both condyles participate in “roll back”.
The axis of rotation shifts posterior on the lateral condyle with knee flexion. Flexion and extension at the knee occur about a constantly changing center of rotation (polycentric rotation
The term “paradoxical motion,” used to describe knee kinematics, is best described by which of the following definitions?
“rollback” describes the posterior movement of the tibiofemoral contact point with knee motion from extension to flexion. Therefore, with “paradoxical rollback” this contact point moves anteriorly. “Paradoxical rollback” is a term used to connote the inability of the anterior cruciate-deficient, posterior cruciate-retaining total knee prosthesis to create normal posterior femoral rollback with knee flexion.
the kinematic behavior of the knee during motion from full extension to flexion?
During normal knee flexion, knee kinematic analysis reveals that the medial tibiofemoral contact point moves very little (translates) in the anterior-posterior direction, whereas the lateral contact point moves much greater in the anterior-posterior direction (translates), resulting in more lateral translation, rollback, and medial pivoting.
During normal human knee flexion (beginning with the knee fully extended), which of the following statements best describes tibial rotation with respect to the femur
During knee flexion, the tibia initially rotates internally in approximately the first 20 degrees and generally maintains this rotational position until flexion past 90 degrees when significantly more internal rotation occurs.
Significant anterior tibial translation occurs during which of the following rehabilitation exercises?
Terminal non-weight-bearing knee extension exercises from 60 degrees to 0 degrees of flexion increase anterior tibial translation. It is for this reason that this type of exercise should be avoided in the early phase of rehabilitation following anterior cruciate ligament reconstruction so as not to place a tensile strain on the graft. The other rehabilitation exercises either lead to posterior tibial translation in relation to the femur or have no significant effect on tibial translation.
What is the most accurate description of the relationship between gender and knee loading during landing while playing basketball?
females landed with greater total valgus knee loading and a greater maximum valgus knee angle than male athletes. Hewett and associates reported in a study of 205 female athletes that those with increased dynamic valgus and high abduction loads were at increased risk of anterior cruciate ligament injury.
Pathophysiology of Hip AVN: Idiopathic: Whats the final idiopathic pathway. Whats the cascade?
AVN 2/2 trauma due to?
What is predictive of worsening pain and future progression of disease in AVN of the hip?
presence of bone marrow edema on MRI is predicitve of worsening pain and future progression of disease
patients with marked bone marrow edema were more likely to experience worsening pain, larger volume of necrosis, and progression of their disease to collapse compared to patients without bone marrow edema on MRI.
what drug main prevent femoral head colapse in osteonecrosis with subchondral lucency? How does this drug work?
Alendronate:
bisphosphonate, which functions to decrease osteoclast resorption and increase osteoclast apoptosis by flattening the ruffled border.
indicated for precollapse AVN (Ficat stages 0-II
THA for AVN hip has increase risk of what complications?
THA performed for AVN has higher complications (intraoperative canal perforation and post-operative dislocation) compared to standard osteoarthritic patients.
When subchondral collapse has occurred in the setting of osteonecrosis, arthroplasty is the most reliable long-term solution.
The localized inflammatory reaction to AVN, combined with prolonged periods of immobilization and/or chronic corticosteroid use, results in poor bone quality and soft tissue laxity which may result in increased risk for intraoperative canal perforation with the femoral stem, medial wall breach when reaming the acetabulum, or post-operative dislocation.
Hip resrufacing: advantages? use for osteonecrosis? Painful eval of hip resurfacing requires what work up?
Hip resurfacing offers several potential advantages over conventional total hip arthroplasty, particularly for patients younger than 75 years of age. This intervention can be relatively bone conserving and is appropriate in settings involving proximal femoral deformity, precluding the use of a traditional femoral component. The use of hip resurfacing in osteonecrosis has been controversial, however. Although there are several reports of successful use of these implants to address osteonecrosis, concerns remain about extensive femoral head involvement (exceeding 40%) and ability to support the femoral head cap. Consequently, hip resurfacing is not recommended for patients with large femoral head lesions.
Evaluation of painful hip resurfacings requires a systematic approach. Radiographs can help surgeons assess implant position, loosening, or fractures. Serological studies including ESR, CRP, and serum cobalt and chromium levels can give clues as to whether infection, metallosis, or both are the underlying cause(s) of failure. Hip aspiration in the setting of metal-on-metal bearings necessitates a manual cell count and differential to avoid falsely elevated automated cell counts.
Revision of failed hip resurfacings should involve revisions of both the femoral and acetabular components. Although successful retention of the acetabular shell has been described, concerns remain regarding cup circumference mismatch, which can lead to suboptimal clearance between the new bearing surfaces.
A 46-year-old male construction worker has right hip pain that has failed to respond to nonsurgical management. His body mass index (BMI) is 32, he is 6’2” tall, and he has no other medical comorbidities. AP and lateral radiographs of the right hip are shown in Figures 1 and 2. The patient inquires about his suitability for metal-on-metal hip resurfacing. The patient should be educated that he is at higher risk for failure secondary to which of the following?
This young patient has osteonecrosis of the femoral head with a large area of collapse. The results of hip resurfacing arthroplasty have been reported to be best in young, male patients who are younger than 55 years of age with a diagnosis of osteoarthritis. Although some authors advocate metal-on-metal hip resurfacing as an option for patients with osteonecrosis of the femoral head, in this particular patient, given the size of the necrotic segment, he would be at higher risk for failure and a conventional total hip arthroplasty would be a more conservative option. As the acetabulum is resurfaced in metal-on-metal hip resurfacing, the secondary changes of the acetabulum are not an issue and his BMI is in an acceptable range for the procedure.
A 30-year-old patient has had severe left hip pain and difficulty ambulating, necessitating the use of a cane, for the past 6 months. A photomicrograph of the femoral head sectioned at the time of surgery is shown in Figure 1. What is the most likely diagnosis
The photomicrograph demonstrates a wedge-shaped infarct with femoral head collapse; therefore, the diagnosis is osteonecrosis of the femoral head. Perthes disease and osteoarthritis do not involve a wedge-shaped defect. Tuberculosis of the hip joint results in greater destruction of the articular cartilage.
A 42-year-old man reports the recent onset of right hip pain. A radiograph and MRI scan are shown in Figures 1 and 2. A WBC count, erythrocyte sedimentation rate, and hip aspiration are within normal limits. Management should now consist of
Transient osteoporosis of the hip is an uncommon problem, usually affecting women in the last trimester of pregnancy and middle-aged men. Symptoms include pain in the involved hip with temporary osteopenia; however, there is no joint space involvement. In this patient, the imaging findings are consistent with transient osteoporosis. Short TR/TE (repetition time/echo time) images reveal diffusely decreased signal intensity in the femoral head and intracapsular region of the femoral neck. Increased signal intensity is seen with increased T2-weighting. Within a few months, the pain, as well as the imaging findings, will completely resolve without intervention. Distinguishing the diffuse features of transient osteoporosis of the hip from the segmental findings of osteonecrosis is essential. Unlike transient osteoporosis of the hip, osteonecrosis will have a double-density signal on MRI and may progress radiographically. Surgical intervention and oral corticosteriods are not indicated for treatment. Protected weight bearing until the pain resolves may decrease symptoms while the transient osteoporosis resolves.
Kerboul measuring of lesion size
A 41-year-old female postal worker reports a 9-month history of left groin and lateral hip pain. She denies pain in the right hip. Her social history reveals that she smokes and drinks on average five alcoholic beverages per week. Her body mass index (BMI) is 26. Radiographs are shown in Figures 31a through 31c and coronal and axial MRI scans are shown in Figures 31d and 31e, respectively. What is the most important factor that will determine if her right hip will become symptomatic
Size of lesion
Several factors have been examined as potentially predictive of progression in the patient with an asymptomatic osteonecrotic lesion of the femoral head. While the presence of ongoing risk factors, lesion location, lesion stage, age, gender, and BMI have all been suspected as important, the size of the lesion, particularly when over one third of the size of the femoral head, is a significant risk factor for progression.
acetabular component design?
posrteriorly placed elevated rim liner may?
lateralize liner results in?
- a posteriorly placed elevated rim liner may increase joint stability
- Lateralized liner: increases soft-tissue tension by increasing offset, has been shown to increase the risk of acetabular component loosening
Acetabular position:
anteverion?
abduction?
medialization of cup increases ?? leading to ??
caveats?
complications of excessive version, abduction/adduction?
soft tissue tensioning: restoration of offset
increase offset leads to?
decreased offset leads to?
techniques to increase offset
Increased Offset:
1. less impingement
2. less joint reaction force
3. increased soft tissue tension w/o increasing Leg Length
Increasing offset improves hip stability
Decreased offset may lead to:
1. instability
2. abductor weakness
3. gluteus med lurch
techniques to increase offset
increasing length of femoral neck
decreasing neck-shaft angle
medializing the femoral neck while increasing femoral neck length
trochanteric advancement
alteration of the acetabular liner (see “component design” above)
What parameter indicates a stiff spinopelvis junction? What does stuck sitting vs stuck standing mean?
stiff spinopelvis, hyper-mobile joint at increased risk for dislocation
- change in sacral slope (SS) of <10° indicates a stiff spinopelvic junction
- stuck standing: pelvis does not tilt posteriorly to accomodate a flexed femur, impingement anteriorly leads to posterior dislocation.
- stuck sitting: pelvis remains fixed in a posteriorly tilted position when going form sitting to standing. hypermobile femur will impinge posteriorly and dislocate anteriorly
In the normal relationship, the pelvis tilts or flexes posteriorly 20-35 degrees and the femur flexes 55-70 degrees when going from standing to sitting, decreasing lumbar lordosis and sacral slope and allowing the patient to sit upright (Illustration A). Abnormal spinopelvic motion is determined by first measuring the sacral slope on both sitting and standing lateral spine-pelvis-hip radiographs (Illustration B). If the difference in the two measurements is < 10 degrees, then the patient is deemed to have a stiff spine and is at increased risk of having an instability event (normal motion is a change in sacral slope between 10 and 30 degrees)
stuck sitting at risk for?
fig B normal change in sacral slope (SS), as well as acetabular anteinclination (AI) and pevic-femoral angle (PFA) when going from standing to sitting.
“stuck sitting” due to decreased spinopelvic motion after spinal fusion surgery, the patient is most at risk for anterior dislocation if combined anteversion is excessive, even when the surgery is performed from a posterolateral approach.
In the normal relationship, the pelvis tilts or flexes posteriorly 20-35 degrees and the femur flexes 55-70 degrees when going from standing to sitting, decreasing lumbar lordosis and sacral slope and allowing the patient to sit upright (Illustration A). Abnormal spinopelvic motion is determined by first measuring the sacral slope on both sitting and standing lateral spine-pelvis-hip radiographs (Illustration B). If the difference in the two measurements is < 10 degrees, then the patient is deemed to have a stiff spine and is at increased risk of having an instability event (normal motion is a change in sacral slope between 10 and 30 degrees). To determine whether a patient is “stuck sitting” versus “stuck standing,” the anterior pelvic plane (APP) is drawn (Illustration B). If it is tilted posteriorly 10-13 degrees in the setting of reduced pelvic motion, the patient is said to be “stuck sitting” (Illustration C) and is at increased risk of posterior impingement and anterior instability when standing. If the APP is neutral in the setting of reduced pelvic motion, the patient is said to be “stuck standing” (Illustration D) and is at risk for anterior impingement and posterior instability when sitting.
restoration of offset?
Restoration of offset improves overall arthroplasty biomechanics with decreased cup strain and polyethylene wear, decreased dislocation risk, increased hip abductor strength, and lower rates of postoperative limp. The drawback of too much femoral offset is an increased risk of lateral prominence and subsequent trochanteric bursitis.
Femoral offset is defined as the distance from the femoral head center of rotation to the center of the long axis of the femur.
cement fixation optimized by?
cemented femoral stems have lower success rates in the revision setting
types of coating
- Porous coated metallic surface
- Grit blastided metallic surface
- Hydroxyapatite (HA)
acetablular screw placement and safe zones
Ideal place for supplemental screws?
Caution zone?
Danger zone?
death zone?
Posterior superior: ideal, elevation hip center in revision can place sciatic nerve at risk in this quadrant
Caution: posterior inferior, screws larger than 20mm, sciatic nerver, inferior gluteal vessels, internal pudenal nerve/vessels
danger: anterior inferior, obturateor n/a/v
death zone: anterior-superior quadrant
Acetabular quadrants are formed from a line extending from the ASIS (Marker A) through the center of the acetabulum (Marker C) to the posterior fovea, forming acetabular halves. The second line is drawn perpendicular to the first at the center of acetabulum, forming four quadrants (Illustration A)
AVOIDING PROSTHESIS IMPINGEMENT
leaving anterior rim of acetabulum proud may result in?
causes of impingement?
external iliac vessels at risk with aberrant retractor placement in what zone?
anterior superior
The external iliac vessels run along the medial border of the psoas muscle when anterior acetabular retractors are placed, these structures can be at risk in this are
- Aberrant retractor placement in the anterior-inferior quadrant typically leads to injury of the obturator nerve, artery, or vein
- Aberrant retractor placement in the posterior-inferior quadrant would lead to potential injury of the sciatic nerve, inferior gluteal vessels/nerve, or internal pudendal vessels/nerve.
- The posterior-superior quadrant is a relatively safe zone, but aberrant retractor placement can injure the superior gluteal nerve/vessels or the sciatic nerve.
- Retractor placement directly inferior to the transverse acetabular ligament would cause potential injury to the obturator vessels/nerve.
Long screws placed into the ??? quadrant may pass into sciatic notch and endanger the sciatic nerve and superior gluteal vessels. This is particularly a risk ??
Long screws placed into the posterior superior or posterior inferior quadrant may pass into sciatic notch and endanger the sciatic nerve and superior gluteal vessels. This is particularly a risk in revision surgery when the acetabular component may be placed in a high hip center position, as the sciatic nerve is at increased risk when placing transacetabular screws posteriorly.
The placement of supplemental screw fixation with acetabular component fixation is a typical adjunct measure but carries the greatest risk of vascular injury if placed in which of the following positions?
aaos
Anatomic studies indicate that the safe areas for screws are superior and posterior. The external illiac artery is at risk with anteromedial placement, and the sciatic nerve may be compromised by posterior inferior screw placement.
THA sciatic nerve palsy
what division is most commonly affected?
Risk factors?
Intra op factors?
Immediate post op palsy?
Prognosis?
Persisent foot drop gets?
peroneal division of sciatic nerve most commonly affected (80%)
* sciatic nerve travels closest to acetabulum at level of ischium
* exercise care with posterior acetabular retraction when hip in flexed position
* Intra-op: adult ddh undergoing THA, subtroch osteotomy”, downsizing components
* Immediate post-op: place hip in extension/knee flexion, decreases tension on nerve; immediate evacuation in OR for hematoma
* only 35-40% complete functional recovery to pre-op strength
* AFO, sciatic neuropathy following THA in a patient that does not tolerate AFO bracing. Posterior tibialis tendon transfer is the next most appropriate step in treatment.
0-3% risk: most common cause for medical malpractice litigation following THA.
Patients with DDH that have undergone a large limb-lengthening procedure are at a greater risk due to the significant stretch of the sciatic nerve. Intra-operative procedures that have been shown to prevent this outcome include good pre-operative planning, limb lengthening <3 cm, subtrochanteric osteotomy, intra-operative wake-up test, and downsizing implant components if presenting with deficits peri-operatively
Squeaking after THA, what are the risks?
Squeaking is multifactorial and may include impingement, edge-loading, loss of fluid film lubrication, and third-body particles. Subclinical infection does not play a role in squeaking.
risk factors for THA dislocation? what to look for on xrays? mgmt?
- increased acetabular inclination > 60°
- increased acetabular anteversion > 20°
- aceabular retroversion
- look for eccentric position of femoral head as an indication of polyethylene wear and risk for impending dislocation
- poly exchange if extensive posly wear thought to be sole reason.
- revision THA, 2+dislocations with evidence of implant malalignment(vertical cup, acetabular retroversion), implant failure, polywear
3 types of corrosion associated with trunnionosis?
Risk factors for trunnionosis?
The adverse reaction to metal debris generation may result in
Metal ion levels?
Galvanic: electrochemic transfer of e- b/t dissimilar metals (CoCr alloy femoral head with titanium alloy stem)
Fretting: corrosion from micromotion b/t two materials causing wear.
Crevice corrosion: physiochemical interaction b/t metal and environment leading to altered mechanical properties. Stainless steel most prone to crevice corrosion.
an aseptic lymphocyte-dominant vasculitis association lesion (ALVAL; also referred to as pseudotumor) similar to that seen in metal-on-metal hips
cobalt levels are elevated substantially more than chromium levels, 2:1 ratio when caused by head neck junction trunnionosis, 1:1 ratio suggests MOM wear
The retrieved stem shows evidence of mechanically-assisted crevice corrosion (MACC), or trunnionosis, a risk factor for which is shorter trunnion geometry with a thinner taper, creating an increasingly flexible construct that allows more fluid ingress and disruption of the passivation layer, generating higher torsional forces, micromotion, and subsequent trunnion wear
THA anatomy: risk of bleeding
placement of inferior retractor under the transverse acetabular ligament places what structure at risk?
Where are the following arteries at risk?
Medial femoral circumflex artery:
Obturator artery:
Acesnding branch of lateral femoral circumflex:
external iliac vessels:
common femoral vessels
quadrants of the acetubulum
- placement of inferior retractor under the transverse acetabular ligament places the obturator arteryat risk. and/or placement of an acetabular screw in the anterior-inferior quadrant.
- MCFA: underneath the gluteus maximus tendon and/or quadratus femoris muscle
- ascending branch of LFCA: ascends between tensor fasciae latae and sartorius encountered during direct anterior approach
- External iliac vessels: lie 7mm away from bone at level of ASIS reports of vessels lying immediately adjacent bone
- Common femoral vessels: lie superficial to iliopsoas separated from hip by only anterior capsule and iliopsoas
A metal-on-metal (MoM) THA pseudotumor,
also known as?
RF?
mechanism?
wear rate association?
Predominant cell type
CoCr levels, trend? whats high?
Aspirate will show?
who can be managed conservatively?
Tx and outcomes?
- aseptic lymphocyte-dominant vasculitis-associated lesion (ALVAL), is a mass-forming tissue reaction caused by metal-on-metal wear
- RF: elevated CoCr levels, Femail, high acetabulum inclination angle 55 plus
- two mechanisms: hypersensitivity to metal ions, local high wear debris
- lymphocyte predominant, macrophages and lympocytes present though
- pseudotumor is associated with increased linear wear of both the acetabulum and the femoral components.
- CoCr levels: highest 12-24 months post op, “wear/run in” then steady state, 7 parts per billion (ppb or ug/L) warrants MARS
- Hip aspirate “dishwater fluid”
- manual cell count: fibrinous debris from metal-on-metal reactions will falsely elevate automated cell counts The presence of >3,000 cells per μL is concerning for a prosthetic hip infection. In metal-on-metal hips, the threshold is >4,350 cells per μL. higher percentage of lymphocytes (>40%).
- MARS MRI best correlates with prognosis in the setting of metal debris. Serum metal ion levels can be followed to monitor the amount of metal debris but have little correlation with fluid collection or soft tissue destruction.
- symptomatic patients with normal serum metal ions (<7 ppb for both serum cobalt or serum chromium) and normal MARS-MRI studies may be managed conservatively with close clinical follow-up (3-6 months) and regular serum metal ion labs.
Tx:
1. observation: well functioning THA, low metal ions, no psuedotumor on MRI, 40% of patients asymptomatic with pseudotumor.
2. revision THA to ceramic-on-poly components
- most patients with pain, elevated ions or a psudotumor on MRI require operative intervention
outcomes: significant bone loss, soft tissue destruction, degree of abductor muscle deficiency and poorlocal environment for healing corresponds to difficulty of revision and functional outcomes
-if severely compromised abductor function or damaged soft-tissue affects implant stability, may require the use of a contrained liner
- gluteus maximus transfer can be used to reconstruct deficient abductor mechanism
-higher rates of dislocation and infection
14-20% of revision THAs performed due to a MoM pseudotumor require a 2nd operation within 5 years
**MRI with Metal Artifact Reduction Sequence (MARS)
** a pseudotumor will appear like a fluid collection or solid mass in periprosthetic soft tissues
T1 weighted images will show signal similar to bladder contents (transudate)
T2 weighted images will generally show hyperintensity as compared to muscle and may be heterogenous or homogenous
the hypointense content observed in T2 sequences may be related to the presence of necrosis or metal deposition
histologic specimen of a joint pseudocapsule surrounding a cobalt-chromium second-generation metal-on-metal (MOM) hip replacement prostheses. The dark areas represent:
typical perivascular and diffuse infiltrates of T- and B-lymphocytes characteristic of metal-on-metal-related delayed type hypersensitivity (DTH).
- paucity of particle-laden histiocytes (compared with conventional metal-on-polyethylene articulations) because of low wear rates and lesser wear particle volume.
- Particle-laden macrophages are typical of metal-on-polyethylene bearing surfaces.
EFFECTOR cell of DTH is the T-CELL. The MOST COMMON cell is the MACROPHAGE, as most DTH-participating cells are macrophages and only 5% of cells present are lymphocytes. Histological examination of the pseudocapsule will reveal BOTH T- and B-lymphocytes. Besides perivascular and diffuse lymphocytic infiltrates, there are also secondary lymphoid follicles suggestive of a hypersensitivity reaction. Released soluble metal (from metal degradation) can activate the immune system by forming complexes with native proteins, creating antigens/allergens. Polymeric wear debris is not known to be a major source of allergic-type immune response.
THA periprosthetic
intra-op acetabular fx:
mechanism? risk factors? evaluation? treatment:
if component stable?
if posterior colum compromised?
- If noticed intra-op, the stability of the component should be assessed by the surgeon to determine treatment. If the component is stable, no additional treatment is necessary. If the acetabular component is unstable, then it should be changed and/or supplemented with component screws until stability is obtained.
- if posterior column is compromised, ORIF + revision is most stable construct
THA periprosthetic
intra-op femur fractures:
prox, mid, distal fractures most likely caused by?
treatment:
long calcar split?
proximal femur fx?
complete 2-part fx in middle region?
distal fxs that cannot be bypassed?
Proximal fxs: occur with** bone preparation (aggressive rasping) and prosthetic insertion (dimension mismatch)
Middle region fxs: excessive force during exposure or bone prep
distal fxs: tip of straight stem prosthesis impacting at femoral bow**
**change in resistance **while inserting stem should raise suspicion for fracture
intra-op periprosthetic fx THA
Type
A1,2,3
B1,2,3
C1,2,3
early vs later post op periprosthetic femur fractures
Description and tx for vancouver fx?
periprosthetic post op femur fxs
Treatments?
non-op with protected WB for?
ORIF of GT?
ORIF of femoral shaft w/ locking plate and cables?
Femoral component revision w/ long stem?
Femoral component revsion w/ proximal femoral allograft?
Femoral component revision w/ PFR?
LLD after THA:
litigation?
2 mechanisms that cause this?
tx options?
2nd most common reason for litigation following total hip arthroplasty (following nerve injury)
contracture leads to pelvic obliquity
* ABDuction contracture causes involved hemipelvis to be lower, creating apparent LONG leg
- ADDuction contracture causes involved hemipelvis to be higher, creating apparent SHORT leg
weakness
**weak abductors may provide the sensation of a long leg in the absence of true LLD **
usually resolve within 3-6 months post-operatively
xrays: increased femoral neck length, increasing femoral offset will not increase limb length
tx: shoe lift, wait 6 months until treat to alloq adequate relaxation of muscles?
revision THA-rare: significant LLD that affect quality of life and has not resolved over 6 to 12 months. concern for dislocation with revision surgery especially if attempting to shorten limb
THA
iliopsoas impingement
malpositioned acetabular component:
groin pain, avg time 20 months post op.
pain w/ resisted hip flexion on SLR
CT scan helpful to determine position of prosthesis
Diagnostic CIS in iliopsoas sheath helpful for dx
tx: Treatment is generallyarthroscopic iliopsoas tenotomy in the setting of normal cup position. Revision of the acetabulum component may be indicated in cases of excessive anterior overhang.
CT demonstrates anterior acetabular overhang in a patient w/ anterior groin pain after tha
Changes in articular cartilage with OA knee? how does it compare to normal aging? What happens to the synovium?
Increased water
decreased in amount of proteoglycans
collagen organization&orientation lost: decreases in cross-linking and stiffness associated with degradation
binding of proteoglycans to hyaluronic acid
synovium becomes increasing thick & vascular (late stages)
Bone: subchondral bone attempts to remodel, lytic lesion w/ sclerotic edges, bone cyst in late stages. Osteophytes mediated by Indian Hedgehog Ihh pathway
Proteolytic enzymes in OA:
Bad ones, regulated by, cytokines?
Matrix Matelloproteases (MMPs) cause cartilage matrix digestion. (stromelysin, plasmin, aggrecanase 1 (adamts-4)
Tissue inhibitors of MMPs (TIMPs): control MMP activity, imbalance b/t MMP and TIMPs demonstrated in OA tissues>
Cytokines: secreted by synoviocytes and increase MMP synthesis: IL-1, IL-6, TNF Alpha
gait in knee oa?
increased adductor moment to limb during gait
antalgic, knee maintained flexed, shortened stride, compensatory toe walking
UKA
Comparison to TKA?
Contraindications?
Most common problem?
Good indication for?
Medial compartment OA?
Best tibial alignment?
HY
