Effect of Polyethylene Crosslinking and Bearing Design on Wear of Unicompartmental Arthroplasty.

Wear and polyethylene damage continue to be important factors affecting outcomes of unicompartmental knee arthroplasty. We compared two design rationales for unicompartmental arthroplasty: fully congruent mobile bearings; or moderately conforming fixed bearings using experimental and computational wear simulation. Experimental wear rates were 3.89 (±0.12) mg/million cycles for the highly crosslinked Triathlon PKR fixed bearing compared to 18.35 (±0.19) mg/million cycles for the low crosslinked Oxford mobile bearing. Finite element analysis was used to calculate the effect of crosslinking and backside wear. Increase in polyethylene crosslinking reduced wear by 68% while backside wear comprised 46% of the total wear in the mobile bearing. Increasing conformity may not be the sole predictor of wear performance and highly crosslinked fixed-bearing polyethylene insert can also provide high wear performance.

Augmented wedge-shaped glenoid component for the correction of glenoid retroversion: a finite element analysis.

BACKGROUND: This study undertook a computational analysis of a wedged glenoid component for correction of retroverted glenoid arthritic deformity to determine whether a wedge-shaped glenoid component design with a built-in correction for version reduces excessive stresses in the implant, cement, and glenoid bone. Recommendations for correcting retroversion deformity are asymmetric reaming of the anterior glenoid, bone grafting of the posterior glenoid, or a glenoid component with posterior augmentation. Eccentric reaming has the disadvantages of removing normal bone, reducing structural support for the glenoid component, and increasing the risk of bone perforation by the fixation pegs. Bone grafting to correct retroverted deformity does not consistently generate successful results. METHODS: Finite element models of 2 scapulae models representing a normal and an arthritic retroverted glenoid were implanted with a standard glenoid component (in retroversion or neutral alignment) or a wedged component. Glenohumeral forces representing in vivo loading were applied and stresses and strains computed in the bone, cement, and glenoid component. RESULTS: The retroverted glenoid components generated the highest compressive stresses and decreased cyclic fatigue life predictions for trabecular bone. Correction of retroversion by the wedged glenoid component significantly decreased stresses and predicted greater bone fatigue life. The cement volume estimated to survive 10 million cycles was the lowest for the retroverted components and the highest for neutrally implanted glenoid components and for wedged components. CONCLUSION: A wedged glenoid implant is a viable option to correct severe arthritic retroversion, reducing the need for eccentric reaming and the risk for implant failure.

Effect of microseparation and third-body particles on dual-mobility crosslinked hip liner wear.

Large heads have been recommended to reduce the risk of dislocation after total hip arthroplasty. One of the issues with larger heads is the risk of increased wear and damage in thin polyethylene liners. Dual-mobility liners have been proposed as an alternative to large heads. We tested the wear performance of highly crosslinked dual-mobility liners under adverse conditions simulating microseparation and third-body wear. No measurable increase in polyethylene wear rate was found in the presence of third-body particles. Microseparation induced a small increase in wear rate (2.9mm(3)/million cycles). A finite element model simulating microseparation in dual-mobility liners was validated using these experimental results. The results of our study indicate that highly crosslinked dual-mobility liners have high tolerance for third-body particles and microseparation.

Assessment of cortical bone with clinical and ultrashort echo time sequences.

We describe the use of ultrashort echo time (UTE) sequences and fast spin echo sequences to assess cortical bone using a clinical 3T scanner. Regular two- and three-dimensional UTE sequences were used to image both bound and free water in cortical bone. Adiabatic inversion recovery prepared UTE sequences were used to image water bound to the organic matrix. Two-dimensional fast spin echo sequences were used to image free water. Regular UTE sequences were used together with bicomponent analysis to measure T*2s and relative fractions of bound and free water components in cortical bone. Inversion recovery prepared UTE sequences were used to measure the T*2 of bound water. Saturation recovery UTE sequences were used to measure the T1 of bone water. Eight cadaveric human cortical bone samples and a lower leg specimen were studied. Preliminary results show two distinct components in UTE detected signal decay, a single component in inversion recovery prepared UTE detected signal decay, and a single component in saturation recovery UTE detected signal recovery. Regular UTE sequences appear to depict both bound and free water in cortical bone. Inversion recovery prepared UTE sequences appear to depict water bound to the organic matrix. Two-dimensional fast spin echo sequences appear to depict bone structure corresponding to free water in large pores.

Wear of polyethylene against oxidized zirconium femoral components effect of aggressive kinematic conditions and malalignment in total knee arthroplasty.

Metallic femoral components with ceramic articulating surfaces can substantially lower polyethylene (PE) wear during walking activities under conditions of normal knee alignment. It is unknown whether these types of components can maintain low wear rates under conditions of knee malalignment and the harsher kinematics associated with younger, athletically active patients. Wear was measured in non-cross-linked, ethylene oxide-sterilized PE inserts against oxidized zirconium or cobalt-chrome femoral components in a knee wear simulator. The vertical load was modified to replicate knee varus malalignment of 3°, and the range of tibial rotation was increased to 20°. Mean gravimetric and volumetric wear rate over 5 million cycles was 55% lower in the oxidized zirconium group. An oxidized zirconium femoral component can significantly reduce PE wear under simulated conditions of athletically active patients with modestly malaligned total knee arthroplasty prostheses.

Ultrashort echo time MR imaging of osteochondral junction of the knee at 3 T: identification of anatomic structures contributing to signal intensity.

PURPOSE: To image cartilage-bone interfaces in naturally occurring and experimentally prepared human cartilage-bone specimens at 3 T by using ultrashort echo time (TE) (UTE) and conventional pulse sequences to (a) determine the appearance of the signal intensity patterns and (b) identify the structures contributing to signal intensity on the UTE MR images. MATERIALS AND METHODS: This study was exempted by the institutional review board, and informed consent was not required. Five cadaveric (mean age, 86 years +/- 4) patellae were imaged by using proton density-weighted fat-suppressed (repetition time msec/TE msec, 2300/34), T1-weighted (700/10), and UTE (300/0.008, 6.6, with or without dual-inversion preparations at inversion time 1 = 135 msec and inversion time 2 = 95 msec) sequences. The UTE images were compared with proton density-weighted fat-suppressed and T1-weighted images and were evaluated by two radiologists. To identify the sources of signal on the UTE images, samples including specific combinations of tissues (uncalcified cartilage [UCC] only, calcified cartilage [CC] and subchondral bone [bone] [CC/bone], bone only; and UCC, CC, and bone [UCC/CC/bone]) were prepared and imaged by using the UTE sequence. RESULTS: On the UTE MR images, all patellar sections exhibited a high-intensity linear signal near the osteochondral junction, which was not visible on protein density-weighted fat-suppressed or T1-weighted images. In some sections, focal regions of thickened or diminished signal intensity were also found. In the prepared samples, UCC only, CC/bone, and UCC/CC/bone samples exhibited high signal intensity on the UTE images, whereas bone-only samples did not. CONCLUSION: These results show that the high signal intensity on UTE images of human articular joints originates from the CC and the deepest layer of the UCC, without a definite contribution from subchondral bone. UTE sequences may provide a way of evaluating abnormalities at or near the osteochondral junction. (c) RSNA, 2010.

Accuracy of CT-based measurements of glenoid version for total shoulder arthroplasty.

BACKGROUND/HYPOTHESIS: The arthritic glenoid is typically in retroversion and restoration to neutral version is recommended. While a method for measurement of glenoid version using axial computed tomography (CT) has been reported and has been widely accepted, its accuracy and reproducibility has not been established. METHODS: In 33 patients scheduled for shoulder arthroplasty, glenoid version and maximum wear of the glenoid articular surface were measured with respect to the scapular body axis on 2-dimensional- (2D) CT slices as well as on 3-dimensional- (3D) reconstructed models of the same CT slices. RESULTS: Clinical CT scans were axially aligned with the patient's torso but were almost never perpendicular to the scapular body. The average absolute error in version measured on the 2D-CT slice passing through the tip of the coracoid was 5.1 degrees (range, 0 - 16 degrees , P < .001). On high-resolution 3D-CT reconstructions, the location of maximum wear was most commonly posterior and was missed on the clinical 2D-CT slices in 52% of cases. CONCLUSION: Error in measuring version and depth of maximum wear can substantially affect the determination of the degree of correction necessary in arthritic glenoids. Accurately measuring glenoid version and locating the direction of maximum wear requires a full 3D-CT reconstruction and analysis.

99mTc-HYNIC octreotide in neuroblastoma.

Disease status assessment of neuroblastoma patients requires computed tomography (or magnetic resonance imaging), bone scan, metaiodobenzylguanidine (MIBG) scan, bone marrow tests, and urine catecholamine measurements. There is no clinical experience concerning the evaluation of these patients by means of technetium-99m (99mTc)-somatostatin analog scintigraphy. Furthermore, these radiopharmaceuticals are promising imaging agents owing to their lower cost, availability, dosimetry, and ease of preparation. An 8-year-old boy already diagnosed with stage-IV neuroblastoma received chemotherapy. In the follow-up, after obtaining the parents' informed consent, iodin 131 (131I)-MIBG and 99mTc-6-hydrazinopyridine-3-carboxylic acid (HYNIC)-octreotide scans were done on separate days to evaluate tumor extension. Even as the 131I-IBG scan showed mild diffuse uptake in the projection of both lung hili, the 99mTc-HYNIC-octreotide scan showed multiple axial and appendicular bone uptakes and paravertebral, abdominal, mediastinal, and supraclavicular ganglionar uptakes. The 99mTc-HYNIC-octreotide showed much more lesion extension than the 131I-MIBG. Therefore, 99mTc-HYNIC-octreotide may be a promising radiopharmaceutical for the evaluation of neuroblastoma patients. This finding justifies the preliminary evaluation of this tracer in the context of a clinical trial.

Optimizing glenoid component position using three-dimensional computed tomography reconstruction.

Glenoid implant design and alignment are critical to the success of shoulder arthroplasty. Computer-aided design models of 3 glenoid implant designs (keel, standard pegs, and modified pegs) were virtually implanted into 3-dimensional computed tomography-reconstructed models of 40 normal scapulae. The incidence of perforation on 3-dimensional computed tomography preoperative templating varied from 8% to 18% for the 3 models. Malalignment of the implants in retroversion was better tolerated than anteversion and varied with implant design. Tolerance for medialization of the implant to correct for glenoid wear was limited (range, 0 degrees-18 degrees ) and varied with implant design. The modified peg design had the lowest incidence of perforation, the greatest tolerance for malalignment, and the ability to correct for glenoid wear effects. These results emphasize the need for accurate preoperative templating and for developing alignment guides or surgical navigation tools for shoulder arthroplasty and may be used to improve implant fixation designs.

Dobutamine modulated Tc-99m MIBI scintigraphy in secondary hyperparathyroidism in uremic patients.

The aim of this study was to determine if low-dose dobutamine infusion can enhance Tc-99m methoxy isobutyl isonitrile (MIBI) uptake of hyperfunctioning parathyroid glands of patients with secondary hyperparathyroidism (SHP). We studied 24 patients with chronic renal failure and SHP. Median age of the sample was 47.5 years. A single-tracer, double-phase technique was performed, acquiring planar images of the neck and thorax after the injection of 740 to 1110 MBq (20-30 mCi) of Tc-99m MIBI. After 2 to 7 days, the study was repeated after the infusion of low-dose dobutamine of 2.0 microg . kg . min for 60 minutes. The scan was considered positive for hyperfunctioning parathyroid tissue when an area of increased uptake that persisted on late imaging was found. Parathyroid-to-thyroid count rates (PT/T) were calculated for each abnormal focus. Hyperplasic parathyroid tissue was confirmed in 12 of 24 patients who underwent neck surgery whereas the remaining group had persistent or worsening disease, verified by clinical follow-up between 6 and 25 months after the nuclear studies (median: 12 months). An MIBI baseline study was positive in 21 of 24 patients (87%), whereas the dobutamine study was positive in all patients. Thirty-five abnormal foci were seen on baseline MIBI studies and 43 on dobutamine scans (1.46 +/- 1.02 vs. 1.79 +/- 0.88, mean +/- SD, respectively, P = 0.043). Dobutamine PT/T ratios were significantly higher than those from the baseline study (1.49 +/- 0.30 vs. 1.38 +/- 0.28, mean +/- SD, respectively, P = 0.0002, n = 43). We concluded that low-dose dobutamine Tc-99m MIBI scintigraphy has the potential of enhancing tracer uptake and retention in patients with SHP.

Patellofemoral forces after total knee arthroplasty: effect of extensor moment arm.

Total knee arthroplasty implant designs with larger extensor moment arms theoretically should generate lower extensor forces for the same externally applied loads. This study measured knee kinematics, quadriceps forces, and patellofemoral forces under conditions of dynamic knee extension under load in two knee designs with differing quadriceps moment arms. Six human cadaver knees were tested both before implantation and after sequential implantation with two posterior cruciate retaining designs. The extensor moment arm of the LMA (long extensor moment arm design, Scorpio, Howmedica Osteonics, Rutherford, NJ) was approximately 1 cm longer than that of the Control design (7000, Howmedica Osteonics). Quadriceps tension was measured during dynamic closed kinetic chain knee extension. Patellar compressive and shear forces were also recorded using a patellar component instrumented with a custom triaxial load transducer. Knee kinematics were monitored using a three-dimensional electromagnetic tracking device. Both designs produced similar patterns of femoral rollback and tibial rotation. Quadriceps tension was lower in the LMA design compared with the Control design. Patellofemoral compressive forces were also significantly reduced in the LMA design when compared with Control (8-18% lower at angles greater than 50 degrees flexion). The design with the longer extensor moment arm required less quadriceps force to extend the knee under load and reduced patellofemoral compressive forces. Reduced quadriceps forces may facilitate postoperative rehabilitation and activities such as stair climbing. Reduction in patellofemoral forces could reduce patellar complications such as anterior knee pain, component wear, and loosening.

Polyethylene cross-linking by two different methods reduces acetabular liner wear in a hip joint wear simulator.

Advances in cross-linking have led to the development of wear resistant ultrahigh molecular weight polyethylene for total joint replacement. This study compared wear reduction by two different cross-linking methods as measured in a hip wear simulator. One highly cross-linked polyethylene was treated with 7.5 Mrad gamma irradiation with post-irradiation annealing and a sterilization dose of 2.5 Mrad (10 Gamma), while the other used 9.5 Mrad warm irradiation with 10 MeV electron-beam (9.5 EB). Liners of the same design, made from nominally cross-linked (gamma sterilized) polyethylene were also tested. Gravimetric wear analysis was performed every 500,000 cycles for 5,000,000 cycles. After correcting for weight gain due to water absorption, the nominally cross-linked liners demonstrated mean wear rates of 15.7 (+/-1.7) and 12.5 (+/-1.0) mg/million cycles. Both highly cross-linked polyethylene liners demonstrated significantly less wear than their respective controls (with mean wear rates of 1.5 (+/-1.2) and -1.4 (+/-1.5) mg/million cycles). The 9.5 EB liners gained weight presumably due to increased fluid absorption, in addition to that measured in loaded-soaked control implants. Any wear occurring was therefore assumed to have been more than offset by weight gain. Highly cross-linked polyethylene was significantly more wear resistant than non- or nominally cross-linked polyethylene. The differences in wear rates between the two highly cross-linked polyethylene designs (9.5 EB or 10 Gamma) are probably too small to be clinically significant.

Comparison of the wear rates of twenty-eight and thirty-two-millimeter femoral heads on cross-linked polyethylene acetabular cups in a wear simulator.

BACKGROUND: The use of larger femoral head sizes in total hip arthroplasty has been shown to reduce the rate of dislocation and to increase the range of motion; however, such components have been associated with unacceptably high polyethylene wear rates. Studies have shown dramatic differences in wear rates between nominally cross-linked polyethylene (i.e., polyethylene that is cross-linked during radiation sterilization) and elevated cross-linked polyethylene (i.e., polyethylene that is cross-linked to a higher degree than that obtained by radiation sterilization alone). The aim of this study was to test the effect of increased cross-linking and of increased head size on polyethylene wear rates. METHODS: Four groups of acetabular liners obtained from a single manufacturer, including 28-mm-diameter nominally cross-linked, 32-mm-diameter nominally cross-linked, 28-mm-diameter elevated cross-linked, and 32-mm-diameter elevated cross-linked polyethylene liners, were tested. Three implants from each group were tested in a twelve-station hip wear simulator with use of 90% bovine serum as a lubricant. The liners were articulated with the appropriately sized cobalt-chromium femoral head. Additional liners from each design were subjected only to the same load without motion to serve as load-soak controls to account for any weight gain due to fluid absorption. Gravimetric analysis was performed every 500,000 cycles for a total of five million cycles. RESULTS: Nominally cross-linked liners demonstrated mean wear rates of 14.97 and 16.92 mg per million cycles for the 28-mm and 32-mm head sizes, respectively. Both of the elevated cross-linked liners had significantly lower wear rates than the nominally cross-linked liners, with a mean of 1.51 and 2.57 mg per million cycles for the 28-mm and 32-mm head sizes, respectively (p < 0.001). CONCLUSION: The dramatic reduction in wear rates with polyethylene cross-linking, even with the larger head size, may increase the potential for use of 32-mm head components in total hip arthroplasty.

An in vivo evaluation of bone response to three implant surfaces using a rabbit intramedullary rod model.

Our study was designed to evaluate osseointegration among implants with three surface treatments: plasma-sprayed titanium (P), plasma-sprayed titanium with hydroxyapatite (PHA), and chemical-textured titanium with hydroxyapatite (CHA). Average surface roughness (Ra) was 27 microns for the P group, 17 microns for the PHA group, and 26 microns for the CHA group. Bilateral distal intramedullary implants were placed in the femora of thirty rabbits. Histomorphometry of scanning electron microscopy images was used to analyze the amount of bone around the implants at 6 and 12 weeks after implantation. Greater amounts of osseointegration were observed in the hydroxyapatite-coated groups than in the noncoated group. For all implant surfaces, osseointegration was greater at the diaphyseal level compared to the metaphyseal level. No significant differences were seen in osseointegration between the 6 and 12 week time points. Although the average surface roughness of the P and the CHA groups was similar, osseointegration of the CHA implants was significantly greater. The results of this in vivo lapine study suggest that the presence of an hydroxyapatite coating enhances osseointegration despite similarities in average surface roughness.

The effect of oxidative aging on the wear performance of highly crosslinked polyethylene knee inserts under conditions of severe malalignment.

First-generation crosslinked polyethylene developed for total hip arthroplasty has not gained wide acceptance for knee arthroplasty because of the increased potential for failure under high stresses and the increased risk for oxidative damage caused by free radicals. Sequentially crosslinked polyethylene (SQXL) is a second-generation crosslinked polyethylene that is reported to reduce the level of free radicals and preserve mechanical properties. Three groups of ultrahigh molecular weight polyethylene inserts were wear tested after artificial aging as per ASTM F2003: gamma-irradiated in air (GA-aged), sequentially crosslinked (SQXL-aged), and electron-beam irradiated and remelted (EBeam-aged). Inserts were tested in an AMTI knee wear simulator under malalignment conditions that were two standard deviations from the mean reported for computer-navigated and conventionally aligned techniques. GA-aged inserts delaminated by 500,000 cycles, and were severely damaged after 1 million cycles. None of the highly crosslinked inserts (SQXL-aged or EBeam-aged) delaminated or showed any signs of severe wear. Mean wear rate for GA-aged inserts was 124.6 +/- 49.4 mg/million cycles. Mean wear rates for SQXL-aged and EBeam-aged inserts were significantly lower (1.74 +/- 0.3 and 4.72 +/- 0.7, respectively). These results support the low levels of free radicals and preservation of mechanical properties reported in second-generation crosslinked ultrahigh molecular weight polyethylene.

Outcome of an acetabular design with hydroxyapatite coating on a rough substrate.

UNLABELLED: Outcomes of hydroxyapatite-coated cups have not been as consistently successful as outcomes of hydroxyapatite-coated stems; therefore, we studied a newer generation acetabular design with a plasma-sprayed hydroxyapatite coating on an arc-deposited rough titanium substrate. Our objective was to determine whether clinical and radiographic outcomes would be better than reported for earlier-generation designs. Ninety consecutive hips in 85 patients implanted with this design were followed up prospectively for 2 to 5 years after surgery. Hip scores improved from a preoperative mean of 59 (+/- 12) to final followup mean of 91 (+/- 12). One hip was revised for recurrent dislocation. No hips were revised for aseptic loosening. No cup had complete continuous radiolucent lines. Incomplete lucent lines were noted on early postoperative radiographs. With followup, radiolucent line length decreased by a mean 32% and radiolucent line density increased by 9%. Mean polyethylene linear and volumetric head penetration rates were 0.17 (+/- 0.16) mm/year and 73 (+/- 70) mm/year, respectively. Head penetration rates were higher in men. No other factor (age, body weight, cup abduction, or anteversion angle) correlated with head penetration rate. Our study presents encouraging short-term results. Improvement in radiolucent lines suggests a beneficial effect of hydroxyapatite coating on osseointegration of the cup. LEVEL OF EVIDENCE: Therapeutic study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Oxidized zirconium femoral components reduce polyethylene wear in a knee wear simulator.

Polyethylene wear remains a major problem that can jeopardize the long-term durability of prostheses used in total knee arthroplasty. Oxidized zirconium is a material that combines the strength of a metal with the wear properties of a ceramic. This study evaluated the wear rates of polyethylene inserts against oxidized zirconium femoral components. Three oxidized zirconium femoral components and three Co-Cr femoral components of identical geometry used in total knee arthroplasty were articulated against standard tibial components with modular tibial inserts made of noncross-linked ultra-high molecular weight polyethylene. Gravimetric and volumetric polyethylene wear rates were calculated after 5 million gait cycles on an AMTI knee wear simulator. Oxidized zirconium reduced polyethylene wear by 42% compared with Co-Cr alloy. This study shows that oxidized zirconium can reduce polyethylene wear substantially when used for fixed-bearing total knee arthroplasty.

Re-HEDP : pharmacokinetic characterization, clinical and dosimetric evaluation in osseous metastatic patients with two levels of radiopharmaceutical dose.

BACKGROUND: A study for pain relief therapy with 188Re-HEDP was done in patients with bone metastases secondary to breast and prostate cancer. MATERIALS AND METHODS: Patients received 1.3 or 2.2 GBq, in single or multiple doses. Platelets, white and red cells were evaluated during 11 weeks. Pharmacokinetic characterization was done from blood and urine samples for 5 patients along 24 hours. Urinary excretion was evaluated in other 16 patients during 6 hours. Bone uptake was estimated as remaining activity in whole body. Scintigraphic images were acquired at 2 and 24 hs post-administration. Absorbed dose in bone marrow was estimated with Mirdose3. Analgesics intake and pain score were daily recorded. Tumour markers (PSA, and Tn-structure) were monitored in 9 patients during 4 to 6 months. Single doses of low activity (1.3 GBq) were given to twelve patients. Nine patients received multiple doses. RESULTS: All except one patient had normal levels of platelets, white and red cells. Remaining dose in blood at 2 hours was 9%. Urinary elimination was 58%. Bone uptake at 24 hours was 43% (mean value; n = 5). No changes of the haematological parameters were detected along follow-up period. Pain relief was evidenced by decrease or supression of opioid analgesic and by subjective index. PSA showed a decrease in prostate cancer patients (n = 4). Tn-structure showed a significant increase after 4 to 8 months. CONCLUSION: Single or multiple dose scheme could be safely used, with administered activity of 188Re-HEDP up to 60 mCi, with low bone marrow absorbed doses.

Sensibilización de la captación de 99m Tc-MIBI por la dobutamina en ganglios regionales de un paciente con melanoma clínicamente localizado / Sensitización of the pick up of 99m Tc-MIBI by the dobutamine in regionals ganglion of a patient with melanoma clinically located

La evaluación centellográfica con 99mTc-MIBI es una técnica de probada utilidad clínica en la evaluación de algunas lesiones tumorales primarias y metastásicas. Presentamos el caso de un hombre de 27 años con diagnóstico de melanoma clínicamente localizado de dorso, tratado mediante resección local ampliada previa. El estudio con 99mTc-MIBI realizado en condiciones basales no mostró alteraciones significativas. Luego de repetir la técnica 72 horas después, luego de la infusión intravenosa de dobutamina a dosis bajas, se observó hipercaptación focal en región axilar derecha. El paciente fue sometido a biopsia quirúrgica de esa región, demostrándose la presencia de compromiso ganglionar metastásico confirmado por histopatología. Se concluye que el centellograma con 99mTc-MIBI sensibilizado con dobutamina a dosis bajas tiene el potencial de aportar información clínicamente relevante en el diagnóstico de extensión regional de pacientes con melanoma.