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Surena Namdari - One of the best experts on this subject based on the ideXlab platform.
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failure to restore the Calcar and locking screw cross threading predicts varus collapse in proximal humerus fracture fixation
Journal of Shoulder and Elbow Surgery, 2020Co-Authors: Eric M Padegimas, Gerard Chang, Kamran Namjouyan, Surena NamdariAbstract:Background Varus collapse is a common failure mode of proximal humerus fracture (PHF) fixation. The purpose of this study was to analyze predictors of varus collapse of PHF after open reduction, internal fixation (ORIF). Methods All patients who underwent ORIF of a PHF from January 2008 to July 2018 were identified. Known predictors of fixation failure were assessed, including Calcar distance, Calcar ratio, and Calcar restoration. Additionally, the presence of cross-threaded screws was determined. The primary outcome analyzed was varus collapse of the fracture defined as a change in neck shaft angulation to less than 120°. Results There were 112 patients identified who underwent ORIF of a PHF that met inclusion criteria. The population was 75.0% female (84/112), average age was 62.5 ± 10.4 years (range 40.0-87.9), and average body mass index was 28.0 ± 5.5 (17.5-46.4). There were 17 with varus collapse. In 11 of the 17 patients (64.7%), there was screw cross-threading (vs. 31/95 [32.6%] in those that did not collapse); P = .012. In addition, 8 of the 17 (47.1%) did not have restoration of the Calcar (vs. 16/95 [16.8%]; P = .005). Conclusion This study identifies 2 surgeon-controlled variables that can contribute to varus collapse after ORIF of PHFs. Cross-threading of locking screws and failure to restore the medial Calcar can be a function of implant design, surgeon technical skill, and/or bone quality.
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Calcar screw position in proximal humerus fracture fixation don t miss high
Injury-international Journal of The Care of The Injured, 2018Co-Authors: Samir Mehta, Surena Namdari, Matthew Chin, Jennifer Sanville, Michael W HastAbstract:Abstract Introduction In locked plate fixation of proximal humerus fractures, the Calcar is an important anchor point for screws providing much-needed medial column support. Most locking plate implants utilize a fixed-trajectory locking screw to achieve this goal. Consequently, adjustments of plate location to account for patient-specific anatomy may result in a screw position outside of the Calcar. To date, little is known about the consequences of “missing” the Calcar during plate positioning. This study sought to characterize the biomechanics associated with proximal and distal placement of locking plates in a two-part fracture model. Materials and methods This experiment was performed twice, first with elderly cadaveric specimens and again with osteoporotic sawbones. Two-part fractures were simulated and specimens were divided to represent proximal, neutral, and distal plate placements. Non-destructive torsional and axial compression tests were performed prior to an axial fatigue test and a ramp to failure. Torsional stiffness, axial stiffness, humeral head displacement and stiffness during fatigue testing, and ultimate load were compared between groups. Results Cadavers: Proximal implant placement led to trends of decreased mechanical properties, but there were no significant differences found between groups. Sawbones: Distal placement increased torsional stiffness in both directions (p = 0.003, p = 0.034) and axial stiffness (p = 0.018) when compared to proximal placement. Distal placement also increased torsional stiffness in external rotation (p = 0.020), increased axial stiffness (p = 0.024), decreased humeral head displacement during fatigue testing, and increased stiffness during fatigue testing when compared to neutral placement. Discussion The distal and neutral groups had similar mechanical properties in many cadaveric comparisons while the proximal group trended towards decreased construct stiffness. Results from the Sawbones model were more definitive and provided further evidence that proximal Calcar screw placements are undesirable and distal implant placement may provide improved construct stability. Conclusion Successful proximal humerus fracture reconstruction is inherent upon anatomic fracture reduction coupled with medial column support. Results from this experiment suggest that missing the Calcar proximally is deleterious to fixation strength, while it is safe, and perhaps even desirable, to aim slightly distal to the intended target.
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defining optimal Calcar screw positioning in proximal humerus fracture fixation
Journal of Shoulder and Elbow Surgery, 2017Co-Authors: Eric M Padegimas, Benjamin Zmistowski, Cassandra Lawrence, Aaron Palmquist, Thema Nicholson, Surena NamdariAbstract:Background Anatomic reduction and placement of an inferior Calcar screw are strategies to prevent fixation failure in proximal humerus factures. Optimal position of the Calcar screw remains unknown. Methods There were 168 shoulders (68.5% female; average age, 63.6 ± 11.5 years) that underwent open reduction and internal fixation of a displaced proximal humerus fracture involving the surgical or anatomic neck. Univariate and multivariate analyses were performed on preoperative clinical, preoperative radiographic, and postoperative radiographic variables to determine association with fixation failure. A receiver operating characteristic curve was performed to determine a maximum distance from the inferior screw to the Calcar (“Calcar distance”) as well as a maximum ratio of this distance and the head diameter (“Calcar ratio”). Results There were 26 of 168 (15.5%) patients with radiographic failures (19 related to fixation failure). Univariate analysis and multivariate analyses found quality of reduction (P Conclusions Quality of reduction, Calcar distance, and Calcar ratio independently correlated with fixation failure. This study provides optimal distances and ratios for Calcar screw placement that can be used clinically.
Maria Byrne - One of the best experts on this subject based on the ideXlab platform.
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noncalcifying larvae in a changing ocean warming not acidification hypercapnia is the dominant stressor on development of the sea star meridiastra Calcar
Global Change Biology, 2012Co-Authors: Hong D Nguyen, Natalie A Soars, Maria ByrneAbstract:Climate change driven ocean warming and acidification is potentially detrimental to the sensitive planktonic life stages of benthic marine invertebrates. Research has focused on the effects of acidification on calcifying larvae with a paucity of data on species with alternate developmental strategies and on the interactive effects of warming and acidification. To determine the impact of climate change on a conspicuous component of the intertidal fauna of southeast Australia, the development of the noncalcifying lecithotrophic larvae of the sea star Meridiastra Calcar was investigated in the setting of predicted ocean warming (+2 to 4 °C) and acidification (−0.4 to 0.6 pH units) for 2100 and beyond in all combinations of stressors. Temperature and pH were monitored in the habitat of M. Calcar to place experiments in context with current environmental conditions. There was no effect of temperature or pH on cleavage stage embryos but later development (gastrula-larvae) was negatively effected by a +2 to 4 °C warming and there was a negative effect of −0.6 pH units on embryos reaching the hatched gastrula stage. Mortality and abnormal development in larvae increased significantly even with +2 °C warming and larval growth was impaired at +4 °C. For the range of temperature and pH conditions tested, there were no interactive effects of stressors across all stages monitored. For M. Calcar, warming not acidification was the dominant stressor. A regression model incorporating data from this study and projected increasing SST for the region suggests an increase in larval mortality to 70% for M. Calcar by 2100 in the absence of acclimation and adaptation. The broad distribution of this species in eastern Australia encompassing subtropical to cold temperate thermal regimes provides the possibility that local M. Calcar populations may be sustained in a warming world through poleward migration of thermotolerant propagules, facilitated by the strong southward flow of the East Australian Current.
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Noncalcifying larvae in a changing ocean: warming, not acidification/hypercapnia, is the dominant stressor on development of the sea star Meridiastra Calcar
Global Change Biology, 2012Co-Authors: Hong D Nguyen, Natalie A Soars, Maria ByrneAbstract:Climate change driven ocean warming and acidification is potentially detrimental to the sensitive planktonic life stages of benthic marine invertebrates. Research has focused on the effects of acidification on calcifying larvae with a paucity of data on species with alternate developmental strategies and on the interactive effects of warming and acidification. To determine the impact of climate change on a conspicuous component of the intertidal fauna of southeast Australia, the development of the noncalcifying lecithotrophic larvae of the sea star Meridiastra Calcar was investigated in the setting of predicted ocean warming (+2 to 4 °C) and acidification (−0.4 to 0.6 pH units) for 2100 and beyond in all combinations of stressors. Temperature and pH were monitored in the habitat of M. Calcar to place experiments in context with current environmental conditions. There was no effect of temperature or pH on cleavage stage embryos but later development (gastrula-larvae) was negatively effected by a +2 to 4 °C warming and there was a negative effect of −0.6 pH units on embryos reaching the hatched gastrula stage. Mortality and abnormal development in larvae increased significantly even with +2 °C warming and larval growth was impaired at +4 °C. For the range of temperature and pH conditions tested, there were no interactive effects of stressors across all stages monitored. For M. Calcar, warming not acidification was the dominant stressor. A regression model incorporating data from this study and projected increasing SST for the region suggests an increase in larval mortality to 70% for M. Calcar by 2100 in the absence of acclimation and adaptation. The broad distribution of this species in eastern Australia encompassing subtropical to cold temperate thermal regimes provides the possibility that local M. Calcar populations may be sustained in a warming world through poleward migration of thermotolerant propagules, facilitated by the strong southward flow of the East Australian Current.
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development of the hyaline layer around the planktonic embryos and larvae of the asteroid patiriella Calcar and the presence of associated bacteria
Invertebrate Reproduction & Development, 1997Co-Authors: Anna Cerra, Maria Byrne, Ove HoeghguldbergAbstract:Summary The hyaline layer (HL) around the embryos and larvae of Patiriella Calcar is examined by transmission electron microscopy. P. Calcar hatches at the gastrula stage and develops through a lecithotrophic planktonic brachiolaria. The hyaline layer of unhatched P. Calcar is poorly developed and is comprised of wispy fibrils scattered among the epithelial microvilli. Fibrils are also occasionally seen associated with the inner surface of the fertilization envelope. By the hatched gastrula stage, the hyaline layer is organized into three strata: the intervillous layer, the supporting layer and the coarse outer meshwork layer. Seven-day-old brachiolaria also have a hyaline layer comprised of three strata. In these larvae the supporting layer elevates away from the epithelial surface due to the tuft-like organization of the underlying microvilli. This results in the formation of local outpockets giving the surface of the HL a lobed appearance. Bacteria are occassionally seen in the intervillous layer, part...
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reproduction of sympatric populations of patiriella gunnii p Calcar and p exigua in new south wales asterinid seastars with direct development
Marine Biology, 1992Co-Authors: Maria ByrneAbstract:Three asterinid seastars, Patiriella gunnii (Gray), P. Calcar (Lamarck) and P. exigua (Lamarck) are sympatric in southeast Australia and form part of a series of Patiriella species endemic to Australian shores. Reproduction of co-occurring populations of P. gunnii, P. Calcar and P. exigua was investigated in New South Wales from December 1988 to February 1991. Their reproductive cycles were documented by the gonad index (GI) method and by histological examination of the gonads. The annual cycle of the pyloric caecae was also documented and the relationship between the two indices was examined. Oogenesis and spermatogenesis are described in histological detail. The three species produce large yolky eggs and have direct development. Vitellogenesis and weight-gain by the ovaries results from accumulation of periodic acid Schiff (PAS +) material by the oocytes. P. gunnii and P. Calcar are gonochoric and have well-defined reproductive cycles, spawning in spring and summer. There was a sharp decline in the GI of P. gunnii in December due to potentially synchronous spawning. Histological examination revealed that initiation of gamete release occurred in August. Gamete release by P. Calcar also started in August, with episodic spawning through December. P. gunnii and P. Calcar have coincident 3 to 4 mo breeding seasons. In general, P. exigua is protandrous with a broad size range over which sex change occurs. Some P. exigua, however are simultaneous hermaphrodites at the outset of gonad formation and become increasingly female with growth. This species has continuous gametogenesis and oviposits its eggs on the undersides of intertidal boulders, with enhanced oviposition during winter and spring. Newly metamorphosed P. exigua occupy intertidal microhabitats and were located in the field from August to October. It is suggested that increasing sea temperature during spring may serve to cue gamete release by P. gunnii and P. Calcar and that enhanced oviposition of P. exigua in winter may be in response to conditions optimal for development of the egg masses at this time. The GI of male and female P. gunnii and P. Calcar did not differ, while male P. exigua had a significantly lower GI than the females. Small males are characteristic of this latter species, and it is suggested that the decreased male investment in P. exigua is associated with its non-planktonic development. The gonad and pyloric caeca (PCI) indices of P. gunnii exhibited a reciprocal relationship, indicating that the transfer of nutrients from the caeca to the gonads supports gametogenesis. These indices were partly reciprocal in P. Calcar. It is suggested that gonadal growth in P. Calcar may be less dependent on caecal reserves than that in P. gunnii. The PCI of P. exigua maintained a similar level throughout the year and was higher than the GI. Although the Patiriella species have coincident breeding periods, temporal differences in the intensity of spawning appears to reproductively isolate them in the field.
Junkyung Hwang - One of the best experts on this subject based on the ideXlab platform.
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cementless Calcar replacement hemiarthroplasty compared with intramedullary fixation of unstable intertrochanteric fractures a prospective randomized study
Journal of Bone and Joint Surgery American Volume, 2005Co-Authors: Junkyung HwangAbstract:Background: Unstable intertrochanteric fractures in elderly patients are associated with a high rate of complications. The purpose of this investigation was to compare the results of long-stem cementless Calcar-replacement hemiarthroplasty with those of treatment with a proximal femoral nail for unstable intertrochanteric fractures in elderly patients. Methods: Fifty-eight elderly patients with an AO/OTA type 31-A2 intertrochanteric fracture of the femur were randomized into two treatment groups and were followed for a minimum of two years. The twenty-nine patients in Group I were treated with a long-stem cementless Calcar-replacement prosthesis, and the twenty-nine patients in Group II were treated with a proximal femoral nail. The two treatment groups were comparable with regard to demographic and injury variables. Results: There were no significant differences between the groups in terms of functional outcomes, hospital stay, time to weight-bearing, or general complications. Patients treated with a proximal femoral nail had a shorter operative time, less blood loss, fewer units of blood transfused, a lower mortality rate, and lower hospital costs compared with those treated with the long-stem cementless Calcar-replacement prosthesis. Conclusions: In elderly patients with an unstable intertrochanteric femoral fracture, a proximal femoral nail provides superior clinical outcomes but no advantage with regard to functional outcome when compared with a long-stem cementless Calcar-replacement arthroplasty. Level of Evidence: Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.
H Lill - One of the best experts on this subject based on the ideXlab platform.
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is there any advantage in placing an additional Calcar screw in locked nailing of proximal humeral fractures
Orthopaedics & Traumatology-surgery & Research, 2015Co-Authors: J C Katthagen, Michael Schwarze, L Bauer, J Meyerkobbe, C Voigt, Christof Hurschler, H LillAbstract:Abstract Background The objective of this study was to evaluate the biomechanical effect of an additional unlocked Calcar screw compared to a standard setting with three proximal humeral head screws alone for fixation of an unstable 2-part fracture of the surgical neck. Hypothesis The additional Calcar screw improves stiffness and failure load. Methods Fourteen fresh frozen humeri were randomized into two equal sized groups. An unstable 2-part fracture of the surgical neck was simulated and all specimens were fixed with the MultiLoc®-nail. Group I represented a basic screw setup, with three locked head screws and two unlocked shaft screws. Group II was identical with a supplemental unlocked Calcar screw (CS). Stiffness tests were performed in torsional loading, as well as in axial and in 20° abduction/20° adduction modes. Subsequently cyclic loading and load-to-failure tests were performed. Resulting stiffness, displacement under cyclic load and ultimate load were compared between groups using the t-test for independent variables (α = 0.05). Results No significant differences were observed between the groups in any of the biomechanical parameters. Backing out of the CS was observed in three cases. Discussion The use of an additional unlocked Calcar screw does not provide mechanical benefit in locked nailing of an unstable 2-part fracture of the surgical neck. Level of evidence Level III. Experimental biomechanical study with human specimen.
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est il avantageux d ajouter une vis supplementaire au travers du Calcar dans l enclouage verrouille de l humerus proximal
Revue de Chirurgie Orthopédique et Traumatologique, 2015Co-Authors: J C Katthagen, Michael Schwarze, L Bauer, J Meyerkobbe, C Voigt, Christof Hurschler, H LillAbstract:Abstract Background The objective of this study was to evaluate the biomechanical effect of an additional unlocked Calcar screw compared to a standard setting with three proximal humeral head screws alone for fixation of an unstable 2-part fracture of the surgical neck. Hypothesis The additional Calcar screw improves stiffness and failure load. Methods Fourteen fresh-frozen humeri were randomized into two equal sized groups. An unstable 2-part fracture of the surgical neck was simulated and all specimens were fixed with the MultiLoc ® -nail. Group I represented a basic screw setup, with three locked head screws and two unlocked shaft screws. Group II was identical with a supplemental unlocked Calcar screw (CS). Stiffness tests were performed in torsional loading, as well as in axial and in 20° abduction/20° adduction modes. Subsequently cyclic loading and load to failure tests were performed. Resulting stiffness, displacement under cyclic load and ultimate load were compared between groups using the t-test for independent variables (α = 0.05). Results No significant differences was observed between the groups in any of the biomechanical parameters. Backing out of the CS was observed in three cases. Discussion The use of an additional unlocked Calcar screw does not provide mechanical benefit in locked nailing of an unstable 2-part fracture of the surgical neck. Level of evidence Level III. Experimental biomechanical study with human specimen.
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Est-il avantageux d’ajouter une vis supplémentaire au travers du Calcar dans l’enclouage verrouillé de l’humérus proximal ?
Revue de Chirurgie Orthopédique et Traumatologique, 2015Co-Authors: J C Katthagen, Michael Schwarze, L Bauer, C Voigt, Christof Hurschler, J. Meyer-kobbe, H LillAbstract:Abstract Background The objective of this study was to evaluate the biomechanical effect of an additional unlocked Calcar screw compared to a standard setting with three proximal humeral head screws alone for fixation of an unstable 2-part fracture of the surgical neck. Hypothesis The additional Calcar screw improves stiffness and failure load. Methods Fourteen fresh-frozen humeri were randomized into two equal sized groups. An unstable 2-part fracture of the surgical neck was simulated and all specimens were fixed with the MultiLoc ® -nail. Group I represented a basic screw setup, with three locked head screws and two unlocked shaft screws. Group II was identical with a supplemental unlocked Calcar screw (CS). Stiffness tests were performed in torsional loading, as well as in axial and in 20° abduction/20° adduction modes. Subsequently cyclic loading and load to failure tests were performed. Resulting stiffness, displacement under cyclic load and ultimate load were compared between groups using the t-test for independent variables (α = 0.05). Results No significant differences was observed between the groups in any of the biomechanical parameters. Backing out of the CS was observed in three cases. Discussion The use of an additional unlocked Calcar screw does not provide mechanical benefit in locked nailing of an unstable 2-part fracture of the surgical neck. Level of evidence Level III. Experimental biomechanical study with human specimen.
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biomechanical effects of Calcar screws and bone block augmentation on medial support in locked plating of proximal humeral fractures
Clinical Biomechanics, 2014Co-Authors: J C Katthagen, Michael Schwarze, J Meyerkobbe, C Voigt, Christof Hurschler, H LillAbstract:Abstract Background The objective of this study was to investigate the biomechanical effects of medial fracture gap augmentation in locked plating of an unstable 2-part proximal humeral fracture with Calcar screws and insertion of a corticocancellous bone block. Furthermore the mechanical behavior of dynamic locking screws in the non-parallel arrangement of a proximal humeral plate was of interest. Methods Thirty-two fresh frozen humeri were randomized in four equal groups. An unstable 2-part fracture was fixed by locked plating in all specimens. The basic screw setup was supplemented by additional Calcar screws in one group. Humeral head screws were replaced by dynamic locking screws in a second group. The third group featured an additional corticocancellous femoral head allograft. Assessment of stiffness was followed by cyclic loading and load to failure tests. Resulting stiffness, fracture gap deflection and ultimate load were compared utilizing Bonferroni corrected t-test for independent samples. Findings The mechanical effect of additional Calcar screws was non-significant as compared to the basic screw configuration whereas bone block insertion significantly increased construct stiffness and failure load. The use of dynamic locking screws did not significantly reduce construct stiffness when compared to conventional locking screws. Interpretation Additional Calcar screws alone did not improve the initial biomechanical properties of an unstable 2-part proximal humeral fracture model. However bone block augmentation appeared to be a reliable alternative of additional bony support by raising stiffness and failure load. Dynamic locking screws did not show their expected dynamic component when used in a non-parallel arrangement.
A. Schepers - One of the best experts on this subject based on the ideXlab platform.
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A POLYETHYLENE PUMP AS THE CAUSE OF Calcar LYTIC LESIONS WHEN USING A COLLARED TITANIUM FEMORAL PROSTHESIS – A FINITE ELEMENT ANALYSIS STUDY
2005Co-Authors: D.r. Van Der Jagt, A. SchepersAbstract:Introduction and Aims: Rapidly progressive lytic lesions of the Calcar develop under the collar of cemented titanium femoral stems inserted in our unit. Progression of the defects slowed after reaching a critical size. Biopsies showed granulomatous lesions with polyethylene particles and multi-nucleate giant cells. The aim of the study was to determine the natural history of these lytic lesions. Method: We developed a finite element analysis model. We determined the parameters of the FEA model, to reflect the geometry and physical characteristics of the prosthesis-bone construct and also factored in both loading and non-loading parameters. We also determined the characteristics of titanium and cobalt-chrome prostheses. Results: We determined from the FEA model that there is some vertical displacement of the collar relative to the Calcar-cement construct. This displacement is larger in the titanium than the cobalt-chrome model. The magnitude of the displacement is larger than the average polyethylene particle size. On loading and non-loading this displacement allows the development of a pump action, thus concentrating polyethylene particles under the collar of the prosthesis and leading to the granulomatous lytic lesions. The FEA studies demonstrated that the pumping action of the collar became less efficient, but did persist, as the lytic lesions increased in size. Conclusion: We have explained the development of Calcar lytic lesions under the collar of femoral stems. A pump action is present in loading and non-loading phases, sucking in polyethylene particles and allowing granulomatous lesions to form. We recommend caution when using collared femoral prostheses, more so titanium than cobalt-chrome, because of the development of Calcar lytic lesions.
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ESTABLISHED Calcar LYTIC LESIONS WHEN USING A COLLARED TITANIUM FEMORAL PROSTHESIS: A FINITE ELEMENT ANALYSIS STUDY
2005Co-Authors: D. Van Der Jagt, A. SchepersAbstract:We have previously reported on early lytic lesions occurring when collared titanium prostheses are used. Previous finite element analysis studies (FEAs) showed that lytic lesions of the Calcar were due to concentration of polyethylene wear particles under the collar by a ‘pumping action’. Further follow-up of these Calcar lytic lesions showed that their rate of increase in size progressively slowed down. Further FEAs were performed to determine why this was so. An FEA mesh construct was developed, incorporating the new parameters of no contact between the collar and the Calcar bone. A mechanical model to determine displacement parameters was also developed. These FEA studies demonstrated that the pumping action of the collar became less efficient as the size of the lytic lesions increased. This led to less concentration of polyethylene particles under the collar and fewer granulomatous reactions. The change in the proximal prosthesis-cement-bone construct may lead to cement mantle deterioration and earlier failure. We still recommend caution when a collared prosthesis is used, and the material and geometry of the prosthesis remain important.
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COLLARED FEMORAL PROSTHESES AND Calcar RESORPTION: A FINITE ELEMENT ANALYSIS
2003Co-Authors: D.r. Van Der Jagt, A. SchepersAbstract:Resorption of the Calcar below the collar of a titanium femoral prosthesis was observed. Biopsies of these lesions showed concentrations of polyethylene. We assessed the size of the resorption, correlating it with the size of the femoral prosthesis and the time since implantation. The age and the weight of the patient was also linked to the size of the prosthesis. We conducted a finite element analysis (FEA) of the femoral component-femur complex in both the loaded and unloaded situation. FEA demonstrated changing pressure under the collar. This can be translated into micro-bending, with the degree of movement dependent on the size of the prosthesis, the material of the prosthesis and the weight of the patient. We postulate the existence of a ‘polyethylene pump’ owing to the bending motion of the collared prosthesis, and that Calcar resorption is due to the resultant polyethylene granulomatous lesions .
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Calcar RESORPTION AFTER USING A CEMENTED COLLARED TITANIUM STEM AND ULTRA-HIGH MOLECULAR WEIGHT POLYETHYLENE CUP
2002Co-Authors: A.a. Papadopoulos, D.r. Van Der Jagt, A. SchepersAbstract:Between January 1990 and October 2000, 108 total hip arthroplasties using a cemented polished titanium stem and a cemented ultra-high molecular weight polyethylene (UHMWP) cup were performed at our hospital. Because during routine follow-up visits we noted instances of resorption of the Calcar, we decided to assess whether this was a problem. We were able to assess 85 of the original 108 hips. Calcar resorption was observed in 43 hips. The extent of Calcar resorption varied from 1 mm to over 15 mm. In one patient a biopsy showed typical polyethylene granuloma. Because there is a risk of long-term failure, we concluded that it is inadvisable to use a cemented polished titanium stem when UHMWP is one of the bearing surfaces.