Michael E Berend

Saint Francis Health System, Tulsa, Oklahoma, United States

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Publications (123)295.07 Total impact

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    ABSTRACT: Prosthetic alignment, patient characteristics and implant design are all factors in long-term survival of total knee arthroplasty (TKA), yet the level at which each of these factors contribute to implant loosening has not been fully described. Prior clinical and biomechanical studies have indicated tibial overload as a cause of early TKA revision. The purpose of this study was to determine the relationship between tibial component design and bone resection on tibial loading. Finite element analysis (FEA) was performed after simulated implantation of metal backed and all-polyethylene TKA components in 5 and 15 mm of tibial resection into a validated intact tibia model. Proximal tibial strains significantly increased between 13% and 199% when implanted with all-polyethylene components (p<0.05). Strain significantly increased between 12% and 209% in the posterior tibial compartment with increased bone resection (p<0.05). This study indicates elevated strains in all-polyethylene implanted tibiae across the entirety of the proximal tibial cortex, as well as a posterior shift in tibial loading in instances of increased resection depth. These results are consistent with trends observed in prior biomechanical studies and may associate the documented device history of tibial collapse in all-polyethylene components with increased bone strain and overload beneath the prosthesis.
    No preview · Article · Jan 2016 · Journal of Biomechanical Engineering
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    ABSTRACT: Previous work, now nearly 30 years dated, is frequently cited as the "gold standard" for the indications and contraindications for medial unicompartmental knee arthroplasty (UKA). The purpose of this article is to review current literature on the indications and contraindications to UKA and develop a consensus statement based on those data. Six surgeons with a combined experience of performing more than 8,000 partial knee arthroplasties were surveyed. Surgeons then participated in a discussion, emerging proposal, collaborative modification, and final consensus phase. The final consensus on primary indications and contraindications is presented. Notably, the authors provide consensus on previous contraindications, which are no longer considered to be contraindications. The authors provide an updated and concise review of the current indications and contraindications for medial UKA using scientifically based consensus-building methodology.
    No preview · Article · Jan 2016 · Journal of surgical orthopaedic advances
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    ABSTRACT: The mechanical properties and thermal history of polymethyl-methacrylate bone cement vary significantly with the preparation procedure used. Because the polymerization reaction is exothermic, many researchers have attempted to minimize thermal osteonecrosis due to heat generation by altering procedures in the preparation of the cement. In most previous studies, only one or two aspects of the preparation procedure were controlled, and there has been little research that comprehensively examines the effects of preparation on the cure kinetics and resulting properties of bone cement. In this study, cement viscosity, cement layer thickness, initial cement temperature, initial metal component temperature, and mixing method were varied to assess the effects on the cement. Maximum temperature, polymerization time, necrosis index, bending strength and porosity were chosen to evaluate the different preparation procedures, where an optimal procedure would minimize necrosis, reduce cement cure time, and maximize bending strength. Design of Experiments (DOE) was used to examine the main effects and interactions of preparation techniques. Among the most prominent results, it was found that the cure kinetics and the related quantities are primarily controlled by the initial metal component temperature and that the bending strength is most dependent on the mixing method. For the two formulations studied, the optimum preparation procedures should keep cement and metal components at room temperature prior to mixing with a vacuum mixing system. Reducing cement mantle thickness may also be advantageous, as it reduces the maximum temperature and the risk of tissue damage. This article is protected by copyright. All rights reserved.
    No preview · Article · Nov 2015 · Journal of Orthopaedic Research
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    ABSTRACT: Introduction: Osteoarthritis (OA) is characterized by pain, loss of function, joint space narrowing, and possible limb deformity. The main changes in knee as a result of OA occur at the articular cartilage, yet there are a variety of changes that can occur to the knee either preceding the development of OA or due to the degeneration. These include damage to soft tissues such as the ligaments and menisci, along with loss of the mechanoreceptors needed to maintain joint function, misalignment of the mechanical axes and resultant changes in stress, and altered weight distribution through the bottom of the foot.[1,2] These changes require different measurement tools to accurately assess the degree of OA severity. A single test that could help evaluate these changes would be a valuable addition to the field. Pressure sensors can be used to reliably and accurately determine a patient’s weight distribution throughout the bottom of the feet. The changes in weight distribution that can be determined with this tool have the potential to provide insight into the condition of the knee as a result of OA damage. The entire lower limb functions as a continuous system, and it is likely that variation in part of this system can be measured and related to changes in another part of it. The purpose of this study was to measure the plantar force distribution in patients with knee OA and to determine if there is any relationship to certain changes seen in the knee, including joint alignment and the extent of soft tissue damage. Methods: A total of 37 subjects (IRB #1139155) were enrolled in the alignment study; 23 of these subjects were included in the damage model. Weight Distribution: Weight distribution data was collected for each patient. Two 20-second unassisted, quiet standing trials were completed prior to surgery using the Matscan pressure mat (Tekscan, Boston, MA). To determine medial weight distribution, a template profile was placed around each foot and adjusted to best fit the areas of measured force, using the middle toe and heel as a line of demarcation between medial and lateral weight distribution. Alignment Models: Initial evaluation of the relationship between medial weight distribution and alignment was completed using data on knees that were operated on. A general linear model, assuming linearity, was constructed using generalized estimating equations (GEE) to examine the relationship between weight distribution and knee alignment on the population of surgery knees only. Repeated measures were used to account for subjects that had surgery on both knees. The model accounted for age, gender, BMI, history of surgical intervention, and which leg (or both) was operated on. SAS statistical software (SAS, North Carolina) was used and p < 0.05 denoted statistical significance. All subsequent evaluations used a complete data set of knees with OA. Following initial evaluation, a generalized linear model was constructed using GEE. Repeated measures were used to account for some of the subjects having two knees with OA. Damage Models: The relationships between weight distribution and various measures of knee damage (femoral/tibial chondromalacia, femoral/tibial osteophytes, meniscus damage, and ACL damage) were evaluated using ordinal logistic regression with repeated measures. A 95% CI was calculated for each odds ratio. Any confounders and other variables believed to play a role in explaining the response were included in the model, along with any interactions of interest. Unadjusted and adjusted models were also examined for each response. The models for chondromalacia, osteophytes, and meniscus damage were adjusted for age, sex, BMI, knee compartment (medial/lateral), history of surgical intervention, presence of OA in the compartment, and the leg/side of interest. The interaction between weight distribution and compartment was included to evaluate how weight distribution might affect the odds of damage for each compartment, separately. The model for ACL condition accounted for age, sex, BMI, history of surgical intervention, and side of interest. Results: Alignment models: After accounting for age, sex, BMI, which knee (or both) was operated on, and history of surgery on the lower limb, medial plantar weight distribution was found to have a significant effect on alignment (0.19, p=0.002). As the proportion of plantar weight transmitted through the medial side of the foot increased, the knee alignment angle increased and moved in a varus-tovalgus direction. Increasing BMI was also statistically significant (0.41, p < 0.001). This indicates that a higher BMI results in alignment changes from a varus-to-valgus direction. A positive history of lower limb surgery was significant in the model with an effect of decreasing the alignment angle and moving towards a varus alignment (-6.71, p < 0.001). Damage Models: Plantar medial weight distribution was significant in the damage model for ACL condition (-.14, p=0.029). This means that an increase in medial plantar weight distribution decreases the likelihood of having more severe levels of ACL damage. For all damage models in which it was considered, a diagnosis of OA was associated with increased likelihood of damage and was statistically significant (p < 0.001). Finally, being female resulted in a significantly greater likelihood of having more severe levels of damage (1.64, p=0.045). The odds ratio results confirmed the significant relationship between ACL damage and plantar medial weight distribution (OR = 0.872, CI [0.772, 0.986]). Discussion: A direct relationship between percentage of weight on the medial portion of the foot and the alignment of OA knees was observed. A positive knee angle corresponded with a valgus alignment in this study; therefore, increasing medial weight was related to moving towards a valgus (or more valgus) alignment. The vast majority of knees included in the alignment model were in varus alignment. This means that the increase in angle related to increasing medial weight was more indicative of a movement away from varus and towards a less severe varus angle (closer to a neutral alignment). This tendency to move away from a varus alignment as medial weight increases is beneficial when considering knee OA. A neutral angle is optimal to lower the effects that knee alignment can have on OA. With the known relationship between varus alignment and OA, a clinician might want to be more aware of possible OA or even suggest corrective measures that can provide for a more even plantar weight distribution, such as braces, orthotics, or physical therapy. The inverse relationship between medial plantar weight distribution and ACL damage indicates that as the percentage of plantar weight increases, the odds of observing more severe ACL condition decrease. Nearly all of the patients included in the damage model had uneven plantar weight distribution, with a lower portion of the total weight on the medial half of the foot. Therefore, the relationship observed can be thought of as the odds of increased ACL damage decreasing as the medial weight percentage increases and the weight becomes more evenly distributed on the bottom of the foot. Another interesting note from the ACL damage model was the effect of gender on the likelihood of damage. It is well established that women have an increased likelihood of ACL injuries compared to men, which reinforces the validity of the current study. Significance: OA is a damaging disease that can impact lower limb function. This study examined how plantar weight distribution was related to the changes in knee alignment and the various types of joint damage in patients with OA. Relationships were observed between medial plantar weight distribution and knee alignment angles, BMI, gender, and ACL damage. ORS 2015 Annual Meeting
    No preview · Conference Paper · Mar 2015
  • Brian Sutterer · Eric Reyes · Michael Berend · Scott Small · Renee Rogge
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    ABSTRACT: Introduction: Osteoarthritis (OA) is characterized by pain, loss of function, joint space narrowing, and possible limb deformity. The main changes in knee as a result of OA occur at the articular cartilage, yet there are a variety of changes that can occur to the knee either preceding the development of OA or due to the degeneration. These include damage to soft tissues such as the ligaments and menisci, along with loss of the mechanoreceptors needed to maintain joint function, misalignment of the mechanical axes and resultant changes in stress, and altered weight distribution through the bottom of the foot.[1,2] These changes require different measurement tools to accurately assess the degree of OA severity. A single test that could help evaluate these changes would be a valuable addition to the field. Pressure sensors can be used to reliably and accurately determine a patient’s weight distribution throughout the bottom of the feet. The changes in weight distribution that can be determined with this tool have the potential to provide insight into the condition of the knee as a result of OA damage. The entire lower limb functions as a continuous system, and it is likely that variation in part of this system can be measured and related to changes in another part of it. The purpose of this study was to measure the plantar force distribution in patients with knee OA and to determine if there is any relationship to certain changes seen in the knee, including joint alignment and the extent of soft tissue damage. Methods: A total of 37 subjects (IRB #1139155) were enrolled in the alignment study; 23 of these subjects were included in the damage model. Weight Distribution: Weight distribution data was collected for each patient. Two 20-second unassisted, quiet standing trials were completed prior to surgery using the Matscan pressure mat (Tekscan, Boston, MA). To determine medial weight distribution, a template profile was placed around each foot and adjusted to best fit the areas of measured force, using the middle toe and heel as a line of demarcation between medial and lateral weight distribution. Alignment Models: Initial evaluation of the relationship between medial weight distribution and alignment was completed using data on knees that were operated on. A general linear model, assuming linearity, was constructed using generalized estimating equations (GEE) to examine the relationship between weight distribution and knee alignment on the population of surgery knees only. Repeated measures were used to account for subjects that had surgery on both knees. The model accounted for age, gender, BMI, history of surgical intervention, and which leg (or both) was operated on. SAS statistical software (SAS, North Carolina) was used and p < 0.05 denoted statistical significance. All subsequent evaluations used a complete data set of knees with OA. Following initial evaluation, a generalized linear model was constructed using GEE. Repeated measures were used to account for some of the subjects having two knees with OA. Damage Models: The relationships between weight distribution and various measures of knee damage (femoral/tibial chondromalacia, femoral/tibial osteophytes, meniscus damage, and ACL damage) were evaluated using ordinal logistic regression with repeated measures. A 95% CI was calculated for each odds ratio. Any confounders and other variables believed to play a role in explaining the response were included in the model, along with any interactions of interest. Unadjusted and adjusted models were also examined for each response. The models for chondromalacia, osteophytes, and meniscus damage were adjusted for age, sex, BMI, knee compartment (medial/lateral), history of surgical intervention, presence of OA in the compartment, and the leg/side of interest. The interaction between weight distribution and compartment was included to evaluate how weight distribution might affect the odds of damage for each compartment, separately. The model for ACL condition accounted for age, sex, BMI, history of surgical intervention, and side of interest. Results: Alignment models: After accounting for age, sex, BMI, which knee (or both) was operated on, and history of surgery on the lower limb, medial plantar weight distribution was found to have a significant effect on alignment (0.19, p=0.002). As the proportion of plantar weight transmitted through the medial side of the foot increased, the knee alignment angle increased and moved in a varus-tovalgus direction. Increasing BMI was also statistically significant (0.41, p < 0.001). This indicates that a higher BMI results in alignment changes from a varus-to-valgus direction. A positive history of lower limb surgery was significant in the model with an effect of decreasing the alignment angle and moving towards a varus alignment (-6.71, p < 0.001). Damage Models: Plantar medial weight distribution was significant in the damage model for ACL condition (-.14, p=0.029). This means that an increase in medial plantar weight distribution decreases the likelihood of having more severe levels of ACL damage. For all damage models in which it was considered, a diagnosis of OA was associated with increased likelihood of damage and was statistically significant (p < 0.001). Finally, being female resulted in a significantly greater likelihood of having more severe levels of damage (1.64, p=0.045). The odds ratio results confirmed the significant relationship between ACL damage and plantar medial weight distribution (OR = 0.872, CI [0.772, 0.986]). Discussion: A direct relationship between percentage of weight on the medial portion of the foot and the alignment of OA knees was observed. A positive knee angle corresponded with a valgus alignment in this study; therefore, increasing medial weight was related to moving towards a valgus (or more valgus) alignment. The vast majority of knees included in the alignment model were in varus alignment. This means that the increase in angle related to increasing medial weight was more indicative of a movement away from varus and towards a less severe varus angle (closer to a neutral alignment). This tendency to move away from a varus alignment as medial weight increases is beneficial when considering knee OA. A neutral angle is optimal to lower the effects that knee alignment can have on OA. With the known relationship between varus alignment and OA, a clinician might want to be more aware of possible OA or even suggest corrective measures that can provide for a more even plantar weight distribution, such as braces, orthotics, or physical therapy. The inverse relationship between medial plantar weight distribution and ACL damage indicates that as the percentage of plantar weight increases, the odds of observing more severe ACL condition decrease. Nearly all of the patients included in the damage model had uneven plantar weight distribution, with a lower portion of the total weight on the medial half of the foot. Therefore, the relationship observed can be thought of as the odds of increased ACL damage decreasing as the medial weight percentage increases and the weight becomes more evenly distributed on the bottom of the foot. Another interesting note from the ACL damage model was the effect of gender on the likelihood of damage. It is well established that women have an increased likelihood of ACL injuries compared to men, which reinforces the validity of the current study. Significance: OA is a damaging disease that can impact lower limb function. This study examined how plantar weight distribution was related to the changes in knee alignment and the various types of joint damage in patients with OA. Relationships were observed between medial plantar weight distribution and knee alignment angles, BMI, gender, and ACL damage.
    No preview · Conference Paper · Mar 2015

  • No preview · Article · Jan 2015 · Open Journal of Orthopedics
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    ABSTRACT: The purpose of this study was to investigate the use for screws and cement, and primary and revision specific prosthesis for revision TKR. Between July 1989 and February 2010, 839 consecutive revision TKAs were performed, with 609 knees meeting inclusion criteria. At 17 years followup, Kaplan-Meier survivorship was .9859 for revision specific prosthesis with screws and cement, .9848 for revision prosthesis with no screws, 0.9118 for primary prosthesis with screws, and .9424 for primary prosthesis with no screws. Revision TKRs using screws had greater defects (p < .0001). Use of revision prosthesis along with screws and cement to correct largely defective revision TKRs is highly recommended.
    No preview · Article · Dec 2014 · The Journal of Arthroplasty
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    ABSTRACT: Return to sexual activity is important to patients, but there is limited information regarding sexual function following total hip arthroplasty (THA) and total knee arthroplasty (TKA). A multicenter study of 806 THA, 542 TKA, and 181 control patients less than 60 years of age was conducted using an independent survey center to question subjects about their sexual function. Only 1.3% of THA and 1.6% of TKA patients stated they were not sexually active due to their operation. No statistically significant differences were noted in any sexual function outcome categories based on the bearing surface, femoral head size, or use of surface replacement arthroplasty in the hip cohort. Multivariate analysis revealed no difference in the percentage of patients sexually active following a THA or TKA (OR 1.19, p = 0.38). Most young active patients return to their baseline or higher level of sexual activity after hip and knee arthroplasty.
    Full-text · Article · Oct 2014 · The Journal of Arthroplasty
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    ABSTRACT: Uncemented stems have been used in THA for well over two decades, but there are relatively few studies reporting on the results after 20 years.
    No preview · Article · Jul 2014 · Clinical Orthopaedics and Related Research
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    ABSTRACT: The purpose of this study was to investigate screws and cement for large tibial bone defects during primary TKA. Of 14,686 consecutive primary TKAs performed between December 1988 and February 2010, 256 received screws and cement for tibial defects. Cox regression was used for the analysis. 20-year survival probability was 0.9897 (screws) and 0.9339 (no screws) (P=.4225 log-rank). Tibial bone condition was significantly worse in knees receiving screws (P<.0001) with 73.0% having defects in the screws group and 3.4% (P<.0001) for non-screws. Radiolucency appeared in 13.7% (screws) and 6.4% (no screws) postoperatively. Screws were $137 each, wedges $910 to $2240. Knees with tibial defects and screws performed similarly if not better than knees without defects at substantially lower cost than alternatives.
    No preview · Article · Dec 2013 · The Journal of arthroplasty
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    ABSTRACT: Limited experimental data exist comparing the mechanical response of the tibial cortex between fixed and rotating platform (RP) total knee arthroplasty (TKA), particularly in the revision setting. We asked if RP-TKA significantly affects tibiofemoral torque and cortical stain response in both the primary and revision settings. Fixed and RP tibial trays were implanted into analogue tibias and biomechanically tested under axial and torsional loading. Torque and strain response were analyzed using digital image correlation. Fixed bearing designs exhibited 13.8 times greater torque (P<0.01), and 69% (P<0.01) higher cortical strain than RP designs. Strain response was similar in the primary and revision cohorts. The decrease in torque transfer could act as a safeguard to reduce stress, micromotion and torsional fatigue in scenario of poor bone stock.
    No preview · Article · Nov 2013 · The Journal of arthroplasty
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    ABSTRACT: Revision knee data from six joint arthroplasty centers were compiled for 2010 and 2011 to determine mechanism of failure and time to failure. Aseptic loosening was the predominant mechanism of failure (31.2%), followed by instability (18.7%), infection (16.2%), polyethylene wear (10.0%), arthrofibrosis (6.9%), and malalignment (6.6%). Mean time to failure was 5.9years (range 10 days to 31years). 35.3% of all revisions occurred less than 2years after the index arthroplasty, 60.2% in the first 5years. In contrast to previous reports, polyethylene wear is not a leading failure mechanism and rarely presents before 15years. Implant performance is not a predominant factor of knee failure. Early failure mechanisms are primarily surgeon-dependent.
    No preview · Article · Aug 2013 · The Journal of arthroplasty
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    ABSTRACT: Many previous biomechanical studies of bone and bone substitutes have estimated strains in these materials using strain gages. The purpose of this study was to compare digital image correlation (DIC) strain measurements to those obtained from strain gages in order to assess the applicability of DIC technology to common biomechanical testing scenarios. Compression and bending tests were conducted on aluminum alloy, polyurethane foam, and laminated polyurethane foam specimens. Results showed no significant differences in the principal strain values (or the variances) between strain gage and DIC measurements on the aluminum alloy and laminated polyurethane foam specimens. There were significance differences between the principal strain measurements of the non-laminated polyurethane foam specimens, but the deviation from the theoretical results was similar for both measurement techniques. In summary, DIC techniques provide similar results to those obtained from strain gages and also provide full field strain results.
    No preview · Conference Paper · Jun 2013
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    ABSTRACT: BACKGROUND: Potential advantages suggested but not confirmed for surface replacement arthroplasty (SRA) over THA include lower frequency of limp, less thigh pain, less limb length discrepancy, and higher activity. QUESTIONS/PURPOSES: We therefore determined whether patients having SRA had a limp, thigh pain, or limb length discrepancy less frequently or had activity levels higher than patients having THA. METHODS: In a multicenter study, we surveyed 806 patients aged 18 to 60 years with a premorbid UCLA activity score of 6 or more who underwent hip arthroplasty for noninflammatory arthritis at one of five orthopaedic centers. Patients had either a cementless THA with an advanced bearing surface (n = 682) or an SRA (n = 124). The patients were demographically comparable. Specific telephone survey instruments were designed to assess limp, thigh pain, perception of limb length, and activity levels. Minimum followup was 1 year (mean, 2.3 years; range, 1.1-3.9 years). RESULTS: When controlled for age, sex, and premorbid activity level, patients with SRA had a higher incidence of complete absence of any limp, lower incidence of thigh pain, lower incidence of perception of limb length discrepancy, greater ability to walk continuously for more than 60 minutes, higher percentage of patients who ran after surgery, greater distance run, and higher percentage of patients who returned to their most favored recreational activity. CONCLUSIONS: When interviewed by an independent third party, patients with SRA reported higher levels of function with fewer symptoms and less perception of limb length discrepancy compared to a similar cohort of young, active patients with THA. LEVEL OF EVIDENCE: Level III, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
    Full-text · Article · Mar 2013 · Clinical Orthopaedics and Related Research
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    ABSTRACT: With increased precision in alignment offered by new generations of instrumentation and customized guides, this study was designed to establish a biomechanically-based target alignment for the balance of tibial loading in order to diminish the likelihood of pain and subsidence related to mechanical overload post-UKA. Sixty composite tibias were implanted with Oxford UKA tibial components with varied sagittal slope, resection depth, rotation and medial shift using patient matched instrumentation. Digital image correlation and strain gage analysis was conducted in static loading to evaluate strain distribution as a result of component alignment. In this model, minimal distal resection and most lateral positioning, neutral component rotation, and 3°of slope (from mechanical axis) exhibited the most balanced strain response to loading following UKA.
    No preview · Article · Mar 2013 · The Journal of arthroplasty
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    ABSTRACT: Introduction Mobile bearing total knee arthroplasty (TKA) tibial components can allow for high tibiofemoral conformity while minimizing polyethylene contact stress and reducing bone-implant interface stress. Prior studies have investigated the cortical strain variance between fixed and mobile bearing components in a limited number of measurement regions. However, no current experimental data exists across the entire proximal tibial cortex, and no comparisons have been made within the context of knee arthroplasty revision surgery. The purpose of this study was to investigate the influence of bearing mobility on torque and torsional strain across the entire cortical surface of the proximal tibia in the primary and revision setting. Specifically of interest is the change in induced strain, the instance of femoral component rotation and rotational malalignment. Methods In order to compare the mechanical response of the tibia following implantation of fixed and rotating platform mobile-bearing TKA components, four experimental groups were included in this study: 1) Fixed-bearing, posterior stabilized primary components (PFC Sigma, DePuy, Warsaw, IN); 2) Rotating platform posterior stabilized primary components (PFC Sigma, DePuy, Warsaw, IN); 3) Fixed-bearing posterior stabilized revision components with 115 mm press-fit distal stem (PFC TC3, DePuy, Warsaw, IN; 4) Rotating platform posterior stabilized revision components with 75 mm press-fit distal stem (PFC TC3, DePuy, Warsaw, IN). Six components in each experimental group were implanted into fourth generation composite tibia specimens (Pacific Research Laboratories, Vashon, WA) using proximal cementing and standard instrumentation. Following implantation, tibias were prepared for surface strain quantification through the use of complimentary strain gage and digital image correlation (DIC) methodologies. Two three-element rectangular rosette strain gages were applied to the tibia in the anteromedial and posterolateral quadrants for direct strain measurement. Digital image correlation techniques (Aramis 6.0, Gom, Inc., Braunschweig, Germany) were used to obtain full-field strain measurements 360 degrees around the proximal tibial cortex. For DIC measurement, a black and white speckled paint was applied to the tibia surface, which was then optically tracked with a set of two high definition cameras throughout the loading cycle. To obtain full-field strain measurements around the entire tibia, tests were repeated in four independent viewing angles. Deformation and strain measurements were calculated within the DIC system software and then analyzed utilizing a custom merging algorithm (Matlab R2012a, Mathworks, Natick, MA) to combine data from specimens and repeated trials within each experimental group. Biomechanical testing was conducted on a biaxial electrodynamic materials testing machine (E10,000 A/T, Instron, Norwood, MA). Specimens were incorporated into the materials testing machine via a custom fixture allowing free x-y translation of the potted base. Appropriate femoral components were integrated into the upper testing grips to allow for repeatable load application through the femoral component onto the polyethylene bearing surface. A silicon-based lubricant (DM-Fluid-350CS, ShinEtsu Chemical Co, Tokyo) was applied between all articulating surfaces to mimic in vivo frictional characteristics. Testing was conducted in two phases: 1) Compressive loading followed by a 5 degree internal rotation with femoral component in a full extension, and 2) Compressive loading followed by a 10 degree external rotation with the femoral component 90 degrees of flexion. In both instances the tibia was loaded at a rate of 60 N/s to a peak load of 2.5 kN, while femoral component rotation was introduced at a rate of 0.5 ˚/s. Five trials were repeated for each of the four DIC viewing angles in all 24 specimens. Statistical analysis was performed utilizing paired t-tests to evaluate significant differences between designs in torque response. Further examination was conducted to evaluate contribution of torsional strain to the total overall strain response in each DIC measurement region. Statistical significance was indicated at p ≤ 0.05. Results Torsional Response: Average torsional moments during rotational testing in both 0 and 90 degrees of flexion are presented in Table 1. In the primary setting, fixed bearing tibias generated 13.7 times the torsional moment of the rotating platform primary design (p<0.01) when the extended femoral component was rotated 5 degrees internally. Torsional moments in the fixed tibias were 11.2 times greater than those in the rotating platform designs in the revision setting (p<0.01). In flexion, fixed bearing designs generated 4.4 times greater torque in the primary (p<0.01) and 4.8 times greater torque in the revision setting (p<0.01) when the femoral component was rotated 10 degrees externally. Strain Response: Representative anterior and posterior DIC strain responses to compressive and torsional loading are presented in Figure 1. Torsional strain response was seen to diminish substantially when rotating platform devices were utilized, most notably in the posterior tibia. This diminished strain response to torsional loading was consistent in both primary and revision tibial trays. In order to numerically quantify DIC data, each field of view was divided into 5 measurement regions, in order from most proximal to most distal, for von Mises strain averaging (Figure 1). Average cortical strain for each measurement region was calculated by merging 8,000 – 30,000 individual strain data points collected within the given region throughout five repeated trials of six specimens in each respective experimental group. As a subset of all DIC strain analysis, the von Mises strain data for fixed and rotating platform primary knee components, with 10˚ external femoral rotation is presented in Table 2. In the primary fixed bearing components, average cortical strain in 6 of 10 measurement regions significantly increased between 17% (p=.0004) and 56% (p=.0001) when the femoral component was rotated 10˚ externally. Conversely, there was no statistically significant change in strain induced in the primary rotating platform group with the introduction of external femoral rotation. In the fixed bearing revision setting (not presented in Table 2), a significant increase from 18% (p=.0001) to 69% (p=.0001) increase in strain was observed with 10˚ of external femoral component rotation in 6 of 10 measurement regions. Similar to the primary components, there was no statistically significant change in strain due to femoral rotation in any anterior or posterior measurement regions in the rotating platform design. Discussion Femoral component rotation about the tibial tray occurs cyclically during the gait cycle and generates a torsional moment at the tibial tray. Relative femoral component rotation and subsequent torsional moments can also be generated in the event of suboptimal rotational positioning during implantation. Both the primary and revision rotating platform designs exhibited vastly reduced torque response between the articulating femoral and tibial components when under compressive loading and femoral rotation. Strain response in the tibia was significantly altered in the majority of measurement regions when the femoral component was rotated on the tibial tray in the fixed bearing designs. However, no significant change in cortical strain loading was observed in anterior and posterior regions when the femoral component was rotated in the rotating platform designs. The clinical application of this study may be limited due to the use of composite, rather than cadaveric tibial specimens. Furthermore, no muscular or ligamentous forces were replicated during loading. Nevertheless, this model is effective in the direct comparison between strain and torsional response fixed and mobile-bearing designs. Significance In a comparison between fixed and rotating platform tibial component designs in both the primary and revision setting, rotating platform tibial trays demonstrated significantly less transfer of rotational moment between the femoral and tibial component than their fixed-bearing counterparts. As a result of this diminished torsional load transfer, minimal increases in cortical strains were observed during femoral component rotation in the rotating platform study group. The decrease in torque transfer between tibial tray and implanted bone in mobile-bearing technology may act as a safeguard to reduce stress and torsional fatigue at the bone-implant interface.
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: Implant survival after total knee arthroplasty has historically been dependent on postoperative knee alignment, although failure may occur when alignment is correct. Preoperative knee alignment has not been thoroughly evaluated as a possible risk factor for implant failure after arthroplasty. The purpose of this study was to analyze the effect of preoperative knee alignment on implant survival after total knee arthroplasty. We performed a retrospective review of 5342 total knee arthroplasties performed with use of cemented Anatomic Graduated Component implants from 1983 to 2006. Each knee was independently measured preoperatively and postoperatively for overall coronal alignment. Neutral ranges for preoperative and postoperative alignment were defined by means of Cox proportional hazards regression. The overall failure rate was 1.0% (fifty-four of 5342 prostheses); failure was defined as aseptic loosening of the femoral and/or tibial component. The average preoperative anatomical alignment (and standard deviation) was 0.1° ± 7.7° of varus (range, 25° of varus to 35° of valgus), and the average postoperative anatomical alignment (and standard deviation) was 4.7° ± 2.5° of valgus (range, 12° of varus to 20° of valgus). The failure rate in knees in >8° of varus preoperatively (2.2%; p = 0.0005) or >11° of valgus preoperatively (2.4%; p = 0.0081) was elevated when compared with knees in neutral preoperatively (0.71%). Knees with preoperative deformities corrected to postoperative neutral alignment (2.5° through 7.4°) had a lower failure rate (1.9%) than undercorrected or overcorrected knees (3.0%) (p = 0.0103). Knees with postoperative neutral alignment, regardless of preoperative alignment, had a lower failure rate (0.74%) than knees with postoperative alignment of <2.5° or >7.4° of anatomic valgus (1.7%) (p < 0.0001). Patients with excessive preoperative alignment (>8° of varus or >11° of valgus) have a greater risk of failure (2.3%). Neutral postoperative alignment (2.5° through 7.4° of valgus) improves (1.9% for preoperatively deformed knees) but does not completely eliminate the risk of failure (0.5% for knees that were neutral both preoperatively and postoperatively). Careful attention should be paid to knee alignment during total knee arthroplasty, especially for patients with severe preoperative deformities. Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.
    No preview · Article · Jan 2013 · The Journal of Bone and Joint Surgery
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    ABSTRACT: Initial stability with limited micromotion in uncemented total hip arthroplasty acetabular components is essential for bony attachment and long-term biomechanical fixation. This study compared porous titanium fixation surfaces to clinically established, plasma-sprayed designs in terms of interface stability and required seating force. Porous plasma-sprayed modular and metal-on-metal (MOM) cups were compared to a modular, porous titanium designs. Cups were implanted into polyurethane blocks with1-mm interference fit and subsequently edge loaded to failure. Porous titanium cups exhibited 23% to 65% improvement in initial stability when compared to plasma-sprayed cup designs (P=.01): a clinically significant increase, based on experience and prior literature. The results of this study indicate increased interface stability in porous titanium-coated cups without significantly increasing the necessary force and energy required for full seating.
    No preview · Article · Nov 2012 · The Journal of arthroplasty
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    ABSTRACT: This conversation represents an attempt by several arthroplasty surgeons to critique several abstracts presented over the last year as well as to use them as a jumping off point for trying to figure out where they fit in into our current understanding of multiple issues in modern hip and knee arthroplasty.
    No preview · Article · Nov 2012 · The Bone & Joint Journal
  • W. G. Lackey · M. E. Berend

    No preview · Article · Nov 2012 · The Bone & Joint Journal

Publication Stats

3k Citations
295.07 Total Impact Points

Institutions

  • 2014
    • Saint Francis Health System
      Tulsa, Oklahoma, United States
  • 2002-2014
    • Saint Francis Hospital
      Tulsa, Oklahoma, United States
  • 2013
    • Spokane Joint Replacement Center
      Spokane, Washington, United States
    • Duke University
      Durham, North Carolina, United States
  • 2011-2013
    • Hip Knee Arkansas Foundation
      Little Rock, Arkansas, United States
  • 2008
    • University of Missouri
      Columbia, Missouri, United States
  • 2007
    • Indiana University School of Medicine
      Indianapolis, Indiana, United States