Timothy M Wright

Stanford University, Palo Alto, California, United States

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Publications (203)492.8 Total impact

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    ABSTRACT: Femoral stems with dual-taper modularity were introduced to allow independent control of length, offset, and version. Corrosion and fretting related to micromotion at the neck-stem junction are thought to stimulate an adverse local tissue reaction (ALTR). Analysis of 60 consecutively retrieved modular-neck stem implants (Rejuvenate, Stryker) revised primarily for ALTR was done to determine the variables influencing corrosion and fretting patterns at the neck-stem interface. Taper damage evaluation was performed with stereomicrocopic analysis with two observers. Evidence of fretting and corrosion was seen at the neck-stem taper in all implants, including three implants revised for periprosthetic fractures within four weeks of the index surgery indicating that this process starts early. Femoral stems paired with the long overall neck lengths had significantly higher corrosion scores. Correlation of the corrosion severity at particular locations with the length of implantation suggests that the neck-stem junction experiences cyclic cantilever bending in vivo. The positive correlation between the length of implantation and fretting/corrosion scores bodes poorly for patients who still have this implant. Scanning electron microscopy on a subset of specimens was also performed to evaluate the black corrosion material. We strongly urge frequent follow-up exams for every patient with this particular modular hip stem. Copyright © 2015. Published by Elsevier Inc.
    The Journal of arthroplasty 03/2015; DOI:10.1016/j.arth.2015.03.010 · 2.37 Impact Factor
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    ABSTRACT: Success of shoulder surgery depends on implant fixation to the glenoid trabecular bone. The purpose of this study was to evaluate the anatomic characteristics of the normal gle-noid trabecular bone microarchitecture to help assist in implant design and provide data for finite element analyses. Eight cadavers without evidence of osteoarthritis were used. Glenoids were scanned with micro-computed tomography and then divided into lateral and medial, then superior, inferior, anterior, and posterior quadrants (8 total segments). Each segment was analyzed for total mineral density, bone volume fraction, structure model index, and trabecular thickness (Tb.Th), number (Tb.N), and separation. Bone volume fraction was significantly higher (P<.05) in the posterolateral (20.8%±4.5%) and posteromedial (18.6%±2.5%) regions. Both Tb.N and Tb.Th were also highest in the pos-terolateral (Tb.N, 1.74±0.374 mm; Tb.Th, 0.148±0.017 mm) and posteromedial (Tb.N, 1.49±0.401 mm; Tb.Th, 0.165±0.016 mm) regions. Trabecular separation was greatest in the superomedial segment (1.00±0.181 mm) and lowest in the posterolateral region (0.663±0.121 mm). For structural model index, both the posterolateral (0.314) and pos-teromedial (0.312) regions had lower values than the other regions. The posterior segment of the normal glenoid in both the lateral and medial regions has the highest density, which is attributed to the increased trabecular number and thickness with decreased separation. This increased density may be attributed to the posterior directed loading of the glenohumeral joint. The trabecular microarchitecture in the glenoid is plate-like, as indicated by the low structural model index.[Orthopedics. 2015; 38(3):e163-e168.]
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    ABSTRACT: Success of shoulder surgery depends on implant fixation to the glenoid trabecular bone. The purpose of this study was to evaluate the anatomic characteristics of the normal glenoid trabecular bone microarchitecture to help assist in implant design and provide data for finite element analyses. Eight cadavers without evidence of osteoarthritis were used. Glenoids were scanned with micro-computed tomography and then divided into lateral and medial, then superior, inferior, anterior, and posterior quadrants (8 total segments). Each segment was analyzed for total mineral density, bone volume fraction, structure model index, and trabecular thickness (Tb.Th), number (Tb.N), and separation. Bone volume fraction was significantly higher (P<.05) in the posterolateral (20.8%±4.5%) and posteromedial (18.6%±2.5%) regions. Both Tb.N and Tb.Th were also highest in the posterolateral (Tb.N, 1.74±0.374 mm; Tb.Th, 0.148±0.017 mm) and posteromedial (Tb.N, 1.49±0.401 mm; Tb.Th, 0.165±0.016 mm) regions. Trabecular separation was greatest in the superomedial segment (1.00±0.181 mm) and lowest in the posterolateral region (0.663±0.121 mm). For structural model index, both the posterolateral (0.314) and posteromedial (0.312) regions had lower values than the other regions. The posterior segment of the normal glenoid in both the lateral and medial regions has the highest density, which is attributed to the increased trabecular number and thickness with decreased separation. This increased density may be attributed to the posterior directed loading of the glenohumeral joint. The trabecular microarchitecture in the glenoid is plate-like, as indicated by the low structural model index.[Orthopedics. 2015; 38(3):e163-e168.]. Copyright 2015, SLACK Incorporated.
    Orthopedics 03/2015; 38(3):e163-8. DOI:10.3928/01477447-20150305-52 · 1.05 Impact Factor
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    ABSTRACT: OBJECT The unique and complex biomechanics of the atlantoaxial junction make the treatment of C1-2 instability a challenge. Several screw-based constructs have been developed for atlantoaxial fixation. The biomechanical properties of these constructs have been assessed in numerous cadaver studies. The purpose of this study was to systematically review the literature on the biomechanical stability achieved using various C1-2 screw constructs and to perform a meta-analysis of the available data. METHODS A systematic search of PubMed through July 1, 2013, was conducted using the following key words and Boolean operators: "atlanto [all fields]" AND "axial [all fields]" OR "C1-C2" AND "biomechanic." Cadaveric studies on atlantoaxial fixation using screw constructs were included. Data were collected on instability models, fixation techniques, and range of motion (ROM). Forest plots were constructed to summarize the data and compare the biomechanical stability achieved. RESULTS Fifteen articles met the inclusion criteria. An average (± SD) of 7.4 ± 1.8 cadaveric specimens were used in each study (range 5-12). The most common injury models were odontoidectomy (53.3%) and cervical ligament transection (26.7%). The most common spinal motion segments potted for motion analysis were occiput-C4 (46.7%) and occiput-C3 (33.3%). Four screw constructs (C1 lateral mass-C2 pedicle screw [C1LM-C2PS], C1-2 transarticular screw [C1-C2TA], C1 lateral mass-C2 translaminar screw [C1LM-C2TL], and C1 lateral mass-C2 pars screw [C1LM-C2 pars]) were assessed for biomechanical stability in axial rotation, flexion/extension, and lateral bending, for a total of 12 analyses. The C1LM-C2TL construct did not achieve significant lateral bending stabilization (p = 0.70). All the other analyses showed significant stabilization (p < 0.001 for each analysis). Significant heterogeneity was found among the reported stabilities achieved in the analyses (p < 0.001; I(2) > 80% for all significant analyses). The C1LM-C2 pars construct achieved significantly less axial rotation stability (average ROM 36.27° [95% CI 34.22°-38.33°]) than the 3 other constructs (p < 0.001; C1LM-C2PS average ROM 49.26° [95% CI 47.66°-50.87°], C1-C2TA average ROM 47.63° [95% CI 45.22°-50.04°], and C1LM-C2TL average ROM 53.26° [95% CI 49.91°-56.61°]) and significantly more flexion/extension stability (average ROM 13.45° [95% CI 10.53°-16.37°]) than the 3 other constructs (p < 0.001; C1LM-C2PS average ROM 9.02° [95% CI 8.25°-9.80°], C1-C2TA average ROM 7.39° [95% CI 5.60°-9.17°], and C1LM-C2TL average ROM 7.81° [95% CI 6.93°-8.69°]). The C1-C2TA (average ROM 5.49° [95% CI 3.89°-7.09°]) and C1LM-C2 pars (average ROM 4.21° [95% CI 2.19°-6.24°]) constructs achieved significantly more lateral bending stability than the other constructs (p < 0.001; C1LM-C2PS average ROM 1.51° [95% CI 1.23°-1.78°]; C1LM-C2TL average ROM -0.07° [95% CI -0.44° to 0.29°]). CONCLUSIONS Meta-analysis of the existing literature showed that all constructs provided significant stabilization in all axes of rotation, except for the C1LM-C2TL construct in lateral bending. There were significant differences in stabilization achieved in each axis of motion by the various screw constructs. These results underline the various strengths and weaknesses in biomechanical stabilization of different screw constructs. There was significant heterogeneity in the data reported across the studies. Standardized spinal motion segment configuration and injury models may provide more consistent and reliable results.
    Journal of Neurosurgery Spine 12/2014; 22(2):1-11. DOI:10.3171/2014.10.SPINE13805 · 2.36 Impact Factor
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    ABSTRACT: The aims of this study were to assess damage on the surface of retrieved oxidized zirconium (OxZr) metal femoral heads, to measure surface roughness of scratches, and to evaluate the extent of surface effacement using scanning electron microscopy (SEM). Ceramic zirconia-toughened alumina heads were analyzed for comparison. OxZr femoral heads explanted for recurrent dislocation had the most severe damage (P<0.001). The median surface roughness of damaged OxZr femoral heads was 1.49μm, compared to 0.084μm for damaged ceramic heads and 0.052μm for undamaged OxZr (P<0.001). This may be of clinical concern because increased surface roughness has the potential to increase the wear of polyethylene liners articulating against these OxZr heads in THA. Copyright © 2014 Elsevier Inc. All rights reserved.
    The Journal of Arthroplasty 11/2014; DOI:10.1016/j.arth.2014.10.036 · 2.37 Impact Factor
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    ABSTRACT: Total shoulder arthroplasty is commonly performed to treat glenohumeral osteoarthritis (OA); however, little is understood of the mechanics of the reconstructed OA shoulder. We sought to establish the effects of OA-induced changes in bone density and retroversion angle on load transfer and stress distribution in the bone-implant system of the scapula. We developed finite element models of reconstructed healthy and OA scapulas with a virtually implanted glenoid prosthesis design. For the OA scapula, models with uncorrected and corrected retroversion were created. Loads were applied at the center or posteriorly on the glenoid surface. Our results suggest that with reconstruction of the corrected glenoid with a contemporary implant, cement stresses increase and the load transfer pattern changes with eccentric loads. The load transfer and local stresses in the bone-implant system in the retroverted glenoid are less sensitive to changes in loading location. Furthermore, the load transfer in the OA glenoid is less sensitive to the effect of peg proximity to the cortical shell than in the healthy glenoid. We provided evidence of how load sharing is altered among healthy, corrected OA, and retroverted OA glenoids. We demonstrated that correction of retroversion in OA glenoids may actually increase the risk for stress shielding and cement failure compared with retroverted glenoids, and OA patients can accommodate shorter pegs because of the higher glenoid bone stiffness in the OA glenoid. Copyright © 2014 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.
    Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.] 10/2014; DOI:10.1016/j.jse.2014.08.011 · 1.93 Impact Factor
  • Stuart B Goodman, Timothy M Wright
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    ABSTRACT: The Carl T. Brighton Workshop on Implant Wear and Tribocorrosion of Total Joint Replacements was held on November 21 to 23, 2013 in Tampa, FL USA under the auspices of the Association of Bone and Joint Surgeons® and Clinical Orthopaedics and Related Research®. Overall, the workshop provided cause for optimism that the current challenges in total joint replacement will be surmounted by ongoing research, innovation and continued outcome studies and national registry data.Total joint replacement has demonstrated great success in relieving pain and improving function for many millions of patients. However, open questions and challenges remain in terms of defining appropriate patient selection and surgical technique, as well as in identifying the best bearing surfaces and implant designs, especially for younger more active patients.The workshop assembled an expert group of clinicians, biologists, bioengineers, and material scientists, and tasked the participants with formulating answers to ...
    Clinical Orthopaedics and Related Research 09/2014; 472(12). DOI:10.1007/s11999-014-3961-7 · 2.88 Impact Factor
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    ABSTRACT: Ceramic femoral heads have had promising results as a bearing surface in total hip arthroplasty. Our objective was to evaluate a series of retrieved alumina-zirconia composite ceramic femoral heads for evidence of the tetragonal to monoclinic zirconia phase transformation, metal transfer and articular surface roughness. Raman spectra showed evidence of the zirconia phase transformation in all retrieved specimens, with distinct monoclinic peaks at 183, 335, 383, and 479 cm− 1. All components displayed metal transfer. An increase in the zirconia phase transformation was seen with increasing time in vivo. No correlation between extent of zirconia phase transformation and the surface roughness was found. These short-term results suggest that the use of an alumina-zirconia composite ceramic is a viable option for femoral heads in THA.
    The Journal of Arthroplasty 08/2014; DOI:10.1016/j.arth.2014.08.011 · 2.37 Impact Factor
  • Mark P Figgie, Timothy M Wright, Denise Drinkwater
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    ABSTRACT: Erratum to: Clin Orthop Relat Res DOI 10.1007/s11999-014-3781-9In the published study, “What Design and Material Factors Impact the Wear and Corrosion Performance in Total Elbow Arthroplasties?” the Bioengineering Working Group consisted of: Thomas D. Brown PhD, University of Iowa, Iowa City, IA, USA; Darryl D. D’Lima MD, PhD, Shiley Center for Orthopaedic Research and Education, La Jolla, CA, USA; A. Seth Greenwald, D.Phil (Oxon), Orthopaedic Research Laboratories, Cleveland, OH, USA; Melinda K. Harman PhD, Clemson University, Clemson, SC, USA; Steven M. Kurtz, PhD, Exponent and Drexel University, Philadelphia, PA, USA; William M. Mihalko MD, PhD, Campbell Clinic Orthopedics and BME, Memphis, TN, USA; Orhun K. Muratoglu PhD, Massachusetts General Hospital, Boston, MA, USA; Clare M. Rimnac, PhD Case Western Reserve University, Cleveland, OH, USA; Markus A. Wimmer PhD, Rush University Medical Center, Chicago, IL.The editors regret this error.
    Clinical Orthopaedics and Related Research 08/2014; DOI:10.1007/s11999-014-3864-7 · 2.88 Impact Factor
  • Mark P Figgie, Timothy M Wright, Denise Drinkwater
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    ABSTRACT: The survivorship of total elbow arthroplasties is lower than surgeons and patients would like it to be, especially in patients with posttraumatic arthritis of the elbow. To improve durability, it is important to understand the failure modes of existing implants. Total elbow arthroplasties were designed primarily for low-demand rheumatoid patients. As surgical indications have extended to more active patient populations, the mechanical performance of current designs must meet an increased mechanical burden. Evaluating the degree to which they do this will guide conclusions about which contemporary devices might still meet the need and, as importantly, what design and material changes might be needed to improve performance. WHERE ARE WE NOW?: The reasons for failures of total elbow arthroplasties include infection, loosening, polyethylene wear, locking mechanism failure, periprosthetic fracture, implant fracture, and instability. Implant design factors that have influenced wear include implant constraint, material, coatings, and metal backing. Surgical factors associated with increased wear and subsequent total elbow arthroplasty failure include soft tissue balancing and restoration of alignment and implant positioning. WHERE DO WE NEED TO GO?: A clear need exists for improving the performance of total elbow arthroplasty. Many of the failures that have limited the survivorship of elbow arthroplasties thus far are mechanical in nature with wear-related problems a dominating influence. Much of what we know about the results of total elbow arthroplasty is from small studies frequently involving the designer of the implant. The establishment of total elbow arthroplasty registries coupled with the increasing regulatory burden of postmarket surveillance would lead to a better understanding of the complications and survivorship of elbow arthroplasties. Another primary goal must be to achieve a better understanding of the biomechanics of the normal elbow and how the mechanics are altered after the insertion of elbow arthroplasty components. HOW DO WE GET THERE?: Improving the performance and survivorship of total elbow arthroplasty will require the integration of clinical and implant performance data gained through the establishment of registries with a concerted basic science effort to better understand the functional loads across the joint and to incorporate these loads into experimental and computational models to allow assessment of design and material changes intended to improve durability.
    Clinical Orthopaedics and Related Research 07/2014; 472(12). DOI:10.1007/s11999-014-3781-9 · 2.88 Impact Factor
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    ABSTRACT: Recent studies suggest the ‘Lewinnek safe zone’ for acetabular component position is outdated. We used a large prospective institutional registry to determine if there is a ‘safe zone’ exists for acetabular component position within which the risk of hip dislocation is low and if other patient and implant factors affect the risk of hip dislocation. Patients who reported a dislocation event within six months after hip replacement surgery were identified, and acetabular component position was measured with anteroposterior radiographs. The frequency of dislocation was 2.1% (147 of 7040 patients). No significant difference was found in the number of dislocated hips among the zones. Dislocators < 50 years old were less active preoperatively than nondislocators (p = 0.006). Acetabular component position alone is not protective against instability.
    The Journal of Arthroplasty 07/2014; DOI:10.1016/j.arth.2014.07.009 · 2.37 Impact Factor
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    ABSTRACT: Recent studies have attributed adverse local tissue reactions (ALTRs) in patients with total hip arthroplasties (THAs) to tribocorrosion debris generated by modular femoral stems. The presentations of ALTR are diverse, as are the causes of it, and the biological responses can be important reasons for failure after THA.
    Clinical Orthopaedics and Related Research 07/2014; 472(12). DOI:10.1007/s11999-014-3746-z · 2.88 Impact Factor
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    ABSTRACT: Background The Optetrak® PS (Exactech, Inc., Gainesville, FL) has been a well-functioning posterior stabilized knee replacement since its introduction in 1995. In 2009, the Optetrak Logic® incorporated modifications to the anterior face of the tibial post and the corresponding anterior articulating surface of the femoral component to reduce edge loading on the polyethylene post. In this study, we provide the rationale for the design change and compare the damage on retrieved tibial components of both designs to demonstrate the effectiveness of the design modifications in decreasing post damage. Methods We integrated retrieval findings of tibial post damage with finite element analysis to redesign the anterior tibial post-femoral box articulation. We then used subsequent retrieval analysis on a 3:1 matched sample of 60 PS and 20 Logic® inserts to examine the impact of the design change on polyethylene damage. Results Polyethylene stresses were markedly reduced when rounded contact geometries were incorporated. The comparison of the new and old design using retrieval analysis demonstrated that the redesign led to reduction in surface damage and deformation on the tibial post. Conclusions This study shows the use of a design cycle by which a problem is identified through retrieval analysis, analytical tools are used to suggest design solutions, and then retrieval analysis is applied again on the new design to confirm improved performance. Clinical Relevance Anterior post damage has been markedly reduced through the introduction of design changes to the post-box geometry.
    The Knee 07/2014; 21(6). DOI:10.1016/j.knee.2014.07.022 · 2.01 Impact Factor
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    ABSTRACT: The major complication in nonconforming total shoulder replacement (TSR) is glenoid loosening and is attributed to posteriorly directed humeral head translations. Whether the posterior translations observed clinically are induced by radial mismatch is unclear. The objective of our study was to explain the posterior glenohumeral translations observed clinically after TSR by determining the glenohumeral translation and contact force as a function of radial mismatch. We hypothesized that the posterior direction of glenohumeral translation during scaption would be related to the radial mismatch and that the joint contact force would increase as the radial mismatch increased.
    Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.] 06/2014; DOI:10.1016/j.jse.2014.03.009 · 1.93 Impact Factor
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    ABSTRACT: Objective: Revision total hip arthroplasty (THA) is associated with increased cost, morbidity, and technical challenge compared to primary THA. A better understanding of the risk factors for early revision is needed to inform strategies to optimize patient outcomes. Methods: 207,256 patients who underwent primary THA between 1997-2005 in California and New York were identified from statewide databases. Unique patient identifiers were used to identify early revision THA (<10 years from index procedure). Patient characteristics (demographics, comorbidities, insurance type, preoperative diagnosis), community characteristics (education level, poverty, population density), and hospital characteristics (annual THA volume, bed size, teaching status) were evaluated using multivariable regression to determine risk factors for early revision. Results: The probabilities of undergoing early aseptic revision and early septic revision were 4% and less than 1% at 5 years, respectively. Women were 29% less likely than men to undergo early septic revision (p<0.001). Patients with Medicaid and Medicare were 91% and 24%, respectively, more likely to undergo early septic revision than privately-insured patients (p=0.01; p<0.001). Hospitals performing <200 THA annually had a 34% increased risk of early aseptic revision compared to hospitals performing >400 THA annually (p<0.001). Conclusion: A number of identifiable factors, including younger age, Medicaid, and low hospital volume increase the risk of undergoing early revision THA. Patient-level characteristics distinctly affect the risk of revision within 10 years, particularly if due to infection. Our findings reinforce the need for continued investigation of the predictors of early failure following THA. © 2013 American College of Rheumatology.
    06/2014; 66(6). DOI:10.1002/acr.22240
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    ABSTRACT: Background: Knee joint stability is important in maintaining normal joint motion during activities of daily living. Joint instability not only disrupts normal motion, but also plays a crucial role in the initiation and progression of osteoarthritis. Method of approach: Our goal was to examine knee joint coronal plane stability under varus or valgus loading and to understand the relative contributions of the mechanisms that act to stabilize the knee in response to varus-valgus moments, namely, load distribution between the medial and lateral condyles and the ligaments. A robot testing system was used to determine joint stability in human cadaveric knees as described by the moment vs. angular rotation behavior under varus and valgus loads at extension and at thirty and ninety degrees of flexion. Results: The anatomic knee joint was more stable in response to valgus than varus moments, and stability decreased with flexion angle. Stretching of the collateral ligaments provided a secondary stabilizing mechanism after the lift-off of a condyle occurred. Compressive loads applied across the knee joint, such as would occur with the application of muscle forces, enhanced the ability of the articular surface to provide varus-valgus moment and, thus, helped stabilize the joint in the coronal plane. Conclusions: The primary mechanism for providing varus-valgus stability was the redistribution of the contact force on the articular surfaces from both condyles to a single condyle. Key words: Human knee joint, varus-valgus stability, loads, robot.
    Journal of Biomechanical Engineering 05/2014; 136(8). DOI:10.1115/1.4027662 · 1.75 Impact Factor
  • Radhika J Patel, Timothy M Wright, Yingxin Gao
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    ABSTRACT: Glenoid loosening is the primary reason for failure after a total shoulder arthroplasty (TSA), but the failure mechanism is not yet known. This study determined how the load transfer and stress distribution are affected by the introduction of a glenoid implant. We developed a finite-element model of a scapula with and without a virtually implanted modern glenoid prosthesis design. Two load magnitudes were considered: normal and high. Loading locations were simulated at the center and at 4 eccentric positions on the glenoid. A metal-backed implant was also simulated to understand the effect of fixation stiffness. In the intact glenoid, for both center and eccentric loading, the majority of stress was distributed in the cancellous bone, whereas after a reconstruction, stresses in that region were lower. Metal-backed implants further decreased the joint load carried by the bone. Stresses in the cement layer increased during eccentric and high-magnitude loading. This study provided a basic understanding of the load-sharing phenomenon after a TSA that could explain glenoid loosening failure. Our results suggest that with reconstruction of the glenoid with a contemporary implant, the load transfer pattern is significantly altered, with eccentric and high-magnitude loads increasing stresses in the cement indicating potential for failure. The use of a metal-backed implant reduces the load carried by the bone, which may be detrimental to long-term TSA survival.
    Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.] 04/2014; 23(10). DOI:10.1016/j.jse.2014.01.038 · 1.93 Impact Factor
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    ABSTRACT: Backside damage of the polyethylene in TKA is a potential source of debris. The location of the tibial post in posterior-stabilized implants may influence micromotion, and thus affect backside damage, as may surface roughness. We used implant retrieval analysis to (1) examine if there were differences in backside damage among three modern posterior-stabilized implants attributable to variable surface roughness; (2) determine if the location of damage on the tibial post affected the pattern of backside damage; and (3) determine if demographics influenced backside damage. We identified 403 posterior-stabilized tibial retrieved inserts (147 NexGen(®), 152 Optetrak(®), 104 Genesis(®) II). The damage on the surfaces of the tibial posts was previously graded. The backside of the inserts (divided into quadrants) were scored for evidence of damage. The total quadrant damage was compared for each implant group, the relationship between post face damage and location of damage on the backside was determined for each implant group, and total backside damage was compared among the three implant groups. No correlation was found between the location of damage on the post and location of damage on the backside of the implant for any of the three groups. The Genesis(®) II polyethylene implants, which articulate with a highly polished tibial tray, showed a significantly lower total backside damage score (p < 0.01) when compared with the other two implant groups. The Genesis(®) II and Optetrak(®) showed significantly more damage in the posterior quadrants of the implants (p < 0.01) when compared with the anterior quadrants. A linear regression analysis revealed that lower tibial tray surface roughness was correlated with decreased damage. An implant design with a highly polished tibial tray was associated with decreased backside damage. However, tibial post design and location did not influence the location of backside damage. Our study showed that a highly polished tibial tray was associated with decreased damage to the backside of polyethylene inserts independent of post design and location. These findings should be taken into consideration when new generations of implants are designed.
    Clinical Orthopaedics and Related Research 04/2014; 472(8). DOI:10.1007/s11999-014-3621-y · 2.79 Impact Factor
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    ABSTRACT: Controversy exists regarding the optimal treatment of isolated fractures of the capitellum that are not amenable to open reduction and internal fixation. Excision of the capitellum could result in instability of the elbow, though only limited the clinical or laboratory evidence exists to support this outcome. The aim of our study was to determine if capitellum excision leads to significant instability by measuring the relative change in varus-valgus displacement of the elbow. The varus-valgus displacement was recorded in 11 cadaveric elbows before and after isolated excision of the capitellum. Specimens were testing in varus-loaded and valgus-loaded positions with and without a 1 kg weight on the forearm. The varus-valgus displacement at the elbow was measured using a 3D motion capture system. Capitellum excision did not significantly change varus-valgus displacements in either the adducted, varus, or valgus position of the elbow (p = 0.80, p = 0.28, p = 0.51). Furthermore, the addition of the 1 kg external functional load to the forearm did not produce a significant change in the varus and valgus loaded positions (p = 0.16, p = 0.36). Our results demonstrate that excision of the capitellum in the setting of intact ligamentous structures does not result in significant instability in either the adducted varus loaded or valgus loaded positions of the elbow. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.
    Journal of Orthopaedic Research 02/2014; 32(2). DOI:10.1002/jor.22496 · 2.88 Impact Factor
  • Radhika J. Patel, Timothy M. Wright, Yingxin Gao
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    ABSTRACT: Background Glenoid loosening is the primary reason for failure after a total shoulder arthroplasty (TSA), but the failure mechanism is not yet known. This study determined how the load transfer and stress distribution are affected by the introduction of a glenoid implant. Methods We developed a finite-element model of a scapula with and without a virtually implanted modern glenoid prosthesis design. Two load magnitudes were considered: normal and high. Loading locations were simulated at the center and at 4 eccentric positions on the glenoid. A metal-backed implant was also simulated to understand the effect of fixation stiffness. Results In the intact glenoid, for both center and eccentric loading, the majority of stress was distributed in the cancellous bone, whereas after a reconstruction, stresses in that region were lower. Metal-backed implants further decreased the joint load carried by the bone. Stresses in the cement layer increased during eccentric and high-magnitude loading. Conclusion This study provided a basic understanding of the load-sharing phenomenon after a TSA that could explain glenoid loosening failure. Our results suggest that with reconstruction of the glenoid with a contemporary implant, the load transfer pattern is significantly altered, with eccentric and high-magnitude loads increasing stresses in the cement indicating potential for failure. The use of a metal-backed implant reduces the load carried by the bone, which may be detrimental to long-term TSA survival.

Publication Stats

3k Citations
492.80 Total Impact Points

Institutions

  • 2014
    • Stanford University
      Palo Alto, California, United States
  • 1981–2014
    • Hospital for Special Surgery
      • • Department of Orthopaedic Surgery
      • • Department of Biomechanics
      • • Research Division
      New York City, New York, United States
  • 1988–2013
    • Weill Cornell Medical College
      • Department of Orthopaedic Surgery
      New York City, New York, United States
  • 2005–2010
    • Cornell University
      • • Department of Biomedical Engineering
      • • Department of Clinical Sciences
      Ithaca, New York, United States
  • 2008
    • University of Helsinki
      Helsinki, Southern Finland Province, Finland
  • 1995
    • New York Medical College
      New York, New York, United States
  • 1993
    • University of California, Irvine
      • Department of Orthopedic Surgery
      Irvine, CA, United States
    • Northwestern University
      • Department of Orthopaedic Surgery
      Evanston, IL, United States