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Background: Use of large clinical and administrative databases for orthopaedic research has increased exponentially. Each database represents unique patient populations and varies in their methodology of data acquisition, which makes it possible that similar research questions posed to different databases might result in answers that differ in important ways., Questions/purposes: (1) What are the differences in reported demographics, comorbidities, and complications for patients undergoing primary TKA among four databases commonly used in orthopaedic research? (2) How does the difference in reported complication rates vary depending on whether only inpatient data or 30-day postoperative data are analyzed?, Methods: Patients who underwent primary TKA during 2010 to 2012 were identified within the National Surgical Quality Improvement Programs (NSQIP), the Nationwide Inpatient Sample (NIS), the Medicare Standard Analytic Files (MED), and the Humana Administrative Claims database (HAC). NSQIP is a clinical registry that captures both inpatient and outpatient events up to 30 days after surgery using clinical reviewers and strict definitions for each variable. The other databases are administrative claims databases with their comorbidity and adverse event data defined by diagnosis and procedure codes used for reimbursement. NIS is limited to inpatient data only, whereas HAC and MED also have outpatient data. The number of patients undergoing primary TKA from each database was 48,248 in HAC, 783,546 in MED, 393,050 in NIS, and 43,220 in NSQIP. NSQIP definitions for comorbidities and surgical complications were matched to corresponding International Classification of Diseases, 9 Revision/Current Procedural Terminology codes and these coding algorithms were used to query NIS, MED, and HAC. Age, sex, comorbidities, and inpatient versus 30-day postoperative complications were compared across the four databases. Given the large sample sizes, statistical significance was often detected for small, clinically unimportant differences; thus, the focus of comparisons was whether the difference reached an absolute difference of twofold to signify an important clinical difference., Results: Although there was a higher proportion of males in NIS and NSQIP and patients in NIS were younger, the difference was slight and well below our predefined threshold for a clinically important difference. There was variation in the prevalence of comorbidities and rates of postoperative complications among databases. The prevalence of chronic obstructive pulmonary disease (COPD) and coagulopathy in HAC and MED was more than twice that in NIS and NSQIP (relative risk [RR] for COPD: MED versus NIS 3.1, MED versus NSQIP 4.5, HAC versus NIS 3.6, HAC versus NSQIP 5.3; RR for coagulopathy: MED versus NIS 3.9, MED versus NSQIP 3.1, HAC versus NIS 3.3, HAC versus NSQIP 2.7; p < 0.001 for all comparisons). NSQIP had more than twice the obesity as NIS (RR 0.35). Rates of stroke within 30 days of TKA had more than a twofold difference among all databases (p < 0.001). HAC had more than twice the rates of 30-day complications at all endpoints compared with NSQIP and more than twice the 30-day infections as MED. A comparison of inpatient and 30-day complications rates demonstrated more than twice the amount of wound infections and deep vein thromboses is captured when data are analyzed out to 30 days after TKA (p < 0.001 for all comparisons)., Conclusions: When evaluating research utilizing large databases, one must pay particular attention to the type of database used (administrative claims, clinical registry, or other kinds of databases), time period included, definitions utilized for specific variables, and the population captured to ensure it is best suited for the specific research question. Furthermore, with the advent of bundled payments, policymakers must meticulously consider the data sources used to ensure the data analytics match historical sources., Level of Evidence: Level III, therapeutic study.

Background: Short stem cementless femoral components were developed to aid insertion through smaller incisions, preserve metaphyseal bone, and potentially decrease or limit the incidence of thigh pain. Despite some clinical success, the senior author (DDG) believed a higher percentage of his patients who had received a cementless short stem design were experiencing thigh pain, which, coupled with concerns about bone ingrowth fixation, motivated the review of this case series., Questions/purposes: (1) What is the proportion of patients treated with a short stem cementless THA femoral component that develop thigh pain and what are the hip scores of this population? (2) What are the radiographic results, specifically with respect to bone ingrowth fixation and stress shielding, of this design? (3) Are there particular patient or procedural factors that are associated with thigh pain with this short stem design?, Methods: Two hundred sixty-one primary THAs were performed in 238 patients by one surgeon between November 2010 and August 2012. During this time period, all patients undergoing primary THA by this surgeon received the same cementless short titanium taper stem. Seven patients (eight hips) died and five patients (five hips) were lost to followup, leaving 226 patients (248 hips) with a mean followup of 3 years (range, 2-5 years). Patients rated their thigh pain during activity or rest at final followup on a 10-point visual analog scale. Harris hip scores (HHS) were obtained at every clinic appointment. Thigh pain was evaluated at the final followup or by contacting the patient by phone. Radiographs were evaluated for bone-implant fixation, bone remodeling, and osteolysis. An attempt was made to correlate thigh pain with patient demographics, implant specifications, or radiographic findings., Results: Seventy-six percent of hips (180 of 238) had no thigh pain, 16% of hips (37 of 238) had mild thigh pain, and 9% (21 of 238) had moderate or severe thigh pain. Preoperatively, mean HHS was 47 (SD, 16) and at last followup, mean HHS was 88 (SD, 13). There were two femoral revisions, one for severe thigh pain and the other for infection. All but two components demonstrated bone ingrowth fixation (99%). Femoral stress shielding was mild in 64% of hips (135 of 212), moderate in 0.5% (one of 212), and severe in no hips. There is an inverse linear relationship between age and severity of thigh pain (r = -0.196; p < 0.0024)., Conclusions: Although reliable fixation was achieved and good HHS were attained, the frequency and severity of thigh pain with this short cementless stem were concerning. The surgeon has subsequently abandoned this short stem design and returned to a conventional length stem. Future study direction might investigate the biomechanical grounds for the thigh pain associated with this stem design., Level of Evidence: Level IV, therapeutic study.

Background: Infection after total knee arthroplasty (TKA) can result in disastrous consequences. Previous research regarding injections and risk of TKA infection have produced conflicting results and in general have been limited by small cohort size., Questions/purposes: The purpose of this study was to evaluate if intraarticular injection before TKA increases the risk of postoperative infection and to identify if time between injection and TKA affect the risk of TKA infection., Methods: The Humana data set was reviewed from 2007 to 2014 for all patients who received a knee injection before TKA. Current Procedural Terminology (CPT) codes and laterality modifiers were used to identify patients who underwent knee injection followed by ipsilateral TKA. Postoperative infection within 6 months of TKA was identified using International Classification of Diseases, 9 th Revision/CPT codes that represent two infectious endpoints: any postoperative surgical site infection (encompasses all severities of infection) and operative intervention for TKA infection (surrogate for deep TKA infection). The injection cohort was stratified into 12 subgroups by monthly intervals out to 12 months corresponding to the number of months that had elapsed between injection and TKA. Risk of postoperative infection was compared between the injection and no injection cohorts. In total, 29,603 TKAs (35%) had an injection in the ipsilateral knee before the TKA procedure and 54,081 TKA cases (65%) did not. The PearlDiver database does not currently support line-by-line output of patient data, and so we were unable to perform a multivariate analysis to determine whether other important factors may have varied between the study groups that might have had a differential influence on the risk of infection between those groups. However, the Charlson Comorbidity index was no different between the injection and no injection cohorts (2.9 for both) suggesting similar comorbidity profiles between the groups., Results: The proportion of TKAs developing any postoperative infection was higher among TKAs that received an injection before TKA than in those that did not (4.4% versus 3.6%; odds ratio [OR], 1.23; 95% confidence interval [CI], 1.15-1.33; p < 0.001). Likewise, the proportion of TKAs developing infection resulting in return to the operating room after TKA was also higher among TKAs that received an injection before TKA than those that did not (1.49% versus 1.04%; OR, 1.4; 95% CI, 1.3-1.63; p < 0.001). Month-by-month analysis of time between injection and TKA revealed the odds of any postoperative infection remained higher for the injection cohort out to a duration of 6 months between injection and TKA (ORs ranged 1.23 to 1.46 when 1-6 months between injection and TKA; p < 0.05 for all) as did the odds of operative intervention for TKA infection when injection occurred within 7 months of TKA (OR ranged from 1.38 to 1.88 when 1-7 months between injection and TKA; p < 0.05 for all). When the duration between injection and TKA was longer than 6 or 7 months, the ORs were no longer elevated at these endpoints, respectively., Conclusions: Injection before TKA was associated with a higher risk of postoperative infection and appears to be time-dependent with closer proximity between injection and TKA having increased odds of infection. Further research is needed to better evaluate the risk injection before TKA poses for TKA infection; a more definitive relationship could be established with a multivariate analysis to control for other known risk factors for TKA infection., Level of Evidence: Level III, therapeutic study.

Background: A patient who dies during the followup period of a study about total hip arthroplasty (THA) cannot subsequently undergo a revision. The presence of competing events (such as deaths, in a study on implant durability) violates an assumption of the commonly used Kaplan-Meier (KM) survivorship approach. In that setting, KM-based estimates of revision frequencies will be high relative to alternative approaches that account for competing events such as cumulative incidence methods. However, the degree to which this difference is clinically relevant, and the degree to which it affects different ages of patient cohorts, has been poorly characterized in orthopaedic clinical research., Questions/purposes: The purpose of this study was to compare KM with cumulative incidence survivorship estimators to evaluate the degree to which the competing event of death influences the reporting of implant survivorship at long-term followup after THA in patients both younger than and older than 50 years of age., Methods: We retrospectively reviewed 758 cemented THAs from a prospectively maintained single-surgeon registry, who were followed for a minimum of 20 years or until death. Revision rates were compared between those younger than or older than age 50 years using both KM and cumulative incidence methods. Patient survivorship was calculated using KM methods. A total of 21% (23 of 109) of the cohort who were younger than 50 years at the time of THA died during the 20-year followup period compared with 72% (467 of 649) who were older than 50 years at the time of surgery (p < 0.001)., Results: In the cumulative incidence analysis, 19% of the younger than age 50 years cohort underwent a revision for aseptic causes within 20 years as compared with 5% in the older than age 50 years cohort (p < 0.001). The KM method overestimated the risk of revision (23% versus 8.3%, p < 0.001), which represents a 21% and 66% relative increase for the younger than/older than age 50 years groups, respectively., Conclusions: The KM method overestimated the risk of revision compared with the cumulative incidence method, and the difference was particularly notable in the elderly cohort. Future long-term followup studies on elderly cohorts should report results using survivorship curves that take into account the competing risk of patient death. We observed a high attrition rate as a result of patient deaths, and this emphasizes a need for future studies to enroll younger patients to ensure adequate study numbers at final followup., Level of Evidence: Level III, therapeutic study.

Background: Cemented femoral total hip arthroplasty may be one of the most successful surgical interventions of all time. However, although results are very encouraging over the early to mid-term followup, relatively few studies have analyzed the durability of these implants beyond 20 years followup. To evaluate the performance of contemporary implants, it is important to understand how previous implants perform at 20 or more years of followup; one way to do this is to aggregate the available data in the form of a systematic review., Questions/purposes: (1) How durable is cemented femoral fixation in the long term (minimum 20-year followup) with respect to aseptic loosening? (2) Is the durability of cemented femoral fixation dependent on age of the patient? (3) Are the long-term results of the cemented femoral fixation dependent on any identifiable characteristics of the prosthesis such as surface finish?, Methods: A systematic review was performed to identify long-term studies of cemented femoral components. After application of inclusion and exclusion criteria to 1228 articles found with a search in PubMed and EMBASE, 17 studies with a minimum of 20-year followup on cemented femoral components were thoroughly analyzed in an attempt to answer the questions of this review. The quality of the studies reviewed was assessed with the Methodological Index for Nonrandomized Studies (MINORS) instrument. All studies were case series and cohort sizes ranged from 110 to 2000 hips for patients older than 50 years of age and 41 to 93 hips for patients younger than 50 years at the time of surgery., Results: Among the six case series performed in patients older than 50 years of age, survivorship for aseptic loosening of the femoral component ranged from 86% to 98% at 20 years followup. There were no obvious differences for younger patients when analyzing the five studies in patients younger than age 50 years in which survivorship free from aseptic loosening for these studies ranged from 77% at 20 years in one study and 68% to 94% at 25 years in the other studies. Although data pooling could not be performed because of heterogeneity of the studies included here, it appeared that stems with a rougher surface finish did not perform as well as polished stems; survivorship of stems with rougher surface finishes varied between 86% and 87%, whereas those with smoother finishes ranged between 93.5% and 98% at 20 years., Conclusions: Excellent long-term fixation in both older and younger patients can be obtained with cemented, polished femoral stems. These results provide material for comparison with procedures performed with newer cementing techniques and newer designs, both cemented and cementless, at this extended duration of followup.

Background: Positioning of total hip bearings involves tradeoffs, because cup orientations most favorable in terms of stability are not necessarily ideal in terms of reduction of contact stress and wear potential. Previous studies and models have not addressed these potentially competing considerations for optimal total hip arthroplasty (THA) function., Questions/purposes: We therefore asked if component positioning in total hips could be addressed in terms of balancing bearing surface wear and stability. Specifically, we sought to identify acetabular component inclination and anteversion orientation, which simultaneously resulted in minimal wear while maximizing construct stability, for several permutations of femoral head diameter and femoral stem anteversion., Methods: A validated metal-on-metal THA finite element (FE) model was used in this investigation. Five dislocation-prone motions as well as gait were considered as were permutations of femoral anteversion (0°-30°), femoral head diameter (32-48 mm), cup inclination (25°-75°), and cup anteversion (0°-50°), resulting in 4320 distinct FE simulations. A novel metric was developed to identify a range of favorable cup orientations (so-called "landing zone") by considering both surface wear and component stability., Results: When considering both wear and stability with equal weight, ideal cup position was more restrictive than the historically defined safe zone and was substantially more sensitive to cup anteversion than to inclination. Ideal acetabular positioning varied with both femoral head diameter and femoral version. In general, ideal cup inclination decreased with increased head diameter (approximately 0.5° per millimeter increase in head diameter). Additionally, ideal inclination increased with increased values of femoral anteversion (approximately 0.3° per degree increase in stem anteversion). Conversely, ideal cup anteversion increased with increased femoral head diameter (0.3° per millimeter increase) and decreased with increased femoral stem anteversion (approximately 0.3° per degree increase). Regressions demonstrated strong correlations between optimal cup inclination versus head diameter (Pearson's r=-0.88), between optimal cup inclination versus femoral anteversion (r=0.96), between optimal cup anteversion versus head diameter (r=0.99), and between optimal cup anteversion and femoral anteversion (r=-0.98). For a 36-mm cup with a 20° anteverted stem, the ideal cup orientation was 46°±12° inclination and 15°±4° anteversion., Conclusions: The range of cup orientations that maximized stability and minimized wear (so-called "landing zone") was substantially smaller than historical guidelines and specifically did not increase with increased head size, challenging the presumption that larger heads are more forgiving. In particular, when the cup is oriented to improve not only stability, but also wear in the model, there was little or no added stability achieved by the use of larger femoral heads. Additionally, ideal cup positioning was more sensitive to cup anteversion than to inclination., Clinical Relevance: Positioning THA bearings involves tradeoffs regarding stability and long-term bearing wear. Cup positions most favorable to minimization of wear such as low inclination and elevated anteversion were detrimental in terms of construct stability. Orientations were identified that best balanced the competing considerations of wear and stability.

Background: Many patients undergoing TKA have both knee and ankle pathology, and it seems likely that some compensatory changes occur at each joint in response to deformity at the other. However, it is not fully understood how the foot and ankle compensate for a given varus or valgus deformity of the knee., Questions/purposes: (1) What is the compensatory hindfoot alignment in patients with end-stage osteoarthritis who undergo total knee arthroplasty (TKA)? (2) Where in the hindfoot does the compensation occur?, Methods: Between January 1, 2005, and December 31, 2009, one surgeon (JJC) obtained full-length radiographs on all patients undergoing primary TKA (N=518) as part of routine practice; patients were analyzed for the current study and after meeting inclusion criteria, a total of 401 knees in 324 patients were reviewed for this analysis. Preoperative standing long-leg AP radiographs and Saltzman hindfoot views were analyzed for the following measurements: mechanical axis angle, Saltzman hindfoot alignment and angle, anatomic lateral distal tibial angle, and the ankle line convergence angle. Statistical analysis included two-tailed Pearson correlations and linear regression models. Intraobserver and interobserver intraclass coefficients for the measurements considered were evaluated and all were excellent (in excess of 0.8)., Results: As the mechanical axis angle becomes either more varus or valgus, the hindfoot will subsequently orient in more valgus or varus position, respectively. For every degree increase in the valgus mechanical axis angle, the hindfoot shifts into varus by -0.43° (95% confidence interval [CI], -0.76° to -0.1°; r=-0.302, p=0.0012). For every degree increase in the varus mechanical axis angle, the hindfoot shifts into valgus by -0.49° (95% CI, -0.67° to -0.31°; r=-0.347, p<0.0001). In addition, the subtalar joint had a strong positive correlation (r=0.848, r2=0.72, p<0.0001) with the Saltzman hindfoot angle, whereas the anatomic lateral distal tibial angle (r=0.450, r2=0.20, p<0.0001) and the ankle line convergence angle (r=0.319, r2=0.10, p<0.0001) had a moderate positive correlation. The coefficient of determination (r2) shows that 72% of the variance in the overall hindfoot angle can be explained by changes in the subtalar joint orientation., Conclusions: These findings have implications for treating patients with both knee and foot/ankle problems. For example, a patient with varus arthritis of the knee should be examined for fixed hindfoot valgus deformity. The concern is that patients undergoing TKA, who also present with a stiff subtalar joint, may have exacerbated, post-TKA foot/ankle pain or disability or malalignment of the lower extremity mechanical axis as a result of the inability of the subtalar joint to reorient itself after knee realignment. A prospective study is underway to confirm this speculation., Level of Evidence: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Background: Long-term evaluation of knee arthroplasty should provide relevant information concerning the durability and performance of the implant and the procedure. Because most arthroplasties are performed in older patients, most long-term followup studies have been performed in elderly cohorts and have had low patient survivorship to final followup; the degree to which attrition from patient deaths over time in these studies might influence their results has been poorly characterized., Questions/purposes: The purpose of this study was to examine the results at 20-year followup of two prospectively followed knee arthroplasty cohorts to determine the following: (1) Are there relevant differences among the two implant cohorts in terms of revision for aseptic causes (osteolysis, or loosening)? (2) How does patient death over the long followup interval influence the comparison, and do the comparisons remain valid despite the high attrition rates?, Methods: Two knee arthroplasty cohorts from a single orthopaedic practice were evaluated: a modular tibial tray (101 knees) and a rotating platform (119 knees) design. All patients were followed for a minimum of 20 years or until death (mean, 14.1 years; SD 5.0 years). Average age at surgery for both cohorts was >70 years. The indications for the two cohorts were identical (functionally limiting knee pain) and was surgeon-specific (each surgeon performed all surgeries in that cohort). Revision rates through a competing risks analysis for implants and survivorship curves for patients were evaluated., Results: Both of these elderly cohorts showed excellent implant survivorship at 20 years followup with only small differences in revision rates (6% revision versus 0% revision for the modular tibial tray and rotating platform, respectively). However, attrition from patient deaths was substantial and overall patient survivorship to 20-year followup was only 26%. Patient survivorship was significantly higher in patients<65 years of age in both cohorts (54% versus 15%, p<0.001 modular tray cohort, and 52% versus 26%, p=0.002 rotating platform cohort). Furthermore, in the modular tray cohort, patients<65 years had significantly higher revision rates (15% versus 3%, p=0.0019)., Conclusions: These two cohorts demonstrate the durability of knee arthroplasty in older patients (the vast majority older than 65 years). Unfortunately, few patients lived to 20-year followup, thus introducing bias into the analysis. These data may be useful as a reference for the design of future prospective studies, and consideration should be given to enrolling younger patients to have robust numbers of living patients at long-term followup., Level of Evidence: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Background: Increasing national expenditures and use associated with TKA have resulted in pressure to reduce costs through various reimbursement cuts. However, within the arthroplasty literature, few studies have examined the association of medical comorbidities on resource use and length of stay after joint arthroplasty., Questions/purposes: The purpose of this study was to examine the association between individual patient characteristics (including demographic factors and medical comorbidities) on resource allocation and length of stay (LOS) after TKA., Methods: We queried the 2009 Nationwide Inpatient Sample dataset for International Classification of Diseases, 9(th) Revision code, 81.54, for TKAs. An initial 621,029-patient cohort was narrowed to 516,745 after inclusion of elective TKAs on patients aged between 40 and 95 years. Using generalized linear models, we estimated the effect of comorbidities on resource use (using cost-to-charge conversions to estimate hospital costs) and the LOS controlling for patient and hospital characteristics. Across the 2009 national cohort with TKAs, 12.7% had no comorbidities, whereas 32.6% had three or more. The most common conditions included hypertension (67.8%), diabetes (20.0%), and obesity (19.8%). Mean hospital costs were USD 14,491 (95% confidence interval [CI], 14,455-14,525) and mean hospital LOS was 3.3 days (95% CI, 3.29-3.31) in this data set., Results: Patients with multiple comorbidities were associated with increased resource use and LOS. Higher marginal costs and LOS were associated with patients who had an inpatient death (USD +8017 [95% CI, 8006-8028], +2.3 [CI, 2.15-2.44] days over baseline), patients with recent weight loss (USD +4587 [95% CI, 4581-4593], +1.5 [CI, 1.45-1.61) days], minority race (USD +1037 [95% CI, 1035-1038], +0.3 [CI, 0.28-0.33] days), pulmonary-circulatory disorders (USD +3218 [95% CI, 3214-3221], +1.3 [CI, 1.25-1.34] days), and electrolyte disturbances (USD +1313 [95% CI, 1312-1314], +0.6 [CI, 0.57-0.60] days). All p values were < 0.001., Conclusion: Multiple patient comorbidities were associated with additive resource use and LOS after TKA. Current reimbursement may not adequately account for these patient characteristics. To avoid potential loss of access to care for sicker patients, payment needs to be adjusted to reflect actual resource use., Level of Evidence: Level IV, economic and decision analysis. See the Instructions for Authors for a complete description of levels of evidence.

Background: Wear and corrosion in joint arthroplasty are important causes of failure. From the standpoint of current clinical importance, there are four main categories of wear and tribocorrosion: polyethylene wear, ceramic-on-ceramic (CoC) bearing wear, metal-on-metal (MoM) bearing wear, and taper tribocorrosion. Recently, problems with wear in the knee have become less prominent as have many issues with hip polyethylene (PE) bearings resulting from the success of crosslinked PE. However, MoM articulations and taper tribocorrosion have been associated with soft tissue inflammatory responses, and as a result, they have become prominent clinical concerns. WHERE ARE WE NOW?: For PE wear in the hip, several advances include improved locking mechanisms and data supporting highly crosslinked polyethylenes (HXLPE). Edge-loading in CoC articulations can contribute to stripe wear and subsequent squeaking. For MoM articulations, the relationship of wear-to-edge loading, sensitivity to component positioning, typical soft tissue response, and use of imaging is increasingly understood. Taper tribocorrosion (from femoral head-neck junctions and other modular elements) and associated soft tissue inflammatory responses appear to be serious clinical issues that are not fully understood. WHERE DO WE NEED TO GO?: In the knee, clinical concerns remain with the efficacy of HXLPE, modular connections, and metal allergies. For PE wear in the hip, concerns remain regarding how to increase crosslinking of PE while minimizing PE fractures. With CoC articulations, questions remain on how to prevent noises, chipping, and impingement and if enhanced designs can contribute to improved results. For MoM articulations, we need to improve imaging tests for soft tissue reactions, determine best practices in terms of monitoring protocols, and better define if, how, and when to act on serum metal levels. For taper tribocorrosion, we need to use modularity wisely and also understand how to improve tapers and materials in the future. For patients at risk for tribocorrosion, we need to define realistic diagnostic and monitoring protocols. We also need to enhance revision methods, and the threshold of acceptable soft tissue damage, to minimize complications associated with soft tissue damage such as hip instability. HOW DO WE GET THERE?: HXLPE and other bearing surfaces will likely continue to be refined. We need to develop tapers with more resistance to tribocorrosion through improved understanding of the manufacturing process and ongoing engineering improvements. Revision procedures for wear and tribocorrosion can be enhanced by determining when partial component retention is appropriate and how best to manage soft tissue damage. For CoC articulations, enhanced designs are required to minimize noises, chipping, and impingement. Importantly, we must continue to promote and analyze joint replacement registries to identify early failures and analyze long-term successes.

Background: Large-diameter femoral heads for metal-on-metal THA hold theoretical advantages of joint stability and low bearing surface wear. However, recent reports have indicated an unacceptably high rate of wear-associated failure with large-diameter bearings, possibly due in part to increased wear at the trunnion interface. Thus, the deleterious consequences of using large heads may outweigh their theoretical advantages., Questions/purposes: We investigated (1) to what extent femoral head size influenced stability in THA for several dislocation-prone motions; and the biomechanics of wear at the trunnion interface by considering the relationship between (2) wear potential and head size and (3) wear potential and other factors, including cup orientation, type of hip motion, and assembly/impaction load., Methods: Computational simulations were executed using a previously validated nonlinear contact finite element model. Stability was determined at 36 cup orientations for five distinct dislocation challenges. Wear at the trunnion interface was calculated for three separate cup orientations subjected to gait, stooping, and sit-to-stand motions. Seven head diameters were investigated: 32 to 56 mm, in 4-mm increments., Results: Stability improved with increased diameter, although diminishing benefit was seen for sizes of greater than 40 mm. By contrast, contact stress and computed wear at the trunnion interface all increased unabatedly with increasing head size. Increased impaction forces resulted in only small decreases in trunnion wear generation., Conclusions: These data suggest that the theoretical advantages of large-diameter femoral heads have a limit. Diameters of greater than 40 mm demonstrated only modest improvement in terms of joint stability yet incurred substantial increase in wear potential at the trunnion., Clinical Relevance: Our model has potential to help investigators and designers of hip implants to better understand the optimization of trunnion design for long-term durability.

Background: There are two unusual remodeling patterns of the proximal femur around well-fixed Charnley total hip arthroplasties: cortical thinning leading to endosteal widening around the femoral component and hypertrophy of the distal femoral cortex. Previous studies have shown remodeling patterns are affected by stem design and occur early postoperatively. It is unclear if these changes are related to patient demographics or if they progress throughout the lifetime of the implant., Questions/purposes: We determined if patient demographic variables influence remodeling patterns after cemented Charnley total hip arthroplasty and if the observed remodeling changes persist long-term., Methods: We retrospectively reviewed the radiographs of 106 well-fixed Charnley femoral components. Using a novel digital edge detection program, we determined the femoral remodeling pattern and time-related changes in femoral dimensions. The minimum followup was 20 years (mean, 25.3 years; range, 19.5-37 years)., Results: We found no association between remodeling type and age at surgery, sex, preoperative diagnosis, body mass index, or postoperative activity level. There was also no association between initial implant alignment and remodeling type. Cortical thickening in the distal hypertrophy group was an early phenomenon occurring primarily within the first 2 years, whereas cortical thinning begins later and is a more progressive process., Conclusions: These data show remodeling after cemented Charnley total hip arthroplasty is not related to patient demographic variables; however, distal cortical hypertrophy can be predicted in the early postoperative period.

Background: There is a paucity of literature concerning functional assessment at long-term followup of THAs in general and in young patients specifically. Functional data may be useful in determining differences in the performance of various implants and surgical techniques in THA., Questions/purposes: The purposes of this study were to evaluate a group of young patients who were still active 10 years after THA to determine (1) which functional tests and (2) which patient-reported outcome assessments predicted long-term THA function, as measured by acetabular UHMWPE wear, and (3) whether medical comorbidities influenced patient performance on activity tests and patient outcome questionnaires., Methods: Fifty patients (58 hips) 50 years and younger at the time of THA were followed clinically and radiographically for a minimum of 10 years. All patients wore step activity monitors for up to 21 days, performed 6-minute walk (6-MW) tests, and every patient had minimum 10-year radiographs and sequential radiographs evaluated for wear using edge detection techniques. Mean age and BMI at surgery were 39 years and 29 kg/m(2), respectively., Results: Patients who walked more as determined by step activity monitor (average daily steps) had more linear acetabular UHMWPE wear per year and more volumetric wear per year. The 6-MW, University of California Los Angeles (UCLA), and Tegner Lysholm scores did not correlate with acetabular wear. Mean 6-MW distance was 335 m and pedometer data averaged 1.56 million steps per year. Average UCLA and Tegner Lysholm scores were 6 and 3, respectively. Mean linear wear rate was 0.266 mm/year; mean volumetric wear rate was 82.6 mm(3)/year. The number of comorbid medical conditions had a detrimental effect on our activity parameters and outcomes questionnaires, but the relationships were not statistically significant., Conclusions: Of functional tools measured, only pedometer data correlated with THA polyethylene wear. Obtaining pedometer data should be considered when trying to distinguish differences in various hip arthroplasty designs and techniques over the long term.

Background: Obesity has reached epidemic proportions in the United States. Recently, obesity, especially morbid obesity, has been linked to increased rates of dislocation after THA. The reasons are unclear. Soft tissue engagement caused by increased thigh girth has been proposed as a possible mechanism for decreased joint stability., Questions/purposes: We asked (1) whether thigh soft tissue impingement could decrease THA stability, and if so, at what level of BMI this effect might become evident; and (2) how THA construct factors (eg, head size, neck offset, cup abduction) might affect stability in the morbidly obese., Methods: The obesity effect was explored by augmenting a physically validated finite element model of a total hip construct previously comprising just implant hardware and periarticular (capsular) soft tissue. The model augmentation involved using anatomic and anthropometric data to include graded levels of increased thigh girth. Parametric computations were run to assess joint stability for two head sizes (28 and 36 mm), for normal versus high neck offset, and for multiple cup abduction angles., Results: Thigh soft tissue impingement lowered the resistance to dislocation for BMIs of 40 or greater. Dislocation risk increased monotonically above this threshold as a function of cup abduction angle, independent of hardware impingement events. Increased head diameter did not substantially improve joint stability. High-offset necks decreased the dislocation risk., Conclusions: Excessive obesity creates conditions that compromise stability of THAs. Given such conditions, our model suggests reduced cup abduction, high neck offset, and full-cup coverage would reduce the risks of dislocation events.