Modes of failure of hip hemiarthroplasty for femoral neck fracture.

BACKGROUND: Hemiarthroplasty is a common treatment for displaced femoral neck fractures, but limited Canadian data are available about hemiarthroplasty failure. We evaluated the frequency and predictors of hemiarthroplasty failure in Manitoba. METHODS: In this retrospective multicentre province-wide study, billing and joint registry databases showed 4693 patients who had hemiarthroplasty for treatment of femoral neck fracture in Manitoba over an 11-year period (2005-2015), including 155 hips with subsequent reoperations (open or closed) for treatment of hemiarthroplasty failure. Hospital records were reviewed to identify modes of hemiarthroplasty failure, comorbidities and reoperations. Data were analyzed using χ2 test and Poisson and γ regression models. RESULTS: During our study period, 155 hips (154 patients [3%]) underwent 230 reoperations. Of these, 131 hips (85%) initially had an uncemented unipolar modular implant. Indications for first-time reoperation included periprosthetic femur fracture (49 hips [32%]), dislocation (45 hips [29%]), acetabular wear (28 hips [18%]) and infection (26 hips [17%]). There were 46 hips (30%) that had 2 or more reoperations. Reoperation for dislocation was associated with presence of dementia; acetabular wear was associated with absence of dementia. Time from hemiarthroplasty to reoperation was associated inversely with age at hemiarthroplasty, dislocation and dementia and was directly associated with acetabular wear. The risk of having 2 or more reoperations was associated independently with dislocation, infection, and alcohol abuse. CONCLUSION: Hemiarthroplasty for femoral neck fracture in Manitoba had a low frequency of failure. Risk factors for multiple reoperations included dislocation, infection and alcohol abuse.

Midterm Results of a Contemporary, Porous-Coated Acetabular System in Patients Undergoing Primary Total Hip Replacement for Degenerative Hip Disease: A Prospective, Multicenter Study.

BACKGROUND: A contemporary, porous-coated acetabular implant designed for uncemented insertion was introduced in Europe and Australia in 2007. A similar previous acetabular system was found in several studies at 10 to 15-year follow-up to demonstrate accelerated polyethylene wear, osteolysis, and early failure. The current study was conducted to determine the midterm safety and effectiveness of this contemporary acetabular system using highly crosslinked polyethylene and ceramic liners at 5-year follow-up. METHODS: A prospective, nonrandomized study was conducted at 8 sites in Canada and the United States. All 148 study participants received a contemporary acetabular shell with proprietary porous coating. The primary outcome was the requirement for revision surgery at 5 years postoperatively. Secondary outcomes included a survival analysis, patient-reported outcome measures, radiographic failure, and postoperative adverse events. RESULTS: At 5-year follow-up there was 1 cup revised for deep infection. No cups were revised for loosening and none were found to be radiographically loose. The overall survival rate with reoperation for any reason was 97.1%. The success rate was 96.8% for polyethylene and 100% for ceramic with no difference in the success rate between either bearing surface (P = 1.0). The mean patient-reported outcome measures all improved significantly between preoperative and 5-year postoperative scores (P < .001). CONCLUSION: Results from this 5-year, multicenter, prospective study indicate excellent survivorship for this acetabular system when used with crosslinked polyethylene or ceramic bearing surfaces.

Guided-motion hinged knee replacement prosthesis: early survival rate and postoperative patient function and satisfaction.

Background: Literature on the survival rates and function of hinged total knee replacement (HTKR) prostheses is scarce, and to our knowledge there is not yet any published literature on the Legion HK Hinge Knee Replacement prosthesis (Smith & Nephew) with guided-motion articulation. The objective of this study was to establish the early survival rate of this modern HTKR at a single institution and to investigate postoperative patient function and satisfaction. Methods: This retrospective study included patients who received the Legion HTKR prosthesis with guided-motion inserts as a primary or revision implant between October 11 and March 2016 at a tertiary care centre in Manitoba, Canada. Preoperative and postoperative functional scores on the 12-item Oxford Knee Score and postoperative patient satisfaction were assessed. Results: Thirty-nine HTKR implantations (38 patients) were included in this study: 12 primary cases and 27 revision cases. Three revision surgeries and 4 perioperative complications were noted at a mean follow-up of 29.1 months. The 2-year survivorship of the HTKR system was 90.7%. Postoperative functional scores improved significantly and the majority of patients were satisfied or very satisfied at all follow-up time points. Conclusion: The early survival rate of a modern guided-motion HTKR prosthesis is similar to the survival rates of other hinged knee prostheses published in the literature. The prosthesis demonstrated substantial postoperative functional improvement when used in the setting of complex primary or revision total knee replacement.

Contexte: Il existe peu d'études sur le taux de survie et la fonction des prothèses totales de genou (PTG) à charnière, et, à notre connaissance, il n'y a pas encore d'étude publiée sur la prothèse Legion HK Hinge Knee (Smith & Nephew), qui guide le mouvement de l'articulation. Cette étude visait à déterminer le taux de survie à 2 ans de cette PTG à charnière moderne dans un seul établissement et à évaluer la fonction du genou et la satisfaction des patients après l'opération. Méthodes: Cette étude rétrospective portait sur des patients qui avaient reçu la PTG Legion HK guidant le mouvement lors d'une première opération ou d'une chirurgie de révision entre octobre 2011 et mars 2016 dans un centre de soins tertiaires du Manitoba, au Canada. On a évalué la fonction préopératoire et postopératoire du genou à l'aide du score Oxford d'évaluation du genou à 12 questions ainsi que la satisfaction des patients après l'opération. Résultats: Trente-neuf arthroplasties totales du genou (38 patients) ont été retenues pour l'étude : 12 cas de première opération et 27 chirurgies de révision. En tout, 3 chirurgies de révision et 4 complications périopératoires ont été notées lors d'une consultation de suivi se déroulant en moyenne à 29,1 mois. Le taux de survie à 2 ans de la PTG à charnière Legion HK était de 90,7 %. Les scores de fonction du genou se sont grandement améliorés après l'opération, et la majorité des patients se sont dit satisfaits ou très satisfaits lors de tous les suivis. Conclusion: Le taux de survie d'une PTG à charnière moderne guidant le mouvement est similaire à celui des autres prothèses à charnière étudiées dans la littérature. La prothèse a permis une amélioration fonctionnelle importante après l'opération lorsqu'elle était utilisée dans le cadre d'une première arthroplastie totale du genou complexe ou d'une chirurgie de révision.

Does oxidized zirconium make a difference? Midterm cohort survivorship of symmetric posterior condyle posterior-stabilized total knee arthroplasty

Background: A novel symmetric posterior condylar design and option of a femoral component with an outer zirconium oxide layer were introduced to a successful asymmetric condylar total knee arthroplasty system in 2005. Given the paucity of information on this modified design, we performed a study to determine its early to midterm survivorship and performance. Methods: Patients who received the Genesis II Symmetric Posterior Condyle or Legion Primary total knee (cobalt­chromium [CoCr] or oxidized zirconium­niobium [OxZr]) (Smith & Nephew) implanted at the study centre between March 2007 and December 2013 were enrolled into a prospective database. We retrospectively reviewed the database and performed survival analysis using Kaplan­Meier techniques. Results: There were 2178 patients (1359 women [62.4%]; mean age 64.6 yr; mean body mass index 35.0) with 2815 knee replacements available for analysis. Survival rates were 98.2% (95% confidence interval [CI] 97.6%­98.7%) for failure for any reason at 2 years and 96.8% (95% CI 96.0%­97.7%) at 5 years. Age (hazard ratio [HR] 0.97, 95% CI 0.94­0.997) and female sex (HR 0.45, 95% CI 0.27­0.75) were protective, whereas body mass index (HR 1.02, 95% CI 0.99­1.05) and OxZr implant (HR 1.11, 95% CI 0.57­2.18) did not influence survivorship. Oxford Knee Score values improved from a mean of 40.2 to 21.8 by 2 years (p < 0.001), with no difference between the CoCr and OxZr groups. Conclusion: The symmetric posterior condylar posterior-stabilized knee offers excellent midterm survivorship. Implant bearing surface did not have an influence on survivorship to 5 years, and, thus, use of OxZr implants may not be justified.

Contexte: Un nouveau modèle à condyles postérieurs symétriques et l'option d'un élément fémoral pourvu d'une couche d'oxyde de zirconium ont été introduits avec succès dans un système de prothèse totale du genou à condyles asymétriques en 2005. Compte tenu du manque de renseignements concernant ce modèle modifié, nous avons procédé à une étude pour en déterminer la survie et le rendement à court et à moyen terme. Méthodes: Les patients ayant reçu la prothèse à condyles postérieurs symétriques Genesis II ou une prothèse totale primaire Legion (au cobalt­chrome [CoCr] ou au zirconium­niobium oxydé [OxZr]) (Smith & Nephew) au centre de recherche entre mars 2007 et décembre 2013 ont été inscrits dans une base de données prospective. Nous avons procédé à une revue rétrospective de la base de données et effectué une analyse de survie à l'aide de techniques de Kaplan­Meier. Résultats: On a dénombré 2178 patients (dont 1359 femmes [62,4 %]; âge moyen 64,6 ans; indice de masse corporelle moyen 35,0) totalisant 2815 arthroplasties du genou pour analyse. Les taux de survie ont été de 98,2 % (intervalle de confiance [IC] à 95 % 97,6 %­98,7 %) pour le paramètre défaillance de toutes causes à 2 ans et de 96,8 % (IC à 95 % 96,0 %­97,7 %) à 5 ans. L'âge (risque relatif [RR] 0,97, IC à 95 % 0,94­0,997) et le fait d'être de sexe féminin (RR 0,45, IC à 95 % 0,27­0,75) ont conféré un effet protecteur, tandis que l'indice de masse corporelle (RR 1,02, IC à 95 % 0,99­1,05) et l'implant OxZr (RR 1,11, IC à 95 % 0,57­2,18) n'ont eu aucune influence sur la survie. Les scores Oxford d'évaluation du genou se sont améliorés, passant d'une moyenne de 40,2 à 21,8 en l'espace de 2 ans (p < 0,001), sans différence entre les groupes CoCr et OxZr. Conclusion: La prothèse du genou à condyles postérieurs symétriques postéro-stabilisée possède une excellente survie à moyen terme. La surface portant l'implant n'a pas eu d'influence sur la survie à 5 ans et, donc, l'utilisation d'implants OxZr ne sera peutêtre pas justifiée.

A double-blind randomized controlled trial of total knee replacement using patient-specific cutting block instrumentation versus standard instrumentation

Background: Patient-specific cutting blocks in total knee arthroplasty have been promoted to improve mechanical alignment, reduce alignment outliers and improve patient outcomes. The aim of this study was to compare the efficacy of patient-specific instrumentation (PSI) and conventional instrumentation (CI) in achieving neutral alignment and accurate component positioning in total knee arthroplasty. Methods: We conducted a double-blinded randomized controlled trial in which patients were randomly assigned to treatment with either PSI or CI. Results: Fifty-four patients were included in the study. No relevant improvement in coronal alignment was found between the PSI and CI groups with post-hoc power of 0.91. Tibial slope was found to be more accurately reproduced to the preoperative target of 3° with PSI than with CI (3.8°± 3.1° v. 7.7°± 3.6°, respectively, p < 0.001). There were no differences found in patient-reported outcome measures, surgical time or length of hospital stay. Conclusion: Given the added cost of the PSI technique, its use is difficult to justify given the small improvement in only a single alignment parameter. Clinical trial registration: Clinicaltrials.gov, no. NCT03416946

Contexte: L'utilisation de guides de coupe sur mesure dans l'arthroplastie totale du genou a été recommandée pour améliorer l'alignement mécanique, réduire les alignements extrêmes et améliorer les résultats des patients. Cette étude cherchait à comparer la capacité des instruments sur mesure et des instruments classiques à engendrer un alignement neutre et un bon positionnement des composants dans le cadre d'une arthroplastie totale du genou. Méthodes: Nous avons mené un essai clinique randomisé à double insu. Les patients étaient répartis aléatoirement entre le groupe de traitement avec instruments sur mesure et le groupe de traitement avec instruments classiques. Résultats: Cinquante-quatre patients ont participé à l'étude. Aucune différence notable de l'alignement coronal entre les groupes n'a été relevée, pour une puissance observée de 0,91. La pente tibiale correspondait plus exactement à la cible préopératoire de 3° avec les instruments sur mesure qu'avec les instruments classiques (3,8° ± 3,1° contre 7,7° ± 3,6°, respectivement; p < 0,001). Il n'y avait aucune différence dans les mesures déclarées par les patients, la durée de l'intervention et la durée d'hospitalisation. Conclusion: Étant donné l'amélioration minime d'un seul paramètre d'alignement et le coût supérieur de la technique sur mesure, son utilisation est difficile à justifier. Enregistrement de l'essai: Clinicaltrials.gov, no NCT03416946.

Retrieval Analysis of Large-Head Modular Metal-on-Metal Hip Replacements of a Single Design.

BACKGROUND: There are limited publications examining modular metal-on-metal (MoM) total hip implants in which a comprehensive analysis of retrieved components is performed. This study examines 24 retrieved modular MoM implants from a single manufacturer and compares retrieval analytics; bearing surface damage, wear, and modular taper corrosion against patient, surgical and implant characteristics to elucidate significant associations. METHODS: Clinical, patient, and surgical data were collected including age, body mass index, blood metal ion levels, and cup inclination. Damage assessment was performed visually in addition to surface profilometry. Acetabular liners and femoral heads were measured for volumetric wear. Femoral head taper bores were similarly measured for material removal due to corrosion and fretting. RESULTS: Patients with MoM-related reasons for revision showed significantly higher levels of blood metal ion levels. Bearing wear was strongly associated with blood metal ion levels and was significantly increased in cups placed more vertically. Younger patients tended to have higher body mass indices as well as poorer cup placement. CONCLUSION: This work details a broad range of analyses on a series of modular MoM total hip implants from a single manufacturer of which there are few published studies. Acetabular cup inclination angle was deemed a primary cause of revision surgery through increased MoM wear, high metal ion levels in the blood, and subsequent adverse local tissue reactions. Heavy patients can increase the surgical difficulty which was shown to be related to poor cup placement in this cohort.

Damage Assessment of Retrieved Birmingham Monoblock Cups: Is Conversion to Dual-Mobility Head a Viable Revision Option?

BACKGROUND: A novel revision technique for failed hip resurfacings involves retention of the acetabular cup, if well-fixed, which is mated to dual-mobility (DM) prosthesis in a traditional hip replacement configuration. It is unknown whether existing damage on the retained cup will result in unacceptable wear of the DM prosthesis. METHODS: Thirty retrieved Birmingham (Smith & Nephew) monoblock cups were visually scored for damage features and area of coverage. Surface roughness measurements were obtained within each damage feature as well as reference points on each cup. Analysis of prior metal-on-metal wear was also performed to determine the maximum change in diameter of the cup. RESULTS: Scratching and grooving (deep, singular scratches) were the most common damage features. Overall bearing surface roughness was estimated as 0.059 µm (±0.030 µm) based on percent area coverage of each damage feature. Dimensional change of the bearing surface was negligible for most cups (18 of 30) but ranged from 0.20 to 0.38 mm for the most severely worn samples (5 of 30). CONCLUSION: Average surface roughness of the retrieved Birmingham cups was low, suggesting an expected 10%-20% increase in DM prosthesis wear. Similarly, dimensional change of the cup due to prior wear is not believed to significantly affect wear. Our findings support the use of a DM head in appropriate scenarios but suggest caution when applied to younger, more active patients whom may be adversely affected by increased prosthesis wear in the long term.

Corrosion on the acetabular liner taper from retrieved modular metal-on-metal total hip replacements.

Eight retrieved metal-on-metal total hip replacements displayed corrosion damage along the cobalt-chromium alloy liner taper junction with the Ti alloy acetabular shell. Scanning electron microscopy indicated the primary mechanism of corrosion to be grain boundary and associated crevice corrosion, which was likely accelerated through mechanical micromotion and galvanic corrosion resulting from dissimilar alloys. Coordinate measurements revealed up to 4.3mm(3) of the cobalt-chromium alloy taper surface was removed due to corrosion, which is comparable to previous reports of corrosion damage on head-neck tapers. The acetabular liner-shell taper appears to be an additional source of metal corrosion products in modular total hip replacements. Patients with these prostheses should be closely monitored for signs of adverse reaction towards corrosion by-products.

Wear of a sequentially annealed polyethylene acetabular liner.

BACKGROUND AND PURPOSE: We previously reported on a randomized controlled trial (RCT) that examined the effect of adding tobramycin to bone cement after femoral stem migration. The present study examined femoral head penetration into both conventional and highly crosslinked polyethylene acetabular liners in the same group of RCT patients, with a minimum of 5 years of postoperative follow-up. PATIENTS AND METHODS: Linear penetration of the femoral head into an X3 (Stryker) crosslinked polyethylene (XLPE) liner was measured in 18 patients (19 hips) using radiostereometric analysis (RSA). Femoral head penetration was also measured in 6 patients (6 hips) with a conventional polyethylene liner (CPE), which served as a control group. RESULTS: The median proximal femoral head penetration in the XLPE group after 5.5 years was 0.025 mm with a steady-state penetration rate of 0.001 mm/year between year 1 and year 5. The CPE liner showed a median proximal head penetration of 0.274 mm after 7.2 years, at a rate of 0.037 mm/year. INTERPRETATION: The Trident X3 sequentially annealed XLPE liner shows excellent in vivo wear resistance compared to non-crosslinked CPE liners at medium-term implantation. The rate of linear head penetration in the XLPE liners after > 5 years of follow-up was 0.001 mm/year, which is in close agreement with the results of previous studies.

Multi-center experience with outpatient total hip arthroplasty via a standard posterolateral approach.

BACKGROUND: This study sought to evaluate the safety, efficacy, and resource utilization of a pilot outpatient surgery program for total hip arthroplasty compared to traditional inpatient total hip arthroplasty performed via the posterolateral approach. METHODS: A cohort of 68 patients from two sites were enrolled in a regional pilot project for outpatient total hip arthroplasty (THA) and matched 1:1 against a cohort of patients undergoing routine inpatient THA. Data was extracted retrospectively from patient and hospital charts including adverse events (AE), readmission within 90 days, emergency room (ER) visits, patient calls, patient-reported outcome measures, length of stay, and multiple surgical variables. RESULTS: The outpatient group had a mean hospital stay of 13 hours, whereas the inpatient group had a mean of 58 hours (p<0.001). Three outpatients and four inpatients experienced post-op complications. Three inpatients and one outpatient visited the ER within 8 weeks of surgery. No difference in pre-operative hemoglobin (p = 0.210), or surgical blood loss (p = 0.550) was found between study groups. There was no difference found between groups regarding Oxford-12 Hip Score improvement, nor satisfaction at six months, one and two years (p>0.125). CONCLUSION: This study demonstrates that outpatient THA using the posterolateral approach is as safe and effective as inpatient THA for overall healthy and carefully screened patients, based on the low rate of AEs observed and similar patient outcomes reported. Significantly reduced time in hospital demonstrates the reduced healthcare resources associated with outpatient THA.

Randomized controlled trial comparing traditional versus enhanced-fixation designs of a novel cemented total knee arthroplasty tibial component.

Aims: A novel enhanced cement fixation (EF) tibial implant with deeper cement pockets and a more roughened bonding surface was released to market for an existing total knee arthroplasty (TKA) system.This randomized controlled trial assessed fixation of the both the EF (ATTUNE S+) and standard (Std; ATTUNE S) using radiostereometric analysis. Methods: Overall, 50 subjects were randomized (21 EF-TKA and 23 Std-TKA in the final analysis), and had follow-up visits at six weeks, and six, 12, and 24 months to assess migration of the tibial component. Low viscosity bone cement with tobramycin was used in a standardized fashion for all subjects. Patient-reported outcome measure data was captured at preoperative and all postoperative visits. Results: The patient cohort mean age was 66 years (SD seven years), 59% were female, and the mean BMI was 32 kg/m2 (SD 6 kg/m2). Mean two-year subsidence of the EF-TKA was 0.056 mm (95% confidence interval (CI) 0.025 to 0.086) versus 0.006 mm (95% CI -0.029 to 0.040) for the Std-TKA, and the two-year maximum total point motion (MTPM) was 0.285 mm (95% upper confidence limit (UCL) ≤ 0.363) versus 0.346 mm (95% UCL ≤ 0.432), respectively, for a mean difference of -0.061 mm (95% CI -0.196 to 0.074). Inducible displacement also did not differ between groups. The MTPMs between 12 and 24 months for each group was below the published threshold of 0.2 mm for predicting early aseptic loosening (p < 0.001 and p = 0.001, respectively). Conclusion: Both the enhanced fixation and the standard tibial implant design showed fixation with a predicted low risk of long-term aseptic loosening.

The influence of head size on corrosion and fretting behaviour at the head-neck interface of artificial hip joints.

The primary goal of this study was to determine if head size affects corrosion and fretting behaviour at the head-neck taper interface of modular hip prostheses. Seventy-four implants were retrieved that featured either a 28 mm or a 36 mm head with a metal-on-polyethylene articulation. The bore of the heads and the neck of the stems were divided into eight regions each and graded by three observers for corrosion and fretting damage separately using modified criteria as reported in the literature. The 36 mm head size featured a significant difference in the corrosion head scores (p=0.022) in comparison to the 28 mm heads. This may be attributed to a greater torque acting along the taper interface due to activities of daily living.

Radiostereometric analysis and clinical outcomes of a novel reverse total hip system at two years.

Aims: Instability is a common cause of failure after total hip arthroplasty. A novel reverse total hip has been developed, with a femoral cup and acetabular ball, creating enhanced mechanical stability. The purpose of this study was to assess the implant fixation using radiostereometric analysis (RSA), and the clinical safety and efficacy of this novel design. Methods: Patients with end-stage osteoarthritis were enrolled in a prospective cohort at a single centre. The cohort consisted of 11 females and 11 males with mean age of 70.6 years (SD 3.5) and BMI of 31.0 kg/m2 (SD 5.7). Implant fixation was evaluated using RSA as well as Western Ontario and McMaster Universities Osteoarthritis Index, Harris Hip Score, Oxford Hip Score, Hip disability and Osteoarthritis Outcome Score, 38-item Short Form survey, and EuroQol five-dimension health questionnaire scores at two-year follow-up. At least one acetabular screw was used in all cases. RSA markers were inserted into the innominate bone and proximal femur with imaging at six weeks (baseline) and six, 12, and 24 months. Independent-samples t-tests were used to compare to published thresholds. Results: Mean acetabular subsidence from baseline to 24 months was 0.087 mm (SD 0.152), below the critical threshold of 0.2 mm (p = 0.005). Mean femoral subsidence from baseline to 24 months was -0.002 mm (SD 0.194), below the published reference of 0.5 mm (p < 0.001). There was significant improvement in patient-reported outcome measures at 24 months with good to excellent results. Conclusion: RSA analysis demonstrates excellent fixation with a predicted low risk of revision at ten years of this novel reverse total hip system. Clinical outcomes were consistent with safe and effective hip replacement prostheses.

Comparison of two hydroxyapatite-coated femoral components: a randomized clinical trial using radiostereometric analysis.

Aims: The primary aim of this trial was to compare the subsidence of two similar hydroxyapatite-coated titanium femoral components from different manufacturers. Secondary aims were to compare rotational migration (anteversion/retroversion and varus/valgus tilt) and patient-reported outcome measures between both femoral components. Methods: Patients were randomized to receive one of the two femoral components (Avenir or Corail) during their primary total hip arthroplasty between August 2018 and September 2020. Radiostereometric analysis examinations at six, 12, and 24 months were used to assess the migration of each implanted femoral component compared to a baseline assessment. Patient-reported outcome measures were also recorded for these same timepoints. Overall, 50 patients were enrolled (62% male (n = 31), with a mean age of 65.7 years (SD 7.3), and mean BMI of 30.2 kg/m2 (SD 5.2)). Results: The two-year subsidence was similar for Avenir (-0.018 mm (95% confidence interval (CI) -0.053 to 0.018) and Corail (0.000 mm (95% CI -0.027 to 0.026; p = 0.428). Both anteversion/retroversion (Avenir 0.139° (95% CI -0.204 to 0.481°); Corail -0.196° (95% CI -0.445 to 0.053°; p = 0.110) and varus/valgus tilt (Avenir -0.024° (95% CI -0.077 to 0.028); Corail -0.049° (95% CI -0.098 to 0.000°; p = 0.473) were not statistically significantly different. After two years, patients reported similar improvements in EuroQol five-dimension five-level health questionnaire (Avenir 0.22 (SD 0.2); Corail 0.22 (SD 0.18); p = 0.965) and other outcomes scores. Patient satisfaction on a five-point Likert scale was also similar between both groups after two years (Avenir 1.38 (SD 0.88); Corail 1.33 (SD 0.57); p = 0.846). Conclusion: The performance of both femoral components was similar in terms of stability and patient outcomes.

Randomized trial of computer-assisted knee arthroplasty: impact on clinical and radiographic outcomes.

Computer-assisted surgery in knee arthroplasty is gaining popularity; however, the resulting outcome improvement is controversial. A double-blinded trial was performed with subjects randomized to undergo surgery with either computer-assisted or nonassisted instruments. Postoperatively, limb and implant alignment and rotation were assessed using both full-length radiographs and computed tomography in addition to clinical scores. One hundred twenty patients (141 knees) were randomized. No differences in Western Ontario MacMaster Osteoarthritis Score, Short Form-36, or flexion were seen. More varus limb alignment was seen in the computer-assisted group (1.9°) vs the nonassisted group (0.9°, P = .04) with no improvement in alignment precision. Rotational alignment of the components did not differ between groups. Computer-assisted surgery appeared to have minimal effect on knee implant arthroplasty with no improvement in limb alignment or early functional outcome.

Paraneoplastic Clostridium septicum infection of a total knee arthroplasty.

We describe a case of a well-functioning total knee arthroplasty acutely infected with Clostridium septicum. This is the first reported infection of a prosthetic joint with this organism. A search for the source of this infection uncovered a colonic malignancy. This organism is highly associated with gastrointestinal malignancy, and appropriate investigation should be carried out when it is discovered. The importance of full anaerobic bacterial identification by the microbiology laboratory is underscored by this case.

Survivorship of constrained polyethylene inserts in primary total knee replacements.

BACKGROUND: Varus-valgus constrained (VVC) inserts are used in primary total knee arthroplasty (TKA) when stability cannot be achieved with a traditional insert. Concern has been raised regarding premature loosening and failure of these primary TKAs due to the increased load transfer through the prosthesis. This study seeks to assess the survival, clinical outcomes and radiographic assessment of VVC total knee inserts used in a single primary TKA system without diaphyseal stem extensions. METHODS: A consecutive cohort of 74 primary TKAs with VVC inserts was identified from an institutional database. A two-to-one matched group of 136 posterior-stabilized (PS) primary TKAs was generated from the same database. Survival analysis was assessed for all-cause revision surgery. Patient outcome measures were the Oxford Knee Score (OKS) and patient reported satisfaction. Radiographs were assessed in accordance with the Knee Society radiographic scoring system for radiolucency. RESULTS: Survival rates at three and five years were 98.1% and 95.1% for the VVC liner group and 98.1% and 98.1% for the PS liner group, respectively. OKS improved from pre-op to post-op for both groups (p < .001). OKS was reduced in the VVC liner group compared to the PS liner group at latest available follow-up (p = .012). However, clinical satisfaction rates did not differ between the two groups. Small, non-progressive radiolucent lines existed on several radiographs; however, no components in either group were deemed radiographically loose. CONCLUSION: The survivorship, clinical, and radiographic outcomes of VVC knees were similar to the PS comparison group at short- to mid-term follow-up.

Clinical and radiographic outcomes of a hybrid fixation revision total knee arthroplasty system at short to mid-term follow-up.

BACKGROUND: Despite the extensive study of primary arthroplasty, revision surgery is rarely discussed due to the reduced frequency and variability between patients. A new revision knee system was introduced to build off the geometry of a successful knee replacement system. This study seeks to assess the survival, clinical outcomes and radiographic assessment of this revision system at the early to mid-term. METHODS: A consecutive cohort of 234 rTKAs was identified from an institutional database. Survival analysis was assessed for aseptic loosening and any-cause failure. Patient outcome measures were the Oxford Knee Score (OKS) and patient reported satisfaction. Radiographs were assessed in accordance with the Knee Society radiographic scoring system. Mechanical alignment was assessed on three-foot standing radiographs. RESULTS: Aseptic survivorship at one year, two years, and five years was 100%, 100%, and 99.1%, respectively. Any-cause survival at one, two, and five years was 99.6%, 98.7%, and 92.3%, respectively. OKS improved from pre-op (average 18.8) to one year (average 31.7), two years (average 30.7), and mid-term (average 30.6) follow-up (p < 0.001 for all). At all intervals, patient satisfaction exceeded 70%. One component (0.4%) failed radiographically and was later revised. Neutral mechanical alignment was achieved in 83% of cases. In the remaining cases, alignment was in varus (10%) or valgus (seven percent). No consistent relationship between radiographs or mechanical alignment and clinical outcomes was noted. CONCLUSION: The survivorship, clinical, and radiographic outcomes of the single rTKA system studied are equivalent or superior to other hybrid fixation rTKA systems reviewed in the literature at similar follow-up intervals.

Failure analysis of a ceramic bearing acetabular component.

BACKGROUND: Alternative bearings have been explored in an attempt to improve the longevity of total hip prostheses. A Food and Drug Administration (FDA)-approved clinical study of a nonmodular acetabular component consisting of a porous metal shell, compression-molded polyethylene, and a ceramic liner inlay was discontinued following reports of early failures. METHODS: Between October 1999 and January 2003, 429 patients were enrolled in a prospective study to evaluate a cementless ceramic-on-ceramic total hip arthroplasty design (Hedrocel ceramic bearing cup; Implex, Allendale, New Jersey). Two hundred and eighty-two patients (315 hips) were treated with the experimental acetabular implant and 147 patients (157 hips) were treated with an acetabular implant that consisted of the same porous shell but an allpolyethylene liner. Clinical data including a Harris hip score and responses to the Short Form-12 (SF-12) health survey were collected preoperatively and at twelve and twenty-four months postoperatively. Serial radiographs were made preoperatively; at six weeks, three months, six months, and twelve months postoperatively; and annually thereafter. Retrieval analysis was performed on all failed explanted components. Failure was defined as fracture or displacement of the ceramic liner out of the acetabular component. In addition, biomechanical testing was performed on unimplanted acetabular components and mechanically altered cups in an effort to recreate the mechanisms of failure. Finite element analysis was used to estimate stress and strain within the ceramic liner under extreme physiologic loading conditions. RESULTS: The ceramic liner failed in fourteen of the 315 experimental acetabular components; all of the failures were at the ceramic-polyethylene interface. Patients with a body weight of >91 kg had a 4.76 times greater odds of the ceramic liner failing than those who weighed < or =91 kg. Retrieval analysis demonstrated stripe and rim wear with evidence of adhesive wear, indicating a potentially high-friction interaction at the articulation. Finite element analysis demonstrated that the forces on the ceramic liner in cups subjected to extreme loading conditions were insufficient to cause fracture. Biomechanical testing was unable to reproduce an initial ceramic liner displacement in vitro; however, when the ceramic liner was forcibly displaced prior to biomechanical testing, complete displacement and eventual fracture of the ceramic liner resulted. CONCLUSIONS: We hypothesized that the combination of a high patient body weight, an extensive range of motion, and subluxation of the femoral head led to high friction at the articulation between the femoral head and the rim of the liner, which initiated displacement of the ceramic liner. Subsequent normal gait led to further displacement of the liner in all of the fourteen failed components and eventually to ceramic fracture in twelve of the fourteen components.